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Ulcers and chronic wounds are a large and expensive problem, costing billions of pounds a year and affecting millions of people. Electrical stimulation has been known to have a positive effect on wound healing since the 1960s and this has been confirmed in numerous studies, reducing the time to heal, and the incidence of adverse events such as infections. However, because each study used different parameters for the treatment, inclusion criteria and metrics for quantifying the success, it is currently hard to combine them statistically and gain a true picture of its efficacy. As such, electrical stimulation has not been universally adopted as a recommended treatment for various types of wound. This paper summarises the biological basis for electrical simulation treatment and reviews the clinical evidence for its effectiveness. Notable is the lack of research focused on the electrodes used to deliver electrostimulation treatment. However, a significant amount of work has been conducted on electrodes for other medical applications in the field of e-textiles. This e-textile work is reviewed with a focus on its potential in electrostimulation and proposals are made for future developments to improve future studies and applications for wound healing via electrical stimulation.

The emergence of wearable and remote sensing devices in e-health has revolutionized personalized healthcare monitoring, but the field of dermatology has yet to witness significant progress in this area. The diagnosis and monitoring of atopic dermatitis (AD), a common skin disease causing inflammation and rashes, depend on in-person assessment, leading to subjective evaluations and treatment procedures. This work presents a novel interdigitated capacitive sensor, specifically designed to detect biomarkers of AD and to empirically estimate the severity of the condition. The design was proven by finite-element analysis software to detect only biomarkers of AD—dehydration of the outermost skin layer. The IDC sensor has a compact and flexible footprint (sensing area of around 40 mm2); it is compatible with a wearable and noninvasive system, and can be used to remotely gather localized data about the condition. To calibrate its measurements, a novel hydration-gradient skin-mimicking phantom was developed, which simulates varying skin hydration conditions on the same substrate. The sensor is compared against a commercial skin hydration device, and its sensitivity is mapped against the arbitrary units (A.U.s) of the commercial device, resulting in a normalized capacitance sensitivity of 13.1 pF/cm2 per 1 A.U. This novel IDC sensor is the first sensor to accurately measure the permittivity of specific layers of the skin. Its bespoke design is the main enabler of the outermost layer’s permittivity to be isolated from the skin. This presents promising prospects for remote patient care, enabling accurate diagnosis, treatment monitoring, and personalized interventions for AD.

Triboelectric nanogenerators (TENG) are one of the most promising candidates for powering wearable and portable devices. Example TENGs have demonstrated flexibility, light weight, biocompatibility, versatility and good performance. Textiles are a potential substrate onto, or into, which wearable technology is increasingly being incorporated but supplying power remains an enduring challenge. TENGs are a potential textile based mechanical energy harvesting power supply and there has been an increasing effort to combine TENGs with fabrics. A significant challenge exists in the integration without losing the performance of the TENG or the original properties (appearance, breathability, washability, and durability) and feel of the textile. Various approaches towards the realisation of textile-based TENGs (T-TENGs) have been demonstrated. Depending on its structure, T-TENGs can be divided into two main types, fabric-based TENG and fibre-based TENG. The fabric-based TENG is composed of conventional and/or modified fabrics, which serve as a substrate and/or a triboelectric material. The fibre-based TENG is fabricated as a single fibre or a collection of interlaced fibres. This paper provides an up to date review of the progress in the research of T-TENGs. The paper covers the basic operating principles, possible operation modes, textile manufacturing methods, material selections, T-TENG fabrication process, surface modification and structural designs. Issues, such as standardised measurement parameters, the challenges and limitations of T-TENG are discussed.

E-textiles are a promising platform for wearable technologies; but it faces the ubiquitous challenge of supplying power. One approach is to harvest ambient solar energy. Here, we present a fully solution processed organic solar cell (OSC) fabricated directly on to the surface of a standard polyester cotton fabric. A flexible screen printed interface layer is used to selectively smooth the fabric surface on to which all subsequent layers were deposited. The active layers making up the OSC were deposited entirely by solution processing using either spray coating or doctor blading in a nitrogen environment. Process temperatures are limited to 150 °C to protect the fabric. Spray coating is found to be a repeatable and reliable way to deposit thin functional films onto the fabric and we have obtained a maximum efficiency of 1.23% demonstrating the feasibility of this approach for fabricating OSCs on any standard textile.

Abstract

This article reviews materials developed to enable energy harvesting from textiles. It includes energy harvesting from mechanical, thermal, and light sources, and covers materials employed into yarns that can be woven into the textile and films that are deposited onto the surface of the textile. The textile places challenging constraints on the materials, for example, by limiting processing temperatures to typically less than 150°C and presenting a rough, inconsistent surface profile. Example materials include a screen-printable low-temperature composite lead zirconate titanate polymer film and poly(vinylidene fluoride) polymer fibers, both of which have been shown to harvest mechanical energy from textiles. Thermoelectric solutions demonstrated thus far are limited and challenging to implement within a textile. Photovoltaic solutions include organic and dye-sensitized solar cells fabricated into functionalized yarns and as films spray-coated onto textiles. While numerous suitable example materials and textile devices have been demonstrated, work is still needed to develop these into practical energy-harvesting solutions.

This paper details the enhancements in the dielectric and piezoelectric properties of a low-temperature screen-printable piezoelectric nano-composite film on flexible plastic and textile substrates. These enhancements involved adding silver nano particles to the nano-composite material and using an additional cold isostatic pressing (CIP) post-processing procedure. These developments have resulted in a 18% increase in the free-standing piezoelectric charge coefficient d33to a value of 98 pC/N. The increase in the dielectric constant of the piezoelectric film has, however, resulted in a decrease in the peak output voltage of the composite film. The potential for this material to be used to harvest mechanical energy from a variety of textiles under compressive and bending forces has been evaluated theoretically and experimentally. The maximum energy density of the enhanced piezoelectric material under 800N compressive force was found to be 34J/m3on a Kermel textile. The maximum energy density of the enhanced piezoelectric material under bending was found to be 14.3J/m3on a cotton textile. These results agree very favourably with the theoretical predictions. For a 10x10cm piezoelectric element 100µm thick this equates to 38μJ and 14.3μJ of energy generated per mechanical action respectively which is a potentially useful amount of energy.

A novel textile-based triboelectric nanogenerator (TENG) with woven structure operating in freestanding triboelectric-layer mode, defined as a woven-TENG, has been developed. Whereas most woven-structured TENGs operate in contact-separation mode and consist of one type of triboelectric material, this woven-TENG comprises woven electrodes and woven strips of positive and negative triboelectric material, which form a checker-like pattern over the electrodes with matching periodicity. The implementation of the positive and negative triboelectric material significantly improves the performance of the woven-TENG. Furthermore, in contrast to the conventional grating-structured and woven-structured TENG, which are designed to operate only in one moving direction, this new design also allows the woven-TENG to harvest energy from all-planar directions of movement. The woven-TENG with woven strips of nylon and polytetrafluoroethylenevinyl (PTFE) fabric can generate a root mean square (RMS) open-circuit voltage of 62.9 V, an RMS short-circuit current of 1.77 µA and a maximum RMS power of 34.8 µW at a load resistance of 50 MΩ, a mechanical oscillation of 2 Hz and a contact force of 5 N. This corresponds to a maximum RMS power density of 5.43 mW/m2.

This paper reports a novel design of textile-based triboelectric nanogenerator (TENG) with alternate grated strips of positive and negative triboelectric material operating in freestanding triboelectric-layer mode, defined as a pnG-TENG. Whereas most grating-structured TENGs operating in a freestanding triboelectric-layer mode comprise gratings of one type of triboelectric material separated by air gaps, this design presents a replacement of the air gaps by another triboelectric material with the opposite polarity to the existing triboelectric material. This is predicted to increase performance by increasing the contact area of the generator. The pnG-TENG with 10 gratings of nylon fabric and PVC heat transfer vinyl delivers an RMS open-circuit voltage of 136 V, an RMS short-circuit current of 2.68 μA and a maximum RMS power of 125 μW at a load resistance of 50 MΩ, a mechanical oscillation of 2 Hz and a contact force of 5 N. This corresponds to a maximum RMS power density of 38.8 mW/m2, which is 1.94 and 6.43 times greater than the power generated by the TENG with a single triboelectric material and the TENG with no gratings, respectively.