2011 5th International IEEE/EMBS Conference on Neural Engineering, 2011
ABSTRACT This communication examines the suitability of a photo-patternable polydimethylsiloxane ... more ABSTRACT This communication examines the suitability of a photo-patternable polydimethylsiloxane (PP-PDMS) elastomer as an insulating material for implantable microelectrodes. PP- PDMS is produced by mixing a photoinitiator (2-hydroxy-2- methylpropiophenone) with the PDMS base and curing agent. Subsequent exposure to UV radiation and development of the elastomeric "photo-resist" allows for the definition of well- defined openings within the PP-PDMS film. The dielectric constants of PP-PDMS and PDMS are similar (ε ≈ 2.6, f
The mechanical mismatch between soft neural tissues and stiff neural implants hinders the long-te... more The mechanical mismatch between soft neural tissues and stiff neural implants hinders the long-term performance of implantable neuroprostheses. Here, we designed and fabricated soft neural implants with the shape and elasticity of dura mater, the protective membrane of the brain and spinal cord. The electronic dura mater, which we call 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. The soft implants extracted cortical states in freely behaving animals for brain-machine interface and delivered electrochemical spinal neuromodulation that restored locomotion after paralyzing spinal cord injury.
ABSTRACT We have developed a stretchable gold microelectrode array (MEA) that can withstand the t... more ABSTRACT We have developed a stretchable gold microelectrode array (MEA) that can withstand the torsion requirements needed for implantable neuroprosthetic interface applications. The array is composed of thin gold (sub-100 nm thick) electrodes on a soft, 120 μm thick polydimethylsiloxane (PDMS) silicone substrate with a patterned encapsulation layer. The impedance of individual electrodes was measured as a function of extreme torsion applied to the device, and was found to be relatively stable in the 15-75 kΩ range (f = 1kHz), and remained stable after 1000 torsion cycles.
Stretchable electronics (i.e., hybrid inorganic or organic circuits integrated on elastomeric sub... more Stretchable electronics (i.e., hybrid inorganic or organic circuits integrated on elastomeric substrates) rely on elastic wiring. We present a technique for fabricating reversibly stretchable metallic films by printing silver-based ink onto microstructured silicone substrates. The wetting and pinning of the ink on the elastomer surface is adjusted and optimized by varying the geometry of micropillar arrays patterned on the silicone substrate. The resulting films exhibit high electrical conductivity (∼11 000 S/cm) and can stretch reversibly to 20% strain over 1000 times without failing electrically. The stretchability of the ≥200 nm thick metallic film relies on engineered strain relief in the printed film on patterned PDMS.
ABSTRACT Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound gener... more ABSTRACT Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound generation and detection up to the fundamental thickness extension resonance. The authors show that the coupling of ferroelectrets to air alters the electromechanical resonance of the foam. In an acoustical cavity, Fabry-Perot resonances are obtained, which is in excellent agreement with the plane wave model calculations. For material assessment in airborne ultrasound applications, a figure of merit is used based on the electromechanical coupling factor and acoustical impedance of the material. The good coupling of ferroelectrets to gases results from the small acoustical impedance of the material.
Thin metal films coated on soft elastomeric foam substrates exhibit enhanced electromechanical pe... more Thin metal films coated on soft elastomeric foam substrates exhibit enhanced electromechanical performance. The open-cell foam structure conveys highly anisotropic mechanical properties within the top, thin capping elastomer at the surface of the foam. Upon stretching, large strain fields inducing cracks and folds localize above the foam cells, while the surrounding cell ligaments remain almost strain-free, enabling stable electrical conduction in the metallic coating.
Soft bioengineered surfaces offer a route towards modulating the tissue responses to chronically ... more Soft bioengineered surfaces offer a route towards modulating the tissue responses to chronically implanted devices and may enhance their functionality. In this communication we fabricate microtopographically rich and mechanically compliant silicone surfaces for use in soft neural interfaces. We observe the interaction of primary rat microglia and astroglia with arrays of tall and short (4.7 and 0.5μm) vertically oriented polydimethylsiloxane (PDMS) micropillars and a flat PDMS surface in vitro. With the pillar size and spacing that we use (1.3μm diameter and 1.6μm edge to edge), glia are found to engulf and bend tall pillars. The cytoskeleton of cells adhering to the pillar arrays lacks actin stress fibers; instead we observe actin ring formations around individual pillars. Tall, but not short pillar arrays are inhibitory to migration and spreading for both microglia and astrocytes. When compared to a flat PDMS surface and short pillar arrays, tall micropillar arrays cause nearly a 2-fold decrease in proliferation rates for both cell types. The antimitotic properties of tall pillar arrays may be useful for reducing the density of the glial capsule around brain-implanted devices.
Electrical neuromodulation of lumbar segments improves motor control after spinal cord injury in ... more 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 the therapeutic approach to continuous stimulation applied to restricted spinal cord locations. Here we developed 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 and flexor synergies with precise temporal resolution. Spatiotemporal neuromodulation therapies improved gait quality, weight-bearing capacity, endurance and skilled locomotion in several rodent models of spinal cord injury. These new concepts are directly translatable to strategies to improve motor control in humans.
2011 5th International IEEE/EMBS Conference on Neural Engineering, 2011
ABSTRACT This communication examines the suitability of a photo-patternable polydimethylsiloxane ... more ABSTRACT This communication examines the suitability of a photo-patternable polydimethylsiloxane (PP-PDMS) elastomer as an insulating material for implantable microelectrodes. PP- PDMS is produced by mixing a photoinitiator (2-hydroxy-2- methylpropiophenone) with the PDMS base and curing agent. Subsequent exposure to UV radiation and development of the elastomeric "photo-resist" allows for the definition of well- defined openings within the PP-PDMS film. The dielectric constants of PP-PDMS and PDMS are similar (ε ≈ 2.6, f
The mechanical mismatch between soft neural tissues and stiff neural implants hinders the long-te... more The mechanical mismatch between soft neural tissues and stiff neural implants hinders the long-term performance of implantable neuroprostheses. Here, we designed and fabricated soft neural implants with the shape and elasticity of dura mater, the protective membrane of the brain and spinal cord. The electronic dura mater, which we call 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. The soft implants extracted cortical states in freely behaving animals for brain-machine interface and delivered electrochemical spinal neuromodulation that restored locomotion after paralyzing spinal cord injury.
ABSTRACT We have developed a stretchable gold microelectrode array (MEA) that can withstand the t... more ABSTRACT We have developed a stretchable gold microelectrode array (MEA) that can withstand the torsion requirements needed for implantable neuroprosthetic interface applications. The array is composed of thin gold (sub-100 nm thick) electrodes on a soft, 120 μm thick polydimethylsiloxane (PDMS) silicone substrate with a patterned encapsulation layer. The impedance of individual electrodes was measured as a function of extreme torsion applied to the device, and was found to be relatively stable in the 15-75 kΩ range (f = 1kHz), and remained stable after 1000 torsion cycles.
Stretchable electronics (i.e., hybrid inorganic or organic circuits integrated on elastomeric sub... more Stretchable electronics (i.e., hybrid inorganic or organic circuits integrated on elastomeric substrates) rely on elastic wiring. We present a technique for fabricating reversibly stretchable metallic films by printing silver-based ink onto microstructured silicone substrates. The wetting and pinning of the ink on the elastomer surface is adjusted and optimized by varying the geometry of micropillar arrays patterned on the silicone substrate. The resulting films exhibit high electrical conductivity (∼11 000 S/cm) and can stretch reversibly to 20% strain over 1000 times without failing electrically. The stretchability of the ≥200 nm thick metallic film relies on engineered strain relief in the printed film on patterned PDMS.
ABSTRACT Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound gener... more ABSTRACT Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound generation and detection up to the fundamental thickness extension resonance. The authors show that the coupling of ferroelectrets to air alters the electromechanical resonance of the foam. In an acoustical cavity, Fabry-Perot resonances are obtained, which is in excellent agreement with the plane wave model calculations. For material assessment in airborne ultrasound applications, a figure of merit is used based on the electromechanical coupling factor and acoustical impedance of the material. The good coupling of ferroelectrets to gases results from the small acoustical impedance of the material.
Thin metal films coated on soft elastomeric foam substrates exhibit enhanced electromechanical pe... more Thin metal films coated on soft elastomeric foam substrates exhibit enhanced electromechanical performance. The open-cell foam structure conveys highly anisotropic mechanical properties within the top, thin capping elastomer at the surface of the foam. Upon stretching, large strain fields inducing cracks and folds localize above the foam cells, while the surrounding cell ligaments remain almost strain-free, enabling stable electrical conduction in the metallic coating.
Soft bioengineered surfaces offer a route towards modulating the tissue responses to chronically ... more Soft bioengineered surfaces offer a route towards modulating the tissue responses to chronically implanted devices and may enhance their functionality. In this communication we fabricate microtopographically rich and mechanically compliant silicone surfaces for use in soft neural interfaces. We observe the interaction of primary rat microglia and astroglia with arrays of tall and short (4.7 and 0.5μm) vertically oriented polydimethylsiloxane (PDMS) micropillars and a flat PDMS surface in vitro. With the pillar size and spacing that we use (1.3μm diameter and 1.6μm edge to edge), glia are found to engulf and bend tall pillars. The cytoskeleton of cells adhering to the pillar arrays lacks actin stress fibers; instead we observe actin ring formations around individual pillars. Tall, but not short pillar arrays are inhibitory to migration and spreading for both microglia and astrocytes. When compared to a flat PDMS surface and short pillar arrays, tall micropillar arrays cause nearly a 2-fold decrease in proliferation rates for both cell types. The antimitotic properties of tall pillar arrays may be useful for reducing the density of the glial capsule around brain-implanted devices.
Electrical neuromodulation of lumbar segments improves motor control after spinal cord injury in ... more 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 the therapeutic approach to continuous stimulation applied to restricted spinal cord locations. Here we developed 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 and flexor synergies with precise temporal resolution. Spatiotemporal neuromodulation therapies improved gait quality, weight-bearing capacity, endurance and skilled locomotion in several rodent models of spinal cord injury. These new concepts are directly translatable to strategies to improve motor control in humans.
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