Tunable Wettability Research Articles

Water-evaporation-induced intermolecular force for nano-wrinkled polymeric membrane

Summary Nano-wrinkled polymeric membranes have received tremendous attention for their broad applications in tunable optics, biomedicine, surface wettability, and flexible electronics. However, achieveing a low-cost and scalable synthesis routine remains highly desirable. Here, we invent a simple, bottom-up, polymer engineering strategy by introducing water molecules into the polymerization process. Water evaporation induces intermolecular forces that build a crosslinking reaction gradient from the material surface to its interior, which buckles the surface-forming wrinkles. The shape, geometry, size, orientation, and arrangement of the wrinkles on the polymer surface can be designed accordingly. Moreover, the as-fabricated nano-wrinkled, polymeric membranes display outstanding performance in energy and sensing applications, boosting output current and sensing sensitivity by 611% and 164%, respectively, compared to their flat counterparts. This work may contribute to a low-cost, scalable, and environmentally friendly strategy to engineer polymer surfaces with controllable wrinkles, showing great potential for the development of various soft-matter technologies.

Biomimetic tubular scaffold with heparin conjugation for rapid degradation in in situ regeneration of a small diameter neoartery

To address the clinical need for readily available small diameter vascular grafts, biomimetic tubular scaffolds were developed for rapid in situ blood vessel regeneration. The tubular scaffolds were designed to have an inner layer that is porous, interconnected, and with a nanofibrous architecture, which provided an excellent microenvironment for host cell invasion and proliferation. Through the synthesis of poly(spirolactic-co-lactic acid) (PSLA), a highly functional polymer with a norbornene substituting a methyl group in poly(l-lactic acid) (PLLA), we were able to covalently attach biomolecules onto the polymer backbone via thiol-ene click chemistry to impart desirable functionalities to the tubular scaffolds. Specifically, heparin was conjugated on the scaffolds in order to prevent thrombosis when implanted in situ. By controlling the amount of covalently attached heparin we were able to modulate the physical properties of the tubular scaffold, resulting in tunable wettability and degradation rate while retaining the porous and nanofibrous morphology. The scaffolds were successfully tested as rat abdominal aortic replacements. Patency and viability were confirmed through dynamic ultrasound and histological analysis of the regenerated tissue. The harvested tissue showed excellent vascular cellular infiltration, proliferation, and migration with laminar cellular arrangement. Furthermore, we achieved both complete reendothelialization of the vessel lumen and native-like media extracellular matrix. No signs of aneurysm or hyperplasia were observed after 3 months of vessel replacement. Taken together, we have developed an effective vascular graft able to generate small diameter blood vessels that can function in a rat model.

Tunable Wettability Pattern Transfer Photothermally Achieved on Zinc with Microholes Fabricated by Femtosecond Laser.

A quickly tunable wettability pattern plays an important role in regulating the surface behavior of liquids. Light irradiation can effectively control the pattern to achieve a specific wettability pattern on the photoresponsive material. However, metal oxide materials based on light adjustable wettability have a low regulation efficiency. In this paper, zinc (Zn) superhydrophobic surfaces can be obtained by femtosecond-laser-ablated microholes. Owing to ultraviolet (UV) irradiation increasing the surface energy of Zn and heating water temperature decreasing the surface energy of water, the wettability of Zn can be quickly tuned photothermally. Then, the Zn superhydrophobic surfaces can be restored by heating in the dark. Moreover, by tuning the pattern of UV irradiation, a specific wettability pattern can be transferred by the Zn microholes, which has a potential application value in the field of new location-controlled micro-/nanofluidic devices, such as microreactors and lab-on-chip devices.

Thermal Oxidation Fabricated Copper Oxide Nanotip Arrays with Tunable Wettability and Robust Stability: Implications for Microfluidic Devices and Oil/Water Separation

Materials with different wettability features have attracted intensive attention due to their outstanding performances and the broad application prospects. In this work, we report an applicable and...

Sucrose solution assisted femtosecond laser ablation of aluminum film to induce nanospikes for efficient and stable oil-water separation

The fabrication of functional surface covered with novel nanostructures for various applications has attracted much attention in recent years. A large area of randomly distributed nanospikes can be induced on the surface of aluminum (Al) film in sucrose solution by using femtosecond (fs) laser, and the distribution density of nanospikes varies with laser pulse energy and mass ratio for sucrose to water. After modification with polydimethylsiloxane (PDMS), the Al film covered with nanospikes exhibits the characteristics of tunable wettability, underwater superoleophilicity (~0°), superhydrophobicity (~155.3°), high water adhesion and environmental stability. Further, an oil-water separation filter was prepared by using fs laser direct writing (LDW) on one side of the Al film in air and then inducing nanospikes in sucrose solution as well as PDMS modification on the other side. After the above treatment, the filter has low water adhesion similar to “lotus effect” and can be used for highly efficient (99.61% ~ 99.63%) and recyclable oil-water separation. In addition, the filter exposed to air for more than 7 months still remains high oil-water separation efficiency (99.46% ~ 99.57%), showing strongly environmental stability. This functional filter fabricated by fs laser can be applied in the separation process of chemical products, biomedical device, and environmental protection fields.

Programming Colloidal Self-Assembled Patterns (cSAPs) into Thermo-Responsible Hybrid Surfaces for Controlling Human Stem Cells and Macrophages.

Hybrid surfaces with tunable topography, chemistry, and stiffness have potential to rebuild native extracellular matrix (ECM) and manipulate cell behavior in vitro. However, the fabrication of controllable hybrid surfaces is still challenging. In this study, colloidal self-assembly technology was used to program particles into highly ordered structures with hybrid chemistry and stiffness at biointerfaces. These colloidal self-assembled patterns (cSAPs), including unary, binary, and ternary cSAPs, composed of silicon (Si), polystyrene (PS), and/or poly(N-isopropylacrylamide) (pNIPAM) nanogels (PNGs), were fabricated using either coassembly or layer-by-layer (LBL) methods. The selected binary cSAPs (i.e., PS/PNG and PNG/PS) have a tunable surface topography and wettability between 25 and 37 °C; thus, they can be used as dynamic cell culture substrates. Human adipose-derived mesenchymal stem cells (hASCs), bone marrow-derived mesenchymal stem cells (hBMSCs), and macrophages (THP-1) were investigated on these hybrid cSAPs under a static or dynamic system. The results showed that hybrid cSAPs significantly influenced the focal adhesions, cell morphology, cell migration, and gene expressions of stem cells. In general, stem cells had more vinculin puncta, smaller spreading size, and faster migration speed than the TCPS control. Hybrid cSAPs up-regulated gene expressions of focal adhesion kinase (FAK) and chondrocytes (AGG and SOX9) under static culture, while they also up-regulated osteocytes (COL1 and RUNX2) under dynamic culture. THP-1 macrophages were at M0 state on all cSAPs under static culture. However, cells became sensitive under dynamic culture. For example, some M1 genes (i.e., IL6, CD68, and TNFα) and M2 genes (i.e., IL10 and CD206) were down-regulated, while other M1 genes (i.e., IL1β) and M2 genes (i.e., TGF-β and IL1ra) were up-regulated, depending on the particle combinations. In conclusion, new hybrid cSAPs with thermoresponsive surface properties are versatile materials for stem cells and macrophages manipulation.

Self-Organized Implanting of Micro/Nanofiltration Membranes in Advanced Flow μ-Reactors.

A low-cost, simple, and one-step synthesis of cellulose acetate nanoparticles (CANPs) has been invented using a continuous-flow advanced microfluidic reactor. For this purpose, the CANPs are self-organized inside a cross-junction microchannel by flowing cellulose acetate (CA) dissolved in N,N-dimethylformamide (DMF) through the axial inlet and the antisolvent water through the pair of side inlets. The preferential solubility (insolubility) of DMF (CA) to antisolvent water stimulates the in situ synthesis of CANPs at the DMF/water miscible interface following a phase-inversion process. Subsequently, nanofiltration, ultrafiltration, and microfiltration membranes of different porosities and permeabilities have been prepared from freshly synthesized CANPs. The porosity, thickness, transparency, and wettability of the membranes are tuned by varying the thickness of the membranes, size of the nanoparticles, and the porosity of the membranes. The as-synthesized CANPs show enhanced bactericidal properties with and without loading an external drug, curcumin, which has been validated against the Gram-negative Pseudomonas aeruginosa species. Importantly, enabling a pulsatile flow during the synthesis, the CANPs are embedded as nanofiltration membranes inside the microfluidic channel. Such microfluidic devices have been used to separate a corrosive dye from water. Concisely, the proposed in situ synthesis of CANPs in the continuous-flow microfluidic reactors, their usage for fabricating membranes with tunable wettability and transparency, and their subsequent integration into the microfluidic channel show the potential of the invention for a host of applications related to health care and environmental remediation.

Tunable Hydrophobicity via Dimensionally Confined Polymerization of Organometallic Adducts

AbstractFabrication of tunable fine textures on solid metal surfaces often demands sophisticated reaction/processing systems. By exploiting in situ polymerization and self‐assembly of inorganic adducts derived from liquid metals (the so‐called HetMet reaction) with concomitant solidification, solid metal films with tunable texture are readily fabricated. Serving as a natural dimensional confinement, interparticle pores and capillary‐adhered thin liquid films in a pre‐packed bed of undercooled liquid metal particles lead to the expeditious surface accumulation of organometallic synthons, which readily oligomerize and self‐assemble into concentration‐dictated morphologies/patterns. Tuning particle size, particle packing (flat or textured), and reactant concentration generates diverse, autonomously organized organometallic structures on a metal particle bed. Concomitant solidification and sintering of the underlying undercooled particle bed led to a multiscale patterned solid metal surface. The process is illustrated by creating tunable features on pre‐organized metal particle beds with concomitant tunable wettability as illustrated through the so‐called petal and lotus effects.

Tunable Hydrophobicity via Dimensionally Confined Polymerization of Organometallic Adducts.

Fabrication of tunable fine textures on solid metal surfaces often demands sophisticated reaction/processing systems. By exploiting in situ polymerization and self‐assembly of inorganic adducts derived from liquid metals (the so‐called HetMet reaction) with concomitant solidification, solid metal films with tunable texture are readily fabricated. Serving as a natural dimensional confinement, interparticle pores and capillary‐adhered thin liquid films in a pre‐packed bed of undercooled liquid metal particles lead to the expeditious surface accumulation of organometallic synthons, which readily oligomerize and self‐assemble into concentration‐dictated morphologies/patterns. Tuning particle size, particle packing (flat or textured), and reactant concentration generates diverse, autonomously organized organometallic structures on a metal particle bed. Concomitant solidification and sintering of the underlying undercooled particle bed led to a multiscale patterned solid metal surface. The process is illustrated by creating tunable features on pre‐organized metal particle beds with concomitant tunable wettability as illustrated through the so‐called petal and lotus effects.

The fabrication of superhydrophobic GF/PEEK composites with integrated structure and function by prepreg modifying and hot-pressing process

ABSTRACT The superhydrophobic surface presents great application potential in self-cleaning, anti-icing, and other efficient filed of surface engineering. In this work, we suggested introducing superhydrophobic property to glass fiber/polyetheretherketone composite surface. The developed route involves preparation of functional prepregs using hydrophobic particles and subsequent thermal pressing of modified composite sheets. The results show that depending on the hydrophobic polytetrafluoroethylene contents in the resin mixture, it is possible to obtain the functional prepreg with tunable surface wetting, and ulteriorly control the interlaminar bonding of laminates. The optimized procedure of hot-pressing temperature indicates that the hierarchical microstructure played a crucial role in governing the super-hydrophobicity of the rough composite surfaces. As the sandblasted mold temperature increases from 300°C to 360°C, the water contact angle of pressed composite surfaces ranges from 98° to 152°. Furthermore, the surface exhibits excellent environmental durability. The main advantages of the proposed procedure are its environmental friendliness and expandability, which makes it very potential for driving the superhydrophobic surface to practical applications.

A shape memory porous sponge with tunability in both surface wettability and pore size for smart molecule release

Recently, smart superwetting porous materials have aroused much attention, and it is well known that tunable surface wettability and pore structure/size are extremely important for their functions. However, only one factor can be regulated on existing materials, which significantly restricts their controllability, functions, and applications. A new material was prepared by electrodepositing a layer of polypyrrole on a shape memory sponge, on which switchable superhydrophobicity/superhydrophilicity and adjustable pore size within the range of about 28 nm to 895 µm can be observed. Through synergistically tuning the wettability and pore size, both ON/OFF water permeation and accurate flux can be obtained. Meanwhile, we also applied the sponge for molecule release, and diverse release manners with precise/smart controllability can be accomplished. This paper reports for the first time a smart material with controllability in both surface wetting and pore size, which provides a new strategy for the preparation of novel smart superwetting porous materials.

Tuning wettability and surface order of MWCNTs by functionalization for water desalination

While multiwall carbon nanotubes (MWCNTs) attract a lot of attention for their remarkable physical and mechanical properties, it is necessary to modify their surface chemistry and wettability with functionalization for successful application of these materials. Vertical and spaghetti MWCNTs were produced and functionalized with H2 and SF6 plasma treatments. Morphological and chemical characterizations were conducted. Molecular dynamics (MD) simulations demonstrated apparent unbundling of the functionalized vertical MWCNTs with the repulsive electrostatic forces between functional agents dominating the attractive van der Waals forces between the CNTs. MD simulations of hydrogenated spaghetti showed an increase in the structural order. Raman scattering provided evidence of the role played by the functional groups in increasing the graphitic character of MWCNTs. Contact angle measurements revealed the wettability tuning of the hydrogenated MWCNTs with a pronounced correlation with surface order. Hydrophobic-hydrophilic transitions of fluorinated MWCNTs with fluorination time also revealed the exchange of nonpolar and polar bonds on the side walls of the MWCNTs. Electrical conductivity measurements reflected the potential of functionalized MWCNT surfaces in holding back the salt, allowing fast transport of water, cancelling the conventional trade-off between selectivity and permeability, and presenting these materials as candidates for new generation of nanomaterials in water desalination.

Re‐Printable Chiral Photonic Paper with Invisible Patterns and Tunable Wettability

AbstractThe construction of invisible patterns via high‐resolution printing and the independent encoding/decoding of complex information can lead to promising applications in steganography and watermarking for optical encryption. Herein, a rewritable chiral photonic paper formed by cholesteric cellulose nanocrystals and polycation is reported. The chemically crosslinked polycation network interpenetrates in the cholesteric structure while retaining the optical properties of the photonic crystals. The film exhibits controllable wettability via anion exchange, leading to extremely low contrast in the dry state but high contrast by a rapid wetting response. Triple invisible information is independently encoded on the films, including invisible patterns caused by reversible counterion‐controlled wettability, permanent fluorescent labels based on fluorescent counterions, and polarization‐dependent structural colors based on cholesteric structures. Full color patterns can be reversibly constructed via inkjet printing, with a high resolution of 100 µm. In addition, the circular polarization characteristics of the cellulose nanocrystals, liquid crystals, endow the system with complex and independent responses, realizing a wetting/polarization double‐key decryption. This work provides a simple and effective optical technique for coding complex information on a single material platform and expands the techniques available to achieve invisible patterns for sensing and anti‐counterfeiting.

Drug powders with tunable wettability by atomic and molecular layer deposition: From highly hydrophilic to superhydrophobic

The wettability of pharmaceuticals is a key physical property which influences their dissolution rate, dispersibility, flowability and solid-state stability. Here, we provide a platform of surface nanoengineering methods capable of tuning the wettability of drug powders from high hydrophilicity to superhydrophobicity with drug loadings up to 95–99%. Specifically, we functionalize gram-scale micronized budesonide, a commercial active pharmaceutical ingredient for respiratory diseases, in a vibrated fluidized bed reactor with inorganic Al2O3, TiO2 and SiO2 by atomic layer deposition (ALD), organic poly(ethylene terephthalate) (PET) by molecular layer deposition (MLD) and inorganic/organic titanicone by hybrid ALD/MLD. Transmission electron microscopy shows the formation of smooth and uniform films for each deposition process without significantly affecting the surface morphology of the budesonide particles. Crucially, the deposition processes do not alter the solid-state structure and cytocompatibility of budesonide. The ceramic ALD films are able to convert the originally hydrophobic budesonide into highly hydrophilic powders with water contact angles (WCAs) of ~10° within a few seconds. The purely organic PET films grown via MLD deliver superhydrophobic powders with a WCA of 145–150°. In contrast, the titanicone hybrid ALD/MLD films lead to mild hydrophilicity with WCAs ranging from ~80° to ~60°. Modifying the wetting properties of inhaled drug powders such as budesonide is relevant to improve bioavailability, enhance the dispersion of formulations in suspension-based inhalers or prevent moisture interactions in dry powder inhalers. Moreover, by tuning the surface chemical composition at the atomic or molecular level, particle ALD, MLD and hybrid ALD/MLD enable control over powder wettability for several pharmaceutical dosage forms with applications in oral, orally inhaled and parenteral delivery.

Controllable wettability tuning of the stainless steel surface through successive ionic layer deposition of Zn-Fe layered double hydroxysulfate

An efficient and scalable technique was proposed to control the wettability of stainless steel through successive ionic layer deposition (SILD) of ZnFe layered double hydroxysulfate (LDHS). The composition, structure, and surface characteristics of the coatings were investigated by EDS, XRD, SEM, Raman spectroscopy, and contact angle (CA) analysis. It was found that the coatings consisted of 2D nanocrystals with a thickness of 5–17 nm and a planar size of 55–416 nm, depending on the number of SILD cycles (n = 1–15). It was shown that their growth was accompanied by substrate-relative orientation change: 2D nanocrystals oriented horizontally at n = 1–2 and vertically at n = 3–15. The vertical orientation occurs due to the positive charge of substrate and nanocrystals surface during the SILD which results in their electrostatic repulsion. The SILD modification also leads to a change in surface wettability from weakly hydrophobic (n = 2, CA = 64.7 ± 0.6°) to superhydrophilic (n = 15, CA = 9.2 ± 0.3°). It correlates with established nanocrystals orientation since hydrophilic sulfate groups became more accessible for interaction with water in case of vertical orientation and practically inaccessible for horizontally directed nanocrystals.

Tunable wettability of polymer films by partial engulfment of nanoparticles

A series of poly(methyl methacrylate) (PMMA) surfaces decorated by Cu nanoparticles (NP) with gradually varied morphology were prepared by high-pressure ${\mathrm{CO}}_{2}$ treatment at various time spans. Combining the characterizations of transmission electron microscopy (TEM) and atomic force microscopy (AFM), an accurate three-dimensional view of the morphology of the surfaces was presented. Subsequently, the wettability of the surfaces decreases near linearly with the increase of the apparent height of the decorating NPs in both static (static contact angle) and dynamic (contact angle hysteresis) aspects. The observed tendency contradicts to the Wenzel or Cassie-Baxter model and is explained by the contribution of nanomeniscus formed between the decorating NP and the flat substrate. The capillary pressure from this meniscus is negative and results in the increase of the contact angle with the apparent height $({H}_{N})$ of the Cu NPs decorating the PMMA surface. In addition, the effect of the coverage $({C}_{N})$ by NPs on the wettability can be explained on the same basis. Our experiment demonstrates the important influence of the nanomeniscus on the wettability, which is usually not taken into account. The results in this work provide a comprehensive understanding of how nanostructure affects the wettability of the decorated surfaces and shed light on how to obtain certain wettability through nanostructuring of the surface morphology.

MWCNT-based surfaces with tunable wettability obtained by He+ ion irradiation

A study of He+ ion irradiation influence on the wettability of the multi-walled carbon nanotubes is presented. Tablets of pressed nanotubes of two types with different diameters were prepared and irradiated by 80 keV He+ ions. Raman and X-ray photoelectron spectroscopies showed the differences in the rate of radiation-induced defect formation for different types of nanotubes. The formation of cross-links between the layers of nanotubes under ion irradiation was demonstrated by the molecular dynamics simulation. Contact angle changes drastically with an increase in the fluence for both types of nanotubes: at low fluences superhydrophobic surfaces are formed, with an increase in the fluence a significant reduction in contact angle is observed, especially for the nanotubes of smaller diameters.

Femtosecond laser-induced shape memory polymer micropillar with tunable wettability and reversible adhesion for underwater oil droplet lossless transfer

Shape memory polymers (SMPs) with tunable wettability and reversible adhesion through adjusting the surface morphology have great prospects in functional devices. However, current functional devices based on SMPs are mainly concentrated on the manipulation of diverse liquid droplets in the air; it is still a challenge to achieve the reversible tuning of underwater oil wettability and adhesion on the microstructured SMP surface. Herein, we fabricate a kind of SMP micropillar array through one-step femtosecond laser irradiation, which could achieve the reversible tuning of underwater oil wettability and adhesion between the tilted and upright states. It is worth noting that the deformed micropillar arrays show underwater oleophobicity and have a larger adhesion force to the oil droplet than that of upright micropillar arrays, which is mainly related to the variation of the contact area between the oil droplet and the micropillar array. Finally, we demonstrate the lossless oil droplet transfer underwater by using the micropillar array surface with different states. We believe the present work will bring some insights for researchers in the field of dynamically responsive tunable underwater oil droplet manipulation.

Fast photocurable thiol-ene elastomers with tunable biodegradability, mechanical and surface properties enhance myoblast differentiation and contractile function

Biodegradable elastomers are important emerging biomaterials for biomedical applications, particularly in the area of soft-tissue engineering in which scaffolds need to match the physicochemical properties of native tissues. Here, we report novel fast photocurable elastomers with readily tunable mechanical properties, surface wettability, and degradability. These elastomers are prepared by a 5-min UV-irradiation of thiol-ene reaction systems of glycerol tripentenoate (GTP; a triene) or the combination of GTP and 4-pentenyl 4-pentenoate (PP; a diene) with a carefully chosen series of di- or tri-thiols. In the subsequent application study, these elastomers were found to be capable of overcoming delamination of myotubes, a technical bottleneck limiting the in vitro growth of mature functional myofibers. The glycerol-based elastomers supported the proliferation of mouse and human myoblasts, as well as myogenic differentiation into contractile myotubes. More notably, while beating mouse myotubes detached from conventional tissue culture plates, they remain adherent on the elastomer surface. The results suggest that these elastomers as novel biomaterials may provide a promising platform for engineering functional soft tissues with potential applications in regenerative medicine or pharmacological testing.

Intrinsically stretchable sheath-core ionic sensory fibers with well-regulated conformal and reprogrammable buckling.

Fiber-based intrinsically stretchable ionic conductors are appealing in the emerging imperceptible sensing devices with an ultrabroad working range, yet still suffer from a low strain sensitivity (gauge factor generally smaller than 3) as compared to electronic conductors. To circumvent this issue, here we report downsized superelastic sheath-core ionic sensory fibers with a fingerprint-like conformal buckling architecture. By delicately regulating the intermolecular interactions in the ionogel core and fluoroelastomer sheath as well as adjusting holding strains, the transparency and buckling density of the fiber are finely modulated. Heat to above 60 °C would further erase the formed buckles, enabling the encoded information of the fiber to be reprogrammable. Importantly, introducing conformal buckles are shown to bring about two-fold sensitivity enhancement of the sensory fibers, leading to a considerably high gauge factor of 10.1 for ionic strain sensors. Furthermore, the water droplet control ability of the buckled fibers with tunable wettability is also demonstrated, contributing to the versatility of the present sensory fibers which may gain promising applications in integrative electronics, optics, and microfluidics.