The electronic devices implanted into living things can be soft and warm. The reporter learned from the Institute of Technology of West Lake University that Zhou Nanjia, a specially appointed researcher of the Institute, has developed a hydrogel support matrix and a silver hydrogel composite conductive ink, which is the first internationally integrated hydrogel electronic device that encapsulates internal circuits through 3D printing. Relevant research results were published in the international journal Nature Electronics on December 20. "Foreign" materials will be recognized by the human body and produce certain rejection reactions, such as steel nails for fracture treatment, dental implants, and even soft artificial cochlea. Faced with the "embarrassment" of electronic devices entering the body, scientists place high hopes on hydrogel because it has both flexibility and good biological compatibility. "Hydrogels are everywhere, such as contact lenses and crystal mud for children to play with." Zhou Nanjia introduced that the traditional hydrogel electronic device is to "wrap" the circuit with gel, and the core part of the circuit is still hard metal. The breakthrough of the team's research is to "unify" the metal parts in the hydrogel electronic devices into the state of hydrogel. The team first found a breakthrough in the design method of materials, found calcium alginate polyacrylamide double network hydrogel and modified it. It is understood that the method of synthesizing calcium alginate and polyacrylamide into a whole hydrogel is common but lacks flexibility. They divided the solidification of these two kinds of hydrogels into two independent steps - first solidifying calcium alginate, and then "breaking" to refine into micro gel particles. In this way, in addition to calcium alginate, the gel particles also contain acrylamide monomer, cross-linking agent and free radical initiator. The particle size is about 20 microns, which can be used as the "support matrix" for 3D printing. After printing, the polyacrylamide can be solidified by heating to make the electronic devices finalized. Micro gel particles are fluid and can be used as the "matrix" for printing electronic devices. Can this micro gel particles conduct electricity and be used to print the circuit of electronic devices through modification? After repeated experiments, researchers found a breakthrough - mixing micro gel particles with a small amount of micro silver flakes and additives to make conductive ink materials. The conductive hydrogel ink can be used to build flexible circuits with three-dimensional structure in the matrix of micro gel particles by embedded printing. On this basis, the team has prepared a full hydrogel electrode that can be used to provide electrical stimulation. This electrode can be wound on the sciatic nerve of mice through simple surgery. Under the pulse voltage stimulation of 1Hz frequency, the 3D printing electrode can cause the regular large angle movement of mouse legs under the voltage as low as 100mV. The electrode of ionic conductive hydrogel, as a control, can only barely trigger the micro movement of mouse legs under the action of 250 mV driving voltage. Hui Yue, a postdoctoral fellow at West Lake University and the first author of the paper, said that this set of technical methods can play an important role in the field of personalized customized implantable electronic devices. (Liu Xinshe)