Interaction between self-assembled protein vesicles and microporous apatite surface.

Self-assembled structures such as vesicles have generated immense interest in recent decades due to their potential in mimicking biological membranes and in acting as drug-delivery systems. Despite the importance of the interaction between these organized assemblies and the surface of biomaterials, little is known about the mechanism involved. In this study, the interaction between giant proline-rich mussel adhesive protein (MAP) vesicles and the microporous apatite surface was investigated by scanning electron microscopy (SEM). We have found that MAP vesicles incubated on the apatite surface similar to osteoclasts, induce site-specific resorption of the apatite surface. However, in contrast to the osteoclastic resorption, the vesicle-induced resorption process appears to be accompanied by an organic matrix-mediated remineralization process. This results in the formation of a variety of complex three-dimensional site-specific "remodelled zones" on the apatite surface of micrometre scale. The mechanism of the formation of "remodelled zones" is discussed in terms of surface phenomena, such as adsorption and deformation of vesicles, site-specific release of resorptive agents, organic matrix-directed remineralization, and Ca-induced fusion, collapse and reshaping of the vesicles on the apatite surface.