Effects of different types of modifiers on structural variation of nano-hydroxyapatite for efficient application

Hydroxyapatite (HAp) has emerged as a biomaterial of significant interest due to its intrinsic biocompatibility and structural similarity to natural bone minerals. While HAp is traditionally derived from natural sources, chemical synthesis via conventional methods, such as wet chemical precipitation and sol-gel processing, and newer techniques like microwave-assisted synthesis and hydrothermal methods have enabled greater control over its physicochemical properties. With the expansion of applications beyond conventional biomedical uses, recent research has concentrated on engineering nanohydroxyapatite with precisely tailored morphologies and structures. This review examines the influence of various organic modifiers on nano-HAp synthesis, highlighting how these agents modulate its crystal growth, crystallinity, surface topology, particle dimensions, and porosity. Potent chelating agents (e.g., citric acid and EDTA) have been shown to yield purer, more uniform nanoparticles, whereas cationic-anionic surfactants (e.g., CTAB and SDS) enhance the surface area. Modifiers such as Triton X-100, chitosan, and polyethylene glycol effectively adjust the pore size. Scientists are also investigating environmentally friendly and toxicant-free modifiers. Through summarization of insights from current literature, this review provides a comprehensive framework for selecting suitable modifiers to fabricate well-defined HAp nanomaterials for diverse applications in future studies.