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Rapid, simple, inexpensive, accurate, and sensitive point-of-care (POC) detection of viral pathogens in bodily fluids is a vital component of controlling the spread of infectious diseases. The predominant laboratory-based methods for sample processing and nucleic acid detection face limitations that prevent them from gaining wide adoption for POC applications in low-resource settings and self-testing scenarios. Here, we report the design and characterization of an integrated system for rapid sample-to-answer detection of a viral pathogen in a droplet of whole blood comprised of a 2-stage microfluidic cartridge for sample processing and nucleic acid amplification, and a clip-on detection instrument that interfaces with the image sensor of a smartphone. The cartridge is designed to release viral RNA from Zika virus in whole blood using chemical lysis, followed by mixing with the assay buffer for performing reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP) reactions in six parallel microfluidic compartments. The battery-powered handheld detection instrument uniformly heats the compartments from below, and an array of LEDs illuminates from above, while the generation of fluorescent reporters in the compartments is kinetically monitored by collecting a series of smartphone images. We characterize the assay time and detection limits for detecting Zika RNA and gamma ray-deactivated Zika virus spiked into buffer and whole blood and compare the performance of the same assay when conducted in conventional PCR tubes. Our approach for kinetic monitoring of the fluorescence-generating process in the microfluidic compartments enables spatial analysis of early fluorescent "bloom" events for positive samples, in an approach called "Spatial LAMP" (S-LAMP). We show that S-LAMP image analysis reduces the time required to designate an assay as a positive test, compared to conventional analysis of the average fluorescent intensity of the entire compartment. S-LAMP enables the RT-LAMP process to be as short as 22 minutes, resulting in a total sample-to-answer time in the range of 17-32 minutes to distinguish positive from negative samples, while demonstrating a viral RNA detection as low as 2.70 × 10

Thermal sensations contribute to our ability to perceive and explore the physical world. Reproducing these sensations in a spatiotemporally programmable manner through wireless computer control could enhance virtual experiences beyond those supported by video, audio and, increasingly, haptic inputs. Flexible, lightweight and thin devices that deliver patterns of thermal stimulation across large areas of the skin at any location of the body are of great interest in this context. Applications range from those in gaming and remote socioemotional communications, to medical therapies and physical rehabilitation. Here, we present a set of ideas that form the foundations of a skin-integrated technology for power-efficient generation of thermal sensations across the skin, with real-time, closed-loop control. The systems exploit passive cooling mechanisms, actively switchable thermal barrier interfaces, thin resistive heaters and flexible electronics configured in a pixelated layout with wireless interfaces to portable devices, the internet and cloud data infrastructure. Systematic experimental studies and simulation results explore the essential mechanisms and guide the selection of optimized choices in design. Demonstration examples with human subjects feature active thermoregulation, virtual social interactions, and sensory expansion.

Summary This work presents the design, fabrication, and characterization of a three-dimensional heat exchanger (HX) having a tube-in-tube architecture using a genetic algorithm design and metal additive manufacturing (AM). The genetic algorithm aids the design of optimal fin geometries that minimize total thermal resistance between hot fluid and cold fluid. The genetic algorithm is coupled to a two-dimensional finite element method simulation to calculate conduction and convection in the device. Through careful thermal-hydraulic experiments, we demonstrate that our HX was able to achieve a power density of 26.6 W/cm3 and specific power of 15.7 kW/kg. The specific power of our additively manufactured device is 20X higher than that of a commercially available tube-in-tube HX with no fins. The optimized device also performs well compared with shell-and-tube and brazed plate heat exchangers that are designed for significantly higher heat transfer.

Biomedical diagnostics based on microfluidic devices have the potential to significantly benefit human health; however, the manufacturing of microfluidic devices is a key limitation to their widespread adoption. Outbreaks of infectious disease continue to demonstrate the need for simple, sensitive, and translatable tests for point-of-care use. Additive manufacturing (AM) is an attractive alternative to conventional approaches for microfluidic device manufacturing based on injection molding; however, there is a need for development and validation of new AM process capabilities and materials that are compatible with microfluidic diagnostics. In this paper, we demonstrate the development and characterization of AM cartridges using continuous liquid interface production (CLIP) and investigate process characteristics and capabilities of the AM microfluidic device manufacturing. We find that CLIP accurately produces microfluidic channels as small as 400 μm and that it is possible to routinely produce fluid channels as small as 100 μm with high repeatability. We also developed a loop-mediated isothermal amplification (LAMP) assay for detection of E. coli from whole blood directly on the CLIP-based AM microfluidic cartridges, with a 50 cfu/μL limit of detection, validating the use of CLIP processes and materials for pathogen detection. The portable diagnostic platform presented in this paper could be used to investigate and validate other AM processes for microfluidic diagnostics and could be an important component of scaling up the diagnostics for current and future infectious diseases and pandemics.

The National Institute for Occupational Safety and Health's methods and requirements for air-purifying respirator breathing resistance in 42 CFR Part 84 do not include work of breathing. The International Organization for Standardization Technical Committee 94, Subcommittee 15 utilized work of breathing to evaluate airflow resistance for all classes of respiratory protective devices as part of their development of performance standards regarding respiratory protective devices. The objectives of this study were: (1) to evaluate the relationship between the International Organization for Standardization's work of breathing measurements and the National Institute for Occupational Safety and Health's breathing resistance test results; (2) to provide scientific bases for standard development organizations to decide if work of breathing should be adopted; and (3) to establish regression equations for manufacturers and test laboratories to estimate work of breathing measurements using breathing resistance data. A total of 43 respirators were tested for work of breathing at minute ventilation rates of 10, 35, 65, 105, and 135 liters per minute. Breathing resistance obtained at a constant flow rate of 85 liters per minute per National Institute of Occupational Safety and Health protocol was correlated to each of the parameters (total work of breathing, inhalation, and exhalation) obtained from the work of breathing tests. The ratio of work of breathing exhalation to work of breathing inhalation for all air-purifying respirators is similar to the ratio of exhalation to inhalation resistance when tested individually. The ratios were about 0.8 for filtering facepiece respirators, 0.5 for half-masks, and 0.25 for full-facepiece respirators. The National Institute for Occupational Safety and Health's breathing resistance is close to work of breathing's minute ventilation of 35 liters per minute, which represents the common walking/working pace in most workplaces. The work of breathing and the National Institute of Occupational Safety and Health's breathing resistance were found to be strongly and positively correlated (r values of 0.7-0.9) at each work rate for inhalation and exhalation. In addition, linear and multiple regression models (R-squared values of 0.5-0.8) were also established to estimate work of breathing using breathing resistance. Work of breathing was correlated higher to breathing resistance for full-facepiece and half-mask elastomeric respirators than filtering facepiece respirators for inhalation. For exhalation, filtering facepiece respirators were correlated much better than full-facepiece and half-mask elastomeric respirators. Therefore, the National Institute for Occupational Safety and Health's breathing resistance may reasonably be used to predict work of breathing for air-purifying respirators. The results could also be used by manufacturers for product development and evaluation.

Litz wire has been widely used in high-frequency electrical machines and transformers to minimize induced current loss and maintain high efficiency. Its heat dissipation capability can be a key design factor for high-power-density, high-frequency electrical machines. Although litz wire equivalent thermal conductivity has been studied, its transposition arrangement on heat dissipation enhancement is usually neglected. This article focuses on developing an analytical model to predict litz wire equivalent thermal conductivity including transposition effects. 3-D finite element models and hardware experiments are used to validate the proposed analytical model. Fast and accurate litz wire thermal conductivity prediction values can be obtained. The transposed and parallel arrangement effects on litz wire equivalent thermal conductivity are compared and discussed. This study shows that the transposition arrangement could improve litz wire heat dissipation capability by 10% to 30%, demonstrating that electrical machine power density can be potentially increased by up to 14%. The proposed method can advance winding design to push the boundaries of electrical machine power density.

Two-dimensional (2D) materials and heterostructures are promising candidates for nanoelectronics. However, the quality of material interfaces often limits the performance of electronic devices made from atomically thick 2D materials and heterostructures. Atomic force microscopy (AFM) tip-based cleaning is a reliable technique to remove interface contaminants and flatten heterostructures. Here, we demonstrate AFM tip-based cleaning applied to hBN-encapsulated monolayer MoS2 transistors, which results in electrical performance improvements of the devices. To investigate the impact of cleaning on device performance, we compared the characteristics of as-transferred heterostructures and transistors before and after tip-based cleaning using photoluminescence (PL) and electronic measurements. The PL linewidth of monolayer MoS2 decreased from 84 meV before cleaning to 71 meV after cleaning. The extrinsic mobility of monolayer MoS2 field-effect transistors increased from 21 cm2/Vs before cleaning to 38 cm2/Vs after cleaning. Using the results from AFM topography, photoluminescence, and back-gated field-effect measurements, we infer that tip-based cleaning enhances the mobility of hBN-encapsulated monolayer MoS2 by reducing interface disorder. Finally, we fabricate a MoS2 field-effect transistor (FET) from a tip-cleaned heterostructure and achieved a device mobility of 73 cm2/Vs. The results of this work could be used to improve the electrical performance of heterostructure devices and other types of mechanically assembled van der Waals heterostructures.

This article reports the design, fabrication, and demonstration of additively manufactured air jet impingement coolers for the thermal management of high-power gallium nitride (GaN) transistors. The polymer jet coolers impinge high-speed airflow with a velocity of 42–195 m/s (Reynolds number between $1.87 \times 10^{4}$ and $8.77 \times 10^{4})$ onto working GaN devices mounted on a printed circuit board (PCB). The air jet provides cooling heat fluxes of up to 58.4 W/cm2, cooling rates of up to 6.6 °C/s, and convective heat transfer coefficient ranging from 5.2 to 17.0 kW/( $\text{m}^{2}\cdot \text{K}$ ). The cooling performance is comparable to that of jet coolers made from other materials and manufacturing technologies. A key benefit of additive manufacturing (AM) is design freedom and geometric complexity, which we highlight by demonstrating three different packaging configurations, each enabled by a different jet cooler design that is customized for different types of packaging configurations: Cooler 1 directs two parallel impinging jets onto the top side of two devices; cooler 2 directs two air jets onto the front side and two air jets onto the back side of two devices; and cooler 3 directs air jets onto the front side of four devices mounted on parallel adjacent circuit boards. The second benefit of AM is the ability to consolidate multiple components into a single part, which we highlight by combining a nozzle, a fluidic delivery system, and a flow distributor within a volume of 80 mm $\times80$ mm $\times100$ mm. This work demonstrates the potential of AM to create complex, lightweight, fluidic delivery systems to achieve thermally and hydrodynamically optimized air jet cooling for high-power-density electronic devices.

The recent growth in electronics power density has created a significant need for effective thermal management solutions. Liquid-cooled heat sinks or cold plates are typically used to achieve high volumetric power density cooling. A natural tradeoff exists between the thermal and hydraulic performance of a cold plate, creating an opportunity for design optimization. Current design optimization methods rely on computationally expensive and time consuming computational fluid dynamics (CFD) simulations. Here, we develop a rapid design optimization tool for liquid cooled heat sinks based on reduced-order models for the thermal-hydraulic behavior. Flow layout is expressed as a combination of simple building blocks on a divided coarse grid. The flow layout and geometrical parameters are incorporated to optimize designs that can effectively address heterogeneous cooling requirements within electronics packages. We demonstrate that the use of population-based searches for optimal layout selection, while not ensuring a global optimum solution, can provide optimal or near-optimal results for most of the test cases studied. The approach is shown to generate optimal designs within a timescale of 60–120 s. A case study based on cooling of a commercial silicon carbide (SiC) electronics power module is used to demonstrate the application of the developed tool and is shown to improve the performance as compared to an aggressive state-of-the-art single-phase liquid cooling solution by reducing the SiC junction-to-coolant thermal resistance by 25% for the same pressure drop.

Summary: Phase change materials (PCMs) having a large latent heat during solid-liquid phase transition are promising for thermal energy storage applications. However, the relatively low thermal conductivity of the majority of promising PCMs (

The COVID-19 pandemic revealed fundamental limitations in the current model for infectious disease diagnosis and serology, based upon complex assay workflows, laboratory-based instrumentation, and expensive materials for managing samples and reagents. The lengthy time delays required to obtain test results, the high cost of gold-standard PCR tests, and poor sensitivity of rapid point-of-care tests contributed directly to society's inability to efficiently identify COVID-19-positive individuals for quarantine, which in turn continues to impact return to normal activities throughout the economy. Over the past year, enormous resources have been invested to develop more effective rapid tests and laboratory tests with greater throughput, yet the vast majority of engineering and chemistry approaches are merely incremental improvements to existing methods for nucleic acid amplification, lateral flow test strips, and enzymatic amplification assays for protein-based biomarkers. Meanwhile, widespread commercial availability of new test kits continues to be hampered by the cost and time required to develop single-use disposable microfluidic plastic cartridges manufactured by injection molding. Through development of novel technologies for sensitive, selective, rapid, and robust viral detection and more efficient approaches for scalable manufacturing of microfluidic devices, we can be much better prepared for future management of infectious pathogen outbreaks. Here, we describe how photonic metamaterials, graphene nanomaterials, designer DNA nanostructures, and polymers amenable to scalable additive manufacturing are being applied towards overcoming the fundamental limitations of currently dominant COVID-19 diagnostic approaches. In this paper, we review how several distinct classes of nanomaterials and nanochemistry enable simple assay workflows, high sensitivity, inexpensive instrumentation, point-of-care sample-to-answer virus diagnosis, and rapidly scaled manufacturing.

Heat dissipation is a key obstacle to achieving reliable, high-power-density electronic systems. Thermal devices capable of actively managing heat transfer are desired to enable heat dissipation optimization and enhanced reliability through device isothermalization. Here, we develop a millimeter-scale liquid metal droplet thermal switch capable of controlling heat transfer spatially and temporally. We demonstrate the thermal switch by integrating it with gallium nitride (GaN) devices mounted on a printed circuit board (PCB) and measure heat transfer and temperature of each device for a variety of switch positions and heat dissipation levels. When integrated with a single GaN device (2.6 mm $\times4.6$ mm face area) dissipating 1.8 W, the thermal switch shows the ability to actively control heat transfer by conducting 1.3 W in the ON mode with the GaN device at 51 °C ± 1 °C, and 0.5 W in the OFF mode with the GaN device at 95 °C ± 1 °C. To elucidate the heat transfer physics, we developed a 1-D system thermal resistance model in conjunction with an independent 3-D finite-element method (FEM) simulation, showing excellent agreement with our experimental data. Finally, we demonstrated that when the switch is integrated with two GaN devices, the switch can balance the device heat transfer rate and enhance junction temperature uniformity and system reliability by lowering the device-to-device temperature difference from > 10 °C (no switch) to 0 °C.

Additive manufacturing (AM) enables the fabrication of complex lattice structures, for which a single part may have hundreds or thousands of individual geometric features. Conventional methods for measuring part geometry and performing quality control, which typically use a small number of low-dimensional measurements, are not well suited for lattice structures. This paper describes a method for scanning and automatically extracting individual features of the lattice and applies this method to characterize AM lattice structures in both two-dimensional and three-dimensional lattices. The research measured 94 lattice parts fabricated from 3 materials in 9 different designs using either a high-resolution document scanner or X-ray computed tomography (CT). A statistical analysis considered manufacturing variances as a function of material type and part design on a subset of the data, comprising the size and location of over 15,000 individual features. We studied the geometric variations of these struts in uniform, hierarchical and gradated parts. For a single design and material, the standard deviation of lattice feature size is quite small. For example, a lattice strut with thickness 0.5 mm has a standard deviation of 30 μm. However, when the same process is used to manufacture multiple parts having different designs and from different materials, the standard deviation of feature size can be larger by 2X or more. This type of automated measurement and analysis may allow for rigorous monitoring, qualification and control of AM lattice parts in production.

This paper investigates heat transfer enhancement by means of additively manufactured static mixers during liquid water cooling of a horizontal, heated flat plate. The static mixers disrupt the thermal boundary layer and induce mixing, resulting in an increased heat transfer rate of about 2X larger than flows without mixers. Simulations of the flows provided insights into the flows near the mixers, and guided selection of specific mixer geometries. The mixers were fabricated directly into the flow channels using additive manufacturing and then assembled onto the heated plate. Two types of mixing structures were analyzed: twisted tape structures that are similar to conventional static mixers; and novel chevron-shaped offset wing structures. Heat transfer performance was measured for liquid water (510 ≤ Re ≤ 1366) cooling the heated section with convective heat flux ranging between 0.1 and 0.8 W/cm2. This work demonstrates the potential of additive manufacturing to enable novel flow geometries that can enhance convection heat transfer whilst minimizing pressure drop penalties and volumes.

Monolayer MoS2 is a promising material for nanoelectronics; however, the lack of nanofabrication tools and processes has made it very challenging to realize nanometer-scale electronic devices from monolayer MoS2. Here, we demonstrate the fabrication of monolayer MoS2 nanoribbon field-effect transistors as narrow as 30 nm using scanning probe lithography (SPL). The SPL process uses a heated nanometer-scale tip to deposit narrow nanoribbon polymer structures onto monolayer MoS2. The polymer serves as an etch mask during a XeF2 vapor etch, which defines the channel of a field-effect transistor (FET). We fabricated seven devices with a channel width ranging from 30 to 370 nm, and the fabrication process was carefully studied by electronic measurements made at each process step. The nanoribbon devices have a current on/off ratio > 104 and an extrinsic field-effect mobility up to 8.53 cm2/(V s). By comparing a 30 nm wide device with a 60 nm wide device that was fabricated on the same MoS2 flake, we found the na...

This paper reports two-phase cooling in compact cross-flow microchannel heat exchangers with high power density up to 180 W/cm3. The performance is enabled by high-speed air flow through microchannels and two-phase condensation of refrigerant R245fa. The heat exchangers were realized in 1 cm3 blocks of copper alloy, using micro-electrical-discharging machining. Two heat exchanger designs were analyzed, fabricated, and tested. The first device has 150 air-side channels of diameter 520 μm, and the second device has 300 air-side channels of diameter 355 μm. In both cases the refrigerant channels are 2.0 × 0.5 mm2. The heat exchangers were operated with Reynolds number between 7500 and 20,500 for the air flow and with mass flux between 330 and 750 kg/m2 s for the refrigerant flow. The refrigerant temperature at the channel entrance was 80 °C, which is near the maximum operating temperature for some electronic devices. For comparison purposes, the devices were also tested with single-phase refrigerant flows. This work demonstrates the potential of high power density heat exchangers that leverage advanced manufacturing technologies to fabricate miniature channels.

This paper describes a nickel-based cellular material, which has the strength of titanium and the density of water. The material’s strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X. The mechanical properties of this material can be controlled by varying the nanometer-scale geometry, with strength varying over the range 90–880 MPa, modulus varying over the range 14–116 GPa, and density varying over the range 880–14500 kg/m3. We refer to this material as a “metallic wood,” because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.

Osteoarthritis (OA) is a progressive degenerative disease that manifests as pain and inflammation and often results in total joint replacement. There is significant interest in understanding how intra-articular injections made from autologous blood or bone marrow could alleviate symptoms and potentially intervene in the progression of the disease. There is in vitro an in vivo evidence that suggests that these therapies, including platelet-rich plasma (PRP), autologous anti-inflammatories (AAIs), and concentrated bone marrow aspirate (cBMA), can interrupt cartilage matrix degradation driven by pro-inflammatory cytokines. This review analyzes the evidence for and against inclusion of white blood cells, the potential role of platelets, and the less studied potential role of blood plasma when combining these components to create an autologous point-of-care therapy to treat OA. There has been significant focus on the differences between the various autologous therapies. However, evidence suggests that there may be more in common between groups and perhaps we should be thinking of these therapies on a spectrum of the same technology, each providing significant levels of anti-inflammatory cytokines that can be antagonists against the inflammatory cytokines driving OA symptoms and progression. While clinical data have demonstrated symptom alleviation, more studies will need to be conducted to determine whether these preclinical disease-modifying findings translate into clinical practice.

Significance An important limitation of current assays for the detection of SARS-CoV-2 stems from their reliance on time-consuming, labor-intensive, and laboratory-based protocols for viral isolation, lysis, and removal of inhibiting materials. While RT-PCR remains the gold standard for performing clinical diagnostics to amplify the RNA sequences, there is an urgent need for alternative testing platforms that are rapid, accurate, simple, and portable. Here, we demonstrate isothermal RT-LAMP nucleic acid-based detection of SARS-CoV-2 with an additively manufactured cartridge and a smartphone-based instrument for testing that can be performed at the point of sample collection., The COVID-19 pandemic provides an urgent example where a gap exists between availability of state-of-the-art diagnostics and current needs. As assay protocols and primer sequences become widely known, many laboratories perform diagnostic tests using methods such as RT-PCR or reverse transcription loop mediated isothermal amplification (RT-LAMP). Here, we report an RT-LAMP isothermal assay for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus and demonstrate the assay on clinical samples using a simple and accessible point-of-care (POC) instrument. We characterized the assay by dipping swabs into synthetic nasal fluid spiked with the virus, moving the swab to viral transport medium (VTM), and sampling a volume of the VTM to perform the RT-LAMP assay without an RNA extraction kit. The assay has a limit of detection (LOD) of 50 RNA copies per μL in the VTM solution within 30 min. We further demonstrate our assay by detecting SARS-CoV-2 viruses from 20 clinical samples. Finally, we demonstrate a portable and real-time POC device to detect SARS-CoV-2 from VTM samples using an additively manufactured three-dimensional cartridge and a smartphone-based reader. The POC system was tested using 10 clinical samples, and was able to detect SARS-CoV-2 from these clinical samples by distinguishing positive samples from negative samples after 30 min. The POC tests are in complete agreement with RT-PCR controls. This work demonstrates an alternative pathway for SARS-CoV-2 diagnostics that does not require conventional laboratory infrastructure, in settings where diagnosis is required at the point of sample collection.

Understanding the atomistic origin of defects in two-dimensional transition metal dichalcogenides, their impact on the electronic properties, and how to control them is critical for future electronics and optoelectronics. Here, we demonstrate the integration of thermochemical scanning probe lithography (tc-SPL) with a flow-through reactive gas cell to achieve nanoscale control of defects in monolayer MoS2. The tc-SPL produced defects can present either p- or n-type doping on demand, depending on the used gasses, allowing the realization of field effect transistors, and p-n junctions with precise sub-μm spatial control, and a rectification ratio of over 104. Doping and defects formation are elucidated by means of X-Ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory. We find that p-type doping in HCl/H2O atmosphere is related to the rearrangement of sulfur atoms, and the formation of protruding covalent S-S bonds on the surface. Alternatively, local heating MoS2 in N2 produces n-character.

Background Teen driving educational events are an effective strategy to increase adolescent drivers’ awareness of safe driving practices. The objectives of this study were to evaluate changing rates of self-reported driving practices and knowledge of the state Graduated Driver Licensing laws (GDL) by teens over a nine-year period in a single state. Methods This was a prospective observational study of high school students ages 14 to 19 years old. Paper surveys were sent to the high schools participating in teen driving educational events (9 schools in 2009 and 4 schools in 2018). Students in those schools completed surveys prior to the events. Students completing the anonymous survey were invited to the event. Questions evaluated awareness of state GDL and safe and risky driving behaviors. Statistical comparisons of survey answers from 2009 to 2018 were analyzed using the z test of proportions (2 tailed, alpha 0.05). Results A total of 397 students participated in 2018 with ages ranging from 14 to 19 years. Racial distribution was 81% white, 14% black, and there were 57% female participants. Only 69% (n = 273) reported “always” wearing their seatbelt. When asked about high risk behaviors, 78% (n = 309) of adolescents reported they personally “never” text while driving; 97% (385); never drive after drinking, and 87% (n = 344) never ride with someone who has been drinking. Compared to 2009 participants (1304 students, 9 schools from central part of state), the students in 2018 (4 schools scattered across state) reported wearing seatbelts “always” (n = 69% vs 39%; p p Conclusion Results are encouraging that participants in 2018 report more use of seatbelts, less texting while driving, less drinking while driving and lower numbers of being in MVC than in 2009. However, rates of high-risk driving behaviors are still concerning.

The COVID-19 pandemic disrupted the world in 2020 by spreading at unprecedented rates and causing tens of thousands of fatalities within a few months. The number of deaths dramatically increased in regions where the number of patients in need of hospital care exceeded the availability of care. Many COVID-19 patients experience Acute Respiratory Distress Syndrome (ARDS), a condition that can be treated with mechanical ventilation. In response to the need for mechanical ventilators, designed and tested an emergency ventilator (EV) that can control a patient’s peak inspiratory pressure (PIP) and breathing rate, while keeping a positive end expiratory pressure (PEEP). This article describes the rapid design, prototyping, and testing of the EV. The development process was enabled by rapid design iterations using additive manufacturing (AM). In the initial design phase, iterations between design, AM, and testing enabled a working prototype within one week. The designs of the 16 different components of the ventilator were locked by additively manufacturing and testing a total of 283 parts having parametrically varied dimensions. In the second stage, AM was used to produce 75 functional prototypes to support engineering evaluation and animal testing. The devices were tested over more than two million cycles. We also developed an electronic monitoring system and with automatic alarm to provide for safe operation, along with training materials and user guides. The final designs are available online under a free license. The designs have been transferred to more than 70 organizations in 15 countries. This project demonstrates the potential for ultra-fast product design, engineering, and testing of medical devices needed for COVID-19 emergency response.

A scalable technique for making octet microlattice topology mechanical metamaterials with a cell size of 1 mm or less from thin stainless steel sheets is described. The microfabrication process used a perforation operation to form planar truss sheets by the periodic removal of rectangular shaped material. A simultaneous perforation and corrugation operation was also used to create a single layer of trusses with a pyramidal topology. A 3D lattice was then assembled by alternatively stacking the pyramidal and planar truss sheets, taking care to align their nodes to form the octet lattice truss topology. A vacuum brazing method was used to metallurgically bond the assembly. The compressive properties of the microlattices are shown to be comparable to those of much larger cell-size structures of similar material and topology. An assessment of geometric imperfection sensitivity indicates where further mechanical property improvements could be realized by improving the precision of both the perforation and assembly process. Keywords: Octet lattice, Microfabrication, Mechanical metamaterials, Mechanical properties

Thermoelectric energy conversion offers a unique solution for generating electricity from waste heat. However, despite recent improvements in the efficiency of thermoelectric materials, the widespread application of thermoelectric generators has been hampered by challenges in fabricating thermoelectric materials with appropriate dimensions to perfectly fit heat sources. Herein, we report an extrusion-based three-dimensional printing method to produce thermoelectric materials with geometries suitable for heat sources. All-inorganic viscoelastic inks were synthesized using Sb2Te3 chalcogenidometallate ions as inorganic binders for Bi2Te3-based particles. Three-dimensional printed materials with various geometries showed homogenous thermoelectric properties, and their dimensionless figure-of-merit values of 0.9 (p-type) and 0.6 (n-type) were comparable to the bulk values. Conformal cylindrical thermoelectric generators made of 3D-printed half rings mounted on an alumina pipe were studied both experimentally and computationally. Simulations show that the power output of the conformal, shape-optimized generator is higher than that of conventional planar generators. Three-dimensional printing is changing the way we manufacture objects. Here, Kim et al. develop inks of inorganic thermoelectric materials to 3D print the legs of conformable thermoelectric generators, allowing waste heat recovery from hot water pipes.

This paper reports heat transfer enhancement of forced internal single-phase flow enabled by additively manufactured internally finned channels. We consider internal liquid coolant flow through a tube with constant heat flux applied to the exterior surface. A genetic algorithm was developed and used to optimize the fin geometry in order to minimize total thermal resistance for laminar flow or convection thermal resistance for turbulent flow. The genetic algorithm sampled more than 500 fin geometries, evaluated thermal resistance, and selected the optimum fin geometry. We selected three designs for experimental testing: a complex fin structure suggested by the genetic algorithm; a straight fin design; and a smooth circular channel as a reference. The devices were made from aluminum silica (AlSi10Mg) using direct metal laser sintering additive manufacturing. The devices were tested using a water ethylene glycol mixture (80:20) over the hydraulic diameter based Reynolds number range of 400 – 18,000, covering both laminar and turbulent flow regimes. Finite element simulations of heat transfer and pressure drop helped to understand and interpret the measurements. Compared to the smooth pipe reference design, the total thermal resistance of the genetically optimized fin design was 77% lower for laminar flow at Reh = 2,000 and 65% lower for turbulent flow at Reh = 10,000. Compared to the straight fin design that is commonly used for enhancing convection heat transfer in internal flows, the total thermal resistance of the genetically optimized fin design was 55% lower for laminar flow at Reh = 2,000 and 29% lower for turbulent flow at Reh = 10,000. We explore the potential design space for different types of heat exchangers by investigating how total heat transfer varies with exterior heat transfer coefficient and channel wall thermal conductivity. This research shows how shape optimization and additive manufacturing can result in devices with improved internal convection heat transfer.

Osteoarthritis (OA) is a progressive and degenerative disease, which may result in significant pain and decreased quality of life. Recent updates in our understanding of OA have demonstrated that it is a whole joint disease that has many similarities to an unhealed wound containing inflammatory cytokines. The nSTRIDE Autologous Protein Solution (APS) Kit is a medical device under development for the treatment of OA. The APS Kit processes a patient's own blood at the point of care to contain high concentrations of anti-inflammatory cytokines and anabolic growth factors. This study assessed the safety and treatment effects of a single intra-articular injection of APS. Eleven patients were enrolled in this study. Sufficient blood could not be drawn from one patient who was subsequently withdrawn, leaving 10 patients treated. Minor adverse events (AEs) were experienced by seven subjects (63.6%). There was one serious AE (diverticulitis) unrelated to the device or procedure. One subject experienced AEs that were judged “likely” to be procedure related (arthralgia/musculoskeletal discomfort) and all resolved within 6 days of injection. All other AEs were unrelated to the device or procedure. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain scores improved significantly over time (ANOVA, p

Condensation is a ubiquitous phenomenon in nature and industry. Heat transfer rates during dropwise condensation on non-wetting substrates can be 6-8X higher than heat transfer rates during traditional filmwise condensation on wetting substrates. Dropwise condensation on lubricant-infused surfaces (LIS, or SLIPS) is particularly interesting due to high droplet mobility on these surfaces. To accurately predict heat transfer rates during dropwise condensation, the distribution of droplet sizes must be known. Here we present condensation studies of water on aluminum-based lubricant-infused surfaces with a wide range of lubricant viscosities (12–2717 cSt) to determine droplet size distributions. Through optical imaging and microscopy, we show that the distribution of droplet sizes on LIS is independent of lubricant viscosity, and agrees well with the model developed by Rose for the distribution of droplet sizes on hydrophobic surfaces, especially in the range 10 100 µm due to a high conduction resistance within these droplets. Our work provides an experimental and analytical framework to predict heat transfer and sweeping rates for water condensation on a vertical plate coated with a LIS or SLIPS surface.