METHOD FOR IMPROVING STENT RETENTION AND DEPLOYMENT CHARACTERISTICS

Medical devices and methods for making, preparing, and using medical devices are disclosed. An example method may include disposing an implantable medical device along an outer surface of a balloon. The implantable medical device may include a polymeric stent having a plurality of openings formed therein. The implantable medical device may be designed to shift between a compressed configuration having a compressed diameter and an expanded configuration having an expanded diameter. The method may also include compressing the implantable medical device to an intermediate diameter between the compressed diameter and the expanded diameter and applying inflation pressure to the balloon so that at least a portion of the balloon extends at least partially into at least one of the plurality of openings in the implantable medical device.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and methods for manufacturing and/or preparing medical devices.

BACKGROUND

BRIEF SUMMARY

This disclosure provides design, material, manufacturing method, and use alternatives for medical devices. An example embodiment method may include a method for preparing a medical device. The method comprises:

disposing an implantable medical device along an outer surface of a balloon;

wherein the implantable medical device includes a polymeric stent having a plurality of openings formed therein;

wherein the implantable medical device is designed to shift between a compressed configuration having a compressed diameter and an expanded configuration having an expanded diameter;

compressing the implantable medical device to an intermediate diameter between the compressed diameter and the expanded diameter; and

applying inflation pressure to the balloon so that at least a portion of the balloon extends at least partially into at least one of the plurality of openings in the implantable medical device.

Alternatively or additionally to the embodiment above, further comprising expanding the implantable medical device to a diameter larger than a manufactured diameter of the implantable medical device before compressing the implantable medical device to the intermediate diameter.

Alternatively or additionally to any of the embodiments above, further comprising applying heat to the implantable medical device.

Alternatively or additionally to any of the embodiments above, applying heat to the implantable medical device includes heating at a temperature of about 30° C. to about 80° C.

Alternatively or additionally to any of the embodiments above, applying heat to the implantable medical device includes heating at a temperature above the glass transition temperature (Tg) of the balloon.

Alternatively or additionally to any of the embodiments above, applying heat to the implantable medical device includes applying heat while compressing the implantable medical device.

Alternatively or additionally to any of the embodiments above, applying inflation pressure to the balloon occurs while compressing the implantable medical device.

Alternatively or additionally to any of the embodiments above, applying inflation pressure to the balloon occurs after compressing the implantable medical device.

Alternatively or additionally to any of the embodiments above, further comprising compressing the implantable medical device to a second intermediate diameter that is smaller than the intermediate diameter.

Alternatively or additionally to any of the embodiments above, the implantable medical device is a bioabsorbable polymeric stent, a drug coated polymeric stent, or a drug coated bioabsorbable polymeric stent.

Alternatively or additionally to any of the embodiments above, applying inflation pressure to the balloon includes applying about 10 psi to about 60 psi of inflation pressure.

A medical device system is disclosed. The system comprises:

an elongate shaft having a distal end region;

an expandable balloon coupled to the distal end region;

a stent secured to the balloon, wherein the stent has a plurality of openings formed therein;

wherein the stent is a polymeric stent, a bioabsorbable metal stent, or a drug coated metal stent; and

wherein at least a portion of the balloon extends at least partially into at least one of the plurality of openings in the stent.

Alternatively or additionally to any of the embodiments above, the stent is a bioabsorbable polymeric stent.

Alternatively or additionally to any of the embodiments above, the stent is a drug coated polymeric stent.

Alternatively or additionally to any of the embodiments above, the stent is a drug coated bioabsorbable polymeric stent.

Alternatively or additionally to any of the embodiments above, the balloon has a distal balloon cone and a proximal balloon cone, and wherein a ledge is formed in the balloon adjacent to the distal balloon cone, the proximal balloon cone, or both, wherein the ledge is configured to enhance securement of the stent to the balloon.

A method for preparing a medical device is disclosed. The method comprises:

disposing a stent along an outer surface of a balloon;

wherein the stent includes a plurality of openings;

wherein the stent is capable of shifting between a fully compressed configuration having a fully compressed diameter and an expanded configuration having an expanded diameter;

wherein the stent has a manufactured diameter that is between the fully compressed diameter and the expanded diameter;

expanding the stent from the manufactured diameter to a first intermediate diameter;

compressing the stent from the first intermediate diameter to a second intermediate diameter, the second intermediate diameter being smaller than the manufactured diameter and being between the fully compressed diameter and the expanded diameter;

applying inflation pressure to the balloon so that one or more sections of the balloon extend through at least some of the plurality of openings in the stent; and

applying heat to the stent while compressing the stent, while applying inflation pressure to the balloon, or while compressing the stent and applying inflation pressure to the balloon.

Alternatively or additionally to any of the embodiments above, applying heat to the stent includes applying heat while compressing the stent.

Alternatively or additionally to any of the embodiments above, further comprising compressing the stent to a third intermediate diameter that is smaller than the second intermediate diameter.

Alternatively or additionally to any of the embodiments above, the stent is a metal stent, a bioabsorbable metal stent, a drug coated metal stent, or a drug coated bioabsorbable metal stent.

Alternatively or additionally to any of the embodiments above, the stent is a polymeric stent, a bioabsorbable polymeric stent, a drug coated polymeric stent, or a drug coated bioabsorbable polymeric stent.

DETAILED DESCRIPTION

FIG. 1schematically illustrates an example medical device system10(system) disposed within a blood vessel12. System10may take the form of a stent delivery system including a catheter shaft14, an expandable member or balloon16coupled to shaft14, and an implantable medical device18coupled to balloon16. In this example, implantable medical device18is a stent that may be used to treat a lesion20. Other implantable medical devices are contemplated. In addition, other systems are contemplated that may be designed to be used in a variety of body lumens including, but not limited to, coronary blood vessels, peripheral blood vessels, along the pancreatic and/or biliary tract, along an airway, along the urinary tract, or the like.

Stents, for example balloon expandable stents, are typically secured to the balloon of a balloon catheter. The processes for securing the stent to the balloon may involve a single stage diameter reduction or crimping step where the stent is compressed onto the balloon in one quick movement to a set force.FIG. 2is a partial cross-sectional view of an example stent118crimped onto balloon116using a single step crimping process. The balloon116may be coupled to catheter shaft114. Here it can be seen that stent118may include a plurality of struts124. Openings126may be defined between struts124. Stent118may be compressed from a first “expanded” diameter D1E to a second “compressed” diameter D2C. For the purposes of this disclosure, the first fully expanded diameter D1E may be understood as the diameter that stent118is designed to be fully expanded to. In use, stent118may be deployed at a diameter that is slightly less that the fully expanded diameter D1E due to, for example, the shape of the target anatomy, intravascular debris/lesions, etc. In at least some instances, the fully expanded diameter D1E corresponds to the diameter of stent118prior to being crimped. For the purposes of this disclosure, the fully compressed diameter D2C may be understood as the diameter that stent118is designed to be compressed to. In at least some instances, the compressed diameter D2C corresponds to the diameter of stent118when it is crimped onto balloon116.

Balloon116may also be folded into a compressed configuration and may define a plurality of folds122. In some instances, folds122may be described as wings. Folds122may include overlapping sections of balloon116. This may include a single overlapping layer or multiple overlapping layers. It can be appreciated that, in at least some instances, the compressed diameter D2C corresponds to the diameter of stent118when it is crimped onto the folded balloon116.

In some cases, it may be desired for a stent to be crimped less than all the way down on to the balloon. For example, some polymeric and/or bioabsorbable stents may utilize wider struts in order to achieve comparable radial strength to metal stents, because of, for example, material differences. Wider struts may increase the minimum crimp diameter that a stent can achieve before struts collide in an undesirable way. In an example, the minimum crimp diameter of a stent may be greater than the compressed diameter D2C. Some previous crimping processes (e.g., single step crimping processes) may take the stent below its minimum crimp diameter, which can cause stent damage or loss of critical mechanical properties, such as radial strength. InFIG. 2, which may be representative of a polymer stent that is crimped below its minimum crimping diameter, strut twisting and deformation can be seen (e.g., the bottom struts at reference number125inFIG. 2).

For larger diameter metal stents (e.g., about 4.50 mm to about 5.00 mm), higher foreshortening (e.g., stent length after deployment minus the stent length before deployment) can be seen during deployment due to the large difference in crimped diameter and deployed stent diameter. In at least some instances, the ends of the balloon may open before the middle of the stent, creating a large diameter gradient within the stent, which can cause the end strut rows to slide towards the middle of the stent as the balloon opens, to the point where several of the end strut rows may overlap each other (e.g., at reference number127inFIG. 2) and shorten the deployed length of the stent. For example,FIG. 3schematically illustrates stent118, including struts124and openings126, in a deployed configuration. As shown inFIG. 3, stent118may be foreshortened such that the length L1A of stent118in an expanded configuration is shorter than the expanded length L2A (e.g., where the expanded length L2A is a length corresponding to the length that stent118is designed to elongate to when expanded), such as a result of end strut rows overlapping each other127. In other words, the difference between length L2A and L1A may be relatively large.

It may be desirable to limit the amount of foreshortening of stent118(and/or other stents disclosed herein). A potential way to reduce stent deformation and/or reduce foreshortening may include crimping the stent to a larger diameter, such as an intermediate diameter between the fully expanded diameter D1E and the fully compressed diameter D2C. This may reduce stent deformation and preserve more of the stent's as-cut mechanical properties, in the case of polymeric stents. However, crimping to a larger diameter may impact stent securement. In other words, a portion of the stent may embolize or shift along the balloon during delivery and/or deployment. It may be desirable to reduce the amount of migration of the stent and/or improve the securement of the stent to the balloon in order to mitigate migration while also controlling for stent deformation and limiting foreshortening.

Reduced foreshortening, reduced stent migration, and/or improved securement of the stent may be achieved through crimping and/or stent securement processes, such as those processes disclosed herein. For example, as described herein, the stent may be retained on the balloon by the plastic deformation of the stent or by the stent becoming partially embedded into the balloon. Stent retention forces may result from the combination of obstructive forces due to balloon material ridges forming around elements of the stent, or residual normal force on the stent from the compressed balloon layers. Heated crimping elements, in one or more embodiment, may also be used to soften the balloon material to allow the stent to emboss or embed into the balloon more readily. In various embodiments, a balloon inflation step is used before and/or during the crimp cycle to form the balloon up against the stent and in-between stent struts for additional securement and stent to balloon engagement. Some additional details of at least some of the crimping processes contemplated herein are discussed below.

FIG. 4is a partial cross-sectional view of an example stent218crimped onto balloon216using a multiple step crimping process that is designed to lessen stent deformation, control for higher foreshortening, or improve securement of stent218to balloon216. Also shown inFIG. 4is catheter shaft214. Balloon216may be folded and define a plurality of folds222. Stent218may include a plurality of struts224. Openings226may be defined between struts224. Stent218may be crimped onto balloon216. Like stent118described in relation toFIG. 2, stent218may be capable of shifting between a first larger diameter D3E to a second smaller diameter D4C. In at least some instances, diameter D3E and diameter D4C may correspond to the largest and smallest diameters, respectively, that stent218may be expanded/compressed to without being damaged/deformed.

In some instances, stent218may be compressed to an intermediate diameter D5I. In other instances, stent218may be expanded to an expanded diameter D6E through balloon inflation before being compressed. More particularly, stent218may be manufactured or otherwise formed to have a “manufactured diameter” D7M and then may be expanded prior to the crimping process (e.g., to diameter D6E). Before, during, and/or after expansion or compression, inflation pressure may be applied to balloon216. In an example, a portion228of balloon216may extend at least partially into or through an opening226. In other words, balloon216may be formed up against and through at least one of the plurality of openings226between struts224to provide a stent to balloon interaction and stent retention at larger diameters. The processes disclosed herein where portions228of balloon216extend at least partially into or through at least one of the plurality of openings226may be termed “pillowing” due to, for example, stent218being held or “pillowed” by balloon216.

In some instances, stent218may undergo an initial compression. In other instances, stent218may undergo an initial expansion through balloon inflation. Stent218may undergo one or more diameter reduction steps where stent218is compressed to an intermediate diameter (e.g., D5I) and inflation pressure is applied to balloon216. For example, stent218may be a polymeric stent that has a manufactured diameter of about 0.05 inches to about 0.2 inches, or about 0.1 inches to about 0.15 inches, or about 0.13 inches and can be compressed to an intermediate diameter D5I of about 0.02 inches to about 0.15 inches, or about 0.04 inches to about 0.06 inches, or about 0.051 inches. In some instances, stent218may undergo multiple compressions. Inflation pressure may be applied to balloon216after compression (e.g., a compression head of the crimping apparatus may be held stationary when inflation pressure is applied) or, in some instances, inflation pressure may be applied to the balloon216before and/or during compression. The inflation pressure may be applied at about 10 psi to about 60 psi, or about 15 psi to about 40 psi, or about 20 psi to about 30 psi.

When inflation pressure is applied while the crimp head is stationary at a given diameter, the action of forming portions228of balloon216at least partially within some of the plurality of openings226may be primarily driven by the temperature and the inflation pressure used, as well as how open the openings226between the struts224are at the given diameter. If openings226are not open or are only partially opened, portions228may not protrude sufficiently into or through openings226to secure stent218to balloon216. Openings226between struts224may vary based on manufacturing variables, so one process may not be ideal for all parts to be manufactured. To address manufacturing variables, for example, the processes disclosed herein may utilize compression steps that compress stent218to a number of different intermediate diameters and apply inflation pressure to balloon216while applying heat, as described herein. The processes disclosed herein may utilize an initial expansion step through balloon inflation before compressing the stent218. For example, the crimping processes may compress stent218to a first intermediate diameter, to a second intermediate diameter, to a third intermediate diameter, to a fourth intermediate diameter, to a fifth intermediate diameter, etc., before the final crimped diameter of stent218is achieved. Inflation pressure may be applied before, during, and/or after any one or more of the compression steps.

Another example process may include the application of compressive force, heat, and inflation pressure, with a relatively slow compression rate, as described herein. In an example, the medical device is exposed to temperatures in a range of about 30 degrees Celsius (° C.) to about 80° C., such as, for example, above the glass transition temperature (Tg) of the balloon. The process may also include an expansion process through balloon inflation before the application of compressive force. This technique may allow stent218to be crimped from larger diameters, with a more open inflation channel/lumen229underneath stent218, while maintaining sufficient stent retention forces (e.g., about 0.5 to about 1 pounds or about 0.75 pounds). During an expansion operation, balloon216may be formed up against the inner surface of stent218and portions228may protrude at least partially into or through openings226between stent struts224by simultaneous application of heat and balloon inflation pressure, while stent218is compressed at a relatively slow rate, as described herein. This technique enhances stent to balloon interaction by applying an inward radial compressive force on stent218into balloon216, and an outward radial expansion force on balloon216at the same time, which may result in more engagement of portions228of balloon material with stent218. The compression rate may be kept relatively slow, such as, for example, over about 15 seconds to about 120 seconds, about 30 seconds to about 60 seconds, or about 45 seconds, to allow sufficient balloon216/stent218contact time for balloon216to be formed up against stent218, and through stent struts224at each diameter (e.g., each intermediate diameter).

FIG. 4ais a graph that illustrates an example crimping process that may be similar to those disclosed herein. The graph includes a line showing changes to the diameter of the stent (e.g., stent218) over time, generally labeled with reference number300, and a line showing changes to the inflation pressure applied to the balloon (e.g., balloon216) over time, generally bearing reference number400. In this example and referencing stent218and balloon216ofFIG. 2, stent218may have an initial diameter at an initial time period301. The initial diameter may correspond to diameter D7M, D6E, D3E, or another diameter larger than D5I. In some instances, an initial expansion may occur (not shown) where stent218may be expanded from manufactured diameter D7M to a larger diameter (e.g., D6E, D3E, or another diameter larger than D7M). This may occur during time period301or prior to time period301. Compression may begin at time period302. Compression during time period302may be relatively slow (e.g., occurring over a time period of about 20 seconds to about 50 seconds or more, or about 25 seconds to about 40 seconds or more, or about 35 seconds to about 40 seconds or more). During the initial time period301and first compression time period302(e.g., at a time period401), there may be no inflation pressure may applied to balloon216. After completion of the first compression time period302, inflation pressure may be increased (e.g., rapidly increased) at time period402and then held constant at time period403. During a portion of time period403, the diameter of stent218may be held constant (e.g., along time period303). Inflation pressure may be decreased (e.g., rapidly decreased) at time period404and then held constant along time period405. Along time period405, the diameter of stent218may be reduced (e.g., along time period304) and then held constant (e.g., along time period305). The constant diameter at time period305may correspond to when stent218has diameter D5I. Inflation pressure applied during time period405may cause one or more portions portion228of balloon216to extend at least partially into openings226.

As shown in the example illustrated inFIG. 5, in at least some instances, portions of balloon216along a distal balloon cone216a,a proximal balloon cone216b,or both may also be formed up against stent218. For example, a portion of balloon216at distal balloon cone216aof balloon216may be formed up against the distal end of stent218. This may define a ledge217athat can further enhance securement of stent218to balloon216. Such a ledge may be formed in addition to or instead of portions228of balloon216extending at least partially into or through openings226of stent218. In some of these and in other instances, a portion of balloon216at proximal balloon cone216bof balloon26may also form a ledge217b.

The processes disclosed herein may also help to control foreshortening. For example, as shown inFIG. 6, stent218, having struts224and openings226, may be fully expanded (e.g., at least foreshortened to a lesser degree that a single crimping process, such as referenced in relation toFIG. 2) such that the length L1B of stent218in an expanded configuration approximates the fully expanded length L2B. Because of the reduction in foreshortening, little or no strut overlap and/or deformation occurs.

In at least some instances, the implantable medical device disclosed herein may include a metal stent, a bioabsorbable metal stent, a drug coated metal stent, a drug coated bioabsorbable metal stent, a polymeric stent, a bioabsorbable polymeric stent, a drug coated polymeric stent, a drug coated bioabsorbable polymeric stent, or the like.

Some examples of suitable metallic materials that may be used for the metal stents contemplated herein may include iron, magnesium, manganese, platinum, chromium, nickel, cobalt, titanium alloys and/or combinations thereof, and the like, or other materials disclosed herein.

Some examples of suitable polymeric materials that may be used the polymeric stents contemplated herein may include poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), poly-lactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), poly(ε-caprolactone) (PCL), desaminotyrosine polycarbonate and the like, or other materials disclosed herein.

Some examples of suitable drugs and/or therapeutic agents that may be used with the medical device contemplated herein may include paclitaxel and/or derivatives thereof, everolimus and/or derivatives thereof (e.g., the “limus” family of drugs), combinations thereof, and the like, or other suitable materials.

The materials that can be used for the various components of system10referenced inFIG. 1(and/or other systems disclosed herein) may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to system10. However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to any of the systems/components disclosed herein, as appropriate.

EXAMPLES

The following disclosure may be understood based on the following Examples, which are not intended to be limiting.

A drug-coated bioabsorbable polymeric stent was disposed about a balloon. The stent had a manufactured diameter of 0.13 inches and was slowly (e.g., a time period of about 30 seconds or longer) compressed to a diameter of 0.07 inches. After the compression step, inflation pressure (30 psi) was applied to the balloon for approximately 10 seconds. The stent was then slowly compressed (e.g., a time period of about 40 seconds or more) to a diameter of 0.04 inches. During this slow compression step, inflation pressure (10 psi) was applied. After the final compression step, an inflation pressure of 10 psi was applied for 60 seconds. Portions of the balloon were observed extending at least partially in and through the openings between the struts of the stent after the cycle was complete.

A metal stent was disposed about a balloon. The stent had a manufactured diameter of 0.08 inches and was slowly (e.g., a time period of about 15 seconds or more) expanded to a diameter of 0.11 inches. After the expansion step, inflation pressure (30 psi) was applied to the balloon for approximately 7 seconds. The stent was then slowly compressed (e.g., a time period of about 50 seconds or more) to a diameter of 0.05 inches. During this slow compression step, inflation pressure (10 psi) was applied. After the final compression step, an inflation pressure of 10 psi was applied for 20 seconds. Portions of the balloon were observed extending through the openings between the struts of the stent after the cycle was complete.