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.

The success of stretchable electronics based on conjugated polymers relies on having a thorough understanding of the polymer’s mechanical behavior over conditions likely encountered during operation. To meet this need, a novel approach to capture the stress–strain response of thin conjugated polymer films is introduced. This is achieved by laminating the polymer film of interest on a thin elastomer substrate and testing the composite specimen in a dynamic mechanical analyzer in a tensile test configuration. We term this approach as film laminated on thin elastomer (FLOTE) method. The benefits of this method include the ability to (1) determine the viscoelastic behavior of the conjugated polymer by testing over a broad range of temperatures and strain rates, (2) measure the film behavior over large cyclic strains, including under in-plane compression, and (3) capture the impact of the neighboring elastomer on the behavior of the polymer film. The focus is on the widely studied poly­(3-hexylthiophene) (P3HT) as a model system. We find that the viscoelastic characteristics of P3HT, varied by changing the specimen temperature, significantly impact film stability under cyclic strain. This includes showing that the hysteresis behavior of the films under cyclic strain changes significantly with sample temperature. In addition, it is found that, under cyclic loading, the composite has features consistent with Mullins’ effect. Based on these results, insights into polymer viscoelastic characteristics necessary to achieve high-performance stretchable electronics are gained.

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.

Stretchable conductive polymer films are required to survive not only large tensile strain but also stay functional after the reduction in applied strain. In the deformation process, the elastomer substrate that is typically employed plays a critical role in response to the polymer film. In this study, we examine the role of a polydimethylsiloxane (PDMS) elastomer substrate on the ability to achieve stretchable PDPP-4T films. In particular, we consider the adhesion and near-surface modulus of the PDMS tuned through UV/ozone (UVO) treatment on the competition between film wrinkling and plastic deformation. We also consider the role of PDMS tension on the stability of films under cyclic strain. We find that increasing the near-surface modulus of the PDMS and maintaining the PDMS in tension throughout the cyclic strain process promote plastic deformation over film wrinkling. In addition, the UVO treatment increases film adhesion to the PDMS resulting in a significantly reduced film folding and delamination. For a 20 min UVO-treated PDMS, we show that a PDPP-4T film root-mean-square roughness is consistently below 3 nm for up to 100 strain cycles with a strain range of 40%. In addition, although the film is plastically deforming, the microstructural order is largely stable as probed by grazing incidence X-ray scattering and UV–visible spectroscopy. These results highlight the importance of neighboring elastomer characteristics on the ability to achieve stretchable polymer semiconductors.

Stretchable electronics are poised to revolutionize personal healthcare and robotics, where they enable distributed and conformal sensors. Transistors are fundamental building blocks of electronics, and there is a need to produce stretchable transistors using low-cost and scalable fabrication techniques. Here, we introduce a facile fabrication approach using laser patterning and transfer printing to achieve high-performance, solutionprocessed intrinsically stretchable organic thin-film transistors (OTFTs). The device consists of Ag nanowire (NW) electrodes, where the source and drain electrodes are patterned using laser ablation. The Ag NWs are then partially embedded in a poly(dimethylsiloxane) (PDMS) matrix. The electrodes are combined with a PDMS dielectric and polymer semiconductor, where the layers are individually transfer printed to complete the OTFT. Two polymer semiconductors, DPP-DTT and DPP-4T, are considered and show stable operation under the cyclic strain of 20 and 40%, respectively. The OTFTs maintain electrical performance by adopting a buckled structure after the first stretch-release cycle. The conformability and stretchability of the OTFT is also demonstrated by operating the transistor while adhered to a finger being flexed. The ability to pattern highly conductive Ag NW networks using laser ablation to pattern electrodes as well as interconnects provides a simple strategy to produce complex stretchable OTFT-based circuits.