Alexandre Larmagnac

Stretchable electronics based on Ag-PDMS composites

Patterned structures of flexible, stretchable, electrically conductive materials on soft substrates could lead to novel electronic devices with unique mechanical properties allowing them to bend, fold, stretch or conform to their environment. For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging. Here we present a simple, cost-effective, cleanroom-free process to produce large scale soft electronic hardware where standard surface-mounted electrical components were directly bonded onto all-elastomeric printed circuit boards, or soft PCBs. Ag-PDMS tracks were stencil printed onto a PDMS substrate and soft PCBs were made by bonding the top and bottom layers together and filling punched holes with Ag-PDMS to create vias. Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles. We also demonstrate the fabrication of a stretchable clock generator.

Combinatory Electrical and Pharmacological Neuroprosthetic Interfaces to Regain Motor Function After Spinal Cord Injury

Severe lesions of the rodent or human spinal cord lead to permanent paralysis of the legs. Here, we review novel evidences suggesting that interventions combining pharmacological and electrical stimulations of the spinal cord have a high potential to promote the recovery of locomotion following severe spinal cord injuries in humans. These strategies are based on the existence of webs of circuits and receptors embedded in the spinal motor infrastructure that each modulate specific aspects of locomotor movements. We show that chemical or electrical stimulations can engage specific elements of this spinal machinery, thus resulting in distinct patterns of locomotion in paralyzed spinal rats. In turn, simultaneous chemical stimulations of neural receptors and/or electrical stimulations of multiple spinal segments can synergistically facilitate locomotor movements. These preliminary results provide a strong rationale for the development of neuroprosthetic chemotrode and electrode arrays that would enable a detailed and distributed access to the different elements of the spinal motor infrastructure. Such novel biomedical technologies may offer unparalleled potential to induce multiple and flexible locomotor states in paralyzed subjects.

Stretchable Silver Nanowire-Elastomer Composite Microelectrodes with Tailored Electrical Properties.

We introduce a photolithography process compatible with soft and rigid substrates, enabling the fabrication of complex 3D interconnected patterns of silver nanowire (AgNW) networks embedded in polydimethylsiloxane (PDMS). Dimensions of the AgNW micropatterns are controlled within the film plane by photolithography, whereas thickness is controlled via a novel and uniform deposition technique using centrifugation. We report the first systematic characterization of the electromechanical properties of such microelectrodes with finest stretchable feature of 15 μm. We observe a geometry-dependent behavior of the gauge factor not only by changing the thickness of the microelectrodes, as it has been commonly reported so far, but also by varying their lateral dimensions. The presented nanocomposites exhibited sheet resistances down to 0.6 Ω/sq, gauge factors ranging from 0.01 to 100, and stretchability above 50% uniaxial strain. This versatile process allows for the production of highly sensitive strain sensors and robust high-density stretchable conductors on a wafer scale with direct implications in mass production of stretchable electronic devices.

Electrically controlling cell adhesion, growth and migration.

We have developed a neurochip to control the adhesion and outgrowth of individual neurons by electrochemical removal of protein repellent molecules from transparent electrodes. The neurochip architecture is based on three parallel indium-tin-oxide (ITO) electrodes on a SiO(2) substrate and a photoresist structure forming a landing spot for the neuron soma and two lateral outgrowth pathways for the neurites. The whole surface was turned protein and cell repellent with poly(ethylene glycol) grafted-poly(L-lysine) (PLL-g-PEG) before enabling neuron soma adhesion by selective PLL-g-PEG removal. After the neuron has settled down a potential was applied to the pathway electrodes to permit the neurite outgrowth along pathways formed by the SU8 structure. We also show the possibility to control cell migration by small pulsed currents. Myoblasts were therefore seeded on a chemical pattern of cell adhesive PLL and cell resistant PLL-g-PEG. The PLL-g-PEG was then removed electrochemically from the electrodes to permit migration onto the cell free electrodes. Electrodes without applied current were confluently overgrown within 24 h but a small pulsed current was able to inhibit cell growth on the bare ITO electrode for more than 72 h. With both techniques, cell adhesion, growth and migration can be controlled dynamically after the cells started to grow on the substrate. This opens new possibilities: we believe the key to control the development of topologically controlled neuron networks or more complex co-cultures is the combination of passive surface modifications and active control over the surface properties at any time of the experiment.

Effects of small pulsed nanocurrents on cell viability in vitro and in vivo: Implications for biomedical electrodes

Using a custom-built, implantable pulse generator, we studied the effects of small pulsed currents on the viability on rat aortic-derived cells (RAOC) in vitro. The pulsed currents (0.37A/m(2)) underwent apoptosis within 24h as shown by the positive staining for cleaved caspase-3 and classically apoptotic morphology. Based on these findings, we examined the effects of nanocurrents in vivo. The pulse generator was implanted subcutaneously in the rat model. The electrode|tissue interface histology revealed no difference between the active platinum surface and the neighboring control surface, however we found a large difference between electrodes that were functional during the entire experiment and non-active electrodes. These non-active electrodes showed an increase in impedance at higher frequencies 21 days post-implantation, whereas working electrodes retained their impedance value for the entire experiment. These results indicate that applied currents can reduce the impedance of implanted electrodes.

Skin-Like PDMS-Based Multi-electrode Array for Epidural Electrical Stimulation to Promote Locomotion in Paralyzed Rats

Abstract- We present a skin-like multi-electrode array for in-vivo epidural electrical stimulation of the spinal cord. This is the first reported implantable electrode array using conductive PDMS as a material for stretchable conductive leads. This all-elastomeric technology provides high flexibility and stretchability to the implant, thus allowing the array to act as a second skin in close contact with the spinal cord. We also report preliminary results on the heuristic value of this novel technology to restore locomotion in rats with complete spinal cord inury.