Metallized printed microstructures for precision biomedical recording and stimulation

Abstract

Implantable electrodes are the central tool for many techniques and treatments in biomedical research and medicine. There is a trend in these tools towards arrays of tissue-penetrating microelectrodes with low geometric surface areas for purposes of both increasing the specificity of recording/stimulation and reducing tissue damage due to insertion trauma and reactive immune responses. However, smaller electrode sizes present new constraints – both difficulty in fabrication as well as significant limitations on effective charge storage/injection capacities as well as higher impedances, making smaller electrodes less capable of easily passing charge safely and efficiently. Fabricating structures on the scale of tens of microns and below poses significant challenges compared to well established machining at larger sizes. Established sets of techniques such as classic MEMS processes are limited to relatively specific shapes, with significant limitations in their ability to produce curved surfaces and surfaces which are not composed of highly distinct stepped layers. We developed a method for improvement of impedance and charge storage capacity of flat electrodes without affecting geometric surface area (footprint) using Resonant Direct Laser Writing (rDLW) 3D printing to fabricate high surface area 3D structures, which were then rendered conductive. The ability to perform DLW printing at a range of laser powers on opaque reflective surfaces is demonstrated, previously a known limitation of direct laser writing. This is demonstrated through a variety of example prints. This capability opens the door to many new possibilities in micron resolution polymer printing which were previously inaccessible, with potentially far reaching ramifications for microfabrication.