No abstract

Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena such as anti-reflective structures and contact time of impacting droplets, the effect of the detailed convex topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared to superhydrophobic surfaces. We envision that our fundamental understanding and innovative design of bumps can be applied to lead enhanced performance in various phase change applications including water harvesting.

Materials that adapt dynamically to environmental changes are currently limited to two-state switching of single properties, and only a small number of strategies that may lead to materials with continuously adjustable characteristics have been reported 1-3 . Here we introduce adaptive surfaces made of a liquid film supported by a nanoporous elastic substrate. As the substrate deforms, the liquid flows within the pores causing the smooth and defect-free surface to roughen through a continuous range of topographies. We show that a graded mechanical stimulus can be directly translated into finely tuned, dynamic adjustments of optical transparency and wettability. In particular, we demonstrate simultaneous control of the film's transparency and its ability to continuously manipulate various low-surface-tension droplets from free-sliding to pinned. This strategy should make possible the rational design of tunable, multifunctional adaptive materials for a broad range of applications.

Living organisms make extensive use of micro-and nanometer-sized pores as gatekeepers for controlling the movement of fluids, vapors and solids between complex environments. The ability of such pores to coordinate multiphase transport, in a highly selective and subtly triggered fashion and without clogging, has inspired interest in synthetic gated pores for applications ranging from fluid processing to 3D printing and labon-chip systems 1,2,3,4,5,6,7,8,9,10 . But although specific gating and transport behaviors have been realized by precisely tailoring pore surface chemistries and pore geometries 6,11-17 , a single system capable of selectively handling and controlling complex multiphase transport has remained a distant prospect, and fouling is nearly inevitable 11,12 . Here, we introduce a gating mechanism that uses a capillary-stabilized fluid to seal pores in the closed state, and reversibly and rapidly reconfigures it under pressure to create a non-fouling, fluid-lined pore in the open state. Theoretical modeling and experiments demonstrate that for each transport substance, the gating threshold -the pressure needed to open pores -can be rationally tuned over a wide pressure range. This allows us to realize in one system differential response profiles for a variety of liquids and gases, even letting liquids flow through the pore while preventing gas escape. These capabilities allow us to dynamically modulate gas/liquid sorting in a microfluidic flow and to separate a three-phase air/water/oil mixture, with the fluid lining ensuring sustained antifouling behavior. Because the liquid gating strategy enables efficient long-term operation and can be applied to a variety of pore structures, membrane materials and micro-as well as macro-scale fluid systems, we expect it to prove useful in a wide range of applications.Our hypothesis that a liquid-filled pore could provide a unified gating strategy derives from the idea that a liquid stabilized inside a micropore offers a unique combination of dynamic and interfacial behaviors, and is inspired by nature's use of fluids as reconfigurable gates. Microscale stomata and xylem control air, water, and microbe exchange in plants by using fluid to mechanically reconfigure the pore 18 . The nuclear pore is directly lined with disordered fluidlike proteins that have been proposed not only to regulate differential transport of a wide range of cargos, but also to completely prevent fouling 19 . Most interestingly, micropores between air sacs in the lung are filled with liquid that has been proposed to reversibly reconfigure into an open, fluid-lined pore in response to pressure gradients 20 . Figure 1 contrasts the gating mechanisms in a traditional and in a liquid-filled pore. In the case of traditional nano/micropores (Fig.1a), gases will flow through passively regardless of 2 pore shape and surface chemistry, while liquids will enter the pore once the applied pressure reaches a critical value dictated by the balance of surface interactions, pore geometry and surface tension....

Single sentence summary: We rationally create arbitrarily sculpted complex hierarchical carbonate/silica microstructures in a reaction-diffusion system.

Approaches for regulated fluid secretion, which typically rely on fluid encapsulation and release from a shelled compartment, do not usually allow for a fine, continuous modulation of secretion, and can be difficult to adapt for monitoring or functionintegration purposes. 1-5 Here, we report self-regulated, self-reporting secretion systems consisting of liquid-storage compartments in a supramolecular polymer-gel matrix with a thin liquid layer on top, and demonstrate that dynamic liquid exchange between the compartments, matrix and surface layer allows for repeated, responsive self-lubrication of the surface layer and for cooperative healing of the matrix. Depletion of the surface liquid or local material damage induces self-regulated secretion of the stored liquid via a dynamic feedback between polymer crosslinking, droplet shrinkage and liquid transport that can be read out through changes in the system's optical transparency. We envision diverse applications in fluid delivery, wetting and adhesion control, and material self-repair.Nearly every form of living tissue autonomously packages, transports, and secretes fluids, mediating defense, adhesion, wound healing, temperature -often several of these at once -through tightly self-regulated release systems. [6][7][8][9] Fundamental to these systems, fluid storage is itself an active, finely regulated balance. Storage droplets or vesicles continuously adjust their size, shape and contents through ongoing exchange with the surroundings, creating intrinsically responsive control mechanisms that tie secretion to a wide range of chemical and physical stimuli and feedback signals. [10][11][12][13] At the same time, collective changes in the stores are reported to the organism, alerting it that it needs to drink or eat to replenish the limited supply. Many synthetic approaches have been developed to enable triggered release from microcapsules, hydrogels, nanoparticles, vesicles, micelles, mesoporous carriers and other containers. [1][2][3][4][5][14][15][16][17] While these systems can secrete fluid in response to various stimuli, it remains a challenge to design a synthetic approach that displays finely tuned, continuous self-adjustment, integrated functionalities, and continuous liquid supply monitoring.2 Figure 1. Schematic of the self-regulated, liquid secretion system. Secretion liquid is stored as shell-less droplets inside a gel matrix composed of dynamic polymers, with ongoing liquid exchange between droplet and gel phases. If S = γ ga -(γ la + γ gl ) > 0, the matrix surface will be coated with a thin liquid overlayer. When this layer is removed, the disjoining pressure will trigger secretion of the stored liquid to restore the original film thickness, while the supramolecular gel matrix reconfigures through reversible bond disassembly and reassembly to release any buildup of mechanical stress due to shrinking droplets. With successive removal/restoring cycles, the liquid droplets will continuously shrink and the gel will become progressively transparent.Inspire...

The development of new technologies is key to the continued improvement of medicine, relying on comprehensive materials design strategies that can integrate advanced therapeutic and diagnostic functions with a variety of surface properties such as selective adhesion, dynamic responsiveness, and optical/mechanical tunability. Liquid-infused surfaces have recently come to the forefront as a unique approach to surface coatings that can resist adhesion of a wide range of contaminants on medical devices. Furthermore, these surfaces are proving highly versatile in enabling the integration of established medical surface treatments alongside the antifouling capabilities, such as drug release or biomolecule organization. Here, the range of research being conducted on liquid-infused surfaces for medical applications is presented, from an understanding of the basics behind the interactions of physiological fluids, microbes, and mammalian cells with liquid layers to current applications of these materials in point-of-care diagnostics, medical tubing, instruments, implants, and tissue engineering. Throughout this exploration, the design parameters of liquid-infused surfaces and how they can be adapted and tuned to particular applications are discussed, while identifying how the range of controllable factors offered by liquid-infused surfaces can be used to enable completely new and dynamic approaches to materials and devices for human health.

Developing adaptive materials with geometries that change in response to external stimuli provides fundamental insights into the links between the physical forces involved and the resultant morphologies and creates a foundation for technologically relevant dynamic systems. In particular, reconfigurable surface topography as a means to control interfacial properties has recently been explored using responsive gels, shape-memory polymers, liquid crystals and hybrid composites, including magnetically active slippery surfaces. However, these designs exhibit a limited range of topographical changes and thus a restricted scope of function. Here we introduce a hierarchical magneto-responsive composite surface, made by infiltrating a ferrofluid into a microstructured matrix (termed ferrofluid-containing liquid-infused porous surfaces, or FLIPS). We demonstrate various topographical reconfigurations at multiple length scales and a broad range of associated emergent behaviours. An applied magnetic-field gradient induces the movement of magnetic nanoparticles suspended in the ferrofluid, which leads to microscale flow of the ferrofluid first above and then within the microstructured surface. This redistribution changes the initially smooth surface of the ferrofluid (which is immobilized by the porous matrix through capillary forces) into various multiscale hierarchical topographies shaped by the size, arrangement and orientation of the confining microstructures in the magnetic field. We analyse the spatial and temporal dynamics of these reconfigurations theoretically and experimentally as a function of the balance between capillary and magnetic pressures and of the geometric anisotropy of the FLIPS system. Several interesting functions at three different length scales are demonstrated: self-assembly of colloidal particles at the micrometre scale; regulated flow of liquid droplets at the millimetre scale; and switchable adhesion and friction, liquid pumping and removal of biofilms at the centimetre scale. We envision that FLIPS could be used as part of integrated control systems for the manipulation and transport of matter, thermal management, microfluidics and fouling-release materials.