Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Utility Patent
1998-10-16
2001-01-02
Millin, V. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
C623S001280
Utility Patent
active
06168619
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to radially expandable stents for insertion into a body lumen. More particularly, the invention relates to an endoluminal stent having a polymer tubular member secured to the support stent with end sleeves.
BACKGROUND OF THE INVENTION
Endoluminal stents, particularly endovascular stents, are of considerable interest in the medical profession, especially to vascular surgeons. Such stents are presently used as a post-angioplasty adjunct to maintain the angioplasty-treated blood vessel in an open condition. Examples of endoluminal stents in the art include pressure-expandable stents which radially expand using a balloon angioplasty catheter, such as the Palmaz stent in U.S. Pat. No. 4,733,665; or self-expanding stents which radially expand due to the inherent spring tension of a wire material, such as the stent described by Gianturco in U.S. Pat. No. 4,580,568. Self-expanding stents which expand upon application of a stimulus, such as Nitinol stents or shape-memory polymer stents that expand when exposed to an increase in temperature, have also been described (Froix, U.S. Pat. No. 5,163,952).
In some applications it is desirable to cover the stent with a biocompatible material, since the stents themselves are often thrombogenic and the open nature of the stents can result in growth of tissue through the stent and into the lumen causing occlusion. Polytetrafluoroethylene (PTFE) has been proposed as a material suitable for such a covering since PTFE is inert, eliciting less of a foreign body response and less of an immunogenic response, and is largely non-thrombogenic. A variety of PTFE-covered stents are reported in the literature and include a basic stent or graft with an external or internal liner which expands in association with the stent (Myers, U.S. Pat. No. 5,700,285; Thompson, U.S. Pat. No. 5,788,626; Colone, WO 96/00103). In these stent/PTFE covering assemblies, the PTFE covering is typically a tubular member that is slipped over the stent and is held in place with an adhesive. This assembly suffers from a number of disadvantages, including the unequal expansion of the stent and the PTFE covering in the axial direction, leaving the ends of the stent exposed. Another disadvantage is uneven expansion of the assembly in the radial direction along the length of the assembly. During expansion with a balloon angioplasty catheter, the balloon expansion forces the stent and the PTFE covering into a torroidal shape with the proximal and distal ends flaring away from the central longitudinal axis of the stent. This results in the stent being non-uniformly radially expanded along its longitudinal axis.
One approach proposed for overcoming this uneven expansion is to include a reinforcing member along the length of the stent-PTFE covering assembly (Banas, U.S. Pat. No. 5,628,786). The reinforcing member evens the resistance to expansion along the length of the assembly. Disadvantages to such a reinforcing member include an increase in profile of the assembly, an increase in the stiffness and loss of flexibility of the assembly, all of which make it difficult to position the assembly in small or difficult to reach lumens
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a stent having a polymer covering, where the assembly retains flexibility and a low profile.
It is a further objective of the invention to provide a stent having a polymer covering with an improved uniformity of expansion.
In one aspect, the invention includes a radially-expandable stent for insertion into a lumen. The stent is composed of a radially-expandable support stent having a selected axial length and having first and second ends. A polymer tubular member is co-axially disposed over the support stent and extends the length of the stent. The polymer member is radially expandable with the support stent to an expanded diameter. The stent is further composed of tubular end sleeves disposed around the first and second ends of the polymer-surrounded support stent, the end sleeves being radially expandable with the support stent to an expanded diameter and covering 50% or less of the total stent length.
In one embodiment, the support stent is composed of a biocompatible metal, such as stainless steel, titanium, tungsten, tantalum, gold, platinum, cobalt, iridium and alloys of these materials. In another embodiment, the metal is a shape-memory alloy.
In another embodiment, the support stent is composed of a polymer, such as a memory polymer. For example, the memory polymer is, in one embodiment, formed of a copolymer.
The polymer tubular member is secured in an unexpanded diameter to the support stent by a mechanical means selected from ultrasonic welding, resistive heating and laser irradiation. Alternatively, the polymer tubular member is secured to the support stent in an unexpanded diameter by a biocompatible adhesive, such as a fluorinated thermoplastic polymer adhesive. Examples of fluorinated thermoplastic include fluorinated ethylene/propylene copolymers, perfluoroalkoxy fluorocarbons, ethylene/tetrafluoroethylene copolymers, fluoroacrylates, and fluorinated polyvinyl ethers.
The polymer tubular member, in one embodiment, is composed of a polymer selected from the group consisting of polyamides, polyimides, silicones and fluorinated polyolefins. A preferred fluorinated polyolefin is polytetrafluoroethylene, which can be either biaxially oriented polytetrafluoroethylene or uniaxially oriented polytetrafluoroethylene. In one embodiment, the polytetrafluoroethylene tubular member has a porosity of at least about 5% and the member further includes a therapeutic agent incorporated into the pores.
In yet another embodiment of the invention, the polymer member of the stent further includes a therapeutic agent. The therapeutic agent is, in one embodiment, an agent effective to inhibit smooth muscle cell proliferation. In other embodiment, the therapeutic agent is an agent effective to inhibit proliferation or migration of fibroblast cells. In another embodiment, the polymer member includes a combination of therapeutic agents, such as a first agent paclitaxel and a second therapeutic agent of camptothecin, colchicine or dexamethasone.
The end sleeves in the stent are composed of a biocompatible metal, such as stainless steel, titanium, tungsten, tantalum, gold, platinum, cobalt, iridium and alloys of these materials. Alternatively, the end sleeves are composed of a shape-memory alloy. Where the end sleeves are composed of metal, the metal is, in one embodiment, coated with polytetrafluoroethylene.
The end sleeves in yet another embodiment are composed of a polymer, such as an elastic polymer, a thermoplastic polymer or a memory polymer. The polymer can be a homopolymer, a copolymer or a polymer blend.
The end sleeves are secured on the ends of the polymer-covered support stent by a mechanical means or by a biocompatible adhesive.
In another aspect, the invention includes an improvement in a stent of a selected axial length and having a polymer tubular member coaxially disposed about the stent. The improvement comprises tubular end sleeves disposed around each end of the stent, the end sleeves being radially expandable with the stent to an expanded diameter, and where the end sleeves cover 50% or less of the total stent length.
In another aspect, the invention includes a method of preparing a stent for insertion into a lumen, comprising providing a radially expandable support stent of a selected axial length and having first and second ends and placing a polymer tubular member co-axially over the support stent. The polymer tubular member, in one embodiment, extends substantially the length of the support stent. The polymer member is radially expandable with the support stent to an expanded diameter. The tubular end sleeves are secured around the first and second ends of the polymer-surrounded support stent. The end sleeves are radially expandable with the support stent to an expanded diameter and the end sleeves cover 50% or l
Alvarado Angelica
Cherkas Paul
Correa Beren
Dinh Linh
Eury Robert
Iota Pi Law Group
Millin V.
Mohr Judy M.
Phan Hieu
Quanam Medical Corporation
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