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Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway of a target vessel. Stents are often used in the treatment of atherosclerotic stenosis and/or restenosis in blood vessels. “Stenosis” refers to a narrowing or constriction of the diameter of a bodily passage or orifice. Typically, stents are capable of being compressed, so that they can be inserted through small cavities via catheters, and then expanded to a larger diameter once they reach their target vessel. Mechanical intervention via stents has reduced the rate of restenosis; restenosis, however, is still a significant clinical problem. “Restenosis” refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty or valvuloplasty) with apparent success. Accordingly, stents have been modified to perform not only as a mechanical scaffolding, but also to provide biological therapy.
Biological therapy can be achieved by medicating a stent, typically referred to as a drug delivery stent. Drug delivery stents provide for the local administration of a therapeutic substance at the diseased site. In contrast, systemic administration of a therapeutic substance may cause adverse or toxic side effects for the patient because large doses are needed in order for the therapeutic substance to have an efficacious effect at the diseased site. Thus, local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery therefore produces fewer side effects and achieves more favorable results.
Stents may be made of biostable materials that remain at an implant site permanently. However, the clinical need for a stent at an implant site may be temporary. Once treatment is complete, which may include structural tissue support and/or drug delivery, it may be desirable for the stent to be removed or disappear from the treatment location. One way of having a stent disappear may be by fabricating a stent in whole or in part from materials that erode or disintegrate through exposure to conditions within the body. Stents fabricated from bioresorbable, biodegradable, bioabsorbable, and/or bioerodable materials such as bioresorbable polymers can be designed to completely erode only after the clinical need for them has ended.
A typical method for medicating an implantable device includes, for example, applying a composition containing a polymer, a solvent, and a therapeutic substance to the implantable device using conventional techniques, such as spray-coating or dip-coating. The method further includes removing the solvent, leaving on the implantable device surface a coating of the polymer with the therapeutic substance impregnated in the polymer.
In a typical spray-coating method, a stent is mounted on a mandrel of a spray-coating device. Generally, the stent will rest on, or contact components of, a mandrel (or the mandrel itself) which supports the stent and allows it to rotate during a spray-coating process. The contact between the portions of the mandrel and stent, however, inevitably cause coating defects. These defects can include cob-webbing, tearing, bridging, clumping and/or lack of coating on portions of the stent. The embodiments of the present invention are intended to address coating defect issues caused by conventional mandrel designs.
Another issue with conventional stent coating operations is one of efficiency and cost. Stent coating is typically performed one stent or scaffold at a time. For each stent coated, the coating equipment must be set up. In addition, each stent or scaffold must be loaded prior to coating and unloaded after coating. Thus, machine utilization is limited by coating only one stent for machine set-up, loading, and unloading processes.
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Various embodiments of the present invention include a medical device comprising: a structure comprising a plurality of stent bodies arranged end to end, wherein adjacent stent bodies of the structure are connected by a severable connecting portion disposed between the adjacent stent bodies, wherein at least one of the stent bodies at an end of the structure comprises a severable end portion at the end of the structure.
Further embodiments of the present invention include a method of coating a plurality of stents comprising: providing a structure comprising a plurality of stent bodies arranged end to end, wherein adjacent stent bodies along the structure are connected by a severable connecting portion disposed between the adjacent stent bodies; and depositing a coating on the plurality of stent bodies; and severing the severable connecting portions to disconnect the plurality of stent bodies.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 illustrates an exemplary stent.
FIG. 2 illustrates a method of coating a stent with a spray-coating device.
FIGS. 3A-B illustrates an alternative manner of supporting a stent during the coating process.
FIG. 4A depicts an exemplary multiple stent structure composed of two stent bodies connected by a severable portion.
FIG. 4B depicts a close-up view of the severable portion of FIG. 4A.
FIG. 4C depicts a close-up view of the proximal end of a multiple stent structure.
FIG. 5A depicts a strut that is a portion of a stent that is connected to a tab by a gate.
FIG. 5B depicts an alternative embodiment of stent bodies connected to a tab by gates.
FIG. 6 depicts a portion of a stent showing a side wall, an inner surface, and an outer surface of a strut.
FIG. 7A depicts a mandrel designed to support a multiple stent structure as shown in FIG. 4A.
FIG. 7B depicts a longitudinal cross section of the mandrel of FIG. 7A.
FIG. 8A depicts a multiple stent structure-mandrel assembly.
FIG. 8B depicts an axial cross section of assembly of FIG. 8A.
FIG. 9 depicts one embodiment of system for coating a multiple stent structure.
FIG. 10 illustrates one form of a method using the multiple stent structure described in FIG. 4A with a modified version of the spray-coating device of FIG. 2.
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The implantable medical device used in conjunction with the present invention may be any implantable medical device, examples of which include self-expandable stents, balloon-expandable stents, micro-depot or micro-channel stents, stent-grafts and grafts. Examples of stents include neurological, coronary, peripheral and urological stents. In some embodiments, the underlying structure of the implantable medical device can be virtually any design.
FIG. 1 illustrates a stent 10, which in various embodiments may be metallic or polymeric. In either form, the stent 10 can include a plurality of struts 12 linked by connecting elements 14, with the struts 12 and connecting elements 14 surrounding or partially surrounding interstitial spaces 16. The plurality of struts 12 can be configured in an annular fashion in discrete “rows” such that they form a series of “rings” throughout the body of the stent 10. Thus, the stent 10 can include a proximal ring 18, a distal ring 20 and at least one central ring 22.
A stent such as stent 10 may be fabricated from a polymeric tube or a sheet by rolling and bonding the sheet to form the tube. A tube or sheet can be formed by extrusion or injection molding. A stent pattern, such as the one pictured in FIG. 1, can be formed in a tube or sheet with a technique such as laser cutting or chemical etching. The stent can then be crimped on to a balloon or catheter for delivery into a bodily lumen.
An implantable medical device of the present invention can be made partially or completely from a biodegradable, bioresorbable, bioabsorbable, or biostable polymer. A polymer for use in fabricating an implantable medical device can be biostable, bioresorbable, bioabsorbable, biodegradable or bioerodable. Biostable refers to polymers that are not biodegradable. The terms biodegradable, bioresorbable, bioabsorbable, and bioerodable are used interchangeably and refer to polymers that are capable of being completely degraded and/or eroded into different degrees of molecular levels when exposed to bodily fluids such as blood and can be gradually resorbed, absorbed, and/or eliminated by the body. The processes of breaking down and absorption of the polymer can be caused by, for example, hydrolysis and metabolic processes.
A stent made from a bioresorbable polymer is intended to remain in the body for a duration of time until its intended function of, for example, maintaining vascular patency and/or drug delivery is accomplished. After the process of degradation, erosion, absorption, and/or resorption has been completed, no portion of the biodegradable stent, or a biodegradable portion of the stent will remain. In some embodiments, very negligible traces or residue may be left behind.