Real-time stress visualization of hydrogels enabled by supramolecularly switched stretch-induced phase separation

Noh, S.*; 菅原 章秀*; 石原 尚昌*; 小西 隆士*; 上田 祐生   ; 元川 竜平   ; 高島 義徳*; 宇山 浩*

Noh, S.*; Sugawara, Akihide*; Ishihara, Naoaki*; Konishi, Takashi*; Ueda, Yuki; Motokawa, Ryuhei; Takashima, Yoshinori*; Uyama, Hiroshi*

Visualizing mechanical stress in soft materials is highly desirable, yet real-time optical readouts remain difficult using conventional sensing approaches, as mechanophore-based systems typically require large-force, threshold-type activation with slow recovery. Herein, we report supramolecular hydrogels that enable continuous and reversible visualization of mechanical stress in real time via stretch-induced phase separation. Mechanical stimuli are converted into a distinct network state transition by exploiting host-guest complexes between -cyclodextrin (-CD) and adamantane (Ad) as supramolecular switches. In this design, guest-functionalized polymers undergo an on-off transition between hydrated and dehydrated states via host-guest complexation and decomplexation. The responsive polymers were incorporated into the hydrogel network via supramolecular bonds that function as reversible cross-links and molecular switches, enabling the formation of phase-separation domains. Upon stretching, the hydrogels exhibited macroscopic transition from transparent to opaque owing to phase separation of the responsive domains. The opacity changed linearly and reversibly with applied stress, attributable to the sacrificial and reversible supramolecular switches, enabling visualization of stress distributions. This design principle offers a direction to spatiotemporally resolved mapping of mechanical states in hydrogels with an intuitive, instrument-free readout, providing a foundation for safer operation, condition monitoring, and timely intervention in soft material systems.