Polymer Fiber Probes Enable Optical Control of Spinal Cord and Muscle Function In Vivo

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 6594 wileyonlinelibrary.com With the introduction of optogenetics, [ 8,9 ] a method that permits ondemand excitation and inhibition of activity in optically-sensitized neurons with light pulses, integration of photonic modules into microelectronic neural recording probes yielded closed-loop sensor-actuator devices. [ 10 ] These probes often combined optical fi bers with established neural recording technologies such as silicon multielectrode arrays, [ 11,12 ] multitrodes [ 13,14 ] and tetrodes. [ 15 ] Recently, microelectromechanical systems (MEMS) and contact printing fabrication methods allowed for innovative structures with multiple integrated modalities. [ 16,17 ] These advances in optoelectronic neural probe technologies have helped further the understanding of brain circuits and contributed to the development of therapies for neurological disorders. [ 18–20 ] Fewer studies have explored application of optogenetics in the spinal cord. [ 21–24 ] Specifi cally, despite pioneering in vitro efforts, [ 21,22 ] direct control of limb movement via optical spinal cord stimulation in a live mammal has yet to be demonstrated. The spinal cord is highly viscoelastic (elastic modulus of 0.5–1 MPa) and experiences up to ∼10% of repeated strain during motion, [ 25,26 ] presenting a challenge to combined intraspinal neural recording and optical stimulation, since the majority of neural probes and light-delivery devices are comprised of brittle materials [ 27–29 ] that may cause damage to the neural tissue and fail under repeated deformation. [ 30 ] To overcome these limitations, we engineered highly fl exible biomimetic all-polymer fi ber probes that combine an optical core for optogenetic stimulation and conductive electrodes for simultaneous neural recording.