Preparation and characterisation of porous silica and silica/titania monoliths for potential use in bone replacement

Inorganic materials used in bone regeneration and replacement have developed rapidly over the last 10 years or so with SiO2 as well as TiO2 showing great potential. In this work, porous SiO2 and SiO2/TiO2 monoliths were prepared from mixtures of powdered meso- and macroporous silica and titanium dioxide (anatase) powders. The mixtures were compacted at pressures between 10 and 100 MPa to form monoliths which were then sintered at 700 °C. It was observed that compaction pressure, composition and sintering directly influenced final monolith porosity, density and surface area due to changes in their pore volume and size. Surface area and pore volume of the monoliths decreased with increasing compaction pressure and sintering whilst density increased. The presence of TiO2 was observed to increase the density of monoliths but not their flexural biaxial strength. When the materials were evaluated for their toxicity by the MTS cell proliferation assays against three human cell lines silica monoliths were observed to be nontoxic. A study of the materials ability to promote cell adherence and growth showed that monoliths containing TiO2 did not support cell adhesion but those composed of SiO2 alone did. Finally it was observed that the materials rapidly promoted the nucleation and surface growth of a hydroxyapatite layer when incubated in simulated body fluid. This study indicates that SiO2 and SiO2/TiO2 monolithic bone implant materials with tailored porosities can be prepared on large scale from simple precursors which are biocompatible and able to support cell growth and hydroxyapatite nucleation.