Development of microporous covered stents: geometrical design of the luminal surface

To reduce in-stent restenosis rates we have developed newly designed covered stents, in which a stent strut is buried into a microporous elastomeric cover film to provide a physical barrier against tissue ingrowth and a pharmacological reservoir for drug-eluting. The covered stents were prepared by dip-coating balloon expandable stents mounted on a stainless steel rod in a segmented polyurethane (SPU) solution, and were subsequently subjected to laser-processed microporing (pore diameter, 100 microm; interpore distance, 200 microm). The covered stents, which possessed flat luminal surfaces and micropores that were homogeneously arranged on the whole surface of the covering film, were deployed into the bilateral common carotid arteries of normal New Zealand white rabbits. Angiography after one month of implantation showed all stents were patent with little thrombus formation. The mean thickness of the formed neointimal layers was 292 +/- 177 microm (n=8), which was close to the size in non-covered bare stent (231 +/- 58 microm, n=7), but markedly decreased (about 2/3) from that in the previously developed wrapping-type covered stents (415 +/- 173 microm, P<0.01, n=8).