Femtosecond laser nano-fabrication and its biomedical applications

This dissertation aims to develop a new technique for fabrication of three-dimensional (3-D) interwoven nanofibrous platforms using femtosecond laser ablation of solids in ambient conditions.;Later, potential practice of the proposed technique for integration of nanostructures on transparent platforms as well as inside microstructures toward device fabrication is investigated. Presented studies show that integrated nanostructure inside microchannels can be fabricated in one single step using this technique.;Finally, to address the potential use of the nanostructures for biomedical application, several studies are performed to evaluate the bioactivity and biocompatibility of the nanostructures. The fabricated nanostructures incorporate the functions of 3-D nano-scaled topography and modified chemical properties to improve osseointegration, while at the same time leaving space for delivering other functional agents. In vitro experiments reveal that the titania nanofibrous platforms possess an excellent bioactivity and can induce rapid, uniform, and controllable bone-like apatite precipitation once immersed in simulated body fluid (SBF). Furthermore, the influence of synthesized titanium platforms on the in vitro proliferation and viability of osteoblast-like MC3T3-E1 cells and NIH 3T3 mouse embryonic fibroblasts is investigated. The results from in vitro studies reveal that the platforms possess excellent biocompatibility and significantly enhance proliferation of both cell lines compared to the untreated titanium specimen. The cell population increases consistently with the density of nanofibrous structures. This approach of nano-engineering 3-D architectures suggests considerable perspective for promoting material interfacial properties to develop new functional biomaterials.;In the first part, the mechanism of ablation of solids by multiple femtosecond laser pulses in ambient air is described in an explicit analytical form. The formulas for evaporation rates and the number of ablated particles for laser ablation by multiple pulses as a function of laser parameters, background gas, and material properties are predicted and compared to experimental results. Later, the formation mechanism of the nanofibrous structures during laser ablation of targets in the presence of air is discussed. The results indicate that femtosecond laser ablation of solids at air background yields crystalline nanostructures. It's also shown that this technique allows synthesis of 3-D nanostructures on a wide range of materials including synthetic and natural materials.