WO2009038501A1

WO2009038501A1 - Systems, device and object comprising electroactive polymer material, methods and uses relating to operation and provision thereof

Info

Publication number: WO2009038501A1
Application number: PCT/SE2007/000813
Authority: WO
Inventors: Daniel Carlsson; Edwin Jager; Magnus Krogh; Mia Skoglund
Original assignee: Micromuscle Ab
Priority date: 2007-09-17
Filing date: 2007-09-17
Publication date: 2009-03-26

Abstract

A method for affecting volume change of an electroactive polymer (EAP) material (23) in a device (50), the method comprising the steps of: providing (41) an electrolyte (13), a first electrode (14) and a second electrode (15), said electrodes being arranged to be in contact with said electrolyte, wherein at least said first electrode (14) comprises said EAP material (23); setting (43) at least one parameter having external influence on volume change of the EAP material (23) to a determined value; and operating (45) the device under influence of the determined parameter value. There is also disclosed a device arranged to execute the method, a system comprising a working electrode and a counter electrode wherein at least the working electrode comprises an EAP material, a method for providing an EAP object, a use of means for removal of EAP material from a grown EAP object, a method for providing an EAP layer on a substrate and a use of a non¬ aqueous polar solvent to confine an EAP layer to a substrate layer.

Description

SYSTEMS, DEVICE AND OBJECT COMPRISING ELECTROACTIVE POLYMER MATERIAL, METHODS AND USES RELATING TO OPERATION

AND PROVISION THEREOF

Technical Field

The present disclosure generally relates to systems and a device comprising an electroactive polymer (EAP) material and to methods and uses for utilizing or affecting properties of EAP material and such that are involved in provision of objects and layers comprising EAP.

More particularly, the present disclosure relates to a method and device arranged to affect volume change of an EAP material in a device using a parameter having external influence on the volume change. It also relates to an electrochemically controlled system comprising a working electrode and a counter electrode wherein at least the working electrode comprises an EAP material.

Moreover, the disclosure relates to a method for providing an EAP object, to a use of a laser or water jet cutter for removal of EAP material from a grown EAP object, to a method for providing an EAP layer on a substrate and to a use of a non-aqueous polar solvent to confine an EAP layer to a substrate layer.

Background Electroactive polymers (EAP) are a comparatively novel class of materials that have electrically controlled properties. An overview on electroactive polymers can be found in "Electroactive Polymers (EAP) Actuators as Artificial Muscles - Reality, Potential, and Challenges" 2nd ed. Y. Bar-Cohen (ed.) ISBN 0-8194-5297-1. One class of EAPs is conducting polymers. These are polymers with a backbone of alternating single and double bonds. These materials are semiconductors and their conductivity can be altered from insulating to conducting with conductivities approaching those of metals. Polypyrrole (PPy) is one conducting polymer and may throughout the present disclosure be taken as a non-limiting example of such EAP materials. PPy can be electrochemically or chemically synthesised from a solution of pyrrole monomer and a salt as is known to those skilled in the art. After synthesis PPy is in its oxidised, or also called doped, state. The polymer is doped with an anion A-. PPy can be electrochemically oxidised and reduced by applying an appropriate potential to the material. This oxidation and reduction is accompanied with the transport of ions and solvents into and out of the PPy. This redox reaction changes the properties of PPy, such as the conductivity, colour, and volume. Two different schemes of redox are possible. If PPy is doped with a large, immobile anion A- scheme 1 occurs, which schematically can be written as:

PPy+(A-) + M+(aq) + e- <-> PPyO(A-M+) (1) OV, Oxidised -1V, reduced

When PPy is reduced to its neutral state cations M+ including their hydration shell and solvent are inserted into the material and the material swells. When PPy is oxidised again the opposite reaction occurs, M+ cations (including hydration shell and solvent) leave the PPy and it decreases its volume.

If on the other hand PPy is doped with small, mobile anions a-, scheme 2 occurs:

PPy+(a-) + e- <-> PPyOQ + a-(aq) (2)

OV, Oxidised -1V, reduced

In this case the opposite behaviour of scheme 1 occurs. In the reduced state the anions leave the material and it shrinks. The oxidised state is now the expanded state and the reduced state the contracted. Non-limiting example of ions A- is dodecylbenzene sulfonate (DBS-), of a- perchlorate (CIO4-), and of M+ sodium (Na+) or lithium (Li+). This volume change for instance can be used to build actuators (see Q. Pei and O. Inganas, "Conjugated polymers and the bending cantilever method: electrical muscles and smart devices", Advanced materials, 1992, 4(4), p. 277-278 and Jager et al., "Microfabricating Conjugated Polymer Actuators", Science 2000 290: 1540-1545).

This redox reaction is typically driven in an electrochemical cell that comprises a working electrode (i.e. the EAP) and a counter electrode, preferably a reference electrode, and an electrolyte.

The electrolyte is typically an aqueous salt solution, but can be a solid polymer electrolyte, gels, non-aqueous solvents, ionic liquids etc. as is known to those skilled in the art, but even biologically relevant environments such as blood, plasma, cell culture media, or other physiological media etc. can be used.

Furthermore, the ability for an EAP-based device to function or fit into a small and narrow environment is often essential for many medical applications. Also, adding additional materials to a device is not desirable due to possible negative side effects, e.g. biocompatibility issues. Actuating EAP requires at least a counter electrode.. Adding such an electrode will typically both add to the overall size of the device, but also introduce additional materials.

Moreover, for devices that include electroactive polymers, it is often important that the amount of deposited electroactive polymer, e.g. thickness, is well defined and controlled. This includes for example medical devices, where quality control during fabrication is important and strictly regulated. A general scheme for the electrosynthesis of conducting polymers, such as PPy is polycondensation of radical cations as is described by Diaz et al. (A.F. Diaz and J. Bargon, "Electrochemical synthesis of conducting polymers", in Handbook of conducting polymers, T.A. Skotheim, Editor, 1986, Marcel Dekker, Inc., New York, p. 81-115.) This can be schematically summarized as:

H-M-H + H-(M)n-H -> H-(M)n+1-H + 2 H+ + 2 e- (3) with M being the monomer.

Normally, the amount of (conducting) polymer deposited during electrochemical synthesis is determined by collecting the amount of charge consumed during the synthesis. Taking PPy as a non-limiting example, the formulations are based on the principle that 2.25 electrons are consumed per monomer. The method assumes that 2 electrons are used for the pyrrole monomer to monomer coupling (1 electron at the 2 position and one at the 5 position) as schematically described in equation 3 and 0.25 electron is used to account for the doping with the dopant A- or a- (equations 1 or 2), assuming a doping density of 1 dopant per 4 monomers (thus 1 electron/4 monomers is 0.25 electron/monomer).

There are two main directions of the volume change exhibited by EAPs like conducting polymers (e.g. polypyrrole, polyaniline, polythiophenes), namely an out-of-plane direction D1 and in-plane direction D2, see Fig. 2c for illustration of the directions. The plane is here the plane of the substrate (e.g. 24 in Fig. 2c) on which the EAP (e.g. 23 in Fig. 2c) is synthesized, i.e. grown. The out-of-plane direction D1 is perpendicular to the plane and the in-plane direction D2 is parallel with the plane. Even when the EAP is removed from the substrate and used as free standing or mounted/assembled on another substrate, there is still an in-plane and out-of-plane volume change direction, referring to the plane of the substrate on which the EAP was synthesized. The volume change of EAPs is typically highly anisotropic. For example, in-plane expansion may be 2-5% while at the same time the out-of-plane expansion may be 20-30%. . Fig. 1 schematically illustrates an electrochemical system 10 with a 3- electrode set-up, which comprises a control device 11, a container 12 containing electrolyte 13, a working electrode (WE) 14, a counter electrode (CE) 15 and a reference electrode (RE) 16. The counter electrode 15 is sometimes addressed as auxiliary electrode (AUX). For EAP actuators the WE is used as the active part of the system, that may be the EAP actuator or sensor. Such actuators are illustrated in Figs 2a-2c. These are typically electrochemically driven EAP actuators comprising a conducting polymer material, such as for instance PPy. In some designs the WE, which comprises the EAP material, and the CE, which also may comprise an EAP material, are integrated into a single multilayer.

An alternative to using a 3-electrode system as in Fig.1, is to use a 2- electrode system with a working electrode and a counter (or auxiliary) electrode only, that is without a reference electrode. A 2-electrode system is less complex to fabricate, especially in small devices, and easier to control. First, one has only to electrically address two electrodes instead of three. Second, the electrical control of 2 electrodes is easier to implement than for 3 electrodes. The 2-electrode system does not require a complex control unit such as a potentiostat/galvanostat. However, 2-electrode systems typically tend to be less stable and reliable than 3-electrode systems and are more dependent on various system factors such as materials and sizes of the electrodes used.

Examples of known EAP actuators are given in Figs 2a-2c. Specifically, Fig. 2a illustrates a longitudinally expanding actuator 20 comprising a strip, tube or other shape of a EAP 23, which upon activation expands (23') or contracts (23) in the longitudinal direction L. Fig. 2b illustrates a bending actuator, which is based on a bi-layer structure 21 , wherein the actuator element comprises an EAP layer 23 layered with an non-EAP layer 24. The actuator element has a fixed end and a movable end. Upon activation, the EAP layer 23 will expand (23') or contract (23), whereas the non-EAP layer 24 is substantially unchanged, whereby the bending motion B is achieved. Such non-EAP layers may be conducting or nonconducting. Examples of suitable materials include, but are not limited to, metals, such as Au, Pt, Ti, and polymer materials.

Fig. 2c illustrates a volume expanding actuator 22, which comprises a body of EAP material 23, that upon actuation expands (23') or contracts (23) in both directions D1 and D2.

Fig. 3a-3b schematically illustrates a balloon catheter 210, such as the one disclosed in US 2005/0187602A1 and US 2005/0187603A1 , which may be rotatable, that is arranged at an outermost portion of a catheter, comprising an outer tube 214 and an inner tube 212. The inner tube 212 presents a channel 211 , wherein a guide wire 213 may be removably received. Between the outer tube 214 and the inner tube 212, there is formed a channel 242, which may be used to provide a fluid to inflate a balloon 216. The balloon 216 comprises an inflatable portion 216 providing an interior lumen 240 and connecting/sealing portions 220, 222 protruding axially therefrom. The connecting/sealing 220, 222 portions are arranged to selectively form a tight seal relative to the inner and outer tubes 212, 214, respectively, such that the balloon 240 can be inflated. To control the sealing, annular EAP actuators 230, 232 are provided between on the one hand the inner tube 212 and the distal connecting/sealing portion 220 of the balloon 216, and on the other hand between the outer tube 214 and the proximal connecting/sealing portion 222 of the balloon 240.

The balloon catheter is provided with marker bands 256, which are used to render the balloon catheter visible on x-ray, on one of which the counter electrode 257 is arranged. Fig. 3b illustrates a detail of the proximal and distal portions of the balloon 216, with an annular EAP actuator 114 arranged on the outer tube 214 (or inner tube 212), forming a first part 101 , and acting against a connecting/sealing portion 222 (or 220) of the balloon, forming a second part 102. Reference numeral 103 designates the proximal side of the EAP actuator 114 and reference numeral 104 designates the distal side of the EAP actuator 114.

Fig. 3c illustrates a micro fluidic channel, with an EAP actuator 114 arranged on a first part 101, and acting against a second part 102. Reference numeral 103 designates the proximal side of the EAP actuator 114 and reference numeral 104 designates the distal side of the EAP actuator 114. An example of a microfluidic valve is disclosed in Y. Berdichevsky and Y.-H. Lo, "Polymer Microvalve Based on Anisotropic Expansion of Polypyrrole", in Mat. Res. Soc. Symp. Proα, 2004, Materials Research Society, p. A4.4.1-7. In view of the fact that electroactive polymer materials are a comparatively new class of materials, little is e.g. known about how to adapt these materials, how to produce, design and operate objects formed of, and devices/systems, based on them in order to e.g. provide better operation, reliability and integration. Also, little is known about how properties pertaining to EAP materials, for example the ability of volume change, i.e. properties utilized in objects, devices and systems based on these materials, can be affected, which factors that have significant influence on the properties, and how this can be utilized for provision of improved objects, devices and systems.

All in all, there is a general need for improvements in this area.

Summary

It is thus a general object of the present disclosure to, in view of the above, provide an improved and/or alternate variant of one or more of any of the following: an object, a device, a system, each comprising an electroactive polymer material, and a method and/or use relating to provision and/or operation of such material, object, device and/or system.

Hence, there is provided a method for affecting volume change of a electroactive polymer (EAP) material in a device, the method comprising the steps of: providing an electrolyte, a first electrode and a second electrode, said electrodes being arranged to be in contact with said electrolyte, wherein at least said first electrode comprises said EAP material; setting at least one parameter having external influence on volume change of the EAP material to a determined value; and operating the device under influence of the determined parameter value.

According to another aspect there is provided a device comprising an EAP material, an electrolyte, a first electrode and a second electrode, said electrodes being arranged to be in contact with said electrolyte and said EAP material being comprised in at least the first electrode, said device further comprising means for setting at least one parameter having external influence on volume change of the EAP material to a determined value and means for operating the device under influence of the determined parameter value.

By external influence is here meant that the parameter exerts influence upon the EAP material from the outside and that the parameter is not part of the EAP material as such.

The determined value may be a value determined long before the actual setting of the value, such as a fixed predetermined value that e.g. has been determined by prior experiments, or the determined value may be determined before but in connection with the setting of the value, such as a value determined based on environmental conditions at the time of operating the device. The determined value may be provided e.g. by calculation or by selection from a table.

The method and device extend the possible areas of use and makes a specific EAP material more versatile. It e.g. makes it possible to adapt the effect being provided by the EAP material to a specific device or situation without the need of manipulating the EAP material as such. It also allows for improvements beyond what can be accomplished by manipulating the EAP material as such. It should be understood that the step of setting the parameter generally may be performed after or in connection with the step of providing the parts of the system.

The device may be arranged to utilize out-of-plane volume change of the EAP material.

The device may be arranged to operate the EAP material in a position being a gap between a first part and a second part. For example, the EAP may be used to close and/or open the gap for passage, control the amount of a substance passing the gap, regulate a flow through the gap, regulate a pressure etc.

The device may be arranged to operate the EAP for substance delivery, preferably in a human or animal body. According to one group of embodiments: The at least one parameter may comprise a temperature of the electrolyte and the corresponding determined value may correspond to a determined temperature level. It is understood that since the first electrode which comprises the EAP material is arranged to be in contact with the electrolyte, the temperature of the electrolyte will influence also the temperature of the EAP material and that the temperatures eventually may be the same. The determined temperature level may be determined so that when setting the determined temperature level of the electrolyte there will be an increase of the temperature of the electrolyte and so that the means for setting the at least one parameter thus is arranged to set the temperature of the electrolyte to a higher temperature.

Typically this means that the electrolyte and thus eventually the EAP are set to a higher temperature than the natural temperature of the electrolyte, such as determined by the ambient temperature of the device, for example room or body temperature.

The determined temperature level may be body temperature or a temperature level significantly above room temperature, or above about 30° C, or above about 35° C, or above about 37° C, or above about 40° C. The determined temperature level may be below a temperature level permanently damaging the device, or below about 100° C, or below about 70° C, or below about 60° C, or below about 50° C, or below about 42° C. By permanently damaging the device is meant such damage that results in permanent, or at least persistent deterioration of device properties, i.e. in this case a deterioration that persists also if the temperature is being lowered.

According to another group of embodiments, which may be combined with any other group or groups of embodiments mentioned herein:

The at least one parameter may comprise an electric potential of the first electrode over a time period and the corresponding determined value may correspond to a determined electric potential over a determined time period which are adapted to bring the EAP material to an expanded or contracted state, the electric potential over the time period may be applied to the first electrode in the step of operating the device and the means for setting the potential over the time period may be adapted to apply the potential to the first electrode when the device is being operated.

The determined electric potential over the determined time period may comprise at least a subperiod during which the potential is a cathodic overpotential that is less than a cathodic vertex potential, or is an anodic overpotential that is greater than an anodic vertex potential, preferably by at least 0.1 V, or 0.2 V, or 0.3 V, or 0.4 V or more.

The cathodic overpotential may be greater than the highest cathodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device. Correspondingly the anodic overpotential may be less than the lowest anodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device. Taking the sign of the potential into account, the cathodic overpotential in an electrochemical system is always less than the anodic overpotential in the same system. Hence by e.g. a cathodic overpotential greater than another cathodic overpotential is meant that the cathodic overpotential is closer to the anodic, or positive, side than said another cathodic overpotential.

An overpotential that during a short subperiod, such as one or a few seconds or less, may result in no gas formation may for longer subperiods still result in gas formation. Hence, by an overpotential that is independent on the length of the subperiod is in practise meant such overpotential for which there is no gas formation even for long subperiods. In this context it can in practise be considered to be independence when there is no gas formation during a subperiod of about 60 s or more. The superiod being used is typically longer than or equal to 0.5 s, or 1 s, or 2 s, or 3 s or 4 s.

Alternatively the cathodic and the anodic overpotential may each be of a voltage level that during a longer period than said subperiod would result in formation of gas. The subperiod is then typically shorter than or equal to 4 s, or 3 s, or 2 s, or 1.5 s, or 1 s, or 0.5 s.

The determined potential may vary over the determined time period in such way that there are, and so that the means for setting the electric potential is adapted to set, at least one potential level between the overpotential and the corresponding vertex potential, preferably so that subsequent such potential levels approach the vertex potential. For example, if the overpotential is positive, the vertex potential may be approached using a positive potential value or values that are greater than the vertex potential value, but less than the overpotential value.

The step of operating the device may comprise the following substep: limiting the current through the first electrode so that no formation of gas occurs. The device may be further arranged to limit current through the first electrode so that no formation of gas occur. The substep of limiting the current may comprise: measuring the current through the first electrode during application of the potential; and selecting and applying a subsequent potential based on the measured current. The device may be further arranged to measure the current through the first electrode during application of the potential and to select and apply a subsequent potential based on the measured current.

The at least one parameter may comprise the electrolyte ion concentration and the corresponding determined value may correspond to a determined ion concentration. It should be noted that the step of setting the ion concentration to a determined value may be combined and/or made in connection with the step involving provision of the electrolyte.

The determined ion concentration may be above about 0.1 M, or above about 0.15 M, or above about 0.3 M, or above about 0.5 M, or above about 0.9 M, or above about 1 M. At higher electrolyte concentrations than these, greater volume change speed to the expense of less, but still substantial, degree of volume change have been observed.

The determined ion concentration may be below about 1 M, or below about 0.5 M, or below about 0.2 M, or below about 0.1 M. At these electrolyte concentrations greater volume change degree to the expense of less, but still substantial, speed of the volume change have been observed.

The step of setting the ion concentration may be repeatedly performed in combination with the step of operating the device so that different ion concentrations are set and the ion concentration changes during operation of the device, and the means for setting the ion concentration may be adapted to repeatedly set the ion concentration when the device is operated so that different ion concentrations are set and the ion concentration changes during operation of the device. This may e.g. enable a high initial volume change speed (at higher concentrations) followed by a slower but greater volume change degree, for example in order to quickly provide a seal and then tighten it for reliability. According to another group of embodiments, which may be combined with any other group or groups of embodiments mentioned herein:

The at least one parameter may comprise a composition of the electrolyte with respect to the kind of cations and the corresponding determined value may correspond to a determined cation type in the composition. The determined cation type may be at least one of the following: K⁺, Ca²⁺, Na⁺ and Li+.

According to another aspect there is provided a system comprising a working electrode, a counter electrode and an electrolyte adapted to be in contact with the electrodes, wherein at least the working electrode comprises an electroactive polymer (EAP) material. The system may be arranged to utilize out-of-plane volume change of the EAP material.

The system may be a 2-electrode system. In a 2-electrode system the electrodes adapted to be active during operation consist of a working electrode and a counter electrode. The counter electrode in a 2-electrode system may also be denoted auxiliary electrode. Alternatively the system may be a 3-electrode system and further comprise a reference electrode in contact with the electrolyte.

According to one group of embodiments, which may be combined with any other group or groups of embodiments mentioned herein:

The counter electrode may comprise silver and may be at least partially covered by silver. The counter electrode may substantially consist of silver. The system with the counter electrode of silver performs good both in 2-electrode and 3-electrode systems and results in. a comparatively small voltage span between redox peaks and between vertex potentials.

The counter electrode may comprise aluminium and may be at least partially covered by aluminium. The counter electrode may substantially consist of aluminium. The aluminium counter electrode allows for redox peaks in the system at potentials of the same polarity.

According to another group of embodiments, which may be combined with any other group or groups of embodiments mentioned herein: The counter electrode may comprise stainless steel and may be at least partially covered by stainless steel. The counter electrode may substantially consist of stainless steel. The counter electrode of stainless steel performs well, is compatible with many medical applications and also facilitates and allows for integration with other medical equipment. For example a stainless steel part of a medical device having a first function may at the same time function and be utilized as a counter electrode in the system.

The reference electrode may comprise silver and may at least partially be covered by silver. The reference electrode may substantially consist of silver. A reference electrode of this kind may be used as a quasi-reference electrode of silver and allows for a small-sized reference electrode with comparatively stable performance.

The working electrode may be located in a 3-dimensional space wherein at least one dimension of the space is less than 10 times the thickness of the working electrode, or less than 5 times, or less than 2 times or even less than the thickness of the working electrode. The reference electrode may have a surface area that is less than 1 cm², or 0.8 cm², or 0.6 cm² or 0.4 cm² or 0.2 cm².

By an electrode substantially consisting of a metal (such as silver, aluminium or stainless steel in the above) is here meant that at least the portion of the electrode adapted to be in contact with the electrolyte is homogenous and comprises the metal to the amount that the part according to applicable standards is regarded as being of the metal in question. This typically means that the amount of metal is at least 80%.

By the surface area is here meant the surface area of the portion of the electrode adapted to be in contact with the electrolyte. According to another aspect there is provided a method for providing an electroactive polymer (EAP) object, comprising the steps of: growing the EAP object; determining a desired object shape before or after the step of growing the EAP object; and removing EAP material from the grown EAP object so that said EAP object becomes more similar to the desired shape. This kind of post-growth removal of EAP material allows for objects that perform better during operation, for example when an EAP object is actuated, and for production of objects that are more similar and stable in performance.

When the desired object shape is determined after the step of growing the object, a larger amount of grown material typically has to be removed after growth. It is therefore in practise typically strived to grow an object as similar to a previously determined desired object shape as the growth process being used allows for, whereby only a small amount of material, such that resulting from an imperfect growth, has to be removed in the step of removing material.

The desired object shape may be that of an EAP object for use in an EAP based actuator.

The grown EAP object may resemble the desired shape and may deviate from the desired shape only by local protrusions, and in the step of removing material, the EAP material may be removed from said local protrusions. The EAP object may be grown on top of a first and a second substrate, said first substrate may be arranged between the EAP object and the second substrate, wherein in the step of removing material, the EAP material may be removed from the second substrate so that the EAP object becomes arranged only on the first substrate. A layer may form the desired shape, such as a substantially rectangular layer forming a 2-dimensional rectangle or a 3-dimensional shape, such as a cylinder. The removal of EAP material may involve removing material protruding from edge portions or edges of said layer, such as material protruding in directions that at least locally are parallel to a plane of the layer.

"At least parallel to a plane of the layer" mainly concerns cases when the layer is arranged in a 3-dimensional structure. Although there is not only one plane in a 3-dimensional structure, the mere fact that it is a layer that forms the shape of the structure means that the layer at least locally is a plane structure. For example, in the case of a cylinder, at each point of the surface a tangential plane to that point can be considered to be the local plane. The removal of EAP material may involve removing material so that recesses, preferably through holes, are formed in the object. Patterning of this kind enables the resulting object to form more complicated shapes, such as spirals, rings etc. Typically patterning of this kind is performed on an object being a layer. By through holes is meant holes that extend through the object from one side to an opposite side.

The removal of EAP material may be made by means of a water jet cutter or by means of a laser.

The laser may generate light having a wavelength in the range of about 193 nm to about 351 nm and may be an excimer laser. According to another aspect there is provided use of a laser or water jet cutter to remove electroactive polymer (EAP) material from an EAP object.

According to another aspect there is provided a method for providing an electroactive polymer (EAP) layer on a substrate, comprising the steps of: providing the substrate, said substrate comprising an electrically conducting first substrate layer, such as an electrode layer, arranged on a second substrate layer having a larger area than and being electrically separated from said first substrate layer; providing a solution comprising: monomers for polymerization of the EAP layer and a non-aqueous polar solvent; and polymerizing the EAP layer on the first substrate layer using the solution. The non-aqueous polar solvent to the monomer solution results in that the EAP grown from the solution becomes better confined to the first layer with less lateral growth, which in turn, e.g. allows for better performance when the EAP has an actuating function in a device.

The polymerization may be provided by means of electro- polymerization.

According to another aspect there is provided use of a non-aqueous polar solvent as an admixture in a monomer solution to confine an electroactive polymer (EAP) layer polymerized from said solution to a first substrate layer. The first substrate layer may be an electrically conducting layer, such as an electrode layer, arranged on a second substrate layer having a larger area than and being electrically separated from said first substrate layer. The EAP layer may be adapted for use in an EAP based actuator and the EAP layer may be polymerized by means of electropolymerization.

The non-aqueous polar solvent in the foregoing may be pentanol, such as 1-Pentanol, and the amount of the non-aqueous polar solvent in the solution may be, or the admixture may result in that the amount of the non- aqueous polar solvent in the solution is, above about 0.1 vol%, or above about 0.5 vol%, or above about 1 vol%, or above about 2 vol%, or above about 3 vol%, or above about 4 vol%, or above about 5 vol% and may be below about 10 vol%, or below about 9 vol%, or below about 8 vol%, or below about 7 vol%, or below about 6 vol%. In the foregoing. ^■

By EAP layer or EAP object is meant a layer or object formed of EAP material. By EAP material is meant a material that substantially consists of at least one type of EAP or that at least comprises such to the extent that the material behave as if it was EAP as to the properties being utilized. The EAP material may comprise or substantially consist of a conducting polymer, such as a polymer of at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers, and the EAP material may be doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

By EAP being grown is meant depositing/fabrication/manufacturing of EAP material where the EAP material may be provided by, but not limited to, electropolymerization, chemical polymerization in liquid or vapor phase, plasma polymerization, photopolymerization, electrospinning etc.

By actuator is meant a device or similar that is arranged to convert energy, such as an electrical control signal, to mechanical action. By an EAP object used in or part of an EAP-based actuator is meant that the EAP object is arranged to have an actuating function in said actuator, such as an electrically controlled volume change.

By utilize out-of-plane volume change is meant that the volume change (expansion and/or contraction) in the out-of-plane direction participates in the intended function or effect. One example of this is when the expansion in the out-of-plane direction of the EAP material is used to close a gap.

Generally, by an electrode is here referred to a part or portion of a conducting structure arranged to be or that are in contact with an electrolyte.

Brief Description of the Drawings

In all figures, the dimensions as sketched are for illustration only and do no reflect the true dimensions or ratios of the disclosure. All figures are schematic and not to scale, and in particular vertical dimensions are generally greatly exaggerated. In addition, some details, such as electrical leads or wires to and from the actuators, electrodes, etc. have been omitted from the drawings for clarity.

Fig. 1 is a schematic overview of an electrochemical system. Figs. 2a-2c schematically illustrate different types of electroactive polymer actuators. Figs. 3a-3c schematically illustrate, in longitudinal cross section, a prior art system with some portions enlarged for increased clarity.

Fig. 4 is a flow chart illustrating a method according to one embodiment.

Fig. 5 shows results from experiments where the temperature has been regulated during electroactive polymer actuation. Fig. 6a illustrates an experimental set-up.

Figs. 6b-6c show results from experiments where different reduction potentials have been used for electroactive polymer actuation.

Fig. 7 shows results from experiments where different electrolytes have been used during electroactive polymer actuation.

Fig. 8 shows results from experiments where different electrolyte concentrations have been used during electroactive polymer actuation (high concentrations). Fig. 9 shows results from experiments where different electrolyte concentrations have been used during electroactive polymer actuation (low concentrations).

Fig. 10 shows experimental results from actuation of one reference electroactive polymer sample under influence of different parameter values (combination of parameters).

Fig. 11 is a schematic overview of an electrochemical system including means for setting parameters having external influencing effect.

Fig. 12a schematically shows experimental setup for "in-channel" EAP actuation with a limited electrolyte volume.

Fig. 12b shows experimental results from electroactive polymer actuation in electrochemical systems in an "in-channel" quasi-reference electrode case compared with an "outside channel" ordinary reference electrode case. Figs. 13a-b show experimental results from electroactive polymer actuation in 2- and 3-electrode electrochemical systems using counter electrodes of different materials.

Fig. 14 shows experimental results from electroactive polymer actuation using counter electrodes of aluminium. Fig. 15 shows experimental results from electroactive polymer actuation using counter electrodes of different materials.

Figs. 16a-d schematically show how an electroactive polymer material may be arranged after growth and corresponding ideal/desired arrangements.

Figs. 17a-b schematically show how an electroactive polymer material may be arranged after growth and corresponding ideal/desired arrangement.

Fig. 18 is a flow chart illustrating a method according to one embodiment.

Fig. 19 is a flow chart illustrating a method according to one embodiment.

Description of Embodiments

In the following, references will be made to "reference sample" and "reference actuation", which now will be described. Reference sample: An Au ring on a non-conducting tube/rod or an Au ring on a conducting metal wire (500-1000 μm diameter and 0.5-5 mm long) is used as a working electrode (WE) substrate onto which PPy(DBS) (polypyrrole doped with dodecylbenzene sulfonate) has been electro-polymerized from an aqueous solution containing 0.1 M pyrrole and 0.1 M NaDBS at a constant current density of 0.4mA/cm². Polymerization is aborted when the PPy thickness reaches 40-55 μm. Gold is used as counter electrode (CE) and Ag/AgCI as reference electrode (RE).

Reference actuation: Actuation of an EAP sample (for example, but not limited to, the reference sample) as working electrode (WE) in 50-200 ml of 0.15 M NaCI aqueous electrolyte in a glass beaker at room temperature(RT). A Pt coated Ti mesh is used as counter electrode (CE) and Ag/AgCI as reference electrode (RE). Actuation of the EAP sample is performed by cycling the WE potential (triangular wave) between -1 V and 0 V at 5-7.5 mV/s vs. the RE, which is followed by a number of potential steps (square wave) between -1 V and 0.2 V vs. the RE for time periods long enough to substantially fully expand/contract, or reduce/oxidize, the EAP. For the reference sample such a time period is about 60 s or longer. The actuation is completed by applying to the WE a voltage step from 0.2 V to -1 V vs. the RE (applied for 2-3 min) during which volume change of the EAP is assessed in real-time. That is, the volume change is measured during the last reduction step at -1 V vs. the RE. Throughout the disclosure, unless mentioned otherwise, WE potentials in 3-electrode systems are specified versus an Ag/AgCI RE. In many applications it is desirable to have as fast and/or as large volume change of an EAP material based actuator as possible. Volume change here means expansion and/or contraction, mainly in the out-of-plane direction of the grown EAP.

For example, in many medical applications, such as the aforementioned balloon catheter case, it is desirable to keep surgical and interventional procedures short, e.g. in order to quickly perform acute interventions and reduce trauma as well as not to allocate expensive resources, such as doctors and equipment, longer than necessary. One way of influencing speed of and/or the degree of volume change may be to replace or manipulate the EAP material as such, i.e. involving fabrication of the material, however, this may not always be a viable option.

As a supplement or alternative to this, a number of parameters having external influence on volume change of the EAP material have been investigated. The parameters may be used to provide control over and/or adapt the speed and/or the degree of volume change of an EAP material.

Fig. 4 is a flow chart describing a generic method for controlling volume change of a conducting EAP material in an EAP-based device using parameters having external influence on volume change of the EAP material. In a first step 41 parts of the device, including electrolyte and electrodes, are being provided, wherein the EAP material is comprised in at least one of the electrodes. Typically the electrodes include at least a working electrode (WE) and a counter electrode (CE) with the EAP material being comprised in the WE. In a second step 43 one or many parameters having the external influencing effect is set to determined value(s). The parameters will be exemplified in detail below. In a third step 45 the device is operated under influence of the set parameter value(s). Hence, by the parameter(s) it is e.g. possible for a user to adapt the volume change speed and/or degree of volume change of the EAP material to a specific situation, application etc.

An example of a first parameter that may be set in step 43 is operational temperature of the electrolyte. Increased speed and a higher volume change have been observed when the operational temperature is elevated, typically from room temperature which is conventionally used. Of particular interest is the increase observed at body temperature levels, i.e. about 37°C, which can be advantageously utilized in the case of applications in vivo.

In one example, a reference sample was fabricated and initially activated according to reference actuation i.e. at room temperature. The sample was subsequently actuated at gradually increased temperatures and the out-of-plane expansion was measured at different temperatures. As can be seen in Fig. 5 both expansion speed and final volume expansion gradually increase with elevated temperatures. Similar results have been obtained for contraction of EAP at elevated temperature, i.e. contraction is larger and faster at elevated temperatures.

However, at too high temperatures there may be permanent damage to the device, e.g. caused by permanent degradation of the EAP material. For example, in the case of an EAP that comprises PPy, the material decomposes at about 220-230°C, at which temperatures there will be permanent damage. In the case of an aqueous electrolyte the electrolyte will boil at about 100⁰C which typically results in a permanent loss of dopant ions and electrolyte and thereby permanent damage of the device. In practise, depending on the type of dopant ions used, there is typically loss of dopant ions and electrolyte and/or deterioration already at temperatures below 100° C, for example, in case of DBS, there may be problems already at about 70° C. Generally this temperature is dependent on the mobility of the dopant ion in the EAP material. Factors such as the type of ion, size and polarity influence the mobility. For dopant ions that are more mobile, (e.g. smaller) than DBS the temperature typically has to be lower than 70°C to avoid permanent damage and for dopant ions that are less mobile (e.g. larger) than DBS the temperature typically can be higher than 70°C without any permanent damage. An example of a second parameter that may be set in step 43 is increased voltage.

Fig. 6a schematically illustrates a cyclic voltammogram (CV, current- voltage plot) of an EAP, such as PPy. A CV is normally accomplished by potential scanning between the conventional minimum and maximum potentials, E_vc and E_va, which are potentials beyond the respective oxidation and reduction peaks (redox peaks) at E_0x and E_red. The E_vc and E_va are also known as vertex potentials or turning potentials (E_vc cathodic vertex potential, Eva anodic vertex potential). At these potentials the current is more or less constant and independent of the applied potential. Mass transport dominates the electrochemical process. E_vc and E_va are the potentials conventionally used for activating EAP actuators. For PPy(DBS) the potentials (vs. Ag/AgCI) typically are: E_0x = - 0.35 V E_red = - 0.7 V

E_va = O V

Evc = - 1.0 V Increased speed of the volume change has been observed when the voltage level used for bringing the actuator to an expanded and/or contracted state is increased beyond the vertex or turning potentials. The CV of Fig. 5a is an extended version of a "normal" CV and shows appearance also beyond Eve and E_Va- An upper limit of the overpotential in aqueous electrolytes is the level where formation of gas occurs. At the cathodic side this is the formation of hydrogen at a potential E_gc and at the anodic side this is the formation of oxygen at a potential E_ga. There is a sudden increase of the current at these potentials. For a particular system these upper limits can be determined by routine experimentation. However, care should be taken not to operate the system too close to the upper limits, since in practice, some margin may be needed so as to avoid that fluctuations that may occur in the potential levels, e.g. due to natural variations in the environment of operation or differences between different individual systems, bring the system over the line where the formation of gas starts.

In one example, a reference sample was initially activated according to reference actuation (-1.0 V) and subsequently at -1.2 V and -1.4 V vs. Ag/AgCI, i.e. the reduction potential is what differs from reference actuation. The out-of-plane expansion was measured. The expansion speed gradually increases with lowered reduction potential as seen in Fig.δb. Similar results have been obtained in LiCI electrolyte.

Improvements at 3 seconds after applying the reduction potential of -1.4 V are generally 25 - 35% at RT (relative to -1V reduction potential), i.e. the increase in expansion speed resulting from the lowered potential enables 25-35% more expansion in 3 s. The improvements were even higher at 10 s.

However, final expansion was not improved by the lowered potential, i.e. a certain volume change was reached faster but the maximum attainable volume change degree was the same. Similar principles apply for oxidation potentials where an increased potential results in that a certain volume change can be reached faster.

In the above example, -1.4 V (vs. the Ag/AgCI RE) has been identified as a potential close to where gas formation starts. Most individual samples were activated at -1.4 V with no indications of gas formation, but at -1.5 V or lower, the samples exhibited gas formation.

However, for short and limited time periods even higher overpotentials may be used initially to achieve fast volume change. This is believed to be enabled by ohmic drop and double layer charging in the electrolyte which prevents gas formation if only the time frame for applying the overpotential is short enough.

In one example a reference sample was activated according to reference actuation but with the reduction potential being "shaped" during the initial 2-4 s for faster expansion. The potential shaping consisted of short sequential potential steps going from lower potentials up to ~1V. The best results were obtained for a sequence of -2.3 V for 1.5 s, -2 V for 1 s and -1.8 V for 1 s, before applying the standard -1 V for 181 s. As can be seen in Fig 6c the expansion speed is significantly improved using this lower, "shaped" reduction potential scheme. No gas was observed. Similar results have been obtained in LiCI electrolyte.

Application of high overpotentials can be made using also other potential shaping methods, e.g. linear sweep, exponential decaying sweep, pulsed, or differential pulse. Common for these methods is that a negative reduction potential is reached from lower potentials during a period of some few seconds, typically less than 3-4 seconds. The potential that is being reached is typically a potential which can be applied during a longer period than the preceding potential or potentials without any significant formation of gas, and is preferably a potential at which there is substantially no gas formation irrespective of how long the potential is being applied, i.e. where any formation of gas is virtually independent on how long the potential is being applied (such as -1 V in the above example). As is realized by the skilled person, the described way of "shaping" potentials can also be adapted for overpotentials during oxidation, where higher potentials are used to approach a lower positive potential.

Moreover, electronic controlled limitation of the current drawn through the circuit, typically represented by current through the WE, may be used in conjunction with high overpotentials. The risk for possible gas formation may be eliminated or reduced by setting a predetermined maximum allowed current level. This level can be determined (e.g. experimentally) to be sufficiently low for not causing gas formation. Another way for avoiding gas formation and still at all times be able to apply a desired electric potential that is close to the greatest possible overpotential resulting in no gas formation, s to use the current being drawn through the circuit, typically by measuring the current through the WE, to regulate the applied potential. Currents required for full reduction/oxidation of the EAP and that results in no gas generation can be determined experimentally. The potential applied to the WE may then be continously regulated so that this current is maintained, i.e. a current for optimum, or near optimum, speed of volume change can thus be used. For example, as long as the current is below a predetermined maximum allowed current level that is not casing gas formation, the applied potential may be increased. This may be combined with current limitation as above to ensure that current level causing gas formation cannot be exceeded.

An example of a third parameter that may be set in step 43 is composition of the electrolyte with respect to the kind of cations. By completely or partially replacing cations, such as K⁺, Ca²⁺ or Na⁺' with Li⁺, or completely or partly using Li⁺ instead of these cations in the electrolyte, greater as well as faster volume change has been observed.

In one example a reference sample was used with an aqueous electrolyte of LiCI instead of a NaCI electrolyte as in reference actuation. The out-of-plane expansion was measured. This increased out-of-plane expansion with about 50%. Fig. 7 illustrates measurements on a reference sample where it can be seen that actuation in LiCI electrolyte is considerably better than in other electrolytes, such as CaCI₂, Na₂SO₃ or KCI. An example of a fourth parameter that may be set in step 43 is electrolyte concentration.

Increased speed of volume change has been observed in electrolytes when the ion concentrations have been increased. In one example a reference sample was activated initially according to the reference actuation (i.e. 0.15 M NaCI) and subsequently in increasing electrolyte concentrations. The out-of-plane expansion was measured. Here 0.3 M₁ 0.6 M, 1 M and 2 M gave faster volume change (expansion) than 0.15 M as is shown in Fig. 8. However for higher concentrations such as 0.6 M, 1 M and 2 M a lower final expansion was observed, as is also seen in Fig. 8.

It has been found that in order to increase the speed but still maintain a substantial, and in practice usable, volume change, a concentration from about 0.1 M to about 1M or more may preferably be used. An upper limit for the effect is at concentrations where saturation occurs, typically at about 3-5 M.

Moreover, greater volume change, but at decreased speed, has been observed in electrolytes with lower ion concentrations. In one example a reference sample was activated initially according to the reference actuation (i.e. 0.15 M NaCI) and subsequently in decreasing electrolyte concentrations. The out-of-plane expansion was measured. Here 0.01 M and 0.05 M resulted in slower but slightly higher final expansion than 0.15 M (Fig. 9).

In general, it has been found that in order to augment the volume change by using the electrolyte concentration, the concentration may preferably be in the range of about 0.1 M to about 1 M or lower. A lower limit for the effect is in practise typically at about 0.01 M

For volume change in the case of contraction similar relations apply as above with the exception that it has been found the speed of volume change is not improved to the same extent by increased concentrations. In one example a reference sample activated according to reference actuation in 0.3 M, 0.6 M, and 1 M gave faster volume change (contraction) than 0.15 M only during the first 5 s. At longer times 0.15 M was faster than 0.6 M and 1M₁ but not 0.3 M. Electrolytes having different concentrations may be applied to a WE e.g. in a sequential manner. Initially an electrolyte having a high ion concentration may be applied for fast expansion and then this is followed by applying, for instance by flushing the electrochemical system, an electrolyte having a low ion concentration so that a high final expansion may be achieved. Thus by changing the electrolyte concentration from high to low during the activation step both a fast expansion and a large expansion can be achieved.

It has been found that the effects from adjustments of the above mentioned parameters are combinable, and that more than one parameter can be set to contribute beneficially to the volume change degree and speed at the same time.

Hence, the parameters and techniques as disclosed above can be combined in order to further increase performance. Figure 10 shows an expansion profile of a reference sample under reference actuation (0.15 M NaCI at RT), the same sample but with the difference that actuation is performed in LiCI at increased concentration (0.3 M), and finally the same sample with an additional difference that actuation is performed at an elevated temperature of 37°C and using an overpotential of - 1.3 V. As can be seen the combinations result in substantial improvements of the expansion.

Fig. 11 schematically shows an electrochemical set-up, or device 50 that may be used when implementing the method illustrated in Fig. 4, as described and exemplified in some detail above. The set-up 50 comprises a control device 11, a container 12 containing electrolyte 13, a working electrode (WE) 14, a counter electrode (CE) 15. It may further comprise a reference electrode (RE) 16 when a 3-electrode set-up is used. The counter electrode 15 is sometimes addressed as auxiliary electrode (AUX). The working electrode 14 comprises an EAP portion 23. The WE is typically used as the active part of the system and may be an EAP actuator or sensor. The control device 11 , such as potentiostat, is typically arranged to set electrical potentials of the electrodes. Instructions to the control device e.g. regarding which potentials to be set where, when and for how long, are typically generated by a computer or CPU (not shown) connected to the control device, and/or the control device 11 may itself be programmable and thus be able to operate more independently. The set-up may further comprise at least one of the following parts for setting one or many of the above mentioned parameter(s) having an external influencing effect on the volume change: temperature measuring means 51 (e.g a thermometer), heating means 52 (e.g. a heater), current measuring means 53 (e.g. an ampmeter), electrolyte input means 54 (e.g. a flow channel including a valve) and electrolyte output means 55 (e.g. a flow channel including a valve). The current measuring means 53 may be part of the control device 11. Any electronic controlled limitation of the current may be performed in the control device 11 , or in a separate device (not shown) controlled by the control device 11. Any potential regulation based on measured current may be part of the control device 11 as well. Means, such as circuitry, for actually setting potentials, measuring and/or limiting current, potential regulation based on feedback of measured current etc. can be any of many conventional solutions that can be found in the prior art, as recognized by the skilled person.

To control EAP actuation it is often desirable to use a 3-electrode system including a reference electrode (RE), such as Ag/AgCI. However, in many applications the RE may not be too large, e.g. when a device must be able to be operable in a volume of limited size, and this makes for example Ag/AgCI impractical. Generally problems may occur when the EAP material is to be used in a three-dimensional space, having at least one relatively small dimension which makes it difficult to use a conventional reference electrode. Such situations may occur when a part, such as a working electrode, comprising the EAP material, is located in a 3-dimensional space wherein at least one dimension of the space is less than 10 times the thickness of the part, or less than 5 times, or less than 2 times or even less than the thickness of the part. Small spaces ot the above kind may be found e.g. in the case where the EAP operates in a tube, such as a catheter, guidewire or endoscope, of limited cross section, or in a two-dimensional space between a pair of closely spaced members, such as substantially parallel planar or curved members. In such small spaces it may in practise be needed to use a reference electrode that is smaller than 0.2 cm² or 0.1 cm² and in some situations even smaller than 0.01 cm². The sizes refer to the surface area of the electrode.

A solution to this is to use a quasi-RE, which typically requires less space, although such an electrode generally is not as stable as e.g. Ag/AgCI. The term quasi-RE is often used to address a RE that is a simpler type of non-standard RE. A typical commercial standard Ag/AgCI RE (such as the RE-5B reference electrode from BioAnalytical Systems, http://www.bioanalytical.com/products/ec/ref.html) comprises an Ag/AgCI wire inserted into a glass body (6 mm outer diameter and 7.5 cm long), containing a saturated Ag+ Cl- electrolyte and has a porous junction made from Vycor that functions as a salt bridge (see also E. W. H. Jager, E. Smela and O. Inganas, Sensors & Actuators B: Chemical (1999) 56, 1-2, pp.73-78 for more information on the quasi-RE principle) To, at least partly, solve the above described problems of limited space and stability of the RE, a quasi-RE made from Ag has been provided. It has been found that the Ag quasi-RE can be made very small and that it is substantially stable during actuation, also in a small, confined volume.

With reference to Fig. 12a, in one example, a reference sample 1001 having a WE comprising a PPy(DBS) ring 1014 was actuated in 0.15 M NaCI in a small tubular channel 1012 (with a rectangular cross-section of 1.5mm x 1.2mm) using a 50μm diameter Ag wire 1016 as quasi-RE and Pt CE 1015, both mounted on one and the same side in the channel 1012. The difference to reference actuation is that actuation was performed in a small confined space instead of in a large volume beaker 12 (such as illustrated in Fig. 1) and without the Ag/AgCI reference electrode 16. The out-of-plane expansion was measured. The expansion over time was comparable to, or even slightly higher than expansion from reference actuation, as can be seen in Fig. 12b. The results support that it is possible to achieve normal expansion and expansion speed using a quasi-RE, such as a small Ag electrode, when a EAP is operated in a small confined space and small surrounding volume.

In another example a reference sample was first actuated according to reference actuation (i.e. with a standard Ag/AgCI RE). Subsequently the sample was actuated with a RE fabricated using a pad printed conductive silver ink, for instance as currently may be supplied by Creative Materials Inc. Tyngsboro, Massachusets, USA. The expansion performance with the Ag ink RE was almost identical to the standard Ag/AgCI RE. A number of substrates and materials composed of or containing silver may be used as Ag quasi-RE. Non-limiting examples are, sheets, parts, wires, or rings of silver that are mounted onto the substrate, and Ag that has been sputtered, evaporated, vapor deposited or plated.

Moreover, also other types of Ag containing materials may be used, such as silver conductive inks, silver containing conductive paste as well as various polymers filled with silver (e.g. thermoset epoxy resins, thermoplastic polyester resins, polyurethane or silicones or various UV-cured polymers) as well as various carbon materials filled with silver. Such silver containing materials may be pad printed, screen printed, stamped, sprayed, syringe dispensed, flexo-printed, rotogravure printed, spin-coated or dip coated onto different substrates.

Low energy consumption is generally desirable. Energy consumption for an EAP actuator is determined by the applied voltage and the charge/current needed to actuate the material. In medical, in vivo applications, low potentials on both the WE and CE are desirable for reasons of biocompatibility. Conventionally, Pt and Au are used as counter electrode materials. However, to actuate PPy using any of these two metals, a voltage span of typically about 2-3 V (over the WE-CE) is required in both 2-electrode and 3-electrode systems. It has been found that the WE-CE voltage can be reduced by replacing or partially covering the CE with Ag and that this typically results in a voltage span less than 1 V. Further, using an Ag CE also enables approximately the same potential levels to be applied to the WE in both 2-electrode and 3- electrode systems. Moreover, in 2-electrode systems the surface area of the CE in relation to the EAP volume on the WE influences expansion performance. Generally the CE area needs to be much larger than the WE for good actuation properties (especially speed), while in 3-electrode systems the CE size is of less importance. By using Ag as CE in a 2-electrode system the CE need not be as large as when other materials are used, such as Pt, Ti/Pt or carbon fibre. This is advantageous for applications in vivo, in small devices and generally in small confined spaces where the total device size may be an issue. In a 2-electrode system, the Ag CE typically needs to be only about 4 times larger than the WE, while for other materials, such as Ti/Pt, the area typically needs to be significantly larger, up to hundreds of times the size of the WE surface area to achieve the same performance as the corresponding 3-electrode system. In one example a reference sample was activated according to reference actuation with the difference that a 2-electrode system was used with an Ag CE about 4 times larger than the WE. The voltage over the WE- CE during the final activation step was from 0.2 V to -1 V. The out-of-plane expansion was measured. As can be seen in Fig.13a, expansion in the 2-electrode Ag CE case is similar to expansion with the same sample in a 3-electrode set-up with a large Ti/Pt mesh as CE (several hundred times the WE size) but also significantly higher than expansion when a Ti/Pt CE of about 30 times the WE size is operated in a 2-electrode set-up using a larger voltage span (0.5 V to -1.5 V over WE-CE).

Fig. 13b compares the WE-CE potential in a 3-electrode setup using different CE materials (Au, SS, Pt and Ag) during activation of PPy(DBS) in a 0.1 M NaDBS electrolyte and using an Ag/AgCI reference electrode. The WE potential (vs. Ag/AgCI) was swept from 0 V to -1 V and back to 0 V at 300 s (i.e. sweep rate=6.7mV/s). As can be seen in Fig. 11b, the voltage span between both redox potential peaks and vertex potentials was significantly reduced when using an Ag CE compared to the other metals.

A number of substrates and materials composed of or containing silver may be used as Ag CE. Examples of such materials are the same as the ones mentioned above in the case of the Ag quasi-RE.

Actuation of PPy(DBS) using a 2-electrode setup typically requires a negative WE potential for actuation by reduction and a slightly positive WE potential for actuation by oxidation. However, in some applications, or for reasons of control circuitry design, it is desirable with single polarity potentials, i.e. only negative or positive potentials on the WE for both reduction and oxidation. Also, in many bio-applications it is advantageous to work with single polarity potentials, for example negative ones, since most plasma proteins have negative polarity and there is a risk for blood coagulation at the WE if positive potentials are used, and this risk may increase with higher potentials.

It has been found that by using Al as CE material, both reduction and oxidation potentials are positive for a PPy with anion dominated ion transport, such as PPy(DBS) in a NaCI electrolyte. In one example, PPy(DBS) was synthesized according to the reference sample, but the polymerization was stopped when the thickness reached 10μm. Actuation was performed using cyclic voltametry in a 2-electrode system with 0.15M NaCI electrolyte at RT with a scan speed of 5 mV/s. That is the reference actuation with only 2 electrodes (CE being Al) and no voltage steps, only cycling.

As can be seen in Fig. 14, the redox potential peaks are located at positive voltages in the case of an Al CE, which is not the case for e.g. an Au or Pt CE.

A number of substrates and materials composed of or containing aluminium may be used as CE. Examples of such materials are the same as the ones mentioned above forin the case of the Ag quasi-RE, with the exception that Ag/silver is replaced by Al/aluminium.

CEs such as gold and platinum typically need to be added or mounted to the device. For medical devices, for instance catheters, size limitations and limiting the number of different materials that are used are important issues. Therefore it is desirable to limit the amount different materials and size of the components or total device. It has been found that stainless steel (SS) beneficially may be used as CE material. An advantage is that SS is commonly used in many medical devices and that hence potentially no additional materials need to be added. In fact, a SS part of a medical device may be used as the CE₁ e.g. when actuating an EAP actuator in vivo. Yet, another advantage is that using SS or an SS part may reduce the number of fabrication steps and thus the manufacturing costs. In one example, reference actuation, with the difference that a stainless steel guide wire was used as CE, was performed on a reference sample. The out-of-plane expansion was measured. The result was compared with corresponding actuation of the same sample using an Au CE. As can be seen in Fig. 15 the performance using the SS CE with respect to total expansion and expansion speed was identical to the performance using an Au CE.

A number of substrates and materials composed of or containing aluminium may be used as SS CE. Examples of such materials are the same as the ones mentioned above in the case of the Ag quasi-RE, with the exception that Ag/silver is replaced by SS/stainless steel.

It has been found that malfunctioning EAP-based actuators often are caused by an imperfect shape of the EAP object on which the actuator is based. The imperfect shape typically is a side-effect from the EAP growth during synthesis and is hard to avoid.

Fig. 16a illustrates an ideal, desirable EAP actuator for a ring-like device. A tubular or rod-like substrate 30 comprises a conducting annular electrode 24 that is at least partially covered with an EAP layer 23. Ideally this EAP layer 23 should cover the electrode 24 uniformly, have an even thickness and no excess outgrowth. However, in practice, EAP synthesis does not result in perfectly shaped EAP objects as would be desirable. Instead, a grown EAP object typically comprises one or more irregularities, such as illustrated in Fig. 16b, deviating from an intended shape. Such irregularities may comprise imperfections such as lateral (side ways) outgrowth 31 (i.e. the EAP layer extends far beyond the electrode contours, often with a declining thickness), local thickness variations 32 (e.g. thicker EAP ring-like structures that occur near the edges of the electrode), spikes, bulges, or protrusions that might be irregularly shaped, formed, and placed in the EAP layer (illustrated by 33a through 33d). These effects are typically independent of the shape of the substrate, here the electrode 24. For instance, similar imperfections also occur on a flat surface having a patterned electrode. Fig. 16c illustrates another ideal EAP actuator on a flat conducting substrate 24. Ideally, the EAP layer 23 is perfectly flat, rectangularly shaped as illustrated in Fig 16c. However, when using a masking layer 34 (e.g. a photoresist or patternable resin like SU8) in order to laterally pattern the EAP layer 23 during synthesis, outgrowth 35 of the EAP layer 23 over the masking layer 34 often occurs near the edges of the holes in the masking layer as illustrated in Fig. 16d. This is similar to the imperfections 32 that occur at the edges of an electrode (Fig. 16b).

After post-growth removal of imperfections, such as the ones exemplified above, a much less degree of malfunctioning devices have been observed. The removal is preferably taking place in connection with manufacturing.

Moreover, conventional methods for patterning EAPs, such as polypyrrole, polyaniline, and polythiophene, include using photoresists to shield certain areas and then use Reactive Ion Etching (RIE) to remove exposed material or using a sharp tool to cut the material. All these methods have one or several disadvantages that limit the process freedom or could potentially contaminate or damage the EAP material. In general, the traditional methods are not suited for critical areas, such as in medical devices, where contamination and well defined structures typically are essential. Rapid and high definition patterning of EAP without contaminating or damaging the material is desirable. Moreover, the conventional kind of patterning makes it hard and complicated to pattern 3D objects such as rings.

It has been found that both the removal of imperfections and patterning may advantageously be done using a laser with low heat generation ablating undesired EAP material from a grown EAP object.

One example of a suitable type of laser is an excimer laser. Excimer lasers generate laser light in ultraviolet to near-ultraviolet spectra, from 193 to 351 nanometers. An excimer laser typically uses a combination of an inert gas (such as argon, krypton or xenon) and an reactive gas (such as flourine or chlorine). A list of typical excimer lasers can be found in Table 1. Since excimer lasers have very short wavelengths, the photons have high energy. The incident photon energy is high enough to break the chemical bonds of the electro-active polymer directly, the polymer is dissociated into its chemical components, and no liquid phase transition occurs in this process. This results in reduced interaction time between laser radiation and the electro- active polymer and therefore the heat affected zone is minimized. This feature, along with the fact that no chemicals are used, make excimer lasers particularly suitable for removing electroactive polymer materials. Heat generation from gas lasers such as CO2, and solid state lasers such as Nd:YAG, have been found to generally generate too much heat, which destroys the material. Low heat generating lasers, including excimer lasers, enables rapid patterning of both planar and non-planar substrates with feature sizes down to a few micrometers.

Table 1 In one experiment an ArF excimer laser was used for micromachining PPy layers that had a thickness ranging from 40-50 μm and that was arranged on an annular Au substrate. The laser was set to 75 mJ. Different pulse repetition rates were used (20, 35 Hz) and different numbers of shots per machined structure were used (100, 150, 200, 500 shots). Holes with a diameter of 27-33 μm were machined, as well as channels that were 42 μm wide. The PPy was completely removed, exposing the underlying Au substrate of the machined structures.

In another experiment another ArF excimer laser (193 nm wave length) was used to pattern PPy with an ablation rate of 0.14 μm per laser pulse. In order to accomplish holes (300 μm long, 50 μm wide) 350 pulses at 40 Hz were used.

Film thickness of the PPy is typically 1-100μm and typical ablation rates are 0.1-1.0 μm per pulse (at 193 nm wavelength). It is understood that when through holes are not desired, the number of pulses can be reduced. For example, the number of pulses can be adapted so as to remove protruding imperfections from the surface of an EAP object.

In yet another experiment a low power Q-switch Nd-YAG laser with an adjustable power of 0 to 6 W was used for patterning PPy. The one skilled in the art realises that also other low power lasers may be used.

Using a laser to remove EAP material for example makes it possible to pattern EAP with feature sizes of just a few micrometers without damaging or contaminating the polymer. One further advantage is that high density bulk material such as solid gold or silicon are not affected, while for instance thin metal films can easily be patterned. This means that for instance a bilayer actuator, which consists of a thin metal film with an electro-active polymer film on top, can be patterned without damaging or affecting a carrier substrate, metal electrodes or support structures inside or beneath the polymer material.

In another embodiment removal of EAP material is made using a water jet cutter instead of a laser. A water jet cutter is a tool that uses a pressurized water stream with high velocity to cut through a material. Such tool is capable of providing intricate cuts. The kerf, or width, of the cut can be as narrow as 50μm or less depending on the equipment (27 μm has been demonstrated). Furthermore, as the method relies on pressurized water, it will not contaminate the material to be cut and there is no heat affected zone, which e.g. are key aspects for functionality of medical devices. Abrasives, such as garnet or aluminium oxide, may be added to the water jet when cutting electro-active polymer materials. However, these abrasives may have a negative effect on resolutions and particles from the abrasive may remain in or on the material. It has been found that using a water jet enables rapid patterning of both planar and non-planar substrates. In one example a water jet cutter was successfully used to pattern a 20 μm thick PPy film supported by a laminate of gold and polyurethane.

Another example of a situation where post growth EAP material removal may improve performance is edge removal. Ion transport in for instance PPy(DBS) films is much faster in the lateral direction (e.g D2 in Fig. 2c) than in the perpendicular direction (e.g D1 in Fig. 2c). Fig 17a illustrates a substrate 36 that comprises an electrode 24 onto which a layer of EAP 23, such as PPy(DBS), has been synthesized. The "growth planes" are indicated by the dashed lines. Ion transport in parallel to these growth planes is much faster than ion transport perpendicular to the planes. The edges 37 may act as a barrier as the growth planes (i.e. slow ion transport) are perpendicular to the ion transport routes. Post production removal of these edges as is shown in Fig. 17b by laser or water jet may result in increased speed, as the ions now have access directly to the fast transport planes, without having to cross the perpendicular growth planes at 37. Yet another removal method is to mechanically remove EAP material.

One may use a sharp object (knife, razor blade, scapel) in order to cut away the defects, or use means for grinding or abrasion.

The removal of the defects is preferably performed in a dry state, such as when the sample has been removed from the (synthesis) electrolyte and dried.

Fig. 18 is a flow chart describing a generic method based for providing an electroactive polymer (EAP) object using what has been presented above relating to removal of undesired EAP material from an EAP object. In a first step 71 a desired object shape is determined, such as the shape of an object to be used in an EAP-based actuator. This can for example be a layer confined to the surface of an electrode and/or an EAP object having certain patterns that cannot be accomplished by EAP growth only. In a second step 73 an EAP object is being grown. Typically this mean growing an EAP object as close to the desired shape as possible according to what is allowed or is convenient to do given the growth process. In a third step 75 EAP material is being removed from the grown object so that the shape of the object becomes, if not identical to, at least more similar to the desired object shape. As mentioned above, the shape and form of the EAP object in an EAP based actuator has been found to be one important factor for the functioning of the actuator and an imperfect shape is a hard to avoid side-effect from the growth of the EAP object. Additionally, when an EAP is grown as part, for example a layered part, of an electrode, unwanted lateral (sideways) growth of EAP outside of the electrode area has been found to often be an undesirable side-effect that may cause problems (see Fig. 17).

However, it has been found that by adding a non-aqueous polar solvent, such as pentanol, during the synthesis the result is smoother EAP films with far less irregularities and drastically reduced lateral growth. When the EAP is a layered part of an electrode arranged on a larger area underlying substrate the EAP film may thus become nicely confined to the electrode area.

In one example, a sample was synthesised according to the reference sample with the difference that 2.4 vol% 1 -Pentanol was added to the synthesis electrolyte solution. The sample was actuated according to reference actuation and the out-of-plane expansion was measured. The pentanol addition during polymerization resulted in substantially the same expansion as the reference samples. However, the pentanol addition also resulted in less polymer growth outside the working electrode area. In other experiments 1, 2, and 2.5% pentanol has been used as additive during PPy-synthesis.

L. Bay, K. West and S. Skaarup, "Pentanol as co-surfactant in polypyrrole actuators", Polymer (2002) 43, 12, pp.3527-3532 describes the addition of pentanol as co-surfactant to increase strain of linear actuating PPy strips. However, pentanol addition in order to better confine the synthesis to a certain area is not disclosed therein.

The performance of the EAP film grown under influence of the non- aqueous polar solvent is typically similar to reference samples grown without such solvent.

Fig. 19 is a flow chart describing a generic method for synthesizing an electroactive polymer (EAP) material using what has been presented above relating to growth under influence of a polar solvent. In a first step 60 a substrate for the growth is provided. The substrate comprises an electrically conducting first substrate layer. The first substrate layer may be arranged on a second substrate layer 36 which may have a larger area than, and is electrically separated from, the first substrate layer. The first substrate layer is typically an electrode layer 24, typically of metal, such as Ag, and the second substrate layer is typically a non-conducting substrate layer, such as of plastic, ceramic, silicon, on which the electrode layer has been deposited, for example by crimping a metal ring or evaporating a metal layer. In a second step 61 a solution comprising monomers for polymerization, such as in production of the reference sample, mixed with a non-aqueous polar solvent, such as pentanol, is provided. The non-aqueous polar solvent may be added to a monomer solution or the monomer solution may be produced under presence of the non-aqueous polar solvent. In a third step 65, the EAP layer is being polymerized on the first layer using the solution, typically by electropolymerization, such as when producing the reference sample, with the substrate provided in the first step placed in the solution.

After growth of the layer presence of non-aqueous polar solvent in the layer may be detected. It may thus be determined post growth whether an EAP layer has been grown using a polar solvent or not.

As understood by the skilled person, owing to the mechanism of volume change of EAPs, conclusions and relations in the foregoing that are based on embodiments, experiments etc. relating to expansion also apply, if not indicated otherwise, in the reverse direction, i.e. for shrinking/contraction of the EAP from an expanded state. The underlying principles are the same for expansion and shrinking, but with the reactions driven in opposite directions, see e.g. reaction schemes 1 and 2 described in the background.

The devices and systems described herein may be medical devices and systems, such as catheters (guide catjeters, urinary catheters, in-dwelling catheters, aspiration catheters, injection catheters, infusion catheters, drainage catheters, venous catheters, arterial catheters, central line and peripheral line catheters, balloon catheters), guide wires, coated or uncoated stents (including vascular stents, cerebral stents biliary stents, and esophogeal stents), vascular grafts, stent grafts, aneurysm fillers (including Guglielmi detachable coils), devices for rotational atherectomy or thrombectomy, temporary occlusion devices, filters (for example, vena cava filters), baskets and snares (e.g. for retrieval), leads or lead tips (e.g. for cardiac rhythm management, internal defibrillators, pacemakers), electrodes, implanted neurovascular devices (e.g. for spinal stimulation, peripheral nerve stimulation, deep brain stimulation or neuromonitoring), vascular patches, electroporation devices, iontophoresis devices, in-dwelling access ports, devices for cardiac mapping or ablation, intraluminal paving systems, heart valves, annuloplasty rings and bands, sewing rings and cuffs, cannulas, trocars, endoscopes, probes, laparoscopes, sutures, staples, myringotomy tubes, wound or nasal packings, dressings, gauze, bone screws, halo screws, total joints, hernia meshes, needles, wound drains, contact lenses, peristaltic pump chambers, arteriovenous shunts, gastroenteric feed tubes, endotracheal tubes, anastomosis devices, vertebral disks, bone pins, suture anchors, hemostatic barriers, clamps, screws, plates, clips, shunts, tissue adhesives and sealants, tissue scaffolds, various types of dressings, extravascular wraps and bone substitutes, joint prosthesis or part thereof, such as a hip prosthesis, a knee prosthesis, a vertebral or spinal disc prosthesis, a spinal cage, infusion devices, embolic protection devices, introducers, sheaths, etc. The devices and systems may be such that are temporarily inserted into the body lumen during a longer or shorter time period, or devices and systems that are (permanently) implanted into the body.

The electroactive polymers (EAPs) described herein may be conducting polymers comprising pyrrole, and/or aniline, and/or thiophene, and/or para- phenylene, and/or vinylene, and/or phenylene polymers and/or copolymers thereof, including substituted forms of the different monomers.

In the above, a number of supportive experiments have been presented in connection with embodiments. It should be understood that these experiments represent only a fraction of all experiments performed by the applicant, which experiments further support results and conclusions drawn.

Any illustration and description in the drawings and in the foregoing description are to be considered exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in different dependent claims does not indicate that a combination of these measured cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A method for affecting volume change of an electroactive polymer (EAP) material (23) in a device (50), the method comprising the steps of: - providing (41) an electrolyte (13), a first electrode (14) and a second electrode (15), said electrodes being arranged to be in contact with said electrolyte, wherein at least said first electrode (14) comprises said EAP material (23);

- setting (43) at least one parameter having external influence on volume change of the EAP material (23) to a determined value; and

- operating (45) the device under influence of the determined parameter value.

2. The method as claimed in as claimed in claim 1, wherein the device is arranged to utilize out-of-plane volume change of the EAP material.

3. The method as claimed in any one of the preceding claims, wherein the device is arranged to operate the EAP material in a position being a gap between a first part (101) and a second part (102).

4. The method as claimed in any one of the preceding claims, wherein the device is arranged to operate the EAP material for substance delivery, preferably in a human or animal body.

5. The method as claimed in any one of the preceding claims, wherein the EAP material comprises a conducting polymer, such as at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

6. The method as claimed in any one of the preceding claims, wherein the EAP material is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

7. The method as claimed in any one of the preceding claims, wherein the at least one parameter comprises a temperature of the electrolyte and the corresponding determined value corresponds to a determined temperature level.

8. The method as claimed in claim 7, wherein the determined temperature level is determined so that when setting the determined temperature level of the electrolyte there will be an increase of the temperature of the electrolyte.

9. The method as claimed in any one of claims 7-8, wherein the determined temperature level is body temperature or a temperature level significantly above room temperature, or above about 30⁰C, or above about 35⁰C, or above about 37°C, or above about 40⁰C.

10. The method as claimed in any one of claims 7-9, wherein the determined temperature level is below a temperature level permanently damaging the device , or below about 100°C, or below about 70⁰C, or below about 60⁰C, or below about 5O⁰C, or below about 42⁰C.

11. The method as claimed in any one of the preceding claims, wherein the at least one parameter comprises an electric potential of the first electrode over a time period and the corresponding determined value corresponds to a determined electric potential over a determined time period which are adapted to bring the EAP material to an expanded or contracted state, the potential over the time period being applied to the first electrode in the step of operating the device.

12. The method as claimed in claim 11 , wherein the determined electric potential over the determined time period comprises at least a subperiod during which the potential is a cathodic overpotential that is less than a cathodic vertex potential (E_vc), or is an anodic overpotential that is greater than an anodic vertex potential (E_va), preferably by at least 0.1 V, or 0.2 V, or 0.3 V, or 0.4 V or more.

13. The method as claimed in claim 12, wherein the cathodic overpotential is greater than the highest cathodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device and the anodic overpotential is less than the lowest anodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device.

14. The method as claimed in any one of claims 12-13, wherein the subperiod is longer than or equal to: 0.5 s, or 1 s, or 2 s, or 3 s or 4 s.

15. The method as claimed in claim 12, wherein the cathodic and the anodic overpotential is of a voltage level that during a longer period than said subperiod would result in formation of gas.

16. The method as claimed in claim 15, wherein the subperiod is shorter than or equal to: 4 s, or 3 s, or 2 s, or 1.5 s, or 1 s, or 0.5 s.

17. The method as claimed in any one of claims 12-16, wherein the determined potential varies over the determined time period in such way that there is at least one potential level between the overpotential and the corresponding vertex potential, preferably with subsequent potentials approaching the vertex potential.

18. The method as claimed in any one of claims 11-17, wherein the step of operating the device comprises the following substep: limiting the current through the first electrode so that no formation of gas occurs.

19. The method as claimed in any one of claims 11-18, wherein the substep of limiting the current comprises: measuring the current through the first electrode during application of the potential ; and selecting and applying a subsequent potential based on the measured current.

20. The method as claimed in any one of claims 1-19, wherein the at least one parameter comprises the electrolyte ion concentration and the corresponding determined value corresponds to a determined ion concentration.

21. The method as claimed in claim 20, wherein the determined ion concentration is above about 0.1 M, or above about 0.15 M, or above about 0.3 M, or above about 0.5 M, or above about 0.9 M, or above about 1 M.

22. The method as claimed in any one of claims 20-21, wherein the determined ion concentration is below about 1 M, or below about 0.5 M, or below about 0.2 M, or below about 0.1 M.

23. The method as claimed in any one of claims 20-22, wherein the step of setting (43) the ion concentration are repeatedly performed in combination with the step of operating (45) the device so that different ion concentration are set and the ion concentration changes during operation of the device.

24. The method as claimed in any one of claims 1-23, wherein the at least one parameter comprises composition of the electrolyte with respect to the kind of cations and the corresponding determined value corresponds to a determined cation type in the composition.

25. The method as claimed in claim 24, wherein the determined cation type is at least one of the following: K⁺, Ca²⁺, Na⁺ and Li+.

26. A device (50) comprising an EAP material (23), an electrolyte (13), a first electrode (14) and a second electrode (15), said electrodes being arranged to be in contact with said electrolyte and said EAP material being comprised in at least the first electrode (14), said device further comprising means (11; 54, 55; 52) for setting at least one parameter having external influence on volume change of the EAP material (23) to a determined value and means (11) for operating the device under influence of the determined parameter value.

27. The device as claimed in claim 26, wherein the device is arranged to utilize out-of-plane volume change of the EAP material.

28. The device as claimed in any one of claims 26-27, wherein the device is arranged to operate the EAP material in a position being a gap between a first part (101) and a second part (102).

29. The device as claimed in any one of claims 26-28, wherein the device is arranged to operate the EAP material for substance delivery, preferably in a human or animal body.

30. The device as claimed in any one of claims 26-29, wherein the EAP material comprises a conducting polymer, such as at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

31. The device as claimed in any one of claims 26-30, wherein the EAP material is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

32. The device as claimed in any one of claims 26-31, wherein the at least one parameter comprises a temperature of the electrolyte and the corresponding predetermined value corresponds to a determined temperature level.

33. The device as claimed in claim 32, wherein the determined temperature level is selected so that the means for setting the at least one parameter is adapted to set the temperature of the electrolyte to a higher temperature than a natural temperature of the electrolyte, such as determined by the ambient temperature of the device.

34. The device as claimed in any one of claims 32-33, wherein the determined temperature level is body temperature or a temperature level significantly above room temperature, or above about 3O⁰C, or above about 35°C, or above about 37°C, or above about 40°C.

35. The device as claimed in any one of claims 32-34, wherein the predetermined temperature level is below a temperature level permanently damaging the device, or below about 100⁰C, or below about 7O⁰C, or below about 60°C, or below about 50⁰C, or below about 42° C.

36. The device as claimed in any one of claims 26-35, wherein the at least one parameter comprises an electric potential of the first electrode and the corresponding determined value corresponds to a determined electric potential over a determined time period which are adapted to bring the EAP material to an expanded or contracted state, the means for setting the electric potential over the time period being adapted to apply the electric potential to the first electrode when the device is being operated.

37. The device as claimed in claim 36, wherein the determined electric potential over the determined time period comprises at least a subperiod during which the potential is a cathodic overpotential that is less than a cathodic vertex potential (E_vc), or is an anodic overpotential that is greater than a anodic vertex potential (E_va), preferably by at least 0.1 V, or 0.2 V, or 0.3 V, or 0.4 V or more.

38. The device as claimed in claim 37, wherein the cathodic overpotential is greater than the highest cathodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device and the anodic overpotential is less than the lowest anodic overpotential that, independent on the length of the subperiod, would result in gas formation in the device.

39. The device as claimed in any one of claims 37-38, wherein the subperiod is longer than or equal to: 0.5 s, or 1 s, or 2 s, or 3 s or 4 s.

40. The device as claimed in claim 37, wherein the cathodic and the anodic overpotential is of a voltage level that during a longer period than said subperiod would result in gas formation.

41. 12 The device as claimed in claim 40, wherein the subperiod is shorter than or equal to: 4 s, or 3 s, or 2 s, or 1.5 s, or 1 s, or 0.5 s.

42. The device as claimed in any one of claims 37-41 , wherein the determined potential varies over the determined time period in such way that the means for setting the potential is adapted to set at least one potential level between the overpotential and the corresponding vertex potential, preferably adapted to set subsequent potentials approaching the vertex potential.

43. The device as claimed in any one of claims 36-42, wherein the device is further arranged to limit current through the first electrode so that no formation of gas occur.

44. The device as claimed in any one of claims 36-43, wherein the device is further arranged to measure the current through the first electrode during application of the potential and to select and apply a subsequent potential based on the measured current.

45. The device as claimed in any one of claims 26-44, wherein the at least one parameter comprises the electrolyte ion concentration and the corresponding determined value corresponds to a determined ion concentration.

46. The device as claimed in claim 45, wherein the determined ion concentration is above about 0.1 M, or above about 0.15 M, or above about

0.3 M, or above about 0.5 M, or above about 0.9 M, or above about 1 M.

47. The device as claimed in any one of claims 45-46, wherein the determined ion concentration is below about 1 M, or below about 0.5 M, or below about 0.2 M, or below about 0.1 M.

48. The device as claimed in any one of claims 45-47, wherein the means for setting (43) the ion concentration is adapted to repeatedly set the ion concentration when the device is operated so that different ion concentration are set and the ion concentration changes during operation of the device.

49. The device as claimed in any one of claims 26-48, wherein the at least one parameter comprises composition of the electrolyte with respect to the kind of cations and the corresponding determined value corresponds to a determined cation type in the composition.

50. The device as claimed in claim 49, wherein the determined cation type is at least one of the following: K⁺, Ca²⁺, Na⁺ and Li+.

51. A system (50) comprising a working electrode (14), a counter electrode (15) and an electrolyte (13) adapted to be in contact with the electrodes, wherein at least the working electrode (14) comprises an electroactive polymer (EAP) material (23).

52. The system as claimed in claim 51, wherein the system is arranged to utilize out-of-plane volume change of the EAP material.

53. The system as claimed in any one of claims 51-52, wherein the EAP material comprises a conducting polymer, such as at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

54. The system as claimed in any one of claims 51-53, wherein the EAP material is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

55. The system as claimed in any one of claims 51-54, wherein the counter electrode comprises silver.

56. The system as claimed in claim 55, wherein the counter electrode is at least partially covered by silver.

57. The system as claimed in claim 55, wherein the counter electrode substantially consists of silver.

58. The system as claimed in any one of claims 51-54, wherein the counter electrode comprises aluminium.

59. The system as claimed in claim 58, wherein the counter electrode is at least partially covered by aluminium.

60. The system as claimed in claim 58, wherein the counter electrode substantially consists of aluminium.

61. The system as claimed in any one of claims 51-54, wherein the counter electrode comprises stainless steel.

62. The system as claimed in claim 61 , wherein the counter electrode is at least partially covered by stainless steel.

63. The system as claimed in claim 61, wherein the counter electrode substantially consists of stainless steel.

64. The system as claimed in any one of claims 51-63, wherein the system is a 2-electrode system.

65. The system as claimed in any one of claims 51-63, wherein the system (50) further comprises a reference electrode (16) in contact with the electrolyte (13).

66. The system as claimed in claim 65, wherein the reference electrode comprises silver.

67. The system as claimed in claim 66, wherein the reference electrode is at least partially covered by silver.

68. The system as claimed in claim 66, wherein the reference electrode substantially consists of silver.

69. The system as claimed in any one of claims 65-68, wherein the working electrode is located in a 3-dimensional space wherein at least one dimension of the space is less than 10 times the thickness of the working electrode, or less than 5 times, or less than 2 times or even less than the thickness of the working electrode.

70. The system as claimed in any one of claims 65-69, wherein the reference electrode has a surface area that is less than: 1 cm², or 0.8 cm², or 0.6 cm² or 0.4 cm² or 0.2 cm².

71. A method for providing an electroactive polymer (EAP) object (23) , comprising the steps of:

- growing (73) the EAP object;

- determining (71) a desired object shape before or after the step of growing the EAP object; and - removing (75) EAP material from the grown EAP object (23) so that said EAP object becomes more similar to the desired shape.

72. The method as claimed in claim 71, wherein the EAP material comprises a conducting polymer, such as at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

73. The method as claimed in any one of claims 71-72, wherein the EAP material is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

74. The method as claimed in any one of claims 71-73, wherein the desired object shape is that of an EAP object for use in an EAP based actuator.

75. The method as claimed in any one of claims 71-74, wherein the grown EAP object resembles the desired shape and deviates from the desired shape by local protrusions (32; 33a; 33b; 33c), and in the step of removing material, the EAP material is being removed from said local protrusions.

76. The method as claimed in any one of claims 71-75, wherein the EAP object (23) is grown on top of a first (24) and a second substrate (36), said first substrate being arranged between the EAP object and the second substrate, wherein in the step of removing material, the EAP material is being removed from the second substrate so that the EAP object becomes arranged only on the first substrate.

77. The method as claimed in any one of claims 71-76, wherein a layer forms the desired shape, such as a substantially rectangular layer forming a 2-dimensional rectangle or a 3-dimensional shape, such as a cylinder.

78. The method as claimed in claim 77, wherein the removal of EAP material involves removing material protruding from edge portions or edges of said layer, such as material protruding in directions that at least locally are parallel to a plane of the layer.

79. The method as claimed in any one of claims 71-78, wherein the removal of EAP material involves removing material so that recesses, preferably through holes, are formed in the object.

80. The method as claimed in any one of claims 71-79, wherein the removal of EAP material is made by means of a water jet cutter.

81. The method as claimed in any one of claims 71-80, wherein the removal of EAP material is made by means of a laser.

82. The method as claimed in claim 81, wherein the laser generate light having a wavelength in the range of about 193 nm to about 351 nm.

83. The method as claimed in any one of claims 81-82, wherein the laser is an excimer laser.

84. Use of a laser or water jet cutter to remove electroactive polymer (EAP) material from an EAP object.

85. The use as claimed in claim 84, wherein the EAP material comprises a conducting polymer, such as at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

86. The use as claimed in any one of claims 84-85, wherein the EAP material is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

87. A method for providing an electroactive polymer (EAP) layer (23) on a substrate (36, 24), comprising the steps of:

- providing (60) the substrate, said substrate comprising an electrically conducting first substrate layer (24), such as an electrode layer, arranged on a second substrate layer (36) having a larger area than and being electrically separated from said first substrate layer; - providing (61) a solution comprising monomers for polymerization of the EAP layer and a non-aqueous polar solvent; and

- polymerizing (65) the EAP layer on the first substrate layer using the solution.

88. The method as claimed in claim 87, wherein the EAP layer comprises a conducting polymer, such as a polymer of at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

89. The method as claimed in any one of claims 87-88, wherein the EAP layer is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

90. The method as claimed in any one of claims 87-89, wherein the EAP layer is adapted for use in an EAP based actuator.

91. The method as claimed in any one of claims 87-90, wherein the polymerization is provided by means of electropolymerization.

92. The method as claimed in any of claims 87-91, wherein the nonaqueous polar solvent is pentanol, such as 1-Pentanol.

93. The method as claimed in any of claims 87-92, wherein the amount of the non-aqueous polar solvent in the solution is above about 0.1vol%, or above about 0.5 vol%, or above about 1 vol%, or above about 2 vol%, or above about 3 vol% or above about 4 vol% or above about 5 vol%.

94. The method as claimed in any of claims 91-93, wherein the amount of the non-aqueous polar solvent in the solution is below about 10 vol%, or below about 9 vol%, or below about 8 vol%, or below about 7 vol%, or below about 6 vol%.

95. Use of a non-aqueous polar solvent as an admixture in a monomer solution to confine an electroactive polymer (EAP) layer (23) polymerized from said solution to a first substrate layer (24).

96. The use as claimed in claim 95, wherein the first substrate layer

(24) is an electrically conducting layer, such as an electrode layer, arranged on a second substrate layer (36) having a larger area than and being electrically separated from said first substrate layer.

97. The use as claimed in any one of claims 95-96, wherein the EAP layer comprises a conducting polymer, such as a polymer of at least one of the following: pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.

98. The use as claimed in any one of claims 95-97, wherein the EAP layer is doped with at least one of the following: dodecylbenzene sulfonate, octylbenzene sulfonate and polystyrenesulfonate.

99. The use as claimed in any one of claims 95-98, wherein the EAP layer is adapted for use in an EAP based actuator.

100. The use as claimed in any one of claims 95-99, wherein the EAP layer is polymerized by means of electropolymerization.

101. The use as claimed in any of claims 95-100, wherein the non- aqueous polar solvent is pentanol, such as 1-Pentanol.

102. The use as claimed in any of claims 95-101, wherein the nonaqueous polar solvent admixture results in that the amount of the polar solvent in the solution becomes above about 0.1vol%, or above about 0.5 vol%, or above about 1 vol%, or above about 2 vol%, or above about 3 vol% or above about 4 vol% or above about 5 vol%.

103. The use as claimed in any of claims 95-102, wherein the nonaqueous polar solvent admixture results in that the amount of the polar solvent in the solution becomes below about 10 vol%, or below about 9 vol%, or below about 8 vol%, or below about 7 vol%, or below about 6 vol%.