Adsorption of proteins and calcium phosphate materials bioactivity

The behaviour of calcium phosphate (CaP) based biomaterials in biological environments determines how they can be used in vivo. The prime requirement for CaP materials to be bioactive and bond to living bone is the formation of a bone-like apatite layer on their surface. This phenomenon can be reproduced in vitro using simulated body fluid (SBF): a protein-free solution with ion concentrations similar to those of human blood plasma. Although proteins are unanimously considered as important actors in CaP material bioactivity and biomineralization processes, a certain confusion exists about their role as promotors or inhibitors of mineral crystal formation or both. The adsorption of proteins on the mineral surface can alter the nucleation rate and lead to antagonistic effects depending on the concentration of the adsorbed proteins. The ambiguity of this general effect is illustrated by the action of albumin on calcium phosphate crystallization on type I collagen and several other examples found in the literature.