Nucleation and biomineralization of apatite on titanium-based material surfaces is crucial to improve surface biocompatibility, osseointegration, and rapid bone ingrowth in biomedical applications such as joint replacements. This work is designed to provide new insights on the molecular processes in the initial nucleation of calcium phosphate on TiO₂ surface by means of classical molecular dynamics (MD) simulations. Aggregation of calcium and phosphate ions in pure aqueous solution was studied, and the free energies during ion adsorption was investigated by the calculation of PMFs. The MD results suggest surface hydroxylation rate and nanotopographies of TiO₂ substrate contribute significantly to the initial nucleation of calcium phosphate. Our simulations suggest that surface hydroxyls on TiO₂ provide active sites for the aggregation of calcium phosphate. Both calcium ions and phosphate ions could bind to the hydroxylated TiO₂ surface directly or indirectly via the first water layer. Surface nanotopographies (e.g., grooves or ridges) seem to be able to restrict the diffusion of calcium ions and phosphate ions, hence offering more opportunities for adsorption by trapping ions inside channels. Therefore, it can be inferred that apatite may be formed more favorably on porous or concave surfaces.

中文翻译：

---

TiO ₂基质上磷酸钙初始成核的分子研究：表面纳米形貌的影响

钛基材料表面上磷灰石的成核和生物矿化对于改善生物医学应用（例如关节置换）中的表面生物相容性，骨整合和快速的骨向内生长至关重要。这项工作旨在通过经典的分子动力学（MD）模拟提供有关TiO ₂表面上磷酸钙初始成核的分子过程的新见解。研究了纯水溶液中钙和磷酸根离子的聚集，并通过计算PMFs考察了离子吸附过程中的自由能。MD结果表明TiO _2的表面羟基化速率和纳米形貌底物对磷酸钙的初始成核有显着贡献。我们的模拟表明，TiO ₂上的表面羟基为磷酸钙的聚集提供了活性位点。钙离子和磷酸根离子都可以直接或间接通过第一水层与羟基化的TiO ₂表面结合。表面纳米形貌（例如，凹槽或脊）似乎能够限制钙离子和磷酸根离子的扩散，因此通过将离子捕获在通道内而提供了更多的吸附机会。因此，可以推断出磷灰石可以更有利地形成在多孔或凹入表面上。