MXenes, a kind of two-dimensional material of early transition metal carbides and carbonitrides, have emerged as a unique class of layered-structured metallic materials with attractive features, as good conductivity comparable to metals, enhanced ionic conductivity, hydrophilic property derived from their hydroxyl or oxygen-terminated surfaces, and mechanical flexibility. With tunable etching methods, the morphology of MXenes can be effectively controlled to form nanoparticles, single layer, or multi-layer nanosheets, which exhibit large specific surface areas and is favorable for enhancing the sensing performance of MXenes based sensors. Moreover, MXenes are available to form composites with other materials facilely. With structure design, MXenes or its composite show enhanced mechanical flexibility and stretchability, which enabled its wide application in the fields of wearable sensors, energy storage, and electromagnetic shielding. In this review, recent progress in MXenes is summarized, focusing on its application in wearable sensors including pressure/strain sensing, biochemical sensing, temperature, and gas sensing. Furthermore, the main challenges and future research are also discussed.

Flexible and wearable electronic devices are emerging as the novel platform for portable health monitoring, human–machine interaction, and some other electronic/optic applications. Future development of human-friendly smart electronics relies on efficient manufacturing and processing of advanced functional materials on flexible/stretchable substrates with effective device integration. Inkjet printing, known as a highly efficient solution-based printing and patterning technology with low-cost, high-quality, and high-throughput advantages, suits large-scale fabrication of flexible and wearable electronics. Over the years, researchers focused on high pattern resolution and uniformity on flexible substrates for advanced electrical/optical performances by various inkjet printing techniques. Different ink materials that can realize multiple functions have been fully investigated for achieving favorable printability and desired interactions with the substrates. Here, the most recently reported inkjet printing strategies, functional ink materials, and diverse inkjet-printed wearable electronic devices for practical applications (e.g., sensors, displays, transistors, and energy storage devices) are summarized. An outlook on future challenges as well as opportunities of inkjet-printed flexible and wearable electronics for research development and industrial commercialization is also presented.

On-skin devices that show both high performance and imperceptibility are desired for physiological information detection, individual protection, and bioenergy conversion with minimal sensory interference. Herein, versatile electrospun micropyramid arrays (EMPAs) combined with ultrathin, ultralight, gas-permeable structures are developed through a self-assembly technology based on wet heterostructured electrified jets to endow various on-skin devices with both superior performance and imperceptibility. The designable self-assembly allows structural and material optimization of EMPAs for on-skin devices applied in daytime radiative cooling, pressure sensing, and bioenergy harvesting. A temperature drop of ~4 °C is obtained via an EMPA-based radiative cooling fabric under a solar intensity of 1 kW m–2. Moreover, detection of an ultraweak fingertip pulse for health diagnosis during monitoring of natural finger manipulation over a wide frequency range is realized by an EMPA piezocapacitive-triboelectric hybrid sensor, which has high sensitivity (19 kPa−1), ultralow detection limit (0.05 Pa), and ultrafast response (≤0.8 ms). Additionally, EMPA nanogenerators with high triboelectric and piezoelectric outputs achieve reliable biomechanical energy harvesting. The flexible self-assembly of EMPAs exhibits immense potential in superb individual healthcare and excellent human-machine interaction in an interference-free and comfortable manner.