Use of a multi-component coil medical construct

#This invention relates to a method of deploying a stent having interior and exterior portions with different melting temperatures.

#There has been a need to replace metallic stents with those formed from biodegradable materials. However, any such replacement needs to maintain the advantages of metallic stents, that is, the strength and resistance against compressive forces that tend to reclose the lumen opened by the stent.

#It is known to provide biodegradable thermoplastic stents that are deployed by heating the plastic until it softens, and then expanding the softened stent until it achieves a desired diameter, such as that of the body lumen in which it is inserted. For example, U.S. Pat. No. 5,670,161 discusses a tubular stent so processed, as well as (in column 2) prior art tubular stents in Beck et al, U.S. Pat. No. 5,147,385. Particularly as to the latter, it explains that the '385 stent is heated above its melting temperature (the polymer "enters a liquid phase in the ›deployment! temperature that Beck discloses"), and hence "improved strength characteristics using the stent described by Beck is limited". The solution of the '161 patent is to use a copolymer of the Beck homopolymer, the copolymer having melting temperatures that greatly exceed the deployment heating temperature so that there is no melting of the copolymer stent.

#FIG. 1 is a fragmentary elevational view of an undeployed coil stent prior to its use in the invention;

#FIG. 2 is a section view taken along the line II--II of FIG. 1;

#FIG. 3 is a fragmentary elevational view of the same stent, following its deployment by expansion while on a balloon catheter inside a body lumen shown in phantom and in section, respectively; and

#What follows is a description of the preferred embodiments, wherein a single coil stent is provided comprising certain preferred materials, and is deployed in certain body lumens at certain preferred heating temperatures and pressures while on a preferred deploying instrument, i.e., a balloon catheter. In addition, the invention is applicable regardless of the materials utilized, how it is used in a living body, at what temperatures and pressures it is deployed, and what the deploying instrument is. It is also useful if multiple helix coils are used.

#As shown in FIG. 1, the preferred construct for use in this invention is a coil stent 10 formed by winding a strand 12 about an axis 14 so that the coil has an unexpanded outside diameter D.sub.1 and an unexpanded inside diameter D.sub.2. Each loop "L" of the coil may, or may not, contact the next adjacent loop.

#As shown in FIG. 2, strand 12 has a thickness "T" and comprises an interior portion 20 and an exterior portion 22. Preferably, portion 20 is a sheath tightly adhering to the interior portion. Most preferably, both portions are biodegradable, biocompatible materials, and particularly, biodegradable polymers such as polyesters, discussed below.