Quantum Oscillations in Graphene Using Surface Acoustic Wave Resonators.

Surface acoustic waves (SAWs) provide a contactless method for measuring wave-vector-dependent conductivity. This technique has been used to discover emergent length scales in the fractional quantum Hall regime of traditional, semiconductor-based heterostructures. SAWs would appear to be an ideal match for van der Waals heterostructures, but the right combination of substrate and experimental geometry to allow access to the quantum transport regime has not yet been found. We demonstrate that SAW resonant cavities fabricated on LiNbO_{3} substrates can be used to access the quantum Hall regime of high-mobility, hexagonal boron nitride encapsulated, graphene heterostructures. Our work establishes SAW resonant cavities as a viable platform for performing contactless conductivity measurements in the quantum transport regime of van der Waals materials.

Palliative vertical vein stenting in a critical neonate with obstructed infradiaphragmatic total anomalous pulmonary venous connection.

Neonatal total anomalous pulmonary venous connection has an incidence of about ∼1-2%.1 The clinical presentation of total anomalous pulmonary venous connection in the neonatal period is dependent on the presence or absence of pulmonary venous obstruction, which is usual when the veins connect to the umbilicovitelline system, as in infradiaphragmatic total anomalous pulmonary venous connection. Obstructed total anomalous pulmonary venous connection presents with severe respiratory distress, metabolic acidosis, and cyanosis and requires urgent surgical intervention. However, critically ill neonates with obstructed total anomalous pulmonary venous connection have a higher surgical morbidity and mortality, and pre-operative stabilisation can improve outcomes in them. We present a case of a septic term neonate with obstructed infradiaphragmatic total anomalous pulmonary venous connection who underwent emergency palliative stent placement for immediate relief of pulmonary venous obstruction.

Cavity-agnostic acoustofluidic manipulations enabled by guided flexural waves on a membrane acoustic waveguide actuator.

This article presents an in-depth exploration of the acoustofluidic capabilities of guided flexural waves (GFWs) generated by a membrane acoustic waveguide actuator (MAWA). By harnessing the potential of GFWs, cavity-agnostic advanced particle manipulation functions are achieved, unlocking new avenues for microfluidic systems and lab-on-a-chip development. The localized acoustofluidic effects of GFWs arising from the evanescent nature of the acoustic fields they induce inside a liquid medium are numerically investigated to highlight their unique and promising characteristics. Unlike traditional acoustofluidic technologies, the GFWs propagating on the MAWA's membrane waveguide allow for cavity-agnostic particle manipulation, irrespective of the resonant properties of the fluidic chamber. Moreover, the acoustofluidic functions enabled by the device depend on the flexural mode populating the active region of the membrane waveguide. Experimental demonstrations using two types of particles include in-sessile-droplet particle transport, mixing, and spatial separation based on particle diameter, along with streaming-induced counter-flow virtual channel generation in microfluidic PDMS channels. These experiments emphasize the versatility and potential applications of the MAWA as a microfluidic platform targeted at lab-on-a-chip development and showcase the MAWA's compatibility with existing microfluidic systems.

GHz ultrasonic sensor for ionic content with high sensitivity and localization.

Sensing the ionic content of a solution at high spatial and temporal resolution and sensitivity is a challenge in nanosensing. This paper describes a comprehensive investigation of the possibility of GHz ultrasound acoustic impedance sensors to sense the content of an ionic aqueous medium. At the 1.55 GHz ultrasonic frequency used in this study, the micron-scale wavelength and the decay lengths in liquid result in a highly localized sense volume with the added potential for high temporal resolution and sensitivity. The amplitude of the back reflected pulse is related to the acoustic impedance of the medium and a function of ionic species concentration of the KCl, NaCl, and CaCl2 solutions used in this study. A concentration sensitivity as high as 1 mM and concentration detection range of 0 to 3 M was achieved. These bulk acoustic wave pulse-echo acoustic impedance sensors can also be used to record dynamic ionic flux.

Microfabricated acoustofluidic membrane acoustic waveguide actuator for highly localized in-droplet dynamic particle manipulation.

Precision manipulation techniques in microfluidics often rely on ultrasonic actuators to generate displacement and pressure fields in a liquid. However, strategies to enhance and confine the acoustofluidic forces often work against miniaturization and reproducibility in fabrication. This study presents microfabricated piezoelectric thin film membranes made via silicon diffusion for guided flexural wave generation as promising acoustofluidic actuators with low frequency, voltage, and power requirements. The guided wave propagation can be dynamically controlled to tune and confine the induced acoustofluidic radiation force and streaming. This provides for highly localized dynamic particle manipulation functionalities such as multidirectional transport, patterning, and trapping. The device combines the advantages of microfabrication and advanced acoustofluidic capabilities into a miniature "drop-and-actuate" chip that is mechanically robust and features a high degree of reproducibility for large-scale production. The membrane acoustic waveguide actuators offer a promising pathway for acoustofluidic applications such as biosensing, organoid production, and in situ analyte transport.

GHz Ultrasound and Electrode Chip-Scale Arrays Stimulate and Influence Morphology of Human Neural Cells.

This study describes the effects of chip-scale gigahertz (GHz) ultrasound (US) and electrical stimulus on the morphology, functionality, and viability of neural cells in vitro. The GHz frequency stimulation is achieved using aluminum nitride piezoelectric transducers fabricated on a silicon wafer, operating at 1.47 GHz, corresponding to the film's thickness mode resonance. These devices are used to stimulate SH-SY5Y neural cells in vitro and observe effects on the morphology and viability of the stimulated cells. It is possible to use these devices to deliver either ultrasonic stimulus alone or US stimulus in conjunction with electrical stimulus. Viability tests demonstrated that the neurons retained structural integrity and viability across a wide range of GHz US stimulus intensities (0-1.2 W/cm2), validating that measurements occur at nontoxic doses of US. Neural stimulation is validated with these devices following the outputs of a previous study, with the normalized fluorescence intensity of activated cells between 1.9 and 2.4. The 300-s ultrasonic stimulation at 1.47 GHz and 0.05 W/cm2 peak intensity led to a decrease in nuclear elongation by 17.5% and a cross-sectional area decrease by 17.8% across three independent trials of over 150 cells per category ( ). The F-actin governed cellular elongation increased in length by up to 16.3% in cells exposed to an ultrasonic stimulus or costimulus ( ). Neurite length increased following ultrasonic stimulation compared with control by 75.8% ( ). This article demonstrates new GHz US and electrical chip-scale arrays with apparent effects in both neural excitation and cell morphology.

Ultrasonically actuated neural probes for reduced trauma and inflammation in mouse brain.

Electrical neural recordings measured using direct electrical interfaces with neural tissue suffer from a short lifespan because the signal strength decreases over time. The inflammatory response to the inserted microprobe can create insulating tissue over the electrical interfaces, reducing the recorded signal below noise levels. One of the factors contributing to this inflammatory response is the tissue damage caused during probe insertion. Here, we explore the use of ultrasonic actuation of the neural probe during insertion to minimize tissue damage in mice. Silicon neural microprobes were designed and fabricated with integrated electrical recording sites and piezoelectric transducers. The microprobes were actuated at ultrasonic frequencies using integrated piezoelectric transducers. The microprobes were inserted into mouse brains under a glass window over the brain surface to image the tissue surrounding the probe using two-photon microscopy. The mechanical force required to penetrate the tissue was reduced by a factor of 2-3 when the microprobe was driven at ultrasonic frequencies. Tissue histology at the probe insertion site showed a reduced area of damage and decreased microglia counts with increasing ultrasonic actuation of the probes. Two-photon imaging of the microprobe over weeks demonstrated stabilization of the inflammatory response. Recording of electrical signals from neurons over time suggests that microprobes inserted using ultrasound have a higher signal-to-noise ratio over an extended time period.

Polymer interdigitated pillar electrostatic (PIPE) actuators.

This work reports a three-dimensional polymer interdigitated pillar electrostatic actuator that can produce force densities 5-10× higher than those of biological muscles. The theory of operation, scaling, and stability is investigated using analytical and FEM models. The actuator consists of two high-density arrays of interdigitated pillars that work against a restoring force generated by an integrated flexure spring. The actuator architecture enables linear actuation with higher displacements and pull-in free actuation to prevent the in-use stiction associated with other electrostatic actuators. The pillars and springs are 3D printed together in the same structure. The pillars are coated with a gold-palladium alloy layer to form conductive electrodes. The space between the pillars is filled with liquid dielectrics for higher breakdown voltages and larger electrostatic forces due to the increase in the dielectric constant. We demonstrated a prototype actuator that produced a maximum work density of 54.6 µJ/cc and an electrical-to-mechanical energy coupling factor of 32% when actuated at 4000 V. The device was operated for more than 100,000 cycles with no degradation in displacements. The flexible polymer body was robust, allowing the actuator to operate even after high mechanical force impact, which was demonstrated by operation after drop tests. As it is scaled further, the reported actuator will enable soft and flexible muscle-like actuators that can be stacked in series and parallel to scale the resulting forces. This work paves the way for high-energy density actuators for microrobotic applications.

Non-contact ultrasound oocyte denudation.

Cumulus removal (CR) is a central prerequisite step for many protocols involved in the assisted reproductive technology (ART) such as intracytoplasmic sperm injection (ICSI) and preimplantation genetic testing (PGT). The most prevalent CR technique is based upon laborious manual pipetting, which suffers from inter-operator variability and therefore a lack of standardization. Automating CR procedures would alleviate many of these challenges, improving the odds of a successful ART or PGT outcome. In this study, a chip-scale ultrasonic device consisting of four interdigitated transducers (IDT) on a lithium niobate substrate has been engineered to deliver megahertz (MHz) range ultrasound to perform denudation. The acoustic streaming and acoustic radiation force agitate COCs inside a microwell placed on top of the LiNbO3 substrate to remove the cumulus cells from the oocytes. This paper demonstrates the capability and safety of the denudation procedure utilizing surface acoustic wave (SAW), achieving automation of this delicate manual procedure and paving the steps toward improved and standardized oocyte manipulation.

Femtometer-amplitude imaging of coherent super high frequency vibrations in micromechanical resonators.

Dynamic measurement of femtometer-displacement vibrations in mechanical resonators at microwave frequencies is critical for a number of emerging high-impact technologies including 5G wireless communications and quantum state generation, storage, and transfer. However, the resolution of continuous-wave laser interferometry, the method most commonly used for imaging vibration wavefields, has been limited to vibration amplitudes just below a picometer at several gigahertz. This is insufficient for these technologies since vibration amplitudes precipitously decrease for increasing frequency. Here we present a stroboscopic optical sampling approach for the transduction of coherent super high frequency vibrations. Phase-sensitive absolute displacement detection with a noise floor of 55 fm/√Hz for frequencies up to 12 GHz is demonstrated, achieving higher bandwidth and significantly lower noise floor simultaneously compared to previous work. An acoustic microresonator with resonances above 10 GHz and displacements smaller than 70 fm is measured using the presented method to reveal complex mode superposition, dispersion, and anisotropic propagation.

Dual oscillator model of the respiratory neuronal network generating quantal slowing of respiratory rhythm.

We developed a dual oscillator model to facilitate the understanding of dynamic interactions between the parafacial respiratory group (pFRG) and the preBötzinger complex (preBötC) neurons in the respiratory rhythm generation. Both neuronal groups were modeled as groups of 81 interconnected pacemaker neurons; the bursting cell model described by Butera and others [model 1 in Butera et al. (J Neurophysiol 81:382-397, 1999a)] were used to model the pacemaker neurons. We assumed (1) both pFRG and preBötC networks are rhythm generators, (2) preBötC receives excitatory inputs from pFRG, and pFRG receives inhibitory inputs from preBötC, and (3) persistent Na(+) current conductance and synaptic current conductances are randomly distributed within each population. Our model could reproduce 1:1 coupling of bursting rhythms between pFRG and preBötC with the characteristic biphasic firing pattern of pFRG neurons, i.e., firings during pre-inspiratory and post-inspiratory phases. Compatible with experimental results, the model predicted the changes in firing pattern of pFRG neurons from biphasic expiratory to monophasic inspiratory, synchronous with preBötC neurons. Quantal slowing, a phenomena of prolonged respiratory period that jumps non-deterministically to integer multiples of the control period, was observed when the excitability of preBötC network decreased while strengths of synaptic connections between the two groups remained unchanged, suggesting that, in contrast to the earlier suggestions (Mellen et al., Neuron 37:821-826, 2003; Wittmeier et al., Proc Natl Acad Sci USA 105(46):18000-18005, 2008), quantal slowing could occur without suppressed or stochastic excitatory synaptic transmission. With a reduced excitability of preBötC network, the breakdown of synchronous bursting of preBötC neurons was predicted by simulation. We suggest that quantal slowing could result from a breakdown of synchronized bursting within the preBötC.

Vacuum-free self-powered parallel electron lithography with sub-35-nm resolution.

The critical dimension, throughput, and cost of nanolithography are central to developing commercially viable high-performance nanodevices. Available top-down lithography approaches to fabricate large-area nanostructures at low cost, such as controllable nanowire (NW) array fabrication for solar cells applications, are challenging due to the requirement of both high lithography resolution and high throughput. Here, a minimum 35 nm resolution is experimentally demonstrated by using a new mask fabrication technique in our demonstrated vacuum-free high-throughput self-powered parallel electron lithography (SPEL) system, which uses large-area planar radioactive beta-electron thin film emitters to parallel expose e-beam resist through a stencil mask. SPEL is the first-time demonstrated vacuum-free electron lithography, which overcomes the membrane mask distortion challenge that was shown to be the Achilles heel of previous attempts at electron projection lithography in vacuum. Monte Carlo simulations show that by using beryllium tritide thin film source in SPEL system, the exposure time can be reduced down to 2 min for each large-area (10000 cm(2) or more) parallel exposure, with resolution not larger than 20 nm. Moreover, experimental demonstration of large-area diameter-and-density controllable vertical NW arrays fabricated by SPEL shows its promising utility for an application requiring large-area nanostructure definition.

High-efficiency ordered silicon nano-conical-frustum array solar cells by self-powered parallel electron lithography.

Nanostructured silicon thin film solar cells are promising, due to the strongly enhanced light trapping, high carrier collection efficiency, and potential low cost. Ordered nanostructure arrays, with large-area controllable spacing, orientation, and size, are critical for reliable light-trapping and high-efficiency solar cells. Available top-down lithography approaches to fabricate large-area ordered nanostructure arrays are challenging due to the requirement of both high lithography resolution and high throughput. Here, a novel ordered silicon nano-conical-frustum array structure, exhibiting an impressive absorbance of 99% (upper bound) over wavelengths 400-1100 nm by a thickness of only 5 µm, is realized by our recently reported technique self-powered parallel electron lithography that has high-throughput and sub-35-nm high resolution. Moreover, high-efficiency (up to 10.8%) solar cells are demonstrated, using these ordered ultrathin silicon nano-conical-frustum arrays. These related fabrication techniques can also be transferred to low-cost substrate solar energy harvesting device applications.

Nanometrology optical ruler imaging system using diffraction from a quasiperiodic structure.

This work demonstrates wafer-scale, path-independent, atomically-based long term-stable, position nanometrology. This nanometrology optical ruler imaging system uses the diffraction pattern of an atomically stabilized laser from a microfabricated quasiperiodic aperture array as a two-dimensional optical ruler. Nanometrology is accomplished by cross correlations of image samples of this optical ruler. The quasiperiodic structure generates spatially dense, sharp optical features. This work demonstrates new results showing positioning errors down to 17.2 nm over wafer scales and long term stability below 20 nm over six hours. This work also numerically demonstrates robustness of the optical ruler to variations in the microfabricated aperture array and discretization noise in imagers.

Scanning probe nanoscale patterning of highly ordered pyrolytic graphite.

In this work we present precision scanning probe etching of highly ordered pyrolytic graphite. We corroborate that the lithography is due to an electrochemical, polarity-dependent, meniscus-mediated etching of the carbon surface. By changing the etching temperature, we are able to reduce the feature size by 24%. External feedback control and probe tip cleaning enables desired cut patterns with high precision. Using a feedback-controlled atomic force microscope, we demonstrate an array of 105 trenches using 370 etching operations, with 136 +/- 6 and 183 +/- 5 nm precision over an area of 2.5 microm x 2.5 microm. This results in a precision of 4.4% and 2.7%, respectively.

What does the multi-peaked respiratory output pattern tell us about the respiratory pattern generating neuronal network?

The respiratory neuronal network activity can be optically recorded from the ventral medulla of the in vitro brainstem-spinal cord preparation using a voltage-sensitive dye. To assess the spatiotemporal dynamics of respiratory-related regions of the ventral medulla, we developed a novel non-linear response model called the sigmoid and transfer function model. It regards the respiratory motor activity recorded from the fourth cervical ventral root (C4VR) as the response to optical signals from pixels within respiratory-related regions. When the C4VR activity had less than three peaks, optical time series of a single suitably chosen pixel could precisely estimate the activity. However, it was difficult to find a single explanatory pixel for multi-peaked C4VR activity. In this paper, we show that the multi-input single-output (MISO) STF model that takes a few different pixels as inputs greatly improves the precision of the estimation. We interpret this result that multi-peaked respiratory output patterns are caused by "migration of recruited area". Here the term "migration" denotes the phenomenon that the transition of respiratory-recruited subareas on the ventral medulla is observed within a single breath. In conclusion, the STF model is useful for analyzing spatiotemporal dynamics of optically recorded respiratory neuronal activities.

GHz Ultrasonic Chip-Scale Device Induces Ion Channel Stimulation in Human Neural Cells.

Emergent trends in the device development for neural prosthetics have focused on establishing stimulus localization, improving longevity through immune compatibility, reducing energy re-quirements, and embedding active control in the devices. Ultrasound stimulation can single-handedly address several of these challenges. Ultrasonic stimulus of neurons has been studied extensively from 100 kHz to 10 MHz, with high penetration but less localization. In this paper, a chip-scale device consisting of piezoelectric Aluminum Nitride ultrasonic transducers was engineered to deliver gigahertz (GHz) ultrasonic stimulus to the human neural cells. These devices provide a path towards complementary metal oxide semiconductor (CMOS) integration towards fully controllable neural devices. At GHz frequencies, ultrasonic wavelengths in water are a few microns and have an absorption depth of 10-20 µm. This confinement of energy can be used to control stimulation volume within a single neuron. This paper is the first proof-of-concept study to demonstrate that GHz ultrasound can stimulate neurons in vitro. By utilizing optical calcium imaging, which records calcium ion flux indicating occurrence of an action potential, this paper demonstrates that an application of a nontoxic dosage of GHz ultrasonic waves [Formula: see text] caused an average normalized fluorescence intensity recordings >1.40 for the calcium transients. Electrical effects due to chip-scale ultrasound delivery was discounted as the sole mechanism in stimulation, with effects tested at α = 0.01 statistical significance amongst all intensities and con-trol groups. Ionic transients recorded optically were confirmed to be mediated by ion channels and experimental data suggests an insignificant thermal contributions to stimulation, with a predicted increase of 0.03 oC for [Formula: see text] This paper paves the experimental framework to further explore chip-scale axon and neuron specific neural stimulation, with future applications in neural prosthetics, chip scale neural engineering, and extensions to different tissue and cell types.

A frequency domain SIM reconstruction algorithm using reduced number of images.

Conventional two-dimensional structured illumination microscopy (SIM) requires 9 raw images to reconstruct a super-resolved image. In order to increase the frame rate of 2DSIM, attempts are being made to reduce the number of raw SIM images. However, all the proposed SIM reconstruction algorithms (SIM-RA) capable of reconstructing super-resolution (SR) image with a reduced number of raw SIM images operate in the spatial domain. Here, we present a frequency domain SIM-RA based on ordinary least squares technique, which enables reconstruction of SR image using 4 raw SIM images. Unlike the spatial domain RA, which produces the SR image through iterative convergence, the presented RA provides a single step solution. It also reveals the fundamental limitation of least number of raw images required for resolution doubling in SIM.

UV-Triggered Transient Electrospun Poly(propylene carbonate)/Poly(phthalaldehyde) Polymer Blend Fiber Mats.

This work reports the first transient electrospun nanofiber mat triggered by UV-irradiation using poly(propylene carbonate) (PPC)/poly(phthalaldehyde) (cPPA) polymer blends. The ability to trigger room temperature transience of nanofiber mats without the need for additional heat or solvent expands its utility in nonbiological fields, especially for transient electronic devices. The addition of a photo-acid-generator to the system, working in combination with UV light, provides an acid source to enhance degradation because both polymer backbones are acid-sensitive. Electrospinning enables the production of PPC/cPPA composite nanofiber mats capable of significant degradation upon exposure to UV radiation while maintaining relatively high mechanical properties. An acid amplifier, an autocatalytically decomposing compound triggered by acid, was used to generate more acid and accelerate nanofiber degradation. The electrospun fiber mats can be post-annealed to achieve an improved mat with a mechanical strength of ∼170 MPa.