Surfactant-assisted synthesis of hydroxyapatite particles: a comprehensive review

Calcium phosphates are extensively used biomaterials for repairing bone tissue due to their osteoconduction and osteoinduction properties. Hydroxyapatite (HAp) is a type of calcium phosphate that has gained the attention of researchers because of its high crystallinity, superior corrosion resistance, and good mechanical and biological properties. This makes it ideal for use in dental and orthopaedic applications. Natural HAp particles present in physiological tissues have plate-like or rod-like morphology in the nanometre range, while synthetic HAp particles exhibit an irregular morphology and are in the micron range. The usage of surfactants as templates during the synthesis has become a successful strategy to regulate the morphology and size of the HAp particles to closely resemble the natural HAp. In this article, the authors have reviewed the effects of various chemical surfactants (such as cationic, anionic, zwitterionic, and non-ionic), biosurfactants (or biomolecules extracted from different parts of plants such as roots and leaves), and bio-wastes on the structural (morphology, size, and shape) and biological (bioactivity and biocompatibility) properties of the HAp particles synthesized through various methods. The nucleation and growth mechanisms of HAp particles in the presence of various surfactants through different methods are discussed. Even though there has been significant research on surfactant-assisted HAp particles, the detailed mechanisms behind the changes in the biological properties with the addition of surfactant are poorly understood. This review paper also highlights the current progress in the synthesis and characterization of surfactant-assisted HAp and provides guidance for future research on this topic.