CA2456046C - Remotely removable covering and support - Google Patents

Abstract

The invention creates a thin tubular multiple filament (film or fiber) structure that can hold high internal pressures. When desired, an extension of the filaments can be pulled in any direction to unfurl the structure. This device is useful for self expanding stent or stent graft delivery systems, balloon dilatation catheters, removable guide wire lumens for catheters, drug infusion or suction catheters, guide wire bundling casings, removable filters, removable wire insulation, removable packaging and other applications.

Description

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WO 99!65420 PCTIUS99II2980 TITLE OF THE tNVENTtUN
REMOTELY REMOVABLE COVERENG AND SUPPORT
BACKGROUND t3F THE INVENTION
1. Field of the Invention The present invention relates to apparatus and methods for covering devices, such as required when delivering an expandable device, such as an intraluminal stent'or graft.

2. Description of Related Art Stent arid ~stertt-graft usage has gained Niidespread acceptance by radiologists, cardiologists, and surgeons. .These devices are being utilized to radially support a variety of tubular passages En the body, including arteries, veins, airways, gastro-intestinal tracts, -and biliary tracts. The preferred method of piacing'these devices has been to use specialized delivery systems to precisely place and.deploy a device afi fhe site to be treated. These.deEivery systems ailow.the practitioner to minimize the trauma and technical difficulties associated wifh device placements. Attr'~butes'of delivery systems include:
low profile; ability to pass through introducer sheaths; ability to negotiate tortuous vasculature, smoothly and atraumatically; protection of constrained devices;
and ability to accurately position and deploy the device.
Traditionally, .scents or stent-grafts have been designed either to plastically defom~ ~e.g., "balloon expandable" stems) or to elastically recover (e:g., "self expandable" stents) from a collapsed, introduced diameter to an expanded., functional diameter. Scents that are typically designed to elastically recover are manufactured at their functional diameter, and then radially compressed to be mounted on 'a delivery catheter. These devices must often be constrained in this compressed state for a prolonged period of time.
AdditionaEly, there must be a i»echanism to release this restraint remotely and allow the device to elastically recover to its functional diameter wf~en properly positioned.
A number of techniques are practiced to constrain elastically compressed stents and allow the restraint to be removed from a remote site.
One technique involves piacEng the stmt in the annular space between two . , _, concentric catheter tubes. The inner tube facilitates passage' of a guide wire through its inner diameter, and the scent or stent graft is elastically compressed on its outer diameter. The outer catheter tube or sheath then is placed over the compressed device, effectively capturing the compressed device. When it is desired to have the stmt recover to its functional diameter, the other tube is pulled back relative to the inner tube; and the device elastically recovers.
This deployment can be activated remotely (for example, at.the hub end of a catheter) by longitudinally displacing the tubes relative to each other.
/A variance of this concept in to have another concentric tube, located concentrically between the outside and inside tube. E3y moving this third tube relative to the other-tubes, the elastically constrained device can be pushed from the catheter, allowing it to elastically recover-to its functional diameter.
The inner tube, through whose lumen a guide wire passes; could be removed for a further variation in this design. in the modified design, the guide wire would pass in the lurrten of fhe pushing tube and through an unprotected lumen of the collapsed endoprosthesis.
Another possible technique that can be employed uses a suture that is stitched to the stent or scent graft in its collapsed, elastically constrained diameter. In ane embodiment of this technique, a "chain" stitch of removable suture is made through the metal struts of a collapsed scent. One end of the stitch can then be pulled, from a remote location, releasing the stmt to elastically recover.
Another technique involves encasing the collapsed endoprosthesis in a thin-walled wall casing that is held in a tubular configuration by a chein stitch of removable thread (e.g., a suture) applied to a longitudinal seam: When the stitch is removed, the seam is opened as the stem elasticalljr recovers to its operational diameter. This release mechanism 8eaves th.e thin wall casing captured between the device and the tube in which it was deployed.
The devices employed for constt-aining elastically deformed scent or stent grafts and remotely deploying them have a number of problems. one desired feature of an undeployed stmt is that it be flexible on the catheter.
This allows the catheter to be easily manipulated through the path it must negotiate from its entry site to the site where the device is to be deployed. When concentric catheter tubes are employed, this cohstruction usually creates large crass-sectional dimensions and is stiff, making navigation through tr~rtuous vascular segments difficult. Also, the need to manipulate multiple tubular WO 99!G5420 PCTfUS99/12980 components can make accurate. placement of the stent or scent gfaft difficult.
Another typical problem is that large fQrees are often required to retract the sheath or t o push out the stem. ., There are many other desirable features for a stent or. stent-graft delivery system. For instance, it is very beneficial for'the exterior surfaces of the collapsed endoprosthesis to be smooth and, therefore, more atraumatic to.
host vascui-ature. Additionally, it is desirable for the system to work with any elasticaaiy recoverable scent. .Further, it is desirable for the delivery system to have-sufficiertt strength to radially constrain the device during its normal shelf life without "cree.p" dilatation.
For delivery systems that include a removable suture through the stent, the systems effectiveness_in restraining the device depends greatly on the endoprosthesis design.. The struts of the endoprosthesis can be exposed ~n its collapsed diameter, and,this can potentially cause traumas during navigation to the treatment site. Additionally, exposed struts may also cause difficulties with deployment (for instance, entanglement of depioyinent suture or struts).
A disadvantage of the thin-walled casing devices is that the encasing w,.
sleeve is left in-vivo after he endnprosthesis has been deployed, which may inhibit healing or endothefiaiization of the luminal surface and cause flow ~0 stream disruption: Also, these devices may add significant profile to the catheter, and are detrimental to the catheter's ~exibifity. Finally, another problem with current delivery systems that use single removable threads to facilitate deployment of the endoprosthesis is that these cords must be designed to be strong in tension so that they do not break durin,g.the removal process. 'fhis_requirernent usually dictates that larger diameter threads must be used than are needed to hold the endoprosthesis in its elastically collapsed configuration to avoid tensile failure during deployment.
Some of 'these deficiencies are addressed in United States Patent 4,878,806 to lrinderriann et al. and United States Patent 5;405;378 to Streck~r.
. Both of these patents employ a one or more contiguous removable thread around an expandable prosthetic that can be remotely removed through a catheter tube or the tike. While these methods of prosthetic deployment may offersome improvement over other deployment methods, the open-structure nature .of these constraints are believed to provide only limited and localized resistance to the farce exerted by a, self expanding prosthesis. Other possible problems with these devices include: uneven distribution of constraining force

3 ... j WO 99!65420 PCT/US99/12980 radially and along the length of the prosthesis; high stresses an a single deployment suture that may lead to breakage risks during depioymerit;
inadequate coverage .of the outside of tfie prosthesis -- possibly leaving a rough exposed surface; and undesirable back=and-forth movement of the constraining/depioymenf filament over the exterior surface of_the device during deployment, which may lead to potential entanglement or embolism formation.
This is sometimes referred to as a "windshield wiper'.' effect.
Accordingly, it is a primary purpose of the present invention to provide an improved apparatus and method of deploying a self-expanding device, such as an endoluminai stem or the Like.
it is a further purpose cif the present invention to provide an apparatus and method for deploying a self-expanding device that provides excellent constraint and coverage of the device in a non-deployed .state and ease of deployment of the device once it has been properly positioned.
These and other purposes of the present invention will become evident from review of the following specifiication.
SUMMARY OF THE INVEhITIOI~
The present invention is an improved cover for a self-expanding device that is both effective at maintaining the self-expanding device in a constrained initial orientation and is easily-removable during the deployment procedure.
In its preferred form; the device of the present invention comprises a warp knit (also known as a "knit-braid"} of two or more interlocking strands of thread that 2b forms a.relatively tight cover (or "encasing"j around the self-expanding device.
Each of the threads covers only a portion of the outer ci~'cumference of a radiaiijr compressed device. By impa~tihg a break in orie filament of the knit-braid at one end of the cover, the cover can be removed in its entirefy through simple application of tension in any direction to a multi-filament "rip cord."
The rip cord is contiguous with the cover, which allows the cover to be removed in its entirety when subjected to tension while the self-expanding device expands in place. This construction has many advantages over previous devices, including allowing removal of the cover along a single vector without the deployment rip cord undergoing the windshield-wiper effect.
The device of the present invention' resists high internal pressures with minimal radial growth, although very low forces are required to remove the

4 _ ~ , _. _~~ f cover. To remove the cover, the high-strength knitted mufti-filament rip-cord can be pulled from any direction. This knitted rip cord is integral to the caver, and is comprised of two or more fibers. Consequently; only thin walled covers (arid consequently small diameter rip-cords) are required to constrain the w device. This cover can be wemaved in a cantrofled fashion and controlled rate:
- Additionally, the knit-braid construction allows radially-constraining forces to be uniformly distributed over the surface of the self-expanding device while . retaining excellent flexibility.
The cover of the present invention can provide a wide degree of f 0 coverage, varying from greater tfian 100% to less than 10%. Additionally, the cover has a relatively smooth surface texture, and is completely removable.
The cover can be made from a thin film or fiber, with the preferred material being an expanded polytetraffuoroethyfene ("ePTFE"). Alsa, the cover of the present invention can be .used to enhance the smoothness of tapers and transition regions in the pre-deployed device and assacfated delivery system, such as where the device is attached to a catheter.
The cover of the present invention can also be sequentially formed over different sections' of a catheter. For example, the warp knit can be formed to ai.iow the ends of a scent to be deployed stage-wise before its center, an outer covering can be released before the inner covering, etc. These.performance characteristics can be achieved using a single rip-cord or multiple rip-cords.
The "density" of the braid can also be varied to provide different deployment functions. This feature can enable an appendage ar a guide wire to exit from the side of the braid.
Additional advantages of the presenf invention are that it is easy to manufacture, can be easily automated, and, during manufacturing, the knitting process supp4ies radial compressive forces to the self-expanding device, potentially further decreasing its profile. The cover of the present invention also allows for adjustment of the flexibility of the entire delivery system, by using the presence, absence, andlor varying degrees ofi coverage of the cover to modify portions of the delivery system to be any where between quite stiff to very flexible. The ability to adjust ttte flexibility of the system allows the pre-deployed device to be tailored to be pushable andlor track-able.
This technology is believed to be particularly useful as a cover around self-expanding endofuminaf devices, such as stems, grafts, scent-graft combinations, and the Pike used in blood vessels, and other body passageways

5 ~ ._. ' WO 99%65420 PCT/US99/12980 (referred to collectively herein as "stents-and graft's"). Additionally, the device has ~rnany other potential medical applications- t=or example, the cover of the present invention scan be used with baltaon dilatation catheters andlor balloon expandable stents and grafts to create variable length and/or diameter balloons. This tecttpique can also be used to control the directioh of deployment of the balloon or implanta.ble device. ~tiler self or mechanically ei~panding devices, such as embolic coils or versa cava filters, can also be delivered using the disclosed delivery system of.the prasent invention. The system of the present invention can likewise be used to deliver multiple devices on one catheter: Further, the :present invention. may be employed to allow for removable guide wire turr~ens to be manufactured on catheters, either by having the cover define a guide wire lumen or having the cover join multiple catheter Pubes together. The cover can also be used to '.bundle tnuitiple guide wires together, increasing them pushability while they are being delivered but allowing them to be separated as appropriate within a patient. Also, the cover can be used on an infusion or suction catheter to vary the fluid resistance into or out of the catheter:
Non-medical applicatipns also exist for this technology. The cover of the present invention can be used as a fitter that is removable from a remote site. This would be advantageous for hazardous environments. The inventive caves may also. be used for insulating wires, allowing for an easy way to strip the insulation from the wires. ~ The cover can be used to aifow for compressed packages to be released with the pull gf a single'rip-cord, for potential use in marine fife saving or parachute-style devices. The cover may also be used to encase highly pressurized packages that can be released to their tower pressurized, higher volume state. Tfiis could be used to rapidtjr pre-inflate devices such a5 bicycle tires. The cover may also be used for packaging, of non-foil density items, such a5 insulation or sponges or bundling supplies (e:g., kits) in a secure fashion requiring rapid use and minimal packaging ~nraste (e.g., . for emergency, EMT, military, or similar applications).
DESCRIPTION OF THE DRAV11'INGS
The operation of the present invention should become apparent from the following description when considered in conjunction with the accompanying drawings, in which:

6 _. -- .
WO 99/65420 ~ PCTlUS99/12980 Figure 9 is a top plan view of a dual lumen catheter with a cover of the present invention installed on a distal. end of the device and a rip-cord of the present inventions routed through one of the lumens;
Figure 2 is a cross section view along line 2-2 of Figure 1; --v Figure 3 is a side elevation view of a cover of the present invention shown partially removed from a balloon dilatation catheter;
Figure 4 is an enlarged plan view of a warp knit pattern used to form the cover of the present invention, the knit-braid employing four different Strands, each of which Covers only a portion of the circumference of the self expanding device;
Figures ~A through 5D are aide elevation vieVV of the cover of the present invention being removed from a tubular substrate; the four figures illustrating, the process of removal of the interlocking strands of the cover;
Figure 6 is a side elevation view of one embodiment of apparatus used to create a warp knit of the cover ~f the present invention;
Figure 7 is a side elevation view of a further embodiirent of a Cover of the present invention, this cover comprising multiple Cover segments each controlled by separate rip cords;
Figure 8 is a side elevation view of another embodiment of a cover of the present invention, this cover including a catheter and a removable guide wire Lumen;
Figure 9A is a side elevation view of a still another embodiment of a oover of the present invention, this cover comprising a multiple guide wire casing;
Figure 9B is a Cross-section view along line .9B-9B of Figure 9A;
Figure 1 p is a side eteuation view of yet another embodirtient -of a Cover of the present invention, this cover comprising multiple caver segments each Controtied by a single rip cord;
Figure 11 is a side elevation view of a further embodiment of a Cover of the present invention; this.cover comprising two separate segments, each separating from a-covered balloon dilatation catheter from a center position, allowing the balloon dilatation device to lengthen axially from its center;
figure 12 is a side elevation view of a still further embodiment of a cover of the present invention, this cover surrounding multiple self expanding devices to be deployed in sequential fashion;
Figure 13 is a side elevation view.of yet another embodiment of a cover of the present invention, this cover comprising a means to provide a drug

7 eS< r .
WO 99/65.420 . ~ PC~'/US99I12980 infusion catheter with variable fluid resistance (the cciver i~eing shown with reduced cover density to show details .of the covered infusion catheter);
Figure 14 is a side elevation view of a stitl further embodiment of.a cowew of the present invention, this cover attaching together multiple tubes of a multiple iumen.catheter;
Figures 15A through 1 bC are side elevation views of a cover of the present invention comprising a removabie cover for an adjustable diameter balloon, illustrating the process of inftatin.g the balloon within the .constraints of the covey and removal of the cover, Figures 16A through 15C are cross-section views along lines 16A-16A, 168-1 fiB-, and 1.6C-16C, respectively: of Figufies 1 ~A thvough~ 15C;
Figure.1 ~ is a. side elevation view of a further embodiment of a cover of the present invention, this cover comprising a rip card threaded into one lumen of a.dual lumen catheter;
Figure 18 is a side, elevation view of.a further. embodiment of a cover of the present invention, one of the covers comprising a removable radio opaque knit for~use in pos'rtiQning the covered device;
Figure 19 is .a side elevation vieviv of'another embodiment of a cover of the present invention,-the cover positioned on a balloon to perform an , angiopiasty by shearing the vessel Walt in addition to radially compressing the obstruction in the artery;
Figure 20 is a side elevation view of a fuither embodiment of a cover of the present invention, the cover comprising a variable density knit with a hole in the side of a covered catheter;
Figure 21 is a side elevation view of an embodiment of the present invention illustrating a non=medical use of the coirer of the present invention, in this instance the cover comprises a readily strippable electrical wire ins.utation;
Figure 22 is a three-quarter isometric view of an embodiment of the present invention wherein the cover used to cover self expanding insulation and the insutation,is being dept~yed within a contained space;
Figure 23A through 23C are side elevation views of a cover of the present inuention comprising a removable delivery sheath for a plastically deformabte device, illustrating the process of inflating the plastically deformaE?le device.

DETAtLEt3 ~DESCRI.PTtON OF THE INVENTION -

8 . _' The present invention is an improved .cover for use on 'a constrained device, and particularly on a self .expanding device. As will become evident from reuiew of the following description, they present invention can be used in a variety of medical and non-medical applications. Although. not'limited to such procedures, the. present invention is particularly useful for use as a cover over endoluminal irnplantabie devices, such as stents and grafts, catheters, endoluminal balloons, arid the like:
The terms "cover," "encasing," "casing," and " heath" as used herein are intended to encompass any structure that contains another device (or multiple devices) or.any part thereof, such as a implantable prosthetic,,.a guide wire, a g~cide wire lumen, a:dalloon catheter, et cetera. The terms include; without iimitation,,struetures that provide an outer sheath to such devices as well as other structures that might be-further encased' in other layers pf materials, other devices, andlar multiple layers of covers of the present invention.
One use of the .present inven3io~ is illustrated in Figures 1 and 2. The present invention comprises a knitted cover 10 that is used to encase another device, such as an elastically deformable stent 12. A mufti-filament rip cord is formed atone end .of the .cover 10. and should be of sufficient length to allow the cover to be unfurled at a distance from the cover 10. As can. be seen, the rip cord 14 actually comprises a multiple-strand extension 'of the knitted cover itself. In the embodirrient ili.ustrated, the rip. cord is mounted .within a first lumen 1fi. of a double Lumen cathefe~ 18 and exits through a Y connector 20. A
second lumen 22 is provided for manipulating the catheter 1$ and stent 12 into position along a guide wire {not shown).
The cover of the present invention has unique properties derived from its particular knitted structure. As is explained in greater detail below, by forming a.kn'ttted cover using a particular knitted pattern known as "warp knit" or a "knit-braid" and then specifically preparing the cover for removal, fhe entire cover of the present invention can be removed by simply pulling on the rip cord 14 device. As is shown. in Figure 3, the cover 10 can .be used to cover, for example, a balloon on a balloon dilatation catheter 24 or a self expanding tubular device.and then removed by pulling on the rip cord 14. The knit-braid cover 10 wilt then unravel to allow the balloon 24 or a seif-expanding device to enlarge along its length concurrently with the removal of the cover, as shown.
Figure 4 illustrates one preferred embodiment of a warp knit cover 1 Q of the present invention. The cover 1fl illustrated comprises four different strands

9 t of fiber 26, 28, 30, and 32 that are interlocked togethdr. Starting with a minimum of two.independerit filaments, as many strands as desired and appropriate .iran be corribined in this maniaer, virtth a tubular structure being fiormed by simply interlocking the final strand with the first. Specifically, this ' structure uirorks in the folloiaving manner. The first strand 26 loops around the second.strand 2$ and the fourth strand 32. lit turn, tE~e second strand 28 loops around both the first strand 2~ and the third strand 30. Similarly; the third stand loops around the second strand 28 and the fourtf~ strand 32. Finally, the fourth strand 32 loops around the third strand 30 and the first strand 26 to form a tube.
This interlocking structure wit! completely uhravel as a coherent intervuoven multi-filament rip cord by simply separating one of the -strands from the:rest at one end. .For instance, with tension applied to the tap side of the knit, if the first strand 26 releases at connection point 34 (such as by Gutting or detaching the strand at that point), then the second stravd 28 wilt release from 1b the ftrst strand 26 at connection point 36, Subsequenfiy, the first strand 26 will release from the second strand 28 at connectiori point 38, and the second strand 28 will release from the first strand 26 at connection point 4Q. This process will continue along the entire length of the device until the entire cower disengages as one long,. continuous, interwoven rip cord.
This process can be further appreciated through review of Figures'SA
through bD, which illustrate the process of disengagement of each of the loops of fiber of the present invention in.a four frber 42; 44 tubular construction.
There are numerous advantages to making a cover in this manner.
First, the cover has proven to.be quite strong with rESpect to radial dilation 2b forces. The' ability to use as many strands as is desired, with as tight a knit pattern as is desired, allows !:he cover to provide very complete containment of the self expanding device and uniform distribution of constraining forces over the surface of the self-e~cpanding device: The term °uniform distribution" is intended to mean that essentially the same constraining. farce is applied around the circumference of the device (i.e., so the device does not bulge on one side}
andlor along the aongitudinal length of the device (i.e., so the device has a consistent profle along the length of the device). Despite the security of containment; the cover will very. rapidlydisengage from the self-expanding device 'by simply pulling on the rip. cord. By way of example, it has been 3b demonstrated that the cover of the present invention can contain a device exerting over 100 psi expansion force. However, once expansion is - .

appropriate, the cover can be completely and easily removed from the device aimply by exerting as little as 1 lb. tehsiie :force along the rip cord. ' Another advantage.of the cover of the present invention is that it can be readily formed in-place around a self expanding device. For instance, Figure 6 illustrates a warp knitting (or knit braiding) machine 46, Model No. 2NBA/Z-TB, ~ available from Lami' Knitting~Machine Corp9ration of Chicopee, ~ , Massachusetts. The. device illustrated comprises a thread finch tensioning device 47, a thread position shuttle 48, awknitting head 49, a~take down unit 50, and a weight 52. The knitting head ~49 employed is an eight needke head with 90 every other needle removed (for a total of four needles) ahd a core diameter of 318 irich.(9.5 mrn). in use, filaments 54a, 54b, 54c, 54d are fed through the tension system and. the filaments guides 47 into the sfiuttle 48. and the knitting head 49 and are attached to weight 52. The knit braiding machine will a:utorrlaticaSly intertwine the filaments 54 into'a joined warp knitted tube 55.
The knot 56 serves to hold the knit:braided tube 55 together. The weight 52 applies. tension to th.e filaments 54 to assist in feeding the filaments through the system. Ttie take dourn unit ~50 is not required in this process and vhouid"be disabled.
This device 46 is readily adapted to create a cover of the present invention. in this regard, a device to be wrapped, such as an endovascular prosthesis (not shown) on. the end of a catheter 57, is fed down through the thread :position. shuttle 48 and,.the. knitting head 49. The.knitter.will apply the warp knit tube 55 around the prosthesis to form a 'cover of the present invention.
The.nature of the knit-braid..created by this machine 46 allows the ends of the final tube to be pulled longitudinally to apply greater compressive force to the wt-apped device.
Following the, wrapping process, the cover is finished over the wrapped device as follows. The knit is unfurled through a length ofi catheter up to the location on the catheter where the eridoprosthesis i.s compressed: This ' unfurling is started by t~reaking one of the fibers on the closed end of the knit.
This unfurled length of knitted thread,then can be routed to the hub of the ' . catheter to serve as the ripcord to deploy the sterit. l Preferably, this rip cord is fed through one lumen of the catheter as depicted in Figure 17.
~ It has been demonstrated that by employing a knit-braid apparatus of this form a-tight wrap can b.e applied around a self-expanding article. In fact;

1 ,.
WO 99f65420 PCTlUS.99/12980 the mere act of forming- the cover has been demonstrated to apply ct~mpressive forces to further assist in constraining the self-expanding device.
One 'particular important advantage of the present inverition is the cover's abi(ify to unfurl along a "single vector". The warp knit pattern of the ' present invention will separate along essentially a straight line (which may be purely linear o<~, where desired, along a spiral or any other pattern, along the .
device). Similarly, the rip cord puNs away from the constrairi~d device along an essentially straight fine. The term '°sing;le vector" as.used 'in this regard refers to the cover separating or removing from the device in an essentially straight fine when tension is applied to the rip cord without the extreme ".windshield wiper"
motion of some current thread-wrapped devices-exhibit, )=or a two-thread symmetwically applied cover, this means that separation of threads wi 1 occur over no more than about 180 degrees of the circumference of the covered device; fcr a symmetrical three=thread cover, separation will occur over no more than about 120 degrees. of the circumference of the covered device; for a symmetrical four-thread cover, separation will,occur over no mare than about 00 degrees of the circumference of the covered device; for a symmetrical five-thread cover, separatian will occur over no snore than about 75 degrees of the circumference of the .covered device; for a symmetrical six-thread cover, separation will occur over no more than about 60 degrees bf the circumference of the covered device; and so on When cover.separates in this .manner; the rip cord will remove all of the fibers from the device in ah essentiaNy straight -line or "single vector". The elimination of the windshield wiper effect is believed to significantly decrease the risk of entangleri~ent during cover removal. Additionally, single vector 'remi~val also imparts significantly less trauma to the host verse! durif~g removal, reducing the risk of embolization and other complications.
It should be appreciated that the threads of the present invention need not be symmetrically applied. For example, different weights of thread may be used: Additionally or alternatively, each of the sets of threads may be applied to cover a different proportion of the circumference of the .device, allowing sepa~~ation to occur over a greater or~lesser proportion of the circumference.
Another important aspect of the present invention is fhe fact that the cover separates as a mufti-filament interlocking structure. This separation mech2~nisrri provides significant increased overall strength to the rip-cord during removal. This vastly improves the design options for creating sheaths, such as allowing thinner material to be used with less risk of breakage. Additionally, the _. ., ' -interlocking structure is amore readily fertioved, with less risk ofi accidental.
separation during the removal process.
Another method of forming a cover of the present invention irivolvrrs using a structure eXternal to the warp knit to allow a .ster~t to be drawn into~the warp knit lumen. For example, a warp knit (four threads, 3/8" root diameter}
can be knitted on a 304 stainless steel one foot long mandrel That has an outside diameter slightly larger than the diameter of the compre$sed deuice.
Then the:warp knitlmanci~ei is hand wrapped witki approximately 15 layers of pipe thread tape (e.g., holy-Terrip TeflonCO Tape, available from Anti-Seizs Technology, Franklin Park, !L} and this assembly .is placed in an air convection oven at 370°C~fouS minutes. After cooling this assembly, the warp knitJexternal pipe thread tape support is stripped,from the mandrel using a concentric tube that snugly fcts the mandrel and pushing the warp knit/ tape support off of the.
mandrel using this concentric tube. The self-expanding stent can the-n be drawn through a funnel directly into this externally supported wasp knit, The pipe thread tape is then removed by carefully remavir~g each layer of this:'tape.
The resulting structure is a collapsed diameter stent~in a warp knit cover:'°This cover can be removed by putaing~two or three of the four threads of the knit from tile end of the knit that was last knitted. The self-expanding stmt is then self deployed with the cover removed.
The cover of the present ir3vention-can be made in.a wide variety of constructions, using a wide variety of possible materials. For instance, the knit structure can employ anywhere from 2 t4_ 15 or more threads, with 3 to 8 threads preferred and ~4 to fi threads most preferred. The density of the knit may range from 2 to 80 knits per centimeter, with 10 to. 50 preferred. The knit may tie constructed with a complete coverage of the covered device (that is, 100°!° of the surface area of the device covered} or more (such as by overlapping the. threads to form niultipte Layers) to as little as 1 to .5 %
coverage of the surfiace area. For most applications,, the preferred coverage will be about

10 to 100%:
Percentage coverage in the context of the present invention may be determined by approximating the~amount of outside surface area of the covered device covered by the warp-knitted cover of the present invention relative to the amount of outside surface area that: is left exposed (that is, the area left without th~reads.of the cover extending over it}.

-.. _ ..-_ _ __ ~?VO 9.9165420 PCT/US99/12980 Ofher structural modifications can also tie incorporated in the cover of the present invention. For example, it is possible to form at-ieast two of the stitches spaced circumferentially close to each other, and,this may be accomplished by Hawing higher pinch tension on at least one of the input 5strands employed during the knitting process as compared to the other input . strands. Stiff another structure! modification is to use input strands with different characteristics, such as employing one or more strands with particular desirable properties (e.g., making a strand radio-opaque to aid in-fluoroscopic visualization, or using strands of different deniers, texture, or other properties) Still another modification of the present invention is to employ a cover thet extends .beyond the ends of a covered device,.to cover an adjacent structure, such as a catheter.. By forming a cover in this manner, a gradual transition in profile can be established from a catheter to a covered device. This construction is shown, for example; in Figures 12; and 23A.
The materials used to make the cover of the present iriven.tion are likewise open to modification and customization fdr,given applications. For most uses discussed herein threads or other.fibers. are used to form the cover.
Suitable threads include: polytetrafluoroethyiene (PTFE}; expanded PTFE; silk;
thermoplastic threads such a5 polypropylene; polyamide (nylon); various plastic or iretat materials (e.g., stainless sleet or nickel-titanium (nitinol) alloy); and bioresorbable materials-; such as-PLA or PGA. The threads relay .be used within a wide range of deniers, such as 25 to 2500 (gramsl9000 meters}. Particularly preferred.for use in covering irriplantable medical devices are polytetrafiuoroethylene (PTFE) threads, and especially expanded PTFE
threads, such as threads available from:W. L. Gore & Associates, Inc., Elkton;
MD, under the 'trademark RASTEX~ or sutures available from W. L. Gore &
Associates, inc., Flagstaff, AZ, under the tradefnark GORE-TEX~.
By way of example, to cover a l0 mrri diameter WA~LSTENT~ stent (available from Schneider; Inca Minneapolis, MN), a four thread cover of CV-8 GORE-TEX~ suture having a denier of about 150 and a percentage coverage of about 25°l° is believed preferred.
it should be appreciated that other materials may also be suitably ,employed with the.present invention. For example, in place .of one or more fibers a film or ether structure may be substituted to impart particular perFormance characteristics. Examples of other suitable materials include tapes, single filament threads, multi-filament threads, beading, etc:

_. _ : _.

As to particular applications for the cover of the present invention, Figures 7 through 23 provide examples of devices that can betsefit from use with a cover ar covers of the present invention.. , Figure 7 is a further embodiment of a cover 60 of the present invention, this cover comprising multiple cover segments 62a, fi2b, 62c, each controlled by separate rip cords 64a, 64b, 64c, respectiveljr. This configuration aNows each of the cover segmehts to be eparatefjr removed .from a covered device 60 in whatever order is most desired. By covering a self-expanding scent device in this manner, a surgeon can opt to selectively expand the distal, middle, or proximal ends of fhe device as best suits a given procedure.
Figure.8 is another embodiment of a cover 88 of the present invention wherein the cover is used to contain multiple devices. In this instance, cover contains a cathefer 70 and a removable guide wire lumen 72. This construction allows for a guide wire lumen to be temporarily joined together for ease in passage through a blood vesset an~l~then separated by removing the cover using the rip cord.76 once they have beers properly positioned. The guidewire then remain in-situ ailowing for an additional catheter device to be positioned.
Figures 9A and 9B itlustrafe still another .embodiment of ,a cover of the present invention. fn this instance, the cover 7-8 contains multiple guide wires 82a, 82b, and 82c. Again, this construction provides means to retain multiple devices. together for insertion into a body and then separate theta from each other once.in place Figure 10 illustrates a cover 84 comprising multiple cover segments 88a, 86b. . A master rip cord.88 is provided attached to segment 86a, and a secondary rip cord 90 is provided attaching segment.86b to segment 88a.
Gonsttucted in this manner, tension an proximal end 92 of the cover via master rip cord 8'8 wilt first release segrtsent 86a. Once segment 86a has been fully released; tfiie secondary rip cord 90 wilt begin releasing segment 86b from the distal cod 94 of the cover. In this manner, a non-end ta-end (or "non-linear") cover release can be effectuated with tens'con on a single rip cord 88.
The embodiment of Figure 11 is a cover 96 having two separate segments 98a, 98b covering a balloon 10~ (with each segment shown partially withdrawn and the balloon shown partially expanded). Each of the segments 98a, 98b covers the balloon '1Q0 with rip cords 102a, 102b releasing from~the center~of the balloon. The rip cord 102a from the. proximal: segment 98a is _. _:_ _..__ _ WO 99/65420 PCTIUS991t2980 external to the covered' device and the rip cord 102b on .the distal segment 98b is threaded through a center lumen 104 of the balloon 100 to aid in release of the distal segment 98b without interference between the rip cord 102b and the expanding balloon 100.' By'coVering an expandable device in this manner it allows the unconstrained expanding device to lengthen axially from its center, allowing for adjustments in the devices length.
The embodiment iltust~ated in Figure 12 is a cover 106 surrounding mulfipfe expanding devices 108a, 108b;108c, 108d to be deployed in a sequential fashion= This construction allows a catheter 1'10 to be moved into a first position and a first device 108a cart then be deployed by pulling rip cord 112 just enough to release the first device 108a.. The catheter 110 can then be repositioned for deployment of the second device 1 DBb. The process can be repeated, deploying each of the devices sequentially, until each of the devices 108 has been deployed. 1t should be appreciated that multiple devices 108 may also be deployed at one 'position using this same construction.
Still another embodiment of the present invention is shown in Figure 1.3.
In this embodiment; a cover 114 is placed over a drug infusion catheter 116.
The cover 114 should be -sufficiently dense (that .is, with a coverage of fi0 ~to 10'0% or more) that it will reduce or eliminate liquid passage through the cover when it is in place. The drug infusion catheter '118 is -filled or coated with some therapeutic substance and has muitiple openings 118x, '118b, 118c, 1184, 118e; 11'8 f, 118g, 118h, 118j, 118k through which the therapeutic substance may.permeate into a patient.. By covering this catheter .116 viiith a dense cover 114 of the present invention, a medical profiessional can use rip cord 120 to ~5 re+inave only enough of the cover 1.14 lo expose a pre-determined number.
of openings 118. in this way,~the amount of drug release can be tightly controlled as to Location andlor amount. .As was taught with respect to the embodiment of Figure 12~ discussed above, this embodiment of the present invent'son may dispense therapeutic substarnces at different locations by simply stripping off more and more of the cover~at each~new location and/or by being:repeatedly repositioned in a patient.
Figure 14 shows a cover 122 of the present invention that attaches together multiple tubes 124a, 124b of a multiple lumen catheter 12$. This allows the multiple lumen catheter.126 to be initially manipulated through a patient as a single unit and then separated as needed using rip cortl.'128.
'tie tube may also serve as a guide wire lumen, allowing it to be removed with the ,.
_..
~ '.
WO 99/65420 RCTfUS991I2980 other tube left in-situ. This permits the guide wire to be freed for use 'by an additional catheter. . w Figures 15A to 15C and 16A to 16C illustrate the process of inflating a balloon 130 within the constraints of a removable cover 132 of the present invention. In this instance, the cover is knitted on the balloon in a radially loose configuration. As should.be appreciated from these drawings, the cover 132 provides a smooth outer surface within which to almost fully expand the balloon 130 (to diameter D~}. Once the balloon '130 is inflated, the cover,132 can then be ,removed, allow+ng the i~alioon 130 to fully expavd (to diameter D3 i.e., D3 >
Dz} and leaving the uncovered balloon as:ifiustrated in Figures 15C av d 16C.
This method of balloon deployment has a number of advantages over balloon deployment without. a covet, iricluding: aiiawing one balloon to have two separate high pressure inflation diameters; making the balloon more resistant to puncture while covered by the removable sheath; and allowing the balloon to be used of higher_pressures than would otherwise not b'e tolerated by the balloon material alone. ..
Alternat'iveiy, a similar effect may be achieved through use of two ~r more concentric sheaths, each having slightly larger diameters: Additionally, the cover Payers may be adapted to be removed in .different orders to achieve different desired results, One. possible means for easing rip card manipulation is illustrated in Figure 17. fn this embodiment, a multiple I'u .men catheter 134 is. employed with a rip cord '136 of the cover 138 of the present invention being threaded through one lumen 140.of the catheter. .In this manner; the rip cowd 136 and cover 138 can be easily removed through.the.catheter lumen 140 without obroidleg against a vessel wall. 'This embodiment is believed to be particularly beneficial where a device is being deployed through a particularly tortuous vessel or other problem area where snagging or ether restrictions might be encountered.
In the embodiment of-Flgure 18, a hover 942 is illustrated that employs a radio opaque knit 144a, 144b for use in fluoroscopic p~sitioning of a covered device 146, In this instance, the radio opaque braid 144 has its own rip cord 148 to allow it to be separately removed frorri'the cover 142. Elements 144a and 144b may be positioned, .for instance, to mark each end of the device to be delivered.
In the embodiment shown in Figure 19, a cover~950 is positioned on a balloon 152 to perform an "extrusion angioptastyn within a blood vessel 154.

WO 9916542~ PCTlUS99/12980 The process of an "extrusion angiopiasty" is designed to augment traditional compressive angiopiasty methods employed to remove or remodel a stenotic lesion 156.or other blockage. Irt addition to providing a radial force, the balloon extrusion arigioplasty also creates a "wave of shear forces (F) tliatwexert 8 complex stresses that can push the blockage alohg the vessel waft, thus reducing its size or steriotic effect aridlor moving it to another portion of the ~bload vessel.. By using the cover '! 50 of the present 'inventign anal refieasing it along the length of the balloon 152 in the manner shown, .the desired shear forces (F} can thus be generated to remodel the lesion°within the blood vessel.
This technology may also be used for thrombectomy baHoc~ns.
A cover 958 of the present .invention shown in Figure 20 comprises a variable densityvnit with an opening 160 in the side of a covered catheter 162.
By providing the cover with cfense~segments lfi4s, 164b and' open segment 166, this.aUows passage of a guide wire 168. or other appendage through the cover arid opening 16o into or out of the catheter 162.
The.present invention may also have many non-medical uses. For example,, illustrated in Figure 21 is a cover 170 mounted under or imbedded in an insulated jacket 172 over an electrical. conductor 174. i3y pulling on rip cord 176, the.jacket and insulation may be readify.stripped from the cond.uctar.174 to any desired degree. if desired, once the jacket 172 is correctly positioned, the rip- cord 176 may then be cut.and sealed to .prevent further stripping of the insulation.
Another possible non-medical use is shown in Figure 22. In this instance, a cover 178 is used to contain self expanding insulation 180, such as foam or,l7berglass insulation. Vllhen placed into a Confined space 182, such as between tuds 184x, 184b in an existing wall 188, the cover 178 can be removed using rip cord 188 to permit the insulation to be' expanded in place.
As coivpared to existing insulation installation methods, this process permits far befter placement of the msufation and far less mess in the process of insulating existing structures.
It should be evident from these two examples that many non-medical applications for the present invention may be possible.
Another medical use of the present invention is shown in Figures 23A
through 23C. In this instance, a cover 190 of the present invention is used as a 3~ delivery sheath for a non-self expanding (that is; a plastically deformable) device 192,~such as a Palmaz-Schatz0 stent available from Joftnson &

,fahnson. This plastically rlefarmable device is deployed through the following , steps:
1. The catheter is manipulated into plape wifh the cover "190 protecting dislodgment of the therapeutic device 192 from the catheter (e:g., angioplasty device};
2. The cover 190 is removed;
3. The device 9 92 is delivered. {e.g., the angioptasty catheter is inflated.) 1,0 Without intending to limit the scope of the present invention, the fvliowing examples illustrate how the present invention,may be.tnade and used:
Example 1 -~Knif Braid Over an Angioplasty Catheter A filament is wound in a knit-braid configuration over a Cook {Cook Incorporated, Bloomington, tN} ,Accent~ 7 mm x 4 cm Balloon Dilatation Catheter. A tubular knit braider by Lamb Knitting Machines {Lamb Knitting .
Machine Corporation, Model. #2NBAIZ-TB Knit Braider, Ct~icopee,~MA}, is set up to produce's 4 f<lament warp knit. This machine is mod~ed, with the AC drive motor replaced with 'a variabie speed DC motor (also available from Lamb Knitting Machine Corporation}. An eight needle, small bore knitting head is mounfed, and every other needle removed, resulting in four needles xernaining.:
Thin, expanded potytetcaftuoroethytene (ePTFE) film {produced in accordance with United States Patent 3,.953,566 to Gore) is slit to achieve four 0.25N
(0.64 cm) width sections of film. The film has a thickness of about 0.02 mm, a density of about 0.2 glee, and a fibril length of about 70 micron. Thickness may be measured using a-snap~gauge (such as, a-Mitutoyo Snap Gauge, Model 2804-10); density maybe calculated based on sample dimensions and mass;
and fibril length may be determined .by taking a representative scanning efectror~ micrograph (SEM) of the material and treasuring .average fibril Lengths between adjacent polymeric nodes within the material.
Each of these fibers are threaded through separate spring tension devices, through the shuttle guides, through the needles, and pulled through the bottorr~ cylinder. The four filaments are knotted together below this cylinder, and a 72 gram weight is hung from the knot. This machine construction is illustrated in Figure 6, as previously described.

. . _.._.

The crank is slowly turned, by. hand and the fibers begin to be knit braided. The machine is adjusted (i.e., the needles lowest travel point is adjusted to approximately 1 mm below the needle holding cylinder) to achieve a tight weave. The motor is then turned on, adjusted to a. slow rate {of .
approximately two knits per second), and the machine allowed to knit braid automatically. After approximately 5 cm of length of cover has been knit braided and the machine is running smoothly, the tip of the balloon catheter may be. threaded through the top bore on the machine such that tote machine starts to knit braid on the dista4 tip of the catheter toward its'hub. The machine viii automatically knit-braid until about 5 ctrl past the balloon of the catheter before the knit braiding operation is ceased. The filaments are then cut at the end of the knit.
Next, 3 of the 4 filaments of the 5 cm length of Knit braid past the balloon of the catheter is pulled at a 90° angle from the end of the catheter ' With the braid and catheter in this position, ~a single filament is cut on the catheter on the opposite side from the position of the knit. The, knit is further tensioned and this allows the knit an the catheter to unfurl.
This cover over the balloon may then be tested. The catheter diameter may be measure using calipers (Mitutoya, Modet CD-6" BS, Japan). A catheter made through this method has a diameter of 0.09g" (2:5 mm) v~ihile the encased Section has a diameter of 0.110° (2.8 mm). The cover that had .started to unfurl has a maximum diameter of 0:024" '( 0.5 mrn). The I~alloon is attached to a Merit Medical balloon inflation device (Merit Medical, Basix 25, Salt lake City, UT? and inflated to 9 00 prig {7:03 kglcm2j. The cover prevents the bafloo.n from significantly diametrically expanding. Next, while the balloon is still pressurized', the-utlfu~led cover is. attached to a farce gauge (Ametek lnc., Accul=orce Ill, Hatfield, PA). The gauge is. pulled toward the hub of the catheter. The portion of the cover over the balloon is unfurled, and the force on the rip cord reaches a maximum pressure of about 1.2 Ibf (0.54 kgf) tension. _ This demonstration shows how a filament casing can withstand high internal pressures, yet only a relatively small amount of force is required to unfurl the casing.
Example 2 -- Knit Braid Over Self Expanding Stent:

Wp 99Ib5420 PCT/U599/12980 This example demonstrates haw a self expanding scent can be restrained bythe knitted cover, and then subsequently deployed by pulling the knitted extension in any direction.
A Lamb Khitting Machine Corporation (Chicopee, MA) 2NBA/Z-TB-.,Knit Braider is set up as specified in its instructions to create a 4 feedl4 needle tube product on an 8 needle machine. The knit braid pattern has an adjacent crossover. Four spools of JOHNSON & JOHNSON REACH'! EASY SLIDE
PTFE Dente! Flbss (Sklllman, NJ) are obtained. This stretched PTFE dente!
floss material has a denier of about 920. Each floss strand is threaded into the machine, creating 4.feeds. The.four strahds are tied in a.,kilot below the toop support spindle, and a 72 gram weight'is hung from these strands.
A self expanding scent, a Schneider, lnc. (Minnea.polis, Minnesota) _WA1:.LSTENT 10 mrn x 40 mm, is placed concentrically outside a 0.092 OD
?2~3 PEBAX (Elf Atochem, Paris, France) tube extruded by Infinity Extrusion and Engineering (Santa Clare, CA). The stent is then radialiy collapsed by digital pressure, causing the scent length to increase. With the stent collapsed completely around the catheter tubing, .thread is used to tie the stem to the-.
catheter at both ends and at the middle of the scent: ~igitaf pressure is then removed. No significant scent radialiy grpwth is observed:
The stent assembly is then fed from above into the knit braiding machine. Using the hand crank at the-rear of the machine, the needles are slowly moved by cranking clockwise (reference the rear of the machine) to start the warp knitting action. The first too.p created by the rna.chine,is positioned just to the' inside of the tied thread:-at the lower end of the stmt. The .machine is 2~ i~anuali~r cranked, as the machine knit braid the length ofthe scent. Just prior to knit braiding overahe middle tie thread, this thread is cut and removed along with the first loop. The knif braiding actiot~'is terminated just-before the other end of the scent and the last pretied thread Loop is removed. The crank, is then cranked once in the counterclockwise direction, causing all four threads to disengage from the needles. The threads arse then cut just below the shuttle extension, releasing the stenflcatheter tubinglkrtit braid assembly from the machine.
- Three of the four threads are then tensioned in a perpend.icuiar direction from the .axial axis of the catheter. Once the unfurling is started, the fourth 3~ str nd is- grabbed along with the other three strands, assuring that path around the tubing of the fourth strand does not interfere with the unfurling process.

-~_ -WO 99/65.42U , PCT/US99/12980 The cover will unfurl when the four strands are tensioned perpendicular or.
toward either end of the tubing. As the cover unfurls, the ,stent will self deploy to its full diameter.
Exai~npte 3 -- Knit Braid with Nitino! Wire:
This example illustrates knit braiding with .a wire, showing that this process creates a compression resistant, radio-opaque structufe.
A knit. braider is set up as specified in ~xampls~2, except the strands are sdbstituted with 0.005" (0.2 mm) diameter nitinol superelastic wire [describe CW and cornpasition) (New England Precision Grinding & Wire Company, Inc., Milfo~d,111tA). hstead oftying the wiresyagether, after they have been threaded through the knitter, wax coated thread is used to connect .the four wires.
A 5 rx~m diameter stainless steel hollow mandrel is inserted into- the 15' machine from above:- With the four wires and~the mandrel fed into the spindles, an approximately 1.5 inch (3.8 cm) long x 0.5 inch (1.3 cm) wide strip of electrical tape is applied to the mandrel fixing the four wires at approximately 90° increments. from each other. .The warp knitting operation is started by rotating the crank clockwise. The crank is rnahuaily rotated, assuring that the latch needfes grabt~e~! the appropriate wire each time. .1f a wire is missed, the wire should be manually placed on the appropriate needle. While warp knitting, manual tension is applied to the wires below the spindle to allow the completed wire loop to travel belovri the latch needier as the latch needles go .up. The warp knitting continues until approximately 5 Cm had i~een knit braided. After stopping cranking, another piece of approxirnatety 1.5 inch (3.8 cm) long x 0.5 inch .(1.3 cm) wide etectrica! tape was used to affix the wires to the top end of the vmandrel. ~ The four vuires are cut at the output to the shuttle, arid the mandrel - knit braider wire is removed from the machine.
Soft stainless steel wire is then fixed to ends of the wire knit braid just inside of the electrical tape holding ~th~ knitted structure on the mandrel.
T'he electrical tape is then removed; and the four wires on either end are trimmed using wire cutters. The assembty is then placed in a oven set to 530°C
for 60 minutes. Afte~.this time, the assembly i removed using tongs from the oven and irrirvediatety quenched in a room temperature water bath. The knit-braid is then removed from the mandrel by cutting the wire that is fixing the ends and .
then sliding the knit-braid from the end of the' mandrel.

._ .. . __ The resulting wire knit braid is stable 'in its knit~braid form, and demonstrates significant radial compressive. resistance to.digital pressure.
With the braid mounted on a tube, the wires can be .removed by initially tensioning of the 4 wires as described in previous examples.
Example 4 --Knit Braid over Angioplasty Catheter:
This. example demonstrates the placement of a cover of.the present invention .over a~ angioplasty catheter and the cover's ability to resist radial dilation. ' A knit braider .is set up as specked in Example 2, except the strands are - -substituted with nylon sewing thread (Upholstery Home Qec. Super Strong Machine & Hand Sewing thread,vCoats & Clark; inc., Greenvifie, SC). The fpur threads are threaded into the rhachine and tied together below the spindle body. Tf~e 72 gram.weight is then hung from this knot.
A Cook Accent An.gioplast.y Catheter (8 mm x 4 cm, Bloomington;~IN) is obtained and a vacuum is drawn in the balloon by attaching a syringeao the baboon lumens lust lock and, retracting its plunger. Vllhile maintaining the vacuum, the catheter is fed from below into the spindle, past the needle and into the shuttle body. Tf~~ knit braiding operation is commenced by cranking the crank clockwise, and the knitting starts 8, cm proximal to the balloon.
The cranking continues until the knit braid continues about 10 cm past the distal tip of the catheter. After stopping the .crank, the four threads are severed at the shuttle,and tile catheter is removed from the machine. The syringe is then detached from the balloon lust lock connector.
One thread of the four is then severed right on the distal tip of the catheter. The 10 .cm extension of the braid is then tensioned, and the knit-braid starts to unfurl proximally toward the balloon and hub of the catheter.
A.syringe is reattached to the balloon lumens lust lock. Approximately 5 aim pressure is applied to the balloon. The ballflon resists significant dilatation from .its collapsed state, end the braid does not unfurl.
Among the advantages of the cover of the .present invention are: the knit-braid'will retain high internal pressures with minima! radial growth;
very low forces are required to unfurl the knit-braided cover; the ripcord can be pulled from any.direction to unfurl the knit-braid cover; because the rip cord is knitted, and multi-ftlamented; the rip cord has high strength; with multiple strong Y ., filaments, only thin casings areweeded, typically adding less than 1 French to the across-section of the delivery catheter; also with strong filaments, the cross section of the rip cord is .small; the cover can be unfurled in a controlled fashion and controlled rate; the Knit can be employed to fully encase the expandable device; the knit is 100% removable along a single vector, leaving only the expandable device in place and minimizing potential embolization andlor ' .
vascular trauma. The entire cover can be constructed from a single material (or multiple materials, as desired), allowing; for example, a:cover constructed entirely from PTFE; no weaving through structure of the expandable device is required;. almost any shape of collapsed device can be encased; with the outer surface made relatively .smooth with the cover of the present invention; the cover is very flexible,. adding minimal stiffness to. the deiiVered device;
the knit can be .applied sequentially over different areas., allowing for a mufti stage deployment, and allowing the ends of the stent to be deployed before the center, an outer covering to be released before the inner.covering, etc.; the "density" of the knit can be varied, allowing a branch or a guide were to exit from the side of the knit; the cover' is easy to riianufacture and can be easily autorriated; during manufacturing, the knitting process supplies some radial inward forces to the expandable. device, potentially decreasing its profile further; the knit allows for use of either films or fibers; the rip cord is signii=tcantly longer than the length of the knitting being "opened," allowing for precise deployment of the expandable device; and the deployment line pull length to deployment length ratio can be adjusted by varying the circufinfereritial length of the narrowest knit.
Other advantages of the present invention include:,the cover provides a relatively uniform distribution of compression over the external surface of the constrained device; by extending the cover beyond the end 'of a covered prosthesis or the like, a smooth transition-of -profile between the catheter shaft and device can be established; and the cover can be used to modify the flexibility of a delivery.system by changing degree or type of coverage.
White particuiar erribodiments of the present avention have been illustrated and described herein, the present invention should not be Limited to such illustrations and descriptions; 1t should,be apparent that changes and modifications may tie incorporated,and enibodied as part of the present invention within'the scope of the following claims.

Claims (15)

The invention claimed is:

1. A removable cover mounted over a device comprising:
a plurality of filaments;
the filaments being attached together to form a multi-filament interlocking structure covering the device;
a rip cord comprising ends of each of the filaments;
wherein the interlocking structure separates from the device with two of the plurality of filaments disconnecting from each other in an essentially straight line when tension is applied to the rip cord.

2. The cover of claim 1 wherein the rip cord comprises a multiple-filament interwoven rip cord.

3. The cover of claim 1 wherein the filaments are interwoven as a warp knit.

4. The cover of claim 1 wherein the rip cord removes all of the filaments from the device in an essentially straight line.

5. A removable cover mounted over a device comprising:
a plurality of filaments;
the filaments being attached together to form a multi-filament interlocking structure covering the device;
a rip cord comprising ends of each of the filaments;
wherein the interlocking structure separates from the device with the rip cord removing all of the filaments from the device in an essentially straight line when tension is applied to the rip cord.

6. The cover of claim 5 wherein the rip cord comprises a multiple-filament interwoven rip cord.

7. The cover of claim 5 wherein the filaments are interwoven as a warp knit.

8. The cover of claim 5 wherein two of the plurality of filaments disconnect from each other in an essentially straight line when tension is applied to the rip cord.

9. A removable cover mounted over a device comprising:
a plurality of filaments;
the filaments being attached together to form a multi-filaments interlocking structure covering the device;
ends of each of the filaments interwoven together to form a multi-filament rip cord;
wherein the interlocking structure separates from the device when tension is applied to the rip cord.

10. The removable cover of claim 9 wherein the interlocking structure separates from the device with the rip cord removing all of the filaments from the device in an essentially straight line when tension is applied to the rip cord.

11. The cover of claim 9 wherein the filaments are interwoven as a warp knit.

12. The cover of claim 9 wherein two of the plurality of filaments disconnect from each other in an essentially straight line when tension is applied to the rip cord.

13. The cover of claim 9 wherein the cover comprises a variable density knit.

14. The cover of claim 5 wherein the cover comprises a variable density knit.

15. The cover of claim 1 wherein the cover comprises a variable density knit.