Scalable, Lithography-Free Fabrication of Stretchable Microneedle Electrode Arrays for Electrophysiological Sensing

Microneedle electrode arrays have been a widely used technological platform for biomedical applications including electrophysiological sensing and electrical stimulation. They can penetrate surface layers of tissues, thereby allowing probing of physiological signals and electrical stimulation of the interior or deep tissues in a minimally invasive manner. Stretchable microneedle electrode arrays (SMNEAs) are highly desirable as dynamic bioelectrode interfaces to tissues or organs as they can follow tissue deformations, leading to enhanced recording signal quality and reduced tissue damage. However, current fabrication approaches for SMNEAs have limitations in achieving high device stretchability, high fabrication scalability, and low cost. Here we present lithography-free fabrication of SMNEA devices for localized electrophysiological sensing in deep tissues. This hybrid fabrication scheme combines 3D printing, physical vapor deposition, and transfer printing, which enables scalable fabrication of SMNEAs with over 100% stretchability. A vat photopolymerization process creates polymeric microneedle arrays with custom geometries connected by a thin layer of serpentine filaments, followed by transfer printing onto a stretchable elastomer and metallization for electrical connection. The customizable electrode geometry, high device stretchability, and fabrication simplicity make our SMNEA a promising platform for sensing or stimulation in the interior of 3D biological tissues, such as the dermis layer, muscle tissues, and cardiac tissues.