GENE-EXPRESSION AND PROTEIN-ACTIVITY IN BONE-BONDING AND NONBONDING PEO PBT COPOLYMERS/

The formation of a reactive carbonate-apatite surface is generally con sidered a critical step for bone-bonding. However, the contribution of proteins in the establishment of bone-bonding is debatable. In the cu rrent study, osteocalcin, osteopontin and beta-actin mRNA expression a nd alkaline phosphatase activity were therefore determined in differen t porous substrates loaded with marrow after subcutaneous implantation for 2 weeks. Two polyethylene oxide (PEO)/polybutylene terephthalate (PBT) copolymers were used for this purpose. First, an 80/20 PEO/PBT w hich generates a carbonate-apatite surface and bonds to bone rapidly. Second, a 30/70 PEO/PBT which previously did not show bone-bonding up to 1 year postoperative. Bone had formed within the pores and occasion ally at the calcified surface of the 80/20 materials. in contrast, 30/ 70 materials did not calcify and bone was not found in the pores. Desp ite these morphological differences, gene expression and protein activ ity was similar in 80/20 and 30/70 PEO/PBT materials. These results su ggested that bone-bonding of PEO/PBT copolymers is more likely to depe nd on the formation of a carbonate-apatite surface than on a specific influence of a bioactive material on osteogenic cells.