Biodegradation,hemocompatibility and covalent bonding mechanism of electrografting polyethylacrylate coating on Mg alloy for cardiovascular stent

Organic coatings are the most widely employed approach for the promotion of corrosion resistance of magnesium(Mg)alloys.Unfortunately,traditional organic coatings are weakly bonded to Mg substrates due to physical adsorption.Herein,a polyethylacrylate(PEA)coating was fabricated on Mg-Zn-YNd alloy via electro-grafting.The surface structure and chemical composition were characterized by means of scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),atomic force microscope(AFM)and Fourier transform infrared(FTIR)as well as time of flight-secondary ion mass spectrometer(To F-SIMS).The results showed that the surface roughness of PEA coating was dominated by scan rate;while the coverage and integrity of PEA coating were mainly affected by the monomer concentration and sweep circles.To F-SIMS results indicated that PEA coating was wholly covered on Mg alloy,and the presence of C2H3Mg-fragment confirmed the covalent bond between PEA coating and Mg alloy.In addition,DFT calculation results of the adsorption of EA molecules with Mg substrate agree well with the experimental phenomena and observation,suggesting that the electrons in 3s orbit of Mg atoms and 2pz orbit of C1 atom participated in the formation of covalent bond between PEA coating and Mg substrate.Potentiodynamic polarization curves and immersion test demonstrated that the PEA coatings could effectively enhance the corrosion resistance of Mg alloy.The platelet adhesion results designated that platelets were barely visible on PEA coating,which implied that PEA coating could effectively prevent the thrombosis and coagulation of platelets.PEA coating might be a promising candidate coating of Mg alloy for cardiovascular stent.

Investigation of long-term implantation of BuMA stent in a porcine coronary model

Background Stent-based delivery of sirolimus has been shown to reduce neointimal hyperplasia significantly. However, the long-term effect of the polymer is thought to initiate and sustain an inflammatory response and contribute to the occurrence of late complications. Our study aimed to evaluate the efficacy and safety of the BuMA biodegradable drug-coated sirolimus-eluting stent （BSES） for inhibiting neointimal hyperplasia in a porcine coronary model. Methods Four types of stents were implanted at random in different coronary arteries of the same pig： BSES （n=24）, bare metal stent （BMS） （n=24）, biodegradable polymer coated stent without drug （PCS） （n=24） and only poly （n-butyl methacrylate） base layer coated stent （EGS） （n=23）. In total, 26 animals underwent successful random placement of 95 oversized stents in the coronary arteries. Coronary angiography was performed after 28 days, 90 days and 240 days of stent implantation. After 14 days, 28 days, 90 days and 240 days, 6 animals at each timepoint were sacrificed for histomorphologic analysis. Results The 28-day, 90-day and 240-day results of quantitative coronary angiography （QCA） showed reduction in luminal loss （LL） in the BSES group when compared with the BMS group; （0.20±0.35） mm vs. （0.82±0.51） mm （P=-0.035）, （0.20±0.30） mm vs. （0.93±0.51） mm （P=-0.013）, and （0.18±0.16） mm vs. （0.19±0.24） mm （P=0.889）, respectively. By 28-day, 90-day and 240-day histomorphomeric analysis results, there was also a corresponding significant reduction in neointimal tissue proliferation with similar injury scores of BSES compared with the BMS control; average neointimal area （0.90±0.49） mm2 vs. （2.16±1.29） mm2 （P=0.049）, （1.53±0.84） mm2 vs. （3.41±1.55） mm2 （P=-0.026）, and （2.43±0.95） mm2 vs. （3.12±1.16） mm2 （P=0.228）, respectively. High magnification histomorphologic examination revealed similar inflammation scores and endothelialization scores in both the BSES and BMS groups. Conclusions The BuMA biodegradable drug-coated sirolimus-eluting stents can significantly reduce neointimal hyperplasia and in-stent restenosis. Re-endothelialization of the BuMA stent is as good as that of the BMS in the porcine coronary model due to the reduced inflammation response to the BuMA stent.