The in vivo and in vitro degradation behavior of poly(trimethylene carbonate)

Abstract

The in vivo and in vitro degradation behavior of poly(trimethylene carbonate) (PTMC) polymers with number average molecular weights of 69×10 3, 89×10 3, 291×10 3 and 457×10 3 g/mol (respectively abbreviated as PTMC 69, PTMC 89, PTMC 291 and PTMC 457) was investigated in detail. PTMC rods (3 mm in diameter and 4 mm in length) implanted in the femur and tibia of rabbits degraded by surface erosion. The mass loss of high molecular weight PTMC 457 specimens was 60 wt% in 8 wks, whereas the mass loss of the lower molecular weight PTMC 89 specimens in the same period was 3 times lower. PTMC discs of different molecular weights immersed in lipase solutions (lipase from Thermomyces lanuginosus) degraded by surface erosion as well. The mass and thickness of high molecular weight PTMC 291 discs decreased linearly in time with an erosion rate of 6.7 μm/d. The erosion rate of the lower molecular weight PTMC 69 specimens was only 1.4 μm/d. It is suggested that the more hydrophilic surface of the PTMC 69 specimens prevents the enzyme from acquiring a (hyper)active conformation. When PTMC discs were immersed in media varying in pH from 1 to 13, the non-enzymatic hydrolysis was extremely slow for both the high and low molecular weight samples. It can be concluded that enzymatic degradation plays an important role in the surface erosion of PTMC in vivo.