Park, H.-G. | bioRxiv Science

bioRxiv2023

Injectable ventral spinal stimulator evokes programmable and biomimetic hindlimb motion

Spinal cord neuromodulation can restore partial to complete loss of motor functions associated with neuromotor disease and trauma. Current technologies have made substantial progress, but have limitations as dorsal epidural or intraspinal devices that are either remote to ventral motor neurons or subject to surgical intervention in the spinal tissue. Here, we describe a flexible and stretchable spinal stimulator design with nanoscale thickness that can be implanted by minimally-invasive injection through a polymeric catheter to target the ventral spinal space of mice. Ventrolaterally implanted devices exhibited substantially lower stimulation threshold currents and more precise recruitment of motor pools than comparable dorsal epidural implants. Functionally relevant and novel hindlimb movements were achieved via specific stimulation patterns of the electrodes. This approach holds translational potential for improving controllable limb function following spinal cord injury or neuromotor disease.

bioengineering↗

bioRxiv2023

Stitching flexible electronics into the brain

Understanding complex neuronal networks requires monitoring long-term neuronal activity in various regions of the brain. Significant progress has been made in multi-site implantations of well-designed probes, such as multi-site implantation of Si-based and polymer-based probes. However, these multi-probe strategies have been limited by the sizes and weights of interfaces to the multiple probes and the inability to track the activity of the same neurons and changes in neuronal activity over longer time periods. Here, we report a long single flexible probe that can be implanted by stitching into multiple regions of the mouse brain and subsequently transmit chronically-stable neuronal signals from the multiple sites via a single low-mass interface. We implanted the probe at four different sites using a glass capillary needle or two sites using an ultrathin metal needle. In-vitro tests in brain-mimicking hydrogel showed that multi-site probe implantations achieved a high connection yield of >86%. In-vivo histological images at each site of probes, implanted by stitching using either glass capillary or ultrathin metal insertion needles exhibit seamless tissue-probe interfaces with negligible chronic immune response. In addition, electrophysiology studies demonstrated the ability to track single neuron activities at every injection site with chronic stability over at least one month. Notably, the measured spike amplitudes and signal-to-noise ratios at different implantation sites showed no statistically significant differences. Multi-site stitching implantation of flexible electronics in the brain opens up new opportunities for both fundamental neuroscience research and electrotherapeutic applications.

bioengineering↗