Wearable biosensors attract significant interest for their capabilities in real-time monitoring of wearers’ health status, as well as the surrounding environment. Sensor patches are embedded onto the human epidermis accompanied by data readout and signal conditioning circuits with wireless communication modules for transmitting data to the computing devices. Wearable sensors designed for recognition of various biomarkers in human epidermis fluids, such as glucose, lactate, pH, cholesterol, etc., as well as physiological indicators, i.e., pulse rate, temperature, breath rate, respiration, alcohol, activity monitoring, etc., have potential applications both in medical diagnostics and fitness monitoring. The rapid developments in solution-based nanomaterials offered a promising perspective to the field of wearable sensors by enabling their cost-efficient manufacturing through printing on a wide range of flexible polymeric substrates. This review highlights the latest key developments made in the field of wearable sensors involving advanced nanomaterials, manufacturing processes, substrates, sensor type, sensing mechanism, and readout circuits, and ends with challenges in the future scope of the field. Sensors are categorized as biological and fluidic, mounted directly on the human body, or physiological, integrated onto wearable substrates/gadgets separately for monitoring of human-body-related analytes, as well as external stimuli. Special focus is given to printable materials and sensors, which are key enablers for wearable electronics.

Conductive nanocomposites have emerged as significant smart engineered materials for realizing flexible electronics on diverse substrates in recent years. Conductive nanocomposites are comprised of conductive fillers mixed with polymeric elastomer (e.g. polydimethylsiloxane). The possibility to tune electrical as well as mechanical properties of nanocomposites makes them suitable for a wide spectrum of applications including sensors and electronics on non-planar and stretchable surfaces. A number of conductive nanofillers and manufacturing technologies have been developed to meet the diverse requirements of various applications. Considering the substantial contribution of conductive nanocomposites, it is opportune time to review the potentials of various nanofillers, their synthesis, processing methodologies and challenges associated to them. This paper reviews conductive nanocomposites, especially in context with their use in the development of electronic components and the sensors exploiting the piezoresistive behavior. The paper is structured around the nanocomposites related studies aiming to develop various building blocks of flexible electronic skin systems such as pressure, touch, strain and temperature sensors as well as stretchable interconnects. Besides this, the use of nanocomposites in other stimulating industrial and biomedical applications has also been explored briefly.

The rapid growth in wearable biosensing devices is pushed by the strong desire to monitor the human health data and to predict the disease at an early stage. Different sensors are developed to monitor various biomarkers through wearable and implantable sensing patches. Temperature sensor has proved to be an important physiological parameter amongst the various wearable biosensing patches. This paper highlights the recent progresses made in printing of functional nanomaterials for developing wearable temperature sensors on polymeric substrates. A special focus is given to the advanced functional nanomaterials as well as their deposition through printing technologies. The geometric resolutions, shape, physical and electrical characteristics as well as sensing properties using different materials are compared and summarized. Wearability is the main concern of these newly developed sensors, which is summarized by discussing representative examples. Finally, the challenges concerning the stability, repeatability, reliability, sensitivity, linearity, ageing and large scale manufacturing are discussed with future outlook of the wearable systems in general.

This paper presents two types of metal insulator field effect transistors (MISFETs) devices fabricated from Si microwires through a new manufacturing route involving a combination of printing and microfabrication technologies. Si microwires, developed through standard photolithography and etching steps, are transferred from a silicon on insulator wafer onto polyimide using stamp-assisted transfer printing. The MISFETs are then obtained by spray coating the dielectric layer and metal contact layer. Spray coating has been introduced here for the first time for deposition of organic dielectric on transfer printed Si microwires. Two groups of the devices are fabricated, one based on a single Si microwire and the other based on the array of 15 microwires of similar dimensions. The variations in the output response of the two groups of devices has been investigated. The devices based on array of microwires are observed to have less variation in the output response, with lesser standard deviations as compared to MISFETs made from single Si microwires.

Memristor got a significant attraction to be the next generation memory device due to its small size, simple architecture, high density, and low power consumption. A memristor is a passive two-terminal primary electronic device with a built-in non-volatile memory function that can be fabricated in a crossbar structure. In the literature, independent studies have been reported on memristor manufacturing concerning the spatial resolution of the crossbar electrodes, and thickness of the active layer. However, this paper presents a comprehensive review different from others by comparing all the additive manufacturing technologies and their limitations for the development of a memristor array. A detailed study is performed about the pattern resolution, active layer fabrication, commonly used substrates, and device encapsulation methods. This review will provide a strong basis for the researchers, especially those working in the field of printed memristor devices.