Capabilities in health monitoring via capture and quantitative chemical analysis of sweat could complement, or potentially obviate the need for, approaches based on sporadic assessment of blood samples. Established sweat monitoring technologies use simple fabric swatches and are limited to basic analysis in controlled laboratory or hospital settings. We present a collection of materials and device designs for soft, flexible and stretchable microfluidic systems, including embodiments that integrate wireless communication electronics, which can intimately and robustly bond to the surface of skin without chemical and mechanical irritation. This integration defines access points for a small set of sweat glands such that perspiration spontaneously initiates routing of sweat through a microfluidic network and set of reservoirs. Embedded chemical analyses respond in colorimetric fashion to markers such as chloride and hydronium ions, glucose and lactate. Wireless interfaces to digital image capture hardware serve as a means for quantitation. Human studies demonstrated the functionality of this microfluidic device during fitness cycling in a controlled environment and during long-distance bicycle racing in arid, outdoor conditions. The results include quantitative values for sweat rate, total sweat loss, pH and concentration of both chloride and lactate.

Battery-free, wireless microfluidic/electronic system for multiparameter sweat analysis.

A highly stretchable and transparent electrical heater is demonstrated by constructing a partially embedded silver nanowire percolative network on an elastic substrate. The stretchable network heater is applied on human wrists under real-time strain, bending, and twisting, and has potential for lightweight, biocompatible, and versatile wearable applications.

A facile fast laser nanoscale welding process uses the plasmonic effect at a nanowire (NW) junction to suppress oxidation and successfully fabricate a Cu-NW-based percolation-network conductor. The "nanowelding" process does not require an inert or vacuum environment. Due to the low-temperature and fast-process nature, plasmonic laser nanowelding may form Cu-nanowire networks on heat-sensitive, flexible or even stretchable substrates.

As is frequently seen in sci-fi movies, future electronics are expected to ultimately be in the form of wearable electronics. To realize wearable electronics, the electric components should be soft, fl exible, and even stretchable to be human-friendly. An important step is presented toward realization of wearable electronics by developing a hierarchical multiscale hybrid nanocomposite for highly fl exible, stretchable, or transparent conductors. The hybrid nanocomposite combines the enhanced mechanical compliance, electrical conductivity, and optical transparency of small CNTs (d ≈ 1.2 nm) and the enhanced electrical conductivity of relatively bigger Ag nanowire (d ≈ 150 nm) backbone to provide effi cient multiscale electron transport path with Ag nanowire current backbone collector and local CNT percolation network. The highly elastic hybrid nanocomposite conductors and highly transparent fl exible conductors can be mounted on any non-planar or soft surfaces to realize human-friendly electronics interface for future wearable electronics.

cost-effective and large-area energy harvesting without any vacuum process. [27][28][29][30][31][32] Although NCGs have been regarded as a concept of stretchy piezoelectric systems, the authentically operating stretchable NCG has not been yet realized due to the absence of proper stretchable electrodes and robust composite matrix. [33][34][35] While these bendable nanogenerators have been intensively studied using diverse piezoelectric materials and structures, the development of stretchable high-output energy harvesters still requires further investigation to realize self-powered stretchable electronic systems.Several researchers have explored buckling structures with piezoelectric ribbons [36][37][38] or micropatterning-notched structures with polyvinylidenefl oride (PVDF)/graphene. [ 39 ] They reported producing output currents of tens of picoamperes to nanoamperes with the elongating/releasing stretchable energy harvesters. However, the generated output was insuffi cient to operate practical electronic devices, due to the narrow/confi ned piezoactive ribbons or the low piezoelectricity. In addition, the stretchable energy harvesters suffer from defi cient stretchability (below a few tens of percentage) and poor reversibility caused by intrinsic material stiffness and structural dependency, resulting in unstable output signals, incompatible integration, and limited mechanical durability. To achieve ideal stretchable nanogenerators, a new concept is needed for resolving critical issues that incorporate highly elastic piezoelectric components with high-output performance and co-assembly with ultrastretchable electrodes.Herein, we demonstrate a simple and facile route to a highperformance and hyper-stretchable elastic-composite generator (SEG) realized by very long Ag nanowires (VAgNWs) stretchable electrodes. This stretchable energy harvester exhibits over ten times larger stretchability (≈200%) and about seven times higher power output (≈4 V and ≈500 nA), compared to the previous stretchable piezo-nanogenerator. The outstanding performance was achieved by employing a rubber-based piezoelectric elastic composite (PEC) and the very long nanowire percolation (VLNP) electrodes, obviating device structural dependency. The remarkable elongation rate of the reinforced rubbery matrix mechanically stimulates the imbedded piezoelectric particles to effi ciently induce piezopotential throughout the entire PEC. To demonstrate the stable and conformal integration of the SEG with highly stretchable VLNP electrodes, the VAgNWs were successfully transferred onto the surfaces of PEC composed of PMN-PT particles and multiwalled carbon nanotubes (MWCNTs) in a silicone elastomer matrix. The principles of robust stretchability and well-distributed piezopotential generation were also simulated using fi nite element analysis (FEA) to investigate the notable stress relaxation of VLNP over short NWs. Our SEG can directly produce electrical Stretchable electronics that offer elastic characteristics in response to large strain deformatio...

Systems for time sequential capture of microliter volumes of sweat released from targeted regions of the skin offer the potential to enable analysis of temporal variations in electrolyte balance and biomarker concentration throughout a period of interest. Current methods that rely on absorbent pads taped to the skin do not offer the ease of use in sweat capture needed for quantitative tracking; emerging classes of electronic wearable sweat analysis systems do not directly manage sweat-induced fluid flows for sample isolation. Here, a thin, soft, "skin-like" microfluidic platform is introduced that bonds to the skin to allow for collection and storage of sweat in an interconnected set of microreservoirs. Pressure induced by the sweat glands drives flow through a network of microchannels that incorporates capillary bursting valves designed to open at different pressures, for the purpose of passively guiding sweat through the system in sequential fashion. A representative device recovers 1.8 µL volumes of sweat each from 0.8 min of sweating into a set of separate microreservoirs, collected from 0.03 cm area of skin with approximately five glands, corresponding to a sweat rate of 0.60 µL min per gland. Human studies demonstrate applications in the accurate chemical analysis of lactate, sodium, and potassium concentrations and their temporal variations.

Thin, soft, skin-like sensors capable of precise, continuous measurements of physiological health have broad potential relevance to clinical health care. Use of sensors distributed over a wide area for full-body, spatiotemporal mapping of physiological processes would be a considerable advance for this field. We introduce materials, device designs, wireless power delivery and communication strategies, and overall system architectures for skin-like, battery-free sensors of temperature and pressure that can be used across the entire body. Combined experimental and theoretical investigations of the sensor operation and the modes for wireless addressing define the key features of these systems. Studies with human subjects in clinical sleep laboratories and in adjustable hospital beds demonstrate functionality of the sensors, with potential implications for monitoring of circadian cycles and mitigating risks for pressure-induced skin ulcers.