Comparative study of the in vitro apatite-forming ability of poly(epsilon-caprolactone)-silica sol-gels using three osteoconductivity tests (static, dynamic, and alternate soaking process).

Abstract

The in vitro apatite-forming ability of poly(epsilon-caprolactone) (70 wt %)-silica sol-gels, with hydroxyl and triethoxysilane end-groups with potential use in bone repair have been assessed using static and dynamic osteoconductivity tests. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and microanalysis techniques were used to observe and characterize precipitates formed on the material's surface. An apatite layer was observed to form on both of the composites' surface. However, variations were observed according to the test method used, in accordance with other studies on bioactive ceramics. A third method, the "alternate soaking process" (ASP) was developed to provide rapid results and quantify the amount of calcium-containing precipitates formed on the surface of potentially "bioactive" materials. The results presented here show that for a material to be bioactive and have the ability to form a precipitate containing calcium and phosphate ions, levels of calcium ions measured by a complexometric assay should be significantly higher than the level of 5 microg/cm(2). This level of calcium ions was obtained after 20 ASP cycles for the hydroxyl and triethoxysilane end-capped poly(epsilon-caprolactone) samples that did not form precipitates on their surfaces even after >50 ASP cycles. For the two sol-gel silica composites containing approximately 70% hydroxyl and triethoxysilane poly(epsilon-caprolactone), there was no significant difference in the amount of calcium-containing precipitate as observed using the in vitro apatite-forming ability tests suggesting that polymer end-group modification is not detrimental to the apatite-forming ability of such composites.