Unnatural hearing—3D printing functional polymers as a path to bio-inspired microphone design

In nature, auditory organs are rarely passive transducers of their environment. Highly localized material properties and complex interdependencies mechanically filter the acoustic signal, reducing the burden of signal processing to the nervous system. Capturing these design traits in engineered systems is important for device miniaturization and energy efficiency, but manufacturing a functional electromechanical device, like a microphone, at the microscale using biologically inspired 3D designs and highly anisotropic materials remains extremely challenging. Our research uses one-pot synthesis methods for a variety of tissue-like hydrogels, polymers, and functionalized piezoelectric composites that are compatible with vat-based photopolymerization 3D printing. These materials can be used to produce reproductions of microphone designs using functional photopolymers for the conductive, piezoelectric, elastomeric, and structural elements. Used to produce mimetic structures, for example, in a device based on the directional sensitivity of the parasitoid fly Ormia ochracea, we can reproduce O. ochracea’s sound localization capability while addressing the impracticalities in frequency, sensitivity and scale of MEMS or micromachined designs. Each of the materials used has a unique set of acoustic, electrical and mechanical properties which can be tailored by altering the synthesis process leading to a truly vast design space which we are only beginning to explore.