A statistical study of poly(ε-caprolactone) crystallinity in poly(ε-caprolactone)-silica sol-gel materials and their in vitro calcium phosphate-forming ability

Composite poly(epsilon-caprolactone) (PCL)-silica materials for potential use in orthopaedic applications have been prepared by a sol-gel method using an experimental design approach to investigate the effect of synthesis variables, separately and together, on the physical form of the organic polymer. A combination of differential scanning calorimetry, X-ray diffraction and Fourier-transform infrared methods were used to obtain information on the arrangement of the organic polymer in the hybrid material. As our studies investigated the effect of synthesis variables simultaneously, it was possible to establish that the increase of tetraethyl orthosilicate (TEOS)/PCL and HCl/TEOS molar ratios decreased the poly(epsilon-caprolactone) crystallinity and provided for a better mixing of the two phases. At a mechanistic level it was possible to show that increase in catalyst content affected the condensation of silicon containing species. In vitro calcium phosphate-forming ability tests using the static biomimetic method have been carried out on selected PCL-silica sol-gels. In vitro bioactivity was only observed for PCL-silica sol-gel composites with high silica content (30% weight). Changes in catalyst levels had a smaller but still significant effect. Calcium phosphate formation on largely non-porous surfaces is proposed to occur via the formation of a silica sol-gel layer, and is influenced by the topography and the chemistry of the materials surface. (C) 2003 Society of Chemical Industry.