Nanomaterial‐enabled flexible and stretchable electronics have seen tremendous progress in recent years, evolving from single sensors to integrated sensing systems. Compared with nanomaterial‐enabled sensors with a single function, integration of multiple sensors is conducive to comprehensive monitoring of personal health and environment, intelligent human–machine interfaces, and realistic imitation of human skin in robotics and prosthetics. Integration of sensors with other functional components promotes real‐world applications of the sensing systems. Here, an overview of the design and integration strategies and manufacturing techniques for such sensing systems is given. Then, representative nanomaterial‐enabled flexible and stretchable sensing systems are presented. Following that, representative applications in personal health, fitness tracking, electronic skins, artificial nervous systems, and human–machine interactions are provided. To conclude, perspectives on the challenges and opportunities in this burgeoning field are considered.

Stretchable electronics based on nanomaterials has received much interest recently. However, it is challenging to print 1D nanomaterials (e.g., nanowires) with high resolution on stretchable elastomeric substrates. Electrohydrodynamic (EHD) printing has been used to print 1D nanomaterials such as silver nanowires (AgNWs) on stretchable substrates, but the resolution and electric conductivity of the printed patterns are typically low because of the poor wettability of the ink on the surface of the substrates. This paper reports a systematic study of two surface modification methods, UV–ozone treatment and dopamine coating, to modify the surface of polydimethylsiloxane (PDMS), which enables reliable and tunable EHD printing of AgNWs. The dynamic contact angle and the contact angle hysteresis were systematically studied to understand and evaluate the two surface modification methods. This work further investigates the hydrophobic stability of the two surface modification methods that is of critical relevance to the EHD printing, as it determines the shelf life of the treated samples. The effects of treatment dose and aging on the EHD printing performances, such as resolution and conductivity, were studied to find the feasible ranges of the parameters for the surface treatment and printing process. The surface modification methods along with the proper printing conditions can be selected to tailor and optimize the printing performance. A wearable electronic patch with a fractal pattern of AgNWs is printed on the modified PDMS substrate to demonstrate the potential of the reported surface modification for reliable EHD printing of AgNWs for stretchable devices.

Multi‐layer electrical interconnects are critical for the development of integrated soft wearable electronic systems, in which functional devices from different layers need to be connected together by vertical interconnects. In this work, electrohydrodynamic (EHD) printing technology is studied to achieve multi‐layer flexible and stretchable electronics by direct printing vertical interconnects as vertical interconnect accesses (VIAs) using a low‐melting‐point metal alloy. The EHD printed metallic vertical interconnection represents a promising way for the direct fabrication of multilayer integrated electronics with metallic conductivity and excellent flexibility and stretchability. By controlling the printing conditions, vertical interconnects that can bridge different heights can be fabricated. To achieve reliable VIA connections under bending and stretching conditions, an epoxy protective structure is printed around the VIA interconnects to form a core‐shell structure. A stable electrical response is achieved under hundreds of bending cycles and during stretching/releasing cycles in a large range of tensile strain (0–40%) for the printed conductors with VIA interconnects. A few multi‐layer devices, including a multiple layer heater, and a pressure‐based touch panel are fabricated to demonstrate the capability of the EHD printing for the direct fabrication of vertical metallic VIA interconnects for flexible and stretchable devices.

Compliant pressure sensors are a key technology for wearable electronics and haptic interfaces. Making transistors pressure‐sensitive provides an opportunity to combine sensing and matrix readout characteristics. However, there is typically a trade‐off in pressure sensitivity, complexity of fabrication, and mechanical resilience. To overcome these challenges, an all solution‐processed kirigami‐inspired stretchable organic thin film transistor (OTFT) based pressure sensor array is introduced. The OTFTs integrate several novel processing and design strategies that include electrohydrodynamic (EHD) jet‐printed Ag nanowire (NW) electrodes that are partially embedded in a polyimide (PI) matrix. The EHD printing provides fine pattern control and the NW/PI composite improves mechanical stability. The OTFTs are made pressure sensitive by employing a porous styrene‐ethylene‐butylene‐styrene gate dielectric achieved using a breath figure method. The pore density can be controlled to achieve tunable pressure sensitivity. The OTFTs are shown to maintain performance under a small bending radius (1 mm) and can sense applied pressure from 0.75 to 25 kPa. Finally, a cut pattern is introduced into the substrate that imparts stretchability while maintaining pressure sensor functionality. The integration of the design features and processing methods introduced in this work enables mechanically resilient stretchable pressure sensors.

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