Systematic Processing of β-Tricalcium Phosphate for Efficient Protein Loading and In Vitro Analysis of Antigen Uptake

Microparticulate calcium phosphate (CaP) powders are promising drug carriers because of their biocompatibility and degradability under physiological conditions. The adsorption capability of CaP microparticles makes them interesting candidates, within the inorganic carrier materials, for delivering protein antigens to professional antigen presenting cells (APC) for vaccination purpose. However, in order to bind and deliver a sufficient amount of protein, the challenge is to effectively increase the binding capacity of this material. In this study, beta-tricalcium phosphate (beta-TCP) powder is engineered to obtain microparticles with increased protein loading, using bovine serum albumin as a model antigen. The decrease in particle size and increase in specific surface area of carrier is shown to strongly affect protein adsorption. Finally, we demonstrate that the processed beta-TCP is capable of delivering its protein payload in vitro to dendritic cells, which are professional APCs and the target cell population for microparticulate vaccines.