Nano-enabled direct contact interfacing of syringe-injectable mesh electronics

Polymer-based electronics with low bending stiffnesses and high flexibility, including recently reported macroporous syringe-injectable mesh electronics, have shown substantial promise for chronic studies of neural circuitry in the brains of live animals. A central challenge for exploiting these highly flexible materials for in-vivo studies has centered on the development of efficient input/output (I/O) connections to an external interface with high yield, low bonding resistance and long-term stability. Here we report a new paradigm applied to the challenging case of injectable mesh electronics that exploits high flexibility of nanoscale thickness two-sided metal I/O pads that can deform and contact standard interface cables in high yield with long-term electrical stability. First, we describe the design and facile fabrication of two-sided metal I/O pads that allow for contact without regard to probe orientation. Second, systematic studies of the contact resistance as function I/O pad design and mechanical properties demonstrate the key role of I/O pad bending stiffness in achieving low resistance stable contacts. Additionally, computational studies provide design rules for achieving high-yield multiplexed contact interfacing in the case of angular misalignment such that adjacent channels are not shorted. Third, in-vitro measurement of 32-channel mesh electronics probes bonded to interface cables using the direct contact method shows a reproducibly high yield of electrical connectivity. Last, in-vivo experiments with 32-channel mesh electronics probes implanted in live mice demonstrate chronic stability of the direct contact interface, enabling consistent tracking of single-unit neural activity over at least 2 months without loss of channel recording. The direct contact interfacing methodology paves the way for scalable long-term connections of multiplexed mesh electronics neural probes for neural recording and modulation, and moreover, could be used to facilitate scalable interconnection of other flexible electronics in biological studies and therapeutic applications.