Team "Wireless Neural Implants"

Research topics

Neural implants are tools to interface the nervous system with both high temporal and spatial resolution allowing to decipher brain functions and behaviours with high accuracy. The main challenge in this field is to build an implant that can record and stimulate the neurons over decades without any degradation of the communication between the neurons and the electrodes. This implies many tough requirements for the devices to be implanted. Mainly: 1. high sensitivity with electrode below 25µm, 2. high biocompatibility, 3. local and focal stimulation with electrode below 25µm, 4. low footprint, 5. easily implantable .

Our team aims at addressing most of these challenges through the development of wireless and battery free strategies that use ultrasound to power and communicate with the implants. Following the pioneering works made by teams from Berkeley in the mid 2010’s, we are developing our own neural implant based on advanced electronic material such as diamond, graphene and PEDOT combined to piezoelectric components in order to stimulate and record neural activity as well as monitoring neurotransmitters with implantable devices below 400µm.

Another part of our activity consists in developing and testing novel rigid and flexible tethered implants as well as implantation strategies to ease their implantation surgery.

The team is thus gathering a wide range a scientific and technical skills ranging from the design of printed circuit board, electrochemistry, clean room fabrication, instrumentation software design, implantation surgery, electrophysiology and neural data analysis.

Currently team is to pushing the use of these technologies for neural circuit reformation after a nerve injury in collaboration with the teams of Homaira Nawabi and Stéphane Belin, experts in this field.

Technics

Clean Room Facility (PTA Grenoble and ESIEE Paris): In collaboration with Lionel Rousseau (ESIEE Paris, ESYCOM lab CNRS-Univ Gustave Eiffel), we develop our own lithography mask design and sets our microfabrication parameters to build new type of implants. The clean room fabrication is partly made at the PTA in Grenoble but mainly at ESIEE Paris where Dr Rousseau’s team fabricate implantable devices on 6” wafers for mass production.

Electrochemical techniques: We developed an electrochemical characterization set up that can perform and automatize standard electrochemical techniques such as electrodeposition, cyclic voltammetry, impedance spectroscopy on 64 electrodes sequentially (upgradable to 128). These characterizations are at the art of neural implant with electrode array since they predict the performances of the electrode for both stimulation and recording as well as their aging.

Transistor array characterization set up: We can test up to 16 transistors in parallel to assess their performance for neural recording as well as detection with neurotransmitters. The flexible solution-gated field effect transistors were proved to be very interesting sensors for neural recording allowing for wide band (DC to few kHz) as well as multiplexing strategies to reduce the number of wires required to connect the implant.

In vivo and in vitro electrophysiology set ups for extracellular recording and neural stimulation (adapted for wireless and battery free technologies): The team has 2 (soon 3) IntanTech RHS stimulation systems that can record and stimulate with up to 128 electrodes. The in vitro set is coupled to a Dragon Fly Imaging system for the team of Homaira Nawabi to combine live optical imaging such as calcium imaging. The system is also being modified to encompass an ultrasonic probe for wireless and battery free simulation and recording.  We use these set up to test novel tethered implant technology and compare them to commercial device in acute and chronic experiments. Our aim is to build a databank comprising strength and drawbacks of all the implants we test. We develop also developed a card to use the RHS with neural transistors.

Wireless and Battery-free technologies characterization set ups: To build and characterize the wireless and battery free devices, we develop a unique set ups that combine, a laser interferometer, a home-made impedance spectrometer, a 3D motorized positioner, a signal generator card, a home ultrasonic pulse echo system and a high speed data acquisition card. This combination allows to measure, the echo amplitude and the deformation of a piezoelectric device as well as the state of a variable load connected to the piezo. Two of this parameters can be recorded at frequencies up 24MHz. A second set up has also been developed without the laser interferometer.

Fast Cyclic Voltammetry for neurotransmitters detection: We are building a set up to perform in vitro and in vivo fast scan cyclic voltammetry to detect neurotransmitters such as dopamine, serotonine, norepinephrine… The action is coordinated with the team of Sebastien Carnicella who studies addiction on preclinical model.

Electronic and mechanical design and workshop: We need to constantly develop custom printed circuit board (PCB) and mechanical adaptor either for the PCB or the chronic implantation surgery. We design PCBs and mechanical parts use standard open source software. We also participate to the development of a dynamic electronic and mechanical workshop at GIN, mainly with a resine 3D printer and Silver ink printer.

Neural Data Analysis: We use and adapt open source python-based code (neo, spike-interface, ephyviewer, tridesclous elephant) to analyse and visualize the data collected during the acute and chronic recordings.