Bioinspired design of honeycomb structure interfaces with controllable water adhesion

Multi-bioinspired hierarchical integrated hydrogel for passive fog harvesting and solar-driven seawater desalination

In recent years, with the outbreak and epidemic of the novel coronavirus in the world, how to obtain clean water from the limited resources has become an urgent issue of concern to all mankind. Atmospheric water harvesting technology and solar-driven interfacial evaporation technology have shown great potential in seeking clean and sustainable water resources. Here, inspired by a variety of organisms in nature, a multi-functional hydrogel matrix composed of polyvinyl alcohol (PVA), sodium alginate (SA) cross-linked by borax as well as doped with zeolitic imidazolate framework material 67 (ZIF-67) and graphene owning macro/micro/nano hierarchical structure has successfully fabricated for producing clean water. The hydrogel not only can reach the average water harvesting ratio up to 22.44 g g-1 under the condition of fog flow after 5 h, but also be capable of desorbing the harvested water with water release efficiency of 1.67 kg m-2 h-1 under 1 sun. In addition to excellent performance in passive fog harvesting, the evaporation rate over 1.89 kg m-2 h-1 is attained under 1 sun on natural seawater during long-term. This hydrogel indicates its potential in producing clean water resources in multiple scenarios in different dry or wet states, and which holds great promise for flexible electronic materials and sustainable sewage or wastewater treatment applications.

Synergetic adhesion in highly adaptable bio-inspired adhesive

Biologically inspired adhesives microstructure requires enough flexibility to make a conformal attachment to the surface as well as high rigidity to maintain the mechanical stability of structure against buckling. To tackle these conflicting factors for the synthetic adhesives is a challenge towards large-scale production and utilizing in practical applications. Addressing this problem, we have fabricated a honeycomb structure with a soft elastic film, partially covering the cavity of the honeycomb pattern. Honeycomb structure provides enough support to maintain the structural stability of the microstructure and soft PDMS film over the pattern provides sufficient flexibility to form a strong attachment with the target surface. Meanwhile, the resemblance of the designed structure to the octopi's sucker generates a negative pressure resulting in suction forces. To justify this suction effect, we compared our results with other controlled honeycomb microstructures (1) without any elastic film (2) with elastic film covering the whole cavity of the honeycomb pattern. Experimental results and theoretical prediction demonstrate the synergistic role of van der Waals and suction forces in the proposed partial-film honeycomb microstructure. The synergistic role of adhesive forces makes this structure a stronger, durable, and surface adaptable adhesive. We also investigated the critical role of the viscous forces for our proposed microstructure in water and silicon oil wetting conditions which signify the contribution of capillary forces.

Strategies to Improve Nanofibrous Scaffolds for Vascular Tissue Engineering

The biofabrication of biomimetic scaffolds for tissue engineering applications is a field in continuous expansion. Of particular interest, nanofibrous scaffolds can mimic the mechanical and structural properties (e.g., collagen fibers) of the natural extracellular matrix (ECM) and have shown high potential in tissue engineering and regenerative medicine. This review presents a general overview on nanofiber fabrication, with a specific focus on the design and application of electrospun nanofibrous scaffolds for vascular regeneration. The main nanofiber fabrication approaches, including self-assembly, thermally induced phase separation, and electrospinning are described. We also address nanofibrous scaffold design, including nanofiber structuring and surface functionalization, to improve scaffolds' properties. Scaffolds for vascular regeneration with enhanced functional properties, given by providing cells with structural or bioactive cues, are discussed. Finally, current in vivo evaluation strategies of these nanofibrous scaffolds are introduced as the final step, before their potential application in clinical vascular tissue engineering can be further assessed.

The polydopamine-enhanced superadhesion and fracture strength of honeycomb polyurethane porous membranes

The superhydrophobic properties of biological surfaces in nature have attracted extensive attention in scientific and industrial circles. Relative to the rolling superhydrophobic state of lotus leaves, the adhesive superhydrophobic state of geckos and Parthenocissus tricuspidata is also significant in many fields. In this work, polydopamine (PDA) with its excellent biological compatibility and strong adhesion was selected as a substance to simulate the secretion of the suckers of P. tricuspidata and it was precipitated at the surface of honeycomb polyurethane porous membranes (PUPM). The results demonstrated that the honeycomb PUPM, as prepared, displayed special super-adhesion properties similar to those of geckos and P. tricuspidata. PDA formed via self-polymerization in aqueous solution was equivalent to a double-sided adhesive, acquiring a micro-nano structure of PDA and PUPM and displaying increased surface hydrophobicity and improved adhesion properties. Even when the surface precipitation of PDA and modification with n-dodecyl mercaptan made the contact angle increase to more than 160°, the surface adhesion to water was rather strong and remained stable. The addition of the PDA adhesive can effectively change the microporous structure of PUPM, enhancing the viscosity, and facilitating an enhancement in the fracture strength.

Synthesis and Properties of Cyclopentyl Cardo-Type Polyimides Based on Dicyclopentadiene

A crucial polymer intermediate, 4-[1-(4-hydroxyphenyl)cyclopentyl]-phenol (bisphenol CP), was developed from dicyclopentadiene (DCPD), a key byproduct of the C5 fraction in petrochemicals. On the basis of bisphenol CP, a diamine, 4,4'-((cyclopentane-1,1-diylbis(4,1-phenylene))bis(oxy))-dianiline (cyclopentyl diamine; CPDA) was subsequently obtained through a nucleophilic substitution of bisphenol CP, followed by the hydrogenation process. By using the CPDA diamine, a series of polyimides with cyclopentyl (cardo) units on the backbone were prepared along with a reference polyimide (API-6F) based on 4,4'-(4,4'-(propane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dianiline (BPAA), and 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) for the exploration of structure-properties relationship. Thanks to the presence of cyclopentyl units, this type of cardo polyimides exhibited comparable tensile properties, especially a large elongation (25.4%). It is also worth noting that CPI-6F exhibited better solubility in organic solvents, such as NMP, DMAc, THF, and chloroform, than the other PIs. Gas separation properties were also evaluated for these cardo-type polyimides.

In Search of a Green Process: Polymeric Films with Ordered Arrays via a Water Droplet Technique

As an efficient technique for the preparation of polymeric hexagonal orderly arrays, the breath figure (BF) process has opened a modern avenue for a bottom-up fabrication method for more than two decades. Through the use of the water vapor condensation on the solution surface, the water droplets will hexagonally pack into ordered arrays, acting as a template for controlling the regular micro patterns of polymeric films. Comparing to the top-down techniques, such as lithography or chemical etching, the use of water vapor as the template provides a simple fabrication process with sustainability. However, using highly hazardous solvents such as chloroform, carbon disulfide (CS2), benzene, dichloromethane, etc., to dissolve polymers might hinder the development toward green processes based on this technique. In this review, we will touch upon the contemporary techniques of the BF process, including its up-to-date applications first. More importantly, the search of greener processes along with less hazardous solvents for the possibility of a more sustainable BF process is the focal point of this review.

Hierarchical Polymer Structures Using Templates and the Modified Breath Figure Method

Hierarchical structures are commonly observed in nature and possess unique properties. The fabrication of hierarchical structures with well-controlled sizes in different length scales, however, is still a great challenge. To further understand the morphologies and properties of the hierarchical structures, here we present a novel strategy to prepare hierarchical polymer structures by combining the modified breath figure method and the template method. Poly(methyl methacrylate) (PMMA) honeycomb films with regular micropores are first prepared using the modified breath figure method by dipping PMMA films into mixtures of chloroform and methanol. The polymer chains on the honeycomb films are then annealed and wetted into the nanopores of anodic aluminum oxide templates via capillary forces, resulting in the formation of hierarchical polymer structures. The morphologies of the polymer structures, which can be controlled by the molecular weights of the polymers and the concentrations of the polymer solutions, are characterized by scanning electron microscopy. The surface wettabilities of the polymer structures are also examined by water contact angle measurements, and the hierarchical structures are observed to be more hydrophobic than the flat films and honeycomb films. This work not only provides a feasible approach to fabricate hierarchical polymer structures with controlled sizes but also gives a better understanding of the relationship between surface morphologies and properties.

Designing 3D Biological Surfaces via the Breath-Figure Method

The fabrication of biointerfaces that mimic cellular physiological environments is critical to understanding cell behaviors in vitro and for the design of tissue engineering. Breath figure is a self-assemble method that uses water droplets condensed from moisture as template and ends up with a highly ordered hexagonal pore array; this approach is used to fabricate various biological substrates. This progress report provides an overview of strategies to achieve topographical modifications and chemical-patterned arrays, such as modulation of the pore size, shape and selective decoration of the honeycomb holes. Using recent results in the biological fields, potential future applications and developments of honeycomb structures are commented upon.

Honeycomb-patterned hybrid films of surfactant-encapsulated polyoxometalates by a breath figure method and its electrocatalysis for BrO3−

Surfactant-encapsulated POMs can self-assemble into ordered porous honeycomb films under a moist atmosphere. We successfully fabricated (DODA)₁₀{Cu₄(PW₉)₂} honeycomb films by using a one-step method.

Fabrication of the graphene honeycomb structure as a scaffold for the study of cell growth

The good biocompatibility of the graphene honeycomb structure was evaluated by the proliferation of HeLa and MCF-7 cell lines.

Dynamic effects and adhesion of water droplet impact on hydrophobic surfaces: bouncing or sticking

This work reported the dynamic effects of water droplet impact on flat, porous and pincushion structure films of star shaped polyhedral oligomeric silsesquioxane (POSS) fluorinated acrylates, POSS-poly(trifluoroethyl methacrylate)₈ (POSS-(PTFEMA)₈) and POSS-(poly(trifluoroethyl methacrylate)-b-poly(methyl methacrylate))₈ (POSS-(PTFEMA-b-PMMA)₈), using the breath figure method. The porous and pincushion structure films with different surface chemical compositions were obtained by controlling the copolymer structure and temperature and by stripping of the surface. The water contact angles on the different films were measured, and the water droplets on the pincushion structure films when reversed at 45°, 90°, 135° and 180° were also studied. It was found that the pincushion structure films revealed a water adhesion ability. Furthermore, the water droplet impact behavior on these films was investigated. The morphology variations of water droplets, spreading diameter of the droplets, energy conversion, restitution coefficient and adhesion force were examined. Finally, the schematic illustration of water droplets under the static and dynamic states in contact with the pincushion and porous structure surfaces was proposed. It is critical to materialize various applications such as microdroplet transportation, soil erosion, spray painting, anti-icing surface and antifouling agents for textiles.

Multiphase Media Antiadhesive Coatings: Hierarchical Self-Assembled Porous Materials Generated Using Breath Figure Patterns

The cleaning of interface pollutants typically consumes a large amount of energy. Therefore, the development of multiphase media antiadhesive materials is urgently required to meet the demand of energy savings and environmental protection. In this study, the antiadhesive properties toward several liquid droplets and bubbles in multiple media are demonstrated on a porous Fe₂O₃ coating, which is prepared via a facile spin-coating-assisted breath figure approach and a phase separation strategy. The prominent antiadhesive characteristic of these porous surfaces lies in their high-surface-energy hierarchical micro/nanoscale structure, which easily entraps one medium (oil or water) in the pore and repels other unmixable liquids and air bubbles. In addition, we successfully demonstrate an antifouling application of the coating, which shows excellent antiadhesive and super-antiwetting characteristics under multiple liquids. Our work extends relevant antiadhesion research from a single medium to multiple media and promises to broaden the applications of antiadhesive materials in sophisticated activities performed under complicated liquid environments, such as marine antifouling or pipeline transportation.

Strengthening of polymer ordered porous materials based on a layered nanocomposite internal structure

Ordered porous polymeric films attract more and more attention because they have many advantages and broad application prospects in many fields. But because of their large flexibility and poor mechanical properties, some of the scope for application is greatly limited. Inspired by the ordered pore structure of the honeycomb and the layered structure of natural nacre, we prepared an ordered porous polymer film with a layered structure in the pore wall by the solvent-evaporation-restriction assisted hard template method. Compared with other samples, this kind of film with the layered structure showed both excellent mechanical properties and good stability. This kind of film with high mechanical strength, is considered to have wide applications in the areas of separation, biomedicine, precision instruments, aerospace, environmental protection and so on.

Biomimetic heterogeneous multiple ion channels: a honeycomb structure composite film generated by breath figures

We design a novel type of artificial multiple nanochannel system with remarkable ion rectification behavior via a facile breath figure (BF) method. Notably, even though the charge polarity in the channel wall reverses under different pH values, this nanofluidic device displays the same ionic rectification direction. Compared with traditional nanochannels, this composite multiple ion channel device can be more easily obtained and has directional ionic rectification advantages, which can be applied in many fields.

Conformal and non-conformal surface modification of honeycomb-patterned porous films via tunable Cassie–Wenzel transition

We describe here a facile and robust approach to conformal and non-conformal surface modification by tuning the wetting transition between the Wenzel state and the Cassie state.

Targeted grafting of thermoresponsive polymers from a penetrative honeycomb structure for cell sheet engineering

Responsive membranes have been used to construct smart biomaterial interfaces. We report a novel approach to fabricate honeycomb films with a pattern of thermoresponsive polymer, namely poly(N-isopropylacrylamide). The approach was based on a combination of the breath figure method and reversible addition-fragmentation chain transfer. The hybrid film had morphological and chemical patterns resulting in varied wettability and morphology at various stages, as well as high thermo-responsiveness. Enhanced cell adhesion was observed at an incubation temperature of 37 °C, which is above its lower critical solution temperature (LCST). Furthermore, cells could be harvested at temperatures below the LCST without trypsin treatment. The non-invasive characteristics give this membrane potential as a substrate for cell sheet engineering.

Conductive Polymer Porous Film with Tunable Wettability and Adhesion

A conductive polymer porous film with tunable wettability and adhesion was fabricated by the chloroform solution of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid-methyl-ester (PCBM) via the freeze drying method. The porous film could be obtained from the solution of 0.8 wt%, whose pore diameters ranged from 50 nm to 500 nm. The hydrophobic porous surface with a water contact angle (CA) of 144.7° could be transferred into a hydrophilic surface with CA of 25° by applying a voltage. The water adhesive force on the porous film increased with the increase of the external voltage. The electro-controllable wettability and adhesion of the porous film have potential application in manipulating liquid collection and transportation.

Bio-inspired design of hierarchical PDMS microstructures with tunable adhesive superhydrophobicity

In this paper, bio-inspired PDMS films with different hierarchical microstructures were designed and tunable adhesive super-hydrophobicity was achieved on these films. The adhesive forces between a water droplet and the PDMS film can be adjusted from extremely low (about 8.3 μN) to very high (about 57 μN), and the tunable effect can be ascribed to different wetting states for the water droplets that result from different microstructures on the films. Noticeably, the obtained super-hydrophobic surfaces are acid/alkali-resisting, and water droplets with different pH values have similar contact angles and adhesive forces on the same surface. Finally, the application of the obtained surfaces for microdroplet transportation and self-cleaning are also discussed. The results reported herein provide a new method to obtain super-hydrophobic surfaces with controlled adhesion, and significantly improve our understanding of the relationship between surface adhesion, surface microstructures and the fabrication principle of tunable adhesive super-hydrophobic surfaces.

Polymer porous interfaces with controllable oil adhesion underwater

Porous montmorillonite (MMT)/poly acrylic acid (PAA) composite surfaces with different oil adhesions were achieved by controlling the MMT arrangement in the pore wall.

Porphyrinated polyimide honeycomb films with high thermal stability for HCl gas sensing

Thermally stable films with ordered pores are fabricated from porphyrinated polyimides and they exhibit excellent property in HCl gas sensing.

Design of honeycomb structure surfaces with controllable oil adhesion underwater

We fabricate honeycomb-like poly acrylic acid (PAA) surfaces and achieve oil adhesion regulation underwater by changing the pore size and the solution pH, which affect triple-phase contact line (TCL) continuity and the negative pressure in the pores.

Biomimetic honeycomb-patterned surface as the tunable cell adhesion scaffold

PS honeycomb structured surfaces were modified into both cell-philic and cell-phobic by dip-coating and casting polySBMA, respectively, which was inspired by two typically adhesive behaviours of fish skin and Parthenocissus tricuspidata.

Multiple interfaces in self-assembled breath figures

Progress in the breath figure method is reviewed by emphasizing the role of the multiple interfaces and the applications of honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces.