This paper introduces materials and architectures for ultrathin, stretchable wireless sensors that mount on functional elastomeric substrates for epidermal analysis of biofluids. Measurement of the volume and chemical properties of sweat via dielectric detection and colorimetry demonstrates some capabilities. Here, inductively coupled sensors consisting of LC resonators with capacitive electrodes show systematic responses to sweat collected in microporous substrates. Interrogation occurs through external coils placed in physical proximity to the devices. The substrates allow spontaneous sweat collection through capillary forces, without the need for complex microfluidic handling systems. Furthermore, colorimetric measurement modes are possible in the same system by introducing indicator compounds into the depths of the substrates, for sensing specific components (OH(-) , H(+) , Cu(+) , and Fe(2+) ) in the sweat. The complete devices offer Young's moduli that are similar to skin, thus allowing highly effective and reliable skin integration without external fixtures. Experimental results demonstrate volumetric measurement of sweat with an accuracy of 0.06 μL/mm(2) with good stability and low drift. Colorimetric responses to pH and concentrations of various ions provide capabilities relevant to analysis of sweat. Similar materials and device designs can be used in monitoring other body fluids.

This paper presents materials and designs for an ultrathin, stretchable class of device that is capable of lamination onto the surface of the skin, for wireless determination of dielectric and surface strain properties. The sensor exploits LC resonators with capacitive electrodes whose radio frequency characteristics change with variations in skin properties, and is capable of conformal and spontaneous integration with skin due to their skin‐like, “epidermal”, mechanical properties. Resonance frequencies of the LC resonators can be measured wirelessly through changes in the absorption of electromagnetic energy from a coil connected to an impedance measurement setup and placed in proximity to the epidermal device. Experimental results demonstrate that the device offers a precision of 1.1 (arbitrary unit of a reference commercial hydration meter) for hydration and 1.3% for strain detection, with good stability and low drift. Measurement of simulated lymphedema using an expandable balloon with an attached sensor further demonstrates the potential for using such a sensor in monitoring skin swelling. Finite element simulation of physical deformation and associated changes in electrical properties enable quantitative interpretation of the experimental results. The results may have relevance for wireless evaluation of the skin, for applications ranging from dermatology and cosmetology to health/wellness monitoring (lymphedema, transdermal water loss, edema, and psychological stress).

This paper presents a class of hydration monitor that uses ultrathin, stretchable sheets with arrays of embedded impedance sensors for precise measurement and spatially multiplexed mapping. The devices contain miniaturized capacitive electrodes arranged in a matrix format, capable of integration with skin in a conformal, intimate manner due to the overall skin-like physical properties. These "epidermal" systems noninvasively quantify regional variations in skin hydration, at uniform or variable skin depths. Experimental results demonstrate that the devices possess excellent uniformity, with favorable precision and accuracy. Theoretical models capture the underlying physics of the measurement and enable quantitative interpretation of the experimental results. These devices are appealing for applications ranging from skin care and dermatology, to cosmetology and health/wellness monitoring, with the additional potential for combined use with other classes of sensors for comprehensive, quantitative physiological assessment via the skin.

The most common pneumococcal serotype in mainland China was 19F. The serotype coverage rates of PCV13 and PPSV23 were 50%-68% in mainland China.