Microscale Characterization of a Mechanically Adaptive Polymer Nanocomposite With Cotton-Derived Cellulose Nanocrystals for Implantable BioMEMS

A mechanically adaptive polymer nanocomposite for use as a structural material for microelectromechanical system (MEMS)-based penetrating implantable biosensors, particularly for the brain, is presented as a solution to the limited clinical implementation of such sensors. Micromechanical testing of MEMS-scale test structures was used to determine the Young's moduli of the polymer nanocomposite in both its dry rigid state (E = 2414 MPa) and its wet compliant state (E = 4.9 MPa), as well as the rate of mechanical switching upon immersion in an aqueous solution. The softening of the composite materials after implantation in the cortex of a Sprague-Dawley rat was studied by ex vivo environmentally controlled microtensile testing. A microfabrication process for producing metallized neural probes for recording of electrical signals was also developed. The results support the mechanically adaptive nanocomposite as a viable option for MEMS-based penetrating implantable biosensors.