Fabrication process development of arrays for strain and pressure sensing with a flexible ionic conductive biopolymer

Healthcare monitoring activities often require a device capable of recording high definition signals from muscles, nervous tissue and skin. The ability to detect local small changes on the curvilinear and dynamic surface of tissues in motion, is essential for an accurate understanding of body physiology. While rigid microelectronic often fails in this attempt because of the mechanical mismatch with soft tissues, a standard solution for this challenge relies in the use of electrode arrays fabricated on flexible platforms, in order to acquire the electrical potential at the interface of skin and biological tissue. This master thesis describes the development of a microfabricated array that, in contrast with the traditional approach, aims to measure the minute bio-mechanical pressure and strain stimuli, using SiPo (Silk & Laponite) as an active substrate. Manufactured from silk fibroin and a nanoclay (Laponite RD), SiPo is a newly developed ionic conductive protein based polymer, which is highly adhesive, flexible and fully biocompatible and bioresorbable. In order to record and evaluate the resisitive and capacitive properties of SiPo at the microscale, and to characterize its response and gauge factor (GF) when subjected to pressure and strain stimuli, an array of interdigitated electrodes pairs was designed and built, using cleanroom micro-fabrication techniques. Following a "top-down" approach, we started using as a supporting substrate a flexible and stretchable membrane of polydimethylsiloxane (PDMS), that is compatible and compliant with SiPo casting. The membrane is first patterned with gold micro electrodes and connections using a low-stress transfer technique of rigid metal thin films on soft silicon-based polymers, which involve an organo- and ammine- silane functionalization. Alongside, we followed an alternative strategy to fabricate the metal electrodes and signal connections directly onto the elastomer through shadow mask patterning, and by exploiting the adhesive bond forces between silk fibroin and gold thin films we were able to transfer the metal to the bio-polymer. Afterwards, the material and the fabricated structures were further characterized to evaluate the performances and properties for in-vivo and tissue-contact application. The results of this work could act as a pathfinder for the development of an high-density pressure and strain sensitive device for conformal 3D mapping of the heart surface and for cardiovascular disease monitoring.