Three-Dimensional Polymeric Capillary Network: Fabrication and Applications

Micro capillary networks widely exist in nature in forms of mass transport pathways, such as blood vessels. However their complicated geometry and the extra fine small features bring a great challenge to their potential applications in term of fabrication. To overcome the fabrication challenge, we presented in this thesis a novel method to fabricate fully three dimensional (3D) microstructures and moving parts using partially crosslinked polymer as sacrificial supports. This was realized on a projection microstereolithography (PmuSL) which produced both the micro structure and the sacrificial part simultaneously using digital grayscale images. To establish the selectivity of the etchant to the partially crosslinked sacrificial parts, we measured the etching rate as a function of photo-crosslinking light intensity and the light exposure time. As one of the applications of polymeric capillary network, here we showed the implementation of polymeric capillaries coupled with numerical simulation to enhance the mass transport in 3D cell culture. A set of poly (ethylene glycol) micro-fabricated bioreactors were demonstrated with PmuSL technology. We observed both experimentally and numerically the regulation of metabolism in the growth of yeast cells and Chinese hamster ovary cells by controlling the density of micro-capillaries. In an effort to increase the response speed of a polymeric hydrogel device during solvent actuation, we also reported on the design, analysis, fabrication and testing of several novel polymeric devices. We introduced a capillary network into polymeric devices in such a way as to dramatically increase the rate of long-range solvent transport (compared with diffusion-based mechanisms), while also providing a means to locally control the swelling of polymeric hydrogel. We realized control of surface-oriented swelling in a curved polymeric beam, which also affected its bending direction. Compared with traditional silicon MEMS devices, using this method we achieved much higher actuation displacement with respect to the length of the beam without sacrificing the actuation speed. To further increase the transient response speed, we introduced the elastic instability into our beam design. Combined with a design criteria analysis based on beam bending theory, we proved in our experiment the existence of a critical value for a dimensionless parameter that determined the buckle of a curved beam.