Calcium-Modified Silk-Based Ultrasound Coupling Medium for Ultrasound Applications

The wearable ultrasound patch systems have great potential in biomedical applications such as home health care and continuous monitoring of biological and physiological conditions. However, developing a stable interface between the ultrasound transducer and human skin remains a challenging issue for the implementation of the patch-type ultrasound system. The interface should not only offer strong adhesion properties to hold the patch but also exhibit acoustic properties similar to those of human skin for high ultrasound transmission. Here, we propose a calcium (Ca)-modified silk patch which serves as both a stable interface and a coupling medium for ultrasound transducer arrays. The Ca-modified silk patch provides not only a stable and conformal interface between an epidermal ultrasound transducer and human skin with high adhesion but also offers acoustic impedance close to that of human skin and low transmission loss (~0.002 dB). The mechanical and acoustic properties of the Ca-modified silk patch lasted over three days, and the silk patch maintained its configuration up to a curing temperature of 80°C. The Ca-modified silk patch is flexible and stretchable (~400% strain), and can be attached to various materials. Additionally, the Ca-modified silk patch was applied as a strong interface between a piezoelectric transducer and an acoustic lens. Finally, the successful demonstration of using the Ca-modified silk patch in ultrasound heating, and transcranial ultrasound neuromodulation applications confirmed the suitability of the Ca-modified silk patch as a promising interface.