Elastomeric Substrate Research Articles

Stretchable Enzymatic Biofuel Cells Based on Microfluidic Structured Elastomeric Polydimethylsiloxane with Wrinkled Gold Electrodes

AbstractVarious sensors and electronic devices are recently developed to monitor human health in mechanically flexible or even stretchable forms for intimate contact with non‐flat curvilinear surfaces of the human body. For successful operation of these devices, finding a proper way to electrically power them is very important. In this work, glucose/oxygen fueled enzymatic biofuel cells (EBFCs) based on microfluidic structured elastomeric polydimethylsiloxane substrate with wrinkled gold (Au) electrodes are suggested for power supply. For doing that, firstly, bottom surface of microfluidic channel is covered with buckled Au electrodes for stretchability. By microfluidic design showing capillary imbibition through fluidic channels, loading of catalyts is promoted. Interestingly, buckled Au electrodes induce much better anodic and cathodic reaction rates than those of non‐buckled Au electrodes by 25% and 33%, respectively. This is because surface area and the amount of catalyst loading in electrodes increase by Au wrinkling. In evaluations of EBFCs using the buckled Au electrodes, maximum power density reaches 7.1 ± 0.64 µW cm−2, while they show decent performance of 5.4 ± 0.49 µW cm−2 even under external stretching. Taken together, it is corroborated that such proposed stretchable EBFCs are alternative for providing electrical power in wearable or implantable devices.

Piezoresistive Performance of a Compliant Scalable Sensor Made of Low‐Cost Exfoliated Graphite Polymer Composites

Compliant sensors have drawn considerable interests in human–robot interactions. However, it is still challenging to obtain reliable and reproducible performance at reduced costs, especially for scaled‐up sensing applications. This work investigates the piezoresistive performance of a low‐cost, scalable sensor, which is made by spray coating exfoliated graphite natural rubber latex composites (EG/latex) over an elastomeric substrate. The EG/latex sensor provides a uniform distribution in the sheet resistance (variation below 4%) over a large 10 cm × 10 cm area. The stabilized piezoresistive response under cyclic tests is found highly related to both the filler concentration and the strain region. The 8 wt% and the 10 wt% sensors show nonlinear piezoresistive response, while the 25 wt% sensor exhibits the best linearity with a high gauge factor (7.6) and the lowest hysteresis (0.043) under a maximum strain of 60%. The distinct piezoresistive behavior is found attributed to the different levels of microbreakage under the applied strain. Scalable sensing performance is demonstrated on a hand‐size glove spray‐coated with 25 wt% EG/latex. Effective localization of contacts over the continuous sensing glove is achieved via the technique of electrical impedance tomography, validating the potential of the cost‐competitive EG/latex sensor for scalable sensing applications.

Deposition and evaluation of thermoplastic polyurethane on paper substrate for test specimen production

This work presents the development and characterization of a process for manufacturing test specimens using thermoplastic polyurethane (TPU) on paper substrates, which serve as elastomeric substrates for the manufacturing of piezoresistive sensor devices using the Graphite on Paper (GoP) technique. The study of piezoresistive sensor elements is based on their behavior in response to physical stimuli such as mechanical stress or compression, resulting in variations in electrical resistance obtained from the deposition of graphite films on paper, combined with the elastomer. By leveraging the piezoresistive effect of graphite, innovative technological solutions are sought, enabling the creation of different types of sensors for measuring and monitoring a wide range of physical quantities. The proposed process utilizes commonly available materials in the market and offers a low-cost alternative compared to traditional techniques used for semiconductor-based devices. To create the test specimens, a perforated matrix made of polylactic acid (PLA) was produced using 3D printing, with dimensions specified in ISO 1924-2/2008, and a thickness limitation of 2 mm. TPU is deposited into the perforated grooves of the developed matrix on the paper substrate, filling the spaces intended for the addition of the elastomeric polymer. The deposition process is carried out similar to silk-screen printing, ensuring uniform thickness of the test specimens. The curing process takes place over a period of 48 h at room temperature under the weight of granite structures covered with PVC sheets. After curing, the test specimens are demolded. The obtained results consist of TPU + Paper strips with an average thickness of approximately 2.1357 mm, with a mean thickness variation of 0.10688 mm, representing an average variation of 4.947 % among the strips. By disregarding the highest and lowest results from the measurement series, samples with an average thickness of 2.1327 mm and variations of 0.09250 mm were obtained, representing an average thickness variation of 4.328 %. These results are promising for the development of flexible sensor devices for applications in industrial equipment, soft robotic systems, healthcare, and bioengineering fields.

Photografting of Surface-assembled Hydrogel Prepolymers to Elastomeric Substrates for Production of Stimuli-Responsive Microlens Arrays.

Hydrogels have emerged as prototypical stimuli-responsive materials with potential applications in soft robotics, microfluidics, tissue engineering, and adaptive optics. To leverage the full potential of these materials, fabrication techniques capable of simultaneous control of microstructure, device architecture, and interfacial stability, i.e., adhesion of hydrogel components to support substrates, are needed. A universal strategy for the microfabrication of hydrogel-based devices with robust substrate adhesion amenable to use in liquid environments would enable numerous applications. This manuscript reports a general approach for the facile production of covalently attached, ordered arrays of microscale hydrogels (microgels) on silicone supports. Specifically, silicone-based templates were used to: i) drive mechanical assembly of prepolymer droplets into well-defined geometries and morphologies, and ii) present appropriate conjugation moieties to fix gels in place during photoinitiated crosslinking via a "graft from" polymerization scheme. Automated processing enabled rapid microgel array production for characterization, testing, and application. Furthermore, the stimuli-responsive microlensing properties of these arrays, via contractile modulated refractive index, were demonstrated. This process is directly applicable to the fabrication of adaptive optofluidic systems and can be further applied to advanced functional systems such as soft actuators and robotics and 3D cell culture technologies.

(Invited) highly Stretchable Self-Powered Sensors Enabled By Vertically-Assembled 2D Materials

Future electronics, such as human health monitoring systems, require highly stretchable strain sensors applicable to various types and ranges of motions. Two-dimensional (2D) materials exhibiting superior mechanical properties have a potential to achieve high range of strain compared to conventional devices and also realize self-powered sensing. In this talk, we present self-powered strain sensor with large stretchability enabled by graphene electrode layers and molybdenum disulfide (MoS2) active layer. In order to maximize the energy harvesting ability, flexoelectric effect was adopted in our device design. Flexoelectric effect induces an electric polarization from strain gradient, and the size of the strain gradient grows quadratically as the material’s length scale decreases. This scaling enables maximum flexoelectric effects in 2D materials with strain gradient. To realize the strain gradient in MoS2 active layer, we first prepared graphene-MoS2 vertical stack on a pre-stretched elastomeric substrate followed by a release of the stretch to create a crumpled heterostructure. The crumpled MoS2/graphene was again stretched to a smaller strain, and the other graphene electrode layer was placed on top of the crumpled MoS2 active layer. Releasing the strain after assembly resulted in a periodic contact between the top graphene electrode and the MoS2 active layer while maintaining a full contact between the bottom graphene electrode and the MoS2 active layer. Our stretchable flexoelectric graphene/MoS2/graphene device demonstrated voltage and current outputs under various mechanical deformations, including bending and stretch-release motions. Our results demonstrate self-powered strain sensing capability under high degree of bending and stretching motions, potentially applicable to human health monitoring sensors.

(Invited) inkjet-Printed Soft Electronic Devices and Sensors for Wearable Health Monitoring Applications

Stretchable electronic devices and sensors built on thin elastomer substrates may find a wide range of applications in wearable health monitoring devices owing to their ability to conformably adapt to human skin for long-term and comfortable wearing. In this talk, I will present our work on developing intrinsically-stretchable electronic materials that are formulated as electronic inks and patterend using a highly scalable and low-cost inkjet printing process. A variety of soft sensors including silver nanoparticle based ultrasensitive resistive strain sensor and pressure sensor, porous elastomer dielectric based capacitive pressure sensor, and multimodal sensor that can differentiate pressure, strain, and temperature stimuli have all been demonstrated on ultrathin polydimethylsiloxane (PDMS) substrate by printing. These devices have been used in applications including motion and gesture tracking, voice recognition, arterial pulse waveform and photoplethysmogram monitoring. In addition, I will also report our work on the development of a unique porous PDMS sponge electrode as a gel-free dry interface for motion-artifact tolerant recording of electrophysiological signals. The porous structure of the soft electrode significantly increases the effective contact area and lowers the electrode-skin impedance, which result in improved signal-to-noise ratio. Compared to commercial rigid electrodes, the soft and thin form factor also makes the spongy electrode well-suited for long-term recording of high quality biopotential signals including electrocardiogram (ECG) and electromyography (EMG) on ambulatory patients. As a demonstration of its clinical usage with a focus on maternal and fetal health monitoring, I will show an array of such soft electrodes integrated on a printed patch of textile-based interconnections, and used for recording and spatiotemporal mapping of the uterine contraction patterns from patients in active labor.

Modulating the Configurations of "Gel-Type" Soft Silicone Rubber for Electro-Mechanical Energy Generation Behavior in Wearable Electronics.

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric substrate. Also, multi-wall carbon nanotube (MWCNT), and diatomaceous earth (DE) were used as reinforcing fillers. This "gel-type" soft SR has crosslinking polymer networks with silicone encapsulated within its structure. Mechanical properties such as modulus or stretchability are of utmost importance for such devices based on "gel-type" soft. From the experiments, some of the mechanical aspect's values are summarized. For example, the stretchability was 99% (control) and changes to 127% (3 phr, MWCNT), 76% (20 phr DE), and 103% (20 phr hybrid). From electro-mechanical tests, the output voltage was 0.21 mV (control) and changed to 0.26 mV (3 phr, MWCNT), 0.19 mV (20 phr DE), and 0.29 mV (20 phr hybrid). Moreover, from real-time biomechanical human motion tests in "gel-type" soft-based composites, a relationship among output voltage from machine to human motions was established. Overall, these configurations make them promising against traditional portable devices such as batteries for small power applications such as mobile phones.

A Skin‐Bioinspired Urchin‐Like Microstructure‐Contained Photothermal‐Therapy Flexible Electronics for Ultrasensitive Human‐Interactive Sensing

AbstractWearable electronic sensors have attracted extensive attention in multifunctional electronic skin, personalized health monitoring, intelligent human–machine interaction, and smart medical treatment. However, critical challenge exists in simultaneously achieving excellent sensing performances with high sensitivity, rapid response, low sensing limit, and excellent cycling stability for full‐scale human healthcare detection and further timely photothermal therapy. For highly sensitive human skin, the spinosum microstructure in epidermis and dermis takes an important part in sensing signal amplification and transmission. Inspired by the spinosum microstructure of human skin for highly sensitive tactile perception, a skin‐inspired flexible electronic sensor is prepared from the face‐to‐face assembly of an as‐prepared polybutylene adipate‐polyurethane (PBAPU) elastomer matrix with conducting MXene nanosheets‐coated urchin‐like microstructure templated from natural chrysanthemum pollen grain microstructures, and an interdigitated electrode‐coated PBAPU elastomer substrate. The PBAPU elastomer matrix is newly prepared, exhibiting outstanding tensile strength (18.87 MPa), high stretchability (1190%), and comparable elastic modulus (1.7 MPa) to human skin. The as‐assembled flexible electronic sensor exhibits a highly sensitive sensitivity (up to 784.02 kPa−1), low detection limit (0.12 Pa), and reliable cycling stability for intelligent human–machine interfacing. The MXene nanosheets‐coated urchin‐like microstructure‐contained PBAPU possesses efficient photothermal heating performance to achieve on‐demand photothermal therapy for rehabilitation training.

Substrate Reshaping for Optically Tuned Liquid‐Printed Microlenses Beyond Their Wetting Properties

AbstractSeveral strategies exist capable of fabricating microlenses for applications such as cameras and solar cells. Among them, techniques based on printing curable liquid prepolymers including inkjet and electrohydrodynamic‐jet printing, or laser‐induced forward‐transfer (LIFT) offer unique advantages in terms of ease of integration, cost, and compatibility with flexible substrates. However, the optical properties of the so‐fabricated microlenses depend on the wettability of the liquid prepolymer, preventing the broad implementation of printing technologies for micro‐optics. Herein, how printing microdroplets on top of reconfigurable substrates allows overcoming this issue is reported. The strategy, called print‐n‐release, is based on depositing prepolymer microdroplets on top of mechanically stretched elastomeric substrates. Once the stress applied to the substrate is released, and provided pinning of the contact line, the microdroplet's base diameter decreases producing an increase in contact angle and reduction in radius of curvature. Following a curing step, the microdroplets are converted into microlenses whose shape no longer depends exclusively on their wetting properties, but also on the substrate elongation. It is demonstrated that, by combining LIFT with substrates elongated up to 80%, microlenses can be fabricated with a 400% increase in contact angle and a 90% reduction in focal length, in good agreement with theoretical predictions.

Design of a Biaxially Stretchable Microstrip Antenna Enabled by Buckled Au Thin Film on an Elastomeric Substrate

Wearable wireless biomedical electronics enable monitoring and wireless transmission of patient physiological and pathological signals to provide remote guidance for appropriate diagnosis and treatment. As a core component, the antenna must be flexible and stretchable to adapt to the complex mechanical deformations (e.g., stretching, bending, and twisting) induced by human motions. This work proposes a biaxially stretchable microstrip antenna based on buckled gold thin films bonded on an elastomeric substrate. A simplified analytic model validated by simulations and experiments is established to investigate the biaxial buckling behaviors of the thin films within 10% tensile strains. The properties, including resonance frequency, bandwidth, and radiation pattern of the fabricated biaxially stretchable microstrip antenna under various stretched states, are studied by combining experiments and finite element analysis. The effects of biaxial tensile deformations on the resonance frequency, bandwidth, and radiation properties are discussed. Results show that the designed microstrip antenna has a relatively stable performance under both natural and deformed states within 10% of uniaxial and biaxial tensile strains, which enables the designed antenna to have broad application prospects in wearable wireless medical devices for stable transmission of signals between body-worn sensors and terminals, especially for situations accompanied with complex deformations.

Advanced Printing Transfer of Assembled Silver Nanowire Network into Elastomer for Constructing Stretchable Conductors

Excellent electrical performance of assemblies of 1D silver nanowires (AgNWs) has been demonstrated in the past years. Up to now, however, there are limited approaches to realize simultaneously deterministic assembly with dense arrangement of AgNWs and desired functional layouts. Herein, an assembly strategy from compressed air‐modulated alignment of AgNWs to heterogeneous integration of stretchable sensing devices through printing transfer is proposed. In this process, a convective flow induced by compressed air brings the AgNWs to the air–droplet interface, where the AgNWs are assembled with excellent alignment and packing due to the surface flow, van der Waals, and capillary interactions. Compared with those random AgNWs networks, the oriented, densely packed AgNWs exhibit a lower and uniform electrical sheet resistance. To incorporate the AgNWs to an elastomer substrate, direct ink writing is employed to transfer the assembled AgNW network to the printed silicone elastomer with desirable patterns. Excellent electrical property is demonstrated including a wide electrical response range from 10% to 120% strain, and high electrical repeatability. An antibacterial property is confirmed, notifying additional benefit as wearable sensors. The printing transfer of preassembled AgNW networks to the printed elastomer patterns provides a facile strategy to construct stretchable electronic devices.

Highly Robust and Strain-Resilient Thin Film Conductors Featuring Brittle Materials.

Stretchable conductors with stable electrical conductivity under various deformations are essential for wearable electronics, soft robots, and biointegrated devices. However, brittle film-based conductors on elastomeric substrates often suffer from unexpected electrical disconnection due to the obvious mechanical incompatibility between stiff films and soft substrates. We proposed a novel out-of-plane crack control strategy to achieve the strain-insensitive electrical performance of thin-film-based conductors, featuring conductive brittle materials, including nanocrystalline metals (Cu, Ag, Mo) and transparent oxides (ITO). Our metal film-based conductors exhibit an ultrahigh initial conductivity (1.3 × 105 S cm-1) and negligible resistance change (R/R0 = 1.5) over wide strain range from 0 to 130%, enabled by film-induced substrate cracking and liquid metal-induced electrical self-repairing. They could function well under multimodal deformations (stretching, bending, and twisting) and severe mechanical damage (cutting and puncturing). We demonstrated the strain-resilient electrical functionality of metal film-based conductors in a flexible light-emitting diode display that shows high mechanical compliance.

Maskless Fabrication of Highly Conductive and Ultrastretchable Liquid Metal Features through Selective Laser Activation.

In the rising field of stretchable electronics, liquid metals are ideal candidate conductors with metallic conductivity and intrinsic deformability. The complex patterning methods of liquid metal features have limited their widespread applications. In this study, we report a maskless fabrication approach for the facile and scalable patterning of liquid metal conductors on an elastomer substrate. Laser-activated patterns are employed as versatile templates to define arbitrary liquid metal patterns. The as-prepared liquid metal features show an excellent conductivity of 3.72 × 104 S/cm, a high resolution of 70 μm, ultrahigh stretchability of up to 1000% strain, and electromechanical durability. The practical suitability of liquid metal conductors is demonstrated by fabricating a stretchable light-emitting diode (LED) matrix and a smart sensing glove. The maskless fabrication technique introduced here allows versatile patterning of liquid metal conductors with affordable costs, which may stimulate a broad range of applications in stretchable electronic devices and systems.

In Situ Co‐transformation of Reduced Graphene Oxide Embedded in Laser‐Induced Graphene and Full‐Range On‐Body Strain Sensor

AbstractOn‐body strain information provides various indicators such as heart rate, physiological pulse, voice waveform, respiratory rate, and body motion status. Recent advances in wearable strain sensors using nanomaterials have significantly enhanced sensor performance with regard to sensitivity, detectable range, and response time. However, it is still challenging to obtain all types of body strain information, from small vibrations to joint movements, using one type of sensor. Herein, a full‐range on‐body strain (FROS) sensor covering ultrasmall‐to‐large strains such as vocal vibration and joint movement is reported. To achieve an ultrawide detectable range, reduced graphene oxide (rGO)‐embedded laser‐induced graphene (LIG) is synthesized by laser engraving on a graphene oxide (GO)‐embedded polyimide (PI) complex film. An rGO‐LIG homostructure based on sp2‐carbons is photothermally reconstructed from the GO‐PI heterostructure in a complex film by in situ co‐transformation and then transferred to an elastomer substrate. The fabricated FROS sensor successfully performs on‐body strain monitoring of various indicators, such as physiological pulse, vocal sound waveform, and body movement, as well as American sign language translation. Furthermore, it is believed that this rGO‐LIG homostructure‐based material synthesized by in situ co‐transformation can potentially provide novel functionalities in fields such as wearable electronics, humanoid, soft robotics, and intelligent prosthetics.

Carbon Nanotube Optoelectronic Synapse Transistor Arrays with Ultra‐Low Power Consumption for Stretchable Neuromorphic Vision Systems

AbstractHigh‐performance stretchable optoelectronic synaptic transistor arrays are key units for constructing and mimicking simulated neuromorphic vision systems. In this study, ultra‐low power consumption and low‐operation‐voltage stretchable all‐carbon optoelectronic synaptic thin film transistors (TFTs) using sorted semiconducting single‐walled carbon nanotubes (sc‐SWCNTs) modified with CdSe/ZnS quantum dots as active layers on ionic liquid‐based composite elastomer substrates are first reported. The resulting stretchable TFT devices show enhancement‐mode characteristics with excellent electrical properties (such as the record on/off ratios up to 105, negligible hysteresis, and small subthreshold swing), excellent mechanical tensile properties (such as the only 12.4% and 6.4% degradations of the carrier mobility after 20% vertical and horizontal strain stretching), and optoelectronic synaptic plasticity (for the recognition of Morse codes) with ultra‐low power consumptions (15.38 aJ) at the operating voltage from −1 to 0.2 V. At the same time, the designed nonvolatile conductance of the stretchable SWCNT optoelectronic synapse thin film transistors (SSOSTFTs) stimulated by UV light and the bending angle are first used to simulate stretchable neuromorphic vision systems (including the functions of the crystalline lens and optic cone cells as bionic eyes) for detecting the atmospheric environment with a record accuracy of 95.1% as a bionic eye.

Stretchable and Robust Silver Nanowire Composites on Transparent Butyl Rubber

Silver nanowires (AgNWs) are leading materials for transparent conductive electrodes in optoelectronic devices. The solution processability of AgNWs combined with the optical transparency and electrical conductivity of solution-deposited AgNW networks makes them a promising alternative to conventional indium tin oxide. Furthermore, the ability of AgNW networks to withstand mechanical deformation means that AgNW networks may be the material of choice for next-generation flexible and stretchable optoelectronics. The drawback with the practical use of AgNWs, however, is that corrosion of AgNWs under ambient conditions damages the AgNW network and reduces the workable life span. Environmental degradation is especially problematic in stretchable electronics, which use elastomeric substrate materials that have a high gas permeability like poly(dimethylsiloxane) (PDMS). Covering individual AgNWs with a protective nanoscale coating to prevent corrosion complexifies their preparation and implementation in practical applications. This study presents an alternative approach in which the elastomeric substrate, transparent butyl rubber (TBR), acts as both a stretchable substrate and a protective gas barrier. TBR, an optically transparent formulation of poly(isobutylene-co-isoprene), is a synthetic rubber with an intrinsically low gas permeability. We demonstrate that AgNW networks embedded in a polyurethane adhesive and adhered to a TBR substrate provide high conductivity and optical transparency and are robust to tensile strain as well as extreme environments of humidified air, underwater storage, and corrosive acid vapors. We show that this system outperforms a comparison system that uses PDMS instead of TBR.

Milliwatt-Scale Body-Heat Harvesting Using Stretchable Thermoelectric Generators for Fully Untethered, Self-Sustainable Wearables

Stretchable thermoelectric generators (s-TEGs) have been regarded as promising energy harvesters for self-powered wearable electronics. However, previous s-TEGs show low power generation capacity due to their high module resistances, originating from the poor electromechanical interfaces between rigid–soft components and the high electrical resistances of stretchable interconnects. Herein, we report strategies to boost thermoelectric performance, which allows us to operate wireless communication systems from body heat by generating a power of 2.6 mW. Electromechanically graded interlayers that mediate discrete functionalities at the interfaces effectively reduce junction resistances, and solution-based welding that transforms scattered networks into mesh-like structures produces highly conductive and strain-resilient interconnects, respectively. Soft heat conductors are included to improve thermal interfaces, minimizing thermal impedance of elastomeric substrates. Consequently, the power generation capacity is significantly enhanced, exhibiting the highest normalized power density of 1.48 μW cm–2 K–2 among reported high-performance s-TEGs. Our s-TEGs provide realistic solutions for sustainable self-powered electronics.

Bio‐Inspired Instability‐Induced Hierarchical Patterns Having Tunable Anisotropic Wetting Properties

AbstractThis paper introduces a method for the bottom‐up fabrication of bio‐inspired hierarchical patterns having tunable anisotropic wetting properties. The method exploits the surface instability of bilayers comprising a gold nanofilm attached to a substantially prestretched elastomer substrate. Upon film formation, highly aligned wrinkles spontaneously form on the surface owing to the surface instability driven by the compressive residual stress in the film. Thereafter, uniaxial compressive strain is applied to the film by prestretch relaxation of the substrate, which generates an array of high‐aspect‐ratio ridges on the surface. Consequently, hierarchical patterns comprising unidirectionally aligned ridges covered with wrinkles are obtained. Water droplets placed on surfaces having the aforementioned hierarchical patterns show direction‐dependent contact angles, resulting in elongated shapes, which indicates the presence of anisotropic wetting properties. The magnitude of wetting anisotropy can be tuned by simple control of the applied compressive strain and film thickness.

189 Novel Wireless Battery-Free Fully Passive Flexible Brain/Spine Implant for Improved Recovery of Function Through Epidural Stimulation

INTRODUCTION: Acquired motor impairment from diseases such as stroke, trauma, epilepsy, and cancer remains an important cause of disability. Current treatments provide insufficient brain/spine recovery, with most patients failing to recover adequate motor function with rehabilitation alone. Brain stimulation can lead to enhanced synaptic density and synaptic response after long-term stimulation and enhanced motor function recovery. However, non-invasive options remain inadequate and invasive approaches are associated with unacceptable risks. METHODS: A flexible and transparent silicone elastomer substrate was used through microfabrication processes, with an external antenna near the implant to control the stimulation. In vitro validation was accomplished by wireless stimulation of human-induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs). In vivo validation was performed by motor cortex stimulation on an anesthetized rat. The corresponding hindlimb motion was captured by video. To separate implant-evoked movement from spontaneous movement, we compared the peak hindlimb velocity during 0.5 sec post-stimulation periods vs. the 0.5 sec pre-stimulation periods, across a continuous series of N = 43 stimulation pulses. RESULTS: Cultured hiPSC-CMs cells demonstrated well-controlled beating behavior under 0.5, 1, and 2Hz wireless stimulation. Statistical analysis further confirmed the change in beating rate corresponded with stimulation frequency (p < 0.001). The recorded hindlimb movement under wireless motor cortex stimulation demonstrated synchronization with the delivered voltage pulse trains. Average peak hindlimb velocity during pre-stimulation periods was 0.8 ± 0.4 mm/sec (± S.D.); during post-stimulation periods, 47 ± 13 mm/sec. A two-sample t-test confirmed the applied wireless power directly evoked movement, (p < 0.001). CONCLUSIONS: We have developed a wireless, battery-less implant with demonstrated efficacy in vitro and in vivo. Efforts at long-term safety evaluation are ongoing in a smaller and larger animal model as a bridge to phase 0/1 clinical trials.

Highly Elastic and Conductive Metallic Interconnect with Crystalline–Amorphous Nanolaminate

Nanolaminate with alternating layers of nanocrystalline Cu and amorphous CuZrTi is suggested as highly stretchable and conductive interconnect material in stretchable devices. 50 nm nanocrystalline Cu and 20 nm amorphous CuZrTi are the optimum thicknesses of the constituent layers, which result in an elastic deformation limit of 3.33% similar to that of the monolithic amorphous CuZrTi film and an electrical conductivity of 11.83 S/μm corresponding to 70% of that of the monolithic nanocrystalline Cu film. The enhanced elastic deformability and conductivity of the nanolaminates enable the maintenance of the interconnect performance for cyclic stretching with a tensile strain of 114% in the form of a free-standing serpentine structure and a tensile strain of 30% in the form of an ordinary circular coil on an elastomer substrate.