Mechanophore-Based Multichannel Colorimetric Force Sensors: Ultrasound-Driven Stress and Strain Quantification

Mechanophores with mechanochromic properties have attracted significant attention as force-responsive materials for structural sensing. However, their applications remain mainly limited to qualitative force visualization, as direct and quantitative extraction of mechanical parameters such as stress and strain from mechanochromic responses has not yet been established in bulk polymer systems. Here, we present a mechanophore-based polymer sensing platform capable of selectively quantifying localized stress or strain through multichannel mechanochromic responses. Two mechanophores with distinct activation thresholds were crosslinked within a single polydimethylsiloxane (PDMS) matrix, enabling differentiated force-dependent color changes and threshold-resolved mechanochromic responses under spatiotemporally resolved focused ultrasound (FUS) stimulation. RGB-based image analysis combined with deep-learning-assisted segmentation enabled quantitative stress estimation, while embedded tracer microbeads and particle tracking velocimetry (PTV) enabled strain quantification within the activated regions. This integrated framework establishes a quantitative mechanochromic sensing strategy capable of extracting both stress and strain from optical signals in a spatially resolved and reversible manner, demonstrating the potential of mechanophore-based polymers as quantitative, electronics-free sensing platforms for next-generation structural health monitoring applications.