Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m²) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

3D printing has been widely used for on-demand prototyping of complex three-dimensional structures. In biomedical applications, PEDOT:PSS has emerged as a promising material in versatile bioelectronics due to its tissue-like mechanical properties and suitable electrical properties. However, previously developed PEDOT:PSS inks have not been able to fully utilize the advantages of commercial 3D printing due to its long post treatment times, difficulty in high aspect ratio printing, and low conductivity. We propose a one-shot strategy for the fabrication of PEDOT:PSS ink that is able to simultaneously achieve on-demand biocompatibility (no post treatment), structural integrity during 3D printing for tall three-dimensional structures, and high conductivity for rapid-prototyping. By using ionic liquid-facilitated PEDOT:PSS colloidal stacking induced by a centrifugal protocol, a viscoplastic PEDOT:PSS-ionic liquid colloidal (PILC) ink was developed. PILC inks exhibit high-aspect ratio vertical stacking, omnidirectional printability for generating suspended architectures, high conductivity (~286 S/cm), and high-resolution printing (~50 µm). We demonstrate the on-demand and versatile applicability of PILC inks through the fabrication of 3D circuit boards, on-skin physiological signal monitoring e-tattoos, and implantable bioelectronics (opto-electrocorticography recording, low voltage sciatic nerve stimulation and recording from deeper brain layers via 3D vertical spike arrays).

Development of neural interfaces from surface electrodes to fibers with various type, functionality, and materials.

This article presents a wireless power transfer (WPT) system that incorporates a seamless uplink data telemetry and a simultaneous shared inductor dual-output (SIDO) regulating rectification (RR) under distance variation over a single WPT link. The proposed double charging keying (DCK) uplink data modulation method assisted by a dynamic zoom control breaks the trade-off between power delivery to the load (PDL) and uplink data such that the high data-rate uplink data telemetry no longer limits the amount of PDLs. Furthermore, DCK alleviates the design difficulty in simultaneous uplink data telemetry and RR. The dynamic ZOOM-based digital control algorithm is employed to ensure reliable uplink data telemetry and rapid transient response of SIDO-RR with two $\Delta \Sigma $ -loops under distance variations. This work achieves 1.695-Mb/s uplink data rate while delivering up to 108 mW to two independent loads over 10–42-mm single-link distance. The chip fabricated in standard 65-nm CMOS occupies 0.2-mm2 active area and its performance is validated through in vivo experiments.

The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness.

Continuous neural signal acquisition during electrical stimulation is essential for neuromodulation; nevertheless, it is often hindered by high-amplitude stimulation artifacts (SAs). This study presents a neuromodulation system with an application-specific integrated circuit (ASIC) that implements 2.9$\times$ faster adaptation than a fixed parameter method for the real-time recovery of neural signals fully overlapped with stimulation artifacts in both time and frequency domains, without any prior calibration. The on-chip SA removal module leverages an adaptive infinite impulse response (IIR)-based template-subtraction method with zero-multiplier operation and low computational complexity, enabling rapid template convergence and high accuracy under time-varying SAs while optimizing area and power efficiency. The stimulator incorporates a stimulation frequency dithering mechanism to minimize neural signal loss at the stimulation frequency and its harmonics during recovery. In vitro and in vivo experimental validation, including local field potential (LFP) and action potential (AP) recordings, demonstrated real-time SA removal, achieving 40 dB reduction of SA component and preserving neural signal integrity. The ASIC, fabricated using the TSMC 65 nm CMOS LP process, occupies a total die area of 1 mm². The SA removal module including on-chip memory occupies 0.15 mm² and consumes 1.3 µW. The presented system enables recovery of neural signals obscured by time-varying SAs in real time, without requiring prior calibration or external processing units.