Soft sensors that might be molded around body parts or squeezed in the hand could be useful in sports and injury rehabilitation or following cerebral stroke. Now, a team from Imperial College London has developed stretchy and squeezable sensor devices by bonding force-sensitive soft materials to electrical components. [Kasimatis, M. et al. ACS Appl. Mater. Interfac., (2019) DOI: 10.1021/acsami.9b17076]

Lead author on the research, Michael Kasimatis of the Department of Bioengineering at Imperial College, explains: "We hope this method will allow us to make low-cost soft sensors that are reliable and portable, and can be used to monitor people's health in their own homes." He adds that "Such sensors could be coupled with a mobile device, such as a smart phone, so that the data they generate can be easily processed and stored on the cloud, which is important for applications in digital healthcare."

Earlier efforts have seen scientists attempting to bond force-sensitive, conductive silicone rubber materials to electrical components using adhesives, but these bonds are generally not long last. Metal clamps to bind the components are cumbersome and inconvenient as well as risking tearing stretchy materials. A direct way to bond the sensor and the electronics together was needed. The team's approach uses metal-coated silicon to create a chemical bond with the rubber components using plasma bonding. The silicon contacts are smooth on one side, where they bond to the rubber, and pitted and plated with copper on the other side, so wires or other electric components can be soldered into place with relative ease

The Imperial College researchers have now shown how their bonding method can resist the strains of stretching without the device being torn apart. They have tested the approach to construct several prototype sensors that might be used in healthcare and rehabilitation. In various proofs of principle they have made a wearable breathing monitor, a leg band for exercise monitoring, and a squeezy ball for monitoring hand rehabilitation after injury, surgery or for people with neurological disorders. The team says these prototypes show the "mechanical robustness and versatility of the technology developed in real-world applications."

Team leader Firat Güder enthuses about the next stage: "Having successfully demonstrated how this new bonding approach could work and be applied in laboratory prototypes, we now want to take this technology out of the lab and make it available to everyone."