Soft Matter
● Royal Society of Chemistry (RSC)
Preprints posted in the last 30 days, ranked by how well they match Soft Matter's content profile, based on 60 papers previously published here. The average preprint has a 0.04% match score for this journal, so anything above that is already an above-average fit.
Hussan, J. R.; Rampadarath, A.; Nickerson, D. P.; Hunter, P. J.
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Plant-derived extracellular vesicles (PDEVs) have emerged as superior candidates for oral drug delivery, exhibiting a gastrointestinal survivability that significantly exceeds that of mammalian exosomes or synthetic liposomes. However, the biophysical rules governing how plant genomic regulation translates into this exceptional mechanical resilience remain unknown. Here, we present a predictive multiscale model of plant-derived extracellular vesicles, linking a parameterised genetic state space to emergent mesoscale mechanics via supra-molecular coarse-grained molecular dynamics (SCG-MD). We demonstrate that the upregulation of sterol methyltransferases (SMT) during the plants theoretical Defence state drives the formation of a phase-separated composite architecture, where rigid domains occupying approximately 36% of the membrane surface area effectively arrest crack propagation. This state achieves a critical rupture tension of 367.0 {+/-} 0.7 mN m-1 corresponding to a 39% increase over the wild-type Ripening state. Crucially, we find that chemical composition alone is insufficient for this reinforcement; vesicles with actively sorted lipid domains (Seeded topology) outperform randomised mixtures (Spontaneous topology) by 23% at identical concentrations. Furthermore, while fluid vesicles stiffen reactively under gastric acid shock (pH 2.5) due to the steric jamming of thermodynamically neutralised headgroups, the Defence state exhibits mechanical homeostasis. These findings suggest that PDEVs function as genetically tunable composite materials, offering a design blueprint for next-generation bio-inspired drug delivery vectors. Ultimately, these theoretical indices provide a predictive biophysical framework awaiting empirical confirmation via in vitro nanomechanical assays.
Nieto, V.; Crowley, J. L.; Deslandes, F.; Thiam, A. R.; Foret, L.; Monticelli, L.
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Lipid droplets (LDs) are cellular organelles responsible for lipid storage and metabolism. The mechanism of biogenesis of LDs involves phase separation of neutral lipids from the surrounding phospholipids, which generates oil lenses embedded in lipid bilayers, also known as nascent LDs. As nascent LDs grow, at some point they bud out of the bilayer, forming nearly spherical droplets. Nascent LDs have different propensity to bud, and it has been proposed that their shape provides information on such propensity; however, LD shape is difficult to determine experimentally. Here we studied the shape of lipid droplets using MD simulations at the coarse-grained level, and compared it to the predictions by an established theory. Our general system setup features an oil lens embedded into a flat, periodic bilayer. We found that the shape of simulated nascent LDs resembles a spherical cap (i.e., it has constant curvature over most of the surface), in excellent agreement with the theory, already for very small droplet sizes. The aspect ratio (height/radius) of nascent LDs increases with increasing LD volume, increasing membrane softness, and increasing surface tension between oil and water, also in agreement with theoretical predictions; however, it remains lower than 1 (i.e., the ratio for a sphere) for LDs of up to 40 nm in diameter. Fitting the simulated LD shapes with a theoretical shape equation suggests that a non-zero surface tension is present in both the monolayer and in the bilayer region. The existence of a relatively high surface tension in the bilayer region is confirmed by local stress calculations, and indicates that the periodic system setup does not reproduce the properties of nascent LDs in the endoplasmic reticulum, where the bilayer tension is two orders of magnitude lower. However, the simulations provide a microscopic view into the properties of droplet embedded vesicles.
Nidriche, A.; Debarre, D.; Verdier, C.
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Poly-L-Lysine (PLL) mediates the non-specific adhesion of cells and is commonly used in Atomic Force Microscopy (AFM) measurements, to ensure that cells remain attached to the substrate. However, it is acknowledged that adhesion affects the measured mechanical properties, in particular in the case Red Blood Cells (RBCs). This results in a wide range of Youngs modulus E reported in the literature. The present study aims at providing a systematic approach to the impact of non-specific adhesion on the rheology of RBCs. It provides a correlation between the topography profile of adherent RBCs and their rheology, from weak (cPLL = 10-3 mg/mL) to strong-adhesion (cPLL = 100 mg/mL) regimes. Using RICM and AFM, we find that there is a continuum of RBC shapes promoted by adhesion, from concave to dome-shaped, as predicted by the theory of vesicle adhesion. Their elastic properties discriminate them into two populations depending on adhesion strength, where stiffer RBCs (E {gtrsim} 100 Pa) correlate with dome-shaped cells. These findings are supported by rheology measurements of the dynamic complex shear modulus G*(f): while the storage modulus increases with cell-substrate adhesion, reflective of an increased membrane shear modulus, the loss modulus remains unchanged. Finally, further analysis inspired by membrane theory shows that different deformation modes may be triggered during indentation of either weakly or strongly adhering RBCs, illustrating the limits of the Hertz model.
Zinga, K.; Stachowiak, J.; Ren, P.
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Liquid-liquid phase separation of proteins has been observed to occur on biological membranes, where it is thought to play a role in diverse cellular behaviors. Recent work has demonstrated colocalization between protein condensates on opposing leaflets of the bilayer, suggesting that protein phase separation may be coupled across the bilayer. However, the mechanism behind this coupling phenomenon remains poorly understood. Here we seek to understand the protein-protein and protein-membrane interactions that give rise to transbilayer coupling of protein condensates. We perform coarse-grained molecular dynamics simulations of a bilayer with a disordered protein condensate tethered to each leaflet surface. In this system, we observe stable, coupled diffusion of the condensates across the membrane. We find that increasing the protein-protein interaction strength leads to decoupling, driven by competing membrane curvatures induced by each condensate. However, by applying membrane tension we suppress curvature and restore coupling even at higher protein interaction strengths. Under coupling conditions, we find that lipid entropy is reduced upon direct contact with proteins, but this effect is not transferred to the opposing leaflet. Interestingly, further analysis reveals increased transverse lipid packing (interdigitation) beneath the condensates relative to protein-free regions. Based on these observations, we propose that enhanced lipid interdigitation mediates interleaflet communication and serves as the primary mechanism driving transbilayer coupling of condensates in this system. This work provides insight into a potential physical mechanism for transmembrane communication in cellular contexts and suggests directions for future investigation. Significance StatementLiquid-like condensates are active participants at cellular membranes, where they act as organizers and catalysts for various cellular processes. Recent work has demonstrated that protein condensates can couple across the bilayer; however, the molecular mechanism of this transbilayer coupling remained unknown. Here, we investigate the molecular basis of transmembrane condensate coupling through detailed analysis and propose a mechanism for the phenomenon. This work advances our understanding of how information is transmitted across the bilayer, with implications in cellular requiring coordination across the membrane, such as signaling, and more broadly in the field of membrane biophysics.
Diaz, U.; Das, M. F.; Thukral, S.; Abuel, J.; Carter, M.; Marino, A.; Galvan, L.; Irungu, A.; Leiva, J.; Ballor, A.; Marshall, W. F.
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The cytoplasm is a crowded and dynamic fluid within which cellular building blocks such as mRNA, proteins, or organelles undergo transport and mixing. Although small things like proteins can eventually mix through diffusion, the high viscosity of cytoplasm means that it should be difficult to obtain significant mixing for structures in the size range of mRNA, multi-protein complexes or organelles. In large amoeboid cells, the cytoplasm undergoes active streaming coupled to cell motility, but this streaming is laminar flow which should not be effective for mixing. In this work we used a combination of live cell tracking of injected beads and computational analysis of motion and mixing in giant amoeba Chaos carolinensis with the initial goal of testing the possibility that large-scale cellular deformations during pseudopod formation might implement chaotic mixing by a Baker-transform like process. Instead, we found that Chaos carolinensis accelerates cytoplasmic mixing using a novel cytoplasmic gel state capture and release strategy. While it was previously thought that the amoeba sol to gel state transitions only occur at the trailing and leading edge of the cell body, our work indicates that these transitions occur frequently throughout the mid-cell region, driving the cytoplasmic mixing of beads and organelles. These results indicate that amoeba achieves nearly complete mixing between 1 and 2 cytoplasmic stream/flow cycle, effectively approximating the Bernoulli mixing regime and thus representing one of the theoretically fastest possible mixers.
Seo, S.; Madhvacharyula, A.; Swett, A.; Li, R.; Du, Y.; Choi, J. H.
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Auxetic metamaterials exhibit negative Poisson's ratio behaviors due to their architecture of periodically arranged unit cells. Although mechanical metamaterials are well established at the macroscale, programmable auxetic units remain scarce at the nanoscale. DNA origami offers a promising platform to bridge this gap, but design principles for dynamically deformable 3D auxetic nanostructures remain largely unexplored. Here, we develop design strategies for such 3D auxetic metastructures built from wireframe DNA origami. As a model system, we use a 3D re-entrant triangular unit composed of double-stranded DNA (dsDNA) bundle edges connected by single-stranded DNA (ssDNA) joints. Using coarse-grained molecular dynamics (MD) and umbrella-sampling free-energy simulations, we examine how edge design and joint-connection scheme govern auxetic responses and the energetics of the structural transformation. Our results show that auxetic performance and deformation energetics emerge from the coupled effects of DNA bundle rigidity and connector mechanics at the joints. This study provides mechanistic insights and design guidelines for programmable auxetic motion and energetics in 3D DNA origami metamaterials, advancing the development of stimuli-responsive nanomechanical devices.
Kafour, N.;Al-Maslamani, N.;Al-Sammak, B.;Horn, H.
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Mechanical forces have a major effect on cell behavior. Most cells in vitro are grown under static conditions on hard tissue culture plastic, conditions that do not accurately reflect living tissues. The ability of cells to sense and respond to mechanical forces is essential for key biological processes, including development, proliferation, and migration. Disruption of the ability to respond to mechanical forces are known to be a critical factor in many diseases, including cardiovascular disease, progeria, and cancer. Here, we present the design, fabrication, and biological testing of a custom-built cell-stretching device that applies controlled biaxial strain to cells cultured on a polydimethylsiloxane (PDMS) membrane. We then used this device to examine how cells respond to strain. In response to biaxial strain, MCF-7 cells activated the mechanosensitive immediate early gene (IEX-1), with its expression increasing significantly after 1 and 3 hours of stretching. Cells exposed to mechanical strain also remodeled their cytoskeleton in a direction-dependent manner. Under uniaxial strain, actin filaments reoriented perpendicular to the stretch direction, whereas biaxially stretched cells do not promote directional reorientation, but instead appear to reinforce actin at the cell periphery. Similarly, cells under uniaxial strain exhibited changes in nuclear orientation and shape that were not observed under biaxial strain. Nuclear area remained unchanged in either strain condition. These results highlight that the biaxial stretcher can be used to apply strain to cells, and that cells respond differently to biaxial strain compared to what has been reported for uniaxial strain.
Yuan, J.;Nawara, T.;Seeley, L.;Tran, Y.;Mattheyses, A.
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Vascular endothelial cells (ECs) form a monolayer lining blood vessels and serve as a barrier between blood and tissues. Clathrin-mediated endocytosis (CME) is a major internalization pathway that involves a physical conformational change of the plasma membrane to form a vesicle and is therefore sensitive to the local environment. ECs are subjected to a myriad of fluid shear stress (FSS) rates from circulating blood, which we hypothesize affects CME. To test this, we used simultaneous two-wavelength axial ratiometry (STAR) microscopy, which provides nanoscale axial resolution, to determine the frequency and morphology of clathrin-coated vesicles as they form. Human umbilical vein endothelial cells (HUVECs) were transfected with dual-tagged clathrin light chain a (CLCa-iRFP-EGFP) and cultured under 10 dyn/cm2 FSS. CME activity was elevated in cells cultured under flow and assayed in static or flow conditions compared to statically cultured and imaged controls, indicating that FSS-induced changes to CME were maintained shortly after flow cessation. Single vesicle analysis showed cells cultured in FSS had a slight preference for vesicle formation with a flat-to-curved clathrin transition compared to control. Next, to assess the impact of different FSS rates, we cultured HUVECs at 20 and 40 dyn/cm2 FSS. We found total CME frequency was elevated compared to control at 20 dyn/cm2, but not 40 dyn/cm2. HUVECs cultured at both 20 and 40 dyn/cm2 had vesicles with increased lifetime and enhanced stability, as well as a higher proportion of vesicles formed through a flat-to-curved transition of clathrin.
Vaiwala, R.; Christy, E.; Waskar, M.; Ayappa, K. G.
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We present a comparative study of the inner membrane of three Gram-positive bacterial strains, namely S. aureus, S. epidermidis and N. lacusekhoensis. A lipidomics study is used to obtain the lipid architecture and composition for S. epidermidis found in the skin microbiome and N. lacusekhoensis, an extremophile present in halophilic and alkophilic environments. Differences between the strains arise from both the lipid architecture and the cardiolipin content varying from 5% in S. aureus to 85% in N. lacusekhoensis. We develop coarse grained (CG) Martini-3 membrane models which reproduce structural properties such as membrane area, thickness, density distributions as well as ion-correlations with all-atom models. Inter-lipid correlations reveal a homogeneous distribution of lipids in the membranes despite the wide variation in lipid types and composition. Mechanical properties such as the area stretch modulus increased with cardiolipin content, however the bending modulus has a more complex dependence on membrane charge and lipid type. Using the CG models we evaluate the insertion free energies for four widely used antimicrobial molecules. Entry barriers for thymol and methylparaben arise from the charge density modulation at the membrane headgroups due to counterion condensation. The entry mechanisms of the antimicrobial peptide cecropin-melittin-15 (CM15) and the preservative molecule ethyl-lauroyl-arginate (ELAR) are found to be similar across all three strains. We also illustrate the manner in which the extremophilic strain, N. lacusekhoensis with its high cardiolipin content, modulates the partitioning kinetics of the antimicrobial molecule thymol with pH and salt. Our study reveals that membrane properties are largely conserved across the three model membranes. The molecular models and insights emerging from the present work should aid in the development of novel antimicrobials against Gram-positive strains.
Mleziva, X.; Maffeo, C.; Aksimentiev, A.
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Rotating helices have been utilized for many purposes, including the transport of solid material and fluids within man-made machines, for a little over two millennia. Here, we show that the rotation of a biological helical molecule--a DNA duplex--can move water and ions through a nanoscale pore. While the rotation-induced flow of water is generated by the steric shape of the DNA molecule, an even faster transport of cations is caused by electrostatic interactions. The rotation-induced ion flux is found to depend on the cation type, offering potential utility for ion separation. Finally, we show that the torque-driven duplex can move ions against a concentration gradient, realizing the Archimedes screw principle at the nanoscale.
van Hilten, N.; Grabe, M.
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Biological membranes contain a diverse set of membrane proteins surrounded by many different lipids, and the lateral organization and function of these molecules are closely intertwined. Here, we use coarse-grained molecular dynamics (MD) simulations to explore how hydrophobic mismatch between the length of transmembrane (TM) proteins and the thickness of the surrounding lipid membrane impacts the spatial distribution of the lipids. We constructed idealized cylindrically symmetric proteins, inspired by the Mattress Model developed in the 1980s, and simulated these model proteins in different lipid compositions. We found that unsaturated lipids were attracted to short TM proteins that thinned the membrane, while fully saturated lipids were attracted to long TM proteins that induced membrane extension. A simple mechanical description of the membrane deformation energy coupled to a lipid mixing model accurately predicted the enrichment/depletion, which was up to 33% in some cases. Our simulations also highlight that lipid sorting behavior is sensitive to protein tilt and protein surface roughness. By teasing out the fundamental physical principles in these simple models, our results provide a foundational understanding of how proteins and lipids form complex and transient assemblies, which we believe will be important for interpreting lipid-protein interactions for a host of membrane proteins that regulate cellular membranes and cell function.
Contri, A.; Francis, E. A.; Massing, A.; Rangamani, P.
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Cell shape and mechanics are intricately connected and tightly regulated by mechanochemical events including biochemical signaling, cytoskeletal remodeling, and plasma membrane mechanics. While experimental advances in microscopy have shed light on the intricate coordination involved in cell shape change in response to different cues, the ability to conduct three-dimensional simulations in realistic geometries remains an open computational challenge. In this work, we develop a finite-element framework that incorporates advection-diffusion-reaction equations coupled with equations governing the kinematics of a deformable interface representing the cell membrane. We applied this framework to three distinct coupled mechanochemical systems, each governed by geometric partial differential equations, resulting in large deformations of the interface. In all three examples, our simulations revealed the emergence of feedback between cellular signaling, cytoskeletal organization, and cell shape. In our first two sets of simulations, we observed that cell migration and neutrophil protrusion were regulated by membrane tension-mediated feedback. In our final application, we predicted shape changes of a dendritic spine starting from a realistic geometry, and found that the complex shape of the spine gives rise to localized regimes of actin cytoskeleton remodeling not previously observed with idealized geometries. Thus, our finite-element framework allows us to generate new mechanistic insights for biophysical problems.
Rios Carrasco, M.; Tambuwun, D. Y. E. L.; Ducarne, Z.; Turner, H. L.; Uslu, E.; Ward, A. B.; Boons, G.-J.; Huskens, J.; de Vries, R. P.
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The multivalent display of surface glycoprotein hemagglutinin (HA) on Influenza A viruses (IAVs) enhances the overall binding avidity to sialylated glycans on host cell surfaces. While precomplexing HA trimers with antibodies increases multivalency and avidity, this method does not replicate the virions geometry and limits insights into the multivalent binding process. Here, we use perfectly controllable icosahedral protein nanoparticles to examine the multivalent HA receptor-binding properties. We compare three HA presentation systems with varying degrees of multivalency: single HA trimers, antibody-precomplexed HA trimers, and HA trimers on nanoparticles. Our results indicate that increasing HA valency enhances binding avidity across various glycan surfaces, including erythrocytes, cells, and lipid bilayers with varying glycan densities, while maintaining receptor specificity. By combining functional and non-functional HA trimers during nanoparticle formation, we create statistical mixtures of nanoparticles with varying valencies. At high receptor densities, nanoparticles with few functional trimers still bind strongly, whereas at low receptor densities, a patch of five HA trimers appears necessary for binding. As a key finding, we observe that such a statistical mixture of nanoparticles with functional and nonfunctional HAs binds to glycan surfaces in a stronger density-dependent manner than fully functional particles. We also observe differences in binding modes that correlate with the number of functional trimers, the glycan structure (linear vs branched), and the densities achievable with these glycans. Overall, our findings demonstrate that the presentation of multivalent HA plays an enormous role in the response to glycan receptor type and density, with implications for the future design of virus monitoring, viral inhibitors, and targeting vectors.
Figueroa Blanco, D. R.; Ballesteros, A.; Delgado, J. M.; Orjuela, J. D.; Cabrera, J. E.; Hartmann, L.; Jaber, J.; Ji, K.; Knox, L.; Suesca, E.; Lopez, G.-D.; Carazzone, C.; Manrique-Moreno, M.; Miscione, G. P.; Tristram-Nagle, S.; Leidy, C.; Aponte-Santamaria, C.
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Staphyloxanthin (STX) is a carotenoid synthesized by the human pathogen Staphylococcus aureus. The golden color of this bacterium is due to this carotenoid. STX protects Staphylococcus aureus from oxidative stress by scavenging free radical species. Furthermore, STX has been shown to mechanically strengthen the Staphylococcus aureus membrane and to form microdomains that recruit antibiotic-resistance factors. Thus, inhibition of STX is a promising strategy for intervening against multidrug-resistant strains of this pathogen. However, the molecular mechanisms by which STX regulates the membrane structure and function of Staphylococcus aureus remain unclear. More specifically, the localization of STX within phosphatidylglycerol (PG) bilayers, the primary phospholipid of this bacteriums membrane, and how this localization drives macroscopic biophysical changes remain unresolved questions. Here, we addressed this issue by integrating molecular dynamics (MD) simulations, X-ray scattering experiments, and fluorescence spectroscopy. We developed an atomistic model of STX, which was validated against X-ray scattering data and which is suitable for all-atom MD simulations. We demonstrate that STX significantly increases lipid packing and acyl chain order of STX-PG bilayer mixtures. In addition, STX self-assembles into clusters, where the long and rigid conjugated triterpenoid chain interdigitates across both leaflets, modifying locally the density of the surrounding PG molecules. These findings provide a molecular explanation to the reduced headgroup spacing and core dynamics observed in fluorescence experiments and are consistent with the formation of structurally-distinct STX-enriched microdomains. Notably, STX reduces the gel-to-liquid crystalline phase transition temperature, indicating a general stabilizing effect for the fluid phase of PG lipids of varying length. Overall, our findings provide molecular insights into how STX enhances membrane mechanical integrity. It will be highly interesting to establish how the membrane remodeling effects observed here connect with STXs dual roles, acting as an antioxidant and preventing pore formation and other mechanical perturbations induced by antimicrobial molecules.
Gerbig, G.; Casadevall, A.; Raja, S.; Sonnenberg, J. L.; Wear, M. P.
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The cryptococcal polysaccharide capsule is a unique eukaryotic virulence factor that is a target for the immune system and the development of therapeutic antibodies. Our understanding of capsular architecture is limited to a few studies suggesting that metal dications play a role. In this work we explore a mechanism of cryptococcal aggregation that depends on calcium phosphate precipitation. We describe the chemical and biophysical properties of calcium interaction with the predominant cryptococcal polysaccharide, glucuronoxylomannan (GXM). We show that cell aggregation is a pH-dependent and occurs in a calcium dose-dependent manner. Furthermore, this cellular aggregation phenomenon as well as interpolymer capsular polysaccharide interactions are unique to calcium dications and do not occur with other mono- or dications as shown by size exclusion chromatography and circular dichroism. Diffusion ordered spectroscopy nuclear magnetic resonance and ab-initio calculations support complexation of calcium with glucuronic acid (GlcA). The ab-initio calculations also suggest that calcium ions can complex up to four GlcA monomers. Not only does calcium act as a scaffold for the cryptococcal capsule, interacting with up to four glucuronic acid residues of GXM, but calcium phosphate treatment of cells reduces the anti-phagocytic properties of the capsule, promoting ingestion by macrophages and altering antibody interactions with the capsule. This work advances our understanding of the cryptococcal capsule, its biophysical properties, by providing a model for the critical role of calcium interactions with capsular polymers of Cryptococcus neoformans including important impacts at the host-cell interface.
Floriach-Clark, J.; Willemsen, V.
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O_LIThe effect of some bioactive compounds on living organisms is dependent on their concentration and gradients, as is the case of hormones and signalling peptides, determining cell identity, activity and organism development. C_LIO_LIThere are a handful of methods that allow to produce spatially confined peaks of concentration local application of biochemicals on plants, such as agar blocks and microinjection, but they lack in precision, throughput and/or simplicity. C_LIO_LIWe developed the MicroTron, a microfluidics-based method specifically for filamentous organisms or life cycle stages, like the moss plant Physcomitrium patens protonemata, that serves as a platform for the application of chemicals on single cells and study the cell response. C_LIO_LIWe show how chemical applications could be performed on cells, either on the side or apically with dyes and hormones, targeting the cell wall, cell membrane, cytosol and nucleus. C_LIO_LITreatments could be applied on single filaments and with a precision of up to single cells in optimal conditions. C_LIO_LIThis method could be used to study live responses to chemicals with high spatiotemporal resolution. C_LI
Caira, T.; Tokihiro, J.; Shaposhnikov, A.; Whitten, J. M.; Su, X.; Shin, A.; Robertson, I. H.; Nicholson, T. M.; Olanrewaju, A. O.; Berthier, E.; Theberge, A. B.; Berthier, J.
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Control of fluids is a hallmark of microfluidic systems and fundamental for the successful application of microfluidic devices. Trigger valves use geometric features to autonomously control the release of fluids in microfluidic devices. Our previous work has adapted geometries used in closed trigger valve systems to enable use in open systems, allowing for open microfluidic devices with up to three trigger valves. Here, we focus on the parallel co-flows produced by sequential release of trigger valves and present a model that predicts their layer widths as a function of the geometric characteristics of the different side channels of each trigger valve. We show layered co-flows with widths as low as 50 microns. Additionally, we expand the use of trigger valves in open microfluidic devices by incorporating 1) varied step heights, 2) devices with up to seven trigger valves, and 3) use of varied fluids and plastics. To validate the implementation and use of these trigger valves in open systems, we have developed a theoretical framework to compare predicted outcomes (i.e., fluid travel distance, velocity, and layering width) with our experimental values. This theoretical work offers applications in various fields, including hydrogel patterning for 3D cell culture, organ-on-a-chip models, at-home sample preparation, and autonomous microfluidic systems for biosensing.
Baugh, N. J.; Huang, M. S.; de Paiva Narciso, N.; Bunch, J. A.; Williams, J. M.; Liu, Y.; Onsongo, R.; Kilian, D.; Navarro, R. S.; Heilshorn, S. C.
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Control over network dynamics at different length scales is a feature of natural materials challenging to replicate in synthetic hydrogels. Hydrogel viscoelasticity is commonly controlled by tuning the kinetics of reversible crosslinks; however, this strategy inherently links the resulting macroscale and nanoscale dynamics of the individual network components. Taking inspiration from biological materials that feature lipids as structural elements, we introduce Lipid Network Crosslinked (LINC) hydrogels that exploit the mobility of individual lipids within self-assembled liposomes as covalent, network-crosslinking points. These mobile, covalent crosslinks increase hydrogel stress relaxation rates over 20-fold compared to polymer-only hydrogels with equivalent crosslinking chemistries and stiffnesses. We demonstrate that liposome design parameters, including degree of surface functionalization and tail saturation, provide a means to independently control the macroscale storage moduli and stress relaxation behavior. Finally, as an application where control over network dynamics at different length scales is critical, we placed cell-adhesive ligands onto more mobile or less mobile network elements. Human neural progenitor cells cultured within LINC hydrogels of identical macroscale viscoelasticity significantly altered their phenotype in response to nanoscale ligand dynamics. These results establish LINC hydrogels as biomimetic materials that leverage nanoscale lipid mobility within a macroscale polymeric network to control dynamics at multiple length scales.
Li, T.;He, J.;Qian, J.;Wang, Y.;Sun, J.;Hu, D.
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Silk proteins, including sericin and fibroin, are natural biopolymers with broad applications in tissue engineering where angiogenesis plays an essential role. However, the pro-angiogenic effects of silk proteins with varying molecular weights (MWs) remain poorly understood. Here, silk proteins with MW distributions at 40-180 kDa or less than 25 kDa were obtained through alkaline hydrolysis to evaluate their effects on angiogenesis. Structurally, reducing MW induced a conformational transition in silk proteins, accompanied by a striking morphological shift in sericin from nanofibers to nanoparticles. Functionally, high-MW sericin (SSH) suppressed, whereas low-MW sericin (SSL) and both high- and low-MW silk fibroin (SFH/SFL) directly promoted endothelial angiogenic activity. Transcriptomic analysis revealed that angiogenesis-related genes such as Id1 and Smad6/9 may underlie the angiostatic effects of SSH. Notably, both SSH and SSL enhanced angiogenesis indirectly via macrophages; however, SSH induced mixed M1/M2-like polarization, while SSL preferentially drove an M2-like phenotype. In a subcutaneous implantation model, SSH promoted angiogenesis but yielded vessels with weak integrity and increased fibrosis, whereas SSL enhanced angiogenesis with improved vascular maturity and reduced fibrotic response. These findings elucidate how the MWs of silk proteins shape angiogenic behavior and highlight the importance of MW tailoring for optimized tissue engineering applications.
Nath, A. D.; Leclerc, E.; Vetter, S. W.
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The extracellular matrix (ECM) is a complex network of ubiquitously present acellular material that plays a critical role in cell proliferation, migration, invasion, and tissue morphogenesis. Non-enzymatic glycation of ECM modifies the structure and function of ECM proteins and can support a pro-inflammatory milieu in the tumor microenvironment. However, the impact of glycated ECM on cancer cell growth remains underexplored despite its importance in facilitating disease progression. Here, we investigate the effect of ECM glycation on cancer cell morphology and migration behavior. We used methylglyoxal (MG) as a glycation agent and collagen as our ECM model protein. For in vitro growth analysis, breast cancer cells were seeded on growth surfaces coated with both non-glycated and glycated collagen. Cell behavior was monitored for 24 hours using a real-time holographic imaging system. Holographic image analysis revealed significant differences between non-glycated and glycated growth substrates in cell spreading area, eccentricity, perimeter length, optical thickness, and optical volume, as well as cell migration and motility, which directly influence cell adhesion and proliferation. These changes were found to be cell line biased. Overall, our findings suggest that ECM glycation has a significant effect on cell morphology, migration and cell growth. Holographic live cell imaging was determined to be an excellent method to monitor cells without the need for any labeling and with minimal perturbations.