Surface modification of hierarchical hydroxyapatite fabricated via hydrothermal method

Surface modification, encompassing both chemical and physical features, plays a crucial role in fulfilling the requirements of biomaterial applications and also improves their performance. Due to that, this study focuses on the optimization of morphology and functionalization of hydroxyapatite (HAP). For this purpose, hydrothermal growth of HAP on (fluorine tin oxide) FTO is carried out in the presence of calcium and phosphate precursors with Ca/P molar ratio of 1.67:1 in the solution. Trisodium nitrilotriacetic acid (NTA) is used as a chelating additive for the first time during hydrothermal process at temperature between 120 and 180 °C for 16–24 h. Further studies on the effect of NTA concentration on HAP formation indicate that hierarchical structures are formed in the presence of NTA with NTA/Ca molar ratio of 1:1 at temperature between 150 and 180 °C for 24 h, improving crystallinity as temperature increasing. To facilitate the functionalization of HAP, the layer deposited at 180 °C with NTA/Ca molar ratio of 1:1 is peeled using two different reagents, Fluoromount™ and polyvinyl alcohol (PVA). The HAP peeled with PVA shows no relevant morphological changes in SEM images, indicating a successful peeling process using PVA. After that, the HAP powders are functionalized with alendronate (AL) molecules and studied using ATR-FTIR, XPS and BET techniques. Chemical shift of PO43− vibrations and appearance of the new peaks assigned to the –NH2 group demonstrate successful AL-functionalization. The AL-HAP hierarchical structures fabricated with the aid of NTA can be introduced as multifunctional biomaterials for future bio-applications.