Stent formed of a Biodegradable material

Description

BACKGROUND OF THE INVENTION

The present invention generally relates to expandable intraluminal vascular grafts, most often referred to as stents, and more particularly pertains to biodegradable stents which completely or partially degrade or are bioabsorbed over a period of time after deployment.

Stents are used to maintain the patency of vessels in the body. They are typically advanced through the vasculature to the deployment site while in a contracted state where they are then expanded to engage the vessel walls and thereby establish a flowpath therethrough. A stent can be moved along a guide wire previously positioned in the vessel and then expanded by the inflation of a balloon about which such stent is disposed. Subsequent deflation of the balloon and removal of it along with the guidewire leaves the stent in place and locked in its expanded state. It has been found that the continued exposure of a stent to blood can lead to undesirable thrombus formation, and the presence of a stent in a blood vessel can over time cause the blood vessel wall to weaken, which creates the potential for an arterial rupture or the formation of aneurisms. A stent can also become so overgrown by tissue after its implantation that its usefulness may be substantially diminished while its continued presence may cause a variety of problems or complications.

In certain situations it is therefore desirable for the stent to be biodegradable or bioabsorbable so as to curtail the adverse risks that would otherwise be associated with the stent's continued presence once its usefulness of the treatment site has ceased or has at least become substantially diminished. To such end, some stents have heretofore been wholly constructed of materials that are biodegradable or bioabsorbable. It is of course necessary to select a material that while biodegradable is nonetheless biocompatible and additionally, has the physical properties necessary to properly serve its function as a stent. Such physical properties include, among others, sufficient strength to support the loads a particular stent is to be subjected to in its function as a splint, the radial flexibility necessary for it to undergo expansion, longitudinal flexibility to allow it to be advanced through a contorted vasculature and conceivably to adapt to a non-linear deployment site.

Such characteristics have heretofore been achieved with the use of certain polymer materials such as polylactic acid, polylactic acid-glycolic acid copolymer, and polycaprolactone. However, all such previously known biodegradable/bioabsorbable stents exhibit bulk erosion and are as a consequence prone to break up into large particles as the matrix breaks down. Additionally, such materials have also been used as stent coatings to gradually release pharmacological agents that are infused throughout the coating. However, the bulk erosion to which such materials are inherently prone to can cause the coating to flake off or otherwise become detached. Should such large particles actually become dislodged before becoming completely degraded, they could be washed downstream and cause emboli.

A biodegradable stent is therefore needed that is initially capable of providing the necessary structural support to a body lumen and then gradually and completely degrades or is absorbed in a manner that precludes a break-up into large particles. Similarly, a biodegradable coating is needed that is not prone to flaking or breaking up into large particles. By preventing the break-up of the stent or of the stent coating into large particles that may subsequently be swept downstream, the potential for embolic complications is thereby avoided.

SUMMARY OF THE INVENTION

The present invention provides a stent or optionally, a stent coating which degrades in a very controlled and uniform manner so as to substantially preclude the possibility of sizeable particles becoming detached and possibly causing embolic problems downstream. This is achieved by employing a material in the construction of the entire stent or in the coating of the stent that erodes in a very controlled manner. Such material is selected for its strength characteristics as well as its tendency to erode from the surface inwardly rather than being subject to bulk erosion. By incorporating pharmacological agents within the material, the stent or stent coating not only eventually vanishes from within the body lumen in which it was implanted but additionally dispenses the incorporated drug in a gradual manner.

Materials that exhibit the desired surface eroding characteristics without being subject to bulk erosion include polymers wherein the degradation rate of the matrix is faster than the rate of water penetration into the interior of the polymeric mass. Such polymers are hydrophobic but have water-labile linkages interconnecting the monomers. The hydrophobic property precludes water from penetrating into the interior of the polymer while water labile linkages nonetheless subject the surface to gradual erosion. As a result, the stent gradually degrades from the surface inwardly, substantially without the risk of large particles becoming dislodged.

While hydrophobic polymers with water-labile linkages are known, their limited strength and processing capabilities have restricted their usage to passive devices that neither perform a structural function nor are subject to stress or distortion. Drugs infused throughout such material implanted in the body in the form of a tablet or other shape are gradually released as the polymer degrades. As such, these surface degrading polymers have functioned as an effective drug delivery vehicle. The use of such polymers in stent applications has however been precluded as they are unable to support a lumen wall or remain attached to a stent as it undergoes deformation during its expansion.

The materials employed in either wholly forming a stent or in coating a stent in accordance with the present invention include hydrophobic polymers having water-liable linkages connecting the monomers that are fortified with the incorporation of ester or imide bonds. Examples of such polymers include polyanhydrides and polyorthoesters. Additionally, by employing such polymers in stent applications, a single device can be called upon to provide the necessary support to a body lumen and simultaneously dispense a pharmacological agent in a controlled manner.

These and other features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiments which illustrate by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The stent of the present invention is employed to support or otherwise treat a targeted site within the vasculature. Such stent is introduced into the vasculature, advanced therethrough to the deployment site and expanded using conventional techniques and delivery systems. Once in position and subject to the continuous flow of blood therethrough, it gradually degrades, substantially without the risk inherent in previously known biodegradable stents or stents with biodegradable coatings of breaking up into or releasing sizeable particles that may be swept downstream and cause emboli.

The material employed in the manufacture of the stent of the present invention is a polymer that is simultaneously hydrophobic and has water-labile linkages interconnecting its monomers that are further fortified by ester or imide bonds. The hydrophobic nature of the polymer precludes the incursion of water into its interior while the water-labile bonds that are exposed on its surface nonetheless cause the polymer to degrade. Degradation thereby exclusively progresses from the material's surface inwardly to yield a much more uniform degradation rate and to preclude bulk erosion. The incorporation of the imide or ester bonds serves to impart sufficient strength to the material to enable it to provide the support that is required of a stent. Alternatively, if the material is used as stent coating, the incorporation of the imide or ester bonds impart sufficient strength to the material to prevent it from flaking off or otherwise becoming detached as the underlying stent undergoes the distortion attendant its being expanded by for example the inflation of a balloon.

Many of the stent's ultimate performance characteristics are controllable by the appropriate selection of the various dimensional parameters of the stent. Increasing the dimensions of various structural elements of the stent will generally serve to increase strength and decrease flexibility. Such effect would result from both an increase in the width or in the wall thickness of the stent's structural elements. The time period in which the stent would become totally degraded or absorbed is a function of the wall thickness of the various elements while the degradation rate is a function of the total area exposed to contact with the blood. By for example selecting a stent configuration which employs a large number of relatively narrow spine and strut elements to achieve a particular level of strength, the time in which the stent degrades when subjected to the blood flow can be substantially accelerated. Conversely, a stent configuration in which a relatively few, wide structural elements are employed causes the degradation rate to be somewhat retarded.

The stent's ultimate performance characteristics are of course also controllable by the appropriate selection of chemical variables. For example, the number of imide or ester bonds that are incorporated in the polymer material not only affects the ultimate strength and flexibility characteristics of the stent, but also has an effect on the rate at which the material degrades when subjected to blood flow. An increased bond content enhances strength, decreases flexibility and increases degradation time. The specific requirements of a particular application will ultimately determine the optimal combination of the stent configuration, wall thickness and ester or imide bond content.

Polymers that satisfy the above-described requirements include polyanhydrides and polyorthoesters. Representative examples of polyanhydride polymers suitable for use in the construction of a stent or formulation of a stent coating in accordance with the present invention include anhydride-co-imide ter polymers containing trimellitylimido-L-tyrosine, sebacic acid (SA) and 1,3 bis(carboxyphenoxy)propane. Other examples of suitable polyanhydrides include poly(fatty acid-sebacic acid) synthesized from erucic acid and sebacic anhydride p(EAD:SA) and poly(L-lactic acid-co-L-aspartic acid). Representative examples of polyorthoester polymers suitable for use in the construction of a stent or formulation of a stent coating in accordance with the present invention include poly(4-hydroxy-L-proline ester), poly(1, 10 decanediol-1, 10 decanediol dilactide) and poly(1, 2, 6 hexanetriol-trimethylorthoacetate). An ester or imide content of 20%-40% has been found to be effective to provide sufficient strength for a stent application.

The process for forming a polymer stent is well known in the art. A stent of the present invention is formed by first causing the appropriate reagents to react to form the desired polyanhydride or polyorthoester composition. During copolymer synthesis, the imide content of such composition is increased by incorporating higher imide containing monomers like trimellitylimido-L-tyrosine. Increasing imide content results in higher strength material. Flexibility of polyanhydrides like p(EAD:SA) can be increased by increasing the percentage of erucic acid dimer (EAD) during polymer synthesis. The ester content of such composition is increased by incorporating higher ester containing monomers such as L-proline ester or trimethyl orthoacetate.

Selected pharmacological agents can be added to the reagents so as to incorporate such materials throughout the polymer to thereby provide for the gradual dispensation of the drug over the service life of the stent. The blending may be accomplished either in solution or in a melt state. Drugs such as for example heparin or other proteins can readily be added to the reactants before or during the polymerization process. Alternatively, some drugs may be infused throughout the polymer after polymerization is completed. If desired, the drug may be applied to the surface of the cured polymer to cause the entire dosage to be released shortly after implantation.

The stent may be formed by any of a number of well known methods including the extrusion of the polymer into the shape of a tube. Preselected patterns of voids are then formed into the tube in order to define a plurality of spines and struts that impart a degree of flexibility and expandability to the tube.

Alternatively, the drug loaded polymer may applied to the selected surfaces of a stent formed of for example stainless steel or Nitinol. In order to coat all of the surfaces of the stent, the stent is immersed in the molten polymer. Alternatively, the polymer may be extruded in the form of a tube which is then codrawn with a tube of stainless steel or Nitinol. By codrawing two tubes of the polymer with the metal tube, one positioned about the exterior of the metal tube and another positioned within such metal tube, a tube having multi-layered walls is formed. Subsequent perforation of the tube walls to define a preselected pattern of spines and struts imparts the desired flexibility and expandability to the tube to create a stent.

While a particular form of the invention has been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.

Claims

1. A stent constructed of a biodegradable polymer, the polymer comprising at least one member of the group consisting of poly(L-lactic acid-co-L-aspartic acid), poly(4-hydroxy-L-proline ester), poly(1,10 decanediol-1,10 decanedioldilactide)and poly(1,2,6 hexanetriol-trimethylorthoacetate); wherein the stent degrades from its surface inwardly when subjected to blood flow, such that bulk erosion is effectively precluded.
2. The stent of claim 1, wherein the polymer is loaded with a pharmacological agent.
3. The stent of claim 2, wherein the pharmacological agent comprises heparin.
4. The stent of claim 1, wherein the biodegradable polymer comprises poly(L-lactic acid-co-L-aspartic acid).
5. The stent of claim 1, wherein the biodegradable polymer comprises poly(4-hydroxy-L-proline ester).
6. The stent of claim 1, wherein the biodegradable polymer comprises poly(1,10 decanediol-1,10 decanediol dilactide).
7. The stent of claim 1, wherein the biodegradable polymer comprises poly(1,2,6 hexanetriol-trimethylorthoacetate).
8. The stent of claim 1, wherein the biodegradable polymer is poly(L-lactic acid-co-L-aspartic acid).
9. The stent of claim 1, wherein the biodegradable polymer is poly(4-hydroxy-L-proline ester).
10. The stent of claim 1, wherein the biodegradable polymer is poly(1,10 decanediol-1,10 decanediol dilactide).
11. The stent of claim 1, wherein the biodegradable polymer is poly(1,2,6 hexanetriol-trimethylorthoacetate).

RELATED APPLICATIONS

The present application is a divisional application of U.S. application Ser. No. 11/968,543, which was filed on Jan. 2, 2008, and issued as U.S. Pat. No. 8,109,994, which is a continuation of U.S. application Ser. No. 10/340,052, which was filed on Jan. 10, 2003, and issued as U.S. Pat. No. 7,390,333, which is a divisional of U.S. application Ser. No. 09/548,533, which was filed on Apr. 13, 2000, and issued as U.S. Pat. No. 6,527,801. The teachings in each of the aforementioned patent applications and patent are incorporated herein by reference in their entirety.

US Referenced Citations (183)

Number	Name	Date	Kind
3407164	Schmidt	Oct 1968	A
3839743	Schwarcz	Oct 1974	A
3900632	Robinson	Aug 1975	A
4110497	Hoel	Aug 1978	A
4321711	Mano	Mar 1982	A
4346028	Griffith	Aug 1982	A
4633873	Dumican et al.	Jan 1987	A
4656083	Hoffman et al.	Apr 1987	A
4718907	Karwoski et al.	Jan 1988	A
4722335	Vilasi	Feb 1988	A
4723549	Wholey et al.	Feb 1988	A
4732152	Wallstén et al.	Mar 1988	A
4733665	Palmaz	Mar 1988	A
4739762	Palmaz	Apr 1988	A
4740207	Kreamer	Apr 1988	A
4743252	Martin, Jr. et al.	May 1988	A
4768507	Fischell et al.	Sep 1988	A
4776337	Palmaz	Oct 1988	A
4816339	Tu et al.	Mar 1989	A
4850999	Planck	Jul 1989	A
4877030	Beck et al.	Oct 1989	A
4878906	Lindemann et al.	Nov 1989	A
4879135	Greco et al.	Nov 1989	A
4902289	Yannas	Feb 1990	A
4977901	Ofstead	Dec 1990	A
4994298	Yasuda	Feb 1991	A
5019090	Pinchuk	May 1991	A
5028597	Kodama et al.	Jul 1991	A
5059211	Stack et al.	Oct 1991	A
5062829	Pryor et al.	Nov 1991	A
5084065	Weldon et al.	Jan 1992	A
5085629	Goldberg et al.	Feb 1992	A
5100429	Sinofsky et al.	Mar 1992	A
5108755	Daniels et al.	Apr 1992	A
5112457	Marchant	May 1992	A
5123917	Lee	Jun 1992	A
5156623	Hakamatsuka et al.	Oct 1992	A
5163951	Pinchuk et al.	Nov 1992	A
5163952	Froix	Nov 1992	A
5163958	Pinchuk	Nov 1992	A
5167614	Tessmann et al.	Dec 1992	A
5192311	King et al.	Mar 1993	A
5197977	Hoffman, Jr. et al.	Mar 1993	A
5234456	Silvestrini	Aug 1993	A
5234457	Andersen	Aug 1993	A
5236447	Kubo et al.	Aug 1993	A
5240963	Domb et al.	Aug 1993	A
5279594	Jackson	Jan 1994	A
5282860	Matsuno et al.	Feb 1994	A
5289831	Bosley	Mar 1994	A
5290271	Jernberg	Mar 1994	A
5306286	Stack et al.	Apr 1994	A
5306294	Winston et al.	Apr 1994	A
5328471	Slepian	Jul 1994	A
5330500	Song	Jul 1994	A
5342348	Kaplan	Aug 1994	A
5342395	Jarrett et al.	Aug 1994	A
5342621	Eury	Aug 1994	A
5356433	Rowland et al.	Oct 1994	A
5383925	Schmitt	Jan 1995	A
5385580	Schmitt	Jan 1995	A
5389106	Tower	Feb 1995	A
5441515	Khosravi et al.	Aug 1995	A
5443458	Eury	Aug 1995	A
5455040	Marchant	Oct 1995	A
5464650	Berg et al.	Nov 1995	A
5486591	Domb et al.	Jan 1996	A
5500013	Buscemi et al.	Mar 1996	A
5502158	Sinclair et al.	Mar 1996	A
5514379	Weissleder et al.	May 1996	A
5527337	Stack et al.	Jun 1996	A
5554120	Chen et al.	Sep 1996	A
5578073	Haimovich et al.	Nov 1996	A
5591607	Gryaznov et al.	Jan 1997	A
5593403	Buscemi	Jan 1997	A
5599301	Jacobs et al.	Feb 1997	A
5599922	Gryaznov et al.	Feb 1997	A
5605696	Eury et al.	Feb 1997	A
5629077	Turnlund et al.	May 1997	A
5631135	Gryaznov et al.	May 1997	A
5637113	Tartaglia et al.	Jun 1997	A
5667767	Greff et al.	Sep 1997	A
5670558	Onishi et al.	Sep 1997	A
5693085	Buirge et al.	Dec 1997	A
5700286	Tartaglia et al.	Dec 1997	A
5707385	Williams	Jan 1998	A
5716981	Hunter et al.	Feb 1998	A
5725567	Wolf et al.	Mar 1998	A
5726297	Gryaznov et al.	Mar 1998	A
5728751	Patnaik	Mar 1998	A
5733925	Kunz et al.	Mar 1998	A
5741881	Patnaik	Apr 1998	A
5756457	Wang et al.	May 1998	A
5756476	Epstein et al.	May 1998	A
5766710	Turnlund et al.	Jun 1998	A
5800516	Fine et al.	Sep 1998	A
5811447	Kunz et al.	Sep 1998	A
4739762	Palmaz	Oct 1998	B1
5824049	Ragheb et al.	Oct 1998	A
5830178	Jones et al.	Nov 1998	A
5830461	Billiar	Nov 1998	A
5830879	Isner	Nov 1998	A
5833651	Donovan et al.	Nov 1998	A
5834582	Sinclair et al.	Nov 1998	A
5837313	Ding et al.	Nov 1998	A
5837835	Gryaznov et al.	Nov 1998	A
5851508	Greff et al.	Dec 1998	A
5854207	Lee et al.	Dec 1998	A
5855618	Patnaik et al.	Jan 1999	A
5858746	Hubbell et al.	Jan 1999	A
5865814	Tuch	Feb 1999	A
5873904	Ragheb et al.	Feb 1999	A
5874165	Drumheller	Feb 1999	A
5876743	Ibsen et al.	Mar 1999	A
5877263	Patnaik et al.	Mar 1999	A
5879713	Roth et al.	Mar 1999	A
5891192	Murayama et al.	Apr 1999	A
5897955	Drumheller	Apr 1999	A
5914182	Drumheller	Jun 1999	A
5916870	Lee et al.	Jun 1999	A
5942209	Leavitt et al.	Aug 1999	A
5948428	Lee et al.	Sep 1999	A
5957975	Lafont et al.	Sep 1999	A
5965720	Gryaznov et al.	Oct 1999	A
5971954	Conway et al.	Oct 1999	A
5980564	Stinson	Nov 1999	A
5980928	Terry	Nov 1999	A
5980972	Ding	Nov 1999	A
5981568	Kunz et al.	Nov 1999	A
5997468	Wolff et al.	Dec 1999	A
6015541	Greff et al.	Jan 2000	A
6042875	Ding et al.	Mar 2000	A
6048964	Lee et al.	Apr 2000	A
6051648	Rhee et al.	Apr 2000	A
6056993	Leidner et al.	May 2000	A
6060451	DiMaio et al.	May 2000	A
6071266	Kelley	Jun 2000	A
6074659	Kunz et al.	Jun 2000	A
6080177	Igaki et al.	Jun 2000	A
6080488	Hostettler et al.	Jun 2000	A
6093463	Thakrar	Jul 2000	A
6096070	Ragheb et al.	Aug 2000	A
6096525	Patnaik	Aug 2000	A
6099562	Ding et al.	Aug 2000	A
6103230	Billiar et al.	Aug 2000	A
6107416	Patnaik et al.	Aug 2000	A
6110188	Narciso, Jr.	Aug 2000	A
6113629	Ken	Sep 2000	A
6117979	Hendriks et al.	Sep 2000	A
6120536	Ding et al.	Sep 2000	A
6120904	Hostettler et al.	Sep 2000	A
6121027	Clapper et al.	Sep 2000	A
6127173	Eckstein et al.	Oct 2000	A
6129761	Hubbell	Oct 2000	A
6153252	Hossainy et al.	Nov 2000	A
4776337	Palmaz	Dec 2000	B1
6159951	Karpeisky et al.	Dec 2000	A
6165212	Dereume et al.	Dec 2000	A
6166130	Rhee et al.	Dec 2000	A
6169170	Gryaznov et al.	Jan 2001	B1
6171609	Kunz	Jan 2001	B1
6174330	Stinson	Jan 2001	B1
6177523	Reich et al.	Jan 2001	B1
6224626	Steinke	May 2001	B1
6228845	Donovan et al.	May 2001	B1
6245103	Stinson	Jun 2001	B1
6251135	Stinson et al.	Jun 2001	B1
6251142	Bernacca et al.	Jun 2001	B1
4733665	Palmaz	Jan 2002	C2
6350277	Kocur	Feb 2002	B1
6379379	Wang	Apr 2002	B1
6395029	Levy	May 2002	B1
6527801	Dutta	Mar 2003	B1
6685928	Uhrich	Feb 2004	B2
7122615	Uhrich	Oct 2006	B1
7390333	Dutta	Jun 2008	B2
7470283	Dutta	Dec 2008	B2
7875283	Hossainy et al.	Jan 2011	B2
8109994	Dutta	Feb 2012	B2
20010047185	Satz	Nov 2001	A1
20040138260	Natchus et al.	Jul 2004	A1
20060136051	Furst et al.	Jun 2006	A1
20120116501	Dutta	May 2012	A1

Foreign Referenced Citations (34)

Number	Date	Country
44 07 079	Sep 1994	DE
0 108 171	May 1984	EP
0 144 534	Jun 1985	EP
0 364 787	Apr 1990	EP
0 397 500	Nov 1990	EP
0 464 755	Jan 1992	EP
0 493 788	Jul 1992	EP
0 554 082	Aug 1993	EP
0 578 998	Jan 1994	EP
0 604 022	Jun 1994	EP
0 621 017	Oct 1994	EP
0 623 354	Nov 1994	EP
0 665 023	Aug 1995	EP
0 970 711	Jan 2000	EP
2 247 696	Mar 1992	GB
2001-515934	Sep 2001	JP
WO 8903232	Apr 1989	WO
WO 9001969	Mar 1990	WO
WO 9004982	May 1990	WO
WO 9006094	Jun 1990	WO
WO 9117744	Nov 1991	WO
WO 9117789	Nov 1991	WO
WO 9210218	Jun 1992	WO
WO 9306792	Apr 1993	WO
WO 9529647	Nov 1995	WO
WO9912990	Mar 1999	WO
WO 9934750	Jul 1999	WO
WO 0012147	Mar 2000	WO
WO 0044309	Aug 2000	WO
WO 0064506	Nov 2000	WO
WO 0074744	Dec 2000	WO
WO 0101890	Jan 2001	WO
WO 0167990	Sep 2001	WO
WO 03080147	Oct 2003	WO

Non-Patent Literature Citations (16)

Entry
A Notification of Refusal issued by JPO on Oct. 13, 2009, in connection with Appl. No. 2003-577971, 3 pgs.
Translation of a Notification of Refusal issued by JPO on Oct. 13, 2009, in connection with Appl. No. 2003-577971, 2 pgs.
Bull, Parylene Coating for Medical Applications, Medical Product Manufacturing News (Mar. 1993).
Casper et al., Fiber-Reinforced Absorbable Composite for Orthopedic Surgery, Polymeric Materials Science and Engineering, 53:497-501 (1985).
Devanathan et al., Polymeric Conformal Coatings for Implantable Electronic Devices, IEEE Transactions on Biomedical Engineering, vol. BME-27(11):671-675 (1980).
Hahn et al., Biocompatibility of Glow-Discharge-Polymerized Films and Vacuum-Deposited Parylene, J Applied Polymer Sci, 38:55-64 (1984).
Hahn et al., Glow Discharge Polymers as Coatings for Implanted Devices, ISA, pp. 109-111 (1981).
Kelley et al., Totally Resorbable High-Strength Composite Material, Advances in Biomedical Polymers, 35:75-85 (1987).
Kubies et al., Microdomain Structure In Polylactide-block-poly(ethylene oxide) Copolymer Films, Biomaterials 21:529-536 (2000).
Muller et al., Advances in Coronary Angioplasty: Endovascular Stents, Coron Arter Dis, 1(4):438-448 (Jul./Aug. 1990).
Nichols et al., Electrical Insulation of Implantable Devices by Composite Polymer Coatings, ISA Transactions, 26(4):15-18 (1987).
Schatz, A View of Vascular Stents, Circulation, 79(2):445-457 (Feb. 1989).
Schmidt et al., Long-Term Implants of Parylene-C Coated Microelectrodes, Med & Biol Eng & Comp, 26(1):96-101 (Jan. 1988).
Hanes et al., “Synthesis and Characterization of Degradable Anhydride-co-imide Terpolymers Containing Tremellitylimido-L-tyrosine: Novel Polymers for Drug Delivery,” Macromolecules 1996, 29, pp. 5279-5287.
Langer, “New Methods of Drug Delivery,” Science, vol. 249, Sep. 28, 1990, Articles pp. 1527-1533.
Middleton et al., “Synthetic Biodegradable Polymer as Medical Devices”, published in MDDI Magazine (1998) downloaded from www.mddionline.com/print/3282 on Mar. 16, 2011, 9 pgs.

Related Publications (1)

	Number	Date	Country
	20120116501 A1	May 2012	US

Divisions (2)

	Number	Date	Country
Parent	11968543	Jan 2008	US
Child	13350669		US
Parent	09548533	Apr 2000	US
Child	10340052		US

Continuations (1)

	Number	Date	Country
Parent	10340052	Jan 2003	US
Child	11968543		US

Stent formed of a Biodegradable material

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