Micro/nano fabrication of polymeric materials by DMD-based micro-stereolithography and photothermal imprinting

The revolutionary advancement in semiconductor device manufacturing promoted micro/nano fabrication technologies viable for research and applications in broader fields such as biology and optics. This dissertation is aimed at developing parallel fabrication technologies for polymeric micro/nano structures that can potentially be used in biomedical or optical devices. The objective of the dissertation is three told: a) develop and characterize a digital micro-mirror device (DMD)-based micro-stereolithographic system and explore the fabrication of hydrogel tissue engineering scaffolds, b) use the micro-stereolithographic system to fabricate microlens arrays, c) develop a photothermal imprinting technique to pattern nanostructures on the surface of polymer composites. In the first part of the dissertation, we demonstrated a simple and fast, layer-by-layer micro-stereolithographic system based on DMD dynamic photomask that allows fabrication of complex internal features along the precise spatial distribution of biological factors inside a single scaffold. Photo-crosslinkable poly(ethylene glycol) diacrylate and diamethacrylate were used as the scaffold material. In situ encapsulation of fluorescently-labeled micro-particles and cells was demonstrated. We investigated the photopolymerization process and its effects on the properties of the scaffolds. This technique could provide a powerful tool in studying progenitor cell behavior and differentiation under biomimetic, three-dimensional (3D) culture conditions. In the second part, we developed a novel fabrication technique for microlens arrays using a modified DMD-based micro-stereolithographic system. The DMD can generate high resolution images with quasi-continuous intensity gradient, thanks to its high density mirror elements with a bandwidth of 10 KHz. The projected UV patterns were simply drawn in a computer software. Topographic patterns were created in photocurable resin by spatially controlling the curing depth. Spherical microlens arrays were fabricated and their optical performance was characterized. This technique is capable of fabricating optical elements with any surface topography. In the third part, we discussed the photo-induced radical polymerization. A numerical model was established to correlate the geometry of the resulting gels and system parameters. In the fourth part, we reported a laser-assisted photothermal imprinting method for directly patterning carbon nanofiber reinforced polyethylene nanocomposite. A single laser pulse was used to melt/soften a thin skin layer of polymer nanocomposite. Meanwhile, high resolution patterns were transferred from a quartz mold to the surface of the composite.