Publications by Year: 2017

Amstad, E. ; Weitz, D. A. Reply to the 'Comment on "Robust Scalable High Throughput Production of Monodisperse Drops. Lab on a Chip 2017, 17, 2332-2333. Publisher's VersionAbstract

This reply to the comment by Nakajima on our article that appeared in Lab on a Chip (E. Amstad, M. Chemama, M. Eggersdorfer, L. R. Arriaga, M. Brenner and D. A. Weitz, Lab Chip, 2016, 16, 4163–4172) highlights the differences between the microchannel step emulsification devices developed by the Nakajima group and the millipede device reported by us in Lab on a Chip.

Kim, S. - H. ; Kim, J. W. ; Cho, J. - C. ; Weitz, D. A. Correction: Double-emulsion drops with ultra-thin shells for capsule templates. Lab on a Chip 2017, 17, 567. Publisher's VersionAbstract

Correction for ‘Double-emulsion drops with ultra-thin shells for capsule templates’ by Shin-Hyun Kim et al.Lab Chip, 2011, 11, 3162–3166.

In the section “Diameter and shell thickness of double-emulsion drops” there are errors in eqn (2) and in the sentence that begins “In the same fashion, we calculate the thickness of the middle layer of double-emulsion drops which are produced at each values of Q1/Q2 and plot the results in Fig. 3c”. The equation should be

The sentence should read “In the same fashion, we calculate the thickness of the middle layer of double-emulsion drops which are produced at each values of Q2/Q1 and plot the results in Fig. 3c”.

In the caption for Fig. 3c, “Relative thickness of shell to radius of the double-emulsion drops (t/R) as a function of Q1/Q2.” should read “Relative thickness of shell to radius of the double-emulsion drops (t/R) as a function of Q2/Q1.” In addition, the x-axis is incorrectly labelled with “Q1/Q2”. The x-axis should be “Q2/Q1”. A corrected version of Fig. 3c is shown.

Jawerth, L. M. ; Weitz, D. A. Tracking the Structural Deformation of a Sheared Biopolymer Network. In Functional Analysis, Harmonic Analysis, and Image Processing: A Collection of Papers in Honor of Björn Jawerth; 2017; Vol. 693, pp. 255-269. Publisher's VersionAbstract

Biopolymer networks provide mechanical integrity in many important environments in vivo ranging from the cytoskeleton within a cell to the structural support of cells themselves in tissues and tendons. Rheolog-ical studies have shown that they exhibit many unique material properties. Modelling these properties requires a precise knowledge of how the individual filaments in the network deform locally during a global deformation. Here, we present an image processing method to track the three-dimensional motion of a biopolymer network as a simple shear deformation is applied. We track the structure of the network from one shear position to the next by determining the displacement of each branch point using a cross-correlation. To illustrate the use of this algorithm, we apply it to a fluorescently labelled fibrin network.

Liber, S. R. ; Indech, G. ; van der Wee, E. B. ; Butenko, A. V. ; Kodger, T. E. ; Lu, P. J. ; Schofield, A. B. ; Weitz, D. A. ; van Blaaderen, A. ; Sloutskin, E. Axial Confocal Tomography of Capillary-Contained Colloidal Structures. Langmuir 2017, 33, 13343–13349. Publisher's VersionAbstract
Confocal microscopy is widely used for three-dimensional (3D) sample reconstructions. Arguably, the most significant challenge in such reconstructions is posed by the resolution along the optical axis being significantly lower than in the lateral directions. In addition, the imaging rate is lower along the optical axis in most confocal architectures, prohibiting reliable 3D reconstruction of dynamic samples. Here, we demonstrate a very simple, cheap, and generic method of multiangle microscopy, allowing high-resolution high-rate confocal slice collection to be carried out with capillary-contained colloidal samples in a wide range of slice orientations. This method, realizable with any common confocal architecture and recently implemented with macroscopic specimens enclosed in rotatable cylindrical capillaries, allows 3D reconstructions of colloidal structures to be verified by direct experiments and provides a solid testing ground for complex reconstruction algorithms. In this paper, we focus on the implementation of this method for dense nonrotatable colloidal samples, contained in complex-shaped capillaries. Additionally, we discuss strategies to minimize potential pitfalls of this method, such as the artificial appearance of chain-like particle structures.
Chen, D. ; Amstad, E. ; Zhao, C. - X. ; Cai, L. ; Fan, J. ; Chen, Q. ; Hai, M. ; Koehler, S. ; Zhang, H. ; Liang, F. ; et al. Biocompatible Amphiphilic Hydrogel–Solid Dimer Particles as Colloidal Surfactants. ACS Nano 2017, 11, 11978–11985. Publisher's VersionAbstract
Emulsions of two immiscible liquids can slowly coalesce over time when stabilized by surfactant molecules. Pickering emulsions stabilized by colloidal particles can be much more stable. Here, we fabricate biocompatible amphiphilic dimer particles using a hydrogel, a strongly hydrophilic material, and achieve large contrast in the wetting properties of the two bulbs, resulting in enhanced stabilization of emulsions. We generate monodisperse single emulsions of alginate and shellac solution in oil using a flow-focusing microfluidics device. Shellac precipitates from water and forms a solid bulb at the periphery of the droplet when the emulsion is exposed to acid. Molecular interactions result in amphiphilic dimer particles that consist of two joined bulbs: one hydrogel bulb of alginate in water and the other hydrophobic bulb of shellac. Alginate in the hydrogel compartment can be cross-linked using calcium cations to obtain stable particles. Analogous to surfactant molecules at the interface, the resultant amphiphilic particles stand at the water/oil interface with the hydrogel bulb submerged in water and the hydrophobic bulb in oil and are thus able to stabilize both water-in-oil and oil-in-water emulsions, making these amphiphilic hydrogel–solid particles ideal colloidal surfactants for various applications.
Liu, J. ; Wang, N. \ddotu\elseü\fi}; Yu, L. - J. ; Karton, A. ; Li, W. ; Zhang, W. ; Guo, F. ; Hou, L. ; Cheng, Q. ; Jiang, L. ; et al. Bioinspired graphene membrane with temperature tunable channels for water gating and molecular separation. Nat. Commun. 2017, 8 2011. Publisher's VersionAbstract
Smart regulation of substance permeability through porous membranes is highly desirable for membrane applications. Inspired by the stomatal closure feature of plant leaves at relatively high temperature, here we report a nano-gating membrane with a negative temperature-response coefficient that is capable of tunable water gating and precise small molecule separation. The membrane is composed of poly(N-isopropylacrylamide) covalently bound to graphene oxide via free-radical polymerization. By virtue of the temperature tunable lamellar spaces of the graphene oxide nanosheets, the water permeance of the membrane could be reversibly regulated with a high gating ratio. Moreover, the space tunability endows the membrane with the capability of gradually separating multiple molecules of different sizes. This nano-gating membrane expands the scope of temperature-responsive membranes and has great potential applications in smart gating systems and molecular separation.
Guo, M. ; Pegoraro, A. F. ; Mao, A. ; Zhou, E. H. ; Arany, P. R. ; Han, Y. ; Burnette, D. T. ; Jensen, M. H. ; Kasza, K. E. ; Moore, J. R. ; et al. Cell volume change through water efflux impacts cell stiffness and stem cell fate. Proc. Natl. Acad. Sci. U.S.A. 2017, 201705179. Publisher's VersionAbstract
Cell volume is thought to be a well-controlled cellular characteristic, increasing as a cell grows, while macromolecular density is maintained. We report that cell volume can also change in response to external physical cues, leading to water influx/efflux, which causes significant changes in subcellular macromolecular density. This is observed when cells spread out on a substrate: Cells reduce their volume and increase their molecular crowding due to an accompanying water efflux. Exploring this phenomenon further, we removed water from mesenchymal stem cells through osmotic pressure and found this was sufficient to alter their differentiation pathway. Based on these results, we suggest cells chart different differentiation and behavioral pathways by sensing/altering their cytoplasmic volume and density through changes in water influx/efflux.
Hu, Y. ; Mao, A. S. ; Desai, R. M. ; Wang, H. ; Weitz, D. A. ; Mooney, D. J. Controlled self-assembly of alginate microgels by rapidly binding molecule pairs. Lab Chip 2017, 17, 2481–2490. Publisher's VersionAbstract
Controlled self-assembly of cell-encapsulating microscale polymeric hydrogels (microgels) could be advantageous in a variety of tissue engineering and regenerative medicine applications. Here, a method of assembly by chemical modification of alginate polymer with binding pair molecules (BPM) was explored. Alginate was modified with several types of BPM, specifically biotin and streptavidin and click chemistry compounds, and fabricated into 25–30 μm microgels using a microfluidic platform. These microgels were demonstrated to self-assemble under physiological conditions. By combining complementary microgels at a high ratio, size-defined assemblages were created, and the effects of BPM type and assembly method on the number of microgels per assemblage and packing density were determined. Furthermore, a magnetic process was developed to separate assemblages from single microgels, and allow formation of multilayer spheroids. Finally, cells were singly encapsulated into alginate microgels and assembled using BPM-modified alginate, suggesting potential applications in regenerative medicine.
Mao, A. S. ; Shin, J. - W. ; Utech, S. ; Wang, H. ; Uzun, O. ; Li, W. ; Cooper, M. ; Hu, Y. ; Zhang, L. ; Weitz, D. A. ; et al. Deterministic encapsulation of single cells in thin tunable microgels for niche modelling and therapeutic delivery. Nat. Mater. 2017, 16, 236–243. Publisher's VersionAbstract

Existing techniques to encapsulate cells into microscale hydrogels generally yield high polymer-to-cell ratios and lack control over the hydrogel’s mechanical properties1. Here, we report a microfluidic-based method for encapsulating single cells in an approximately six-micrometre layer of alginate that increases the proportion of cell-containing microgels by a factor of ten, with encapsulation efficiencies over 90%. We show that in vitro cell viability was maintained over a three-day period, that the microgels are mechanically tractable, and that, for microscale cell assemblages of encapsulated marrow stromal cells cultured in microwells, osteogenic differentiation of encapsulated cells depends on gel stiffness and cell density. We also show that intravenous injection of singly encapsulated marrow stromal cells into mice delays clearance kinetics and sustains donor-derived soluble factors in vivo. The encapsulation of single cells in tunable hydrogels should find use in a variety of tissue engineering and regenerative medicine applications.

Chen, D. ; Zhao, C. - X. ; Lagoin, C. ; Hai, M. ; Arriaga, L. R. ; Koehler, S. ; Abbaspourrad, A. ; Weitz, D. A. Dispersing hydrophobic natural colourant β-carotene in shellac particles for enhanced stability and tunable colour. R. Soc. Open Sci. 2017, 4 170919. Publisher's VersionAbstract
Colour is one of the most important visual attributes of food and is directly related to the perception of food quality. The interest in natural colourants, especially β-carotene that not only imparts colour but also has well-documented health benefits, has triggered the research and development of different protocols designed to entrap these hydrophobic natural molecules to improve their stability against oxidation. Here, we report a versatile microfluidic approach that uses single emulsion droplets as templates to prepare microparticles loaded with natural colourants. The solution of β-carotene and shellac in the solvent is emulsified by microfluidics into droplets. Upon solvent diffusion, β-carotene and shellac co-precipitates, forming solid microparticles of β-carotene dispersed in the shellac polymer matrix. We substantially improve the stability of β-carotene that is protected from oxidation by the polymer matrix and achieve different colour appearances by loading particles with different β-carotene concentrations. These particles demonstrate great promise for practical use in natural food colouring.
Thiery, J. ; Rodts, S. ; Weitz, D. A. ; Coussot, P. Drying regimes in homogeneous porous media from macro- to nanoscale. Phys. Rev. Fluids 2017, 2 074201. Publisher's VersionAbstract
Magnetic resonance imaging visualization down to nanometric liquid films in model porous media with pore sizes from micro- to nanometers enables one to fully characterize the physical mechanisms of drying. For pore size larger than a few tens of nanometers, we identify an initial constant drying rate period, probing homogeneous desaturation, followed by a falling drying rate period. This second period is associated with the development of a gradient in saturation underneath the sample free surface that initiates the inward recession of the contact line. During this latter stage, the drying rate varies in accordance with vapor diffusion through the dry porous region, possibly affected by the Knudsen effect for small pore size. However, we show that for sufficiently small pore size and/or saturation the drying rate is increasingly reduced by the Kelvin effect. Subsequently, we demonstrate that this effect governs the kinetics of evaporation in nanopores as a homogeneous desaturation occurs. Eventually, under our experimental conditions, we show that the saturation unceasingly decreases in a homogeneous manner throughout the wet regions of the medium regardless of pore size or drying regime considered. This finding suggests the existence of continuous liquid flow towards the interface of higher evaporation, down to very low saturation or very small pore size. Paradoxically, even if this net flow is unidirectional and capillary driven, it corresponds to a series of diffused local capillary equilibrations over the full height of the sample, which might explain that a simple Darcy's law model does not predict the effect of scaling of the net flow rate on the pore size observed in our tests.
Habib, N. ; Avraham-Davidi, I. ; Basu, A. ; Burks, T. ; Shekhar, K. ; Hofree, M. ; Choudhury, S. R. ; Aguet, F. ; Gelfand, E. ; Ardlie, K. ; et al. Massively parallel single-nucleus RNA-seq with DroNc-seq. Nat. Methods 2017, 14, 955. Publisher's VersionAbstract
Single-nucleus RNA sequencing (sNuc-seq) profiles RNA from tissues that are preserved or cannot be dissociated, but it does not provide high throughput. Here, we develop DroNc-seq: massively parallel sNuc-seq with droplet technology. We profile 39,111 nuclei from mouse and human archived brain samples to demonstrate sensitive, efficient, and unbiased classification of cell types, paving the way for systematic charting of cell atlases.
Du, J. S. ; Park, J. ; Kim, Q. H. ; Jhe, W. ; Dravid, V. P. ; Yang, D. ; Weitz, D. A. Multistage Transformation and Lattice Fluctuation at AgCl–Ag Interface. J. Phys. Chem. Lett. 2017, 8 5853–5860. Publisher's VersionAbstract
Solid-state transformation between different materials is often accompanied by mechanical expansion and compression due to their volume change and structural evolution at interfaces. However, these two types of dynamics are usually difficult to monitor in the same time. In this work, we use in situ transmission electron microscopy to directly study the reduction transformation at the AgCl–Ag interface. Three stages of lattice fluctuations were identified and correlated to the structural evolution. During the steady state, a quasi-layered growth mode of Ag in both vertical and lateral directions were observed due to the confinement of AgCl lattices. The development of planar defects and depletion of AgCl are respectively associated with lattice compression and relaxation. Topography and structure of decomposing AgCl was further monitored by in situ scanning transmission electron microscopy. Silver species are suggested to originate from both the surface and the interior of AgCl, and be transported to the interface. Such mass transport may have enabled the steady state and lattice compression in this volume-shrinking transformation.
Wang, L. ; Chen, D. ; Gutierrez-Cuevas, K. G. ; Bisoyi, H. K. ; Fan, J. ; Zola, R. S. ; Li, G. ; Urbas, A. M. ; Bunning, T. J. ; Weitz, D. A. ; et al. Optically reconfigurable chiral microspheres of self-organized helical superstructures with handedness inversion. Mater. Horiz. 2017, 4 1190–1195. Publisher's VersionAbstract
Optically reconfigurable monodisperse chiral microspheres of self-organized helical superstructures with dynamic chirality were fabricated via a capillary-based microfluidic technique. Light-driven handedness-invertible transformations between different configurations of microspheres were vividly observed and optically tunable RGB photonic cross-communications among the microspheres were demonstrated.
Weitz, D. A. Perspective on droplet-based single-cell sequencing. Lab Chip 2017, 17, 2539. Publisher's Version weitz2017.pdf
Shi, W. ; Weitz, D. A. Polymer Phase Separation in a Microcapsule Shell. Macromolecules 2017, 50, 7681–7686. Publisher's VersionAbstract
Phase separation has been used for engineering microscale fluids and particles with designed structures. But it is challenging to use phase separation to create complicated microcapsules because phase separation in the shell correlates with applied osmotic pressure and affects capsule stability significantly. Here we employ two biodegradable polymers to study the phase separation in microcapsule shells and its effect on the mechanical stability. The dynamic process reveals that phase separation creates a patchy shell with distinct regions transiently, then transports the discrete domains across the shell, and coalesces them at the surface. The equilibrium structure with balanced osmotic pressure is a Janus shell, where one component forms the shell and the other component dewets on the surface. Under slight osmotic pressure to the shell, phase separation reaches a different Janus shape, which consists of two partial shells of each component. We can in further take advantage of phase separation and osmotic pressure to rupture microcapsules at specific locations. Phase separation in the shell provides a facile approach to create versatile capsule structures and affords a reliable strategy to harness the shell mechanics.
Egan, P. F. ; Moore, J. R. ; Ehrlicher, A. J. ; Weitz, D. A. ; Schunn, C. ; Cagan, J. ; LeDuc, P. Robust mechanobiological behavior emerges in heterogeneous myosin systems. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, E8147-E8154. Publisher's VersionAbstract
Biological complexity presents challenges for understanding natural phenomenon and engineering new technologies, particularly in systems with molecular heterogeneity. Such complexity is present in myosin motor protein systems, and computational modeling is essential for determining how collective myosin interactions produce emergent system behavior. We develop a computational approach for altering myosin isoform parameters and their collective organization, and support predictions with in vitro experiments of motility assays with α-actinins as molecular force sensors. The computational approach models variations in single myosin molecular structure, system organization, and force stimuli to predict system behavior for filament velocity, energy consumption, and robustness. Robustness is the range of forces where a filament is expected to have continuous velocity and depends on used myosin system energy. Myosin systems are shown to have highly nonlinear behavior across force conditions that may be exploited at a systems level by combining slow and fast myosin isoforms heterogeneously. Results suggest some heterogeneous systems have lower energy use near stall conditions and greater energy consumption when unloaded, therefore promoting robustness. These heterogeneous system capabilities are unique in comparison with homogenous systems and potentially advantageous for high performance bionanotechnologies. Findings open doors at the intersections of mechanics and biology, particularly for understanding and treating myosin-related diseases and developing approaches for motor molecule-based technologies.
Alim, K. ; Parsa, S. ; Weitz, D. A. ; Brenner, M. P. Local Pore Size Correlations Determine Flow Distributions in Porous Media. Physical Review Letters 2017, 119, 144501. Publisher's VersionAbstract
The relationship between the microstructure of a porous medium and the observed flow distribution is still a puzzle. We resolve it with an analytical model, where the local correlations between adjacent pores, which determine the distribution of flows propagated from one pore downstream, predict the flow distribution. Numerical simulations of a two-dimensional porous medium verify the model and clearly show the transition of flow distributions from δ-function-like via Gaussians to exponential with increasing disorder. Comparison to experimental data further verifies our numerical approach.
Zhang, H. ; Qu, X. ; Chen, H. ; Kong, H. ; Ding, R. ; Chen, D. ; Zhang, X. ; Pei, H. ; Santos, H. A. ; Hai, M. ; et al. Fabrication of Calcium Phosphate-Based Nanocomposites Incorporating DNA Origami, Gold Nanorods, and Anticancer drugs for Biomedical Applications. Advanced Healthcare Materials 2017, 6 1700664. Publisher's VersionAbstract
DNA origami is designed by folding DNA strands at the nanoscale with arbitrary control. Due to its inherent biological nature, DNA origami is used in drug delivery for enhancement of synergism and multidrug resistance inhibition, cancer diagnosis, and many other biomedical applications, where it shows great potential. However, the inherent instability and low payload capacity of DNA origami restrict its biomedical applications. Here, this paper reports the fabrication of an advanced biocompatible nano‐in‐nanocomposite, which protects DNA origami from degradation and facilities drug loading. The DNA origami, gold nanorods, and molecular targeted drugs are co‐incorporated into pH responsive calcium phosphate [Ca3(PO4)2] nanoparticles. Subsequently, a thin layer of phospholipid is coated onto the Ca3(PO4)2 nanoparticle to offer better biocompatibility. The fabricated nanocomposite shows high drug loading capacity, good biocompatibility, and a photothermal and pH‐responsive payload release profile and it fully protects DNA origami from degradation. The codelivery of DNA origami with cancer drugs synergistically induces cancer cell apoptosis, reduces the multidrug resistance, and enhances the targeted killing efficiency toward human epidermal growth factor receptor 2 positive cells. This nanocomposite is foreseen to open new horizons for a variety of clinical and biomedical applications.
Wu, J. ; Cai, L. - H. ; Weitz, D. A. Tough Self-Healing Elastomers by Molecular Enforced Integration of Covalent and Reversible Networks. Advanced Materials 2017, 29, 1702616. Publisher's VersionAbstract
Self‐healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to “dry” elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid “dry” elastomer that is very tough with fracture energy 13500 Jm−2 comparable to that of natural rubber. Moreover, the elastomer can self‐heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self‐healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self‐healing polymers of practical usage.