Fully Passive Flexible Wireless Neural Recorder for the Acquisition of Neuropotentials from a Rat Model

Flexible silk-fibroin-based microelectrode arrays for high-resolution neural recording

High-precision neural recording plays a pivotal role in unraveling the intricate mechanisms that underlie information transmission of the nervous system, raising increasing interest in the development of implantable microelectrode arrays (MEAs). The challenge lies in providing a truly soft, highly conductive and low-impedance neural interface for precise recording of the electrophysiological signals of individual neurons or neural networks. Herein, by implementing a novel topological regulation strategy of silk fibroin (SF) crosslinking, we prepared a flexible, hydrophilic, and biocompatible MEA substrate, facilitating a biocompatible neural interface that minimizes mechanical mismatch with biological tissues. Additionally, we established a strategy involving screen-printing combined with post-coating to prepare MEAs with high conductivity, low impedance and high capacitance, by coating PEDOT:PSS on titanium carbide (Ti3C2) microarrays. The Ti3C2 nanosheets, as the conductive track of the MEAs, avoided the charge drifting associated with metals and facilitated the processing of the MEAs. Further coating PEDOT:PSS on the electrode points reduced the impedance 100-fold, from 105 to 103 Ω. Experimental validation confirmed the superior electrophysiological signal recording capabilities of the SF-based MEA (SMEA) in peripheral and cerebral nerves with a much higher signal-to-noise ratio (SNR) of 20. In particular, we achieved high-precision recording of the action potential (AP) induced by flash visual stimulation, demonstrating high performance in weak signal recording. In summary, the development of SMEA provides a robust foundation for future investigations into the mechanisms and principles of neural circuit information transmission in complex nervous systems.

Through-polymer, via technology-enabled, flexible, lightweight, and integrated devices for implantable neural probes

In implantable electrophysiological recording systems, the headstage typically comprises neural probes that interface with brain tissue and integrated circuit chips for signal processing. While advancements in MEMS and CMOS technology have significantly improved these components, their interconnection still relies on conventional printed circuit boards and sophisticated adapters. This conventional approach adds considerable weight and volume to the package, especially for high channel count systems. To address this issue, we developed a through-polymer via (TPV) method inspired by the through-silicon via (TSV) technique in advanced three-dimensional packaging. This innovation enables the vertical integration of flexible probes, amplifier chips, and PCBs, realizing a flexible, lightweight, and integrated device (FLID). The total weight of the FLIDis only 25% that of its conventional counterparts relying on adapters, which significantly increased the activity levels of animals wearing the FLIDs to nearly match the levels of control animals without implants. Furthermore, by incorporating a platinum-iridium alloy as the top layer material for electrical contact, the FLID realizes exceptional electrical performance, enabling in vivo measurements of both local field potentials and individual neuron action potentials. These findings showcase the potential of FLIDs in scaling up implantable neural recording systems and mark a significant advancement in the field of neurotechnology.

Porous microneedle patch with sustained delivery of extracellular vesicles mitigates severe spinal cord injury

The transplantation of mesenchymal stem cells-derived secretome, particularly extracellular vesicles is a promising therapy to suppress spinal cord injury-triggered neuroinflammation. However, efficient delivery of extracellular vesicles to the injured spinal cord, with minimal damage, remains a challenge. Here we present a device for the delivery of extracellular vesicles to treat spinal cord injury. We show that the device incorporating mesenchymal stem cells and porous microneedles enables the delivery of extracellular vesicles. We demonstrate that topical application to the spinal cord lesion beneath the spinal dura, does not damage the lesion. We evaluate the efficacy of our device in a contusive spinal cord injury model and find that it reduces the cavity and scar tissue formation, promotes angiogenesis, and improves survival of nearby tissues and axons. Importantly, the sustained delivery of extracellular vesicles for at least 7 days results in significant functional recovery. Thus, our device provides an efficient and sustained extracellular vesicles delivery platform for spinal cord injury treatment.

Multichannel Wireless Neurosensing System for battery-free monitoring of neuronal activity

Electrical activity recordings are critical for evaluating and understanding brain function. We present a novel wireless, implantable, and battery-free device, namely the Wireless Neurosensing System (WiNS), and for the first time, we evaluate multichannel recording capabilities in vivo. For a preliminary evaluation, we performed a benchtop experiment with emulated sinusoidal signals of varying amplitude and frequency, representative of neuronal activity. We later performed and analyzed electrocortical recordings in rats of evoked somatosensory activity in response to three paradigms: hind/fore limb and whisker stimulation. Wired recordings were used for comparison and validation of WiNS. We found that through the channel multiplexing element of WiNS, it is possible to perform multichannel recordings with a maximum sampling rate of ∼10 kHz for a total of eight channels. This sampling rate is appropriate for monitoring the full range of neuronal signals of interest, from low-frequency population recordings of electrocorticography and local field potentials to high-frequency individual neuronal spike recordings. These in vivo experiments demonstrated that the evoked neuronal activity recorded with WiNS is comparable to that recorded with a wired system under identical circumstances. Analysis of critical parameters for interpreting the somatosensory evoked activity showed no statistically significant difference between the parameters obtained by a wired system versus those obtained using WiNS. Therefore, WiNS can match the performance of more invasive recording systems. WiNS is a groundbreaking technology with potential applications throughout neuroscience as it offers a simple alternative to address the pitfalls of battery-powered neuronal implants.

Wireless Addressable Cortical Microstimulators Powered by Near-Infrared Harvesting

Ensembles of autonomous, spatially distributed wireless stimulators can offer a versatile approach to patterned microstimulation of biological circuits such as the cortex. Here, we demonstrate the concept of a distributed, untethered, and addressable microstimulator, integrating an ultraminiaturized ASIC with a custom-designed GaAs photovoltaic (PV) microscale energy harvester, dubbed as an "optical neurograin (ONG)". An on-board Manchester-encoded near-infrared downlink delivers incident IR power and provides a synchronous clock across an ensemble of microdevices, triggering stimulus events by remote command. Each ONG has a unique device address and, when an incoming downlink bit sequence matches with this device identification (ID), the implant delivers a charge-balanced current stimulus to the target cortex. Present devices use 7-bit metal fuses fabricated during the CMOS process for their device ID, laser-scribed in post-processing, allowing in principle for a stimulator network of up to 128 nodes. We have characterized small ensembles of ONGs and shown a proof of concept of the system both on benchtop and in vivo rat rodent model.

A Polyimide-Based Flexible Monopole Antenna Fed by a Coplanar Waveguide

A 2.4 GHz flexible monopole antenna fed by a coplanar waveguide (CPW) was presented on polyimide (PI) as the dielectric substrate, which was fabricated by in situ self-metallization. The technology does not depend on expensive equipment or complex experimental environments, including hydrolysis, ion exchange, and reduction reaction. The measurement results show that the resonance frequency of the proposed antenna is 2.28 GHz, the bandwidth is 2.06–2.74 GHz, and the relative bandwidth is 28.33% under the flat state. The bending and folding test was also carried out. Whether it was flat, bent, or folded, the measured results met the requirements of the antenna. A fatigue test was carried out to illustrate that the prepared film has high mechanical flexibility, which expands the application field of antenna.

Flexible Bandpass Filter Fabricated on Polyimide Substrate by Surface Modification and In Situ Self-Metallization Technique

Polymer, especially polyimide (PI), is the best suitable substrate material for the design of flexible electronics. The compact silver can be reduced on the surface of PI films by surface modification and in situ self-metallization technique. The formed silver layers have good electrical and mechanical flexibility. A flexible bandpass filter on a PI flexible substrate by surface modification and in situ self-metallization technique at room temperature are presented in this work. Measured results show that the proposed flexible bandpass filter could achieve a fractional bandwidth of 80.8% with an insertion loss (IL) of less than 0.6 dB. The performance of the designed filter is almost constant under different bending, folding, and rolling conditions. The formed silver layers also present good adhesion with PI substrates. This technology provides an alternative approach for manufacturing flexible filters without high-temperature thermal annealing, costly equipment, and vacuum conditions.

Flexible Bandpass Filter Fabricated on Polyimide Substrate by Surface Modification and In Situ Self-Metallization Technique

Polymer, especially polyimide (PI), is the best suitable substrate material for the design of flexible electronics. The compact silver can be reduced on the surface of PI films by surface modification and in situ self-metallization technique. The formed silver layers have good electrical and mechanical flexibility. A flexible bandpass filter on a PI flexible substrate by surface modification and in situ self-metallization technique at room temperature are presented in this work. Measured results show that the proposed flexible bandpass filter could achieve a fractional bandwidth of 80.8% with an insertion loss (IL) of less than 0.6 dB. The performance of the designed filter is almost constant under different bending, folding, and rolling conditions. The formed silver layers also present good adhesion with PI substrates. This technology provides an alternative approach for manufacturing flexible filters without high-temperature thermal annealing, costly equipment, and vacuum conditions.