Human-machine interfaces require thin and conformal epidermal electrodes to detect physiological signals from the human body. A key challenge of such epidermal electrodes is to combine two contradictory but highly desired properties: stable electrode-skin adhesion that enables high-fidelity signal acquisition, and poor adhesion for easy and injury-free removal. Here, we report a soft conducting electrode that well combines the two contradictory properties by tailoring a T-shaped finger and a U-shaped finger and by tuning the stickiness to a mild level. When peeling from the U-finger to the T-finger, the two fingers "pinch" the skin with a large co-deformation between the skin and the electrode for enhanced adhesion. When peeling back, the U-finger is disabled, and the electrode behaves like a non-patterned layer that exhibits poor adhesion for easy detachment. The kirigami-enabled co-deformation of bilayer soft system with a thin surface and thick substrate for switchable adhesion and low interfacial damage might be extended to other human-machine interfaces and beyond.

Soft iontronic pressure sensors, utilizing the supercapacitive nature of the electric double layers, present advantages of exceptional sensing properties, including high sensitivity over a broad range, and high flexibility. This sensing modality has become an important branch of flexible pressure sensing technologies since its inception 13 years ago. There is a strong correlation between the properties of materials and sensing performances of iontronic sensors, while existing work often focuses on active materials only. Herein, key materials of iontronic sensors are reviewed, including soft ionic conductors, electronically conductive materials, and encapsulating materials, among which encapsulating materials have seldom been discussed before, while this class of materials plays a key role in stable functionality. The molecular structure‐sensing property correlation of electronic electrodes and soft ionic materials is discussed. Potential future directions of iontronic pressure sensors and their applications in robotics and biomedical devices are also discussed at the end of this review article.

Plaque accumulation in coronary arteries causes stenoses, reducing blood flow and increasing the risk of cardiovascular disorders such as heart attacks. To assess the physiological impact of blood pressure across a stenosis, commercial pressure guidewires measure the fractional flow reserve using optical, piezoresistive or piezoelectric sensors, which suffer from brittleness, limited manoeuvrability and high costs. Here we report an iontronic tip-sensing guidewire (ITG) that integrates a thin iontronic tip sensor in a commercial workhorse guidewire via iontronic-based signal transmission, leveraging the ionic nature of human tissues. Intravascular pressure changes induce a capacitance difference at the interface of the metal and ionic gel of the ITG, allowing detection of subtle pressure changes in blood flow, substantially outperforming commercial guidewires. The ITG is free of embedded conductive leads needed in other pressure guidewires to ensure an ideal torque ratio for high manoeuvrability, and we validated its effectiveness and sensitivity in rabbit, goat and pig models in vivo. The compatibility of the ITG with commercial horsework guidewires will upgrade the design of interventional medical devices. An iontronic tip-sensing guidewire measures haemodynamic and contact pressure in animal stenosis models and can be integrated with commercial workhorse guidewires.

Skin-like sensors are key for humanoid robots and wearables. Achieving both robust interfaces and promoted sensing performances in soft sensors may enable their applications in extreme mechanical conditions of high shear. However, strong interfacial adhesion in multilayer sensors often compromise sensing properties. Here, we design hyperbranched polyurethane micropillars with (diameter < length of flaw sensitivity) that serve dual roles as an adhesion layer for exceptional mechanical stability, and adaptive spacer for enhanced sensing properties. We show a strong size effect of the structure to toughen the interface, with ultrahigh interfacial toughness up to 5,095 J m(-2) at a 50-mu m pillar diameter. Simultaneously, the micropillars enhance sensitivity and limit of detection by decreasing the stiffness via elastic buckling and enable a rapid response to the acoustic range by reducing energy loss during loading and unloading. The sensors are ideal for the manipulation of heavy objects in humanoid robots and other applications.

There is an increasing demand for sensitive, selective, and convenient detection tools for disease-related biomarker, potassium ion (K+). Electrospinning nanofibrous film as a novel sensing platform exhibits unique advantages due to high surface area ratio and network structure. In this study, electrospinning technique was employed to construct poly(vinyl alcohol) (PVA) nanofibrous film to assist K+ sensing. To find the best recipe, these factors including probe concentration, solvent composition, spinning time and cross-linking time were explored, and 8 groups of sensing films (F0-F7) were obtained in which F2 was considered the best and used for subsequent tests. Under optimized conditions, the sensing platform F2 was constructed by relatively continuous, uniform fibers with diameters in the range of 150???250 nm, and showed excellent selectivity, reusability, considerable response speed, and high sensitivity in which the fluorescence enhanced factor was as high as 8.9 with 10 mM K+. Moreover, F2 showed high accuracy in real samples detection, and it was used as a real-time K+ sensing platform. The excellent performance of F2 not only proved the reasonable design principle using PVA fibers for K+ sensing, but also could be extended to other probes and lead to different selectivity which was significant for biological diagnosis.

Real-time, continuous and non-invasive glucose monitoring is essential for the health of diabetic. In this work, we developed soft and transparent smart contact lenses which could detect glucose in tear with high sensitivity. The smart contact lenses were prepared by immobilizing a sensitive glucose fluorescent probe and another reference fluorescent dye into the hydrogel network of the contact lenses. With the increase of glucose concentration, the fluorescent color of the smart contact lenses changed from pink to blue. The fluorescent images could be collected by a smartphone and transformed into RGB signals to quantify the glucose levels. These smart contact lenses could successfully monitor glucose level of 23 mu M-1.0 mM in tears by a smart phone. The animal experiments further demonstrate the biosafety of smart contact lenses and the potential application of glucose monitoring. The fluorescence sensor platform is expected to be a new method for painless glucose monitoring.