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

Abstract

Restoration of motor and sensory functions in paralyzed patients requires the development of tools for simultaneous recording and stimulation of neural activity in the spinal cord. In addition to its complex neurophysiology, the spinal cord presents technical challenges stemming from its flexible fibrous structure and repeated elastic deformation during normal motion. To address these engineering constraints, we developed highly flexible fiber probes, consisting entirely of polymers, for combined optical stimulation and recording of neural activity. The fabricated fiber probes exhibit low-loss light transmission even under repeated extreme bending deformations.Using our fiber probes, we demonstrate simultaneous recording and optogenetic stimulation of neural activity in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements that correlate with electromyographical (EMG) activity.

Materials and technologies for soft implantable neuroprostheses

“…In both the brain 94,95 and spinal cord 96 , soft neurotechnology strategies also include fibre-like designs and injectable devices (FIGS 3,4). Ultrasmall carbon fibres with subcellular cross-sections insulated with parylene N and conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-coated tips enable chronic recordings of single-unit activity in rats for several weeks 94 .…”

Controlled Sub‐Micrometer Hierarchical Textures Engineered in Polymeric Fibers and Microchannels via Thermal Drawing

“…More recently, this technique was shown to also enable the fabrication of multimaterial fibers that integrate polymers or glasses but also metals, inorganic semiconductors, or nanocomposites, uniformly integrated in prescribed positions along the fiber length. [1][2][3] Such advanced multimaterial fiber systems have been proposed for applications, in optics [16][17][18][19] and imaging, [20][21][22] optoelectronics, [23][24][25][26] sensing, [27,28] energy harvesting, [29,30] bioengineering, [31,32] health care or smart textiles. [21,33,34] So far however, the use of micro-and sub-micrometer surface textures to impart fibers with novel functionalities has not been exploited.…”

Bioelectric Medicine and Devices for the Treatment of Spinal Cord Injury

“…As an alternative method to prevent the tissue response, stiff arrays are coated with an anti-inflammatory drug to reduce the activation of glia surrounding the electrode array [Asplund et al, 2014]. Other approaches include using smaller interfaces, utilizing soft polymer substrates [Lu, 2014;Canales et al, 2015;Park et al, 2015b], injectable electronics to lower the tissue footprint , and creating implants that encircle a specific target site [Plachta et al, 2013;Ordonez et al, 2014]. These technologies have not only improved the flexibility of the arrays, but also branched into arrays that target specific needs depending on the tissue location that they target.…”

“…These fibers were able to perform up to a deformation of 270° and able to bend to as small as a 500-μm radius of curvature. These probes were used to stimulate and record from both the spinal cord [Lu, 2014] and the brain [Canales et al, 2015], and the device was able to record single neuron cell activity in the medial prefrontal cortex at 1 month and continued to retain functionality after 2 months. One drawback to these designs is the requirement for a transcranial tether and mounted printed circuit board that could be damaged by the animal since it is exposed outside the body.…”