A soft implantable energy supply system that integrates wireless charging and biodegradable Zn-ion hybrid supercapacitors.

The advent of implantable bioelectronic devices offers prospective solutions toward health monitoring and disease diagnosis and treatments. However, advances in power modules have lagged far behind the tissue-integrated sensor nodes and circuit units. Here, we report a soft implantable power system that monolithically integrates wireless energy transmission and storage modules. The energy storage unit comprises biodegradable Zn-ion hybrid supercapacitors that use molybdenum sulfide (MoS2) nanosheets as cathode, ion-crosslinked alginate gel as electrolyte, and zinc foil as anode, achieving high capacitance (93.5 mF cm-2) and output voltage (1.3 V). Systematic investigations have been conducted to elucidate the charge storage mechanism of the supercapacitor and to assess the biodegradability and biocompatibility of the materials. Furthermore, the wirelessly transmitted energy can not only supply power directly to applications but also charge supercapacitors to ensure a constant, reliable power output. Its power supply capabilities have also been successfully demonstrated for controlled drug delivery.

Bioadhesive polymer semiconductors and transistors for intimate biointerfaces.

The use of bioelectronic devices relies on direct contact with soft biotissues. For transistor-type bioelectronic devices, the semiconductors that need to have direct interfacing with biotissues for effective signal transduction do not adhere well with wet tissues, thereby limiting the stability and conformability at the interface. We report a bioadhesive polymer semiconductor through a double-network structure formed by a bioadhesive brush polymer and a redox-active semiconducting polymer. The resulting semiconducting film can form rapid and strong adhesion with wet tissue surfaces together with high charge-carrier mobility of ~1 square centimeter per volt per second, high stretchability, and good biocompatibility. Further fabrication of a fully bioadhesive transistor sensor enabled us to produce high-quality and stable electrophysiological recordings on an isolated rat heart and in vivo rat muscles.

Achieving tissue-level softness on stretchable electronics through a generalizable soft interlayer design.

Soft and stretchable electronics have emerged as highly promising tools for biomedical diagnosis and biological studies, as they interface intimately with the human body and other biological systems. Most stretchable electronic materials and devices, however, still have Young's moduli orders of magnitude higher than soft bio-tissues, which limit their conformability and long-term biocompatibility. Here, we present a design strategy of soft interlayer for allowing the use of existing stretchable materials of relatively high moduli to versatilely realize stretchable devices with ultralow tissue-level moduli. We have demonstrated stretchable transistor arrays and active-matrix circuits with moduli below 10 kPa-over two orders of magnitude lower than the current state of the art. Benefiting from the increased conformability to irregular and dynamic surfaces, the ultrasoft device created with the soft interlayer design realizes electrophysiological recording on an isolated heart with high adaptability, spatial stability, and minimal influence on ventricle pressure. In vivo biocompatibility tests also demonstrate the benefit of suppressing foreign-body responses for long-term implantation. With its general applicability to diverse materials and devices, this soft-interlayer design overcomes the material-level limitation for imparting tissue-level softness to a variety of bioelectronic devices.

Si/Organic Integrated Narrowband Near-Infrared Photodetector.

Spectrally selective narrowband photodetection is critical for near-infrared (NIR) imaging applications, such as for communicationand night-vision utilities. It is a long-standing challenge for detectors based on silicon, to achieve narrowband photodetection without integrating any optical filters. Here, this work demonstrates a NIR nanograting Si/organic (PBDBT-DTBT:BTP-4F) heterojunction photodetector (PD), which for the first time obtains the full-width-at-half-maximum (FWHM) of only 26 nm and fast response of 74 µs at 895 nm. The response peak can be successfully tailored from 895 to 977 nm. The sharp and narrow response NIR peak is inherently attributed to the coherent overlapping between the NIR transmission spectrum of organic layer and diffraction enhanced absorption peak of patterned nanograting Si substrates. The finite difference time domain (FDTD) physics calculation confirms the resonant enhancement peaks, which is well consistent with the experiment results. Meanwhile, the relative characterization indicates that the introduction of the organic film can promote carrier transfer and charge collection, facilitating efficient photocurrent generation. This new device design strategy opens up a new window in developing low-cost sensitive NIR narrowband detection.

High-efficiency stretchable light-emitting polymers from thermally activated delayed fluorescence.

Stretchable light-emitting materials are the key components for realizing skin-like displays and optical biostimulation. All the stretchable emitters reported to date, to the best of our knowledge, have been based on electroluminescent polymers that only harness singlet excitons, limiting their theoretical quantum yield to 25%. Here we present a design concept for imparting stretchability onto electroluminescent polymers that can harness all the excitons through thermally activated delayed fluorescence, thereby reaching a near-unity theoretical quantum yield. We show that our design strategy of inserting flexible, linear units into a polymer backbone can substantially increase the mechanical stretchability without affecting the underlying electroluminescent processes. As a result, our synthesized polymer achieves a stretchability of 125%, with an external quantum efficiency of 10%. Furthermore, we demonstrate a fully stretchable organic light-emitting diode, confirming that the proposed stretchable thermally activated delayed fluorescence polymers provide a path towards simultaneously achieving desirable electroluminescent and mechanical characteristics, including high efficiency, brightness, switching speed and stretchability as well as low driving voltage.

Emerging Iontronic Neural Devices for Neuromorphic Sensory Computing.

Living organisms have a very mysterious and powerful sensory computing system based on ion activity. Interestingly, studies on iontronic devices in the past few years have proposed a promising platform for simulating the sensing and computing functions of living organisms, because: 1) iontronic devices can generate, store, and transmit a variety of signals by adjusting the concentration and spatiotemporal distribution of ions, which analogs to how the brain performs intelligent functions by alternating ion flux and polarization; 2) through ionic-electronic coupling, iontronic devices can bridge the biosystem with electronics and offer profound implications for soft electronics; 3) with the diversity of ions, iontronic devices can be designed to recognize specific ions or molecules by customizing the charge selectivity, and the ionic conductivity and capacitance can be adjusted to respond to external stimuli for a variety of sensing schemes, which can be more difficult for electron-based devices. This review provides a comprehensive overview of emerging neuromorphic sensory computing by iontronic devices, highlighting representative concepts of both low-level and high-level sensory computing and introducing important material and device breakthroughs. Moreover, iontronic devices as a means of neuromorphic sensing and computing are discussed regarding the pending challenges and future directions.

Stretchable Redox-Active Semiconducting Polymers for High-Performance Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) represent an emerging device platform for next-generation bioelectronics owing to the uniquely high amplification and sensitivity to biological signals. For achieving seamless tissue-electronics interfaces for accurate signal acquisition, skin-like softness and stretchability are essential requirements, but they have not yet been imparted onto high-performance OECTs, largely due to the lack of stretchable redox-active semiconducting polymers. Here, a stretchable semiconductor is reported for OECT devices, namely poly(2-(3,3'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-[2,2'-bithiophen]-5)yl thiophene) (p(g2T-T)), which gives exceptional stretchability over 200% strain and 5000 repeated stretching cycles, together with OECT performance on par with the state-of-the-art. Validated by systematic characterizations and comparisons of different polymers, the key design features of this polymer that enable the combination of high stretchability and high OECT performance are a nonlinear backbone architecture, a moderate side-chain density, and a sufficiently high molecular weight. Using this highly stretchable polymer semiconductor, an intrinsically stretchable OECT is fabricated with high normalized transconductance (≈223 S cm-1 ) and biaxial stretchability up to 100% strain. Furthermore, on-skin electrocardiogram (ECG) recording is demonstrated, which combines built-in amplification and unprecedented skin conformability.

A stretchable and strain-unperturbed pressure sensor for motion interference-free tactile monitoring on skins.

A stretchable pressure sensor is a necessary tool for perceiving physical interactions that take place on soft/deformable skins present in human bodies, prosthetic limbs, or soft robots. However, all existing types of stretchable pressure sensors have an inherent limitation, which is the interference of stretching with pressure sensing accuracy. Here, we present a design for a highly stretchable and highly sensitive pressure sensor that can provide unaltered sensing performance under stretching, which is realized through the synergistic creations of an ionic capacitive sensing mechanism and a mechanically hierarchical microstructure. Via this optimized structure, our sensor exhibits 98% strain insensitivity up to 50% strain and a low pressure detection limit of 0.2 Pa. With the capability to provide all the desired characteristics for quantitative pressure sensing on a deformable surface, this sensor has been used to realize the accurate sensation of physical interactions on human or soft robotic skin.

Recent Advances in Flexible and Stretchable Sensing Systems: From the Perspective of System Integration.

Biological signals generated during various biological processes are critically important for providing insight into the human physiological status. Recently, there have been many great efforts in developing flexible and stretchable sensing systems to provide biological signal monitoring platforms with intimate integration with biological surfaces. Here, this review summarizes the recent advances in flexible and stretchable sensing systems from the perspective of electronic system integration. A comprehensive general sensing system architecture is described, which consists of sensors, sensor interface circuits, memories, and digital processing units. The subsequent content focuses on the integration requirements and highlights some advanced progress for each component. Next, representative examples of flexible and stretchable sensing systems for electrophysiological, physical, and chemical information monitoring are introduced. This review concludes with an outlook on the remaining challenges and opportunities for future fully flexible or stretchable sensing systems.

Facile ultrasonic synthesized NH2-carbon quantum dots for ultrasensitive Co2+ ion detection and cell imaging.

The amine decorated carbon quantum dots (NH2-CQDs) were synthesized through ultrasonic method from graphite rods derived CQDs and ammonia hydroxide and utilized as the sensing probes for cobalt (II) ions and nucleic acids. The sensing technique was investigated to be the fluorescence quenching effect, which demonstrated linear relationship between cobalt (II) ions concentration and the emission intensity deviation ratio in the concentration range of 50 nM to 40 µM with the detection limit of 12 nM. In brief, this sensitive and selective detection method was confirmed to demonstrate high potential in cobalt (II) ions detection in real samples and nucleic acid sensing in biological cells.

Carbon quantum dots and carbon layer double protected cuprous oxide for efficient visible light CO2 reduction.

We designed a composite of carbon quantum dots (CQDs) with a carbon layer (CL) covering Cu2O nanocatalysts (CL@CQDs/Cu2O), which exhibited better photocatalytic performance than pure Cu2O and CQDs/Cu2O particles with good stability and efficiency for CO2 conversion.

Kirigami-Inspired Deformable 3D Structures Conformable to Curved Biological Surface.

By introducing stretchability and/or deformability to planar electronics, devices can conformably attach to 3D curved surfaces with minimal invasiveness, which is of great interest for next-generation wearables in clinical and biological applications. Here, a feasible route is demonstrated to generate deformable 3D structures as a robust platform to construct electronic systems by utilizing silver nanowires/parylene hybrid films in a way analogous to the art of kirigami. The hybrid films exhibit outstanding electrical conductivity along with decent optical transparency, flexibility, and long-term stability. These merits enable these films to work as electrodes for electrocardiogram recording with comparable accuracy to a commercial counterpart, and to fabricate a 7-GHz monopole antenna with good omni-directionality and a peak gain of 1.35 dBi. More importantly, a general scheme for constructing 3D deformable electronic systems is presented, including unique patterning procedures and rational cut designs inspired by kirigami. As an example, deformable transparent humidity sensors are fabricated to work on elbows and finger joints for sweating monitoring. The strategy demonstrated here for 3D deformable system construction is versatile and holds great promise for future advanced health monitoring at diverse and complex epidermal surfaces.

Wafer-Scale Fabrication of Ultrathin Flexible Electronic Systems via Capillary-Assisted Electrochemical Delamination.

Electronic systems on ultrathin polymer films are generally processed with rigid supporting substrates during fabrication, followed by delamination and transfer to the targeted working areas. The challenge associated with an efficient and innocuous delamination operation is one of the major hurdles toward high-performance ultrathin flexible electronics at large scale. Herein, a facile, rapid, damage-free approach is reported for detachment of wafer-scale ultrathin electronic foils from Si wafers by capillary-assisted electrochemical delamination (CAED). Anodic etching and capillary action drive an electrolyte solution to penetrate and split the polymer/Si interface, leading to complete peel-off of the electronic foil with a 100% success rate. The delamination speed can be controlled by the applied voltage and salt concentration, reaching a maximum value of 1.66 mm s-1 at 20 V using 2 m NaCl solution. Such a process incurs neither mechanical damage nor chemical contamination; therefore, the delaminated electronic systems remain intact, as demonstrated by high-performance carbon nanotube (CNT)-based thin-film transistors and integrated circuits constructed on a 5.5 cm × 5.0 cm parylene-based film with 4 µm thickness. Furthermore, the CAED strategy can be applied for prevalent polymer films and confers great flexibility and capability for designing and manufacturing diverse ultrathin electronic systems.