Nano-injection molding with resin mold inserts for prototyping of nanofluidic devices for single molecular detection.

While injection molding is becoming the fabrication modality of choice for high-scale production of microfluidic devices, especially those used for in vitro diagnostics, its translation into the growing area of nanofluidics (structures with at least one dimension <100 nm) has not been well established. Another prevailing issue with injection molding is the high startup costs and the relatively long time between device iterations making it in many cases impractical for device prototyping. We report, for the first time, functional nanofluidic devices with dimensions of critical structures below 30 nm fabricated by injection molding for the manipulation, identification, and detection of single molecules. UV-resin molds replicated from Si masters served as mold inserts, negating the need for generating Ni-mold inserts via electroplating. Using assembled devices with a cover plate via hybrid thermal fusion bonding, we demonstrated two functional thermoplastic nanofluidic devices. The first device consisted of dual in-plane nanopores placed at either end of a nanochannel and was used to detect and identify single ribonucleotide monophosphate molecules via resistive pulse sensing and obtain the effective mobility of the molecule through nanoscale electrophoresis to allow its identification. The second device demonstrated selective binding of a single RNA molecule to a solid phase bioreactor decorated with a processive exoribonuclease, XRN1. Our results provide a simple path towards the use of injection molding for device prototyping in the development stage of any nanofluidic or even microfluidic application, through which rapid scale-up is made possible by transitioning from prototyping to high throughput production using conventional Ni mold inserts.

Nanofluidic devices for the separation of biomolecules.

Over the last 30-years, microchip electrophoresis and its applications have expanded due to the benefits it offers. Nanochip electrophoresis, on the other hand, is viewed as an evolving area of electrophoresis because it offers some unique advantages not associated with microchip electrophoresis. These advantages arise from unique phenomena that occur in the nanometer domain not readily apparent in the microscale domain due to scale-dependent effects. Scale-dependent effects associated with nanochip electrophoresis includes high surface area-to-volume ratio, electrical double layer overlap generating parabolic flow even for electrokinetic pumping, concentration polarization, transverse electromigration, surface charge dominating flow, and surface roughness. Nanochip electrophoresis devices consist of channels with dimensions ranging from 1 to 1000 nm including classical (1-100 nm) and extended (100 nm - 1000 nm) nanoscale devices. In this review, we highlight scale-dependent phenomena associated with nanochip electrophoresis and the utilization of those phenomena to provide unique biomolecular separations that are not possible with microchip electrophoresis. We will also review the range of materials used for nanoscale separations and the implication of material choice for the top-down fabrication and operation of these devices. We will also provide application examples of nanochip electrophoresis for biomolecule separations with an emphasis on nano-electrophoresis (nEP) and nano-electrochromatography (nEC).

Air bubble removal: Wettability contrast enabled microfluidic interconnects.

The presence of air bubbles boosts the shear resistance and causes pressure fluctuation within fluid-perfused microchannels, resulting in possible cell damage and even malfunction of microfluidic devices. Eliminating air bubbles is especially challenging in microscale where the adhesive surface tension force is often dominant over other forces. Here, we present an air bubble removal strategy from a novel surface engineering perspective. A microfluidic port-to-port interconnect was fabricated by modifying the peripheral of the microfluidic ports superhydrophobic, while maintaining the inner polymer microchannels hydrophilic. Such a sharp wettability contrast enabled a preferential fluidic entrance into the easy-wetting microchannels over the non-wetting boundaries of the microfluidic ports, while simultaneously filtering out any incoming air bubbles owing to the existence of port-to-port gaps. This bubble-eliminating capability was consistently demonstrated at varying flow rates and liquid analytes. Compared to equipment-intensive techniques and porous membrane-venting strategies, our wettability contrast-governed strategy provides a simple yet effective route for eliminating air bubbles and simultaneously sealing microfluidic interconnects.

Leakage pressures for gasketless superhydrophobic fluid interconnects for modular lab-on-a-chip systems.

Chip-to-chip and world-to-chip fluidic interconnections are paramount to enable the passage of liquids between component chips and to/from microfluidic systems. Unfortunately, most interconnect designs add additional physical constraints to chips with each additional interconnect leading to over-constrained microfluidic systems. The competing constraints provided by multiple interconnects induce strain in the chips, creating indeterminate dead volumes and misalignment between chips that comprise the microfluidic system. A novel, gasketless superhydrophobic fluidic interconnect (GSFI) that uses capillary forces to form a liquid bridge suspended between concentric through-holes and acting as a fluid passage was investigated. The GSFI decouples the alignment between component chips from the interconnect function and the attachment of the meniscus of the liquid bridge to the edges of the holes produces negligible dead volume. This passive seal was created by patterning parallel superhydrophobic surfaces (water contact angle ≥ 150°) around concentric microfluidic ports separated by a gap. The relative position of the two polymer chips was determined by passive kinematic constraints, three spherical ball bearings seated in v-grooves. A leakage pressure model derived from the Young-Laplace equation was used to estimate the leakage pressure at failure for the liquid bridge. Injection-molded, Cyclic Olefin Copolymer (COC) chip assemblies with assembly gaps from 3 to 240 µm were used to experimentally validate the model. The maximum leakage pressure measured for the GSFI was 21.4 kPa (3.1 psig), which corresponded to a measured mean assembly gap of 3 µm, and decreased to 0.5 kPa (0.073 psig) at a mean assembly gap of 240 µm. The effect of radial misalignment on the efficacy of the gasketless seals was tested and no significant effect was observed. This may be a function of how the liquid bridges are formed during the priming of the chip, but additional research is required to test that hypothesis.

System Modularity Chip for Analysis of Rare Targets (SMART-Chip): Liquid Biopsy Samples.

Liquid biopsies are becoming popular for managing a variety of diseases due to the minimally invasive nature of their acquisition, thus potentially providing better outcomes for patients. Circulating tumor cells (CTCs) are among the many different biomarkers secured from a liquid biopsy, and a number of efficient platforms for their isolation and enrichment from blood have been reported. However, many of these platforms require manual sample handling, which can generate difficulties when translating CTC assays into the clinic due to potential sample loss, contamination, and the need for highly specialized operators. We report a system modularity chip for the analysis of rare targets (SMART-Chip) composed of three task-specific modules that can fully automate processing of CTCs. The modules were used for affinity selection of the CTCs from peripheral blood with subsequent photorelease, simultaneous counting, and viability determinations of the CTCs and staining/imaging of the CTCs for immunophenotyping. The modules were interconnected to a fluidic motherboard populated with valves, interconnects, pneumatic control channels, and a fluidic network. The SMART-Chip components were made from thermoplastics via microreplication, which lowers the cost of production making it amenable to clinical implementation. The utility of the SMART-Chip was demonstrated by processing blood samples secured from colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC) patients. We were able to affinity-select EpCAM expressing CTCs with high purity (0-3 white blood cells/mL of blood), enumerate the selected cells, determine their viability, and immunophenotype the cells. The assay could be completed in <4 h, while manual processing required >8 h.

A High-adhesion Binding Strategy for Silica Nanoparticle-based Superhydrophobic Coatings.

One of the long-standing problems for the nanoparticle-based liquid-repellent coatings is their poor adhesion to substrates. For polymers of low glass transition temperature, it is highly desirable to have low temperature coating strategy to fabricate robust superhydrophobic films. Here, we report a facile method for fabricating robust, transparent, superhydrophobic films on polymer substrates. A mixture of silica particles and silica-based oligomers was spin coated on polymer substrates, followed by oxygen plasma treatment and vapor deposition of 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (FDTS). The resulting superhydrophobic surface has a static contact angle at 160° and contact angle hysteresis lower than 5°. This study provides a practical solution to improve the adhesion of superhydrophobic films on polymer substrates in ambient conditions.

Flexible-templated imprinting for fluorine-free, omniphobic plastics with re-entrant structures.

HYPOTHESIS: Compared to vertical micro-pillars, re-entrant micro-structures exhibited superior omniphobicity for suspending liquids to Cassie-Baxter state. However, the existing re-entrant structures rely on complex multi-step deposition and etching procedures. The conventional, rigid-templated imprinting would instead damage the re-entrant structures. This leads to the question: is it possible to preserve the re-entrant curvatures by a flexible-templated imprinting? EXPERIMENTS: We facilely imprinted the re-entrant structures on a plastic substrate using a flexible nylon-mesh template. The effect of imprinting time (15-35 min), temperature (110-120 °C) and pressure (15-50 Bar) was investigated. To further improve the liquid-repellency and abrasion resistance, the silica nanoparticles (30-650 nm) along with epoxy resin binder (10 mg/mL) were pre-coated. FINDINGS: A one-step imprinting is sufficient to fabricate the re-entrant structures by utilizing flexible nylon-mesh template, without damaging the imprinted structures after the demolding process. The pre-coated silica nanoparticles and epoxy resin (1) improved liquid repellency by introducing hierarchical surface structures (e.g. contact angle hysteresis of olive oil reduced > 10°), and (2) acted as a protective layer against mechanical abrasion (omniphobicity maintained after 25 cycles, ~1.6 kPa sand paper abrasion). Additionally, the fluorine-free post-treatment was sufficient for the omniphobicity on the obtained plastic structures.

Affinity enrichment of extracellular vesicles from plasma reveals mRNA changes associated with acute ischemic stroke.

Currently there is no in vitro diagnostic test for acute ischemic stroke (AIS), yet rapid diagnosis is crucial for effective thrombolytic treatment. We previously demonstrated the utility of CD8(+) T-cells' mRNA expression for AIS detection; however extracellular vesicles (EVs) were not evaluated as a source of mRNA for AIS testing. We now report a microfluidic device for the rapid and efficient affinity-enrichment of CD8(+) EVs and subsequent EV's mRNA analysis using droplet digital PCR (ddPCR). The microfluidic device contains a dense array of micropillars modified with anti-CD8α monoclonal antibodies that enriched 158 ± 10 nm sized EVs at 4.3 ± 2.1 × 109 particles/100 µL of plasma. Analysis of mRNA from CD8(+) EVs and their parental T-cells revealed correlation in the expression for AIS-specific genes in both cell lines and healthy donors. In a blinded study, 80% test positivity for AIS patients and controls was revealed with a total analysis time of 3.7 h.

Robust, transparent, superhydrophobic coatings using novel hydrophobic/hydrophilic dual-sized silica particles.

HYPOTHESIS: The superhydrophobic lotus leaf has dual-scale surface structures, that is, nano-bumps on micro-mountains. Large hydrophilic particles, due to its high surface energy and weight, have high affility to substrates and tend to precipitate at the bottom of coating films. Small hydrophobic particles, due to its low surface energy and weight, tends to sit on the top of coating films and form porous structures. To mimic the lotus leaf surface, it may be possible to develop dual-sized particle films, in which small particles are decorated on large particles. EXPERIMENTS: A one-step spin coating of a mixture of dual-sized silica particles (55/200 nm) was used. Epoxy resin was added to improve the adhesion of particle films. The single-sized and dual-sized particle films were compared. The mechanical robustness of particle films was tested by tape peeling and droplet impact. FINDINGS: The novel combination of hydrophobic silica (55 nm) and hydrophilic silica (200 nm) is essential in creating the hierarchical structures. By combining the strong adhesion of hydrophilic silica (bottom of coating film) to polymer substrates and porous structures of hydrophobic silica (top of coating film), we first time report a one-step and versatile approach to create uniform, transparent, robust, and superhydrophobic surface.

Microfluidic gasketless interconnects sealed by superhydrophobic surfaces.

Existing methods for sealing chip-to-chip (or module-to-motherboard) microfluidic interconnects commonly use additional interconnect components (O-rings, gaskets, and tubing), and manual handling expertise for assembly. Novel gasketless superhydrophobic fluidic interconnects (GSFIs) sealed by transparent superhydrophobic surfaces, forming liquid bridges between the fluidic ports for fluidic passages were demonstrated. Two test platforms were designed, fabricated, and evaluated, a multi-port chip system (ten interconnects) and a modules-on-a-motherboard system (four interconnects). System assembly in less than 3 sec was done by embedded magnets and pin-in-V-groove structures. Flow tests with deionized (DI) water, ethanol/water mixture, and plasma confirmed no leakage through the gasketless interconnects up to a maximum flow rate of 100 µL/min for the multi-port chip system. The modules-on-a-motherboard system showed no leakage of water at a flow rate of 20 µL/min and a pressure drop of 3.71 psi. Characterization of the leakage pressure as a function of the surface tension of the sample liquid in the multi-port chip system revealed that lower surface tension of the liquid led to lower static water contact angles on the superhydrophobic-coated substrate and lower leakage pressures. The high-density, rapidly assembled, gasketless interconnect technology will open up new avenues for chip-to-chip fluid transport in complex microfluidic modular systems.

Point-of-Care Ultrasonography (POCUS) in a Community Emergency Department: An Analysis of Decision Making and Cost Savings Associated With POCUS.

OBJECTIVES: Point-of-care ultrasonography (POCUS) is an increasingly integral part of emergency medicine. This study investigated community emergency department physicians' choices regarding ultrasonography as a branch point in clinical decision making. METHODS: During shifts covering all days of the week and all time-spans over a 3-month period, emergency department physicians were interviewed whenever POCUS was used. Questions focused on the role of POCUS in clinical management and on tests avoided because of ultrasonography use. Cost savings attributable to POCUS were calculated using Center for Medicare and Medicaid Services and FairHealth data. Anonymization of data precluded follow-up testing to account for misdiagnosis. RESULTS: On average, POCUS use eliminated $1134.31 of additional testing for privately insured patients, $2826.31 for out-of-network or uninsured patients, and $181.63 for Center for Medicare and Medicaid Services patients. Differences were significant when the total cost of eliminated additional testing was compared to a baseline of no savings (p < .001). Aggregate cost savings remained significant when analyses were broadened to include POCUS encounters that did not yield changes in management (p < .001). CONCLUSIONS: When physicians' clinical expertise suggests that POCUS may be indicated, its use results in significant cost savings, even in encounters in which management is not directly impacted. POCUS, when incorporated earlier and more frequently into community hospital emergency medicine diagnostic protocols, can lower direct and indirect costs associated with diagnostic workups. Community emergency departments, in particular, would benefit from additional investigation informing specific guidelines for the integration of POCUS into clinical management and the role that this has in cost savings.

Microfluidic-based solid phase extraction of cell free DNA.

Cell-free DNA (cfDNA) is a liquid biopsy marker that can carry signatures (i.e., mutations) associated with certain pathological conditions. Therefore, the extraction of cfDNA from a variety of clinical samples can be an effective and minimally invasive source of markers for disease detection and subsequent management. In the oncological diseases, circulating tumor DNA (ctDNA), a cfDNA sub-class, can carry clinically actionable mutations and coupled with next generation sequencing or other mutation detection methods provide a venue for effective in vitro diagnostics. However, cfDNA mutational analyses require high quality inputs. This necessitates extraction platforms that provide high recovery over the entire ctDNA size range (50 → 150 bp) with minimal interferences (i.e., co-extraction of genomic DNA), and high reproducibility with a simple workflow. Herein, we present a novel microfluidic solid-phase extraction device (µSPE) consisting of a plastic chip that is activated with UV/O3 to generate surface-confined carboxylic acid functionalities for the µSPE of cfDNA. The µSPE uses an immobilization buffer (IB) consisting of polyethylene glycol and salts that induce cfDNA condensation onto the activated plastic microfluidic surface. The µSPE consists of an array of micropillars to increase extraction bed load (scalable to loads >700 ng of cfDNA) and can be produced at low-cost using replication-based techniques. The entire µSPE can be fabricated in a single molding step negating the need for adding additional extraction supports to the device simplifying production and keeping device and assay cost low. The µSPE allowed for recoveries >90% of model cfDNA fragments across a range of sizes (100-700 bp) and even the ability to extract efficiently short cfDNA fragments (50 bp, >70%). In addition, the composition of the IB allowed for reducing the interference of co-extracted genomic DNA. We demonstrated the clinical utility of the µSPE by quantifying the levels of cfDNA in healthy donors and patients with non-small-cell lung and colorectal cancers. µSPE extracted cfDNA from plasma samples was also subjected to a ligase detection reaction (LDR) for determining the presence of mutations in the KRAS gene for colorectal and non-small cell lung cancer patients.

Accurate, predictable, repeatable micro-assembly technology for polymer, microfluidic modules.

A method for the design, construction, and assembly of modular, polymer-based, microfluidic devices using simple micro-assembly technology was demonstrated to build an integrated fluidic system consisting of vertically stacked modules for carrying out multi-step molecular assays. As an example of the utility of the modular system, point mutation detection using the ligase detection reaction (LDR) following amplification by the polymerase chain reaction (PCR) was carried out. Fluid interconnects and standoffs ensured that temperatures in the vertically stacked reactors were within ± 0.2 C° at the center of the temperature zones and ± 1.1 C° overall. The vertical spacing between modules was confirmed using finite element models (ANSYS, Inc., Canonsburg, PA) to simulate the steady-state temperature distribution for the assembly. Passive alignment structures, including a hemispherical pin-in-hole, a hemispherical pin-in-slot, and a plate-plate lap joint, were developed using screw theory to enable accurate exactly constrained assembly of the microfluidic reactors, cover sheets, and fluid interconnects to facilitate the modular approach. The mean mismatch between the centers of adjacent through holes was 64 ± 7.7 µm, significantly reducing the dead volume necessary to accommodate manufacturing variation. The microfluidic components were easily assembled by hand and the assembly of several different configurations of microfluidic modules for executing the assay was evaluated. Temperatures were measured in the desired range in each reactor. The biochemical performance was comparable to that obtained with benchtop instruments, but took less than 45 min to execute, half the time.

Acute Aortic Syndromes: Diagnosis and Treatment.

Acute aortic syndromes are disorders of the thoracic and abdominal aorta that are usually symptomatic and require urgent evaluation and treatment. They include acute aortic dissection, intramural hematoma, and penetrating atherosclerotic ulcer. Knowledge of the natural history of these conditions, prompt diagnosis, and surgical intervention, when indicated, are the keys to successful outcomes.

Assembly of Polymer Microfluidic Components and Modules: Validating Models of Passive Alignment Accuracy.

Low-cost modular polymer microfluidic platforms integrating several different functional units may potentially reduce the cost of molecular and environmental analyses, and enable broader applications. Proper function of such systems depends on well-characterized assembly of the instruments. Passive alignment is one approach to obtaining such assemblies. Model modular devices containing passive alignment features, hemispherical pins in v-grooves, and integrated alignment standards for characterizing the accuracy of the assemblies were replicated in polycarbonate using doubled-sided injection molding. The dimensions and locations of the assembly features and alignment standards were measured. The assemblies had mismatches from 16 ± 4 to 20 ± 6 µm along the x-axis and from 103 ± 7 to 118 ± 11 µm along the y-axis. The vertical variation from the nominal value of 287 µm ranged from -10 ± 4 to 34 ± 7 µm. An assembly tolerance model was used to estimate the accuracy of the assemblies based on the manufacturing variations of the alignment structures. Variation of the alignment structure features were propagated through the assembly using Monte Carlo methods. The estimated distributions matched the measured experimental results well, with differences of 2%-13% due to unmodeled aspects of the variations Accurate assembly of advanced polymer microsystems is feasible and predictable in the design phase. [2014-0125].

Modeling of misalignment effects in microfluidic interconnects for modular bio-analytical chip applications.

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 µm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le ). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.

Influence of material transition and interfacial area changes on flow and concentration in electro-osmotic flows.

This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0-75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.

Ultrasound-guided procedures in the emergency department-diagnostic and therapeutic asset.

Bedside ultrasound is an extremely valuable and rapidly accessible diagnostic and therapeutic modality in potentially life- and limb-threatening situations in the emergency department. In this report, the authors discuss the role of ultrasound in quick assessment of pathologic conditions and its use to aid in diagnostic and therapeutic interventions.

Thermoplastic fusion bonding using a pressure-assisted boiling point control system.

A novel thermoplastic fusion bonding method using a pressure-assisted boiling point (PABP) control system was developed to apply precise temperatures and pressures during bonding. Hot embossed polymethyl methacrylate (PMMA) components containing microchannels were sealed using the PABP system. Very low aspect ratio structures (AR = 1/100, 10 µm in depth and 1000 µm in width) were successfully sealed without collapse or deformation. The integrity and strength of the bonds on the sealed PMMA devices were evaluated using leakage and rupture tests; no leaks were detected and failure during the rupture tests occurred at pressures greater than 496 kPa. The PABP system was used to seal 3D shaped flexible PMMA devices successfully.