Encapsulated Organohydrogel Couplants for Wearable Ultrasounds

The couplant layer that transmits sound waves to the skin is essential for ultrasound imaging. Conventional liquid-based couplants are unsuitable for wearable detectors, while polymer-based dry couplants often suffer from high acoustic attenuation. Hydrogel-based couplants possess ideal acoustic and mechanical properties; however, water evaporation restricts their application in long-term monitoring. Current strategies to improve water retention, such as encapsulating hydrogels with elastomers, typically overlook the issue of curing shrinkage. This shrinkage induces a wrinkled interface between the elastomer and hydrogel, which can cause scattering and reflection of acoustic waves, thereby compromising ultrasound quality. To address this problem, a prefabricated hydrogel is employed as a template to mitigate the curing shrinkage at the interface. In the meantime, a large amount of glycerol is added to the template to form the organohydrogel, which reduces interactions between polymer chains, further minimizing curing shrinkage and resulting in a smooth interface. Additionally, the glycerol within the organohydrogel, combined with the external encapsulation layer, enhances long-term water retention. The results demonstrate that the prepared couplants maintain stable attenuation coefficients and produce clear imaging over 8 days.