Neonatal jaundice occurs in >80% of newborns in the first week of life owing to physiological hyperbilirubinemia. Severe hyperbilirubinemia could cause brain damage owing to its neurotoxicity, a state commonly known as kernicterus. Therefore, periodic bilirubin monitoring is essential to identify infants at-risk and to initiate treatment including phototherapy. However, devices for continuous measurements of bilirubin have not been developed yet. Here, we established a wearable transcutaneous bilirubinometer that also has oxygen saturation (SpO2) and heart rate (HR) sensing functionalities. Clinical experiments with neonates demonstrated the possibility of simultaneous detection of bilirubin, SpO2, and HR. Moreover, our device could consistently measure bilirubin during phototherapy. These results demonstrate the potential for development of a combined treatment approach with an automatic link via the wearable bilirubinometer and phototherapy device for optimization of the treatment of neonatal jaundice.

Hydrogel actuators, comprising gels that convert external stimuli into mechanical motion for actuation, are attracting attention for their promising applications, such as in robotics. The driving force is the absorption or release of water or another solvent, which results in swelling and shrinking motions, leading in turn to more complex functionalities. However, practical hydrogel actuators that can be controlled locally, such as ones that allow local actuation around the joints in rigid‐bodied robots, do not exist. Herein, the driving target of a thermo‐responsive hydrogel, poly(N‐isopropyl acrylamide), is integrated with the stimulation module using a liquid metal. The stimulation module provides heat as an external stimulus to the hydrogel actuator. The motion of the actuator is triggered by the heat supplied by an ultrasoft hydrogel coil, with liquid metal surrounding the driving target. The heat generated by current flowing through the liquid metal changes the temperature only around the desired part of the actuator, which enables the electrical control of an individual part of the hydrogel actuator. The concept of integrating the driving target and stimulator is expected to facilitate functional movement of actuators and expand the range of potential applications of hydrogels.

of the pressure sensor (iii). Sugar was added into the hole to create pores inside Ecoflex. Liquid Ecoflex was then poured into this part. By vacuuming the substrate, Ecoflex penetrated the regions in which sugar was deposited. After curing Ecoflex, the substrate was sonicated through ultrasonication to dissolve sugar (v). A solution of Super P carbon, fluoropolymer, PVDF, and N-methylpyrrolidone (NMP) was poured into the porous Ecoflex and penetrated this part (vi). This porous structure increased the resistance of the pressure sensing part. Finally, the column and row electrodes of the carbon paste were formed on the top and bottom sides of the substrate for the detection of the x and y strains. Acquisition of highly magnified images and analysis of molecules was performed using scanning electron microscopy (SEM) and with energy dispersive X-ray spectroscopy (EDS) of the carbon and fluorine elements (Fig. 2b-f). The resistance of the porous silicone pressure sensing element was different, depending on the material used in coating the surface of the porous silicone (Fig. 2g).

Research on liquid metals has been steadily garnering more interest in recent times, especially in flexible electronics applications because of their properties like possesing high conductivity and being liquid state at room temperature.

In recent years, wiring and system construction on ultrasoft materials such as biological tissues and hydrogels have been proposed for advanced wearable devices, implantable devices, and soft robotics. Among the soft conductive materials, Ga-based liquid metals (LMs) are both biocompatible and ultrasoft, making them a good match for electrodes on the ultrasoft substrates. However, gels and tissues are softer and less wettable to the LMs than conventional soft substrates such as Ecoflex and polydimethylsiloxane. In this study, we demonstrated the transfer of LM paste composed of Ga-based LM and Ni nanoparticles onto ultrasoft substrates such as biological tissue and gels using sacrificial polyvinyl alcohol (PVA) films. The LM paste pattern fabricated on the PVA film adhered to the ultrasoft substrate along surface irregularities and was transferred without being destroyed by the PVA film before the PVA's dissolution in water. The minimum line width that could be wired was approximately 165 μm. Three-dimensional wiring, such as the helical structure on the gel fiber surface, is also possible. Application of this transfer method to tissues using LM paste wiring allowed the successful stimulation of the vagus nerve in rats. In addition, we succeeded in transferring a temperature measurement system fabricated on a PVA film onto the gel. The connection between the solid-state electrical element and the LM paste was stable and maintained the functionality of the temperature-sensing system. This fundamental study of wiring fabrication and system integration can contribute to the development of advanced electric devices based on ultrasoft substrates.