3-Dimensional flexible device for measuring concentric contractile force of in vitro ring-shaped smooth muscle tissue

Real-time quantification of concentric contractile force in engineered ring-shaped smooth muscle tissue remains challenging because conventional optical readouts provide indirect deformation-based measurements, whereas force-based systems often distort the circular tissue geometry. Here, we present a 3-dimensional flexible device for measuring the contractile force of in vitro ring-shaped smooth muscle tissue by electrical readouts while preserving its circular configuration. The device consists of a circular array of FEM-optimized n-shaped flexible pillars that convert tissue-derived contraction into n-shaped pillar bending and an electrical resistance change. To improve electrical robustness during bending, an air-sprayed SEBS polymer interlayer was introduced before Au deposition, reducing deformation-induced cracking and enabling continuous electrical response. The selected 300 μm pillar design showed a force-displacement relationship consistent with FEM prediction, and the calibrated ΔV-force relationship exhibited an approximately linear response up to ∼200 μN. Ring-shaped human aortic smooth muscle tissues formed by collagen-based self-assembly showed spontaneous compaction and expression of α-SMA and calponin. During 15 h of spontaneous compaction, the device detected a progressive increase in single-pillar force, reaching 125.3 ± 44.2 μN at 15 h. The device also detected high-K⁺/Ca²⁺-evoked active contraction, with a peak single-pillar force of ∼70 μN. These results demonstrate a calibrated electrical force-readout approach for ring-shaped smooth muscle tissue contractility and establish a device-level basis for future force-based evaluation of pharmacological responses and disease-associated contractile differences.