Self-assembly is a process in which interacting bodies are autonomously driven into ordered structures. Static structures such as crystals often form through simple energy minimization, whereas ...dynamic ones require continuous energy input to grow and sustain. Dynamic systems are ubiquitous in nature and biology but have proven challenging to understand and engineer. Here, we bridge the gap from static to dynamic self-assembly by introducing a model system based on ferrofluid droplets on superhydrophobic surfaces. The droplets self-assemble under a static external magnetic field into simple patterns that can be switched to complicated dynamic dissipative structures by applying a time-varying magnetic field. The transition between the static and dynamic patterns involves kinetic trapping and shows complexity that can be directly visualized.
Lubricated surfaces have shown promise in numerous applications where impinging foreign droplets must be removed easily; however, before they can be widely adopted, the problem of lubricant ...depletion, which eventually leads to decreased performance, must be solved. Despite recent progress, a quantitative mechanistic explanation for lubricant depletion is still lacking. Here, we first explain the shape of a droplet on a lubricated surface by balancing the Laplace pressures across interfaces. We then show that the lubricant film thicknesses beneath, behind, and wrapping around a moving droplet change dynamically with the droplet’s speed—analogous to the classical Landau-Levich-Derjaguin problem. The interconnected lubricant dynamics results in the growth of the wetting ridge around the droplet, which is the dominant source of lubricant depletion. We then develop an analytic expression for the maximum amount of lubricant that can be depleted by a single droplet. Counterintuitively, faster-moving droplets subjected to higher driving forces deplete less lubricant than their slower-moving counterparts. The insights developed in this work will inform future work and the design of longer-lasting lubricated surfaces.
We study the fusion of homogeneous cell aggregates and of hybrid aggregates combining cells and microparticles. In all cases, we find that the contact area does not vary linearly over time, as ...observed for liquid drops, but rather it follows a power law in
. This result is interpreted by generalizing the fusion model of soft viscoelastic solid balls to viscoelastic liquid balls, akin to jelly pearls. We also explore the asymmetric fusion between a homogeneous aggregate and a hybrid aggregate. This latter experiment allows the determination of the self-diffusion coefficient of the cells in a tissue by following the spatial distribution of internalized particles in the cells.
Abstract
Phase separation is a universal physical transition process whereby a homogeneous mixture splits into two distinct compartments that are driven by the component activity, elasticity, or ...compositions. In the current work, we develop a series of heterogeneous colloidal suspensions that exhibit both liquid-liquid phase separation of semiflexible binary polymers and liquid crystal phase separation of rigid, rod-like nanocellulose particles. The phase behavior of the multicomponent mixture is controlled by the trade-off between thermodynamics and kinetics during the two transition processes, displaying cholesteric self-assembly of nanocellulose within or across the compartmented aqueous phases. Upon thermodynamic control, two-, three-, and four-phase coexistence behaviors with rich liquid crystal stackings are realized. Among which, each relevant multiphase separation kinetics shows fundamentally different paths governed by nucleation and growth of polymer droplets and nanocellulose tactoids. Furthermore, a coupled multiphase transition can be realized by tuning the composition and the equilibrium temperature, which results in thermotropic behavior of polymers within a lyotropic liquid crystal matrix. Finally, upon drying, the multicomponent mixture undergoes a hierarchical self-assembly of nanocellulose and polymers into stratified cholesteric films, exhibiting compartmentalized polymer distribution and anisotropic microporous structure.
Renewable high‐performance macroscopic functional fibers are prepared by a simple wet‐extrusion and coagulation process of hydrogels of native cellulose nanofibrils. The fibers are functionalized to ...be transparent, conducting, or magnetic and they can host and release guests as payloads. These biobased macrofibers provide a sustainable approach for high‐performance and functional fiber technology in 21st century technologies.
The generation of highly reactive oxygen species (ROS) at room temperature for application in organic synthesis and wastewater treatment represents a great challenge of the current chemical industry. ...In fact, the development of biodegradable scaffolds to support ROS‐generating active sites is an important prerequisite for the production of environmentally benign catalysts. Herein, the electrostatic cocrystallization of a cationic phthalocyanine (Pc) and negatively charged tobacco mosaic virus (TMV) is described, together with the capacity of the resulting crystals to photogenerate ROS. To this end, a novel peripherally crowded zinc Pc (1) is synthesized. With 16 positive charges, this photosensitizer shows no aqueous aggregation, and is able to act as a molecular glue in the unidimensional assembly of TMV. A step‐wise decrease of ionic strength in mixtures of both components results in exceptionally long fibers, constituted by hexagonally bundled viruses thoroughly characterized by electron and confocal microscopy. The fibers are able to produce ROS in a proof‐of‐concept microfluidic device, where they are immobilized and irradiated in several cycles, showing a resilient performance. The bottom‐up approach also enables the light‐triggered disassembly of fibers after use. This work represents an important example of a biohybrid material with projected application in light‐mediated heterogeneous catalysis.
Light‐mediated oxidation in heterogeneous catalysis represents a desirable goal for several technologies. The synthesis of a sterically hindered phthalocyanine with maintained properties in aqueous media is presented. This photosensitizer triggers the assembly of tobacco mosaic virus into hexagonal lattices that bundle into high‐aspect‐ratio fibers with the generation of reactive oxygen species (ROS). The applicability of the fibers as heterogeneous catalysts is demonstrated in a proof‐of‐concept device.
Mechanical forces in the cell's natural environment have a crucial impact on growth, differentiation and behaviour. Few areas of biology can be understood without taking into account how both ...individual cells and cell networks sense and transduce physical stresses. However, the field is currently held back by the limitations of the available methods to apply physiologically relevant stress profiles on cells, particularly with sub-cellular resolution, in controlled in vitro experiments. Here we report a new type of active cell culture material that allows highly localized, directional and reversible deformation of the cell growth substrate, with control at scales ranging from the entire surface to the subcellular, and response times on the order of seconds. These capabilities are not matched by any other method, and this versatile material has the potential to bridge the performance gap between the existing single cell micro-manipulation and 2D cell sheet mechanical stimulation techniques.
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