Flexible fibers for optoelectronic probing of spinal cord circuits

Abstract

The majority of the neural engineering efforts in the past decade have focused on brain interfaces. The searching of tools for recording and modulation of neural activity in the spinal cord limits fundamental understanding of neural dynamics in this organ. Spinal cord poses a challenge to probe design due to its fibrous structure, repeated deformation, low elastic modulus, and sensitivity to implantation procedures. This work addresses the elastic modulus mismatch between spinal cord tissue and synthetic devices by designing flexible multifunctional neural probes capable of conforming to the spinal cord geometry and mechanical properties, while providing functions for optical stimulation and neural recording. In this thesis, fiber drawing techniques are applied to produce flexible and stretchable probes. The utility of the devices for recording and optical stimulation is demonstrated in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, it is shown that the optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements. Finally, the modest dimensions and high flexibility of the devices permitting chronic implantation into the mouse spinal cord with minimal damage to the neural tissue are demonstrated. The findings of this thesis are anticipated to aid the studies of the spinal cord circuits and pave way to new directions in flexible fiber-based optoelectronic devices.