This paper presents flexible pressure sensors based on free-standing and biodegradable glycine−chitosan piezoelectric films. Fabricated by the self-assembly of biological molecules of glycine within a water-based chitosan solution, the piezoelectric films consist of a stable spherulite structure of β-glycine (size varying from a few millimeters to 1 cm) embedded in an amorphous chitosan polymer. The polymorphic phase of glycine crystals in chitosan, evaluated by X-ray diffraction, confirms formation of a pure ferroelectric phase of glycine (β-phase). Our results show that a simple solvent-casting method can be used to prepare a biodegradable β-glycine/chitosan-based piezoelectric film with sensitivity (∼2.82 ± 0.2 mV kPa −1 ) comparable to those of nondegradable commercial piezoelectric materials. The measured capacitance of the β-glycine/chitosan film is in the range from 0.26 to 0.12 nF at a frequency range from 100 Hz to 1 MHz, and its dielectric constant and loss factor are 7.7 and 0.18, respectively, in the high impedance range under ambient conditions. The results suggest that the glycine−chitosan composite is a promising new biobased piezoelectric material for biodegradable sensors for applications in wearable biomedical diagnostics.

Flexible electronics has huge potential to bring revolution in robotics and prosthetics as well as to bring about the next big evolution in electronics industry. In robotics and related applications, it is expected to revolutionise the way with which machines interact with humans, real-world objects and the environment. For example, the conformable electronic or tactile skin on robot's body, enabled by advances in flexible electronics, will allow safe robotic interaction during physical contact of robot with various objects. Developing a conformable, bendable and stretchable electronic system requires distributing electronics over large non-planar surfaces and movable components. The current research focus in this direction is marked by the use of novel materials or by the smart engineering of the traditional materials to develop new sensors, electronics on substrates that can be wrapped around curved surfaces. Attempts are being made to achieve flexibility/stretchability in e-skin while retaining a reliable operation. This review provides insight into various materials that have been used in the development of flexible electronics primarily for e-skin applications.

This paper presents novel Neural Nanowire Field Effect Transistors (υ-NWFETs) based hardware-implementable neural network (HNN) approach for tactile data processing in electronic skin (e-skin). The viability of Si nanowires (NWs) as the active material for υ-NWFETs in HNN is explored through modeling and demonstrated by fabricating the first device. Using υ-NWFETs to realize HNNs is an interesting approach as by printing NWs on large area flexible substrates it will be possible to develop a bendable tactile skin with distributed neural elements (for local data processing, as in biological skin) in the backplane. The modeling and simulation of υ-NWFET based devices show that the overlapping areas between individual gates and the floating gate determines the initial synaptic weights of the neural network - thus validating the working of υ-NWFETs as the building block for HNN. The simulation has been further extended to υ-NWFET based circuits and neuronal computation system and this has been validated by interfacing it with a transparent tactile skin prototype (comprising of 6 × 6 ITO based capacitive tactile sensors array) integrated on the palm of a 3D printed robotic hand. In this regard, a tactile data coding system is presented to detect touch gesture and the direction of touch. Following these simulation studies, a four-gated υ-NWFET is fabricated with Pt/Ti metal stack for gates, source and drain, Ni floating gate, and Al2O3 high-k dielectric layer. The current-voltage characteristics of fabricated υ-NWFET devices confirm the dependence of turn-off voltages on the (synaptic) weight of each gate. The presented υ-NWFET approach is promising for a neuro-robotic tactile sensory system with distributed computing as well as numerous futuristic applications such as prosthetics, and electroceuticals.

Electronic skin (eSkin) with various types of sensors over large conformable substrates has received considerable interest in robotics. The continuous operation of large number of sensors and the readout electronics make it challenging to meet the energy requirements of eSkin. In this article, we present the first energy generating eSkin with intrinsic tactile sensing without any touch sensor. The eSkin comprises a distributed array of miniaturized solar cells and infrared light emitting diodes (IRLEDs) on soft elastomeric substrate. By innovatively reading the variations in the energy output of the solar cells and IRLEDs, the eSkin could sense multiple parameters (proximity, object location, edge detection, etc.). As a proof of concept, the eSkin has been attached to a 3-D-printed hand. With an energy surplus of 383.6 mW from the palm area alone, the eSkin could generate more than 100 W if present over the whole body (area ∼1.5 m 2 ). Further, with an industrial robot arm, the presented eSkin is shown to enable safe human−robot interaction. The novel paradigm presented in this article for the development of a flexible eSkin extends the application of solar cell from energy generation alone to simultaneously acting as touch sensors.Index Terms-Electronic skin (eSkin), energy harvesting, human−robot interaction (HRI), proximity sensing, solar cell, touch sensing. I. INTRODUCTIONElectronic skin or "eSkin" has recently emerged as a novel platform for advances in robotics, prosthesis, health diagnostics, therapeutics, and monitoring [1]. It allows robots and prosthetic limbs to gather tactile information from large area contacts and to exploit the same to operate in unstructured environment or to improve human−robot interaction (HRI) [2]-[6]. Likewise, eSkin has been explored for measurement of vital health parameters and to provide reliable, effective, and, sometimes, life-saving functions [7]-[9]. With increasing number and type of sensors (pressure, temperature, texture, proximity, etc.) and electronics associated with them on large area eSkin [10]-[13], a stable power supply is critical for practical usage [11], [14]. Thus, a realistic and accessible power source is urgently needed for a next-generation of smart, stand-alone, always-on eSkins. This is a challenge as the continuous power supply through batteries is not practical because they add weight, are not flexible, and may require redesigning of robotics platform [15], [16]. Likewise, for applications requiring intimate integration of eSkin

Fabric‐based supercapacitors have received considerable interest as energy storage devices for wearable systems. This work demonstrates the use of metal coated fabrics as the active material and current collector with nontoxic polyvinyl alcohol (PVA)‐KCl gel electrolyte for wearable supercapacitors (SCs). To evaluate the influence of the metal coating, the electrochemical and capacitive studies are carried out and results are compared with a newly developed metal free graphite printed textile (cellulose‐polyester) (CP‐Gr) based SC. It is evident that the homemade graphite paste electrode printed on the top of Armor FR (Ni/Cu coated polyester fabric) (AFR‐Gr) and Nora Dell (Ni/Cu/Ag coated polyamide) (ND‐Gr) based SCs with PVA‐KCl electrolyte exhibits the specific capacitance of 99.06 and 46.88 mF cm−2, respectively, at sweep rate of 5 mV s−1. These values are 24 and 52 times greater than that of CP‐Gr based SC. The AFR‐Gr and ND‐Gr based SCs have an excellent energy density of 8.81 and 4.17 µWh cm−2, respectively, at 5 mV s−1. The fabricated ND‐Gr based SC gives a stable response for more than 5000 charging/discharging cycles. Finally, the nontoxic nature of the PVA‐KCl gel electrolyte is evaluated and confirmed through in vitro cytocompatibility assessment with adult human dermal fibroblasts cells for wearable applications.