Application of Calcium Phosphate based gels for encapsulation of therapeutic molecules

Abstract

There is increasing clinical need for bone substitutes because of the limited supply of autogenous tissue, and the significance of inherited or other bone diseases. The ultimate aim of this study was to form calcium phosphate (CaP) based matrices as bone grafts for medical applications. Amongst CaP based materials, CaP gels made by the sol-gel process have attracted much interest since they can be processed at room temperature allowing the incorporation of environmentally sensitive molecules such as growth factors. CaP gels can be engineered by changing process conditions. There is little previous work however on the effect of drying regimes on the CaP materials formed using the sol-gel process. The objectives of this research were to investigate the influence of drying conditions on the physicochemical properties of CaP gels and the effect of the resultant structures of CaP gels on the function of the incorporated therapeutic molecules. In addition, surface modification of the CaP gels was investigated as a means to enhance biological interaction and also a potential way of creating primary bonds between apatite crystals enabling mechanical reinforcement of the material, which is currently too weak to bear load. This work has confirmed that different drying regimes have a significant influence on the formation of the gel pore structure, with the storage of gel in humid conditions, enabling reprecipitation of an apatitic phase. This variation in pore structure has a significant influence on the catalytic of encapsulated enzymes. In addition, the pH fluctuation of CaP based matrices during processing determines the activity of biomolecules after incorporation. It has also been shown that it is possible to form thiol functional groups on the surface of CaP gels, which could be used in future for mechanical reinforcement or for the attachment of biological moieties