Moving research direction in the field of metallic bioresorbable stents-A mini-review

In contrast to polymer bioresorbable stents(BRS)that exhibited suboptimal performance in clinical trials due to their deficient mechanical properties,metallic BRS with improved mechanical strength have made their way into the clinic and have demonstrated more promising results.In the roadmap of research and development of metallic BRS,magnesium and iron based biodegradable metal stents had been clinically used,and the zinc based biodegradable metal stents had been trailed in Mini-Pigs.In this mini-review paper,we demonstrate the current technology levels and point out the future R&D direction of metallic BRS.Magnesium based BRS should target for decreasing struct thickness meanwhile balancing with enough supporting strength.Iron based BRS should move towards high efficient absorption,conversion,metabolism,elimination of its degradation products.Zn based BRS should strive to improve mechanical stability,creep resistance and biocompatibility.Future R&D directions of metallic BRS should move towards new materials such as Molybdenum,intelligent stent integrated with degradable biosensors,and new stent with multiple biofunctions,such as NO release.

A“built-up”composite film with synergistic functionalities on Mg-2Zn-1Mn bioresorbable stents improves corrosion control effects and biocompatibility

Control of premature corrosion of magnesium(Mg)alloy bioresorbable stents(BRS)is frequently achieved by the addition of rare earth elements.However,limited long-term experience with these elements causes concerns for clinical application and alternative methods of corrosion control are sought after.Herein,we report a“built-up”composite film consisting of a bottom layer of MgF2 conversion coating,a sandwich layer of a poly(1,3-trimethylene carbonate)(PTMC)and 3-aminopropyl triethoxysilane(APTES)co-spray coating(PA)and on top a layer of poly(lactic-co-glycolic acid)(PLGA)ultrasonic spray coating to decorate the rare earth element-free Mg-2Zn-1Mn(ZM21)BRS for tailoring both corrosion resistance and biological functions.The developed“built-up”composite film shows synergistic functionalities,allowing the compression and expansion of the coated ZM21 BRS on an angioplasty balloon without cracking or peeling.Of special importance is that the synergistic corrosion control effects of the“built-up”composite film allow for maintaining the mechanical integrity of stents for up to 3 months,where complete biodegradation and no foreign matter residue were observed about half a year after implantation in rabbit iliac arteries.Moreover,the functionalized ZM21 BRS accomplished re-endothelialization within one month.

Reduction in the Corrosion Rate of Magnesium and Magnesium Alloy Specimens and Implications for Plain Fully Bioresorbable Coronary Artery Stents: A Review

The most popular treatment/management modality for coronary artery disease, which is one of the leading causes of death, is percutaneous transluminal coronary intervention (popularly known as “plain old balloon angioplasty”) followed by implantation of a stent (“stenting”). Stent types have evolved from bare metal stents through first-generation drug-eluting stents to fully bioresorbable stents (FBRSs). Two examples of FBRSs are 1) Mg scaffold with no coating;and 2) Mg alloy scaffold coated with a bioresorbable polymer in which an anti-proliferative drug is embedded. In the case of Mg/Mg alloy FBRSs, one of the reported clinical results is that the resorption time of the stent is too short (in vivo resorption time (and, hence, improving the clinical efficacy) of the current generation of fully-bioresorbable Mg/Mg-alloy stents as well as guide the development of the next generation of these stents.