Hydrolytic degradation of polyglyconate B: the relationship between degradation time, strength and molecular weight

Bioresorbable polymers have found a wide range of uses in medical implants, from sutures to scaffolds for tissue engineering applications. Increasingly they are being used in internal orthopaedic fixation devices, in which the strength retention profile is important. Polyglyconate B, a block co-polymer of glycolic acid and trimethylene carbonate, is one polymer used in these applications. In this study, the hydrolytic degradation of polyglyconate B has been studied in vitro. Specimens were prepared with two initial molecular weights and aged in PBS solution at 37°C for up to 31 days. The polymers were characterised by gel permeation chromatography, for molecular weight, tensile testing and mass change, as a function of degradation time. A further aim of the work was to determine whether the measured changes in tensile strength over time could be fitted to a simple model. The results showed that the observed relationship between strength and molecular weight was more complex than that used in our model. However, the data could be modelled using an empirically derived relationship between tensile strength and number average molecular weight (Mn). Changes in other mechanical properties, such as strain at break, were also found to be strongly dependent on changes in the single parameter of Mn.