Gradient ionic gels have received extensive attention in the field of pressure sensing due to their gradient variation of structure and elastic moduli, which can achieve a broad-range pressure response. However, designing and fabricating gradient gels with good mechanical and sensing properties remains a challenge. In this study, a physically cross-linked PVA ionic hydrogel with gradient structure is successfully synthesized by a directional ion diffusion process in NaCl solution at low temperature (–15 °C). Along the direction of ion diffusion, the gradient gel exhibits a continuous change from dense to porous structure, which is attributed to the synergy of freezing and salt-out effect. Cyclic compression test proves the good fatigue resistance of the gradient gel. The gradient ionic gel is applicated as a flexible capacitive pressure sensor, which exhibits high sensitivity of 1.09 kPa⁻¹ (<100 kPa) and a broad sensing range (400 Pa to 0.8 MPa), while the response times can achieve to 92 ms. The gradient gel sensor demonstrates the signal stability in a long-term loading-unloading process and independence to the test frequency, as well as high sensitivity and instantaneous response under repeated tiny compressive strains and water droplets. Moreover, the excellent sensing capability enable the gradient hydrogel to be a versatile platform for flexible wearable sensors to monitor subtle vital signal and human movement. This strategy provides an innovative route to fabricate gradient hydrogels and develops the applications in flexible pressure-responsive smart materials.

梯度离子凝胶由于其结构和弹性模量的梯度变化，可以实现宽范围的压力响应，在压力传感领域受到广泛关注。然而，设计和制造具有良好机械和传感特性的梯度凝胶仍然是一个挑战。在这项研究中，在低温（–15 °C）下，通过在 NaCl 溶液中的定向离子扩散过程，成功合成了具有梯度结构的物理交联 PVA 离子水凝胶。沿离子扩散方向，梯度凝胶呈现出由致密到多孔结构的连续变化，这归因于冷冻和盐析效应的协同作用。循环压缩试验证明梯度凝胶具有良好的抗疲劳性。梯度离子凝胶用作柔性电容压力传感器，^-1 (<100 kPa) 和广泛的感应范围（400 Pa 至 0.8 MPa），而响应时间可达到 92 ms。梯度凝胶传感器展示了在长期加载-卸载过程中的信号稳定性和独立于测试频率，以及在重复微小压缩应变和水滴下的高灵敏度和瞬时响应。此外，出色的传感能力使梯度水凝胶成为灵活的可穿戴传感器的多功能平台，以监测细微的生命信号和人体运动。该策略为制造梯度水凝胶提供了一条创新途径，并开发了在柔性压力响应智能材料中的应用。