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

Real-time measurements of the total loss of sweat, the rate of sweating, the temperature of sweat, and the concentrations of electrolytes and metabolites in sweat can provide important insights into human physiology. Conventional methods use manual collection processes (e.g., absorbent pads) to determine sweat loss and lab-based instrumentation to analyze its chemical composition. Although such schemes can yield accurate data, they cannot be used outside of laboratories or clinics. Recently reported wearable electrochemical devices for sweat sensing bypass these limitations, but they typically involve on-board electronics, electrodes, and/or batteries for measurement, signal processing, and wireless transmission, without direct means for measuring sweat loss or capturing and storing small volumes of sweat. Alternative approaches exploit soft, skin-integrated microfluidic systems for collection and colorimetric chemical techniques for analysis. Here, we present the most advanced platforms of this type, in which optimized chemistries, microfluidic designs, and device layouts enable accurate assessments not only of total loss of sweat and sweat rate but also of quantitatively accurate values of the pH and temperature of sweat, and of the concentrations of chloride, glucose, and lactate across physiologically relevant ranges. Color calibration markings integrated into a graphics overlayer allow precise readout by digital image analysis, applicable in various lighting conditions. Field studies conducted on healthy volunteers demonstrate the full capabilities in measuring sweat loss/rate and analyzing multiple sweat biomarkers and temperature, with performance that quantitatively matches that of conventional lab-based measurement systems.

Sound-evoked vibrations transmitted into the mammalian cochlea produce traveling waves that provide the mechanical tuning necessary for spectral decomposition of sound. These traveling waves of motion that have been observed to propagate longitudinally along the basilar membrane (BM) ultimately stimulate the mechano-sensory receptors. The tectorial membrane (TM) plays a key role in this process, but its mechanical function remains unclear. Here we show that the TM supports traveling waves that are an intrinsic feature of its visco-elastic structure. Radial forces applied at audio frequencies (2-20 kHz) to isolated TM segments generate longitudinally propagating waves on the TM with velocities similar to those of the BM traveling wave near its best frequency place. We compute the dynamic shear storage modulus and shear viscosity of the TM from the propagation velocity of the waves and show that segments of the TM from the basal turn are stiffer than apical segments are. Analysis of loading effects of hair bundle stiffness, the limbal attachment of the TM, and viscous damping in the subtectorial space suggests that TM traveling waves can occur in vivo. Our results show the presence of a traveling wave mechanism through the TM that can functionally couple a significant longitudinal extent of the cochlea and may interact with the BM wave to greatly enhance cochlear sensitivity and tuning.cochlear mechanics ͉ dynamic mechanical properties ͉ longitudinal mechanical coupling T he mammalian cochlea is a remarkable sensor that can detect motions smaller than the diameter of a hydrogen atom and can perform high-quality spectral analysis to discriminate as many as 30 frequencies in the interval of a single semitone (1, 2). These extraordinary properties of the hearing organ depend on traveling waves of motion that propagate along the basilar membrane (BM) (3) and ultimately stimulate the mechanosensory receptors. There are two types of cochlear receptors: the inner and outer hair cells (OHCs). Both types of hair cells contain densely packed arrays of stereocilia called hair bundles that transduce mechanical energy into electrical signals (4). These hair bundles project from the apical surface of hair cells toward an overlying gelatinous matrix called the tectorial membrane (TM).The strategic anatomical configuration of the TM relative to the hair bundles suggests that the TM plays a key role in stimulating hair cells. Mouse models with genetically modified structural components of the TM have been shown to exhibit severe loss of cochlear sensitivity and altered frequency tuning (5-9), thereby providing further evidence that the TM is required for normal cochlear function. However, the mechanical processes by which traveling wave motion along the BM leads to hair cell stimulation remain unclear (10), largely because the important mechanical properties of the TM have proved difficult to measure. Consequently, the mechanical function of the TM has been variously described as a rigid pivot, a resonant structure, and a free-flo...

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