GRAphene-based Flexible neural Interfaces for the control of Neuroprosthetic devices – GRAFIN

GRAFIN WP1 will fabricate graphene microelectrode arrays on flexible substrates, using a novel reduced graphene oxide thin film technology developed by ICN2 that allows high charge injection capacitances. Prototypes will be produced for CNS, PNS and surface interfaces, integrating recording and stimulation capabilities within the same device. WP2 (UAB) will demonstrate in vivo bidirectional communication with peripheral nerve fibers. GRAFIN devices for the PNS will be implanted in rat nerves and biocompatibility assessed over time. Electrophysiology characterization will be performed on recording and stimulation capability of graphene-based devices. WP3 will perform studies by implanting brain electrodes in vivo and assessing the ability to stimulate primary somatosensory cortex to provide sensory feedback, and for signal recording of motor commands in the motor area. The function of CNS electrodes will be first tested in acute rat experiments by discrimination of cortical tactile neurons responding to mechanical skin stimulation. Chronic experiments will be performed by conditioning rats to electrical stimulation through graphene electrodes implanted on/in the somatosensory cortex. WP4 will perform clinical assessment of high performance surface graphene electrodes for acquisition of bioelectric signals in able-body and amputee subjects. Close-loop control of prosthetic and virtual limbs will be demonstrated using graphene electrodes to provide sensory feedback via electrical stimulation. Integration of the obtained signals to provide a realistic stimulation of the nervous system via a controlled multi-channel stimulator, as well as the recording hardware will be performed. In collaboration with the other partners, WP5 (AXO) will work on fabrication of a microstimulator to activate different subgroups of cell populations using the graphene devices and will collect data to address medical device regulations.

WP1. The prototypes of GRAFIN electrodes have been designed for the PNS and the CNS, and fabricated using the new graphene related material (GRM) as active electrode. The first devices have been delivered to UAB and BOUN partners for initial tests in experimental models. ICN2 has electrochemically characterized the new GRM, and the produced electrodes.
WP2. UAB has performed preliminary biocompatibility tests for devices implanted in peripheral nerve. No alterations were found in function and histological reaction to the GRM-containing implants. Several implantations either transversally or obliquely in rat sciatic nerves have been made to test feasibility of the implant technique, and to define the physical characteristics of the device. The first set of functional tests indicates promising results in terms of lower threshold for stimulation.
WP3. BOUN performed cortical recording and stimulation experiments in anesthetized rats with commercial surface electrodes for comparison with GRAFIN electrodes. Evoked potentials on S1 cortex were recorded due to vibrotactile stimulation of the hindpaw. BU and ICN2 participated in the design of devices and adapters for GRAFIN CNS electrodes. The first batch of CNS electrodes has been used in acute rat experiments. AXONIC stimulator has been tested, and proved to work according to its specifications.
WP4. CTH together with ICN2 has designed several electrode configurations for surface EMG recording and sensory stimulation. ICN2 is currently finalizing the design and fabrication of the surface electrodes. CTH developed a test rig to measure basic electrical characteristics of clinical standard and GRM-based electrodes before human trials.
WP5. Axonic has developed a neurostimulator SWAM (Stimulator Wireless Axonic Multipolar) designed to activate different subgroups of cell populations using the GRAFIN devices. A dedicated software, ASF (Axonic Software Framework), has been developed to program and control the stimulator.

The first prototypes of GRAFIN electrodes for nervous system interfaces have been designed to fit the planned applications. The GRM devices have been fabricated, overcoming some difficulties in material deposition and design configuration. The first devices have been already delivered to UAB and BOUN partners for initial tests in experimental models.
During the second year of the project, we will focus on the experimental studies to fully investigate biocompatibility of the new GRM devices and their functional capability for bidirectional interfacing with the PNS and the CNS
The later design of large-dimension surface electrodes based on GRM is undergoing, with good chances to be tested in human subjects in the next period.

Papers published in peer-reviewed journals
Masvidal-Codina E, Illa X, Dasilva M, …, Garrido JA, Guimerà-Brunet A. High-resolution mapping of infraslow cortical brain activity enabled by graphene microtransistors. Nat Mater 2019; 18: 280-288.
de la Oliva N, Del Valle J, Delgado-Martínez I, Mueller M, Stieglitz T, Navarro X. Long-term functionality of transversal intraneural electrodes is improved by dexamethasone treatment. IEEE Trans Neural Systems Rehab Eng 2019; 27: 457-464
Öztürk S, Devecioglu I, Beygi M, Atasoy A, Mutlu S, Özkan M, Güçlü B. Real-time performance of a tactile neuroprosthesis on awake behaving rats. IEEE Trans Neural Systems Rehab Eng 2019; 27: 1053-1062.
Ortiz-Catalan M. The stochastic entanglement and phantom motor execution hypotheses: a theoretical framework for the origin and treatment of PLP. Front Neurology 2018; 9: 748.
Günter C, Delbeke J, Ortiz-Catalan M. Safety of long-term electrical peripheral nerve stimulation: review of the state of the art. J Neuroeng Rehab 2019; 16.1: 13.

Conference papers
Garrido JA. Graphene technologies in neural interfaces. ICN2 Severo Ochoa International Conference, Barcelona (Spain), 15 Feb, 2018.
del Valle J, De la Oliva N, Rodríguez B, Delgado-Martínez I, Müller M, Stieglitz T, Navarro X. Long-term functionality of transversal intraneural electrodes is improved by dexamethasone treatment. Cell-NERF Symposium: Neurotechnologies, Leuven, Belgium, September 2018.
Navarro X. Interfacing the peripheral nervous system with advanced prostheses. Anatomical and physiological contributions. Plenary conference. International Congress of Clinical Anatomy, Madrid, Spain, 24-26 June 2019.
Güçlü B. From mechanoreceptors to perception by electrovibration. Koç University, Mechanical Engineering Dept, Istanbul, March 26th, 2019

Patents
Amorphous highly porous reduced graphene oxide film and its applications, EP19382146 (submitted Feb 27, 2019)

Loss of sensory and motor functions as a result of spinal cord injury, peripheral nerve injury or loss of a limb affects several million people worldwide, serving as a powerful motivation for the development of rehabilitation strategies that can partially restore or substitute the lost sensory - motor functions. A broad variety of electronic devices to bidirectionally interface the central and peripheral nervous system have been proposed and more are currently under development. However, given the stringent requirements for the materials and technologies to be used in these neural interfaces, progress in this field is rather slow. This project aims at exploring the potential of graphene-based technologies in neural interfaces for motor neuroprostheses. Taking advantage of intrinsic properties of graphene, such as biocompatibility, electronic performance, and easy integration within flexible substrates, we will develop graphene flexible devices to record and stimulate in the nervous system. Efficient stimulation will be based on novel highly porous reduced graphene thin films exhibiting extreme charge injection capacity. Recording with high signal-to-noise ratio will be provided by low noise CVD-grown single layer graphene field-effect transistors. Different designs will be developed to serve as extraneural and intraneural electrodes in peripheral nerve and in brain cortex. Biocompatibility and functionality will be extensively tested in chronic implants in animal models. The ability of these novel interfaces to record electrical signals from nerve and brain and to stimulate for providing sensory feedback will be determined in experimental models of nerve injury and of somatosensory cortex, in order to generate the proof of concept for the usability of interfaces for the control of neuroprostheses and for the neuromodulation of sensory dysfunctions (pain and touch) after nervous lesions. Multichannel stimulator will be developed and tailored for investigating the capability of the graphene based interface to provide sensory feedback. As a first trial in humans, surface devices with graphene electrodes will be tested on the stump of human amputees, to assess suitability for recording electromyographic signals with higher resolution than obtained with commercial electrodes, and for providing some sensory feedback. The results of the GRAFIN project will significantly push forward the forefront of graphene technology and innovation by increasing the TRL of graphene medical devices and by advancing towards clinical acceptance of graphene materials.