Recently, the Shenzhen International Graduate School of Tsinghua University Xu Xiaomin’s team The team led by Takao Someya at the University of Tokyo published a research paper in PNAS titled “An exceptionally conductive hydrogel for all-organic, ultraflexible, and chronic neural interfaces.” This work developed an ultra‑highly conductive hydrogel, CHIP (Conductive Hydrogel with Interfacial Percolation), which features an interfacial percolation structure, and successfully fabricated… All-organic, ultra-flexible electrocorticography (ECoG) electrode array , for Long-term stable brain-computer interface has provided new materials and manufacturing solutions for its development.

Traditional neural interfaces have long faced the challenge of simultaneously achieving both high electrical conductivity and high mechanical flexibility. While metal- or silicon-based electrodes exhibit excellent conductivity, their significant mismatch in mechanical modulus with brain tissue can trigger inflammatory responses and glial scar formation upon long-term implantation, ultimately degrading signal quality. To address this issue, the research team engineered a unique interfacial percolation‑based conductive network, enabling PEDOT chains to form continuous conductive pathways at the hydrogel–interface region. This approach maintains a high water content and outstanding mechanical flexibility while delivering an electrical conductivity as high as 2512 S/cm, placing it at the forefront of the current state-of-the-art in conductive hydrogels.

In device fabrication, the research team utilized   Aerosol Jet Printing (Aerosol Jet Printing) Technology to   Precision patterning of the CHIP conductive network , achieving a width of 40 μm Electrodes and interconnect lines and verified that this process can stably achieve a 20 μm line width and a 20 μm pitch. Based on this fabrication strategy, the researchers fabricated   128-channel all-organic EEG electrode array ， Channel density reaches 853 channels/cm². , representing an improvement of more than one order of magnitude compared to previously reported all‑water hydrogel electrodes.

Furthermore, the research team adopted a structural design that combines an ultrathin Parylene insulating layer with a PAAm–Alginate hydrogel interfacial layer, resulting in a device with an overall thickness of only about 9 μm and exhibiting excellent flexibility and tissue‑adhesive properties. In animal experiments, this brain–machine interface achieved… A stable neural signal recording lasting 550 days , demonstrating excellent long-term implantation performance and biocompatibility.

This study not only demonstrates Ultra-high conductivity hydrogel In Brain-computer interface The enormous potential of the field also demonstrates   The Significant Value of Aerosol Jet Printing in the Fabrication of Flexible Bioelectronic Devices . Through a non-contact digital direct-write process, Aerosol Jet Printing can achieve Construction of High-Precision Conductive Networks , offering new manufacturing solutions for flexible neural interfaces, implantable electronic devices, and next-generation bioelectronic systems. The deep integration of materials innovation and precision additive manufacturing is propelling brain–machine interfaces from laboratory research into a new phase of long-term, stable clinical applications.

The first author of the paper is a doctoral student at the Shenzhen International Graduate School of Tsinghua University. Zhu Ruiqi Professor Xiaomin Xu of the Shenzhen International Graduate School of Tsinghua University, Professor Takao Someya of the RIKEN Institute and the University of Tokyo, and Researcher Xiaojian Li of the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, served as the corresponding authors of the paper.

Image and Text Guide

Figure 1. Design of the CHIP and ECoG arrays.

(A)   Schematic diagram of the CHIP, illustrating the compositional gradient in its vertical cross-section and highlighting interfacial fluid flow and charge-carrier transport pathways. (B)   The Young’s modulus and electrical conductivity of the CHIP (red asterisks; in both the as‑prepared state and the fully swollen state) are compared with those of metals commonly used in conventional neural interfaces (gray triangles) and doped silicon (green diamonds), as well as with existing hydrogels categorized into three groups: conductive hydrogels based on conductive polymers (CPs) (orange solid circles), conductive hydrogels containing other types of conductive fillers (orange hollow circles), and ionically conductive hydrogels (blue solid circles). Relevant references can be found in Supplementary Information, References S3, S11–S18, and S25–S33. (C)   The schematic illustrates the chip’s front-end electrode–tissue interface. (D)   Schematic diagram of an ultra-flexible 128-channel ECoG array with a four-layer structure. (E)   Photograph of a CHIP-based ECOG array mounted on a fresh pig brain. (Scale bar: 1 cm)

Figure 2. Microstructure and properties of CHIP.

(A)   Schematic illustration of the pathways through which conductive polymer (CP) ink infiltrates the polyacrylamide–alginate hydrogel during the casting process. (B and C)   XPS spectra of sulfur 20 (S 2p) measured on the conductive side (B) and the backside (C) of a 20‑μm‑thick CHIP. (D and E)   Two-dimensional grazing-incidence wide-angle X-ray scattering (2DGIWAXS) patterns measured from the conductive side (D) and the bottom surface (E) of the CHIP. (F)   Electrical conductivity and elongation at break of CHIP in the fully dehydrated (pentagonal) state, the initial preparation state (circular), and the fully swollen (hexagonal) state. Inset: A photograph showing the “CHIP” pattern serving as an interconnect wire to light up a purple light-emitting diode (LED), with an unlit LED below for comparison. (Scale bar: 1 cm.)   (G)   Stress–strain curve of the initially prepared CHIP. (H)   The electrical conductivity and tensile elongation of CHIP (red asterisk) were compared with those of three previously reported conductive hydrogels: pure poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hydrogel (blue circle), PEDOT:PSS‑incorporated hydrogel (orange hexagon), and hydrogel doped with other conductive fillers (purple triangle). The complete list of references is provided in the Supplementary Information (SI Appendix, References S3, S16–S32, S36–S38, and S40). (I)   CHIP-normalized impedance spectra compared with those of the flexible, stretchable polymeric ionic electronic skin (PPEL) reference sample, both measured in air. (J)   Impedance spectra of the CHIP and PPEL reference samples measured in phosphate-buffered saline (PBS) solution. (K)   Bipolar input pulse (top) and the current density–time profiles corresponding to the CHIP and platinum (Pt) electrodes (bottom).

Figure 3. CHIP-based ECoG array, processing pipeline, and performance characteristics.

(A)   The schematic illustrates the fabrication process of a CHIP-based ECoG array. (B)   The schematic diagram illustrates the strategy for achieving controllable in-plane swelling. (C)   Peel‑force‑per‑unit‑width (F/W)–displacement curves measured on a plasma‑treated poly(p‑xylylene) substrate, with a pre‑fixed polyacrylamide–alginate hydrogel. The inset shows a photograph of the measurement setup: a polyimide tape is adhered to the top surface of the polyacrylamide–alginate hydrogel to enable sample pulling without causing tearing. (Scale bar, 2 cm)   (D)   Scanning electron microscopy images reveal the porous structure of a pre‑swollen polyacrylamide–alginate hydrogel adhered to a parylene substrate, both after dehydration (left) and following rehydration (right). (Scale bar, 20 µm)   (E)   Cross-sectional SEM images of a 9‑μm‑thick chip‑based ECoG array in the unstressed state (left) and under bending (right). Bending radii as small as 10 μm can be observed. (Scale bar, 20 μm)   (F)   The schematic diagram highlights the back-end interface between the conductive hydrogel wire and the flexible printed circuit board (FPCB).   (G)   The photograph shows a CHIP‑based ECoG array, with its front‑end sensing portion floating in phosphate‑buffered saline (PBS). The sensing area, rear‑end connection pads, flexible printed circuit board, and external connector are labeled. (Scale bar: 10 mm)   (H and I)   Immunofluorescence staining of the right cerebral hemisphere in rats 16 weeks after implantation of a CHIP-based ECoG array, compared with the sham‑operated control group (I). Magnified images show the morphology of astrocytes (glial fibrillary acidic protein–stained, green), microglia (ionized calcium‑binding adapter molecule 1–stained, red), and nuclei (4′,6‑diamidino‑2‑phenylindole–stained, blue) within the boxed regions. (Scale bar: main panel, 500 µm; inset, 50 µm.)

Figure 4. In vivo acute recordings.

(A)   The photograph shows the CHIP-based ECOG array and a commercial platinum electrode array positioned on the cortical surfaces of the left and right hemispheres of a rat, respectively. (Scale bar, 1 cm.)   (B and C)   Neural signals recorded by the platinum electrode (B) and the CHIP-based ECOG electrode (C). (D and E)   Time–frequency analysis of neural signals recorded from the platinum electrode (D) and the CHIP-based ECoG electrode (E).   (F)   Schematic of the distribution of a 128-channel array (black dots) across cortical regions in CS7BL/6 mice, with anatomical details shown on the right. (G)   Images of the CHIP-based ECOG array implanted in the mouse cortex. (Scale bar, 1 mm.)   (H)   Schematic illustration of spontaneous whisker movements in mice. (I)   The normalized two-dimensional power spectral density map, computed using the Welch method (50), integrates frequencies over a 50-millisecond period of spontaneous whisker movements, based on recordings from 128 channels. Channel locations are indicated in yellow, with three selected electrodes—located in the MI, S1, and V2 cortices—highlighted by black dots for analysis. (J)   Waveform profiles recorded from selected electrodes in these cortical areas during spontaneous whisker movements. (K)   Schematic illustration of the externally induced fine-tuning of mouse whiskers. (L)   Normalized two-dimensional power spectral density maps recorded from 128 channels during the 50-millisecond period of externally induced whisker fine-tuning. Channel locations are marked in yellow, with three selected electrodes in the M1, S1, and V2 cortices highlighted by black dots. (M)   During the fine-tuning of the tactile probes, the waveform profiles of these selected cortical electrodes are recorded.

Figure 5. Chronic brain signal atlas of freely moving domestic rabbits.

(A)   Schematic diagram of the placement of the 128-channel array in the brain of a New Zealand rabbit. Black dots indicate the electrocorticography (ECoG) electrode sites. (B)   Photograph of an ultra‑flexible electrocorticography array implanted in the rabbit cerebral cortex, covering the cingulate cortex (CgCx) and the piriform cortex (PaCx) regions. (Scale bar, 1 mm.)   (C)   On day 1 post-implantation, raw electrocorticographic signals were simultaneously recorded from 128 channels during exploratory behavior. (D and E)   Day 1 post-implantation, signal power–frequency plots from representative electrocorticographic electrodes in the piriform cortex (PaCx), stratified by behavioral state: exploration (orange), stereotypic behavior (yellow), and rest (light blue). The figures show the low-frequency band (0 to 30 Hz) (D) and the high-frequency band (60 to 120 Hz) (E). (F and G)   Statistical comparisons of signal power across different frequency bands in the piriform cortex (PaCx), contrasting three behavioral states. Data are presented for day 1 post-implantation (F) and day 90 post-implantation (G). The P-values for each comparison, listed from left to right and top to bottom, are as follows: (F) 1.7×10⁻², 47×10⁻³, 41×10⁻¹, 1.2×10⁻², 50×10⁻¹, 47×10⁻⁵, and 82×10⁻⁵; (G) 1.5×10⁻¹, 1.6×10⁻⁴, 94×10⁻³, 14×10⁻², 24×10⁻³, and 98×10⁻⁴. (H)   Signal-to-noise ratio (SNR) of cortical electrocorticographic signals recorded from 128 channels in five rabbits under exploratory conditions. Data represent measurements obtained over several consecutive days following implantation.