Explore the vast range of titles available.

Active matter consists of units that generate mechanical work by consuming energy 1 . Examples include living systems (such as assemblies of bacteria 2 – 5 and biological tissues 6 , 7 ), biopolymers driven by molecular motors 8 – 11 and suspensions of synthetic self-propelled particles 12 – 14 . A central goal is to understand and control the self-organization of active assemblies in space and time. Most active systems exhibit either spatial order mediated by interactions that coordinate the spatial structure and the motion of active agents 12 , 14 , 15 or the temporal synchronization of individual oscillatory dynamics 2 . The simultaneous control of spatial and temporal organization is more challenging and generally requires complex interactions, such as reaction–diffusion hierarchies 16 or genetically engineered cellular circuits 2 . Here we report a simple technique to simultaneously control the spatial and temporal self-organization of bacterial active matter. We confine dense active suspensions of Escherichia coli cells and manipulate a single macroscopic parameter—namely, the viscoelasticity of the suspending fluid— through the addition of purified genomic DNA. This reveals self-driven spatial and temporal organization in the form of a millimetre-scale rotating vortex with periodically oscillating global chirality of tunable frequency, reminiscent of a torsional pendulum. By combining experiments with an active-matter model, we explain this behaviour in terms of the interplay between active forcing and viscoelastic stress relaxation. Our findings provide insight into the influence of bacterial motile behaviour in complex fluids, which may be of interest in health- and ecology-related research, and demonstrate experimentally that rheological properties can be harnessed to control active-matter flows 17 , 18 . We envisage that our millimetre-scale, tunable, self-oscillating bacterial vortex may be coupled to actuation systems to act a ‘clock generator’ capable of providing timing signals for rhythmic locomotion of soft robots and for programmed microfluidic pumping 19 , for example, by triggering the action of a shift register in soft-robotic logic devices 20 . Introducing viscoelasticity by addition of DNA into the fluid surrounding a suspension of Escherichia coli produces a giant oscillating vortex with a period controllable through the DNA concentration.

Background There is emerging evidence for enhanced blood coagulation in coronavirus 2019 (COVID-19) patients, with thromboembolic complications contributing to morbidity and mortality. The mechanisms underlying this prothrombotic state remain enigmatic. Further data to guide anticoagulation strategies are urgently required. Methods We used viscoelastic rotational thromboelastometry (ROTEM) in a single-center cohort of 40 critically ill COVID-19 patients. Results Clear signs of a hypercoagulable state due to severe hypofibrinolysis were found. Maximum lysis, especially following stimulation of the extrinsic coagulation system, was inversely associated with an enhanced risk of thromboembolic complications. Combining values for maximum lysis with D-dimer concentrations revealed high sensitivity and specificity of thromboembolic risk prediction. Conclusions The study identifies a reduction in fibrinolysis as an important mechanism in COVID-19-associated coagulopathy. The combination of ROTEM and D-dimer concentrations may prove valuable in identifying patients requiring higher intensity anticoagulation.

Severe corneal injuries often result in permanent vision loss and remain a clinical challenge. Human bone marrow‐derived mesenchymal stem cells (MSCs) and their secreted factors (secretome) have been studied for their antiscarring, anti‐inflammatory, and antiangiogeneic properties. We aimed to deliver lyophilized MSC secretome (MSC‐S) within a viscoelastic gel composed of hyaluronic acid (HA) and chondroitin sulfate (CS) as a way to enhance corneal re‐epithelialization and reduce complications after mechanical and chemical injuries of the cornea. We hypothesized that delivering MSC‐S within HA/CS would have improved wound healing effects compared the with either MSC‐S or HA/CS alone. The results showed that a once‐daily application of MSC‐S in HA/CS enhances epithelial cell proliferation and wound healing after injury to the cornea. It also reduced scar formation, neovascularization, and hemorrhage after alkaline corneal burns. We found that combining MSC‐S and HA/CS increased the expression of CD44 receptors colocalized with HA, suggesting that the observed therapeutic effects between the MSC‐S and HA/CS are in part mediated by CD44 receptor upregulation and activation by HA. The results from this study demonstrate a reproducible and efficient approach for delivering the MSC‐S to the ocular surface for treatment of severe corneal injuries. Stem Cells Translational Medicine 2019;8:478–489 Once daily secretome treatment in hyaluronic acid and chondroitin sulfate can enhance corneal wound healing and preserve cornea transparency.

Preparation and evaluation of new polyurethane membranes for wound dressing application was considered in this work. The membranes were prepared through amine curing reaction of epoxy-terminated polyurethane prepolymers and an antibacterial epoxy-functional quaternary ammonium compound (glycidyltriehtylammonium chloride, GTEACl. To render the prepared membranes to be highly absorptive of wound exudates, poly (ethylene glycol) polyols were introduced into the polyurethane networks. Evaluation of biocompatibity via both MTT assay and direct contact with two different cell lines (fibroblast and epidermal keratinocytes) reveled that membranes with appropriate loading of GTEACl showed proper biocompatibility. Promising antibacterial activity of the prepared membranes against Staphylococcus aureus and Escherichia coli bacteria was confirmed by both agar diffusion and shaking flask methods. The membranes with balanced crosslink density and ionic groups’ concentration possessed appropriate hydrophilicity and water vapor transmission rate; therefore, they could prevent the accumulation of exudates and decrease the surface inflammation in the wounded area.

A new method of obtaining functional foam material has been proposed. The materials were created by mixing the poly lactic acid (PLA) solution in chloroform, chitosan (CS) dissolved in water saturated with CO and polyethylene glycol (PEG), and freeze-dried for removal of the solvents. The composite foams were characterized for their structural (SEM, FT-IR, density, porosity), thermal (DSC), functional (hardness, elasticity, swelling capacity, solubility), and biological (antimicrobial and cytotoxic) properties. Chitosan in the composites was a component for obtaining their foamed form with 7.4 to 22.7 times lower density compared to the neat PLA and high porosity also confirmed by the SEM. The foams had a hardness in the range of 70-440 kPa. The FT-IR analysis confirmed no new chemical bonds between the sponge ingredients. Other results showed low sorption capacity (2.5-7.2 g/g) and solubility of materials (less than 0.2%). The obtained foams had the lower T value and improved ability of crystallization compared to neat PLA. The addition of chitosan provides the bacteriostatic and bactericidal properties against and . Biocompatibility studies have shown that the materials obtained are not cytotoxic to the L929 cell line.

Background Sodium alginate is currently used in medical products, including drugs and cosmetic materials. It can also be used as a submucosal injection material due to its excellent water retention ability. Alginate with a high water retention ability is called alginate hydrogel (AH). The aim of this study was to investigate the usefulness of AH as a submucosal injection material. Methods To investigate the optimal viscosity of AH as a submucosal injection material, we observed the changes in submucosal height from the initial submucosal height in the stomachs of six miniature pigs for each injection material tested (0.3 % AH, 0.5 % hyaluronic acid, glycerol). All submucosal heights were compared serially over time (3, 5, 10, 20, and 30 min). Both immediate and 1-week delayed tissue reactions were investigated endoscopically in the same living pigs. Histological analyses were performed after the animals had been sacrificed. Results In a preliminary study, we determined that 0.3 % sodium alginate mixed with BaCl 2 (400 μl) was the optimal viscosity of AH as an injection material. Our comparison of submucosal height changes over time showed that there was a significant decrease in submucosal height just 3 min following the injection of hyaluronic acid and glycerol, but that following the injection of AH a significant decrease in submucosal height was observed only after 10 min ( p  < 0.05). The histological analyses revealed that there were mild capillary dilations with congestion and mild fibrotic changes with some lymphocytic infiltration at the AH injection site. Conclusion Alginate hydrogel demonstrated long-lasting maintenance of submucosal elevation, safety, and cost-effectiveness in a pig model, which makes it a potential alternative to hyaluronic acid.

Living tissues are non-linearly elastic materials that exhibit viscoelasticity and plasticity. Man-made, implantable bioelectronic arrays mainly rely on rigid or elastic encapsulation materials and stiff films of ductile metals that can be manipulated with microscopic precision to offer reliable electrical properties. In this study, we have engineered a surface microelectrode array that replaces the traditional encapsulation and conductive components with viscoelastic materials. Our array overcomes previous limitations in matching the stiffness and relaxation behaviour of soft biological tissues by using hydrogels as the outer layers. We have introduced a hydrogel-based conductor made from an ionically conductive alginate matrix enhanced with carbon nanomaterials, which provide electrical percolation even at low loading fractions. Our combination of conducting and insulating viscoelastic materials, with top-down manufacturing, allows for the fabrication of electrode arrays compatible with standard electrophysiology platforms. Our arrays intimately conform to the convoluted surface of the heart or brain cortex and offer promising bioengineering applications for recording and stimulation. Bioelectronic interfacing with living tissues should match the biomechanical properties of biological materials to reduce damage to the tissues. Here, the authors present a fully viscoelastic microelectrode array composed of an alginate matrix and carbon-based nanomaterials encapsulated in a viscoelastic hydrogel for electrical stimulation and signal recording of heart and brain activities in vivo.

Substantial research over the past two decades has established that extracellular matrix (ECM) elasticity, or stiffness, affects fundamental cellular processes, including spreading, growth, proliferation, migration, differentiation and organoid formation. Linearly elastic polyacrylamide hydrogels and polydimethylsiloxane (PDMS) elastomers coated with ECM proteins are widely used to assess the role of stiffness, and results from such experiments are often assumed to reproduce the effect of the mechanical environment experienced by cells in vivo. However, tissues and ECMs are not linearly elastic materials—they exhibit far more complex mechanical behaviours, including viscoelasticity (a time-dependent response to loading or deformation), as well as mechanical plasticity and nonlinear elasticity. Here we review the complex mechanical behaviours of tissues and ECMs, discuss the effect of ECM viscoelasticity on cells, and describe the potential use of viscoelastic biomaterials in regenerative medicine. Recent work has revealed that matrix viscoelasticity regulates these same fundamental cell processes, and can promote behaviours that are not observed with elastic hydrogels in both two- and three-dimensional culture microenvironments. These findings have provided insights into cell–matrix interactions and how these interactions differentially modulate mechano-sensitive molecular pathways in cells. Moreover, these results suggest design guidelines for the next generation of biomaterials, with the goal of matching tissue and ECM mechanics for in vitro tissue models and applications in regenerative medicine. This Review explores the role of viscoelasticity of tissues and extracellular matrices in cell–matrix interactions and mechanotransduction and the potential utility of viscoelastic biomaterials in regenerative medicine.

Purpose To compare two ophthalmic viscosurgical devices (OVDs), DisCoVisc (viscous dispersive) and Healon5 (viscoadaptive), in terms of their overall clinical performance during phacoemulsification and intraocular lens (IOL) implantation. Methods In 323 patients (DisCoVisc; 157, Healon5; 166), the surgeons evaluated on a three-point scale, the maintenance of anterior chamber (AC) during continuous curvilinear capsulorhexis (CCC), maintenance of AC during IOL implantation, retention during phacoemulsification, ease of injection, facilitation of CCC, transparency during surgery, and ease of removal from the eye. The time needed to completely remove OVDs after IOL implantation was measured. Masked examiners measured intraocular pressure (IOP), corneal thickness, and corneal endothelial cell count up to 90 days postoperatively. Results DisCoVisc was assessed to be significantly better than Healon5 in maintenance of AC during CCC ( P =0.0008, Cochran–Mantel–Haenszel test) and IOL implantation ( P =0.0055), retention during phacoemulsification ( P =0.0009), ease of injection ( P <0.0001), facilitation of CCC ( P <0.0001), transparency ( P <0.0001), and ease of removal ( P <0.0001). The washout time was 29.6±13.4 and 36.2±17.5 s in the DisCoVisc and Healon5 groups, respectively ( P =0.0002, unpaired t -test). The mean endothelial cell loss was 1.8±8.7% in the DisCoVisc group and 3.8±8.3% in the Healon5 group ( P =0.0358). There were no statistically significant between-group differences in IOP and corneal thickness. Conclusion DisCoVisc was better retained in the eye during phacoemulsification and was easier to remove after IOL implantation. The corneal endothelial cell loss was significantly less with DisCoVisc than with Healon5. It was indicated that the whole surgical process can be efficiently covered by DisCoVisc alone.

Membrane invagination and vesicle formation are key steps in endocytosis and cellular trafficking. Here, we show that endocytic coat proteins with prion-like domains (PLDs) form hemispherical puncta in the budding yeast, Saccharomyces cerevisiae. These puncta have the hallmarks of biomolecular condensates and organize proteins at the membrane for actin-dependent endocytosis. They also enable membrane remodeling to drive actin-independent endocytosis. The puncta, which we refer to as endocytic condensates, form and dissolve reversibly in response to changes in temperature and solution conditions. We find that endocytic condensates are organized around dynamic protein–protein interaction networks, which involve interactions among PLDs with high glutamine contents. The endocytic coat protein Sla1 is at the hub of the protein–protein interaction network. Using active rheology, we inferred the material properties of endocytic condensates. These experiments show that endocytic condensates are akin to viscoelastic materials. We use these characterizations to estimate the interfacial tension between endocytic condensates and their surroundings. We then adapt the physics of contact mechanics, specifically modifications of Hertz theory, to develop a quantitative framework for describing how interfacial tensions among condensates, the membrane, and the cytosol can deform the plasma membrane to enable actin-independent endocytosis.