A Gradiently Crosslinked Polysiloxane‐Based Coupling Layer for Stable Wearable Ultrasound Imaging

Abstract Wearable ultrasound patches have the potential to transform medical diagnostics by eliminating spatiotemporal constraints. A key challenge lies in developing coupling layers that combine sufficient rigidity for probe support with softness and adhesion to eliminate air gaps and maintain stable skin contact. Inspired by biological gradient structures, this rigid‐soft conflict was addressed by engineering a gradiently crosslinked polydimethylsiloxane (PDMS) coupling layer. The high‐modulus upper layer provided mechanical support for the probe, while the low‐modulus, adhesive bottom layer ensured conformal contact with skin. This gradient structure was achieved by pouring PDMS prepolymers onto a glass slide functionalized with N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (AEAPS), which anchored platinum (Pt) catalyst near the surface. A diffusion‐driven Pt gradient resulted in a corresponding crosslinking density gradient upon immediate curing. Incorporating 3 vol.% tungsten and 25 vol.% aluminum oxide further optimized acoustic impedance (1.53 MRayl) to match skin and maintained high adhesion strengths (7.33 and 6.55 N m −1 ). This gradient PDMS layer enabled long‐term, stable coupling and high‐quality imaging of radial artery blood flow, advancing the field of wearable ultrasound diagnostics.