| Cardiovascular stents constitute a kind of medical devices used in the treatment of vascular stenosis or blockage. The conventional bare metal stents and drug eluting stents cannot degrade and will stay in the human vessel for the whole life, which will induce endothelial proliferation and late thrombus. The newly developed biodegradable stents can provide radial support for vessels for3-6months and totally degrade in1-2years.A series of high molecular weight polymers, PLLA, PTMC-LLA (PTLA), PTMC-LLA-GA (PTLGA) were prepared by ring-opening polymerization of cyclic monomers using stannous octoate as catalyst. The polymers were characterized by Fourier transform infrared spectroscopy,1H nuclear magnetic resonance, differential scanning calorimeter, and gel permeation chromatography. Film samples were prepared by solution casting method. Tensile tests, in vitro degradation, in vivo degradation, platelet adhesion and tissue compatibility studies were carried out to evaluate the potential of these polymers as cardiovascular stent material.The crystallinity of PTLA and PTLGA is lower than PLLA. Compared with PLLA, PTLGA1/10/0.5maintains high ultimate stress and the toughness increases significantly. Thus, it exhibits superior mechanical properties for cardiovascular stents.In vitro degradation shows that PTLGA is more hydrophilic and degrades faster than PLLA. With degradation, the molecular weight decreases, and no significant mass loss is observed. Amorphous chains fold into crystalline region, which results in an increase of the degree of crystallinity. Meanwhile, the crystallization ability of polymers increases due to the decrease of molecular weight.The film samples were implanted subcutaneously for periods of time up to6months. During in vivo degradation, PTLGA degrades much faster than PTLA and PLLA. The changes of the physico-chemical properties are similar to in vitro degradation, but water uptake is lower. After90days, the materials still maintain high strength. Thus PTLGA can provide mechanical support for a long period although it degrades faster than PLLA, which fulfils the requirement of biodegradable cardiovascular stent.The platelet adhesion test indicates the low activation of platelets of all polymers, and PTLGA and PTLA exhibit better blood biocompatibility than PLLA. During the subcutaneous implantation in rats, no severe inflammation is caused as no large amount of degradation product is released. All the polymers exhibit good biocompatibility.In conclusion, compared with PLLA, the high molecular weight copolymer PTLGA exhibits higher toughness, appropriate degradation rate and better biocompatibility, and thus is promising as biodegradable cardiovascular stent material. |
