Thermoelastic and superelastic Ni-Ti-W alloy

#The present invention generally relates to self-expanding endoprosthetic devices including self-expanding intraluminal vascular grafts, generally called stents. More precisely, the present invention relates to stents made of radiopaque nitinol that can be used in essentially any body lumen.

#Stents are typically implanted in a body lumen, such as carotid arteries, coronary arteries, peripheral arteries, veins, or other vessels to maintain the patency of the lumen. These devices are frequently used in the treatment of atherosclerotic stenosis in blood vessels especially after percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA) procedures with the intent to reduce the likelihood of restenosis of a vessel. Stents are also used to support a body lumen, tack-up a flap or dissection in a vessel, or in general where the lumen is weak to add support.

#During PTCA procedures it is common to use a dilation catheter to expand a diseased area to open the patient's lumen so that blood flows freely. Despite the beneficial aspects of PTCA procedures and its widespread and accepted use, it has several drawbacks, including the possible development of restenosis and perhaps acute thrombosis and sub-acute closure. This recurrent stenosis has been estimated to occur in seventeen to fifty percent of patients despite the initial PTCA procedure being successful. Restenosis is a complex and not fully understood biological response to injury of a vessel which results in chronic hyperplasia of the neointima. This neointimal hyperplasia is activated by growth factors which are released in response to injury. Acute thrombosis is also a result of vascular injury and requires systemic antithrombotic drugs and possibly thrombolytics as well. This therapy can increase bleeding complications at the catheter insertion site and may result in a longer hospital stay. Sub-acute closure is a result of thrombosis, elastic recoil, and/or vessel dissection.

#FIG. 1 is a side elevational view, partially in section, depicting a stent mounted on a delivery catheter and expanded within a damaged vessel, pressing a damaged vessel lining against the vessel wall.

#FIG. 2 is a side elevational view, partially in section, depicting an expanded stent within the vessel after withdrawal of the delivery catheter.

#FIG. 3 is an idealized stress-strain hysteresis curve for a superelastic material.

#The present invention relates to stents made of radiopaque nitinol. The stents of the present invention can have virtually any configuration that is compatible with the body lumen in which they are implanted. The stent should preferably be configured so that there is a substantial amount of open area and preferably the open area to metal ratio is at least 80 percent. The stent should also be configured so that dissections or flaps in the body lumen wall are covered and tacked up by the stent.

#Referring to FIGS. 1, 2, and 4, in a preferred embodiment, a stent 10 of the present invention is formed partially or completely of alloys such as nitinol (NiTi) which have superelastic (SE) characteristics. Stent 10 is somewhat similar to the stent disclosed in U.S. Pat. No. 5,569,295, “Expandable Stents and Method for Making Same,” issued to Lam on Oct. 29, 1996, which patent is incorporated herein by reference. Some differences of the present invention stent from that disclosed in the '295 patent is that the present invention stent is preferably constructed of a superelastic material with the addition of a ternary element, and the strut pattern has changed. Of course, the configuration of the stent 10 is just one example of many stent configurations that are contemplated by the present invention.

#Turning to FIG. 4, stent 10 preferably includes a plurality of radially expandable cylindrical elements 24 disposed generally coaxially and interconnected by members 26 disposed between adjacent cylindrical elements 24. The shapes of the struts 12 forming the pattern are designed so they can preferably be nested. This strut pattern is best seen from the flattened plan view of FIG. 4. The serpentine shaped struts 12 are nested such that the extended portions of the struts of one cylindrical element 24 intrude into a complementary space within the circumference of an adjacent cylindrical element. In this manner, the plurality of cylindrical elements 24 can be more tightly packed lengthwise.