Liquid Metal–Hydrogel Biosensor for Behavior and Sweat Monitoring

Flexible electronic devices have been widely investigated by researchers over the last few years. However, due to poor biocompatibility and nondegradability in vivo, there are currently no sufficient flexible electronics that can be implanted in the body to monitor heart health in situ. Gelatin methacryloyl (GelMA)─a gelatin-based hydrogel with a porous interior─is widely used in bioengineering given its unique biocompatibility. Liquid metal (GaInSn alloy, 68.5 wt % Ga, 21.5 wt % In, and 10.0 wt % Sn) has been considered the materials of choice for flexible electronics relating to body function because of low toxicity, excellent rheology, and outstanding electrical conductivity. Whether the liquid metal can be used in combination with hydrogels to make implantable flexible electronics was therefore our research question. By reasonably controlling the replacement rate of amine and hydroxyl functional groups in gelatin with methacrylic anhydride, we successfully prepared a hydrogel with excellent mechanical properties. Liquid metal was added to the microchannel of the hydrogel to create implantable liquid metal-based flexible electronic (LMFE) devices. Such LMFE devices can be implanted in the body to detect heart-related conditions in situ as well as be utilized as in vitro sensors to monitor the physical state of humans during exercise.