APPLYING A CALCIUM-PHOSPHATE LAYER ON PEO/PBT COPOLYMERS AFFECTS BONE-FORMATION IN-VIVO

Recently a copolymer (Polyactive(R)) has been introduced that combines elastomeric and bone-bonding properties. Since calcification of the copolymer is a prerequisite for bone bonding, Polyactive was precalcified in vitro in order to increase the bone-bonding rate. Precalcification was performed by subsequent incubation in Ca and P solutions and resulted in formation of a hydroxyapatite layer on the surface of the implant. Within one week after implantation this layer had disappeared from the surface and a new calcification zone was formed under the surface of the copolymer. Longer implantation periods showed that in precalcified implants bone was apposited along the walls of the pores, while in control implants new bone was first formed in the centre of the pores. Consequently, the percentage of bone contact was increased in precalcified implants, however, the amount of bone ingrowth was equal in both control and precalcified implants. Transmission electron microscopy showed the presence of an electron-dense layer at the bone implant interface, which was indicative for bone-bonding. It is concluded from these experiments that precalcification of PEO/PBT copolymers affected the direction of bone apposition and increased the bone-bonding rate.