Pursuit of improved living quality has stimulated great demand for high-performance conformal healthcare devices in modern human society. However, manufacturing of efficient, comfortable and stretchable biomedical apparatus faces huge challenges using traditional materials. Liquid metals (LMs) show remarkable potential to solve this problem due to their extraordinary biocompatibility, stretchability, thermal and electrical conductivity. In recent years, tremendous explorations have attempted to make stretchable biomedical devices with LMs. Herein, we review the stretchable LM-based biomedical devices on the topics of disease treatment and human function augmenting. The representative and up-to-date neural interfaces, alloy cement, e-vessels, soft heaters, exoskeletons, and e-skins are summarized. The existing issues of LMs applied for biomedical devices are also discussed. This review can provide guidance for the follow-up research in LM-based biomedical devices.

Wearable sensor enables continuous and ubiquitous real-time monitoring of the gait pattern of a patient and it eliminates the need of frequent visit to the clinics and the use of costly medical facilities. Attaching gait sensors on body, however, may not be easy as most of the reported gait sensors are made of non-stretchable materials and they are non-conformal to human skin. In this paper, we have presented an in-shoe pressure measurement system that is developed using multiple stretchable microfluidic sensors for monitoring gait parameters ergonomically. The sensor here has employed Eutectic Gallium-Indium (EGaIn) as the conductive liquid to fill up a spiral-patterned microchannel which is encapsulated inside an Ecoflex 00–50 elastomer. Fundamental studies have been performed to investigate the sensor’s behaviours when it is exposed to normal and axial applied forces. As proof-of-concept demonstration of the applicability of the proposed sensor for gait monitoring application, we have measured the localised foot pressure and dynamically by attaching two sensors on a shoe insole for detecting pressure changes around the heel and metatarsal regions. The experiment was then extended to evaluate the strain sensing by measuring the ankle angle. It has been shown that data can be captured wirelessly and displayed on a smartphone using the Bluetooth communication protocol. Owing to its unique and stretchable structure, the sensor is able to distinguish walking and running motions by analysing their stance and swing phases. This work has explored the possibility of applying a microfluidic-based structure for designing a wearable gait sensor that has good flexibility.

This paper reports a radio-frequency controlled ionic polymer metal composite (IPMC) actuator for aqueous environment. The actuator can be activated through magnetic resonant coupling when the frequency of an external field is tuned to match with the resonant frequency (∼13.6 MHz) of the antenna of the planar receiver. A polydimethylsiloxane based drug reservoir, which has an IPMC actuator integrated, is developed. Under wireless activation, the IPMC actuator unseals the reservoir to initiate drug releases to the aqueous surroundings. The concentration of the released solution was experimentally characterized using a fluorescent microscope well plate reader with the release of the fluorescein dye from a 0.072 ml reservoir by wirelessly activating the actuator with an RF power of 0.65 W. In vitro study was further performed by wireless releases of tetracycline hydrochloride to an Escherichia-coli ( E. coli ) suspension. The reduction of E. coli colony formation from 89 × 10 ⁶ to 35 × 10 ⁶ CFU ml ⁻¹ shows that proof of concept on wireless drug delivery was successfully demonstrated.