Metamaterial‐Integrated Bioadhesive Hydrogel Transducer for Long‐Term Ultrasound Monitoring

ABSTRACT Wearable ultrasound transducers are emerging tools for noninvasive health monitoring, yet their performance can still be compromised by insufficient acoustic transmission due to an acoustic impedance mismatch between piezoelectric materials and soft tissue. To overcome this critical challenge, we developed a metamaterial‐integrated, bioadhesive hydrogel ultrasound transducer (MMBA), achieving enhanced acoustic transmission, broader operational bandwidth, and reliable bioadhesion. By integrating a metamaterial into a tailor‐designed bioadhesive hydrogel, we created a gradient impedance transition from high‐impedance piezoelectric element to low‐impedance soft tissue, facilitating stable wearable ultrasound monitoring. Finite‐element method demonstrated that metamaterial integration into the bioadhesive hydrogel considerably improves the transmission coefficient across a broad frequency range. Experimental pulse‐echo tests confirmed an increase in bandwidth from 15% to 41% with respect to transducers with only the bioadhesive hydrogel couplant. Moreover, in vitro and in vivo experiments demonstrated the MMBA's capability to accurately monitor arterial diameter and blood pressure waveforms. Long‐term evaluations demonstrated stable and robust performance over 10 days, highlighting MMBA's durability and bioadhesive properties. This work paves the way for reliable wearable ultrasound systems suitable for long‐term clinical monitoring.