Publications

2020
Kong, T. ; Shum, H. C. ; Weitz, D. A. The Fourth Decade of Microfluidics. Small 2020, 16, 2000070. Publisher's Version kong2020.pdf
Zhu, Z. ; Liu, J. - D. ; Liu, C. ; Wu, X. ; Li, Q. ; Chen, S. ; Zhao, X. ; Weitz, D. A. Microfluidics-Assisted Assembly of Injectable Photonic Hydrogels Toward Reflective Cooling. Small 2020, 16, 1903939. Publisher's VersionAbstract
Development of fast curing and easy modeling of colloidal photonic crystals is highly desirable for various applications. Here, a novel type of injectable photonic hydrogel (IPH) is proposed to achieve self‐healable structural color by integrating microfluidics‐derived photonic supraballs with supramolecular hydrogels. The supramolecular hydrogel is engineered via incorporating β‐cyclodextrin/poly(2‐hydroxypropyl acrylate‐coN‐vinylimidazole) (CD/poly(HPA‐co‐VI)) with methacrylated gelatin (GelMA), and serves as a scaffold for colloidal crystal arrays. The photonic supraballs derived from the microfluidics techniques, exhibit excellent compatibility with the hydrogel scaffolds, leading to enhanced assembly efficiency. By virtue of hydrogen bonds and host–guest interactions, a series of self‐healable photonic hydrogels (linear, planar, and spiral assemblies) can be facilely assembled. It is demonstrated that the spherical symmetry of the photonic supraballs endows them with identical optical responses independent of viewing angles. In addition, by taking the advantage of angle independent spectrum characteristics, the IPH presents beneficial effects in reflective cooling, which can achieve up to 17.4 °C in passive solar reflective cooling. The strategy represents an easy‐to‐perform platform for the construction of IPH, providing novel insights into macroscopic self‐assembly toward thermal management applications.
zhu2020.pdf
Parsa, S. ; Santanach-Carreras, E. ; Xiao, L. ; Weitz, D. A. Origin of anomalous polymer-induced fluid displacement in porous media. Physical Review Fluids 2020, 5 022001. Publisher's VersionAbstract

Immiscible displacement of fluids with large viscosity mismatch is inherently unstable due to viscous fingering, even in porous media where capillary forces dominate. Adding polymer to the displacing fluid reduces the viscosity mismatch and suppresses the viscous fingering instability thereby increasing the fluid displacement leading to extensive use in applications such as oil recovery. Surprisingly, however, an increase in displacement occurs even for very large viscosity mismatches. Moreover, significant additional displacement is observed when the polymer solution is followed by additional water flow. Thus, the fundamental physics of this phenomenon remains unclear. To understand this behavior, we use confocal microscopy to visualize the displacement of oil in a three-dimensional micromodel of a porous medium and simultaneously measure the local flow velocities of the displacing fluid. We find that the increased displacement results from a counterintuitive effect: polymer retention in the medium and the resultant local changes in flow. Typically retention is avoided since it reduces the permeability of the medium; instead, we find that large and heterogeneous local changes in flow lead to sufficiently large enough viscous forces at the interface of the immiscible fluids resulting in increased displacement.

    parsa2020.pdf
    Wheeler, M. A. ; Clark, I. C. ; Tjon, E. C. ; Li, Z. ; Zandee, S. E. J. ; Couturier, C. P. ; Watson, B. R. ; Scalisi, G. ; Alkwai, S. ; Rothhammer, V. ; et al. MAFG-driven astrocytes promote CNS inflammation. Nature 2020, 2020, 593-599. Publisher's VersionAbstract

    Multiple sclerosis is a chronic inflammatory disease of the CNS1. Astrocytes contribute to the pathogenesis of multiple sclerosis2, but little is known about the heterogeneity of astrocytes and its regulation. Here we report the analysis of astrocytes in multiple sclerosis and its preclinical model experimental autoimmune encephalomyelitis (EAE) by single-cell RNA sequencing in combination with cell-specific Ribotag RNA profiling, assay for transposase-accessible chromatin with sequencing (ATAC–seq), chromatin immunoprecipitation with sequencing (ChIP–seq), genome-wide analysis of DNA methylation and in vivo CRISPR–Cas9-based genetic perturbations. We identified astrocytes in EAE and multiple sclerosis that were characterized by decreased expression of NRF2 and increased expression of MAFG, which cooperates with MAT2α to promote DNA methylation and represses antioxidant and anti-inflammatory transcriptional programs. Granulocyte–macrophage colony-stimulating factor (GM-CSF) signalling in astrocytes drives the expression of MAFG and MAT2α and pro-inflammatory transcriptional modules, contributing to CNS pathology in EAE and, potentially, multiple sclerosis. Our results identify candidate therapeutic targets in multiple sclerosis.

    wheeler2020.pdf
    Selective cell encapsulation, lysis, pico-injection and size-controlled droplet generation using traveling surface acoustic waves in a microfluidic device
    Mutafopulos, K. ; Lu, P. J. ; Garry, R. ; Spink, P. ; Weitz, D. A. Selective cell encapsulation, lysis, pico-injection and size-controlled droplet generation using traveling surface acoustic waves in a microfluidic device. Lab on a Chip 2020, 20, 3914-3921. Publisher's VersionAbstract
    We generate droplets in a microfluidic device using a traveling surface acoustic wave (TSAW), and control droplet size by adjusting TSAW power and duration. We combine droplet production and fluorescence detection to selectively-encapsulate cells and beads; with this active method, the overwhelming majority of single particles or cells are encapsulated individually into droplets, contrasting the Poisson distribution of encapsulation number that governs traditional, passive microfluidic encapsulation. In addition, we lyse cells before selective encapsulation, and pico-inject new materials into existing droplets.
    mutafopulos2020.pdf
    Prodanović, R. ; Ung, W. L. ; Đurđić, K. I. ; Fisher, R. ; Weitz, D. A. ; Ostafe, R. A High-Throughput Screening System Based on Droplet Microfluidics for Glucose Oxidase Gene Libraries. molecules 2020, 25, 2418. Publisher's VersionAbstract

    Glucose oxidase (GOx) is an important industrial enzyme that can be optimized for specific applications by mutagenesis and activity-based screening. To increase the efficiency of this approach, we have developed a new ultrahigh-throughput screening platform based on a microfluidic lab-on-chip device that allows the sorting of GOx mutants from a saturation mutagenesis library expressed on the surface of yeast cells. GOx activity was measured by monitoring the fluorescence of water microdroplets dispersed in perfluorinated oil. The signal was generated via a series of coupled enzyme reactions leading to the formation of fluorescein. Using this new method, we were able to enrich the yeast cell population by more than 35-fold for GOx mutants with higher than wild-type activity after two rounds of sorting, almost double the efficiency of our previously described flow cytometry platform. We identified and characterized novel GOx mutants, the most promising of which (M6) contained a combination of six point mutations that increased the catalytic constant kcat by 2.1-fold compared to wild-type GOx and by 1.4-fold compared to a parental GOx variant. The new microfluidic platform for GOx was therefore more sensitive than flow cytometry and supports comprehensive screens of gene libraries containing multiple mutations per gene.

    prodanovic2020.pdf
    Haney, B. ; Werner, J. G. ; Weitz, D. A. ; Ramakrishnan, S. Stimuli responsive Janus microgels with convertible hydrophilicity for controlled emulsion destabilization. Soft Matter 2020, 16, 3613-3620. Publisher's VersionAbstract

    Although the utilization of rigid particles can afford stable emulsions, some applications require eventual emulsion destabilization to release contents captured in the particle-covered droplet. This destabilizing effect is achieved when using stabilizers that respond to controlled changes in environment. Microgels can be synthesized as stimuli responsive polymeric gel networks that adsorb to oil/water interfaces and stabilize emulsions. These particles are commonly hydrogels that swell and collapse in water in response to environmental changes. However, amphiphilic functionality is desired to enhance the adsorption abilities of these hydrogels while maintaining their stimuli responsivity. Microfluidic techniques are used to synthesize Janus microgels with two opposing stimuli responsive hemispheres. The particles have a temperature responsive domain connected to a pH responsive network where each side changes its hydrophilicity in response to a change in temperature or pH, respectively. The Janus microgels are amphiphilic in acidic conditions at 19 °C and alkaline conditions at 40 °C, while the opposite conditions cause a reduction of the amphiphilicity. By stabilizing emulsions with these dual responsive microgels, “smart” droplets that respond to environmental cues are formed. Emulsion droplets remain stable with smaller diameters when aqueous solution conditions favor amphiphilic particles yet, coalesce to larger droplets upon changing pH or temperature. These responsive Janus microgels represent the advancing technology of responsive droplets and demonstrate the applicability of microgels as emulsion stabilizers.

    haney2020.pdf
    Yuan, Y. ; Brouchon, J. ; Calvo-Calle, J. M. ; Xia, J. ; Sun, L. ; Zhang, X. ; Clayton, K. L. ; Ye, F. ; Weitz, D. A. ; Heyman, J. Droplet encapsulation improves accuracy of immune cell cytokine capture assays. Lab on a Chip 2020, 20, 1513-1520. Publisher's VersionAbstract

    Quantification of cell-secreted molecules, e.g., cytokines, is fundamental to the characterization of immune responses. Cytokine capture assays that use engineered antibodies to anchor the secreted molecules to the secreting cells are widely used to characterize immune responses because they allow both sensitive identification and recovery of viable responding cells. However, if the cytokines diffuse away from the secreting cells, non-secreting cells will also be identified as responding cells. Here we encapsulate immune cells in microfluidic droplets and perform in-droplet cytokine capture assays to limit the diffusion of the secreted cytokines. We use microfluidic devices to rapidly encapsulate single natural killer NK-92 MI cells and their target K562 cells into microfluidic droplets. We perform in-droplet IFN-γ capture assays and demonstrate that NK-92 MI cells recognize target cells within droplets and become activated to secrete IFN-γ. Droplet encapsulation prevents diffusion of secreted products to neighboring cells and dramatically reduces both false positives and false negatives, relative to assays performed without droplets. In a sample containing 1% true positives, encapsulation reduces, from 94% to 2%, the number of true-positive cells appearing as negatives; in a sample containing 50% true positives, the number of non-stimulated cells appearing as positives is reduced from 98% to 1%. After cells are released from the droplets, secreted cytokine remains captured onto secreting immune cells, enabling FACS-isolation of populations highly enriched for activated effector immune cells. Droplet encapsulation can be used to reduce background and improve detection of any single-cell secretion assay.

    yuan2020.pdf
    Liu, J. ; Chen, H. ; Shi, X. ; Nawar, S. ; Werner, J. ; Huang, G. S. ; Ye, M. ; Weitz, D. A. ; Solovev, A. A. ; Mei, Y. F. Hydrogel microcapsules with photocatalytic nanoparticles for removal of organic pollutants . Environmental Science Nano 2020, 7 656-664. Publisher's VersionAbstract

    Droplet-based microfluidics is used to fabricate thin shell hydrogel microcapsules for the removal of methylene blue (MB) from aqueous solutions. The microcapsules composed of a poly(methacrylic acid) hydrogel shell exhibit unique properties, including permeation, separation, purification, and reaction of molecular species. Photocatalytic TiO2 and ZnO nanoparticles encapsulated in the microcapsules, i.e. photocatalyst in capsule (PIC), are used to remove organic pollutants using an adsorption–oxidation mechanism. A prototype flow microreactor is assembled to demonstrate a controllable water purification approach in short time using photocatalysts. Our studies of aqueous and homogeneous hydrogel environments for the photocatalysts provide important insights into understanding the effectiveness of MB removal. Hydrogel capsules have MB removal rate comparable to homogeneous particles. Further reduction of both capsule and photocatalyst sizes can potentially aid in quicker water purification.

    liu2020.pdf
    Sun, Z. ; Yang, C. ; Eggersdorfer, M. ; Cui, J. ; Li, Y. ; Hai, M. ; Chen, D. ; Weitz, D. A. A General Strategy for One-Step Fabrication of Biocompatible Microcapsules with Controlled Active Release. Chinese Chemical Letters 2020, 31, 249-252. Publisher's VersionAbstract
    Fabrication of biocompatible core-shell microcapsules in a controllable and scalable manner remains an important but challenging task. Here, we develop a one-step microfluidic approach for the high-throughput production of biocompatible microcapsules, which utilizes single emulsions as templates and controls the precipitation of biocompatible polymer at the water/oil interface. The facile method enables the loading of various oils in the core and the enhancement of polymer shell strength by polyelectrolyte coating. The resulting microcapsules have the advantages of controllability, scalability, biocompatibility, high encapsulation efficiency and high loading capacity. The core-shell microcapsules are ideal delivery vehicles for programmable active release and various controlled release mechanisms are demonstrated, including burst release by vigorous shaking, pH-triggered release for targeted intestinal release and sustained release of perfume over a long period of time. The utility of our technique paves the way for practical applications of core-shell microcapsules.
    sun2020.pdf
    Haney, B. ; Werner, J. G. ; Weitz, D. A. ; Ramakrishnan, S. Absorbent-Adsorbates: Large Amphiphilic Janus Microgels as Droplet Stabilizers. ACS Applied Materials & Interfaces 2020, 12, 33439-33446. Publisher's VersionAbstract
    Microgel particles are cross-linked polymer networks that absorb certain liquids causing network expansion. The type of swelling-fluid and extent of volume change depends on the polymer-liquid interaction and the network’s cross-link density. These colloidal gels can be used to stabilize emulsion drops by adsorbing to the interface of two immiscible fluids. However, to enhance the adsorption abilities of these predominantly hydrophilic gel particles, some degree of hydrophobicity is needed. An amphiphilic Janus microgel with spatially distinct lipophilic and hydrophilic sides is desired. Here, we report the fabrication of polyethylene glycol diacrylate/ polypropylene glycol diacrylate Janus microgels (JM) using microfluidic drop making. The flow streams of the two separate and immiscible monomer solutions are brought into contact and intersected by a third immiscible fluid in a flow-focusing junction to form Janus droplets. The individual droplets are crosslinked via UV irradiation to form monodispersed microgel particles with opposing hydrophilic and hydrophobic 3D-networked polymer matrices. By combining two chemically different polymer gel networks, an amphiphilic emulsion stabilizer is formed that adsorbs to the oil/water interface while its faces absorb their respective water or hydrocarbon solvents. Both particle sides swell at the liquid/liquid interface as water in oil emulsions are stabilized and destabilized via thermal responsive hydrogel. Stimuli responsive droplets are demonstrated by adding a short chain oligo ethylene glycol acrylate molecule to the hydrogel formulation on the Janus microgel particle. Droplets stabilized by these particles experience a sudden increase in droplet diameter around 60˚C. This work with absorbent particles may prove useful for applications in bio catalysis, fuel production, and oil transportation.
    haney2020.pdf
    Cohen, L. ; Cui, N. ; Cai, Y. ; Garden, P. M. ; Li, X. ; Weitz, D. A. ; Walt, D. R. Single Molecule Protein Detection with Attomolar Sensitivity Using Droplet Digital Enzyme-Linked Immunosorbent Assay. ACS Nano 2020, 14, 9491-9501. Publisher's VersionAbstract
    Many proteins are present at low concentrations in biological samples, and therefore, techniques for ultrasensitive protein detection are necessary. To overcome challenges with sensitivity, the digital enzyme-linked immunosorbent assay (ELISA) was developed, which is 1000× more sensitive than conventional ELISA and allows sub-femtomolar protein detection. However, this sensitivity is still not sufficient to measure many proteins in various biological samples, thereby limiting our ability to detect and discover biomarkers. To overcome this limitation, we developed droplet digital ELISA (ddELISA), a simple approach for detecting low protein levels using digital ELISA and droplet microfluidics. ddELISA achieves maximal sensitivity by improving the sampling efficiency and counting more target molecules. ddELISA can detect proteins in the low attomolar range and is up to 25-fold more sensitive than digital ELISA using Single Molecule Arrays (Simoa), the current gold standard tool for ultrasensitive protein detection. Using ddELISA, we measured the LINE1/ORF1 protein, a potential cancer biomarker that has not been previously measured in serum. Additionally, due to the simplicity of our device design, ddELISA is promising for point-of-care applications. Thus, ddELISA will facilitate the discovery of biomarkers that have never been measured before for various clinical applications.
    cohen2020.pdf
    Wu, B. ; Yang, C. ; Li, B. ; Feng, L. ; Hai, M. ; Zhao, C. - X. ; Chen, D. ; Liu, K. ; Weitz, D. A. Active Encapsulation in Biocompatible Nanocapsules. Small 2020, 16, 2002716. Publisher's VersionAbstract
    Co‐precipitation is generally refers to the co‐precipitation of two solids and is widely used to prepare active‐loaded nanoparticles. Here, it is demonstrated that liquid and solid can precipitate simultaneously to produce hierarchical core–shell nanocapsules that encapsulate an oil core in a polymer shell. During the co‐precipitation process, the polymer preferentially deposits at the oil/water interface, wetting both the oil and water phases; the behavior is determined by the spreading coefficients and driven by the energy minimization. The technique is applicable to directly encapsulate various oil actives and avoid the use of toxic solvent or surfactant during the preparation process. The obtained core–shell nanocapsules harness the advantage of biocompatibility, precise control over the shell thickness, high loading capacity, high encapsulation efficiency, good dispersity in water, and improved stability against oxidation. The applications of the nanocapsules as delivery vehicles are demonstrated by the excellent performances of natural colorant and anti‐cancer drug‐loaded nanocapsules. The core–shell nanocapsules with a controlled hierarchical structure are, therefore, ideal carriers for practical applications in food, cosmetics, and drug delivery.
    wu2020.pdf
    Wu, H. ; Shen, Y. ; Wang, D. ; Herrmann, H. ; Goldman, R. D. ; Weitz, D. A. Effect of divalent cations on the structure and mechanics of vimentin intermediate filaments. Biophysical Journal 2020, 119, 55-64. Publisher's VersionAbstract
    Divalent cations behave as effective cross-linkers of intermediate filaments (IFs) such as vimentin IF (VIF). These interactions have been mostly attributed to their multivalency. However, ion-protein interactions often depend on the ion species, and these effects have not been widely studied in IFs. Here, we investigate the effects of two biologically important divalent cations, Zn2+ and Ca2+, on VIF network structure and mechanics in vitro. We find that the network structure is unperturbed at micromolar Zn2+ concentrations, but strong bundle formation is observed at a concentration of 100 μM. Microrheological measurements show that network stiffness increases with cation concentration. However, bundling of filaments softens the network. This trend also holds for VIF networks formed in the presence of Ca2+, but remarkably, a concentration of Ca2+ that is two orders higher is needed to achieve the same effect as with Zn2+, which suggests the importance of salt-protein interactions as described by the Hofmeister effect. Furthermore, we find evidence of competitive binding between the two divalent ion species. Hence, specific interactions between VIFs and divalent cations are likely to be an important mechanism by which cells can control their cytoplasmic mechanics.
    wu2020.pdf
    Zhang, W. ; Zhao, X. ; Yuan, Y. ; Miao, F. ; Li, W. ; Ji, S. ; Huang, X. ; Chen, X. ; Jiang, T. ; Weitz, D. A. ; et al. Microfluidic Synthesis of Multimode Au@CoFeB-Rg3 Nanomedicines and Their Cytotoxicity and Anti-Tumor Effects. Chemistry Materials 2020, 32, 5044-5056. Publisher's VersionAbstract
    Nanomedicines (i.e., Au@CoFeB-Rg3) were developed by conjugating multimode nanohybrids with active ingredients of natural herbs using Au@CoFeB nanoparticles as one model of multimode nanohybrids and the ginsenoside Rg3 as one model of active ingredients of natural herbs. Au@CoFeB nanoparticles were first synthesized using a temperatureprogrammed microfluidics process. Then, the surface of Au@ CoFeB nanoparticles was modified via an amino-silane coupling agent of (3-aminopropyl) trimethoxysilane (APTMS) and then activated by the bifunctional amine-active cross-linker. They were thereafter conjugated to ginsenosides preactivated by APTMS by cross-linking the surface-activated nanohybrids, forming Au@ CoFeB-Rg3 nanomedicines. Their multimode imaging functions were evaluated with the characterization of their magnetic and optical properties and the response to X-ray radiation. They can be optically detected via dark-field microscopy and can be imaged through X-ray computed tomography. They can also be used as magnetic resonance imaging contrast agents with excellent T2-weighted spin−echo imaging effects. Au@CoFeB-Rg3 nanomedicines exhibited distinct cytotoxicity and inhibitory effects on the proliferation of human hepatocellular carcinoma cells (HepG2/C3) and human chronic myeloid leukemia cells (K562) but were less toxic to 3T3 cells than other cells at concentrations more than 200 μg/ mL. However, Au@CoFeB nanoparticles showed markedly lower cytotoxicity and inhibitory effects on the proliferation of these cell lines, particularly at concentrations <100 μg/mL, than Au@CoFeB-Rg3 nanomedicines. Clearly, there is a distinct synergistic effect between nanohybrids and Rg3. Additionally, Au@CoFeB nanohybrids showed almost no toxicity to Jurkat-CT cells at low concentrations (47 μg/mL), indicating that they may be used as multimode nanoprobes at a suitable concentration. These findings provide an efficient alternative for the synthesis of multifunctional antitumor nanomedicines based on multimode nanohybrids and active ingredients of natural resources.
    zhang2020.pdf
    Xia, J. ; Yuan, Y. ; Wu, H. ; Huang, Y. ; Weitz, D. A. Decoupling the effects of nanopore size and surface roughness on the attachment, spreading and differentiation of bone marrow-derived stem cells. Biomaterials 2020, 248, 120014. Publisher's VersionAbstract
    The nanopore size and roughness of nanoporous surface are two critical variables in determining stem cell fate, but little is known about the contribution from each cue individually. To address this gap, we use two-dimensional nanoporous membranes with controlled nanopore size and roughness to culture bone marrow-derived mesenchymal stem cells (BMSCs), and study their behaviors such as attachment, spreading and differentiation. We find that increasing the roughness of nanoporous surface has no noticeable effect on cell attachment, and only slightly decreases cell spreading areas and inhibits osteogenic differentiation. However, BMSCs cultured on membranes with larger nanopores have significantly fewer attached cells and larger spreading areas. Moreover, these cells cultured on larger nanopores undergo enhanced osteogenic differentiation by expressing more alkaline phosphatase, osteocalcin, osteopontin, and secreting more collagen type I. These results suggest that although both nanopore size and roughness can affect BMSCs, nanopore size plays a more significant role than roughness in controlling BMSC behavior.
    xia2020.pdf
    Adams, L. L. A. ; Lee, D. ; Mei, Y. F. ; Weitz, D. A. ; Solovev, A. A. Nanoparticle‐Shelled Catalytic Bubble Micromotor. Advanced Materials Interfaces 2020, 7 1901583. Publisher's VersionAbstract
    Nanoparticle‐shelled bubbles, prepared with glass capillary microfluidics, are functionalized to produce catalytic micromotors that exhibit novel assembly and disassembly behaviors. Stable microbubble rafts are assembled at an air–solvent interface of nonaqueous propylene carbonate (PC) solvent by creating a meniscus using a glass capillary. Upon the addition of hydrogen peroxide fuel, catalytic microbubbles quickly break free from the bubble raft by repelling from each other and self‐propelling at the air–fuel interface (a mixture of PC and aqueous hydrogen peroxide). While most of micromotors generate oxygen bubbles on the outer catalytic shell, some micromotors contain cracks and eject bubbles from the hollow shells containing air. Nanoparticle‐shelled bubbles with a high buoyancy force are particularly attractive for studying novel propulsion modes and interactions between catalytic bubble micromotors at air–fuel interfaces.
    adams2020.pdf
    Tiribocchi, A. ; Montessori, A. ; Aime, S. ; Milani, M. ; Lauricella, M. ; Succi, S. ; Weitz, D. Novel nonequilibrium steady states in multiple emulsions. Physics of Fluids 2020, 32, 017102. Publisher's VersionAbstract
    We numerically investigate the rheological response of a noncoalescing multiple emulsion under a symmetric shear flow. We find that the dynamics significantly depends on the magnitude of the shear rate and on the number of the encapsulated droplets, two key parameters whose control is fundamental to accurately select the resulting nonequilibrium steady states. The double emulsion, for instance, attains a static steady state in which the external droplet stretches under flow and achieves an elliptical shape (closely resembling the one observed in a sheared isolated fluid droplet), while the internal one remains essentially unaffected. Novel nonequilibrium steady states arise in a multiple emulsion. Under low/moderate shear rates, for instance, the encapsulated droplets display a nontrivial planetarylike motion that considerably affects the shape of the external droplet. Some features of this dynamic behavior are partially captured by the Taylor deformation parameter and the stress tensor. Besides a theoretical interest on its own, our results can potentially stimulate further experiments, as most of the predictions could be tested in the lab by monitoring droplets’ shapes and position over time.
    tiribocchi2020.pdf
    Nawar, S. ; Stolaroff, J. K. ; Ye, C. ; Wu, H. ; Nguyen, D. T. ; Xin, F. ; Weitz, D. A. Parallelizable microfluidic dropmakers with multilayer geometry for the generation of double emulsions. Lab on a Chip 2020, 20, 147–154. Publisher's VersionAbstract
    We present a multilayer dropmaker geometry that enables the modular fabrication of microfluidic devices containing precisely patterned channel surface wettability. The platform is used for the scalable production of uniform double emulsion drops. , Microfluidic devices enable the production of uniform double emulsions with control over droplet size and shell thickness. However, the limited production rate of microfluidic devices precludes the use of monodisperse double emulsions for industrial-scale applications, which require large quantities of droplets. To increase throughput, devices can be parallelized to contain many dropmakers operating simultaneously in one chip, but this is challenging to do for double emulsion dropmakers. Production of double emulsions requires dropmakers to have both hydrophobic and hydrophilic channels, requiring spatially precise patterning of channel surface wettability. Precise wettability patterning is difficult for devices containing multiple dropmakers, posing a significant challenge for parallelization. In this paper, we present a multilayer dropmaker geometry that greatly simplifies the process of producing microfluidic devices with excellent spatial control over channel wettability. Wettability patterning is achieved through the independent functionalization of channels in each layer prior to device assembly, rendering the dropmaker with a precise step between hydrophobic and hydrophilic channels. This device geometry enables uniform wettability patterning of parallelized dropmakers, providing a scalable approach for the production of double emulsions.
    nawar2020.pdf
    Shi, W. ; Chen, X. ; Li, B. ; Weitz, D. A. Spontaneous Creation of Anisotropic Polymer Crystals with Orientation-Sensitive Birefringence in Liquid Drops. ACS Applied Materials & Interfaces 2020, 12, 3912-3918. Publisher's VersionAbstract
    It remains a grand challenge to prepare anisotropic crystal superstructures with sensitive optical properties in polymer science and materials field. This study demonstrates that semicrystalline polymers develop into anisotropic hollow spherulitic crystals spontaneously at interfaces of liquid drops. In contrast to conventional spherulites with centrosymmetric optics and grain boundaries, these anisotropic spherulitic crystals have vanished boundary defects, tunable aspect ratios, and noncentrosymmetric, orientationsensitive birefringence. The experimental finding is elaborated in poly(L-lactic acid) crystals and is further verified in a broad class of semicrystalline polymers, irrespective of molecular chirality, chemical constitution, or interfacial modification. The facile methods and general mechanism revealed in this study shed light on developing new types of optical microdevices and synthesis of anisotropic semicrystalline particles from liquid emulsions.
    shi2020.pdf

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