Review: Surfactants as Strategies for the Dimensional and Morphological Modulation of Hydroxyapatite

Hydroxyapatite (HAp), Ca10(PO4)6(OH)2, is one of the most widely studied calcium phosphates in biomaterials due to its chemical similarity to the mineral phase of bone and teeth. However, its performance depends not only on its composition or crystalline phase, but also on particle size, morphology, crystallinity, surface area, porosity, and agglomeration degree. In this context, surfactants represent an effective strategy to modulate nucleation, crystal growth, and the final organization of HAp. This review analyzes cationic, anionic, nonionic, zwitterionic, and catanionic surfactant systems, whose characteristics enable interaction with the nucleation and crystal growth processes of hydroxyapatite, providing a stabilizing effect and restricting growth along specific crystallographic planes, thereby promoting controlled and oriented crystal growth. The literature shows that their effects depend on variables such as pH, supersaturation, Ca/P ratio, temperature, and reaction time. Understanding this interaction is essential for designing nanostructured HAp for biomedical applications.