|Title:||Optical µ-printing of polymer 3D micro-optics/components for opto-bio-microsystems|
|Advisors:||Zhang, A. Ping (EE)|
Tam, Hwa-yaw (EE)
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Electrical Engineering|
|Pages:||150 pages : color illustrations|
|Abstract:||Bio-microsystems or biochips are an ensemble of microfluidic systems with bioassay and manipulation micro-components and have many advantages ranging from low expense and high throughput to miniaturization and multifunction, which thus promise great potentials in e.g. biomedical diagnostics and tissue engineering. Recently, optical micro-devices have been demonstrated as a promising component to be integrated within bio-microsystems for a new generation of biochips, called opto-bio-microsystem. Compared with conventional bio-microsystems, it has potentials in ultrasensitive measurement of variations of cellular phenotypes and biomolecules and provides a new technology for study cell behavior. In this thesis, two kinds of polymer optical micro-devices, i.e. top-lensed microlens array and 3D μ-printed microlaser biosensors, and a cellular-scale 3D microscaffold array are developed for bio-microsystem applications. Firstly, polymer microlens arrays with lens-on-lens structures were designed and fabricated by using custom-built digital mirror devices (DMD)-based optical μ-printing technology. Top-lensed microlens (TLML) were designed to achieve special focal structures with either elongated focal length or two distinct foci. For precise fabrication of the complex profiles, the relation between the exposure dose of UV light and cured depth of photopolymer was studied, which can be utilized to correct the bitmaps of dynamic exposure schemes of the microlenses. We experimentally demonstrated that the TLML with elongated focal structure has a depth of focus at half maximum of 767.11 μm, and another TLML has two separate foci with a gap of 280 μm. The microlenses with the capability of advanced beam shaping have potentials in integration of biochips for fluctuating target detection. Secondly, polymer optical whispering-gallery mode (WGM) resonator laser sensors were 3D printed and integrated into an optofluidic biochip for detection of vascular endothelial growth factor (VEGF). By using the bitmaps with corrected exposure dose, three groups of optical microresonators with suspended microdisks of different radius, whose quality (Q) factor can reach around 9800, were successfully fabricated. By coating a thin layer of gain material, the WGM resonators can support lasing operation with very low threshold (around 0.2 nJ). The microlasers were then integrated into a microfluidic chip to achieve an optofluidic platform for enzyme-linked immunosorbent assay (ELISA) processing. Such an ELISA biochip can detect VEGF at the detection limit as low as 17.8 fg/mL. Lastly, 3D cellular-scale microscaffold arrays with various dimensions and combinations were designed and fabricated by using custom-built optical 3D μ-printing technology for 3D cell culture. Single-cell-size cubic microscaffolds were fabricated and utilized to facilitate cells to spread along the suspended beams of microscaffolds. It is found that with the increasingly top-opening area of the cubic microscaffolds, the area of cell spreading will be larger, which will enhance the mechanosensing signaling, and hence promote osteogenesis in cell differentiation. Furthermore, on the top of the suspended beams of 3D microscaffolds, bioactive material (gelatin methacrylate) were selectively patterned, which enabled controlled cell adhesion and spreading in 3D microenvironment.|
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