Abstract:

To construct a structure with a structure-inducing function favors the personalized design and processing of the implant. Pulse lasers provide convenient conditions for the preparation of functional structures. The laser with a wavelength of 355 nm and pulse width of 50 ns was employed to prepare the structure with cauliflower-like (C_f), sputtered droplets (S_d), and lattice (L_t) characteristics. We analyzed the influence of laser process parameters on the formation of morphology, roughness, surface chemical composition (X-ray photoelectron spectroscopy, XPS), phase, and wettability of titanium alloys. We ascertained the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) on C_f, S_d, and L_t structures. The results showed that multiple depositions, aggregation, and oxidation of droplets with a thick oxide layer played an essential role in forming the C_f. With the reduction of scanning speed (v) and pitch (D_y), pollutants containing O-C=O were removed, and the chemical composition of the surface gradually transformed from Ti, Ti₂O₃, and TiO₂ to complete TiO₂. The rough C_f structure had super-hydrophilic and underwater oleophobic properties, and the near-surface was mostly rutile. Nevertheless, the high interfacial tension and fractal dimension inhibited cell adhesion and proliferation. Interestingly, the stem cells had outstanding osteogenic differentiation on the surface of the S_d structure with higher hardness (450 HV) and appropriate roughness (S_a=1 μm). The L_t had a gradient of roughness and hardness at low laser spot overlap. Stem cells adhered and migrated to the ablation ring under locally amplified traction, and there was excellent osteogenic differentiation through mechanotransduction.

Key words: Laser ablation, Ti6Al4V, Surface topography, Wettability, Biocompatibility