People who suffer tendon, ligament and joint injuries often require surgery followed by a rehabilitation period to restore the repair site to its pre-injury function. Existing implantable sensors – designed to be able to measure typical tendon strains after the surgery – either have an inadequate sensing capability or use materials with unreliable biocompatibility. To combat these problems, researchers from Stanford University have devised a biodegradable sensor compatible with living organisms that can satisfy tissue recovery requirements by discriminating strain and pressure stimuli. The sensor is designed to degrade after its useful lifetime thus avoiding the need for a second surgery to remove the device.
The sensor consists of two stacked sensors that can accurately measure strain and pressure independently, which are constructed from two biodegradable elastomers: poly-glycerol sebacate (PGS) and poly-octamethylene maleate citrate (POMaC). Two thin-film comb electrodes are sandwiched between two stretchable elastomer layers and when strain is applied, a change in capacitance is observed as the two electrodes slide relative to each other.The pressure signal is monitored with a flexible, sensitive capacitor that is supported by a thin elastic dielectric layer on both sides. This design allows the pressure sensor to work independently, without inducing any strain signal.
The researchers believe that this sensor – with high-sensitivity, faster response time and biodegradability – can play a valuable role in biomedical applications such as monitoring cardiovascular patches and reconstructive surgery. Sensors transmitting real-time information in vivo will open avenues for refined and personalized medicine. The research team now plans to develop a biodegradable circuit capable of wirelessly transmitting measured signals through the skin.