Silicon-based planar microelectronics is a powerful tool for scalably recording and modulating neural activity at high spatiotemporal resolution, but it remains challenging to target neural structures in three dimensions (3D). We present a method for directly fabricating 3D arrays of tissue-penetrating microelectrodes onto silicon microelectronics. Leveraging a high-resolution 3D printing technology based on 2-photon polymerization and scalable microfabrication processes, we fabricated arrays of 6,600 microelectrodes 10-130 µm tall and at 35-μm pitch onto a planar silicon-based microelectrode array. The process enables customizable electrode shape, height and positioning for precise targeting of neuron populations distributed in 3D. As a proof of concept, we addressed the challenge of specifically targeting retinal ganglion cell (RGC) somas when interfacing with the retina. The array was customized for insertion into the retina and recording from somas while avoiding the axon layer. We verified locations of the microelectrodes with confocal microscopy and recorded high-resolution spontaneous RGC activity at cellular resolution. This revealed strong somatic and dendritic components with little axon contribution, unlike recordings with planar microelectrode arrays. The technology could be a versatile solution for interfacing silicon microelectronics with neural structures and modulating neural activity at large scale with single-cell resolution.

Implantable medical devices require protective encapsulation to isolate them from the biological environment. Parylene-C (PaC) is a prevalent encapsulation polymer but is susceptible to cracking, delamination, oxidation, and moisture penetration over time. This study demonstrates that 3D micro-anchors fabricated by direct laser writing (DLW) greatly enhance PaC lifetime and encapsulation properties. The PaC film is vapor deposited onto these anchor points, followed by ultraviolet radiation (UV)-curing-induced shrinkage. Electrochemical impedance spectroscopy (EIS) during accelerated aging tests in reactive solutions (87 degrees C, 15 mM H2O2) is performed to monitor film degradation over time. Unpatterned PaC films failed before reaching the 3.25 accelerated year benchmark, while 100 mu m spaced micro-anchors extended encapsulation up to 5.5 equivalent years. Subsequent improvements are achieved with a spacing of 50 mu m, demonstrating viability up to approximate to 6 equivalent years. This research demonstrates the benefit of engineering anchor points for preventing delamination of the PaC layer and significantly enhancing encapsulation properties. Printed 3D micro-anchors are an extremely flexible platform, with many different shapes and sizes possible which can further enhance longevity. The success in increasing coating lifetimes offers a promising direction for improving long-term implantable medical devices, potentially revolutionizing their longevity and reliability. This study reveals that 3D micro-anchors, created through direct laser writing, enhance PaC encapsulation properties. Vapor-deposited PaC on these anchors, with UV-induced shrinkage, extends viability and prevents PaC layer delamination. Micro-anchors at 100 mu m spacing extend encapsulation to 5.5 equivalent years, and improvements at 50 mu m spacing demonstrate viability up to approximate to 6 equivalent years. This approach can revolutionize implantable device longevity. image

This paper presents a neural recording IC featuring lossy compression during digitization, thus preventing data deluge and enabling a compact active digital pixel design. The wired-OR-based compression discards unwanted baseline samples while allowing the reconstruction of spike samples. The IC features a 32x32 MEA with $36 \mu m$ pixel pitch and consumes 268nW per pixel from a single 1V supply. It achieves $9.8 \mu V_{RMS}$ input-referred noise and 0.3-5kHz bandwidth, resulting in NEF/PEF of 3.7/14.1.

Perception, thoughts, and actions are encoded by the coordinated activity of large neuronal populations spread over large areas. However, existing electrophysiological devices are limited by their scalability in capturing this cortex-wide activity. Here, we developed an electrode connector based on an ultra-conformable thin-film electrode array that self-assembles onto silicon microelectrode arrays enabling multithousand channel counts at a millimeter scale. The interconnects are formed using microfabricated electrode pads suspended by thin support arms, termed Flex2Chip. Capillary-assisted assembly drives the pads to deform toward the chip surface, and van der Waals forces maintain this deformation, establishing Ohmic contact. Flex2Chip arrays successfully measured extracellular action potentials ex vivo and resolved micrometer scale seizure propagation trajectories in epileptic mice. We find that seizure dynamics in absence epilepsy in the Scn8a +/− model do not have constant propagation trajectories.

This article presents a data-compressive neural recording IC for single-cell resolution high-bandwidth brain–computer interfaces (BCIs). The IC features wired-OR lossy compression during digitization, thus preventing data deluge and massive data movement. By discarding unwanted baseline samples of the neural signals, the output data rate is reduced by 146 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> on average while allowing the reconstruction of spike samples. The recording array consists of pulse-position modulation (PPM)-based active digital pixels (ADPs) with a global single-slope (SS) analog-to-digital conversion scheme, which enables a low-power and compact pixel design with significantly simple routing and low array readout energy. Fabricated in a 28-nm CMOS process, the neural recording IC features 1024 channels (i.e., 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 32 array) with a pixel pitch of 36 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m that can be directly matched to a high-density micro-electrode array (MEA). The pixel achieves 7.4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_\text{rms}$</tex-math> </inline-formula> input-referred noise with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 3-dB bandwidth of 300 Hz–5 kHz while consuming only 268 nW from a single 1-V supply. The IC achieves the smallest area per channel (36 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 36 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^\text{2}$</tex-math> </inline-formula> ) and the highest energy efficiency among the state-of-the-art neural recording ICs published to date.

Flexible origami structures can mimic the complicated motions of small creatures that are otherwise difficult to be achieved by rigid robots with limited degree of motion freedom. However, actuating origami structures in a compact and self-contained way has been a critical challenge. Here, we demonstrate a versatile approach of actuating origami micro-robots by printed self-folding creases made of a type of stimuli-responsive transition metal hydroxides/oxides that can undergo large actuation under electrochemical or light stimulations. Two enabling technologies are pivotal: (i) a microfluidic electrochemical writing method to selectively print the stimuli-responsive material (SRM) at the actuating creases to enable them to self-fold independently "on demand", and (ii) a micro-scale riveting method to provide strong adhesion of the SRM on the origami body. Such strategies allow the successful construction of actuating creases made from different stimuli-responsive transition metal hydroxides/oxides that can self-fold into curvature exceeding 1 mm(-1) under low-intensity visible-light stimulation in ambient conditions, or low-potential electrochemical stimulation in electrolytic environments, with response time as fast as in seconds. Based on the high performance of such active creases, complex miniaturized origami designs powered by hinges activated in an independently controllable way are demonstrated, including self-folding Miura and a full micro-robotic hand with independently programmable finger joints. These results prove a new, versatile paradigm for robotics, where a transferrable approach is applicable to design and fabricate a wide variety of customizable micro-robots with compact construction and complex motions using different stimuli-responsive ceramic-based materials. (c) 2020 Elsevier Ltd. All rights reserved.

Brain-machine interfaces (BMIs) have demonstrated potential both for neuroscience studies and for neural-prosthetic or therapeutic devices. Given the high density of brain neurons, engineering a dense array of neural recording sites across a large brain region is important for BMIs with significantly improved capabilities such as high-dexterity motor control. In our development of a high-channel-count and high-density BMI system using complementary metal-oxide semiconductor (CMOS) arrays mated with massively parallel microelectrodes, we determined that the connection between the microelectrode and chip interface (MCI) is a crucial process for device performance and scalability. Here we report our results extending flip chip bonding technique to establish the electrical connections en masse at the MCI. Key parameters affecting bonding quality were identified and optimized, and the quality of bonding was evaluated by electrochemical impedance spectroscopy (EIS) in phosphate buffered saline (PBS). With proper packaging, the bonding technique can be directly transferred to the fabrication of high-channel-count BMIs and standardized for broader applications where interconnection between massively parallel interfaces is required.

Developing cost-effective capabilities to fabricate materials into desired shapes and sizes has always been a prime focus of materials research. Selective-laser sintering, which is based on sintering of tiny particles, is currently limited to polymers and metals, and is generally not directly applicable to ceramic powders because of their high melting temperatures. Electrodeposition has the advantages of low costs, availability at room temperature and easy scalability. In this paper, an efficient technique for writing 2D oxide patterns on conductive substrates is demonstrated. In this method, a minimum quantity of liquid electrolyte is delivered through an extrusion nozzle and manipulated into the desired shape on the substrate, meanwhile being electrodeposited into the product by an applied voltage across the nozzle and substrate. Using this method, patterns of primarily Cu2O were successfully fabricated on stainless steel substrates. This is intriguing because, according to the Pourbaix diagram, the equilibrium deposited product at the low voltage used should be metallic Cu. A key factor that allows the product to be primarily oxide Cu2O is the non-equilibrium condition involved in the process due to the short deposition time; hence the nature of the product is shown to be tunable by printing conditions. A second material printed using this method was nickel hydroxide/oxyhydroxide which exhibits an interesting electrochemical actuation effect in alkaline media. Applications in printing micro-robots involving this material will also be discussed.

An efficient technique for writing 2D oxide patterns on conductive substrates is proposed and demonstrated in this paper. The technique concerns a novel concept for selective electrodeposition, in which a minimum quantity of liquid electrolyte, through an extrusion nozzle, is delivered and manipulated into the desired shape on the substrate, meanwhile being electrodeposited into the product by an applied voltage across the nozzle and substrate. Patterns of primarily Cu2O with 80-90% molar fraction are successfully fabricated on stainless steel substrates using this method. A key factor that allows the solid product to be primarily oxide Cu2O instead of metal Cu - the product predicted by the equilibrium Pourbaix diagram given the unusually large absolute deposition voltage used in this method, is the non-equilibrium condition involved in the process due to the short deposition time. Other factors including the motion of the extrusion nozzle relative to the substrate and the surface profile of the substrate that influence the electrodeposition performance are also discussed.