Increasing the dimensionality of transistors with hydrogels.

Transistors, fundamental to modern electronics, are traditionally rigid, planar, and two-dimensional (2D), limiting their integration with the soft, irregular, and three-dimensional (3D) nature of biological systems. Here, we report 3D semiconductors, integrating organic electronics, soft matter, and electrochemistry. These 3D semiconductors, in the form of hydrogels, realize millimeter-scale modulation thickness while achieving tissue-like softness and biocompatibility. This breakthrough in modulation thickness is enabled by a templated double-network hydrogel system, where a secondary porous hydrogel guides the 3D assembly of a primary redox-active conducting hydrogel. We demonstrate that these 3D semiconductors enable the exclusive fabrication of 3D spatially interpenetrated transistors that mimic real neuronal connections. This work bridges the gap between 2D electronics and 3D living systems, paving the way for advanced bioelectronics systems such as biohybrid sensing and neuromorphic computing. Editor's summary: With the development of organic bioelectronics, there has been interest in making stretchable semiconductors with acceptable performance. Most approaches to date rely on blending a semiconductor with an elastomer and perform well electronically, but they have a modulus much higher than biological tissue and cannot be modulated through the insertion of ions. Liu et al. created a secondary hydrogel network that facilitated the formation of a continuous phase of a primary redox-active polymer. This composition makes it possible to produce millimeter-thick semiconducting layers with biological compatibility. By controlling the hydrogel's porosity, the researchers optimized ionic and electronic mobility and demonstrated electrochemical transistors with a high on/off switching ratio. —Marc S. Lavine [ABSTRACT FROM AUTHOR]