Flexible biosensors are a popular new field of research. Soft pressure sensors are of particular interest because there are many applications for them in healthcare. Most flexible pressure sensors are based on solid-state components that tend to rely on carbon nanotubes and graphene. Carbon nanotubes or graphene flakes are seeded through a stretchy material to maintain conductivity while being squeezed and pulled, but the signal that is passed through changes when the material is deformed. This makes sensing using such materials somewhat inaccurate. Now researchers at KAIST, South Korea’s institute of science and technology, have been able to use a liquid metal to make highly accurate flexible pressure sensors that can be manufactured relatively inexpensively.
Liquid metals, such as Galinstan, an alloy of gallium, indium, and tin, have been tried inside flexible pressure sensors but the devices produced were not sensitive enough to detect heartbeats and other biological signals. The KAIST team created a 3D printed sensor that integrates liquid metal and a rigid microbump array to produce accurate, highly sensitive pressure readings.
The 3D printing makes manufacturing of such devices relatively easy, specifically the integration of the microbump array and a channel for the liquid metal. The capability allows for high sensitivity, enough to detect heartbeats on the skin, and a signal drift next to nonexistent, even after 10,000 stretching cycles.
These sensors can withstand moisture and other environmental variables and have already been integrated into a proof-of-concept wristband that monitors the pulse rate, heel pressure monitor, and as a non-invasive blood pressure sensor that estimates BP readings based on pulse travel times.
“It was possible to measure health indicators including pulse and blood pressure continuously as well as pressure of body parts using our proposed soft pressure sensor,” said Inkyu Park, the senior author of the study published in journal Advanced Healthcare Materials. “We expect it to be used in health care applications, such as the prevention and the monitoring of the pressure-driven diseases such as pressure ulcers in the near future. There will be more opportunities for future research including a whole-body pressure monitoring system related to other physical parameters.”