Abstract:We introduce a new class of neural implants with the topology and compliance of dura mater, the protective membrane of the brain and spinal cord. These neural interfaces, which we called e-dura, achieve chronic bio-integration within the subdural space where they conform to the statics and dynamics of neural tissue. e-dura embeds interconnects, electrodes and chemotrodes that sustain millions of mechanical stretch cycles, electrical stimulation pulses, and chemical injections. These integrated modalities enable multiple neuroprosthetic applications. e-dura extracted cortical states in freely behaving animals for brain machine interface, and delivered electrochemical spinal neuromodulation that restored locomotion after paralyzing spinal cord injury. e-dura offers a novel platform for chronic multimodal neural interfaces in basic research and neuroprosthetics.3 Neuroprosthetic medicine is improving the lives of countless individuals. Cochlear implants restore hearing in deaf children, deep brain stimulation alleviates Parkinsonian symptoms, and spinal cord neuromodulation attenuates chronic neuropathic pain (1). These interventions rely on implants developed in the 1980s (2, 3). Since then, advances in electroceutical, pharmaceutical, and more recently optogenetic treatments triggered development of myriad neural interfaces that combine multiple modalities (4-9). However, the conversion of these sophisticated technologies into chronic implants mediating long-lasting functional benefits has yet to be achieved. A recurring challenge restricting chronic bio-integration is the substantial biomechanical mismatch between implants and neural tissues (10-13). Here, we introduce a new class of soft multimodal neural interfaces that achieve chronic bio-integration, and we demonstrate their long-term efficacy in clinically relevant applications. e-dura fabrication. We designed and engineered soft interfaces that mimic the topology and mechanical behavior of the dura mater (Fig. 1A-B). The implant, which we called electronic dura mater or e-dura, integrates a transparent silicone substrate (120µm in thickness), stretchable gold interconnects (35nm in thickness), soft electrodes coated with a novel platinum-silicone composite (300µm in diameter), and a compliant fluidic microchannel (100µm x 50µm in crosssection) (Fig. 1C-D, fig. S1-S2-S3). The interconnects and electrodes transmit electrical excitation and transfer electrophysiological signals.The microfluidic channel, termed chemotrode (14), delivers drugs locally (Fig. 1C, fig. S3). Microcracks in the gold interconnects (15) and the newly developed soft platinum-silicone composite electrodes confer exceptional stretchability to the entire implant (Fig. 1B, Movie S1). The patterning techniques of metallization and microfluidics support rapid manufacturing of customized neuroprostheses.4 e-dura implantation. Most implants used experimentally or clinically to assess and treat neurological disorders are placed above the dura mater (3,(16)(17)(18). The compliance of e-...

Stripes of thin gold films are made on an elastomeric substrate with built-in compressive stress to form surface waves. Because these waves can be stretched flat they function as elastic electrical conductors. Surprisingly, we observe electrical continuity not only up to an external strain of ϳ2% reached by stretching the films first flat (ϳ0.4%) and then to the fracture strain of free-standing gold films (ϳ1%), but up to ϳ22%. Such large strains will permit making stretchable electric conductors that will be essential to three-dimensional electronic circuits.

| Implantable neuroprostheses are engineered systems designed to restore or substitute function for individuals with neurological deficits or disabilities. These systems involve at least one uni-or bidirectional interface between a living neural tissue and a synthetic structure, through which information in the form of electrons, ions or photons flows. Despite a few notable exceptions, the clinical dissemination of implantable neuroprostheses remains limited, because many implants display inconsistent long-term stability and performance, and are ultimately rejected by the body. Intensive research is currently being conducted to untangle the complex interplay of failure mechanisms. In this Review, we emphasize the importance of minimizing the physical and mechanical mismatch between neural tissues and implantable interfaces. We explore possible materials solutions to design and manufacture neurointegrated prostheses, and outline their immense therapeutic potential. NATURE REVIEWS | MATERIALSADVANCE ONLINE PUBLICATION | 1 REVIEWS© 2 0 1 6 M a c m i l l a n P u b l i s h e r s L i m i t e d , p a r t o f S p r i n g e r N a t u r e . A l l r i g h t s r e s e r v e d .

No abstract

Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percent. The films initially form in two different structures, one continuous and the other containing tribranched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network. To accommodate the large elongation of the elastomeric substrate, the metal network twists and deflects out of the plane but remains bonded to the soft substrate. Consequently, the metal film experiences only small strains and deforms elastically without suffering fatigue.

Electrical neuromodulation of lumbar segments improves motor control after spinal cord injury in animal models and humans. However, the physiological principles underlying the effect of this intervention remain poorly understood, which has limited this therapeutic approach to continuous stimulation applied to restricted spinal cord locations. Here, we developed novel stimulation protocols that reproduce the natural dynamics of motoneuron activation during locomotion. For this, we computed the spatiotemporal activation pattern of muscle synergies during locomotion in healthy rats. Computer simulations identified optimal electrode locations to target each synergy through the recruitment of proprioceptive feedback circuits. This framework steered the design of spatially selective spinal implants and real–time control software that modulate extensor versus flexor synergies with precise temporal resolution. Spatiotemporal neuromodulation therapies improved gait quality, weight–bearing capacities, endurance and skilled locomotion in multiple rodent models of spinal cord injury. These new concepts are directly translatable to strategies to improve motor control in humans.

Human skin is capable of transducing pressures in the range of 100 Pa (light touch) to 1 MPa (full body weight bearing); common tasks such as object manipulation develop contact pressures on the order of 10 kPa. [ 21,22 ] Moreover, sensitivity of human skin to applied pressures is complex and varies widely by type of mechanoreceptor and type of stimulation (normal pressure, shear pressure, frequency, magnitude). [ 23 ] Although distributed sensing using arrays of thin-fi lm transistors on ultrathin plastic foils combined with soft mechanical sensors has also been demonstrated, [ 11,[24][25][26] most reported skin-like sensors are discrete elements. An unmet demand for truly wearable e-skin is mechanical compliance. Natural skin is soft and elastic. Electronic skins should therefore wrap over the external surface of the body and accompany movement, in particular over joints and articulations. To date, pressure sensing data gloves and tactile skins are mainly prepared with fl exible polymers [27][28][29] and conductive textiles. [ 30,31 ] These constructs conform well to developable surfaces (e.g., the arm and fi nger phalanges) but wrinkle and often fail when placed over articulations (e.g., the elbow and fi nger joints). [ 32 ] E-skins prepared entirely with stretchable materials appear as a necessary starting point. Over the last decade, multiple designs of stretchable tactile sensors using elastomers, thin fi lms, composites, [ 19,33 ] and conductive liquids [34][35][36] have been reported, but their systematic characterization in real-life conditions is often incomplete. Stretchable strain sensors are often demonstrated in complex real-life scenarios, [ 37,38 ] but in the literature related to stretchable tactile sensors, demonstrations involving dynamic states where bending and stretching of the sensors occur simultaneously are not common, likely due to the challenges of removing cross-sensitivities to strain and noise received from the body. [ 19,20,39 ] In this paper, we report on a stretchable e-skin designed to be worn over the hand, monitor live fi nger movement, and register distributed pressure along the entire length of the fi nger. The sensory skin is thin and made entirely of elastic materials, thereby can be mounted on a glove and worn without impeding hand movement ( Figure 1 ). The read-out electronics are integrated in a small printed circuit board (PCB) located immediately at the base of each fi nger. Capacitive pressure sensors combine stretchable gold thin-fi lm electrodes with porous silicone foam (Figure 1 a) and display high sensitivity across much of the large dynamic pressure range of human skin. Six adjacent pressure sensors cover the entire length of the fi nger; two soft metallic shielding layers eliminate noise and cross-sensitivity over the skin and enable multi-touch with This report demonstrates a wearable elastomer-based electronic skin including resistive sensors for monitoring fi nger articulation and capacitive tactile pressure sensors that register distributed pressure along ...

Gold thin-films (50 nm thick) on silicone membranes are reversibly stretchable. They exhibit continuous electrical conduction when pulled and relaxed by tens of percent. Here, we show that gold thin-film conductors on elastomeric substrates can withstand extensive uniaxial stretch cycling without electrical failure. The gold film develops into an interconnected network of islands, which reversibly move on the surface of the elastomer with applied strain. The resulting electrical resistance of the conductor remains finite and reproducible over 250 000 cycles to 20% applied strain.