Microwave-assisted preparation of Nano-hydroxyapatite for bone substitutes

Calcium phosphate-based biomaterials have been frequently used as bone substitutes and osteoconductive scaffolds due to their chemical similarity to the inorganic phase of bone. Hydroxyapatite (HA) is the most frequently used calcium phosphate-based biomaterials and it could be prepared from natural or synthesized sources via several processes. Nano-HA (nHA) particles were suggested to have superior bioresorbtion and close chemical and crystallographic structure to natural bone apatite.Currently, microwave-assisted (MW) processing of biomaterials, particularly bioceramics, has more appealing advantages than conventional heating methods. It works through an internally generated heat inside the materials molecules instead of originating external heating source and subsequent radiative transfer as in the conventional heating. Thus, MW synthesis of HA offers several benefits including rapid heating, shorter synthesis time, efficient energy transformation and throughout volume heating.The purpose of this review is to highlight the various methods and the paradigm shift of MW techniques to synthesize nHA in the past 25 years. Peer-reviewed journal publications (Scopus and Google Scholar indexed articles) in which titles and keywords combining “Microwave AND Nano-Hydroxyapatite” were collected from 1990 till May 2015. The discussions include the state-of-the-art and the role of reaction parameters on the HA structures, size, morphology and biocompatibility to be further used for bone regeneration applications.