Bioabsorbable coronary stents.

Placing a coronary stent during angioplasty minimizes reduces of acute vessel occlusion [1] and restenosis [2]. Although permanent metallic stents are effective in preventing recoil and late restenosis after coronary angioplasty, they continue to have limitations such as stent thrombosis and mismatch of the stent to the vessel size. In-stent restenosis is the major shortcoming of conventional (permanent-implant) stent therapy. To mitigate the adverse effects of metallic stents, drug-eluting stents have been developed. These also act as time-released delivery mechanisms for antiproliferative agents, thus further reducing restenosis. There is no clear advantage, however, of having stents remaining in the coronaries after they are endothelized. On the contrary, there are documented disadvantages since incomplete healing can induce a chronic inflammatory state increasing the risk for thrombosis [3]. Permanently implanted stents can also impair endothelial function [4], prevent late favourable remodelling [5], and hamper future imaging and reintervention. Thus, the concept of bioabsorbable stents has emerged as a viable alternative to permanent stents. The idea behind the bioabsorbable stents is to develop a device that provides scaffolding in the periprocedural phase and during short-term follow-up. Bioabsorbable stents, once they are bioabsorbed, leave behind only the healed natural vessel, allowing restoration of vasoreactivity with the potential of vessel remodelling. Late stent thrombosis is unlikely since the stent is gone, and prolonged antiplatelet therapy is not necessary in this instance. Bioabsorbable stents can also be suitable for complex anatomy where stents impede on vessel geometry and morphology and are prone to crushing and fractures, such as is seen in saphenous femoral and tibial arteries. Bioabsorbable implant stents can be used as a delivery device for agents such as drugs and genes, and will perhaps play a role in the treatment of vulnerable plaque [6]. In addition, drug-eluting bioabsorbable stents can deliver antiproliferative agents to reduce restenosis and then dissolve over time, thereby eliminating the disadvantages associated with permanent stents. In this paper we will briefly review the technology, preclinical, and initial clinical experimental studies regarding bioabsorbable stents.