Apparatus for compressing an expandable medical device

Various systems for compressing and loading an expandable medical device into a sheath are disclosed. One system comprises an array of moveable blades radially disposed about a central axis and forming a radially contractible aperture. The blade array includes at least a first plurality of blades and a second plurality of blades. The first plurality of blades is independently moveable with respect to the second plurality of blades. Additional aspects of the invention include methods of using the various compressor systems to compress and load an expandable medical device into a sheath.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system and an apparatus for, and a method of compressing an expandable medical device, for example, a stent, and for loading the compressed device into a sheath.

2. Description of Related Art

Intraluminally delivered expandable medical devices have been used to treat damaged or diseased body lumens. Many structures and functions are known in the art. For example, expandable medical devices, namely stent grafts, have been used to treat aortic and thoracic abdominal aneurysms. Expandable medical devices include, but are not limited to, stents, stent grafts, and vena cava filters.

Expandable medical devices may be delivered and deployed using various techniques. For example, a compressed, self-expanding stent graft may be intraluminally delivered and deployed using a catheter delivery system. A stent graft is placed in a radially reduced configuration within the lumen of a catheter or sheath. The catheter is inserted into the vasculature, whereupon the stent graft is delivered to the deployment site. Once the stent graft is properly positioned, the sheath is withdrawn from the stent graft so that the stent graft is allowed to radially expand within the body lumen.

Various apparatuses have been provided for compressing an expandable medical device and for loading the compressed device into a sheath. Examples of such apparatuses are described in U.S. Pat. No. 6,629,350, entitled “Stent Crimping Apparatus and Method,” which is herein incorporated by reference. Typically, a compressor is provided that includes a plurality of blades that forces the device into a compressed configuration. Once the device is compressed, a pusher is used to force the device out of the compressor and into the sheath.

Such a pusher must provide sufficient force to overcome the frictional resistance that can build up between the medical device and the blades. This resistance can be particularly large where the medical device is self-expanding and is biased against the blade surfaces. Prior art apparatuses are effective for compressing and loading short devices and for compressing and loading relatively rigid devices that possess a column strength that is sufficient to withstand the force exerted by the pusher. Longer and/or axially flexible medical devices may present challenges where they do not possess sufficient column strength, and can buckle or crush under the force of the pusher.

SUMMARY

According to an aspect of the present invention, a system for compressing and loading an expandable medical device into a sheath is provided and comprises an array of moveable blades. The blades are radially disposed about a central axis and form a radially contractible aperture. The blade array is configured to receive and compress an expandable medical device within the aperture. The array may comprise two or more independently moveable groups of blades. For example, the array may comprise at least a first plurality of blades and a second plurality of blades, where the first plurality of blades is independently moveable with respect to the second plurality of blades.

The first plurality of blades may be slidably disposed along the central axis in a first and second direction with respect to the second plurality of blades and/or the second plurality of blades may be slidably disposed along the central axis in a first and second direction with respect to the first plurality of blades. Alternatively, or additionally, the first plurality of blades may be moveable radially inwardly and outwardly with respect to the second plurality of blades and/or the second plurality of blades may be moveable radially inwardly and outwardly with respect to the first plurality of blades.

A compressor system may comprise a first operating mechanism for selectively moving the first plurality of blades independently with respect to the second plurality of blades. Another compressor system may comprise a first operating mechanism for selectively moving the first and second pluralities of blades between an expanded configuration and a contracted configuration. The system may additionally comprise a second operating mechanism for selectively moving the first plurality of blades independently with respect to the second plurality of blades. The second operating mechanism may be configured to move the first plurality of blades radially inwardly and outwardly with respect to the second plurality of blades and/or vice versa. Alternatively, the second operating mechanism may be configured to slide the first plurality of blades along the central axis in a first and second direction with respect to the second plurality of blades and/or vice versa.

A compressor system of the present invention is particularly useful for compressing and loading a self-expanding medical device into a sheath. When the medical device is compressed within the first aperture by the first plurality of blades, any engagement between the medical device and the blades will tend to limit the ability of the medical device to slide within the aperture. One of the goals of the present invention is to regulate or control the engagement between the blades, and the medical device. Accordingly, the first plurality of blades may be configured to disengage from the medical device when the device is held by the second plurality of blades. Additionally, or alternatively, the second plurality of blades may be configured to disengage from the medical device when the device is held by the first plurality of blades.

According to yet another aspect of the present invention, a method of compressing and loading an expandable medical device into a sheath is provided. An exemplary method may include providing a compressor that includes an array of moveable blades that are radially disposed about a central axis and that form a radially contractible aperture. The blade array may include two or more groups of blades, for example a first plurality of blades and a second plurality of blades.

The method may further comprise the steps of compressing an expandable medical device within the aperture, and moving the medical device within the aperture by selectively moving the first plurality of blades independently with respect to the second plurality of blades.

The moving step may further comprise any of the steps of pushing the medical device within the aperture with a pusher; moving the first plurality of blades along the central axis in a first direction while the medical device is held by the first plurality of blades; selectively disengaging and engaging the first plurality of blades from the medical device while the medical device is held by the second plurality of blades; and selectively disengaging and engaging the first plurality of blades from the medical device while the medical device is held by the second plurality of blades.

An exemplary method may include the following steps:i. moving the first plurality of blades along the central axis in a first direction while the medical device is held by the first plurality of blades;ii. disengaging the first plurality of blades from the medical device while the medical device is held by the second plurality of blades;iii. moving the first plurality of blades along the central axis in a second direction;iv. engaging the first plurality of blades with the medical device; andv. disengaging the second plurality of blades from the medical device while the medical device is held by the first plurality of blades.
The preceding steps may be repeated one or more times to transfer the medical device into a sheath that is aligned with the aperture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the specification, the term “medical device” shall mean any device that is configured to support, repair, or replace a body part or function of that body part. It can also mean a device that enhances or adds functionality to a physiological system. A stent is an example of a medical device.

The term “stent” means any device or structure that provides or is configured to provide rigidity, expansion force, or support to a body part, for example, a diseased or otherwise compromised body lumen. A stent may be bare, or it may include a covering or graft material. Thus the term “stent” includes devices such as stent grafts. Suitable coverings or graft materials for stents include biocompatible polymers, such as poly(ethylene terephthalate), polylactide, polyglycolide and copolymers thereof; fluorinated polymers, such as polytetrafluoroethylene (PTFE), expanded PTFE and poly(vinylidene fluoride); polysiloxanes, including polydimethyl siloxane; and polyurethanes, including polyetherurethanes, polyurethane ureas, polyetherurethane ureas, polyurethanes containing carbonate linkages and polyurethanes containing siloxane segments.

The term “expandable” describes an object, device, or structure that is capable of being expanded, either by virtue of its own resilience, or upon the application of an external force. Expandable stents include both self-expanding and balloon-expandable devices. Self-expanding stents can be made of stainless steel, materials with elastic memory properties, such as NITINOL, or any other suitable material. Exemplary self-expanding stents include Z-STENTS® and ZILVER® stents, which are available from Cook Incorporated, Bloomington, Ind. USA. Balloon-expandable stents may be made, for example, of stainless steel (typically 316LSS, CoCr, etc.). Hybrid stents may be provided by combining one or more self-expanding stents or stent portions with one or more balloon-expandable stents or stent portions.

FIGS. 1 and 2illustrate a blade array10for a stent compressor. The blade array10includes a plurality of moveable compressor blades12. The blades12are arranged to form an iris14that defines a contractible aperture15. The aperture15has a central axis A.

The blade array10is configured to receive and compress an expandable medical device, such as a stent, within the aperture15. The blades12are moveable between an expanded configuration, as shown inFIG. 1, and a contracted configuration, as shown inFIG. 2. In the expanded configuration, the radius of the aperture15is generally equal to or greater than an expanded radius of the medical device so that the medical device can be loaded into the compressor. In the contracted configuration, the radius of the aperture15is generally less than the expanded radius of the medical device.

The blade array10shown inFIGS. 1 and 2comprises twelve blades12. Blade arrays10can comprise a greater or a fewer number of blades, for example, as few as three, or more than twelve blades12. Generally, as the number of blades12increases, the contour of the aperture15will become smoother, and the contact area between the blades12and the medical device will increase, thereby increasing the area of frictional contact between the compressor blades12and the medical device.

FIGS. 3A-3Cillustrate an example of a prior art compressor that is described in U.S. Pat. No. 6,629,350, entitled “Stent Crimping Apparatus and Method.” The compressor comprises a crimp head502that includes an array504of moveable blades512. The crimp head502further comprises a set of drive hubs520, pivot pins522, drive pins524, and stationary base plates526. Each of the blades512is pivotally connected to the stationary base plates526via pivot pins522that are disposed within cylindrical bores formed in the blades512and in each of the base plates526. Each of the blades512is connected to the drive hubs520via drive pins524that are disposed within cylindrical bores in each of the drive hubs520and in drive slots formed in the blades512. The drive slots have a cylindrical configuration with a cross-section that is slightly radially elongated, rather than a circular cross-section.

The crimp head502is actuated by a drive mechanism508which includes a pair of rotation arms510, each connected to a respective drive hub520. The rotation arms510are driven in a synchronized manner to rotate the drive hubs520, thereby moving the blade array504between an expanded configuration and a contracted configuration.

FIG. 3Bshows the stent compressor ofFIG. 3Ain an expanded configuration, wherein the aperture515is expanded and is capable of receiving a stent.FIG. 3Cshows the stent compressor ofFIG. 3Ain a contracted configuration, wherein the aperture515is reduced. The blades512move between the expanded and contracted configuration by rotating the drive hubs520via rotation arms510.

Prior art compressors, such as the one described in U.S. Pat. No. 6,629,350 are configured so that all of the blades in the blade array move in collaboration—the blades are coupled so that movement of each blade is coordinated with the movement of all of the other blades. Accordingly, prior art compressors do not permit independent movement of separate portions or groups within the blade array.

FIGS. 4A-4Cillustrate a new compressor system. The compressor system is specially configured to receive and compress an expandable medical device, such as a stent, and comprises a blade array110having two or more independently moveable groups of blades. Such a system may be provided by converting a suitable commercially available compressor. Suitable compressors include Models SC100 and SC900, sold by Machine Solutions, Inc. of Flagstaff, Ariz.

The system shown inFIGS. 4A-4Ccomprises an array110of moveable compressor blades, arranged to form a contractible aperture115. The array110includes a first plurality of blades112A and a second plurality of blades112B. The blades112A,112B are radially disposed about a common central axis A and are moveable between an expanded configuration and a contracted configuration. When the blades112A,112B are in the expanded configuration, an expandable medical device, (not shown) may be inserted into the aperture115. In the contracted configuration, the blades112A,112B hold the device in a contracted configuration.

Each of the blades112A,112B in the blade array may be coupled to an inner hub mechanism122. The inner hub mechanism122shown in the figures includes a first hub124A and a second hub (hidden). As shown inFIG. 4C, each of the blades112A,112B may have a pair of inner elongated slots126(only one of the pairs of slots is visible in the figures). Each slot126has a cylindrical configuration with a cross-section that is radially elongated. The inner slots126are arranged in circular patterns about the central axis A. The first hub124A and the second hub (hidden) of the inner hub mechanism122may each have a plurality of cylindrical bores128(only one of the pluralities of bores is visible in the figures). Inner pins130(only one of the pairs of pins is visible in the figures) couple the blades112A,112B to the inner hub mechanism122via slots126and corresponding bores128. The pins130may be friction fitted with the bores128and are configured to move radially and axially within the slots126.

In an alternative embodiment, each of the blades112may have an inner cylindrical bore, rather than an elongated slot, and each of the first and second hubs of the inner hub mechanism122may have a corresponding elongated slot.

Each of the blades112A,112B may be coupled to an outer hub mechanism142. The outer hub mechanism142shown in the figures includes a first hub144A and a second hub144B. Each of the blades112A,112B may have an outer cylindrical bore146A,146B. Outer bores146A,146B are arranged in circular patterns about the central axis A and are disposed radially outwardly from inner slots126. The first outer hub144A has a plurality of cylindrical bores148A, each corresponding with a bore146A in the first plurality of blades112A. Likewise, the second outer hub144B has a plurality of cylindrical bores148B, each corresponding with a bore146B in the second plurality of blades112B. The first plurality of blades112A is coupled to the first hub144A via pins150A disposed in bores146A and148A, and the second plurality of blades112B is coupled to the second hub144B via pins150B disposed in bores146B and148B.

To move the blades112A,112B between an expanded and a contracted configuration, the inner hubs124A,124B (hidden) may be rotated while holding the outer hubs144A,144B stationary. The system may comprise a control member, such as the tie bar155shown inFIG. 4A, for synchronizing the rotation of the inner hubs124A,124B. When the inner hubs124A,124B are rotated, each inner pin130moves in an arc about the central axis A and each blade112A,112B pivots within a respective outer hub144A,144B about an axis defined by a respective outer pin150A,150B. As the blades112A,112B pivot, the radius of the aperture115increases or decreases, depending on the direction of rotation of hubs124A,124B.

Alternatively, the blades112A,112B can be moved between the expanded and contracted configurations by rotating the first and second outer hubs144A,144B while holding the first and second inner hubs124A,124B stationary.

In an alternative embodiment of the present invention, the first and second pluralities of blades112A,112B may each be coupled to both the first and second outer hubs144A,144B. The first plurality of blades112A may be coupled only to the first inner hub124A, and the second plurality of blades112B may be coupled only to the second inner hub124B (hidden). To move the blades112A,112B between expanded and contracted configurations, the outer hubs144A,144B may be rotated together while holding the inner hubs124A,124B stationary, or vice versa.

The movement of a blade of the system shown inFIGS. 4A-4Cis illustrated inFIG. 5. The expanded configuration of the blade is indicated by the position α and the contracted configuration of the blade is indicated by the position β. The blade moves between positions α and β by pivoting about an axis Ro corresponding with outer bore146. The blade112moves along an arc such that the distal end114swings towards or away from the central axis A.

In the system shown inFIGS. 4A-4C, the outer hub mechanism142decouples the first plurality of blades112A and the second plurality of blades112B. Accordingly, the blades112A,112B may have radial and axial freedom of movement, unlike the blades in prior art stent compressors. The first and second pluralities of blades112A,112B can therefore be operated independently of each other. For example, the outer hubs144A,144B can be rotated independently to move the first plurality of blades112A radially inwardly and outwardly with respect to the second plurality of blades112B and vice versa. Further, blades112A,112B can move along the central axis A independently of one another by moving the outer hubs144A,144B axially with respect to each other.

The system shown inFIGS. 4A-4Cincludes first and second rotation arms152A,152B that are coupled to the first and second outer hubs144A,144B respectively. The first rotation arm152A can be operated to selectively rotate the first outer hub144A with respect to the second outer hub144B. Similarly, the second rotation arm152B can be operated to selectively rotate the second outer hub144B with respect to the first outer hub144A.

Rotation of the first outer hub144A with respect to the second outer hub144B causes each outer pin150A to move in an arc about the central axis A and each blade112A to pivot within the inner hubs124A,124B (not shown) about an axis defined by a respective inner pin130. As the blades112A pivot, they swing radially towards or away from the central axis A and radially inwardly or outwardly with respect to the second plurality of blades112B. Likewise, rotation of the second outer hub144B with respect to the first outer hub144A causes each of the outer pins150B to move in an arc about the central axis A and each of the second plurality of blades112B to pivot within the inner hubs124A,124B about an axis defined by a respective inner pin130. As the blades112B pivot, they swing radially towards or away from the central axis and radially inwardly or outwardly with respect to the first plurality of blades112A.

FIG. 5shows the movement of a blade between a contracted configuration β and a retracted configuration γ as described above. The blade112moves between positions β and γ by pivoting about an axis Ri corresponding with inner slot126. The blade112moves along an arc such that the distal end114swings towards or away from the central axis A.

According to an aspect of the invention, a compressor system may optionally include one or more slide mechanisms154. In the embodiment shown inFIG. 4A, the compressor system has two slide mechanisms154A,154B. A first slide mechanism154A is coupled to the first outer hub144A and is configured to slide the first plurality of blades112A along the central axis A independently of the second plurality of blades112B and the second slide mechanism154B is configured to slide the second plurality of blades112B along the axis A independently of the first plurality of blades112A.

A slide mechanism may comprise a transfer mechanism156, as shown inFIG. 4B, that translates rotational movement into linear movement. The transfer mechanism156may include first and second levers157A,157AA. One end of each lever157A,157AA includes an engagement member158A,158AA that engages the outer hub144A along an axis A1perpendicular to the central axis A. A tie bar159couples the levers along an axis A2parallel to A1. Rotation of tie bar159causes the first plurality of blades112A to move along the axis A. Because the first and second pluralities of blades112A,112B are decoupled, the blades112A,112B can move independently of one another.

Various new and useful applications for compressors of the present invention will now be described. InFIG. 6A, a compressor of the present invention is shown and includes a blade array110comprising a first plurality of blades112A and a second plurality of blades112B. The blades112A,112B are shown in an expanded configuration. An expandable medical device120, for example a self-expanding stent, is disposed within the aperture115of the blade array110and is shown in an expanded configuration. A sheath160is provided for receiving and retaining the stent120in a contracted configuration. The lumen162of the sheath160may be positioned in alignment with the central axis A. The sheath160has an inner diameter that is generally equal to or slightly larger than the contracted diameter of the stent120.

InFIG. 6B, the blades112A,112B have moved from the expanded configuration ofFIG. 6Ato a contracted configuration. The first and second pluralities of blades112A,112B compress and hold the expandable stent120in a contracted configuration.

At this point, a pushing device (not shown) may be provided for pushing the compressed stent120into the sheath160. The pushing device may engage an end of the stent120and push the stent towards the sheath160and into the sheath lumen162. The pushing device must apply sufficient force to overcome any frictional resistance between the blades112A,112B and the stent120. If the stent120is particularly flexible, or if it is sufficiently long, the force required to overcome the frictional resistance may be greater than the column strength of the stent120. In either case, the pushing device may cause the stent120to longitudinally compress, buckle, or crush.

InFIG. 6C, the first plurality of blades112A has moved radially away from the stent120and is shown in a retracted configuration. The first plurality of blades112A is disengaged from the stent120and the stent is held in a contracted configuration by the second plurality of blades112B.

Because the first plurality of blades112A is no longer in contact with the stent120, the area of frictional contact between the blade array110and the stent120is reduced. Accordingly, the friction between the blades112A,112B and the stent120will be reduced. A pusher (not shown) may be provided at this point to push the stent120into the sheath160. Because friction has been reduced, the stent120is less likely to compress, buckle, or crush under the force of the pusher.

The compressor system may be operated so that the first plurality of blades112A alternately engages and disengages the stent120and the second plurality of blades112B alternately disengages and engages the stent120. Repetitively engaging and disengaging blades112A and repetitively disengaging and engaging blades112B may reduce the surface contact area between the blades112A,112B at any given time, and may reduce the effects of static friction between the blades and the stent120. The frequency with which the blades112A,112B engage and disengage the stent120may vary. For example, the first and second pluralities of blades112A,112B may move between engaged and disengaged configurations at a rate of once per second. The frequency may be more or less depending on the desired effect. The first and second outer hubs144A,144B may be controlled to engage and disengage the stent120using a standard input/output device, for example, a computer.

It is important to note that the blades112A,112B need only move away from the stent a distance that is necessary to disengage the blades from the stent120. In many cases, it may only be necessary to move the blades as little as ten thousandths of an inch from the stent120in order to effect frictional disengagement.

Other methods of compressing and loading an expandable medical device into a sheath are contemplated. A preferred method may be described with reference toFIGS. 6A-6Gand7A-7G and with respect to the exemplary compressor system shown inFIGS. 4A-4Cand described above. InFIG. 6A, the blade array110is shown with the first and second pluralities of blades112A,112B in an expanded configuration. A stent120is placed within the aperture115of the blade array115.FIG. 7Aillustrates the relative positions of the blades112A,112B in the expanded configuration. A sheath160is provided and is aligned with the axis A so that the sheath lumen162is positioned to receive the stent120in the contracted configuration.

The blade array110contracts and the stent120is compressed, for example, by rotating the inner hubs124A,124B of the compressor ofFIGS. 4A-4Cwhile holding the outer hubs144A,144B stationary. InFIG. 6B, the blade array is shown in a contracted configuration. The stent120is compressed into a contracted configuration and the first and second pluralities of blades112A,112B engage the stent. As shown inFIG. 7B, each of the blades112A,112B moves radially inwardly along an arc between the expanded and contracted configurations.

Next, the first plurality of blades112A disengages and retracts from the stent120while the second plurality of blades112B holds the stent. This may be done via rotation of the first outer hub144A with respect to the second outer hub144B. InFIG. 6C, the first plurality of blades112A is moved radially outwardly with respect to the second plurality of blades112B. The configuration of the blades112A,112B is shown in7C. Each of the first plurality of blades112A moves radially outwardly along an arc between the contracted and retracted configurations.

InFIG. 6D, the first plurality of blades112A has moved along the axis A away from the sheath160while the second plurality of blades112B remains stationary. The blades112A may be moved by actuating the first sliding mechanism154A. At this point, the stent120is still held by the second plurality of blades112B. The configuration of the blades112A,112B is shown inFIG. 7D.

Next, the first plurality of blades112A engages the stent120, for example, by rotating the first outer hub144A while holding the second outer hub144B stationary. In this step; the first outer hub144A is rotated in a direction that is opposite the direction of rotation in the disengagement step ofFIG. 6C. The first plurality of blades112A moves radially inwardly with respect to the second plurality of blades112B. The stent120is now held by both the first and second pluralities of blades112A,112B, as shown inFIGS. 6E and 7E.

Next, as shown inFIGS. 6F and 7F, the second plurality of blades112B disengages and retracts from the stent120while the stent is held in the contracted configuration by the first plurality of blades112A, for example, by rotating the second outer hub144B with respect to the first outer hub144A. Each of the second plurality of blades112B moves radially outwardly along an arc between the contracted and the retracted configurations.

InFIGS. 6G and 7G, the first plurality of blades112A has moved along the axis A towards the sheath160while the second plurality of blades112B remains stationary. The blades112A may be moved by actuating the first sliding mechanism154A. Because the first plurality of blades112A engages the stent120, the stent moves with the blades towards the sheath160. After this step, the blades may return to the configuration shown inFIGS. 6B and 7B, for example, by rotating the second outer hub144B while holding the first outer hub144A stationary, thereby reengaging the second plurality of blades112B with the stent.

Alternatively, at this point, the second plurality of blades112B may be moved along the axis A away from the sheath160while holding the first plurality of blades112A stationary, for example, using the second sliding mechanism154B. The second plurality of blades112B may then reengage the stent120and the first plurality of blades112A may disengage from the stent120while the device is held by the second plurality of blades112B. Next, using the second sliding mechanism154B, the second plurality of blades112B may be moved along the axis A towards the sheath160while holding the first plurality of blades stationary to advance the stent120further into the sheath.

It will be apparent that many combinations and permutations of the steps recited above may be performed and repeated successively, as required, to completely transfer the stent120into the lumen of the sheath160, with or without the need for a pusher.

The compressor blades may engage a medical device by various means, including, but not limited to, mechanical interaction between the blades and the device. For example, the blades may engage the medical device merely via frictional contact. According to an aspect of the invention, at least one of the first and second plurality of blades may be treated to selectively increase the friction between the treated blades and the medical device. For example, the blades may comprise a rough or textured surface finish. The surface finish may be provided, for example, by sand blasting or laser etching, or the surface finish may comprise a textured coating.

Alternatively, at least one of the first and second plurality of blades may be treated to selectively decrease the friction between the blades and the medical device. For example, the blades may comprise a smooth surface finish. The surface finish may be provided by mechanical means including by polishing. Alternatively, a smooth or lubricious coating may be applied to the blade surface. Other engagement structures and devices are contemplated and are within the scope of the invention. For example, the blades may be provided with structures or details that are configured to engage with corresponding structures or details of the medical device.

According to another aspect of the invention, the blades may be configured to engage the medical device when the blades slide in a first direction and to disengage the device when the blades slide in a second, opposite direction.FIG. 8shows a stent120compressed within the aperture315formed by a plurality of blades312. Blades312have a selective engagement interface. The surface of blades312includes a plurality of longitudinally oriented asymmetric ridges345. Ridges345have apices347that are oriented in a first direction with respect to the central axis A, forming a saw-tooth pattern. The ridges345are configured so that when the stent120is compressed and the blades312slide in the first direction, the blades312engage the stent120. Conversely, when the blades312slide in the second direction, the blades312disengage from the stent120.

A compressor system according to the present invention may be provided wherein the second plurality of blades112B is treated to minimize frictional resistance with a medical device and the first plurality of blades112A is treated to maximize frictional resistance with the device. Accordingly, the apparatus could be operated to advance the device as described above. If the friction between the first plurality of blades112A and the stent is sufficiently greater than the friction between the second plurality of blades112B and the stent, the first plurality of blades112A may be able to move the device without having to retract the second plurality of blades112B from the device.

In another embodiment, a compressor system may be provided wherein each of the first plurality of blades112A and the second plurality of blades112B includes a selective engagement interface. The blades are configured so that the first plurality of blades112A engages the medical device and the second plurality of blades112B disengages from the medical device when the first plurality of blades moves in a first direction with respect to the second plurality of blades. Conversely, the blades are configured so that the first plurality of blades112A disengages from the medical device and the second plurality of blades112B engages the medical device when the first plurality of blades112A moves in a second opposite direction with respect to the second plurality of blades. Accordingly, when the first plurality of blades112A moves in the first direction with respect to the second plurality112B, the device will move in the first direction, and when the first plurality of blades112A moves in the second direction with respect to the second plurality112B, the device will remain stationary. It will be immediately apparent that as configured, it will not be necessary to retract any of the blades112A,112B from the stent during operation.

Throughout this specification various indications have been given as to preferred and alternative embodiments of the invention. However, it should be understood that the invention is not limited to any one of these. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the appended claims, including all equivalents, that are intended to define the spirit and scope of this invention.