Controllable hydrophilic titanium surface with micro-protrusion or micro-groove processed by femtosecond laser direct writing

Abstract

Smart surfaces with switchable wettability have aroused enormous interest, due to their multifunction in chemistry, biology and medicine. In this paper, a controllable hydrophilic titanium surface with either micro-protrusion or micro-groove is processed by femtosecond laser. The relationship between laser processing parameters of defocus value (Df), scanning speed (Vs), power (Po) and the shape/size of structures are systematically studied. Results show that Df and Vs mainly affect the shape of structures, while Vs and Po influence size. The surface structures can change from micro-groove to micro-protrusion, for the first time, by adjusting processing parameters. After laser processing, morphology and chemical composition are analyzed. It is found that the oxygen content in the middle area of micro-protrusion is higher than the recast layer of micro-groove. The formation mechanism can be attributed to the photo-thermal effect and Marangoni convection effect. Furthermore, the surface roughness and contact angle (CA) measurement results show that the surface roughness of micro-groove array is greater than micro-protrusion array, while micro-protrusion array can promote hydrophilicity compared with micro-groove array. Moreover, the micro-protrusion array with high scanning interval (△) can maintain the hydrophilicity better than micro-groove array even after 90 days. The selected area modification of femtosecond laser processing can potentially be applied to improve biological activity in titanium implants.