Synthesis, photothermal effects, and antibacterial properties of lanthanum-doped hydroxyapatite

Abstract

Hydroxyapatite (HA) is a weakly alkaline, bioactive calcium phosphate material with a composition similar to that of human bones and teeth. However, the high crystallinity of HA materials slows their degradation and new bone formation in a physiological environment, and their poor antibacterial properties make them susceptible to bacterial infections. Human bones contain trace amounts of rare earth elements (e.g. La, Yb, and Ce), with accumulation varying with age. La3+ in the proper concentration range promotes stem cell proliferation and differentiation. Polydopamine (PDA) has a maximum absorption wavelength up to the near-infrared region and can be used as a photothermal reagent. In this study, LaHA (La-doped HA) was prepared using a hydrothermal method with different doping amounts and pH values, and then surface-coated with PDA. This final product, LaHA@PDA, exhibited bone induction properties and photothermal stability, achieving a synergistic antibacterial effect. The results showed that the solution pH and La3+ concentration affected the La3+ doping content and surface morphology. The nanoparticles synthesised at pH = 13 were pure HA in the form of short rods, while the doping amount substantially increased by decreasing the solution pH. The pH and doping amount also influenced the photothermal effect of LaHA@PDA, with 1LaHA13@PDA (pH = 13, doping amount of 1) exhibiting the best photothermal performance. The antibacterial ability of the nanomaterial was further demonstrated through bacterial and in vitro immersion experiments, thereby demonstrating its promising applications in the biomedical field.