Effects of hydrolysis on a new biodegradable co-polymer.

The aim of this study was to examine the feasibility of using a new low-modulus biodegradable thermoplastic elastomer for in vivo application as a stent cover. The new polymer, a thermoplastic elastomer, consists of a three-armed co-polymer of poly(lactide)acid (PLLA), poly(trimethylene carbonate) (PTMC) and poly(caprolactone) (PCL). A degradation study was performed in a buffer solution at 37 degrees C for 4 and 6 weeks. The effect of degradation on mechanical properties was studied by stress-strain measurements and explained by using modulated DSC, GPC and mass measurements. A tapered block of PLLA and trimethylene carbonate connecting the crystalline outer part and the inner elastic part was highly susceptible to hydrolysis and caused rapid degradation and subsequent loss of mechanical properties. Random chain scission and homogenous hydrolysis resulted in a loss in mass and molecular weight. After 6 weeks of in vitro hydrolysis the molecular weight had decreased 54% and the elongation-at-break dropped from more than 300% to 90%. A medium free cell seeding study showed that endothelial cells adhered well to the polymeric material. An indicative animal study with the polymer acting as a stent cover showed very low levels of inflammation; however, pronounced neointima thickening was observed which was probably due to the premature failure of the material.