Bioactive Aerogels: Novel Synthetic Bone Graft Substitute Materials in Dentistry

Objectives: This work presents the development of a novel synthetic bone graft, Bioactive Aerogels. They are ultra-low density silicate based amorphous materials, made of a polymerized silicon network, calcium and phosphate, that when immersed in aqueous solution form hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) on their surface. The objective of this project was to develop a bone graft substitute material that shows high osseointegration and rapid remodeling in vivo within 3-6 months.
Methods: Six compositions were produced, via the sol-gel process of tetraethyl orthosilicate, calcium nitrate and triethyl phosphate, after which samples were critically dried using liquid CO₂. Porosity, surface area and density were measured using N₂ adsorption; followed by bioactivity studies which involved immersion in simulated body fluid over 3 days, after which hydroxyapatite formation and ion release was measured.
Results: The results showed densities below 0.2 g cm^-3, pore volumes of around 5 cm³ g^-1 and surface areas of approximately 900 m² g^-1. The compositions formed of hydroxyapatite on their surface within 3 hours of immersion, demonstrating their potential for rapid osseointegration. The results also demonstrated the materials have extremely low density, with a high surface area and degree of porosity and are bioactive. Being able to form hydroxyapatite is important because in silicate based biomaterials this has been shown to be an important factor in their high rates of bone-to-graft contact values in-vivo. The release of silicon in-vivo has been shown to enhance proliferation of osteoblasts, promoting bone formation.
Conclusions: The method developed is able to alter the density of the material at will. It is anticipated that by altering the density of the material will have a related change to the remodeling rates in-vivo. This enables tailoring of the performance in-vivo, offering alternative choices for different clinical situations. It is the aim in future to develop tailored compositions for different clinical procedures.