Flexible and Stretchable Self‐Powered Multi‐Sensors Based on the N‐Type Thermoelectric Response of Polyurethane/Na x (Ni‐ett) n Composites

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Abstract

Flexible and stretchable electronic devices have a broad range of potential uses, from biomedicine, soft robotics, and health monitoring to the internet‐of‐things. Unfortunately, finding a robust and reliable power source remains challenging, particularly in off‐the‐grid and maintenance‐free applications. A sought‐after development overcome this challenge is the development of autonomous, self‐powered devices. A potential solution is reported exploiting a promising n‐type thermoelectric compound, poly nickel‐ethenetetrathiolates (Na _x (Ni‐ett) _n ). Highly stretchable n‐type composite films are obtained by combining Na _x (Ni‐ett) _n with commercial polyurethane (Lycra). As high as 50 wt% Na _x (Ni‐ett) _n content composite film can withstand deformations of ≈500% and show conductivities of ≈10 ⁻² S cm ⁻¹ and Seebeck coefficients of approx. −40 µV K ⁻¹. These novel materials can be easily synthesized on a large scale with continuous processes. When subjected to a small temperature difference (<20 °C), the films generate sufficient thermopower to be used for sensing strain (gauge factor ≈20) and visible light (sensitivity factor ≈36% (kW m ⁻²) ⁻¹), independent of humidity (sensitivity factor ≈0.1 (%RH) ⁻¹). As a proof‐of‐concept, a wearable self‐powered sensor is demonstrated by using n‐type Na _x (Ni‐ett) _n /Lycra and PEDOT:PSS/Lycra elements, connected in series by hot pressing, without employing any metal connections, hence preserving good mechanical ductility and ease of processing.

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Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis.

Wei Gao, Sam Emaminejad, Hnin Nyein … (2016)

Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiological information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and requires full system integration to ensure the accuracy of measurements. Here we present a mechanically flexible and fully integrated (that is, no external analysis is needed) sensor array for multiplexed in situ perspiration analysis, which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temperature (to calibrate the response of the sensors). Our work bridges the technological gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their respective inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and to make a real-time assessment of the physiological state of the subjects. This platform enables a wide range of personalized diagnostic and physiological monitoring applications.

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An integrated design and fabrication strategy for entirely soft, autonomous robots.

Michael Wehner, Ryan Truby, Daniel J Fitzgerald … (2016)

Soft robots possess many attributes that are difficult, if not impossible, to achieve with conventional robots composed of rigid materials. Yet, despite recent advances, soft robots must still be tethered to hard robotic control systems and power sources. New strategies for creating completely soft robots, including soft analogues of these crucial components, are needed to realize their full potential. Here we report the untethered operation of a robot composed solely of soft materials. The robot is controlled with microfluidic logic that autonomously regulates fluid flow and, hence, catalytic decomposition of an on-board monopropellant fuel supply. Gas generated from the fuel decomposition inflates fluidic networks downstream of the reaction sites, resulting in actuation. The body and microfluidic logic of the robot are fabricated using moulding and soft lithography, respectively, and the pneumatic actuator networks, on-board fuel reservoirs and catalytic reaction chambers needed for movement are patterned within the body via a multi-material, embedded 3D printing technique. The fluidic and elastomeric architectures required for function span several orders of magnitude from the microscale to the macroscale. Our integrated design and rapid fabrication approach enables the programmable assembly of multiple materials within this architecture, laying the foundation for completely soft, autonomous robots.