Polymer microelectromechanical systems: Fabrication and applications in biology and biological force measurements

Polymer materials are increasingly being utilized in biomedical micro- and nanotechnolgy applications. This trend has been driven by a several factors ranging from materials compatibility to cost. The manufacturing techniques used to produce these devices are considerably less mature than their silicon-based counterparts. New manufacturing techniques are needed to address unique processing challenges posed by polymer materials. To this end, we have developed a set of soft lithography based micromolding techniques for fabrication of polymer microstructures and devices from a wide range of materials. Materials include common thermoplastic polymers such as poly(methyl methacrylate) (PMMA) and polystyrene as well as functional materials such as conducting polymers. The processing techniques developed through this work are capable of producing a wide range of structures including continuous microstructured films, isolated polymer microstructures, and suspended structures. The nature of the materials and the non-cleanroom based micromolding processes makes these techniques considerably more cost effective with respect to both materials and processing costs.; In addition to developing processing techniques, characterization of the processes as well as the materials is a critical step for implementation of polymers in practical device applications. Process characterization was performed by systematically varying process parameters and evaluating the resulting microstructures using common micro- and nanoscale characterization techniques. Scanning electron microscopy, atomic force microscopy, and optical microscopy were all used to evaluate the resulting polymer structures. Nanoindentation techniques were used to characterize the mechanical properties of the materials. Elastic modulus, hardness, creep, scratch resistance, and yield strength of several polymer MEMS materials were evaluated.; Application of these techniques for development of functional devices is ultimately the goal. We have used the processing techniques that we have developed to fabricate and test three polymer MEMS devices for biological applications. The first is a microfabricated membrane system for isolation of individual cells or cell clusters. This device could be utilized in a variety of cell biology applications including single cell experimentation, cell cluster biology, and tissue engineering. The other two devices were developed for measuring low magnitude biological forces. A polymer cantilever force sensor was developed for measuring contractile forces produced by fibroblast cells. This device could be used in cell mechanobiology studies, drug evaluation, and cell-based biosensing. The final device is an adapted polymer cantilever sensor for measuring forces produced by protein aggregates known a forisomes. This unique biomaterial could be utilized as a valve or actuator in microdevices.