Evaluation of copolymers of polyethylene oxide and polybutylene terephthalate (polyactive): mechanical behaviour

Polyether-polyester segmented block copolymers (Polyactive) on the basis of polybutylene terephthalate (PBT) and polyethylene oxide (PEO) were mechanically tested. Tensile strength and modulus of elasticity in compressive and tensile deformation were recorded according to ASTM standards. These tests were done in vitro under dry and wet conditions, and after 3, 9 and 25 wk subcutaneous implantation of these materials in goats. Strength and modulus of elasticity were higher with increased contents of PBT in the copolymers. After water uptake, the polymer displayed a lower strength and stiffness. Disintegration of the materials with 70% PEO content and dumb-bell shape was noted at 3 wk. Disintegration of the cylinders of the same material was seen after 25 wk implantation. Of the materials with 60% PEO content, only four of the five dumb-bells had disintegrated after 25 wk implantation. The in vivo test results of all other implants did not show a clinically relevant decrease of strength and stiffness with time after implantation of the copolymers in the goats. Mechanical behavior of the various copolymers seemed mainly determined by the amount and integrity of the PBT phase.