Both self-healable conductors and stretchable conductors have been previously reported. However, it is still difficult to simultaneously achieve high stretchability, high conductivity, and self-healability. Here, we observed an intriguing phenomenon, termed “electrical self-boosting”, which enables reconstructing of electrically percolative pathways in an ultrastretchable and self-healable nanocomposite conductor (over 1700% strain). The autonomously reconstructed percolative pathways were directly verified by using microcomputed tomography and in situ scanning electron microscopy. The encapsulated nanocomposite conductor shows exceptional conductivity (average value: 2578 S cm–1; highest value: 3086 S cm–1) at 3500% tensile strain by virtue of efficient strain energy dissipation of the self-healing polymer and self-alignment and rearrangement of silver flakes surrounded by spontaneously formed silver nanoparticles and their self-assembly in the strained self-healing polymer matrix. In addition, the conductor maintains high conductivity and stretchability even after recovered from a complete cut. Besides, a design of double-layered conductor enabled by the self-bonding assembly allowed a conducting interface to be located on the neutral mechanical plane, showing extremely durable operations in a cyclic stretching test. Finally, we successfully demonstrated that electromyogram signals can be monitored by our self-healable interconnects. Such information was transmitted to a prosthetic robot to control various hand motions for robust interactive human-robot interfaces.

Conventional stretchable electronics entailing the adoption of a wavy design, a neutral mechanical plane, and a conformal contact between abiotic and biotic interfaces have shown diverse skin-interfaced applications. Despite such remarkable progress, there have been challenged to be evolved to intelligent skin prosthetics due to the absence of the monolithic integration of neuromorphic constituents into individual sensing and actuating components. Herein, we demonstrate a golden tortoise beetle-inspired stretchable sensory-neuromorphic system comprising an arti cial mechanoreceptor, an arti cial synapse, and an epidermal photonic actuator as three biomimetic functionalities that correspond to a stretchable capacitive pressure sensor, a resistive random-access memory, and a quantum dot light-emitting diode, respectively. This system features a rigid-island structure interconnected with a sinter-free printable conductor (stretchability ~ 160%, conductivity ~ 18,550 S/cm), which allows one to improve both areal density and structural reliability while avoiding the thermal degradation of heat-sensitive stretchable electronic components. Moreover, even in the skin deformation range, the system accurately recognizes various patterned stimuli via an arti cial neural network with training/inferencing functions. Our new bioinspired system is therefore expected to be an important step toward the implementation of intelligent wearable electronics.

Advanced prosthetics have significantly improved the quality of life of patients with neuronal injuries. The use of novel biocompatible materials, [1,2] the development of soft neuroprosthetics, [3][4][5] and clinical trials of synthetic neurografts [6,7] have enabled the modulation of neuronal activity for sustained neuroregenerative therapy. However, many of the previous breakthroughs are only relevant to the static environment of the central nervous system [8,9] and not ideal for the dynamic environment in peripheral nerves. The unpredictable, cyclic deformations on peripheral nerves accumulate fatigue on the device, causing the material and performance to degrade in vivo. [4,10] Furthermore, dynamic movements around peripheral nerves prevent the formation of a stable device-nerve interface. [10,11] Soft and stretchable bioelectronics that interface well with curvilinear nerves under dynamic environment have been developed. [12,13] They used unconventional Soft neuroprosthetics that monitor signals from sensory neurons and deliver motor information can potentially replace damaged nerves. However, achieving long-term stability of devices interfacing peripheral nerves is challenging, since dynamic mechanical deformations in peripheral nerves cause material degradation in devices. Here, a durable and fatigue-resistant soft neuroprosthetic device is reported for bidirectional signaling on peripheral nerves. The neuroprosthetic device is made of a nanocomposite of gold nanoshell (AuNS)-coated silver (Ag) flakes dispersed in a tough, stretchable, and self-healing polymer (SHP). The dynamic self-healing property of the nanocomposite allows the percolation network of AuNS-coated flakes to rebuild after degradation. Therefore, its degraded electrical and mechanical performance by repetitive, irregular, and intense deformations at the devicenerve interface can be spontaneously self-recovered. When the device is implanted on a rat sciatic nerve, stable bidirectional signaling is obtained for over 5 weeks. Neural signals collected from a live walking rat using these neuroprosthetics are analyzed by a deep neural network to predict the joint position precisely. This result demonstrates that durable soft neuroprosthetics can facilitate collection and analysis of large-sized in vivo data for solving challenges in neurological disorders.

The progress in 3D printing research has led to significant developments ranging from customized printing to rapid prototyping. However, the 3D printing of electrodes, especially stretchable electrodes for the fabrication of 3D printable electronic devices, is challenging due to the inherent weakness with respect to the printing material. A novel preparation method is reported for a 3D printable conductive ink with a self‐wiring effect during heat treatment, which pushes the silicone rubber outward and results in the accumulation of the conductors within the wire. This effect results in the formation of a polymer shell around the conductor, thus yielding conductors with larger stretchability and soft passivation characteristics. The conductive ink is prepared via the following steps: i) mixing of conductive filler, silicone rubbers, and solvent; followed by ii) soft heat treatment for soft curing and solvent evaporation. Furthermore, a capacitive sensor is fabricated using this dielectric polymer layer. As a demonstration, a mouse controller is fabricated using a capacitive sensor array prepared using the conductors developed in this study.

Conjugated polymer-based energy-harvesting devices hold distinctive advantages in terms of low toxicity, high flexibility, and capability of large-area integration at low cost for sustainable development. An organic thermoelectric (OTE) device has been considered one of the promising energy-harvesting candidates in recent years because it can efficiently convert low-temperature waste heat into electricity over its inorganic counterparts. However, a cruel irony is that environmentally toxic solvents and acids are utilized for fabrication and performance improvement of the OTE devices, retarding the development and use of genuinely green energy-harvesting. Here, we present eco-friendly, non-toxic strategies for a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based high-performance OTE device by incorporating a nature-abundant material, vitamin C (VC), as an additive. We found that the intrinsic polar nature and reducing ability of VC induce synergy effects of microstructure alignment with PSS removal and dedoping of PEDOT, leading to simultaneous enhancement of the electrical conductivity (>400 S cm–1) and the Seebeck coefficient (>30 μV K–1) and a resultant high thermoelectric power factor of 51.8 μW m–1 K–2. In addition, inspired by the eco-friendly fabrication process, we further demonstrated a transient OTE device, which can be fully degraded with naturally occurring substances, by fabricating it on a bio-based cellulose acetate substrate. We believe that our eco-friendly strategies from fabrication to disposal of the OTE can be applied to the development of high-performance, wearable, and bio-compatible OTE devices with minimal waste and further trigger the research on genuinely green thermal energy harvesting.

In article number 2007346, Dae‐Hyeong Kim, Taeghwan Hyeon, Donghee Son, and co‐workers develop a durable and fatigue‐resistant soft bidirectional neuroprosthetic device composed of a biocompatible nanocomposite of gold‐nanoshell‐coated silver flakes dispersed in a tough, stretchable, and self‐healing polymer. The electrical conductivity of our neuroprosthetics spontaneously recovers even after repetitive degradations by irregular and severe mechanical deformations.

High stability, stretchable speed insensitive properties, high stretchability, and electrical conductivity are key characteristics for the realisation of wearable devices. However, conventional research is mainly focused on achieving only high stretchability and electrical conductivity. Studies on the stability and stretching speed insensitive properties generally require complex fabrication processes, which are in need of further improvement. In this study, we propose a facile formation of a conductive bridge in composites by using surface damage and the viscoelastic property of the polymer. Surface cracks due to repeated stretching cycles formed conductive bridges via stress relaxation of the viscoelastic polymer matrix. The conductive bridge resulted in the conductor having highly stable resistance values at target strains and stretching speed insensitive resistance, even at stretching speeds that were 20 times faster than the minimum.There have been great interests in stretchable conductors for the past few decades; as such, many methods for the fabrication of highly stretchable and conductive conductors have been researched. Instead of conventional rigid substrates and electrodes, stretchable substrates and conductors have been studied via various methods such as printing with composite ink 1-4 , prestraining 5-8 , and embedding nanowires in a stretchable matrix 9-12 . In addition, practical applications such as stretchable displays 13-17 , wearable motion sensors 18-21 , and stretchable energy storage devices [22][23][24][25] have been studied using the stretchable conductors mentioned above. Furthermore, stretchable conductors are studied as an interconnection electrode for future transparent devices, such as flexible photodetectors 26,27 , and tiny devices, such as memristors and memory 28,29 . These researchers have made great progress in making highly stretchable and conductive conductors. However, for practical uses of these stretchable devices, there are new stability conditions, where the conductors are required to withstand thousands of stretching/contraction cycles and be independent of the stretching speed.From this point of view, self-healing polymer conductors are gaining more interest as a promising method to modify the stability of conductors [30][31][32] . Cracks are generated by repeated stretching/contraction cycles; this can make the conductive pathway longer, or even break it, making the conductor dielectric. Even after the conductors are separated, a self-healing polymer conductors can reform the network and make it conductive again. Although this healing process restores mechanical and electrical properties, there are still problems to be solved. Self-healing polymer conductors require many conditions such as broken conductors should be placed to contact each other and number of restores are limited. So, forming conductive bridge along the broken conductors can be an alternative for highly stable and stretching speed insensitive conductor.Recently, the concept of conductive bridges in s...

Experimental and clinical studies on the accuracy of the intramedullary alignment method have produced different results, and few have addressed accuracy in the sagittal plane. Reported deviations are not only attributable to the alignment method but also to radiological errors. The purpose of this study was to evaluate the accuracy of the intramedullary alignment method in the sagittal plane using computed tomography (CT) and 3-dimensional imaging software. Thirty-one TKAs were performed using an intramedullary alignment method involving the insertion of a long 8-mm diameter rod into the medullary canal to the distal metaphysis of the tibia. All alignment instruments were set to achieve an ideal varus/valgus angle of 0° in the coronal plane and a tibial slope of 0° in the sagittal plane. The accuracy of the intramedullary alignment system was assessed by measuring the coronal tibial component angle and sagittal tibial slope angles, i.e., angles between the tibial anatomical axis and the tangent to the medial and lateral tibial plateau or the cut-surface. The mean coronal tibial component angle was 88.5° ± 1.2° and the mean tibial component slope in the sagittal plane was 1.6° ± 1.2° without anterior slope. Our intramedullary tibial alignment method, which involves passing an 8-mm diameter long rod through the tibial shaft isthmus, showed good accuracy (less than 3 degrees of variation and no anterior slope) in the sagittal plane in neutral or varus knees.