Preparation And Study Of Metal-based Bionic Functional Microstructure By Laser

The surface of the organism in nature has a variety of special functions. Acquiring inspiration by investigating microstructure of living beings surface, and fabricating bionic functional microstructure are one of the hotspots of biomimics. The investigation has wide application prospect in several fields such as industrial, aerospace, military, medical and daily life.In this paper, the preparation experimental system of biomimetic microstructure has been constructed with femtosecond laser and nanosecond laser. Various microstructures have been fabricated on stainless steel using the experimental system. The formed mechanism, hydrophobicity, optical character, and biocompatibility of these topography on stainless steel surface have been studied to achieve preparation and application of bionic functional microstructure. The main content and conclusion of this thesis are as follows:1. The preparation experimental system of biomimetic microstructure was constructed with femtosecond laser. Preparation of biomimetic microstructure using laser on stainless steel surface in high vacuum was investigated. The formed mechanism of microstructure using single pulse and multiple pulses was studied. Large area multi-scale microstructure has been obtained by scanning with femtosecond laser. With these experiments, the effect of laser parameters on the microstructure was determined. The results of these experiments suggest that the single-pulse laser ablation diameter depends on single pulse energy and single pulse energy threshold. Multiple pulse experiment indicates that the energy threshold of specific microstructure decreases with the number of laser pulses increasing. With low laser fluence, we fabricated typical laser-induced periodic surface structures (LIPSS) on the submicron level. With laser fluence increasing, we fabricated periodic ripples and periodic cone-shaped spikes on the micron scale, both covered with LIPSS. These surface topography are micro- and submicron double-scale structures. By comparing topography at the starting point and that at the end point, it is obvious that microstructure of high laser fluence can only lead to roughness on the micron scale instead of LIPSS. This controllable multi-scale microstructure preparation and investigation provide abundant choise for bionic functional microstructure fabrication.2. Based on the geometry analysis method, an influence model of multi-scale microstructure on wettability was established. The wettability of the stainless steel surface, after microstructured with femtosecond laser flowed silanizing, was examined. The results suggest that with laser fluence increasing, the superhydrophobicity of the microtructured surface is enhanced, particularly the lotus-leaf-like papillary double-scale structure surface of high laser fluence has extremely high apparent contact angle (CA) and extremely low sliding angle (SA). The uniformity between the calculated value and the experimental result indicates that the influence model can be used to guide designing multi-scale superhydrophobic microstructure.3. Through a large area microstruture fabricating method comprising two scanning with different fluence femtosecond laser, a multi-scale light trapping structure with cone-shaped micro-spikes and submicro-particles was obtained. The microstructure surface has an extremly low reflectivity in the wavelength range of 200-900 nm. The XRD result suggests that strongly enhanced optical absorption of the stainless steel surfaces should be attributed to the micro- and nano-structures on the surfaces rather than the surfaces' chemical changes. We established an optical absorption model of multi-scale microstructure surface. Based on the model, the light trapping mechanism of the microstructure was analysed. The preparation experimental system of microstructure was constructed with nanosecond laser. The reflectivity of the microholes fabricated on the stainless steel surface using nanosecond laser was examined. The effect of laser parameters on the microstructure and light trapping function was determined. We designed a light trapping structure of microholes quincuncial distributing on the sample surface. The experimental result suggests that the structure surface has an extremly low reflectivity. The preparation and study of light trapping structure on metal have significant research value and application prospect in the field of optical response materials. 4. Blood compatibility for stainless steel superhydrophobic surface microstructured using femtosecond laser was studied through the platelet adhesion experiment, dynamic coagulation and hemolysis test experiment. The results of these experiments suggest that the microstructures on the sample's surface can significantly decrease the number of adhered and activated platelets, extend the dynamic clotting time and decrease haemolysis ratio. In addition, we investigated the function of the microstructure to blood compatibility from the point of superhydrophobicity.5. We established a contact guidance model to reveal how the microstructure can influence cell growth and attachment. The model was validated by cell culture experiment. The results are in good agreement with the predictions, suggesting that the LIPSS have significant contact guidance effect, which was enhanced with extending of the cell cultured time. In addition, the LIPSS could increase the speed of the cells adhesion and proliferation. The period of the LIPSS fabricated using femtosecond laser is much smaller than the common cell size. Therefore, the microstructure can be used to implement a variety of cell adhesion, proliferation and motion control. The study provides a theoretical guidance for multi-scale biomimetic microstructure surface in biomedical applications.