We present our efforts toward enabling a wearable sensor system that allows for the correlation of individual environmental exposures with physiologic and subsequent adverse health responses. This system will permit a better understanding of the impact of increased ozone levels and other pollutants on chronic asthma conditions. We discuss the inefficiency of existing commercial off-the-shelf components to achieve continuous monitoring and our system-level and nano-enabled efforts toward improving the wearability and power consumption. Our system consists of a wristband, a chest patch, and a handheld spirometer. We describe our preliminary efforts to achieve a submilliwatt system ultimately powered by the energy harvested from thermal radiation and motion of the body with the primary contributions being an ultralow-power ozone sensor, an volatile organic compounds sensor, spirometer, and the integration of these and other sensors in a multimodal sensing platform. The measured environmental parameters include ambient ozone concentration, temperature, and relative humidity. Our array of sensors also assesses heart rate via photoplethysmography and electrocardiography, respiratory rate via photoplethysmography, skin impedance, three-axis acceleration, wheezing via a microphone, and expiratory airflow. The sensors on the wristband, chest patch, and spirometer consume 0.83, 0.96, and 0.01 mW, respectively. The data from each sensor are continually streamed to a peripheral data aggregation device and are subsequently transferred to a dedicated server for cloud storage. Future work includes reducing the power consumption of the system-on-chip including radio to reduce the entirety of each described system in the submilliwatt range.

Low-voltage and extremely flexible electrothermal bimorph actuators were fabricated in a simple, efficient and scalable process. The bimorph actuators were made of flexible silver nanowire (AgNW) based heaters, which exhibited a fast heating rate of 18 °C s⁻¹ and stable heating performance with large bending. The actuators offered the largest bending angle (720°) or curvature (2.6 cm⁻¹) at a very low actuation voltage (0.2 V sq⁻¹ or 4.5 V) among all types of bimorph actuators that have been reported to date. The actuators can be designed and fabricated in different configurations that can achieve complex patterns and shapes upon actuation. Two applications of this type of soft actuators were demonstrated towards biomimetic robotics – a crawling robot that can walk spontaneously on ratchet surfaces and a soft gripper that is capable of manipulating lightweight and delicate objects.

Skin-integrated haptic interfaces that can relay a wealth of information from the machine to the human are of great interest. However, existing haptic devices are not yet able to produce haptic cues that are compatible with the skin. In this work, we present the stretchable soft actuators for haptic feedback, which can match the perception range, spatial resolution, and stretchability of the skin. Pressure-amplification structures are fabricated using a scalable self-assembly process to ensure an output pressure beyond the skin perception threshold. Due to the minimized device size, the actuator array can be fabricated with a sufficiently high spatial resolution, which makes the haptic device applicable for skin locations with the highest spatial acuity. A haptic feedback system is demonstrated by employing the developed soft actuators and highly sensitive pressure sensors. Two proof-of-concept applications are developed to illustrate the capability of transferring information related to surface textures and object shapes acquired at the robot side to the user side.

On‐skin electronics have drawn extensive attention as they revolutionize many aspects of healthcare, motion tracking, rehabilitation, robotics, human–machine interaction, among others. Flexible and stretchable strain sensors represent one of the most explored devices for on‐skin electronics. Many printing techniques have recently emerged showing great promises for manufacturing strain sensors. Herein, it is aimed to provide a timely survey of recent advancements in printed strain sensors for on‐skin electronics. This review starts with an overview of sensing mechanisms for printed strain sensors, followed by a review of various printing techniques employed in fabricating these sensors. The materials, structures, and printing processes of representative strain sensors are discussed in detail for each printing method. Finally, potential applications of printed flexible and stretchable strain sensors are presented focusing on three areas: healthcare, sports performance monitoring, and human–machine interfaces. The review concludes with a discussion of challenges and opportunities for future research.