Biomimetic self-assembly of apatite hybrid materials: From a single molecular template to bi-/multi-molecular templates

The self-assembly of apatite and proteins is a critical process to induce the formation of the bones and teeth in vertebrates. Although hierarchical structures and biomineralization mechanisms of the mineralized tissues have been intensively studied, most researches focus on the self-assembly biomimetic route using one single-molecular template, while the natural bone is an outcome of a multi-molecular template co-assembly process. Inspired by such a mechanism in nature, a novel strategy based on multi-molecular template co-assembly for fabricating bone-like hybrid materials was firstly proposed by the authors. In this review article we have summarized the new trends from single-molecular template to bi-/multi-molecular template systems in biomimetic fabrication of apatite hybrid materials. So far, many novel apatite hybrid materials with controlled morphologies and hierarchical structures have been successfully achieved using bi-/multi-molecular template strategy, and are found to have multiple common features in comparison with natural mineralized tissues. The carboxyl, carbonyl and amino groups of the template molecules are identified to initiate the nucleation of calcium phosphate during the assembling process. For bi-/multi-molecular templates, the incorporation of multiple promotion sites for calcium and phosphate ions precisely enables to regulate the apatite nucleation from the early stage. The roles of acidic molecules and the synergetic effects of protein templates have been significantly recognized in recent studies. In addition, a specific attention is paid to self-assembling of apatite nanoparticles into ordered structures on tissue regenerative scaffolds due to their promising clinical applications ranging from implant grafts, coatings to drug and gene delivery.