Understanding the morphology transformation of hydrothermally prepared hydroxyapatite via attachment energy model

Hydroxyapatite (HA), a crucial biomaterial for bone repair and tissue engineering, exhibits properties highly influenced by its crystal morphology. The hydrothermal synthesis of HA usually involves alcohols such as methanol (MeOH), ethanol (EtOH), and isopropanol (iPrOH) to control the reaction environment. Currently, a prediction model that explains the alcohol-induced morphology transformation in HA is still lacking. In this study, we introduce the modified attachment energy (AE) model to predict the HA morphology in alcohol-water solvents. We optimize model parameters by analyzing the crystal structure and intermolecular interactions of HA. Through a detailed study of predicted morphology, surface-solvent interfaces, radial distribution functions, and coordination numbers, we reveal that as the alcohol content increases, the aspect ratio of the crystal morphology decreases. This trend can be attributed to alcohol molecules gradually replacing water molecules in the solvation shell, altering the interaction energy between the crystal face and the solvent. As a result, the relative growth rates of the crystal faces are modified. Notably, iPrOH has a more pronounced effect on reducing the aspect ratio compared to MeOH and EtOH, which benefits from its unique molecular structure and adsorption conformation. This work expands the application of the AE model to complex ionic crystals, enriching the theoretical foundation for the morphology control of HA and providing valuable insights into alcohol-induced morphology transformation.