Structure And Wettability Of Titanium Alloy Surface Textured By Femtosecond Laser

Titanium alloy has become a common material for dental and orthopedic implants.However,after long-term implantation,it may induce inflammation around the implant and even lead to implant failure.The biocompatibility of implants depends on various properties such as surface morphology,wettability,and surface chemistry.Although conventional surface modification techniques have achieved improvements in the biocompatibility of implants,they are limited by the random distribution of the prepared surface structures,the complexity of the procedural steps involved and the tendency to introduce surface contaminants.Femtosecond laser texturing has become one of the most potential surface modification technologies in recent years because of its advantages of high processing accuracy,non-contact and high flexibility.However,there are a wide variety of structures prepared by this technology,and the wetting response mechanism of different textured surfaces and the biological function of wettability remain to be revealed.In this thesis,a femtosecond laser with a wavelength of 1030 nm and a pulse duration of 300 fs was used to study the texture morphology and wettability of the titanium alloy surface at different laser parameters.The effects of surface texture and wetting modification on the proliferation and growth morphology of MC3T3 cells were preliminarily discussed.This thesis provides guiding ideas for enhancing the bioactivity of the implant surface and further improving the osseointegration rate and age range of the implant.The main research results obtained in this thesis are as follows:1.A femtosecond laser texturing experimental system was built,and the ablation threshold of the titanium alloy surface was studied by using a femtosecond laser with a wavelength of 1030 nm,a pulse duration of 300 fs,and a repetition rate of 100 kHz.The results showed that the ablation threshold of titanium alloy material under the action of single-pulse femtosecond laser was 0.256 J/cm~2,and the ablation threshold decreased with the increase of the number of femtosecond laser pulses.When the number of femtosecond laser pulses was less than 200,the ablation threshold of titanium alloy decreased rapidly with the increase of pulse number,while the ablation threshold tended to level off gradually after the number of femtosecond laser pulses reached 400.2.A series of square and diamond-shaped microstructures were prepared on the surface of titanium alloy using two femtosecond laser cross-line array scanning strategies with cross-scanning angles of 90° and 60°,respectively,and the evolution of the surface structure morphology and wettability of titanium alloy under different femtosecond laser parameters were systematically investigated.The results showed that the profile of the surface structure was more dependent on the scanning line spacing and energy density of the laser,while the number of scans mainly affected the height of the microstructure and the surface roughness.Compared with the number of laser scans,the scanning line spacing and energy density can significantly improve the hydrophilicity of the titanium alloy textured surface.3.The scanning line spacing,energy density and number of scans of the femtosecond laser were optimized,and five different micro-and nanoscale structured surfaces were prepared.The reasons for the change of surface contact angle after textured with different femtosecond laser parameters were analyzed from both surface morphology and surface chemical composition.The results showed that femtosecond laser texturing improved the roughness of the titanium alloy surface,which leaded to an increase in the actual contact area with the droplet.Meanwhile,the surface of titanium alloy was affected by high-energy laser irradiation,and a large number of metal oxides were generated,which can provide unsaturated metal and oxygen atoms as Lewis acid-base sites on the surface and rapidly adsorb water molecules leading to hydroxylation reactions in the air,both of which synergistically promoted the wetting process of liquid droplets.4.The biocompatibility study of femtosecond laser textured titanium alloy surface was carried out.The influence of structural morphology and wettability on the biocompatibility of titanium alloy surfaces was investigated by MC3T3 cell proliferation and morphological observation experiments.The results showed that femtosecond laser texturing can effectively change the growth and diffusion patterns of MC3T3 cells on the titanium alloy surface.MC3T3 cells were induced to assume an elongated spindle shape with a regular diamond-shaped microstructure surface formed by laser scanning line spacing of 25μm,energy density of 0.15 J/cm~2,and number of scans of 40,which had the best cell proliferation level.An improvement of 11.4%over the untextured surface.With the increase of energy density and number of scans,the roughness of textured surface increased,the number of cellular filamentous pseudopods decreased significantly,and the growth spreading ability decreased significantly.Compared with the untextured titanium alloy surface,the moderately hydrophilic textured surface facilitated the proliferation of MC3T3 cells.