Flexible stent having a pattern formed from a sheet of material

Abstract

A flexible stent having a waveform pattern formed from a sheet of biocompatible material and into a tubular shape for maintaining the patency of a lumen such as in a coronary vessel. The waveform pattern of the stent is formed from a flat sheet of malleable, biocompatible material by, for example, photochemically etching the sheetbiocompatible material and leaving a framework or plurality of closed cells. The waveform pattern is formed into a tubular shape around a deflated, delivery catheter balloon with segments of the closed cells being interposed only overlapping a reinforcing member extending longitudinally along the stent. The stent material is treated to reduce the coefficient of friction of the material and to aid in the radial expansion of the stent with the balloon. Radiopaque markers are positioned at the ends of the stent to aid the physician in positioning the stent at an occlusion site.

Description

[0001]This is a reissue of application Ser. No. 08 / 748,669, now U.S. Pat. No. 6,409,752 B1, which is a continuation of Ser. No. 08 / 378,073 filed on Jan. 25, 1995 now U.S. Pat. No. 5,632,771 which is a file wrapper continuation of Ser. No. 08 / 097,392 filed on Jul. 23, 1993, now abandoned.TECHNICAL FIELD[0002]This invention relates generally to balloon expandable stents and, in particular, to a flexible stent having a waveform pattern formed from a sheet of biocompatible material and into a cylindrical surface or tubular shape. References herein to forming the stent from a “sheet” or “sheets” describe preferred embodiments of the invention, and are not to be construed to limit the claims. BACKGROUND OF THE INVENTION[0003]Vascular stents are deployed at a narrowed site in a blood vessel of a patient for widening the vessel lumen and circumferentially supporting the vessel wall. Vascular stents desirably present a small cross-sectional dimension or profile for introducing the stent in...

AI Technical Summary

Benefits of technology

[0008]The foregoing problems are solved and a technical advance is achieved in an illustrative embodiment of a flexible stent comprising a waveform pattern that is formed from a sheet of malleable, biocompatible material having a specified uniform thickness. The pattern is formed into a tubular shape and into an overlapping state around a delivery catheter balloon for introduction through tortuous vessels to, for example, an occlusion site in a coronary vessel. To provide longitudinal flexibility while preventing longitudinal contraction or expansion of the stent during radial expansion of the stent, the pattern advantageously includes a reinforcing member extending longitudinally therealong. A plurality of cells extends laterally from the reinforcing member with selected of the closed cells each having a fixedly sized aperture therein. The closed cells are interposed when the stent is in the tubular shape. To minimize the thickness of the stent and the growth of endothelial cells therearound, each segment of the cells extends laterally from the reinforcing member and does not overlap itself or any adjacent laterally extending segment of the cells. The sheet of biocompatible material with the pattern formed therein is formed into a radially alterable tubular shape around a delivery catheter balloon for introduction to the occlusion site. The balloon radially expands the stent to engage the vessel wall surface and to maintain the vessel lumen in an open condition. The expanded stent in a nonoverlapping state advantageously has a minimal thickness for endothelial tissue to form thereover. As a result, the vessel lumen is advantageously maintained with the largest diameter possible.

[0010]To maintain the moment of inertia or stiffness of the stent, each segment of the cells has a width substantially greater than the specified thickness of the sheet material. Increasing the width of the laterally extending segments also increases the surface area of the stent and support of the vessel wall.

[0012]Radiopaque markers are advantageously positioned at one or more ends of the waveform pattern to aid the physician in positioning the stent at the occlusion site.

Problems solved by technology

Although suitable for its intended use, a problem with these bent wire stents is that stress points are formed at each wire bend or turn.

As a result, the wire stent is structurally compromised at a number of points.

Furthermore, bent wire stents lack longitudinal stability.

A problem with this attempted remedy is that the cross-sectional dimension of the stent, or stent profile, is increased, and the stent intrudes into the effective lumen of the blood vessel.

As a result, the stent and tissue growth impede fluid flow and cause turbulence in the vessel lumen.

Another problem with this attempted remedy is that galvanic action, exposure to a reactive surface, or ion migration, occurs at the wire-to-wire contact points.

A problem with the use of a metal cannula stent is that the stent is rigid and inflexible.

As a result, the stent is difficult, if not impossible, to introduce through the tortuous vessels of the vascular system for deployment at a narrowed site.

Furthermore, the stent is too rigid to conform with a curvature of a blood vessel when deployed at an occlusion site.

Another problem with the use of a metal cannula stent is that the stent longitudinally shrinks during radial expansion.

A problem with the use of a wire mesh stent is that the overlapping wires forming the mesh increase the stent profile, thereby reducing the effective lumen of the blood vessel.

The growth of endothelial tissue layers over the wire mesh further reduces the effective blood vessel lumen.

Another problem with this approach is that ion migration also occurs at the wire-to-wire contact points.

A problem with the use of the flat metal sheet stent is that the overlapping edges of the stent increase the stent profile.

Again, the stent profile and endothelial growth reduce the effective blood vessel lumen.

Another problem with the use of the flat metal sheet stent is that the fingers or projections along one edge of the stent make wire-to-wire contact with the opposite edge of the stent.

Yet another problem with the use of the flat metal sheet stent is that the fingers or projections extend radially outwardly and into the vessel wall.

As a result, the intimal layer of the vessel wall is scraped, punctured, or otherwise injured.

Injury and trauma to the intimal layer of the vessel wall result in hyperplasia and cell proliferation, which in turn effect stenosis or further narrowing of the vessel at the stent site.

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