Portable Seawater Desalination System for Generating Drinkable Water in Remote Locations.

A portable seawater desalination system would be highly desirable to solve water challenges in rural areas and disaster situations. While many reverse osmosis-based portable desalination systems are already available commercially, they are not adequate for providing reliable drinking water in remote locations due to the requirement of high-pressure pumping and repeated maintenance. We demonstrate a field-deployable desalination system with multistage electromembrane processes, composed of two-stage ion concentration polarization and one-stage electrodialysis, to convert brackish water and seawater to drinkable water. A data-driven predictive model is used to optimize the multistage configuration, and the model predictions show good agreement with the experimental results. The portable system desalinates brackish water and seawater (2.5-45 g/L) into drinkable water (defined by WHO guideline), with the energy consumptions of 0.4-4 (brackish water) and 15.6-26.6 W h/L (seawater), respectively. In addition, the process can also reduce suspended solids by at least a factor of 10 from the source water, resulting in crystal clear water (<1 NTU) even from the source water with turbidity higher than 30 NTU (i.e., cloudy seawater by the tide). We built a fully integrated prototype (controller, pumps, and battery) packaged into a portable unit (42 × 33.5 × 19 cm3, 9.25 kg, and 0.33 L/h production rate) controlled by a smartphone, tested for battery-powered field operation. The demonstrated portable desalination system is unprecedented in size, efficiency, and operational flexibility. Therefore, it could address unique water challenges in remote, resource-limited regions of the world.

Nano-Interstice Driven Powerless Blood Plasma Extraction in a Membrane Filter Integrated Microfluidic Device.

Blood plasma is a source of biomarkers in blood and a simple, fast, and easy extraction method is highly required for point-of-care testing (POCT) applications. This paper proposes a membrane filter integrated microfluidic device to extract blood plasma from whole blood, without any external instrumentation. A commercially available membrane filter was integrated with a newly designed dual-cover microfluidic device to avoid leakage of the extracted plasma and remaining blood cells. Nano-interstices installed on both sides of the microfluidic channels actively draw the extracted plasma from the membrane. The developed device successfully supplied 20 µL of extracted plasma with a high extraction yield (~45%) in 16 min.

Techno-economic analysis of multi-stage ion concentration polarization with recirculation for treatment of oil produced water.

The concept of recirculation of diluate/concentrate stream is implemented in multi-stage ion concentration polarization (ICP) desalination to deal with the issue of uncontrolled concentrate streams and deteriorated overall recovery rate to treat highly concentrated oil produce water from refineries. An improved empirical optimization model was established to calculate total energy consumption for operating cost and required membrane area for capital cost for a given set of operating parameters, feed salinity, salt removal ratio, and flow velocity. Using the empirical optimization model, a techno-economic analysis is performed to evaluate the feasibility of two-stage ICP system with recirculation loops. Brine of 160 g/kg is set as the system feed stream, whereas other operating conditions such as dilaute and concentrate streams are being controlled/fixed with 20 g/kg and ~250 g/kg respectively. Also, the system can be flexibly controlled to produce a specific concentration of product water and a recovery ratio with a corresponding water cost. With careful choices of recirculation rates, one can significantly increase the recovery ratio of two-stage ICP brine treatment process (from 25% to 39%) with only minor increase in overall cost (from $16.4-25.9/m3 to $20.6-22.54/m3), which is favourable for brine waste treatment application.

On-Chip Lipid Extraction Using Superabsorbent Polymers for Mass Spectrometry.

Pretreatment of samples is one of the most important steps in analytical methods for efficient and accurate results. Typically, an extraction method used for lipid analysis with mass spectrometry is accompanied by complex liquid-liquid extraction. We have devised a simple, rapid, and efficient lipid extraction method using superabsorbent polymers (SAPs) and developed a high-throughput lipid extraction platform based on a microfluidic system. Since SAPs can rapidly absorb an aqueous solution from a raw sample and convert it into the gel, the lipid extraction process can be remarkably simplified. The hydrophobic lipid components were captured into the fibrous SAP gel and then solubilized and eluted directly into the organic solvent without significant interference by this polymer. The small-scale lipid extraction process minimizes the liquid handling and unnecessary centrifugation steps, thereby enabling the implementation of a SAP-integrated microfluidic lipid extraction platform. The SAP method successfully induced reproducible extraction and high recovery rates (95-100%) compared to the conventional Folch method in several lipid classes. We also demonstrated the feasibility of the SAP method for the analysis of lipids in complex biological samples, such as the brain and liver, as well as Escherichia coli. This small-scale SAP method and its microfluidic platform will open up new possibilities in high-throughput lipidomic research for diagnosing diseases because this new technique saves time, labor, and cost.

Ethanol-dispersed and antibody-conjugated polymer nanofibers for the selective capture and 3-dimensional culture of EpCAM-positive cells.

Electrospun and ethanol-dispersed polystyrene-poly(styrene-co-maleic anhydride) (PS-PSMA) nanofibers (NFs) were used as a platform for the selective capture and three-dimensional culture of EpCAM-positive cells in cell culture medium and whole blood. The NFs were treated with streptavidin to facilitate bond formation between the amino groups of streptavidin and the maleic anhydride groups of the NFs. A biotinylated anti-EpCAM monoclonal antibody (mAb) was attached to the streptavidin-conjugated NFs via the selective binding of streptavidin and biotin. Upon simple mixing and shaking with EpCAM-positive cancer cells in a wide concentration range from 10 to 1000,000 cells per 10mL, the mAb-attached NFs (mAb-NFs) captured the Ep-CAM positive cells in an efficiency of 59%-67% depending on initial cell concentrations, with minor mechanical capture of 14%-36%. Captured cells were directly cultured, forming cell aggregates, in the NF matrix, which ensures the cell proliferation and follow-up analysis. Furthermore, the capture capacity of mAb-NFs was assessed in the presence of whole blood and blood lysates, indicating cluster formation that captured target cells. It is anticipated that the antibody-attached NFs can be employed for the capture and analysis of very rare EpCAM positive circulating cancer cells.

Ion concentration polarization for pre-concentration of biological samples without pH change.

In this paper, a method was developed for pre-concentrating large-volume biological samples for subsequent analysis. We previously developed another pre-concentration device, but it unfortunately altered the pH of the sample when an electric field was applied to the sample reservoir. Changes in the pH are not suitable for subsequent antibody-antigen reactions because of the stability issues that arise based on the target molecule's isoelectric point (pI). Here, this problem was overcome using ion concentration polarization (ICP) with a cation selective membrane (Nafion). Phosphate buffered saline was used as a test solution for the sample. The sample was contained in a reservoir that was not affected by the electric field, and an ICP barrier was formed in front of the reservoir. This device could concentrate microliter-scale samples without changing the pH because the biomolecules were blocked from passing through the ICP barrier while the sample (phosphate buffered saline) was drained. A 40 µL sample was successfully pre-concentrated to 20 µL in a single channel device and 10 µL in a dual channel device, resulting in 2.1-fold and 3.3-fold increases, respectively, in influenza hemagglutinin concentrations. These changes in the concentration were confirmed by ELISA.

Engineering a deformation-free plastic spiral inertial microfluidic system for CHO cell clarification in biomanufacturing.

Inertial microfluidics has enabled many impactful high throughput applications. However, devices fabricated in soft elastomer (i.e., polydimethylsiloxane (PDMS)) suffer reliability issues due to significant deformation generated by the high pressure and flow rates in inertial microfluidics. In this paper, we demonstrated deformation-free and mass-producible plastic spiral inertial microfluidic devices for high-throughput cell separation applications. The design of deformable PDMS spiral devices was translated to their plastic version by compensating for the channel deformation in the PDMS devices, analyzed by numerical simulation and confocal imaging methods. The developed plastic spiral devices showed similar performance to their original PDMS devices for blood separation and Chinese hamster ovary (CHO) cell retention. Furthermore, using a multiplexed plastic spiral unit containing 100 spirals, we successfully demonstrated ultra-high-throughput cell clarification (at a processing rate of 1 L min-1) with a high cell-clarification efficiency of ∼99% (at the cell density changing from ∼2 to ∼10 × 106 cells mL-1). Benefitting from the continuous and clogging-free separation with an industry-level throughput, the cell clarification device could be a critical breakthrough for the production of therapeutic biologics such as antibodies or vaccines, impacting biomanufacturing in general.

Current efficiency and selectivity reduction caused by co-ion leakage in electromembrane processes.

In electromembrane processes such as electrodialysis (ED) and ion concentration polarization (ICP), the diffusion layers on both diluate and concentrate sides influence permselectivity of the ion-exchange membrane and current utilization. The diffusion layer in the diluate stream, due to lower salinity and higher resistivity, has been regarded as the primary source of energy loss. In contrast, very few studies have focused on the diffusion layer in the concentrate stream. In this paper, we evaluate the influence of hydrodynamic convective flow on the development of diffusion layers on both concentrate and diluate sides, specifically in the ICP desalination process. Interestingly, the higher convective flow in the concentrate side was shown to drastically improve the current utilization drop in high operating current, which has been a recurring challenge in electromembrane processes. We attribute this to the prevention of co-ion leakage into the membrane, confirmed by both experimentation and numerical modeling. This new insight has a clear design implication for optimizing electromembrane processes for higher energy efficiency.

Simulation and Experimental Study of Ion Concentration Polarization Induced Electroconvective Vortex and Particle Movement.

Ion concentration polarization (ICP) has been widely applied in microfluidic systems in pre-concentration, particle separation, and desalination applications. General ICP microfluidic systems have three components (i.e., source, ion-exchange, and buffer), which allow selective ion transport. Recently developed trials to eliminate one of the three components to simplify the system have suffered from decreased performance by the accumulation of unwanted ions. In this paper, we presented a new ICP microfluidic system with only an ion-exchange membrane-coated channel. Numerical investigation on hydrodynamic flow and electric fields with a series of coupled governing equations enabled a strong correlation to experimental investigations on electroconvective vortices and the trajectory of charged particles. This study has significant implications for the development and optimization of ICP microfluidic and electrochemical systems for biomarker concentration and separation to improve sensing reliability and detection limits in analytic chemistry.

Return flow ion concentration polarization desalination: A new way to enhance electromembrane desalination.

In electromembrane desalination processes such as electrodialysis (ED) and ion concentration polarization (ICP) desalination, ion-depleted boundary layers constitute the desalted, product stream, yet also cause high resistivity and voltage drop. Directly manipulating fluid flow streams is a new method to break this fundamental trade-off for electromembrane desalination. In this work, we are introducing a novel electromembrane desalination architecture that allows a feed stream to return to the feed inlet side of the membrane (hereby named as return-flow (RF) architecture) to improve the energy efficiency by re-distributing and controlling the depleted boundary layer, even at high current values. The technical feasibility of this idea was examined in ICP desalination process (RF-ICP) with a wide range of feed salinity from 10 to 70 g/L. For a partial desalination, RF-ICP (∼75 cm2 of membrane area) has achieved similar power consumption compared to batch-ED with 3 times bigger membrane area (200 cm2) with a higher area efficiency for salt removal, which translates into lower optimal desalination cost. The techno-economic analysis of RF-ICP have been performed for the treatment of 70 g/L brine waste. For partial desalination of 70 g/L brine down to 35 g/L, RF-ICP desalination achieved overall water cost as low as $2.57/m3 ($0.41/barrel). This could translate into reduction in total water cost up to 31% for zero brine release scenarios, depending on the concentrated brine treatment cost. These results show that return-flow architecture can improve the performance of electromembrane desalination, enabling more flexible water treatment for many real-world applications.

Techno-economic analysis of ion concentration polarization desalination for high salinity desalination applications.

A techno-economic analysis is used to evaluate the economic feasibility of ion concentration polarization (ICP) desalination for seawater desalination and brine management. An empirical optimization model based on a limited set of experimental data, which was obtained from a lab-scale ICP desalination prototype, was established to calculate the required energy and membrane area for a given set of operating parameters. By calculating operating and capital expenses in various feed and product cases, the optimal levelized cost of water is determined over a range of feed salinities, mostly above seawater salinity (35 g/kg). Through these analyses, we study the economic feasibility of three applications: 1) partial desalination of brine discharge by ICP (feed varied from 35 to 75 g/kg) to common seawater RO feed level (35 g/kg) in a hybrid ICP-RO system; 2) the concentration of seawater desalination brine for salt production, and 3) partial desalination of oilfield wastewater. The economic feasibility of ICP desalination processes has been evaluated and the rough cost of treatment has been generated for several relevant applications. The approach taken in this work could be employed for other new and existing desalination processes, where a priori process modeling and optimization is scientifically and/or numerically challenging.

Enhanced oxygen permeability in membrane-bottomed concave microwells for the formation of pancreatic islet spheroids.

Oxygen availability is a critical factor in regulating cell viability that ultimately contributes to the normal morphogenesis and functionality of human tissues. Among various cell culture platforms, construction of 3D multicellular spheroids based on microwell arrays has been extensively applied to reconstitute in vitro human tissue models due to its precise control of tissue culture conditions as well as simple fabrication processes. However, an adequate supply of oxygen into the spheroidal cellular aggregation still remains one of the main challenges to producing healthy in vitro spheroidal tissue models. Here, we present a novel design for controlling the oxygen distribution in concave microwell arrays. We show that oxygen permeability into the microwell is tightly regulated by varying the poly-dimethylsiloxane (PDMS) bottom thickness of the concave microwells. Moreover, we validate the enhanced performance of the engineered microwell arrays by culturing non-proliferated primary rat pancreatic islet spheroids on varying bottom thickness from 10 µm to 1050 µm. Morphological and functional analyses performed on the pancreatic islet spheroids grown for 14 days prove the long-term stability, enhanced viability, and increased hormone secretion under the sufficient oxygen delivery conditions. We expect our results could provide knowledge on oxygen distribution in 3-dimensional spheroidal cell structures and critical design concept for tissue engineering applications. STATEMENT OF SIGNIFICANCE: In this study, we present a noble design to control the oxygen distribution in concave microwell arrays for the formation of highly functional pancreatic islet spheroids by engineering the bottom of the microwells. Our new platform significantly enhanced oxygen permeability that turned out to improve cell viability and spheroidal functionality compared to the conventional thick-bottomed 3-D culture system. Therefore, we believe that this could be a promising medical biotechnology platform to further develop high-throughput tissue screening system as well as in vivo-mimicking customised 3-D tissue culture systems.

Generation of digitized microfluidic filling flow by vent control.

Quantitative microfluidic point-of-care testing has been translated into clinical applications to support a prompt decision on patient treatment. A nanointerstice-driven filling technique has been developed to realize the fast and robust filling of microfluidic channels with liquid samples, but it has failed to provide a consistent filling time owing to the wide variation in liquid viscosity, resulting in an increase in quantification errors. There is a strong demand for simple and quick flow control to ensure accurate quantification, without a serious increase in system complexity. A new control mechanism employing two-beam refraction and one solenoid valve was developed and found to successfully generate digitized filling flow, completely free from errors due to changes in viscosity. The validity of digitized filling flow was evaluated by the immunoassay, using liquids with a wide range of viscosity. This digitized microfluidic filling flow is a novel approach that could be applied in conventional microfluidic point-of-care testing.

Fabrication of type I collagen microcarrier using a microfluidic 3D T-junction device and its application for the quantitative analysis of cell-ECM interactions.

We presented a new quantitative analysis for cell and extracellular matrix (ECM) interactions, using cell-coated ECM hydrogel microbeads (hydrobeads) made of type I collagen. The hydrobeads can carry cells as three-dimensional spheroidal forms with an ECM inside, facilitating a direct interaction between the cells and ECM. The cells on hydrobeads do not have a hypoxic core, which opens the possibility for using as a cell microcarrier for bottom-up tissue reconstitution. This technique can utilize various types of cells, even MDA-MB-231 cells, which have weak cell-cell interactions and do not form spheroids in conventional spheroid culture methods. Morphological indices of the cell-coated hydrobead visually present cell-ECM interactions in a quantitative manner.

Viscoelastic lithography for fabricating self-organizing soft micro-honeycomb structures with ultra-high aspect ratios.

High-aspect ratio micro- and nano-structures have been used for the production of a variety of applications. In this paper, we describe a simple and cost-effective approach to fabricate an arrayed microarchitecture with an ultra-high aspect ratio using soft materials. The shapes and sizes of the honeycomb structure can be easily modulated by changing the dimensions and position of the base mould pattern and the pressure. The honeycomb structure is used to prepare a drug delivery patch and a microwell array to form cell spheroids without cell loss. The honeycomb structures prepared using natural ECM (collagen-Matrigel) materials are successfully fabricated. The hepatocytes and endothelial cells are seeded and co-cultured in the ECM-based micro-honeycomb to prepare a 3D liver model successfully mimicking an ultrastructure of liver and providing enhanced liver function.

Angiogenic Type I Collagen Extracellular Matrix Integrated with Recombinant Bacteriophages Displaying Vascular Endothelial Growth Factors.

Here, a growth-factor-integrated natural extracellular matrix of type I collagen is presented that induces angiogenesis. The developed matrix adapts type I collagen nanofibers integrated with synthetic colloidal particles of recombinant bacteriophages that display vascular endothelial growth factor (VEGF). The integration is achieved during or after gelation of the type I collagen and the matrix enables spatial delivery of VEGF into a desired region. Endothelial cells that contact the VEGF are found to invade into the matrix to form tube-like structures both in vitro and in vivo, proving the angiogenic potential of the matrix.

Microfluidic in-reservoir pre-concentration using a buffer drain technique.

Pre-concentration methods are essential for detecting low concentrations of influenza virus in biological samples from patients. Here, we describe a new method for draining buffer from solution in the reservoir of a microfluidic device to increase the concentration of virus in the reservoir. Viruses were captured in the reservoir by an ion depletion barrier from connected ion selective microfluidic channels. 75 µl of buffer was successfully drained from a 100 µl sample, resulting in a 4-fold increase in influenza hemagglutinin concentration in the reservoir. The volume of the final concentrated sample was suitable for detection of influenza hemagglutinin by the enzyme-linked immunosorbent assay, demonstrating the usefulness of the developed platform for enhanced sensitivity of virus detection in a conventional analysis.