Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Surgical sealing and repair of injured and resected gastrointestinal (GI) organs are critical requirements for successful treatment and tissue healing. Despite being the standard of care, hand-sewn closure of GI defects using sutures faces limitations and challenges. In this work, we introduce an off-the-shelf bioadhesive GI patch capable of atraumatic, rapid, robust, and sutureless repair of GI defects. The GI patch integrates a nonadhesive top layer and a dry, bioadhesive bottom layer, resulting in a thin, flexible, transparent, and ready-to-use patch with tissue-matching mechanical properties. The rapid, robust, and sutureless sealing capability of the GI patch is systematically characterized using ex vivo porcine GI organ models. In vitro and in vivo rat models are used to evaluate the biocompatibility and degradability of the GI patch in comparison to commercially available tissue adhesives (Coseal and Histoacryl). To validate the GI patch’s efficacy, we demonstrate successful sutureless in vivo sealing and healing of GI defects in rat colon, stomach, and small intestine as well as in porcine colon injury models. The proposed GI patch provides a promising alternative to suture for repair of GI defects and offers potential clinical opportunities for the repair of other organs.

The pulse is a key biomedical signal containing various human physiological and pathological information highly related to cardiovascular diseases. Pulse signals are often collected from the radial artery based on Traditional Chinese Medicine, or by using flexible pressure sensors. However, the wrist wrapped with a flexible pressure sensor exhibits unstable signals under hand motion because of the concave surface of the wrist. By contrast, fingertips have a convex surface and therefore show great promises in stable and long‐term pulse monitoring. Despite the promising potential, the fingertip pulse signal is weak, calling for highly sensitive detecting devices. Here, a highly sensitive and flexible iontronic pressure sensor with a linear sensitivity of 13.5 kPa−1, a swift response, and remarkable stability over 5000 loading/unloading cycles is developed. This sensor enables stable and high‐resolution detection of pulse waveform under both static condition and finger motion. Fingertip pulse waveforms from subjects of different genders, age, and health conditions are collected and analyzed, suggesting that fingertip pulse information is highly similar to that of the radial artery. This work justifies that fingertip is an ideal platform for pulse signals monitoring, which would be a competitive alternative to existing complex health monitoring systems.

Next-generation flexible electronics require highly stretchable and transparent electrodes. Few electronic conductors are both transparent and stretchable, and even fewer can be cyclically stretched to a large strain without causing fatigue. Fatigue, which is often an issue of strained materials causing failure at low strain levels of cyclic loading, is detrimental to materials under repeated loads in practical applications. Here we show that optimizing topology and/or tuning adhesion of metal nanomeshes can significantly improve stretchability and eliminate strain fatigue. The ligaments in an Au nanomesh on a slippery substrate can locally shift to relax stress upon stretching and return to the original configuration when stress is removed. The Au nanomesh keeps a low sheet resistance and high transparency, comparable to those of strain-free indium tin oxide films, when the nanomesh is stretched to a strain of 300%, or shows no fatigue after 50,000 stretches to a strain up to 150%. Moreover, the Au nanomesh is biocompatible and penetrable to biomacromolecules in fluid. The superstretchable transparent conductors are highly desirable for stretchable photoelectronics, electronic skins, and implantable electronics.fatigue-free | adhesion | biocompatibility | topology | stretchability F lexible transparent electrodes are crucial to the emerging fields of flexible solar cells (1, 2), flexible electronics (3-5), electronic skins (e-skins) (6), and implantable electronics (7,8). Among the several modes of flexibility, including bending, folding, twisting, and stretching, stretching generates the largest strain and therefore is the most demanding (9). What is even more challenging is to make transparent electrodes fatigue-free under cyclic stretches. Fatigue often happens during strain cycling, even if the strain level is relatively low. It determines the real loading that can be applied to a material in practical applications. However, metallic materials often exhibit high cycle fatigue (10), and fatigue has been a deadly disease for metals.Several types of transparent conductors, including graphene sheets, carbon nanotube (CNT) films, metal nanowire (NW) networks, composites based on Ag NWs, metal meshes, and ultrathin metal films have been found to be stretchable (1,3,6,(11)(12)(13)(14)(15)(16)(17)(18). However, sheet resistance (R sh ) of existing stretchable transparent electrodes often sharply increases when highly stretched, or repeatedly stretched to relatively small strains for thousands of cycles. Graphene can be stretched one time to 30%, or cyclically stretched to 6% for a few times (11). Metal meshes made of straight lines and ultrathin metal films are also stretchable, but typically they cannot be stretched to more than 100% (16, 17). The Bao group has shown that CNT network film with a serpentine morphology can be stretched one time to 170% before failure, or repeatedly stretched to 25% for 12,500 cycles with a modest increase of resistance (6). Here we show that optimizing topology of a Au nanomesh can ...

Flexible pressure sensors with high sensitivity are desired in the fields of electronic skins, human–machine interfaces, and health monitoring. Employing ionic soft materials with microstructured architectures in the functional layer is an effective way that can enhance the amplitude of capacitance signal due to generated electron double layer and thus improve the sensitivity of capacitive-type pressure sensors. However, the requirement of specific apparatus and the complex fabrication process to build such microstructures lead to high cost and low productivity. Here, we report a simple strategy that uses open-cell polyurethane foams with high porosity as a continuous three-dimensional network skeleton to load with ionic liquid in a one-step soak process, serving as the ionic layer in iontronic pressure sensors. The high porosity (95.4%) of PU-IL composite foam shows a pretty low Young’s modulus of 3.4 kPa and good compressibility. A superhigh maximum sensitivity of 9,280 kPa−1 in the pressure regime and a high pressure resolution of 0.125% are observed in this foam-based pressure sensor. The device also exhibits remarkable mechanical stability over 5,000 compression-release or bending-release cycles. Such high porosity of composite structure provides a simple, cost-effective and scalable way to fabricate super sensitive pressure sensor, which has prominent capability in applications of water wave detection, underwater vibration sensing, and mechanical fault monitoring.