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Driven by the growing threat of antimicrobial resistance, the design of intrinsically bactericidal surfaces has been gaining significant attention. Proposed surface topography designs are often inspired by naturally occurring nanopatterns on insect wings that mechanically damage bacteria via membrane deformation. The stability of and the absence of chemicals in such surfaces support their facile and sustainable employment in avoiding surface-born pathogen transmission. Recently, the deflection of controllably nanofabricated pillar arrays has been shown to strongly affect bactericidal activity, with the limits of mechanical effectiveness of such structures remaining largely unexplored. Here, we examine the limits of softer, commonly used polymeric materials and investigate the interplay between pillar nanostructure sizing and flexibility for effective antibacterial functionality. A facile, scalable, UV nanoimprint lithography method was used to fabricate nanopillar array topographies of variable sizes and flexibilities. It was found that bacterial death on nanopillars in the range of diameters ≤100 nm and Young's moduli ≥1.3 GPa is increased by 3.5- to 5.6-fold, while thicker or softer pillars did not reduce bacterial viability. To further support our findings, we performed a finite element analysis of pillar deformation. It revealed that differences in the amount of stress exerted on bacterial membranes, generated from the stored elastic energy in flexible pillars, contribute to the observed bactericidal performance.

Mammalian cells respond to tactile cues from topographic elements presented by the substrate. Among these, anisotropic features distributed in an ordered manner give directionality. In the extracellular matrix, this ordering is embedded in a noisy environment altering the contact guidance effect. To date, it is unclear how cells respond to topographical signals in a noisy environment. Here, using rationally designed substrates, we report morphotaxis, a guidance mechanism enabling fibroblasts and epithelial cells to move along gradients of topographic order distortion. Isolated cells and cell ensembles perform morphotaxis in response to gradients of different strength and directionality, with mature epithelia integrating variations of topographic order over hundreds of micrometers. The level of topographic order controls cell cycle progression, locally delaying or promoting cell proliferation. In mature epithelia, the combination of morphotaxis and noise-dependent distributed proliferation provides a strategy to enhance wound healing as confirmed by a mathematical model capturing key elements of the process., Science Advances, 9 (14), ISSN:2375-2548

Superhydrophobic nanostructured surfaces can enhance water condensation efficiency by facilitating droplet departure via coalescence-induced jumping. However, condensed droplets tend to transit from a mobile jumping mode to a highly pinned state at high condensation heat flux because excessive water nucleates within the nanostructures and anchors the condensed droplets. The large pinned droplets act as a thermal barrier and insulate the cooling surface, thus severely degrading its heat transfer efficiency. This work developed a nanohierarchical structured surface by growing branched TiO₂ nanorod arrays to prevent condensation-induced droplet pinning. After hydrophobization, the nano-hierarchical structure can spontaneously push the water out of nanostructures with an outward Laplace capillary pressure gradient when the droplet size is only at the nanoscale level. This effective de-wetting process maintains the high droplet mobility on the nano-hierarchical surface over a wide subcooling range, resulting in an up to ~ 90 % increase in heat transfer coefficient at a high heat flux of 132 kW•m⁻² compared to the single-tier nanorod surface. Our investigation of how the nanohierarchical structures fundamentally suppress the condensation-induced wetting on superhydrophobic surfaces represents a significant advance in understanding multiphase wetting phenomena and paves the way for the rational design of cooling surfaces. ISSN:0300-9467 ISSN:1385-8947 ISSN:1873-3212 ISSN:0923-0467

Counteracting surface fogging to maintain surface transparency is important for a variety of applications including eyewear, windows and displays. Energy-neutral, passive approaches predominantly rely on engineering the surface wettability, but suffer from non-uniformity, contaminant deposition and lack of robustness, all of which substantially degrade durability and performance. Here, guided by nucleation thermodynamics, we design a transparent, sunlight-activated, photothermal coating to inhibit fogging. The metamaterial coating contains a nanoscopically thin percolating gold layer and is most absorptive in the near-infrared range, where half of the sunlight energy resides, thus maintaining visible transparency. The photoinduced heating effect enables sustained and superior fog prevention (4-fold improvement) and removal (3-fold improvement) compared with uncoated samples, and overall impressive performance, indoors and outdoors, even under cloudy conditions. The extreme thinness (~10 nm) of the coating—which can be produced by standard, readily scalable fabrication processes—enables integration beneath other coatings, rendering it durable even on highly compliant substrates., Nature Nanotechnology, 18 (2), ISSN:1748-3387, ISSN:1748-3395

The global challenge of clean water scarcity needs to be confronted with novel sustainable, climate neutral solutions, over the entire spectrum of possible clean water availability. Atmospheric moisture represents a major untapped resource that can be harvested by sorbents, enabling water production in dry inland regions where it is needed. While benefiting from the utilization of an important renewable energy source, solar-driven, sorbent-based atmospheric water harvesting systems are inseparably based on a single water harvesting cycle per day, which severely limits the daily water productivity and the competitiveness of this very promising technology. Here, we rationally design an atmospheric water harvesting strategy, using durable hydrogel sorbents, that operates with sorption “ratcheting” ─ a large sequence of rapid adsorption and subsequent desorption steps ─ activated by direct sunlight. Employing theoretical considerations, we tailor the ratcheting timescales to the inherent sorption properties of the hydrogels, optimally exploiting their natural harvesting capabilities, while maintaining the sustainable utility of the daily cycle. Amplified by the favorable sorption properties and ratcheting stability of the sorbent, this strategy demonstrates an impressive ∼80% increase in water harvesting yield over the daily cycle systems. The generic nature of the ratcheting concept shows great potential to advance the water harvesting capabilities of a range of related systems., ACS Applied Materials & Interfaces, 14 (1), ISSN:1944-8244, ISSN:1944-8252

Counteracting surface fogging to maintain surface transparency is significant to a variety of applications, including automotive lighting. Current energy-neutral approaches mostly rely on engineering the surface wettability, but suffer from contaminant deposition and lack of robustness and hence require frequent maintenance or renewal. This is particularly bothersome when the coating is within an enclosure, such as that of an automotive headlamp. Here, we design a maintenance-free, transparent, light-activated, photothermal composite material coating, to fully mitigate fogging-related issues. The coating contains dispersed indium tin oxide (ITO) nanoparticles in a dielectric matrix and is most absorptive in the near-infrared range, where a significant fraction of the thermal energy source lies, thus maintaining visible transparency. Based on nucleation thermodynamics, the photo-induced heating effect enables sustained and superior fog removal, also prevention when compared to uncoated samples. The coating is fabricated with readily and cost-effectively scalable industrial methods such as spray or dip coating. Its functionality is evidenced with standard visible thermal sources and on predominant materials employed in car headlights (glass and polycarbonate), which enables its direct application also on existing such surfaces, or similar.

Supercooled droplet freezing on surfaces occurs frequently in nature and industry, often adversely affecting the efficiency and reliability of technological processes. The ability of superhydrophobic surfaces to rapidly shed water and reduce ice adhesion make them promising candidates for resistance to icing. However, the effect of supercooled droplet freezing—with its inherent rapid local heating and explosive vaporization—on the evolution of droplet–substrate interactions, and the resulting implications for the design of icephobic surfaces, are little explored. Here we investigate the freezing of supercooled droplets resting on engineered textured surfaces. On the basis of investigations in which freezing is induced by evacuation of the atmosphere, we determine the surface properties required to promote ice self-expulsion and, simultaneously, identify two mechanisms through which repellency falters. We elucidate these outcomes by balancing (anti-)wetting surface forces with those triggered by recalescent freezing phenomena and demonstrate rationally designed textures to promote ice expulsion. Finally, we consider the complementary case of freezing at atmospheric pressure and subzero temperature, where we observe bottom-up ice suffusion within the surface texture. We then assemble a rational framework for the phenomenology of ice adhesion of supercooled droplets throughout freezing, informing ice-repellent surface design across the phase diagram., Nature Physics, 19 (5), ISSN:1745-2473, ISSN:1745-2481

Dropwise condensation (DWC) is a phenomenon of common occurrence and significant utility in nature and technology. In energy applications, sustenance of DWC and avoidance of transition to film formation is directly related to efficient heat removal, ensuring high performance of related devices and processes. The efficiency of heat transfer in DWC depends on the heat transfer rates of individual droplets and the droplet size distribution. While the former can be summarily captured in engineering analysis through thermal resistance modeling, the theoretical analysis of the droplet size distribution involves assumptions often oversimplifying the complexity of droplet interactions, especially in the important sub–10 μm regime. Here, a modeling framework based on the thermal resistance approach is coupled with a dynamic model of droplet interactions: Droplet growth, coalescence, jumping, and removal of condensate due to gravity are all present during the unfolding of the phenomenon to accurately predict the droplet size distribution. The motivation is condensation experiments on superhydrophobic surfaces, namely rough aluminum substrates with a hydrophobic coating. Through the “interaction” of computations with measurements, the experimental findings are explained and critical parameters for condensation heat transfer on superhydrophobic surfaces are illuminated. Although larger droplets can be easily observed in experiments, it is shown that large droplets do not significantly affect heat transfer after reaching such state of growth. Instead, it is the small (with radius < 10 μm) and what we term “shadowed” droplets, i.e., the droplets grown in the shadow of the vertical projection area of the larger droplets, that play an important role in the heat transfer process. Due to the growth of these droplets and their concomitant shadowed coalescence and ensuing re-nucleation, the shift in the droplet size distribution towards smaller sizes is significant-enough to render the heat transfer rate rather insensitive to the presence of large droplets. In this regime, the effect of contact angle hysteresis on heat transfer is not crucial. Through the comparison with measurements, the dominant role of the density of nucleation sites on heat transfer is revealed and an estimation of the density of sites (∼105 mm−2) as a function of subcooling is extracted. Finally, the distribution of sites is found critical for heat transfer; an ordered distribution of sites outperforms random and clustered distributions. ISSN:0017-9310 ISSN:1879-2189

Rapid and sustained condensate droplet departure from a surface is key toward achieving high heat-transfer rates in condensation, a physical process critical to a broad range of industrial and societal applications. Despite the progress in enhancing condensation heat transfer through inducing its dropwise mode with hydrophobic materials, sophisticated surface engineering methods that can lead to further enhancement of heat transfer are still highly desirable. Here, by employing a three-dimensional, multiphase computational approach, we present an effective out-of-plane biphilic surface topography, which reveals an unexplored capillarity-driven departure mechanism of condensate droplets. This texture consists of biphilic diverging microcavities wherein a matrix of small hydrophilic spots is placed at their bottom, that is, among the pyramid-shaped, superhydrophobic microtextures forming the cavities. We show that an optimal combination of the hydrophilic spots and the angles of the pyramidal structures can achieve high deformational stretching of the droplets, eventually realizing an impressive “slingshot-like” droplet ejection process from the texture. Such a droplet departure mechanism has the potential to reduce the droplet ejection volume and thus enhance the overall condensation efficiency, compared to coalescence-initiated droplet jumping from other state-of-the-art surfaces. Simulations have shown that optimal pyramid-shaped biphilic microstructures can provoke droplet self-ejection at low volumes, up to 56% lower than superhydrophobic straight pillars, revealing a promising new surface microtexture design strategy toward enhancing the condensation heat-transfer efficiency and water harvesting capabilities. ISSN:0743-7463 ISSN:1520-5827

Realizing membranes of atomic thickness functioning reliably constitutes a giant leap forward for a plethora of applications where the efficient separation of fluid constituents at the molecular level is critical. Here, by employing density functional theory, we explore the energy landscape of typical gas molecules attempting permeation through graphene nanopores and determine the minimum energy permeation pathways, based on the precise knowledge of the related molecular level interactions. With this approach we investigate two basic permeation routes: direct permeation and surface-based transport. We find that for subnanometer pores, the diffusion barrier of direct and surface transport depends on the pore chemical functionalization, while the molecule pore permeation barrier is independent of the gas-pore approach due to the overlap of surface and direct diffusion paths over the pore center. The overall minimum energy permeation pathway of He, H2, CO2, and CH4 molecules, across nanopores of different dimensions and chemical functionalization, defines the pore diameter (∼1.2 nm) below which effusion theory is inaccurate, as well as the critical pore diameter (∼0.8 nm) required to achieve positive permeation barriers driving molecular sieving. We determine that achieving positive permeation barriers required for high selectivity gas separation is inseparably combined with postpermeation desorption barriers due to attractive van der Waals interactions. The discovered permeation energetics are pore-molecule-specific and are incorporated into an analytical model extending existing theory. Our results provide a scientific background for rational pore design in graphene membranes, which can lead to gas separation at a commercially relevant performance level.

Organic hydrophobic layers targeting sustained dropwise condensation are highly desirable but suffer from poor chemical and mechanical stability, combined with low thermal conductivity. The requirement of such layers to remain ultrathin to minimize their inherent thermal resistance competes against durability considerations. Here, we investigate the long-term durability and enhanced heat-transfer performance of perfluorodecanethiol (PFDT) coatings compared to alternative organic coatings, namely, perfluorodecyltriethoxysilane (PFDTS) and perfluorodecyl acrylate (PFDA), the latter fabricated with initiated chemical vapor deposition (iCVD), in condensation heat transfer and under the challenging operating conditions of intense flow (up to 9 m s

Traditional fluorescence-based tags, used for anticounterfeiting, rely on primitive pattern matching and visual identification; additional covert security features such as fluorescent lifetime or pattern masking are advantageous if fraud is to be deterred. Herein, we present an electrohydrodynamically printed unicolour multi-fluorescent-lifetime security tag system composed of lifetime-tunable lead-halide perovskite nanocrystals that can be deciphered with both existing time-correlated single-photon counting fluorescence-lifetime imaging microscopy and a novel time-of-flight prototype. We find that unicolour or matching emission wavelength materials can be prepared through cation-engineering with the partial substitution of formamidinium for ethylenediammonium to generate “hollow” formamidinium lead bromide perovskite nanocrystals; these materials can be successfully printed into fluorescence-lifetime-encoded-quick-read tags that are protected from conventional readers. Furthermore, we also demonstrate that a portable, cost-effective time-of-flight fluorescence-lifetime imaging prototype can also decipher these codes. A single comprehensive approach combining these innovations may be eventually deployed to protect both producers and consumers., Nature Communications, 12 (1), ISSN:2041-1723

Bacterial colonization poses significant health risks, such as infestation of surfaces in biomedical applications and clean water unavailability. If maintaining the surrounding water clean is a target, developing surfaces with strong bactericidal action, which is facilitated by bacterial access to the surface and mixing, can be a solution. On the other hand, if sustenance of a surface free of bacteria is the goal, developing surfaces with ultralow bacterial adhesion often suffices. Here we report a facile, scalable, and environmentally benign strategy that delivers customized surfaces for these challenges. For bactericidal action, nanostructures of inherently antibacterial ZnO, through simple immersion of zinc in hot water, are fabricated. The resulting nanostructured surface exhibits extreme bactericidal effectiveness (9250 cells cm–2 h–1) that eliminates bacteria in direct contact and also remotely through the action of reactive oxygen species. Remarkably, the remote bactericidal action is achieved without the need for any illumination, otherwise required in conventional approaches. As a result, ZnO nanostructures yield outstanding water disinfection of >99.98%, in the dark, by inactivating the bacteria within 3 h. Moreover, Zn2+ released to the aqueous medium from the nanostructured ZnO surface have a concentration of 0.73 ± 0.15 ppm, markedly below the legal limit for safe drinking water (5–6 ppm). The same nanostructures, when hydrophobized (through a water-based or fluorine-free spray process), exhibit strong bacterial repulsion, thus substantially reducing bacterial adhesion. Such environmentally benign and scalable methods showcase pathways toward inhibiting surface bacterial colonization. ISSN:1520-5045 ISSN:0888-5885

Bitumen is a widely used material employed as a binder in pavement engineering and as a surface sealant in construction. Its surface microstructure and microscale properties have been shown to be temperature-dependent, with effects manifesting themselves on surface composition and texture, including the formation of the visually striking catana 'bee'-like structures. Despite the importance of a good performance of bitumen in subzero environments (

After skin tissue injury or pathological removal, vascularization timing is paramount in graft survival. As full thickness skin grafts often fail to become perfused over larger surfaces, split-thickness grafts are preferred and can be used together with biomaterials, which themselves are non-angiogenic. One way of promoting vascular ingrowth is to “pre-vascularize” an engineered substitute by introducing endothelial cells (ECs). Since it has been previously demonstrated that surface structured biomaterials have an effect on wound healing, skin regeneration, and fibrosis reduction, we proposed that a microvascular-rich lipoconstruct with anisotropic topographical cues could be a clinically translatable vascularization approach. Murine lipofragments were formed with three polydimethylsiloxane molds (flat, 5 µm, and 50 µm parallel gratings) and implanted into the dorsal skinfold chamber of male C57BL/6 mice. Vascular ingrowth was observed through intravital microscopy over 21 days and further assessed by histology and protein identification. Our investigation revealed that topographical feature size influenced the commencement of neovascular ingrowth, with 5 µm gratings exhibiting early construct perfusion at 3 days post-operation, and 50 µm being delayed until day 5. We therefore postulate that surface structured lipoconstructs may serve as an easily obtained and produced construct suitable for providing soft tissue and ECs to tissue defects. Statement of Significance Skin graft failures due to inadequate or uneven perfusion frequently occur and can be even more complicated in deep, difficult to heal wounds, or bone coverage. In complex injuries, biomaterials are often used to cover bone structures with a standard split thickness graft; however, perfusion can take up to 3 weeks. Thus, any means to promote faster and uniform vascularization could significantly reduce healing time, as well as lower patient down-time. As pre-vascularized constructs have reported success in research, we created a cost-efficient, translatable method with no additional laboratory time as adipose tissue can be harvested and used immediately. We further used surface topography as an aspect to modulate construct perfusion, which has been reported for the first time here.

Phosphatidylinositol-5-phosphate (PtdIns5P)-4-kinases (PIP4Ks) are stress-regulated phosphoinositide kinases able to phosphorylate PtdIns5P to PtdIns(4, 5)P2. In cancer patients their expression is typically associated with bad prognosis. Among the three PIP4K isoforms expressed in mammalian cells, PIP4K2B is the one with more prominent nuclear localization. Here, we unveil the role for PIP4K2B as mechanosensor. PIP4K2B protein level, indeed, strongly decreases in cells growing on soft substrates. Its direct silencing or pharmacological inhibition, mimicking cell response to soft, triggers a concomitant reduction of the epigenetic regulator UHRF1 and induces changes in nuclear polarity, nuclear envelope tension and chromatin compaction. This substantial rewiring of the nucleus mechanical state drives YAP cytoplasmic retention and impairment of its activity as transcriptional regulator, finally leading to defects in cell spreading and motility. Since YAP signalling is essential for initiation and growth of human malignancies, our data suggest that potential therapeutic approaches targeting PIP4K2B could be beneficial in the control of the altered mechanical properties of cancer cells.

Water condensation and freezing on asphalt roads can lead to slippery conditions, which are responsible for many winter accidents and have caused an overreliance on mostly environmentally damaging and pavement degrading deicing chemicals and salt, which requires active maintenance. Bitumen is a mechanically and chemically complex material mainly consisting of various hydrocarbon-based chemicals groups. Additionally, bitumen makes up approximately 5 wt.% of the asphalt concrete mixture because of its binder role and coating function of the aggregates, can control the bulk mechanical properties and surface properties of the asphalt mixture. Condensation as the first step and later freezing phenomena are investigated in this study and from ambient humidity toward understanding the fundamentals of icing on bituminous surfaces. Condensation experimental results show selective wettability of chemically and mechanically district bitumen surface domains. The effect of different bitumen modifiers of polyethylene terephthalate, polyamide (PA 66), polyacrylonitrile, and Sasobit wax at 1 wt.% were studied on condensation freezing and bitumen water affinity. ISSN:0090-3973 ISSN:1945-7553

Surface icing is detrimental to applications ranging from transportation to biological systems. Soft elastomeric coatings can engender remarkably low ice adhesion strength, but mechanisms at the microscale and resulting ice extraction outcomes need to be understood. Here we investigate dynamic ice-elastomer interfacial events and show that the ice adhesion strength can actually vary by orders of magnitude due to the shear velocity. We study the detailed deformation fields of the elastomer using confocal traction force microscopy and elucidate the underlying mechanism. The elastomer initially undergoes elastic deformation having a shear velocity dependent threshold, followed by partial relaxation at the onset of slip, where velocity dependent "stick-slip" micropulsations are observed. The results of the work provide important information for the design of soft surfaces with respect to removal of ice, and utility to fields exemplified by adhesion, contact mechanics, and biofouling., Materials Horizons, 9 (4), ISSN:2051-6347, ISSN:2051-6355

Nanostructured surfaces usually exhibit complicated morphologies that cannot be described in terms of Euclidean geometry. Simultaneously, they do not constitute fully random noise fields to be characterized by simple stochastics and probability theory. In most cases, nanomorphologies consist of complicated mixtures of order and randomness, which should be described quantitatively if one aims to control their fabrication and properties. In this work, inspired by recent developments in complexity theory, we propose a method to measure nanomorphology complexity that is based on the deviation from the average symmetry of surfaces. We present the methodology for its calculation and the validation of its performance, using a series of synthetic surfaces where the proposed complexity measure obtains a maximum value at the most heterogeneous morphologies between the fully ordered and fully random cases. Additionally, we measure the complexity of experimental micro and nanostructured surfaces (polymeric and metallic), and demonstrate the usefulness of the proposed method in quantifying the impact of processing conditions on their morphologies. Finally, we hint on the relationship between the complexity measure and the functional properties of surfaces., Comment: 13 pages, 13 figures. Materials Today: Proceedings, 2021

The phenomenon of icing, and the derived processes for its mitigation, are of great importance in many applications, ranging from transportation and energy to food and refrigeration. This phenomenon has been studied mostly with respect to its manifestation on rigid, homogeneous surfaces, with soft materials being the topic of more recent investigations. Although, icing often occurs on substrates that are chemically and mechanically heterogeneous, e.g., widely used asphalt concrete, which consists of rigid aggregates embedded in soft bitumen, to date, ice adhesion behavior on such substrates needs to be better understood. Here, we study ice adhesion stresses—the stresses necessary to remove ice—of ice blocks on heterogeneous materials, juxtaposing the behavior of the two main constituents of asphalt concrete, the rigid aggregates (modeled by Macor®) and bitumen, to the behavior of bitumen-Macor® composites. We show that the ice adhesion shear stress on Macor® is almost twice as large as that on bitumen, whereas the ice adhesion normal stress and the normal and shear components of composite stress are in a similar range. We synthesize composite substrates that consist of bitumen stripes on Macor® and find that increasing bitumen width leads to lower ice adhesion stress, while the stripe direction with respect to the applied force direction has a minor effect. Based on our findings, we then coat the most ice-adhesive component (Macor®) with a thin superhydrophobic coating and show that this can reduce ice adhesion stress on the heterogeneous substrates. We also find that for ice formed half on bitumen and half on Macor®, if Macor® is first and bitumen second with respect to the applied force direction (material order), then the measured ice adhesion stress is less compared to the reverse case in material order. ISSN:0165-232X ISSN:1872-7441

Freezing of atmospheric water on bituminous construction and road surfaces is a recurring event during winter. However, droplet freezing on bitumen and passive inhibition methods are poorly understood. Here we investigate relative humidity and substrate cooling effects on condensation freezing on subzero temperature bituminous surfaces and find that droplet freezing is explosive, with rapid local heating. We explain the related physics and find that relative humidity and cooling rate can affect droplet sizes and freezing temperatures. We then rationally embed phase change material microcapsules in bitumen, harnessing their latent heat to significantly delay freezing, demonstrating a viable option for frost mitigation. ISSN:0950-0618