Hydroxyapatite Nanocrystals as Bone Tissue Substitute

Nano-science, where the properties of materials are exploited for innovative amazing applications is involved in the size dependent chemical and biological activity of bone substitute materials, which is an indeed fascinating field. The article reviews the synthesis and chemical-physical characteristics of hydroxyapatite nano-crystals which have excellent properties to represent an elective material covering a wide range of applications for bone substitution. We have started from the examination of biogenic bone and tooth hydroxyapatite nanocrystals morphological and chemical-physical characteristics. The highlighted concepts have been used to review the up-to date main new ideas about the preparation of synthetic apatitic bone substitutes mimicking the above biogenic properties among which the nano size is the basis of their self assembly, self mineralization and bone regeneration ability. High bioreabsorbability and containing foreign ions mimicking bone hydroxyapatite chemical-physical and physiological behavior HA nanocrystals has been described, pointing out the possibilty of using them also to prepare scaffolds with a porosity simulating that of spongy bone and upon which cells can be seeded developing “in vitro autologous bone”. Biologically inspired HA nanocrystals/collagen composites have been reviewed focusing the role of self assembling strategy in conditioning the bone repairing activity of this biomaterial. Furthermore, considering that calcium phosphate/collagen composites are limited to not loading application, the possibility of preparing bio-inspired coating onto the surface of metallic implants has been described as an advantageous approach. Finally, the surface functionalization of HA nano-crystals with bioactive molecules makes them able to transfer information and to act selectively on the biological environment and can be considered one of the main future challenges for innovative bone substitute materials.