Laser interference lithography for applications in biomedicine

Abstract

Surface modification of implant biomaterials has become the commonly used methods for the long life artificial implants and successful orthopaedic implantation. Numbers of technologies have been developed to improve the performances of artificial implants in biological systems. However, most of the technologies are associated with complex, time-consuming and not fully controllable processes, resulting in undesirable micro and nano structures. DLIL provides an effective method for nanomanufacturing of well-designed structures with controllability. The research reported in this thesis tackles the issues with particular focus on DLIL for the fabrication of well-designed micro and nano structures with functionalities including superhydrophobic, wear resistant property and biocompatibility on various biomaterials. Four-beam DLIL was developed to design and fabricate the micro and nano convex structures on silicon surfaces. Parameters such as incident angle, azimuthal angle and polarisation direction were adjusted to simulate micro patterns in period of 5.5 μm for structure design, and laser fluence and exposure duration were set to fabricate micro and nano hierarchical structures with the aspect ratio of 2-3. The CA value of 153.2° was obtained with excellent superhydrophobic property. Three-beam DLIL was used to design and fabricate micro circular dimpled structures on Co-Cr-Mo alloy. The optimal setting of incident angle, azimuthal angle and polarisation direction for three interference beams was developed to form the circular dimpled patterns in period of 8 μm. Laser fluence and exposure duration were properly adjusted to fabricate circular dimpled structures with the optimal area density of 14.8%. The modified surfaces performed the improved wear resistant property with a 64% reduction of friction coefficient and 42% enhancement of hardness. Two-beam DLIL was employed to fabricate micro grooved structures and three-beam DLIL was used to form micro dotted and dimpled structures on Ti6-Al-4V alloy by adjusting incident angle, azimuthal angle and polarisation direction. Microstructures in grooves, dots and dimples with roughness value ranged from 0.6 μm to 1.7 μm were achieved by the proper setting of laser fluence and exposure duration. MG-63 osteoblast cells were used to culture on modified Ti6-Al-4V alloy surfaces and the biocompatibility was improved by promoting cell proliferation, spreading and adhesion. In this work, DLIL were developed to modify the biomaterials including silicon, Co-Cr-Mo alloy and Ti6-Al-4V alloy for their specific functions in artificial joint. The wear resistant property has been studied on modified Co-Cr-Mo alloy for the bearing surface of artificial femoral head and the biocompatibility of modified Ti6-Al-4V alloy has been investigated for the interfaces of artificial joint stem and bone tissue. The silicon has been also used to achieve the superhydrophobic performance for the foundation preliminary study of anti-bacteria property and bacteria infection.