Freestanding Multi-gate IZO-based Neuromorphic Transistors on Composite Electrolyte Membranes

Brain-inspired neuromorphic computing would bring a breakthrough to the classical computing paradigm through its massive parallelism and potential low power consumption advantages. Introduction of flexibility may bring vitality to this area by expanding its application areas to such as wearable and implantable electronics. At present, the development of flexible neuromorphic devices makes it a choice with wide prospect for next-generation wearable artificial neuromorphic computing. In this study, a freestanding graphene oxide (GO)/polyvinyl alcohol (PVA) composite solid electrolyte membrane is utilized as the gate dielectric and support material, and indium–zinc-oxide (IZO) neuromorphic transistors are fabricated on such membrane. Based on the in-plane gate modulation, many key synaptic plasticity behaviors have been successfully emulated, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), high-pass filtering, and spatiotemporal signal processing. Moreover, transition of the spiking logic and the superlinear and sublinear dendritic integration function are realized. Our results indicate that these freestanding IZO-based neuromorphic transistors may of great significance for future flexible anthropomorphic robots, wearable bionic perception.

A Method for Quantitatively Separating the Piezoelectric Component from the as-received "Piezoelectric" Signal

Polymer-based piezoelectric devices are promising for developing future wearable force sensors, nanogenerators, and implantable electronics etc. The electric signals generated by them are often assumed as solely coming from piezoelectric effect. However, triboelectric signals originated from contact electrification between the piezoelectric devices and the contacted objects can produce non-negligible interfacial electron transfer, which is often combined with the piezoelectric signal to give a triboelectric-piezoelectric hybrid output, leading to an exaggerated measured “piezoelectric” signal. Herein, a simple and effective method is proposed for quantitatively identifying and extracting the piezoelectric charge from the hybrid signal. The triboelectric and piezoelectric parts in the hybrid signal generated by a poly(vinylidene fluoride)-based device are clearly differentiated, and their force and charge characteristics in the time domain are identified. This work presents an effective method to elucidate the true piezoelectric performance in practical measurement, which is crucial for evaluating piezoelectric materials fairly and correctly.

Self-Powered Sensors: New Opportunities and Challenges from Two-Dimensional Nanomaterials

Nanomaterials have gained considerable attention over the last decade, finding applications in emerging fields such as wearable sensors, biomedical care, and implantable electronics. However, these applications require miniaturization operating with extremely low power levels to conveniently sense various signals anytime, anywhere, and show the information in various ways. From this perspective, a crucial field is technologies that can harvest energy from the environment as sustainable, self-sufficient, self-powered sensors. Here we revisit recent advances in various self-powered sensors: optical, chemical, biological, medical, and gas. A timely overview is provided of unconventional nanomaterial sensors operated by self-sufficient energy, focusing on the energy source classification and comparisons of studies including self-powered photovoltaic, piezoelectric, triboelectric, and thermoelectric technology. Integration of these self-operating systems and new applications for neuromorphic sensors are also reviewed. Furthermore, this review discusses opportunities and challenges from self-powered nanomaterial sensors with respect to their energy harvesting principles and sensing applications.

In vivo Monitoring of Glucose using Ultrasound-induced Resonance in Implantable Smart Hydrogel Microstructures

A novel glucose sensor is presented that uses smart hydrogels as a biocompatible implantable sensing element, which completely eliminates the need for any implanted electronics and uses an external conventional medical-grade ultrasound transducer for readout. The readout mechanism makes use of resonance absorption of ultrasound waves in glucose-sensitive hydrogels. Changes in in vivo glucose concentration in the interstitial tissue lead to swelling and de-swelling of the gels which in turn lead to changes in resonance behavior. The hydrogels are designed and shaped such as to exhibit specific mechanical resonance frequencies while remaining sonolucent to other frequencies. Thus, they allow conventional and continued ultrasound imaging, while yielding a sensing signal at specific frequencies that is correlated with glucose concentration. The resonance frequencies can be tuned by changing the shape and mechanical properties of the gel structures, such as to allow for multiple, co-located implanted hydrogels with different sensing characteristics or targets to be employed and read out, without interference, using the same ultrasound transducer, by simply toggling frequencies. The fact that there is no need for any implantable electronics, also opens the path towards future use of biodegradable hydrogels, thus creating a platform that allows injection of sensors that do not need to be retrieved when they reach the end of their useful lifespan.

Self-Healing, Stretchable, Biocompatible, and Conductive Alginate Hydrogels through Dynamic Covalent Bonds for Implantable Electronics

Implantable electronics have recently been attracting attention because of the promising advances in personalized healthcare. They can be used to diagnose and treat chronic diseases by monitoring and applying bioelectrical signals to various organs. However, there are challenges regarding the rigidity and hardness of typical electronic devices that can trigger inflammatory reactions in tissues. In an effort to improve the physicochemical properties of conventional implantable electronics, soft hydrogel-based platforms have emerged as components of implantable electronics. It is important that they meet functional criteria, such as stretchability, biocompatibility, and self-healing. Herein, plant-inspired conductive alginate hydrogels composed of “boronic acid modified alginate” and “oligomerized epigallocatechin gallate,” which are extracted from plant compounds, are proposed. The conductive hydrogels show great stretchability up to 500% and self-healing properties because of the boronic acid-cis-diol dynamic covalent bonds. In addition, as a simple strategy to increase the electrical conductivity of the hydrogels, ionically crosslinked shells with cations (e.g., sodium) were generated on the hydrogel under physiological salt conditions. This decreased the resistance of the conductive hydrogel down to 900 ohm without trading off the original properties of stretchability and self-healing. The hydrogels were used for “electrophysiological bridging” to transfer electromyographic signals in an ex vivo muscle defect model, showing a great bridging effect comparable to that of a muscle-to-muscle contact model. The use of plant-inspired ionically conductive hydrogels is a promising strategy for designing implantable and self-healable bioelectronics.

Intrinsically stretchable organic light-emitting diodes

Soft and conformable optoelectronic devices for wearable and implantable electronics require mechanical stretchability. However, very few researches have been done for intrinsically stretchable light-emitting diodes. Here, we present an intrinsically stretchable organic light-emitting diode, whose constituent materials are all highly stretchable. The resulting intrinsically stretchable organic light-emitting diode can emit light when exposed to strains as large as 80%. The turn-on voltage is as low as 8 V, and the maximum luminance, which is a summation of the luminance values from both the anode and cathode sides, is 4400 cd m−2. It can also survive repeated stretching cycles up to 200 times, and small stretching to 50% is shown to substantially enhance its light-emitting efficiency.