Expandable biodegradable polymeric stents for combined mechanical support and pharmacological or radiation therapy

Abstract

An expandable biodegradable polymeric stent is fabricated with biodegradable polymer fibers (Poly-L-lactic acid, PLLA) in a coil shape that is constructed with both central and external or internal peripheral lobes. It is delivered and expanded using a conventional angioplasty balloon system. The disclosed stent can serve as a temporary scaffold for coronary vessels after PTCA or for peripheral endovascular stenting, or it can provide mechanical palliation for strictures of ductile organs (trachea, esophagus, bile and pancreatic ducts, ureter etc.). The disclosed stent also serves as a unique device for specific local drug delivery. Therapeutic agents (chemical compounds, protein enzyme and DNA sequences) and cells can be loaded into the stent and gradually released to target tissues. Local radiation therapy can also be delivered by a specially adapted stent.

Description

TECHNICAL FIELD OF THE INVENTION [0001] This invention generallyrelates to stents for implantation into blood vessels or other organs, and more specifically to stents that are absorbable over time and capable of local drug / gene delivery for enhancing therapeutic effects. BACKGROUND OF THE INVENTION [0002] Intraluminal stents are commonly employed for treatment of various vascular conditions such as arteriosclerosis, often as coronary artery implants. A stent can be implanted at the site of a vessel stricture or stenosis using a conventional balloon catheter delivery system as used in angioplasty. Stents also maybe employed in bodypassageways other than blood vessels to treat strictures or prevent luminal occlusion. Such stents ordinarily consist of a cylindrical network of very small metal wires. The stent is inserted in a small-diameter configuration and then expanded to a large-diameter final configuration against the walls of the blood vessel or other body lumen. Such stent struc...

AI Technical Summary

Benefits of technology

[0004] In accordance with a principal object of the present invention, luminal support and localized treatment of lesion sites within body passageways is accomplished by the implantation of an expandable biodegradable polymeric stent that includes therapeutic agents. By virtue of its gradual absorption over time, the inventive stent avoids residual stress, and permits local drug delivery or local radiation treatment.

[0005] In its preferred implantation, the stent of the present invention provides adequate mechanical support during and following the interventional procedure, and, by being absorbed over controllable periods, avoids chronic mechanical disturbance of the vessel wall. The residual stress against the vessel wall is eliminated after the stent is degraded. During the degradation process, loaded therapeutic agents are released in a controlled fashion, and effective concentrations at target lesions can be maintained. Local radiation treatment can likewise be maintained.

[0006] The stent of the present invention preferably has the following features: (1) it has an all-polymer construction with similar mechanical function to conventional metallic stents; (2) it is constructed with fiber cords having both central and peripheral lobes and is stabilized by longitudinal rods, thus presenting a low profile during delivery and a large effective diameter following expansion; (3) it is expandable with an expansion ratio that can be customized to meet various needs; (4) it can be deployed at body temperature with low inflation pressure (3 atm); (5) it is a temporary implant; (6) it may be a local drug or gene delivery device; (7 ) it may be a local radiation therapy device; and (8) it can include fibers with various functions (mechanical support, acute drug burst, long-term drug release, etc.), enabling a variety of treatment options including multiple functions with a single stent and using a single stent-implant procedure.

[0007] The present invention has a number of advantages over conventional stents. Firstly, in contrast to metal stents, the polymeric stent of the present invention is a temporary implant. The temporary residence permits the residual stress against the vessel wall to be resolved, a factor commonly leading to in-stent restenosis in the case of metallic stents. Secondly, the inventive stent is also capable of carrying therapeutic agents either incorporated in the polymer bulk or coated on the polymer surface. Thirdly, it is possible to control the operation of the inventive stent by selection of the polymer composition, the polymer molecular weight, fiber cord diameter and processing conditions, thus controlling the degradation rate, drug release rate and period of mechanical support. Fourthly, compared with tubular-shaped polymeric stents, the inventive stent has superior expandability and flexibility. Additionally, the inventive stent also has advantages over the “zigzag” polymeric stent recently disclosed in the prior art (Circulation, vol. 102, pp. 399-404, 2000), since it is deployed at body temperature with low inflation pressure.

[0008] In addition to being biodegradable, the stent of the present invention synergistically combines excellent mechanical support and local drug delivery, for both short-term and long-term applications. Current metallic stents are incapable of delivering drugs without polymer coatings. Moreover, metallic stents are known to be a stimulus for chronic vessel injury. Other current approaches, such as the combination of a metallic stent and bolus drug delivery by a porous angioplasty balloon, provide both mechanical support and short-term drug delivery. However, other than initial control of drug concentration at the lesion site, the porous angioplasty balloon approach is limited in its application and is incapable of performing certain desirable functions, such as prolonged drug delivery and transient radiation therapy. The biodegradable polymeric stent of the present invention provides sufficient mechanical strength as well as controllable short-term and long-term drug delivery while eliminating the stimulus for chronic vessel wall injury.

Problems solved by technology

However, metallic stents still present a potential vessel injury problem.

Furthermore, the delivery of medicine to a lesion site either by local or systemic means is unsatisfactory with current stent and catheter technology.

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