Content area
Full Text
Intravascular stents, first developed in the 1980s,[1] have now become the most effective method of coronary stenosis treatment. The first generation stent, a bare-metal stent, has already revealed its defect of low biocompatibility by stimulating vascular walls and causing restenosis. The second generation stent, a drug-eluting stent, was found to reduce the restenosis rate but potential risks of late-stent thrombosis still exist.[2] The third generation of intravascular stent, biodegradable intravascular stents (BIS) that can be totally absorbed by the human body, has been widely researched and developed.[3] As a temporary stent for treatment of vascular stenosis, BIS could be degraded into micro-molecules and be absorbed or excreted out of the body by the metabolism after supporting vascular walls, without causing long-term effects in vivo and lowering the risk of restenosis.
Biodegradable polymers offer a number of advantages for developing BIS, including their excellent ability to be shaped and biodegradation kinetics that suit the healing period. As a result, they have attracted much interest from biomaterial researchers.[4] Polydioxanone (PDO), which is a novel biodegradable polymer belonging to aliphatic polymers,[5] has been authenticated by the US Food and Drug Administration (FDA) for use in clinical applications. PDO was totally degraded within 6 months;[6] animal experiments have verified its ideal biocompatibility.[7] The presence of an ether bond and an additional -CH2 - group in its molecular chain give PDO great flexibility and elasticity, which makes it suitable for fabrication of implanted stents by textile processing.[8] Li et al. used PDO monofilament to fabricate intestinal stents with weft-knitting structure.[9] Stivaros et al. fabricated an esophageal stent with a braiding structure and inserted it into patients who were observed for 8 weeks with no evident symptoms.[10]
Designs of commercial metal intravascular stents can be classified into three categories: coil-structural, braiding-structural, and sequential rings structural.[11] Coil-structural stents were the earliest used design, made from metal sheet or wire. With no internal connections, this design is very flexible but insufficient in radial force. Braiding-structural stents, which are net-like stents fabricated by a braiding or knitting method, offer excellent coverage and flexibility. The most common braiding-structural stent is the WallStent (Boston Scientific Cooperation, USA), which uses multiple alloy wires braided...