Interface reactions to PEO/PBT copolymers (Polyactive) after implantation in cortical bone.

The bone reaction at the interface of a range of PEO/PBT copolymers (Polyactive) after press-fit implantation in the diaphyseal femur of 20 goats was investigated. The animals were sacrificed at 1, 4, 12, 26, and 52 weeks. Undecalcified histologic sections were prepared, evaluated qualitatively, and quantified with the aid of an image analysis system. The percentage of bone contact was determined morphometrically for all PEO/PBT proportions; for the 70/30 ratio, the percentage of calcification of the material surface and of bone-bonding (defined as a continuum at the light microscopic level between calcification within the material surface and bone tissue) were also assessed. PEO/PBT copolymers possess hydrogelic properties, and a direct relation has been established between water-uptake and PEO content. The swelling behavior of all PEO/PBT substrates resulted in a high degree of bone contact (over 95%) at early stages. From the 12-week survival time onward the 70/30 revealed higher percentages of bone contact (over 80%) when compared with the other ratios (60/40, 55/45, 40/60, and 30/70). This difference was statistically confirmed 1 year postoperatively. The materials with the higher PEO contents showed the highest amounts of calcification, which is reflected by the rate of bone-bonding (70% of bone-bonding for the 70/30 at 52 weeks). Calcification and bone-bonding were not observed for 40/60 and 30/70 proportions. The quantitative results confirmed the relation between PEO content, water-uptake, calcification, and bone-bonding. It was furthermore demonstrated that PEO/PBT copolymers initially establish a high degree of bone contact, whereas the bone-bonding properties, especially of the 70/30, accomplish a long-term implant fixation.