Chronic multichannel neural recordings from soft regenerative microchannel electrodes during gait

Reliably interfacing a nerve with an electrode array is one of the approaches to restore motor and sensory functions after an injury to the peripheral nerve. Accomplishing this with current technologies is challenging as the electrode-neuron interface often degrades over time, and surrounding myoelectric signals contaminate the neuro-signals in awake, moving animals. The purpose of this study was to evaluate the potential of microchannel electrode implants to monitor over time and in freely moving animals, neural activity from regenerating nerves. We designed and fabricated implants with silicone rubber and elastic thin-film metallization. Each implant carries an eight-by-twelve matrix of parallel microchannels (of 120 x 110 mu m(2) cross-section and 4 mm length) and gold thin-film electrodes embedded in the floor of ten of the microchannels. After sterilization, the soft, multi-lumen electrode implant is sutured between the stumps of the sciatic nerve. Over a period of three months and in four rats, the microchannel electrodes recorded spike activity from the regenerating sciatic nerve. Histology indicates mini-nerves formed of axons and supporting cells regenerate robustly in the implants. Analysis of the recorded spikes and gait kinematics over the ten-week period suggests firing patterns collected with the microchannel electrode implant can be associated with different phases of gait.

Long-term usability and bio-integration of polyimide-based intraneural stimulating electrodes

Quentin Barraud, Marco Capogrosso, Grégoire Courtine, Jérôme Gandar, Nawal Noëlle Kinany, Silvestro Micera, Natalia Pavlova, Alessandra Piersigilli, Stanisa Raspopovic, Jacopo Rigosa, Polina Shkorbatova, Sophie Marie Marthe Wurth

Stimulation of peripheral nerves has transiently restored lost sensation and has the potential to alleviate motor deficits. However, incomplete characterization of the long-term usability and bio-integration of intra-neural implants has restricted their use for clinical applications. Here, we conducted a longitudinal assessment of the selectivity, stability, functionality, and biocompatibility of polyimide-based intraneural implants that were inserted in the sciatic nerve of twenty-three healthy adult rats for up to six months. We found that the stimulation threshold and impedance of the electrodes increased moderately during the first four weeks after implantation, and then remained stable over the following five months. The time course of these adaptations correlated with the progressive development of a fibrotic capsule around the implants. The selectivity of the electrodes enabled the preferential recruitment of extensor and flexor muscles of the ankle. Despite the foreign body reaction, this selectivity remained stable over time. These functional properties supported the development of control algorithms that modulated the forces produced by ankle extensor and flexor muscles with high precision. The comprehensive characterization of the implant encapsulation revealed hyper-cellularity, increased microvascular density, Wallerian degeneration, and infiltration of macrophages within the endoneurial space early after implantation. Over time, the amount of macrophages markedly decreased, and a layer of multinucleated giant cells surrounded by a capsule of fibrotic tissue developed around the implant, causing an enlargement of the diameter of the nerve. However, the density of nerve fibers above and below the inserted implant remained unaffected. Upon removal of the implant, we did not detect alteration of skilled leg movements and only observed mild tissue reaction. Our study characterized the interplay between the development of foreign body responses and changes in the electrical properties of actively used intra-neural electrodes, highlighting functional stability of polyimide-based implants over more than six months. These results are essential for refining and validating these implants and open a realistic pathway for long-term clinical applications in humans. (C) 2017 Elsevier Ltd. All rights reserved.

Elsevier Sci Ltd2017

Soft multimodal neural interfaces for unravelling sensory neurological circuits

Frédéric Pierre Gérald Michoud

Diseases or injuries affecting the nervous system can dramatically disrupt the quality of life. Despite extensive efforts towards treating dysfunctional nervous systems, the pharmacological and electrical approaches generally involved lack the temporal and spatial resolutions needed to selectively modulate neural activity. The somatosensory system intertwines numerous neural populations with distinct functionalities, whose specific neuromodulation would be beneficial for the alleviation of chronic pain and the restoration of locomotion after spinal cord injury. This thesis aims to develop a new generation of electrical and optical neural interfaces to selectively parse the somatosensory system. At the peripheral nerve level, we proposed an optical cuff and a wireless optoelectronic system to deliver epineural optogenetic stimulations in freely-behaving mice. The former consists of a soft elastomeric cuff wrapped around the sciatic nerve and integrated into a thin optic fiber. We demonstrated consistent orderly recruitment of motor units with optical stimulations in Thy1::ChR2 mice. This optocuff represents a simple, yet efficient, solution to probe the peripheral nervous system using optogenetics. However, untethered experimentation offers more versatility for fine neuromodulation applications. Within this framework, we developed a system comprising an ultra-miniaturized wireless stimulator and a soft circumneural ÎŒ-LED array to deliver optogenetic stimulations to the sciatic nerve. This optoelectronic implant conformed to the nerveâs morphology and complied with its dynamic motion. We demonstrated the systemâs efficacy via optogenetic activation of nociceptors in TRPV1::ChR2 mice. Both the optocuff and the wireless optoelectronic system exhibited seamless bio-integration after chronic implantation, thus highlighting the benefits of soft neurotechnology for interfacing with peripheral nerves. At the spinal level, we introduced a transversal electrode array for multipolar epidural stimulation of the spinal cord. The silicone materials used for its fabrication conferred this implant with mechanical properties matching the dura mater, allowing for remarkable biocompatibility following long-term implantation. Based on the spinal cord anatomy, this implant displayed a wide distribution of neural electrodes at a single spinal level, which enabled selective recruit- ment of posterior spinal roots. This novel paradigm was implemented to a spatio-temporal stimulation protocol and demonstrated potential in restoring locomotion after spinal cord injury. Finally, we reported a soft ÎŒ-LED array to deliver optogenetic stimulations in deep spinal structures. Insertion of this thin (< 100 ÎŒm) optoelectronic implant in the mouse epidural space did not provoke tissue damages while maintaining its functionality with normal dynamic motion. As a proof-of-principle, we showed concomitant electromyographic activity with epidural optical stimulations in Thy1::ChR2 mice. This premise offers a large range of opportunities to probe the spinal circuits involved in sensory processing and locomotion. In conclusion, these selective neural interfaces are proposed as innovative tools to unravel peripheral and spinal neural circuits. This venue will support the development of relevant clinical treatments for tackling dysfunctional neural systems. Eventually, these implant concepts pave the way for the translation of fine neuromodulation therapies in humans.

EPFL2019

Spatial and Functional Selectivity of Peripheral Nerve Signal Recording With the Transversal Intrafascicular Multichannel Electrode (TIME)

Silvestro Micera, Stanisa Raspopovic

The selection of suitable peripheral nerve electrodes for biomedical applications implies a trade-off between invasiveness and selectivity. The optimal design should provide the highest selectivity for targeting a large number of nerve fascicles with the least invasiveness and potential damage to the nerve. The transverse intrafascicular multichannel electrode (TIME), transversally inserted in the peripheral nerve, has been shown to be useful for the selective activation of subsets of axons, both at inter-and intra-fascicular levels, in the small sciatic nerve of the rat. In this study we assessed the capabilities of TIME for the selective recording of neural activity, considering the topographical selectivity and the distinction of neural signals corresponding to different sensory types. Topographical recording selectivity was proved by the differential recording of CNAPs from different subsets of nerve fibers, such as those innervating toes 2 and 4 of the hindpaw of the rat. Neural signals elicited by sensory stimuli applied to the rat paw were successfully recorded. Signal processing allowed distinguishing three different types of sensory stimuli such as tactile, proprioceptive and nociceptive ones with high performance. These findings further support the suitability of TIMEs for neuroprosthetic applications, by exploiting the transversal topographical structure of the peripheral nerves.

Ieee-Inst Electrical Electronics Engineers Inc2016

Soft multimodal neural interfaces for unravelling sensory neurological circuits

Frédéric Pierre Gérald Michoud

EPFL2019

Long-term usability and bio-integration of polyimide-based intraneural stimulating electrodes

Elsevier Sci Ltd2017