EP3385413A1

EP3385413A1 - Microfluidic processing of polymeric fibres

Info

Publication number: EP3385413A1
Application number: EP17165605.1A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA
Current assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA
Priority date: 2017-04-07
Filing date: 2017-04-07
Publication date: 2018-10-10
Also published as: WO2018185349A1

Abstract

A microfluidic device for creating sheathed flow, comprises a tubular flow chamber (2) with a longitudinal centre axis (A), the flow chamber having an inlet section (4) and an outlet section (6) axially displaced therefrom in a downstream direction, the inlet section comprising a core inlet (8) and at least one sheath inlet (10). To improve compactness and operational flexibility, the core inlet comprises a core inlet tube (14) disposed coaxially within the flow chamber and having a terminal opening (16) which is selectively positionable between a first core axial position (z c 1) and a second core axial position (z c 2). The sheath inlet comprises at least one group of at least two inlet channels (18a, 18b) leading into the flow chamber at respective inlet openings (20a, 20b), the inlet channels of each channel group being formed as substantially identical elongated channels within said chamber body and being disposed symmetrically around the longitudinal centre axis in a manner converging in downstream direction at an inclination angle ±, the inlet openings of a given channel group having substantially identical axial positions (z s ) and the inclination angle ± of each channel group being selected in the range of 10º to 45º.

Description

Field of the Invention

The present invention generally relates to microfluidic processing of polymeric fibres. More particularly, the invention relates to a microfluidic device for creating sheathed flow, to a system for producing a polymeric fibre comprising such a device and to a method of forming a polymeric fibre.

Background of the Invention

Production of multi-functional and multi-layered fibres and coatings with precise spatial resolution by combining microfluidic setup and fibre processing methods is known and is currently being developed further.
Two types of commercial devices already employed to yield well-defined layered micro and nano fibres are a co-axial co-flowing device made of glass as disclosed in EP 1818432 A2 and a setup comprising commercially available co-axial and tri-axial stainless steel needles, which can be obtained from ramé-hart instrument co. (see http://www.ramehart.us/coaxial-needles/). However, these known setups present severe limitations. In the first case, the use of glass as fabrication material impedes the application for high viscosity solutions or under high pressure conditions due to its inherent brittleness and breakability. In the second case, the device composed of stainless steel requires the presence of rubber seals between the junctions of each needle, which limits the durability of the device. Moreover, both devices have limitations in their fabrication design as the use of concentric needles or glass capillaries requires different magnitudes for the outer diameter of each needle/glass capillary.
An essential feature required for the controlled formation of layered micro and nanofibres is the establishment of a sheath flow, i.e. of a flow pattern comprising at least two concentrically disposed layers of flowing medium. This is disclosed, e.g., in US 2011/0193259 A1 , which relates to a method of creating a sheathed flow comprising a first and second fluid. The method relies on a device with a flow channel having opposed facing top and bottom surfaces each provided with a so-called fluid transporting structure serving to divert the flow direction of one of the fluids in a transversal direction. Although such fluid transporting structure can be realized e.g. as a comparatively simple arrangement of oblique grooves, formation of a very regular layered structure appears difficult and variability of the process to yield differently dimensioned layered structures is limited.
A different approach is described in US 8834780 B2 , which discloses a process of forming a polymer fibre by hydrodynamic spinning wherein a plurality of fluids is forced to flow through a conduit and to form a laminar flow comprising three or more layers of generally coaxial fluid flows. The conduit is selected to define a cross-section of a tubular middle layer comprising a cross-linkable polymer precursor while another layer comprises a cross-linking agent. Substantial diffusion of the polymer precursor away from the middle layer is prevented but a portion of cross-linking agent is allowed to diffuse into the middle layer to facilitate cross linking of the polymer precursor in the middle layer. This approach requires formation of at least three layers, and variation of layered structures is essentially limited to changing the input flow rates of the respective layers of fluid flows.
Therefore, in spite of the technical solutions already known, it would still be highly desirable to provide further improvements and to overcome some of the disadvantages and limitations of current methods and devices.

Summary of the Invention

According to one aspect of the invention, there is provided a microfluidic device for creating sheathed flow, comprising

a tubular flow chamber with a longitudinal centre axis, the flow chamber having an inlet section and an outlet section axially displaced therefrom in a downstream direction,
the inlet section comprising a core inlet and at least one sheath inlet,

the flow chamber is formed as an elongated channel within a polymeric chamber body;
the core inlet comprises a core inlet tube disposed coaxially within the flow chamber, the core inlet tube having a terminal opening which is selectively positionable between a first core axial position and a second core axial position, the terminal opening having a pre-selected diameter;
the sheath inlet comprises at least one group of at least two inlet channels leading into the flow chamber at respective inlet openings, the inlet channels of each channel group being formed as substantially identical elongated channels within said chamber body and being disposed symmetrically around the longitudinal centre axis in a manner converging in downstream direction at an inclination angle, the inlet openings of a given channel group having substantially identical axial positions and the inclination angle of each channel group being selected in the range of 10º to 45º.

According to another aspect, there is provided a system for producing a polymeric fibre, comprising a microfluidic device according to the invention, wherein each inlet channel is connected to an individual supply device providing a controllable inlet flow rate and wherein the outlet section is connected to fibre processing device selected from a dry and melt spinning system, a wet spinning system, an electrospinning system and a 3D-printing system. The combination of the microfluidic device with fibre processing techniques allows a further tuning of the morphological properties of the fibres, such as their crystallinity, surface topography, fibre diameter and overall mechanical properties.
According to yet another aspect, there is provided a method of forming a polymeric fibre by means of a microfluidic device according to the invention, the method comprising pumping a polymerizable liquid into one of said core inlet and sheath inlet, and pumping an additional liquid into the other one of said core inlet and sheath inlet, in such manner as to form a sheathed laminar flow region comprising a core region of one of said liquids surrounded by a sheath layer of the other one of said liquids, the method further comprising inducing polymerization of the polymerizable liquid in the sheathed laminar flow region.
The term "microfluidic" shall be understood as known in the field of microfluidics, which field deals with the behaviour, control and manipulation of fluids that are geometrically constrained to a small, typically sub-millimetre, scale. Accordingly, the relevant regions of the tubular flow chamber and of the inlet channels, and also the terminal opening of the core inlet tube have a cross sectional size not exceeding 10 mm. There will also be some lower bound to the dimensions of the above mentioned features, which will be determined by the limitations of machining, but also by the practical requirement of achieving certain minimal flow rates. In the above context, "relevant regions" means regions of a component which have an impact on the sheath flow pattern generally pursued by the invention. A non-relevant region of an inlet channel could be, e.g. a liquid supply tube located clearly upstream of the microfluidic device.
A key feature of the present invention is the ability to vary the longitudinal position of the terminal opening of the core inlet tube in relation to the inlet openings of the one or optionally several sheath inlets, thereby allowing to modify and control the reaction time for the various components introduced into the flow chamber. In principle, the range of longitudinal positions may reach from a position upstream of the most upstream inlet openings to a position downstream of the most downstream inlet openings.
The person skilled in the field of microfluidics will know that establishing a substantially laminar sheathed flow pattern for a specified configuration of the microfluidic device will require that certain fluid dynamics criteria are obeyed, e.g. that the Reynolds number shall not exceed a certain threshold value.
Advantageous embodiments are defined in the dependent claims and are described below.
As will be understood, the microfluidic device of the present invention is intended to provide sheathed flow of certain liquids that are useful for forming polymeric fibres. Depending on the specific application, these liquids comprise but are not limited to liquids containing polymerizable species, liquids containing polymerization agents, liquids containing inert species serving e.g. to assist an intended layering structure and liquids containing effective species such as dyes, chemical agents or biological agents. The liquids may be in the form of aqueous or nonaqueous solutions.
According to an advantageous embodiment (claim 2), the tubular flow chamber is substantially cylindrical. By "substantially cylindrical" is meant that the elongated channel formed in the chamber body has a cylindrical shape. Such a shape is convenient for the manufacturing process and is favourable for establishing the desired laminar flow. Nevertheless, according to another embodiment, a cylindrically symmetric shape with variable cross section along the longitudinal axis, for example a slowly converging circular cross section could be used. On the other hand it will be understood that the chamber body may have outer shapes substantially deviating from cylindrical. For example, in some embodiments the outer shape of the chamber body has a cylindrical or nearly cylindrical main part and a frusto-conically shaped distal part near the outlet.
In a further advantageous embodiment (claim 3), the sheath inlet comprises a first group of at least two first inlet channels with inlet openings at a first axial position Z_s1 and it further comprises a second group of at least two second inlet channels with inlet openings at a second axial position Z_s2 axially displaced therefrom in a downstream direction. As will be outlined in more detail below, this arrangement allows for additional flexibility in forming a layered laminar flow. As already mentioned, variation of the longitudinal position of the terminal opening of the core inlet tube in relation to the one or optionally several sheath inlets represents an important control parameter for the laminar flow and the process occurring therein. In the case where there is more than one group of inlet channels, the axial separation between the inlet channel groups constitutes a further design parameter providing even more flexibility in adjusting the polymerization processes occurring in the flow chamber. In some embodiments the sheath inlet comprises a third group or even further groups of inlet channels.
According to a convenient embodiment (claim 4) the inlet section and the outlet section are provided with coupling elements for forming a medium-tight connection with a supply device and with a fibre processing device, respectively. Preferably, the coupling elements are configured according to some established laboratory standard for fluid connectors.
There are several suitable choices for the polymeric material forming the chamber body. Preferably (claim 5) the polymeric chamber body is made of polycarbonate or PMMA. These materials are convenient to handle during assembly and use of the system, and they are suitable for contact with many media used in the field of polymeric fibre processing technology. Moreover, PMMA is sufficiently transparent to allow implementation of photolytic polymerization through the chamber body, i.e. without the need of additional window elements. This does not exclude further embodiments in which only specific regions of the device are made of such transparent material.
Advantageously, the core inlet tube is made of stainless steel. In certain embodiments, the core inlet tube is formed as a simple, substantially cylindrical tube. According to another embodiment (claim 6), the core inlet tube comprises at least two substantially parallel core inlet channels, which allows forming multiple core fluids running in parallel. In one of these embodiments the core inlet tube has a core-shell structure, i.e. it is formed of two concentric channels,
It will be understood that the polymerization step required for fibre formation can be induced in any suitable manner.
According to an advantageous embodiment (claim 9), polymerization is induced photolytically, i.e. by irradiation with light of a suitable wavelength.
According to another advantageous embodiment (claim 10), polymerization is induced by reaction of the polymerizable liquid and a polymerization agent contained in the additional liquid. For this purpose, the method relies on a controlled exchange at the interface between the polymerizable liquid and the additional liquid. Such a controlled exchange is provided according to the invention by establishing sheathed laminar flow having a flow pattern that can be appropriately controlled over a significant operational range. The term "reaction" shall be understood broadly and shall include not only chemical reactions in the strict sense but also physical processes that lead to polymerization upon contacting two or more species.
According to a particularly advantageous embodiment (claim 11), the polymerizable liquid is pumped into the first inlet channels, a first additional liquid is pumped into the core inlet and a second additional liquid is pumped into the second inlet channels. In this manner a laminar flow pattern of three concentric layers can be established, which allow implementation of a multitude of fibre forming processes. According to one embodiment (claim 12), the first and second additional liquids are identical. For example, the first and second additional liquids may be a polymerization agent which will form, respectively, a core region and an external region embedding therebetween a polymerizable liquid introduced via the first inlet channels.
According to a further advantageous embodiment (claim 13), the polymerizable liquid contains an admixture of a species of interest. In the present context such a "species of interest" can be any species selected from a whole variety of small molecules or nanoparticles that may serve a specific purpose when incorporated in a defined region of a polymeric fibre.

Brief description of the drawings

The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1: shows a microfluidic device for creating sheathed flow, as a schematic representation, in a longitudinal sectional view;
Fig. 2: shows a further microfluidic device for creating sheathed flow, as a schematic representation, in a longitudinal sectional view;
Fig. 3: shows the microfluidic device of Fig. 2, (a) in an oblique perspective view, and (b) in a side elevational view;
Fig. 4: shows an arrangement comprising a microfluidic device for creating sheathed flow connected to a dry and melt spinning system, in a perspective view;
Fig. 5: shows an arrangement comprising a microfluidic device for creating sheathed flow connected to a wet spinning system, in a perspective view;
Fig. 6: shows an arrangement comprising a microfluidic device for creating sheathed flow connected to an electrospinning system, in a perspective view;
Fig. 7: shows an arrangement comprising a microfluidic device for creating sheathed flow connected to a 3D printing system, in a perspective view;
Fig. 8: shows the assembly of an arrangement having (a) one group of inlet channels, and (b) two groups of inlet channels, in a perspective view;
Fig. 9: shows formation of two different shapes of alginate fibre formed with two different devices, visualized as fluorescence images, wherein A) is a device with one group of inlet channels, B) is a device with two groups of inlet channels, C) shows a full fibre formed with device A), and D) shows a hollow fibre formed with device B);
Fig. 10: shows formation of two different shapes of alginate fibre formed with a given device, visualized as SEM images, wherein A) and B) are schematic representation of the laminar flow patterns of the device with two groups of inlet channels, C) shows a thick walled fibre formed with conditions A) and D) shows a thin walled fibre formed with conditions B);
Fig. 11: shows formation of a dye-loaded alginate fibre, visualized as optical images, wherein A) is a device with two groups of inlet channels and B) shows the fibre loaded with blue dye;
Fig. 12: shows formation of alginate fibres surface coated and core loaded, respectively, with Trizo-Fe²⁺ crystals by means of two different devices, visualized as optical images, wherein A) is a device with one group of inlet channels, B) is a device with two groups of inlet channels, C) shows a surface coated fibre formed with device A), and D) shows a core loaded fibre formed with device B);
Fig. 13: shows a comparison of alginate fibres: A), B) surface coated and C), D) core loaded, respectively, with Trizo-Fe²⁺ crystals, wherein A) and C) are SEM images and B) and D) show EDX results;
Fig. 14: shows the size of Trizo-Fe²⁺ crystals, A) on the surface and B) in the core of an alginate fibre, visualized as SEM images; and
Fig. 15: shows the patterning of an alginate fibre coated with Trizo-Fe²⁺ crystals deposited on a glass coverslip, wherein A) is a device with one group of inlet channels, B) is a freshly deposited fibre, and C) is the same fibre after about 5 min, visualized as optical images.

Detailed description of the invention

It will be understood that the figures are not necessarily drawn to scale. In some instances, relative dimensions are substantially distorted for ease of visualization.
A first embodiment of a microfluidic device for creating sheathed flow as shown in Fig. 1 comprises a tubular flow chamber 2 with a longitudinal centre axis A. The flow chamber has an inlet section 4 and an outlet section 6 axially displaced therefrom in a downstream direction. The inlet section comprises a core inlet 8 and one sheath inlet 10. The flow chamber is formed as an elongated channel 11 within a polymeric chamber body 12. The core inlet comprises a core inlet tube 14 disposed coaxially within the flow chamber and having some entrance opening 15 and a terminal opening 16, wherein the latter is selectively positionable between a first core axial position (not shown in this figure) and a second core axial position shown in the figure. In the example shown, the core inlet tube 14 is disposed in an axially slidable manner within the channel 11 by means of a schematically indicated element 17 forming a medium-tight sliding connection.
In the example shown in Fig. 1, the sheath inlet comprises a group of two inlet channels 18a, 18b leading into the flow chamber at respective inlet openings 20a, 20b. The inlet channels of this channel group are formed as substantially identical elongated channels within the chamber body and are disposed symmetrically at opposed sides of the longitudinal centre axis in a manner converging in downstream direction at an inclination angle α. As also seen from Fig. 1, the inlet openings have substantially identical axial positions z_s and the inclination angle shown for illustration purposes is approximately 30º.
A second embodiment of a microfluidic device for creating sheathed flow as shown in Figs. 2 and 3 comprises, in addition to the features of the first embodiment, a second group of two inlet channels 22a, 22b. As shown in Fig. 2, the first group of first inlet channels 18a, 18b has inlet openings at a first axial position z_s1 and the second group of second inlet channels 22a, 22b has inlet openings 24a, 24b at a second axial position z_s2 axially displaced therefrom in a downstream direction.
As also shown in Fig. 2, the terminal opening 16 of the core inlet tube 14 is selectively positionable between a first core axial position z _c1 and a second core axial position z _c2.
Figs. 4 to 7 show various embodiments of a system for producing a polymeric fibre, wherein each system comprises a microfluidic device of the above described kind. In all cases the various inlet channels are connected to a respective supply device providing a controllable inlet flow rate. Moreover, the outlet section is connected to a basically known fibre processing device, which can be a dry and melt spinning system 26 (Fig. 4), a wet spinning system 28 (Fig. 5), an electrospinning system 30 (Fig. 6) and a 3D-printing system 32 (Fig. 7).

Example: Microjet and Functional Alginate Fibber

Materials and Equipment

Two types of microjet devices were used: 3 inlets with 1 outlet or 5 inlets with 1 outlet. The diameters of inlets and outlet were the same, namely around 1.4 mm in this example. The stainless steel core inlet tube for forming a microjet is fabricated by using BD-syringe needle (Ø 0.6 mm i.d.), which was bought from VWR. The body's material of microjet is PTFE. The connecting PTFE tubes (Ø 1 mm i.d. & Ø 1.4 mm o.d.) were obtained from VWR International, Switzerland. The 5 ml and 2.5 ml syringe (Discardit II) was purchased from VWR. PEEK microfluidic tubing connectors (from IDEX Europe GmbH, Germany) were used. The neMESYS syringe pump system was purchased from Cetoni GmbH in Germany. ZEISS Axio Observer A1 inverted microscope with 488 nm and 350 nm wavelength lasers (Zeiss, Germany) was applied. Adobe Photoshop and Image J were applied to process images. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDX) were used for visualization and characterization.

Solution preparation

The 0.099g Sodium Alginate was solved in 5 ml distilled water with stirring (approx. 2hrs). The 0.099g Sodium Alginate was mixed with 0.691 g Phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide in 5ml distilled water with stirring (approx. 2hrs.). The 1.126 g Iron (II) tetrafluoroborate hexahydrate 97% was solved into 5ml 99.8% ethanol. The 0.435g CaCl₂ powder was solved into 5ml distilled water. The 0.01 g Rhodamine B (for fluorescence) was solved in 10 ml distilled water. Finally, the 1ml 25% Glutaraldehyde solution was mixed into 9 ml 99.8% ethanol. All chemicals above were purchased from Sigma-Aldrich, Switzerland.

Hydrodynamic flow focusing technique

In this project work, we fabricated 2 types of microjet device : one is with 3 inlets, while another has 5 inlets. The microjet device was used to form controllable laminar flows by adjusting injection pressure at inlets. It works for us to confine the central flow stream between the side flows (such as Figure 4 A-B). In this project, 150 µl/min was regarded as optimized flow rate for all inlets, depending on properties of selected materials. Then, functional fibre with different structure design or functional properties could be produced. Hence, by using hydrodynamic flow focusing technique, with producing fibre, we can successfully fabricate hollow fibre, solid fibre, functional fibre (such as surface functionalization or materials filling into fibre).

Results

The microjet ("µ-Jet") device successfully fabricated and used in our project work is shown in Figs. 8a and 8b, which are schematic drawing showing two types of µ-Jet devices. One stainless tube with adjustable length was fixed at middle inlet. The adjustable length will help to control different flow mixing point between core flow and shell flows inside the device. Finally, all inlets and 1 outlet were connected with PTFE tubes. The two types of microjet devices (3 inlets and 5 inlets) were fabricated and used for different aims. The middle inlet is formed by a stainless tube with adjustable length. The adjustable length of stainless tube will allow defining, i.e. positioning, the mixing point between core flow and shell flows inside system of microjet device. The microjet device can be connected to syringe pumps through PTFE tubing.

Initially we used a 3 inlets µ-Jet device to produce Alginate fibre with different diameter by changing the flow ratio inside of the device. This helped in finding the maximum and minimize diameter of fibres that could be produce by applying this device. The data is shown in Table 1. In this experimental work, the middle core flow rate (Alginate solution) was fixed at 150 µl/ min, while each shell flow rate (10% Glutaraldehyde ethanol solution) gradually increased from 150 µl/ min to 3750 µl/ min. The table clearly shows that with increasing flow rate ratio, the diameter of fibre diameter can be decreased, even the minimizing diameter of alginate fibre was close to nanoscale.

Table 1. Alginate fibre diameter control by adjusting flow rate ratio.

No.	Core flow rate (µl/min)	Shell flow rate 1 (µl/min)	Shell flow rate 2 (µl/min)	Flow rate ratio (Core vs.2 Shells)	Fibre diameter (µm)
1	150	150	150	2	220 to 330
2	150	300	300	4	130 to 170
3	150	600	600	8	50 to 80
4	150	1200	1200	16	20 to 30
5	150	2250	2250	30	15 to 20
6	150	3000	3000	40	10 to 15
7	150	3750	3750	50	5 to 10

The other available µ-Jet device with 5 inlets and 1 outlet is useful for producing fibres with structure control. For example, we can use a 3 inlet µ-Jet device to fabricate solid alginate fibre, while we could use a 5 inlet µ-Jet device to produce a hollow centre alginate fibre. The cross-sections of fresh alginate fibres with Rhodamine B fluorescence dye are shown in Figure 9,
In this work, 3 inlets µ-Jet device (for producing solid fibre) was used first. The alginate solution with Rhodamine B fluorescence dye was injected into inlet 1 (Figure 9-A), while CaCl₂ solution was injected into inlets 2 and 3 (as shell flow). In figure 9-B, we used a 5 inlets µ-Jet device for producing hollow centre alginate fibre. The alginate solution with Rhodamine B fluorescence dye was injected into inlets ii and iii, while the other inlets were supplied with injected CaCl₂ solution. All the flow rates in this work (incl. core and shells) were fixed at 150 µl/ min. We were able to produce two types of alginate fibres: solid alginate fibre (Figure 9-C) and hollow centre alginate fibre (Figure 9-D).
Subsequently, the core size of the hollow centre alginate fibre was varied by controlling the laminar flow rate ratio inside the system of 5 inlets µ-Jet device as shown in Figure 10: A-B) 5 inlets µ-Jet device was used to fabricate hollow alginate fibre with changing 5 inlets flow rate ratio. The inlets 1, 4 and 5 were supplied with injected ethanol solution with increasing flow rate (from 150 µl/ min to 300 µl/ min). Meanwhile, the inlets 2 and 3 were supplied with injected alginate solution with constant flow rate at 150 µl/ min. C-D) SEM images show two fabricated alginate fibre with different core size. For example, in Figure 10A, the inlets 2 and 3 were supplied with injected Alginate solution, while the inlets (1, 4 and 5) were supplied with injected Ethanol solution. All flow rates in 5 inlets were 150 µl/ min. Then, the core size of produced alginate fibre was approx. 31 µm (Figure 10 C). In contrast, if inlets 2 and 3 were supplied with injected Alginate solution with 150 µl/ min as each flow rate, while the inlets (1, 4 and 5) were supplied with injected Ethanol solution with 300 µl/ min as each flow rate, the core size of produced alginate fibre could be increased to 250 µm (Figure 10 D).
Still further, we used 5 a inlets µ-Jet device to fabricate alginate fibre with blue colour dye loading into hollow alginate fibre, as shown in Figure 11: A) The 5 inlets µ-Jet device was applied to fabricate hollow alginate fibre with blue colour dye loading. The inlet i was supplied with injected blue colour dye solution. The inlets of iv and v were supplied with injected CaCl2 solution, while the inlets of ii and iii were supplied with injected Alginate solution. B) The optical image shows the fabricated fibre with blue colour dye loading. The flow rate at all of the inlets was constantly at 150 µl/ min.
So far, we established the function of µ-Jet devices to fabricate required fibres (incl. length and diameter control, structure control, even loading and coating etc.). In a further step the relationship between crystallization and alginate fibre physical property was studied. In this project, we fabricated Alginate fibre with crystalline Fe(II)-1,2,4-triazole complexes (henceforth called "Trizo-Fe²⁺") inside or outside of the fibre by applying two types of µ-Jet devices.
Figure 12 shows the visible difference while the Trizo-Fe²⁺ crystals were formed at inside or outside of alginate fibre under optic microscope. In these experiments, the 3 inlets µ-Jet device (in Figure 12-A) was used to fabricate alginate fibre with coating Trizo-Fe²⁺ crystals on surface (Figure 12-C). For this purpose, inlet 1 was supplied with injected Alginate-Trizo solution, while inlets 2 and 3 were supplied with injected Fe²⁺ solution. We can clearly to see that the fibre (Figure 12-C) was totally covered by red colour Trizo-Fe²⁺ crystals. Meanwhile, the 5 inlets µ-Jet device (Figure 12-B) was applied to produce alginate fibre with inside layer coating Trizo-Fe²⁺ crystals (Figure 12-D). When applying this 5 inlets µ-Jet device, inlet i was supplied with injected Fe²⁺ solution, while inlets ii and iii were supplied with injected Alginate-Trizo solution and the inlets iv and v were supplied with injected ethanol solution. One can clearly observe the red colour of Trizo-Fe²⁺ crystals to be coating at inside of alginate fibre (Figure 12-D).
For further proof that Trizo-Fe²⁺ crystals are formed at different locations on the alginate fibre (inside or outside), a combination of SEM and EDX was used. In Figure 13A and B, Trizo-Fe²⁺ crystals were covered onto the surface of Alginate fibre. In contrast, Figures 13C and 13D show that the Trizo-Fe²⁺ crystals were coated in core layer inside alginate fibre. Based on SEM images (B and D), we could easily observe a difference between the alginate surface and Trizo-Fe²⁺ crystals coating layer. Furthermore, by applying EDX to run chemical elements analysis (in Figure 13B and D), the selected region 1 (Trizo-Fe²⁺ crystals coating region) clearly show Fe²⁺ element with higher percentage (around 40% of all elements). In contrast, the selected region 2 (Only alginate layer) barely shows any Fe²⁺ element. That means, we can control Trizo-Fe²⁺ crystals to be formed at selected regions (inside or outside of fibre) during the production of alginate fibre. It will be helpful to compare their physical difference in following tests.
As mentioned above, the Trizo-Fe²⁺ crystals were synthesized on alginate fibre, and we next focused on the size of induvial Trizo-Fe²⁺ crystal particles. The mean diameter of induvial Trizo-Fe²⁺ crystal particles on the surface of alginate fibre was 0.123 ± 0.022 µm (Figure 14 A), while the mean diameter of individual Trizo-Fe²⁺ crystal particles on core layer inside alginate fibre was 0.103 ± 0.021 µm (Figure 14 B).
Finally, patterning of Trizo-Fe²⁺ crystal surface coating an alginate fibre was shown on a glass coverslip with designed graph by applying 3 inlets µ-Jet device. In this work, inlet 1 was supplied with injected Alginate-Trizo solution, while inlets 2 and 3 were supplied with injected Fe²⁺ solution. Then, a fresh Trizo-Fe²⁺ crystal surface coating Alginate fibre with white colour was produced (Figure 15 B). After around 5 mins, the colour of the fibre had changed into red colour (Figure 15 C), due to the beginning of formation and reaction of Trizo-Fe²⁺ crystals.

Claims

A microfluidic device for creating sheathed flow, comprising
- a tubular flow chamber (2) with a longitudinal centre axis (A), the flow chamber having an inlet section (4) and an outlet section (6) axially displaced therefrom in a downstream direction,

- the inlet section comprising a core inlet (8) and at least one sheath inlet (10),
characterized in that

- the flow chamber is formed as an elongated channel within a polymeric chamber body (12);

- the core inlet comprises a core inlet tube (14) disposed coaxially within the flow chamber, the core inlet tube having a terminal opening (16) which is selectively positionable between a first core axial position (z_c1) and a second core axial position (z_c2), the terminal opening having a pre-selected diameter;

- the sheath inlet comprises at least one group of at least two inlet channels (18a, 18b) leading into the flow chamber at respective inlet openings (20a, 20b), the inlet channels of each channel group being formed as substantially identical elongated channels within said chamber body and being disposed symmetrically around the longitudinal centre axis in a manner converging in downstream direction at an inclination angle α, the inlet openings of a given channel group having substantially identical axial positions (z_s) and the inclination angle α of each channel group being selected in the range of 10º to 45º.
The microfluidic device according to claim 1, wherein the tubular flow chamber is substantially cylindrical.
The microfluidic device according to claim 1 or 2, wherein the sheath inlet comprises a first group of at least two first inlet channels (18a, 18b) with inlet openings at a first axial position (z_s1) and further comprises a second group of at least two second inlet channels (22a, 22b) with inlet openings (24a, 24b) at a second axial position (z_s2) axially displaced therefrom in a downstream direction.
The microfluidic device according to one of claims 1 to 3, wherein the inlet section and the outlet section are provided with coupling elements for forming a medium-tight connection with a supply device and with a fibre processing device, respectively.
The microfluidic device according to one of claims 1 to 4, wherein the polymeric chamber body is made of polycarbonate or PMMA.
The microfluidic device according to one of claims 1 to 5, wherein the core inlet tube comprises at least two substantially parallel core inlet channels.
A system for producing a polymeric fibre, comprising a microfluidic device according to one of claims 1 to 6, wherein each inlet channel is connected to an individual supply device providing a controllable inlet flow rate and wherein the outlet section is connected to fibre processing device selected from a dry and melt spinning system, a wet spinning system, an electrospinning system and a 3D-printing system.
A method of forming a polymeric fibre by means of a microfluidic device according to claim 1, the method comprising pumping a polymerizable liquid into one of said core inlet and sheath inlet, and pumping an additional liquid into the other one of said core inlet and sheath inlet, in such manner as to form a sheathed laminar flow region comprising a core region of one of said liquids surrounded by a sheath layer of the other one of said liquids, the method further comprising inducing polymerization of the polymerizable liquid in the sheathed laminar flow region.
The method according to claim 8, wherein polymerization is induced photolytically.
The method according to claim 8, wherein polymerization is induced by reaction of the polymerizable liquid and a polymerization agent contained in the additional liquid.
The method according to one of claims 8 to 10 by means of a microfluidic device according to one of claims 3 to 5, wherein the polymerizable liquid is pumped into the first inlet channels and wherein a first additional liquid is pumped into the core inlet and a second additional liquid is pumped into the second inlet channels.
The method according to claim 11, wherein the first and second additional liquids are identical.
The method according to one of claims 8 to 12, wherein the polymerizable liquid contains an admixture of a species of interest.