Collagen Films as Substrates for Flexible Electronics
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With fast progress in the field of implantable electronics, pushing towards an integration of technology with humans, the biocompatibility of these electronics is a key issue. Collagen, one of the most abundant proteins in mammalian tissues, is a well-known biomaterial used in tissue engineering and bone scaffolds. Our preliminary studies showed that collagen could be used as a substrate for flexible electronics made using with E-Beam (electron beam) deposition by shadow mask. This allows you to make passive sensors with electrodes such as temperature sensors and strain sensors as well as active devices such as antennas and heaters. However, in order to make more advanced electronic devices, manufacturing strategies need to be developed in order to overcome limitations of collagen for these applications, namely processing temperature and mechanical stability in water. Transfer printing of electronics is one such strategy, using sacrificial layers of plastics, which also have their own temperature limitations. Germanium oxide is presented in this dissertation as novel water based sacrificial layer, which is amenable to high temperature processes such as the annealing and doping of Zinc Oxide (ZnO) via Pulse Laser Deposition (PLD). A number of devices presented in this dissertation include capacitors, transistors, and an integrated inverter transistor circuit. After etching in water overnight, devices made on wafers are lifted off and transferred to collagen films. By using crosslinkers, devices built on collagen films can be programmatically enhanced to resist enzymatic digestion. Cross-linked collagen was shown to have enhanced mechanical and thermal properties Encapsulated integrated electrical devices transferred onto collagen were shown to have minimal effects on cell viability on assays on MC3T3 osteoblast and A549 epithelial cells. Together, this dissertation demonstrates a manufacturing strategy of developing biocompatible integrated electrical devices on collagen.