Arraying of microphotosynthetic power cells for enhanced power output

Microphotosynthetic power cells (µPSCs) generate power through the exploitation of living photosynthetic microorganisms by harvesting sunlight. The thermodynamic limitations of this process restrict the power output of a single µPSC. Herein, we demonstrate µPSCs in four different array configurations to enhance power output from these power cells. To this effect, six µPSCs were arrayed in series, parallel, and combinations of series and parallel configurations. Each µPSC was injected with a 2 mL liquid culture of photosynthetic microorganisms (Chlamydomonas reinhardtii) in the anode and 2 mL of 25% (w/v) electron acceptor potassium ferricyanide (K₃Fe(CN)₆) in the cathode. The combinations of µPSCs connected in series and parallel generated higher power than the individual series and parallel configurations. The combinations of six µPSCs connected in series and in parallel produced a high power density of 1914 mWm^-2 in the presence of white fluorescent light illumination at 20 µEm^-2s^-1. Furthermore, to realize the array strategy for real-time applications, a 1.7 V/2 mA rating light-emitting diode (LED) was powered by combinations of series and parallel array configurations. The results indicate the reliability of µPSCs to produce electricity from photosynthetic microorganisms for low-power applications. In addition, the results suggest that a combination of microlevel photosynthetic cells in array format represents a powerful optimal design strategy to enhance the power output from µPSCs.

Reagent elution combined with positive pressure filtration: A zero-discharge method for cyanide tailings remediation

At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution method developed in this research was extended for engineering. Results showed that the optimum elution conditions were determined to be: stirring elution, tailings/water ratio (M/V; 1:1) and operating time (10-20 min). Besides, 4 reagents (sodium dodecyl benzene sulfonate, cyclodextrin, sodium silicate and calcium hydroxide) were selected from four categories of 21 reagents for further composite elution. The cyanide elution rate was the highest (90.7%±0.1%) while the molar ratio of these 4 reagents was 5:2:2:1. Moreover, the combination of reagent elution and positive pressure filtration improved the elution efficiency of cyanide (92.6%±0.8%). And the cyanide content in the toxic leaching solution was lower than the standard value (5.0 mg/L). Furthermore, the composite elution method developed in this study was also extended for engineering. The concentration of cyanide in the leachate was < 5.0 mg/L, and was stable during 189 days of detection. Notably, the effluent can be reused directly, or reused after further treatment. The zero discharge of effluents and solid wastes was realized in the processes. The above results provided supports for the engineering treatment of cyanide tailings.

Scalable batch fabrication of ultrathin flexible neural probes using a bioresorbable silk layer

Flexible intracerebral probes for neural recording and electrical stimulation have been the focus of many research works to achieve better compliance with the surrounding tissue while minimizing rejection. Strategies have been explored to find the best way to insert flexible probes into the brain while maintaining their flexibility once positioned. Here, we present a novel and versatile scalable batch fabrication approach to deliver ultrathin and flexible probes consisting of a silk-parylene bilayer. The biodegradable silk layer, whose degradation time is programmable, provides a temporary and programmable stiffener to allow the insertion of ultrathin parylene-based flexible devices. Our innovative and robust batch fabrication technology allows complete freedom over probe design in terms of materials, size, shape, and thickness. We demonstrate successful ex vivo insertion of the probe with acute high-fidelity recordings of epileptic seizures in field potentials as well as single-unit action potentials in mouse brain slices. Our novel technological solution for implanting ultraflexible devices in the brain while minimizing rejection risks shows high potential for use in both brain research and clinical therapies.

High-resolution fabrication of nanopatterns by multistep iterative miniaturization of hot-embossed prestressed polymer films and constrained shrinking

The fabrication of nanostructures and nanopatterns is of crucial importance in microelectronics, nanofluidics, and the manufacture of biomedical devices and biosensors. However, the creation of nanopatterns by means of conventional nanofabrication techniques such as electron beam lithography is expensive and time-consuming. Here, we develop a multistep miniaturization approach using prestressed polymer films to generate nanopatterns from microscale patterns without the need of complex nanolithography methods. Prestressed polymer films have been used as a miniaturization technique to fabricate features with a smaller size than the initial imprinted features. However, the height of the imprinted features is significantly reduced after the thermal shrinking of the prestressed films due to the shape memory effect of the polymer, and as a result, the topographical features tend to disappear after shrinking. We have developed a miniaturization approach that controls the material flow and maintains the shrunken patterns by applying mechanical constraints during the shrinking process. The combination of hot embossing and constrained shrinking makes it possible to reduce the size of the initial imprinted features even to the nanoscale. The developed multistep miniaturization approach allows using the shrunken pattern as a master for a subsequent miniaturization cycle. Well-defined patterns as small as 100 nm are fabricated, showing a 10-fold reduction in size from the original master. The developed approach also allows the transfer of the shrunken polymeric patterns to a silicon substrate, which can be used as a functional substrate for many applications or directly as a master for nanoimprint lithography.

Better by design: What to expect from novel CAR-engineered cell therapies?

Chimeric antigen receptor (CAR) technology, and CAR-T cells in particular, have emerged as a new and powerful tool in cancer immunotherapy since demonstrating efficacy against several hematological malignancies. However, despite encouraging clinical results of CAR-T cell therapy products, a significant proportion of patients do not achieve satisfactory responses, or relapse. In addition, CAR-T cell applications to solid tumors is still limited due to the tumor microenvironment and lack of specifically targetable tumor antigens. All current products on the market, as well as most investigational CAR-T cell therapies, are autologous, using the patient's own peripheral blood mononuclear cells as starting material to manufacture a patient-specific batch. Alternative cell sources are, therefore, under investigation (e.g. allogeneic cells from an at least partially human leukocyte antigen (HLA)-matched healthy donor, universal "third-party" cells from a non-HLA-matched donor, cord blood-derived cells, immortalized cell lines or cells differentiated from induced pluripotent stem cells). However, genetic modifications of CAR-engineered cells, bioprocesses used to expand cells, and improved supply chains are still complex and costly. To overcome drawbacks associated with CAR-T technologies, novel CAR designs have been used to genetically engineer cells derived from alpha beta (αβ) T cells, other immune cells such as natural killer (NK) cells, gamma delta (γδ) T cells, macrophages or dendritic cells. This review endeavours to trigger ideas on the next generation of CAR-engineered cell therapies beyond CAR-T cells and, thus, will enable effective, safe and affordable therapies for clinical management of cancer. To achieve this, we present a multidisciplinary overview, addressing a wide range of critical aspects: CAR design, development and manufacturing technologies, pharmacological concepts and clinical applications of CAR-engineered cell therapies. Each of these fields employs a large number of ground-breaking scientific advances, where coordinated and complex process and product development occur at their interfaces.

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.

Mechanical memory operations in piezotransistive GaN microcantilevers using Au nanoparticle-enhanced photoacoustic excitation

Nonlinear oscillations in micro- and nanoelectromechanical systems have emerged as an exciting research area in recent years due to their promise in realizing low-power, scalable, and reconfigurable mechanical memory and logic devices. Here, we report ultralow-power mechanical memory operations utilizing the nonlinear oscillation regime of GaN microcantilevers with embedded piezotransistive AlGaN/GaN heterostructure field effect transistors as highly sensitive deflection transducers. Switching between the high and low oscillatory states of the nonlinear oscillation regime was demonstrated using a novel phase-controlled opto-mechanical excitation setup, utilizing a piezo actuator and a pulsed laser as the primary and secondary excitation sources, respectively. Laser-based photoacoustic excitation was amplified through plasmonic absorption in Au nanoparticles deposited on a transistor. Thus, the minimum switching energy required for reliable memory operations was reduced to less than a picojoule (pJ), which translates to one of the lowest ever reported, when normalized for mass.

Toroidal electromagnetically induced transparency based meta-surfaces and its applications

The vigorous research on low-loss photonic devices has brought significance to a new kind of electromagnetic excitation, known as toroidal resonances. Toroidal excitation, possessing high-quality factor and narrow linewidth of the resonances, has found profound applications in metamaterial (MM) devices. By the coupling of toroidal dipolar resonance to traditional electric/magnetic resonances, a metamaterial analogue of electromagnetically induced transparency effect (EIT) has been developed. Toroidal induced EIT has demonstrated intriguing properties including steep linear dispersion in transparency windows, often leading to elevated group refractive index in the material. This review summarizes the brief history and properties of the toroidal resonance, its identification in metamaterials, and their applications. Further, numerous theoretical and experimental demonstrations of single and multiband EIT effects in toroidal-dipole-based metamaterials and its applications are discussed. The study of toroidal-based EIT has numerous potential applications in the development of biomolecular sensing, slow light systems, switches, and refractive index sensing.

Accelerating the simulation of annual bifacial illumination of real photovoltaic systems with ray tracing

Accurate modeling of bifacial illumination is critical to improve the prediction of the energy yield of bifacial solar systems. Monte Carlo ray tracing is the most powerful tool to accomplish this task. In this work, we accelerate Monte Carlo ray tracing of large solar systems by nearly 90%. Our model achieves root-mean-square error values of 7.9% and 37.2% for the front and rear irradiance compared against single-axis tracking field reference data, respectively. The rear irradiance modeling error decreases to 18.9% if suspected snow periods are excluded. Crucially, our full system simulations show that surrounding ground surfaces affect the rear irradiance deep into the system. Therefore, unit system simulations cannot necessarily ignore the influence of the perimeter of large installations to accurately estimate annual yield. Large-scale simulations involving high-performance supercomputing were necessary to investigate these effects accurately, calibrate our simplified models, and validate our results against experimental measurements.

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

Hybrid lead halide ABX3 perovskite solar cells (PSCs) have emerged as a strong competitor to the traditional solar cells with a certified power conversion efficiency beyond 25% and other remarkable features such as light weight, solution processability, and low manufacturing cost. Further development on the efficiency and stability brings forth increasing attention in the component regulation, such as partial or entire substitution of A/B/X sites by alternative elements with similar size. However, the relationships between composition, property, and performance are poorly understood. Here, the instability of PSCs from the photon-, moisture-, thermal-, and mechanical-induced degradation was first summarized and discussed. In addition, the component regulation from the A/X sites is highlighted from the aspects of band level alignment, charge-carrier dynamics, ion migration, crystallization behavior, residual strain, stoichiometry, and dimensionality control. Finally, the perspectives and future outlooks are highlighted to guide the rational design and practical application of PSCs.

Length-based separation of Bacillus subtilis bacterial populations by viscoelastic microfluidics

In this study, we demonstrated the label-free continuous separation and enrichment of Bacillus subtilis populations based on length using viscoelastic microfluidics. B. subtilis, a gram-positive, rod-shaped bacterium, has been widely used as a model organism and an industrial workhorse. B. subtilis can be arranged in different morphological forms, such as single rods, chains, and clumps, which reflect differences in cell types, phases of growth, genetic variation, and changing environmental factors. The ability to prepare B. subtilis populations with a uniform length is important for basic biological studies and efficient industrial applications. Here, we systematically investigated how flow rate ratio, poly(ethylene oxide) (PEO) concentration, and channel length affected the length-based separation of B. subtilis cells. The lateral positions of B. subtilis cells with varying morphologies in a straight rectangular microchannel were found to be dependent on cell length under the co-flow of viscoelastic and Newtonian fluids. Finally, we evaluated the ability of the viscoelastic microfluidic device to separate the two groups of B. subtilis cells by length (i.e., 1-5 μm and >5 μm) in terms of extraction purity (EP), extraction yield (EY), and enrichment factor (EF) and confirmed that the device could separate heterogeneous populations of bacteria using elasto-inertial effects.

A magnetically enabled simulation of microgravity represses the auxin response during early seed germination on a microfluidic platform

For plants on Earth, the phytohormone auxin is essential for gravitropism-regulated seedling establishment and plant growth. However, little is known about auxin responses under microgravity conditions due to the lack of a tool that can provide an alteration of gravity. In this paper, a microfluidic negative magnetophoretic platform is developed to levitate Arabidopsis seeds in an equilibrium plane where the applied magnetic force compensates for gravitational acceleration. With the benefit of the microfluidic platform to simulate a microgravity environment on-chip, it is found that the auxin response is significantly repressed in levitated seeds. Simulated microgravity statistically interrupts auxin responses in embryos, even after chemical-mediated auxin alterations, illustrating that auxin is a critical factor that mediates the plant response to gravity alteration. Furthermore, pretreatment with an auxin transportation inhibitor (N-1-naphthylphthalamic acid) enables a decrease in the auxin response, which is no longer affected by simulated microgravity, demonstrating that polar auxin transportation plays a vital role in gravity-regulated auxin responses. The presented microfluidic platform provides simulated microgravity conditions in an easy-to-implement manner, helping to study and elucidate how plants correspond to diverse gravity conditions; in the future, this may be developed into a versatile tool for biological study on a variety of samples.

Educational trends post COVID-19 in engineering: Virtual laboratories

The rapid advance of Information and Communication Technology (ICT) in recent times and the current pandemic caused by COVID-19 have profoundly transformed society and the economy in most of the world. The education sector has benefited from this ICT-driven revolution, which has provided and expanded multiple new tools and teaching methods that did not exist just a few decades ago. In light of this technological change, virtual laboratories (VLs) based on the use of virtual reality (VR) have emerged, which are increasingly used to facilitate the teaching–learning process in a wide range of training activities, both academic and professional types. The set of advantages offered by this type of VL, the main of which are listed in this article, has made its use increasingly common as support for engineering classes at universities. This paper presents a study involving 420 engineering students from Spanish and Portuguese universities and associated analyses on the assessment of different parameters in various VLs designed by the authors. The results obtained indicate that, in general, VR-based VLs are widely accepted and demanded by students, who likewise consider real laboratories (RLs) necessary in face-to-face teaching. In the current post-COVID-19 educational scenario, VLs and RLs will coexist within the new hybrid models that combine face-to-face and online teaching and learning.

Fabrication and in vivo 2-photon microscopy validation of transparent PEDOT:PSS microelectrode arrays

Transparent microelectrode arrays enable simultaneous electrical recording and optical imaging of neuronal networks in the brain. Electrodes made of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) are transparent; however, device fabrication necessitates specific processes to avoid deterioration of the organic material. Here, we present an innovative fabrication scheme for a neural probe that consists of transparent PEDOT:PSS electrodes and demonstrate its compatibility with 2-photon microscopy. The electrodes show suitable impedance to record local field potentials from the cortex of mice and sufficient transparency to visualize GCaMP6f-expressing neurons underneath the PEDOT:PSS features. The results validate the performance of the neural probe, which paves the way to study the complex dynamics of in vivo neuronal activity with both a high spatial and temporal resolution to better understand the brain.

FRESH 3D Bioprinting a Ventricle-like Cardiac Construct Using Human Stem Cell-Derived Cardiomyocytes

Here we describe a method to engineer a contractile ventricle-like chamber composed of human stem cell-derived cardiomyocytes using freeform reversible embedding of suspended hydrogels (FRESH) 3D bioprinting. To do this, we print a support structure using a collagen type I ink and a cellular component using a high-density cell ink supplemented with fibrinogen. The gelation of the collagen and the fibrinogen into fibrin is initiated by pH change and enzymatic crosslinking, respectively. Fabrication of the ventricle-like chamber is completed in three distinct phases: (i) materials preparation, (ii) bioprinting, and (iii) tissue maturation. In this protocol, we describe the method to print the construct from a high-density cell ink composed of human stem cell-derived cardiomyocytes and primary fibroblasts (~300 × 10⁶ cells/mL) using our open-source dual-extruder bioprinter. Additional details are provided on FRESH support preparation, bioink preparation, dual-extruder needle alignment, print parameter selection, and post-processing. This protocol can also be adapted by altering the 3D model design, cell concentration, or cell type to FRESH 3D bioprint other cardiac tissue constructs.

Manipulation of single cells via a Stereo Acoustic Streaming Tunnel (SteAST)

At the single-cell level, cellular parameters, gene expression and cellular function are assayed on an individual but not population-average basis. Essential to observing and analyzing the heterogeneity and behavior of these cells/clusters is the ability to prepare and manipulate individuals. Here, we demonstrate a versatile microsystem, a stereo acoustic streaming tunnel, which is triggered by ultrahigh-frequency bulk acoustic waves and highly confined by a microchannel. We thoroughly analyze the generation and features of stereo acoustic streaming to develop a virtual tunnel for observation, pretreatment and analysis of cells for different single-cell applications. 3D reconstruction, dissociation of clusters, selective trapping/release, in situ analysis and pairing of single cells with barcode gel beads were demonstrated. To further verify the reliability and robustness of this technology in complex biosamples, the separation of circulating tumor cells from undiluted blood based on properties of both physics and immunity was achieved. With the rich selection of handling modes, the platform has the potential to be a full-process microsystem, from pretreatment to analysis, and used in numerous fields, such as in vitro diagnosis, high-throughput single-cell sequencing and drug development.

Agonist antibody discovery: Experimental, computational, and rational engineering approaches

Agonist antibodies that activate cellular signaling have emerged as promising therapeutics for treating myriad pathologies. Unfortunately, the discovery of rare antibodies with the desired agonist functions is a major bottleneck during drug development. Nevertheless, there has been important recent progress in discovering and optimizing agonist antibodies against a variety of therapeutic targets that are activated by diverse signaling mechanisms. Herein, we review emerging high-throughput experimental and computational methods for agonist antibody discovery as well as rational molecular engineering methods for optimizing their agonist activity.

Modeling and measuring glucose diffusion and consumption by colorectal cancer spheroids in hanging drops using integrated biosensors

As 3D in vitro tissue models become more pervasive, their built-in nutrient, metabolite, compound, and waste gradients increase biological relevance at the cost of analysis simplicity. Investigating these gradients and the resulting metabolic heterogeneity requires invasive and time-consuming methods. An alternative is using electrochemical biosensors and measuring concentrations around the tissue model to obtain size-dependent metabolism data. With our hanging-drop-integrated enzymatic glucose biosensors, we conducted current measurements within hanging-drop compartments hosting spheroids formed from the human colorectal carcinoma cell line HCT116. We developed a physics-based mathematical model of analyte consumption and transport, considering (1) diffusion and enzymatic conversion of glucose to form hydrogen peroxide (H₂O₂) by the glucose-oxidase-based hydrogel functionalization of our biosensors at the microscale; (2) H₂O₂ oxidation at the electrode surface, leading to amperometric H₂O₂ readout; (3) glucose diffusion and glucose consumption by cancer cells in a spherical tissue model at the microscale; (4) glucose and H₂O₂ transport in our hanging-drop compartments at the macroscale; and (5) solvent evaporation, leading to glucose and H₂O₂ upconcentration. Our model relates the measured currents to the glucose concentrations generating the currents. The low limit of detection of our biosensors (0.4 ± 0.1 μM), combined with our current-fitting method, enabled us to reveal glucose dynamics within our system. By measuring glucose dynamics in hanging-drop compartments populated by cancer spheroids of various sizes, we could infer glucose distributions within the spheroid, which will help translate in vitro 3D tissue model results to in vivo.

Pico-washing: simultaneous liquid addition and removal for continuous-flow washing of microdroplets

Droplet microfluidics is based on a toolbox of several established unit operations, including droplet generation, incubation, mixing, pico-injection, and sorting. In the last two decades, the development of droplet microfluidic systems, which incorporate these multiple unit operations into a workflow, has demonstrated unique capabilities in fields ranging from single-cell transcriptomic analyses to materials optimization. One unit operation that is sorely underdeveloped in droplet microfluidics is washing, exchange of the fluid in a droplet with a different fluid. Here, we demonstrate what we name the "pico-washer," a unit operation capable of simultaneously adding fluid to and removing fluid from droplets in flow while requiring only a small footprint on a microfluidic chip. We describe the fabrication strategy, device architecture, and process parameters required for stable operation of this technology, which is capable of operating with kHz droplet throughput. Furthermore, we provide an image processing workflow to characterize the washing process with microsecond and micrometer resolution. Finally, we demonstrate the potential for integrated droplet workflows by arranging two of these unit operations in series with a droplet generator, describe a design rule for stable operation of the pico-washer when integrated into a system, and validate this design rule experimentally. We anticipate that this technology will contribute to continued development of the droplet microfluidics toolbox and the realization of novel droplet-based, multistep biological and chemical assays.

Single-cell system using monolithic PMUTs-on-CMOS to monitor fluid hydrodynamic properties

In this work, a single cell capable of monitoring fluid density, viscosity, sound velocity, and compressibility with a compact and small design is presented. The fluid measurement system is formed by a two-port AlScN piezoelectric micromachined ultrasonic transducer (PMUT) with an 80 μm length monolithically fabricated with a 130 nm complementary metal-oxide semiconductor (CMOS) process. The electrode configuration allows the entire system to be implemented in a single device, where one electrode is used as an input and the other as an output. Experimental verification was carried out by exploiting the features of piezoelectric devices such as resonators and acoustic transducers, where a frequency shift and amplitude variation are expected because of a change in density and viscosity. A sensitivity of 482 ± 14 Hz/kg/m³ demonstrates the potential of the system compared to other dual-electrode PMUTs. In addition, according to the acoustic measurement, the sound velocity, fluid compressibility, and viscosity coefficient can be extracted, which, to the best of our knowledge, is novel in these PMUT systems.

Low-power-consumption CMOS inverter array based on CVD-grown p-MoTe2 and n-MoS2

Two-dimensional (2D) semi-conductive transition metal dichalcogenides (TMDCs) have shown advantages for logic application. Complementary metal-oxide-semiconductor (CMOS) inverter is an important component in integrated circuits in view of low power consumption. So far, the performance of the reported TMDCs-based CMOS inverters is not satisfactory. Besides, most of the inverters were made of mechanically exfoliated materials, which hinders their reproducible production and large-scale integration in practical application. In this study, we demonstrate a practical approach to fabricate CMOS inverter arrays using large-area p-MoTe₂ and n-MoS₂, which are grown via chemical vapor deposition method. The current characteristics of the channel materials are balanced by atomic layer depositing Al₂O₃. Complete logic swing and clear dynamic switching behavior are observed in the inverters. Especially, ultra-low power consumption of ∼0.37 nW is achieved. Our work paves the way for the application of 2D TMDCs materials in large-scale low-power-consumption logic circuits.

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A practical approach to fabricate large-scale CMOS inverter arrays is demonstrated

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A method to balance the current characteristics of the channel materials is developed

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Complete logic swing and clear dynamic switching behavior are observed

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Ultra-low power consumption of ∼0.37 nW is achieved