Piezoionic hydrogels are emerging as innovative smart materials for integrating biological and electronic functionalities in sensors, energy harvesters, and medical devices. However, a clear understanding of the relationship between mechanical microstructures and directional ion transport remains elusive. A significant limitation of existing hydrogel electronics is their ultralow voltage response. To address this knowledge gap, we systematically analyze the influence of structural characteristics on the electrical response of piezoionic hydrogels and introduce a material property termed "tortuosity." Guided by this concept, we develop an artificial ion pump (AIP) hydrogel, characterized by low tortuosity in ion transport pathways and anisotropic deformability, attributed to its modified surface polarity and aligned porous structure. The reduced tortuosity factor (reduced to 35%) provides ordered pathways for ion transportation, reducing random diffusion in the matrix and enhancing directional ion transport efficiency. Simultaneously, the aligned porous structure concentrates stress during mechanical deformation, improving stress transfer and amplification within the hydrogel. This promotes the relative displacement of mobile ions, thereby enhancing the piezoionic effect. Consequently, the new AIP hydrogel achieved over 20 times higher coefficient compared to its unoptimized counterpart. These findings provide valuable insights into the structure-performance correlation in piezoionic materials. What's more, in the peripheral nerve regulation experiment in mice, the AIP hydrogel generator demonstrated the ability to synchronize with physiological rhythms while effectively regulating neural activity. This capability highlights potential applications in implant devices for self-powered sensing and electrical stimulation.
Yang et al. (Thu,) studied this question.