Framework-Densified Isotropic Cellulose Ionogel for Omnidirectional Flexible Sensing

Flexible omnidirectional sensors are increasingly important for monitoring complex multidirectional mechanical stimuli, yet soft ionic materials that simultaneously provide high mechanical robustness and direction-insensitive electrical response remain limited. However, most existing gel-reinforcement strategies inevitably involve trade-offs among mechanical robustness, structural homogeneity, isotropy, and ionic transport. Here, we report a high-strength isotropic cellulose ionogel enabled by a densification-engineering strategy based on molecular framework reconstruction. Through ionic liquid-assisted thermoactivation and compression-induced hydrogen-bond reconfiguration, the regenerated cellulose framework is transformed into a dense fibrillar skeleton via crystal reconstruction and isotropic densification, converting the weak ionogel into a mechanically efficient network while preserving in-plane isotropy. The resulting ionogel exhibits a tensile strength of 45.4 MPa, a toughness of 10.2 MJ/m³, and Young's modulus of 6.59 MPa, corresponding to 76- and 166-fold increases in strength and toughness over the untreated sample, respectively. Meanwhile, the homogenized network retains stable ionic conduction, enabling an omnidirectional sensor with direction-independent pressure sensing over 50-400 kPa, a maximum sensitivity of 0.002 kPa^-1, and reliable operation over 1500 cycles. Its performance is further demonstrated by early warning monitoring of irregular motions and unpredictable mechanical events, providing a general route to a robust cellulose ionogel for omnidirectional flexible sensing.