Continuously Tunable Wettability by Using Surface Patterned Shape Memory Polymers with Giant Deformability

Designing smart surfaces with tunable wettability has drawn much attention in recent years for academic research and practical applications. Most of the previous methods to achieve such surfaces demand some particular materials that inherently have special features or complicated structures which are usually not easy to obtain. A novel strategy to achieve such smart surfaces is proposed by using the surface patterned shape memory polymers of chemically crosslinked polycyclooctene which shows a giant deformability of up to ≈730% strain. The smart surfaces possess the ability to continuously tune the wettability by controlling the recovery temperature and/or time. Coating the modified titanium dioxide nanoparticles onto such surfaces renders the surface superhydrophobicity and expands the tunable range of contact angles (CAs). Theoretical calculations of the CAs at different strains via modified Cassie model well explain the tunable wettability behaviors of such smart surfaces.     

润湿性可控智能表面的研究进展

论述了表面润湿性的基本原理,综述了可控润湿性智能表面研究的最新进展,介绍了热化学法、电润湿法、光致表面化学反应法、溶剂法、pH法和多重响应法等调控表面润湿性的方法和机理,展望了润湿性可控智能表面的发展方向.     

Superwettability‐Based Interfacial Chemical Reactions

Superwetting interfaces arising from the cooperation of surface energy and multiscale micro/nanostructures are extensively studied in biological systems. Fundamental understandings gained from biological interfaces boost the control of wettability under different dimensionalities, such as 2D surfaces, 1D fibers and channels, and 3D architectures, thus permitting manipulation of the transport physics of liquids, gases, and ions, which profoundly impacts chemical reactions and material fabrication. In this context, the progress of new chemistry based on superwetting interfaces is highlighted, beginning with mass transport dynamics, including liquid, gas, and ion transport. In the following sections, the impacts of the superwettability‐mediated transport dynamics on chemical reactions and material fabrication is discussed. Superwettability science has greatly enhanced the efficiency of chemical reactions, including photocatalytic, bioelectronic, electrochemical, and organic catalytic reactions, by realizing efficient mass transport. For material fabrication, superwetting interfaces are pivotal in the manipulation of the transport and microfluidic dynamics of liquids on solid surfaces, leading to the spatially regulated growth of low‐dimensional single‐crystalline arrays and high‐quality polymer films. Finally, a perspective on future directions is presented.     

Biomaterial surface properties modulate in vitro rat calvaria osteoblasts response: Roughness and or chemistry?

The aim of this study was a better understanding of the regulation mechanisms of in vitro osteoblast activity on biomaterials. Rat osteoblast behaviour on different surfaces was studied. Surfaces with different roughness (and a similar surface chemistry) or with different surface chemistry (and a similar roughness) were compared. Cellular morphology was observed by scanning electron microscopy and cell adhesion was quantified using an image analysis system. Osteoblast proliferation was quantified by a MTT test and total protein content and alkaline phosphatase (ALP) activity were evaluated by spectrophotometry. Data were compared by statistical analysis.

Results showed that NiTi surface roughness did not influence osteoblasts morphology, adhesion, total protein content and ALP activity whereas it modulated cell proliferation. Roughness was shown to stimulate cell proliferation. For smooth surfaces exhibiting two different chemical compositions, adhesion rate was found to be higher on Thermanox® than on NiTi whereas proliferation was shown to be smaller. ALP activity was also modulated by surface chemistry. Thus, cell adhesion and ALP activity were found to be more governed by surface chemistry than by roughness whereas cell proliferation was shown to be modulated by roughness (this effect increasing during cell culture) and by chemistry (this effect remaining stable in time) together. Total protein content and cell morphology were found to be independent of both parameters (roughness and chemistry). Effects of surface chemistry were discussed in terms of wettability and electron acceptor/donor properties of the surfaces of interest. Immunofluorescence images of adhesion proteins could not demonstrate differences between the three surfaces.     

润湿性可切换的表面

超疏水性和超亲水性是表面润湿性的两个极端,受表面的形貌和化学组成的共同作用。通过施加外界刺激可以改变表面形貌和/或表面化学组成,实现表面润湿性在超疏水性和超亲水性之间的切换。本文综述了润湿性可切换表面的最新研究进展。概述了以光照、温度、pH值、溶剂、电势等作为外界刺激以及表面反离子切换实现表面润湿性在超疏水和超亲水之间切换的方法。介绍了由于非对称的润湿性而导致液体定向传递的现象。展望了可控润湿性表面发展趋势,通过调控表面微米-纳米多级粗糙结构和化学组成,可实现在各种基材表面实现超疏水和超亲水之间的切换。     

表面浸润性对冰粘附强度的影响研究

表面浸润性对冰粘附强度有较大影响,通过对裸铝表面进行NaOH溶液化学刻蚀、氟硅烷修饰制备得到不同表面试片,测量试片的表面接触角获得其浸润性,再采用ZDY法计算各试片的表面能,通过冰粘附强度实验装置测量试片表面的冰粘附强度。结果表明,疏水表面冰粘附强度普遍小于亲水表面的粘附强度,表面能较小的试片,冰粘附强度也较小。     

Surface wettability of plasma SiOx:H nanocoating-induced endothelial cells' migration and the associated FAK-Rho GTPases signalling pathways

Vascular endothelial cell (EC) adhesion and migration are essential processes in re-endothelialization of implanted biomaterials. There is no clear relationship and mechanism between EC adhesion and migration behaviour on surfaces with varying wettabilities. As model substrates, plasma SiO_x:H nanocoatings with well-controlled surface wettability (with water contact angles in the range of 98.5 ± 2.3° to 26.3 ± 4.0°) were used in this study to investigate the effects of surface wettability on cell adhesion/migration and associated protein expressions in FAK-Rho GTPases signalling pathways. It was found that EC adhesion/migration showed opposite behaviour on the hydrophilic and hydrophobic surfaces (i.e. hydrophobic surfaces promoted EC migration but were anti-adhesions). The number of adherent ECs showed a maximum on hydrophilic surfaces, while cells adhered to hydrophobic surfaces exhibited a tendency for cell migration. The focal adhesion kinase (FAK) inhibitor targeting the Y-397 site of FAK could significantly inhibit cell adhesion/migration, suggesting that EC adhesion and migration on surfaces with different wettabilities involve (p)FAK and its downstream signalling pathways. Western blot results suggested that the FAK-Rho GTPases signalling pathways were correlative to EC migration on hydrophobic plasma SiO_x:H surfaces, but uncertain to hydrophilic surfaces. This work demonstrated that surface wettability could induce cellular behaviours that were associated with different cellular signalling events.     

Superwetting Surfaces under Different Media: Effects of Surface Topography on Wettability

Superwetting surfaces in air, such as superhydrophobic and superoleophobic surfaces that are governed by surface chemical compositions and surface topographies, are one of the most extensively studied topics in this field. However, it is not well‐understood how surface topographies affect the behaviors of immiscible liquids and gases under other kinds of media, although it is significant in diverse fields. The main aim of this work is to systematically investigate the wetting behaviors of liquids (water and oil) and gas (air) on silicon surfaces with different topographies (i.e., smooth, micro, nano, and micro‐/nanostructures) under various media (i.e., air, water, and oil). The contact angles, as well as contact‐angle hysteresis, sliding angles, and adhesive forces, were utilized to evaluate the wettability of these surfaces. As a result, the microstructured surfaces typically exhibit high contact‐angle hysteresis, high sliding angles, and high adhesive forces, whereas the micro‐/nanostructured surfaces display low contact‐angle hysteresis, low sliding angles, and low adhesive forces, even if they have high (>150°) and similar contact angles. Furthermore, when transferring the same surface from one kind of medium to another, different superwetting states can be reversibly switched.     

Antimicrobial surfaces: a review of synthetic approaches,applicability and outlook

The rapid spread of microorganisms such as bacteria, fungi, and viruses can be extremely detrimental and can lead to seasonal epidemics or even pandemic situations. In addition, these microorganisms may bring about fouling of food and essential materials resulting in substantial economic losses. Typically, the microorganisms get transmitted by their attachment and growth on various household and high contact surfaces such as doors, switches, currency. To prevent the rapid spread of microorganisms, it is essential to understand the interaction between various microbes and surfaces which result in their attachment and growth. Such understanding is crucial in the development of antimicrobial surfaces. Here, we have reviewed different approaches to make antimicrobial surfaces and correlated surface properties with antimicrobial activities. This review concentrates on physical and chemical modification of the surfaces to modulate wettability, surface topography, and surface charge to inhibit microbial adhesion, growth, and proliferation. Based on these aspects, antimicrobial surfaces are classified into patterned surfaces, functionalized surfaces, superwettable surfaces, and smart surfaces. We have critically discussed the important findings from systems of developing antimicrobial surfaces along with the limitations of the current research and the gap that needs to be bridged before these approaches are put into practice.

     

Plasma-modified and polyethylene glycol-grafted polymers for potential tissue engineering applications

Modified and grafted polymers may serve as building blocks for creating artificial bioinspired nanostructured surfaces for tissue engineering. Polyethylene (PE) and polystyrene (PS) were modified by Ar plasma and the surface of the plasma activated polymers was grafted with polyethylene glycol (PEG). The changes in the surface wettability (contact angle) of the modified polymers were examined by goniometry. Atomic Force Microscopy (AFM) was used to determine the surface roughness and morphology and electrokinetical analysis (Zeta potential) characterized surface chemistry of the modified polymers. Plasma treatment and subsequent PEG grafting lead to dramatic changes in the polymer surface morphology, roughness and wettability. The plasma treated and PEG grafted polymers were seeded with rat vascular smooth muscle cells (VSMCs) and their adhesion and proliferation were studied. Biological tests, performed in vitro, show increased adhesion and proliferation of cells on modified polymers. Grafting with PEG increases cell proliferation, especially on PS. The cell proliferation was shown to be an increasing function of PEG molecular weight.     

微观结构表面接触角模型及其润湿性

润湿性是固体表面的重要性质之一,固液界面润湿性与表面微观结构、界面能等有关.研究了微观结构固体表面固液界面润湿性以及界面能、液滴重力、微观结构参数对润湿性的影响.分析表明,Young、Wenzel、Cassie、Cassie-Baxter等4种接触角模型分别把固体表面看成光滑、粗糙(液滴完全填满)、粗糙(液滴不填充)以及粗糙(液滴部分填充),后3种模型可用于实际固体表面,并可在3种状态下实现转换.设计了方柱凹坑、圆柱凹坑等微观结构表面,调控横径比、纵径比、深径比等微观结构参数,可以改变固液界面润湿性.研究发现,液滴重力对表面接触角存在稍许影响,界面能的大小决定着材料表面的疏/亲水性.     

Self-assembly of diverse alumina architectures and their morphology-dependent wettability

This work reports the fabrication of diverse nanostructured alumina films under high-field anodization in oxalic-acid electrolytes. Different surface morphologies of these alumina films can be obtained by adjusting reaction parameters, which was ascribed to the anisotropic chemical etching induced by the reaction heat and the concentration gradient of the oxalic-acid solution along the nanopore channels during the high-field anodization process. These alumina surfaces without coating low energy materials show remarkable morphology-dependent wettability. Specially, the alumina surface consisting of porous underlayer and nanowire pyramids with no chemical modification reveals excellent super water-repellent behavior for the first time. This study could provide a new approach for designing functional surfaces with tunable wettability.     

Control of bacterial biofilm growth on surfaces by nanostructural mechanics and geometry

Surface-associated communities of bacteria, called biofilms, pervade natural and anthropogenic environments. Mature biofilms are resistant to a wide range of antimicrobial treatments and therefore pose persistent pathogenic threats. The use of surface chemistry to inhibit biofilm growth has been found to only transiently affect initial attachment. In this work, we investigate the tunable effects of physical surface properties, including high-aspect-ratio (HAR) surface nanostructure arrays recently reported to induce long-range spontaneous spatial patterning of bacteria on the surface. The functional parameters and length scale regimes that control such artificial patterning for the rod-shaped pathogenic species Pseudomonas aeruginosa are elucidated through a combinatorial approach. We further report a crossover regime of biofilm growth on a HAR nanostructured surface versus the nanostructure effective stiffness. When the 'softness' of the hair-like nanoarray is increased beyond a threshold value, biofilm growth is inhibited as compared to a flat control surface. This result is consistent with the mechanoselective adhesion of bacteria to surfaces. Therefore by combining nanoarray-induced bacterial patterning and modulating the effective stiffness of the nanoarray--thus mimicking an extremely compliant flat surface--bacterial mechanoselective adhesion can be exploited to control and inhibit biofilm growth.     

Plant surfaces with cuticular folds are slippery for beetles

Plant surfaces covered with three-dimensional (3D) waxes are known to strongly reduce insect adhesion, leading to slippery surfaces. Besides 3D epicuticular waxes, cuticular folds are a common microstructure found on plant surfaces, which have not been quantitatively investigated with regard to their influence on insect adhesion. We performed traction experiments with Colorado potato beetles on five plant surfaces with cuticular folds of different magnitude. For comparison, we also tested (i) smooth plant surfaces and (ii) plant surfaces possessing 3D epicuticular waxes. Traction forces on surfaces with medium cuticular folds, of about 0.5 µm in both height and thickness and a spacing of 0.5–1.5 µm, were reduced by an average of 88 per cent in comparison to smooth plant surfaces. Traction forces were reduced by the same order of magnitude as on plant surfaces covered with 3D epicuticular waxes. For surface characterization, we performed static contact angle measurements, which proved a strong effect of cuticular folds also on surface wettability. Surfaces possessing cuticular folds of greater magnitude showed higher contact angles up to superhydrophobicity. We hypothesize that cuticular folds reduce insect adhesion mainly due to a critical roughness, reducing the real contact area between the surface and the insect''s adhesive devices.     

Unidirectional Wetting Properties on Multi‐Bioinspired Magnetocontrollable Slippery Microcilia

Here, a smart fluid‐controlled surface is designed, via the rational integration of the unique properties of three natural examples, i.e., the unidirectional wetting behaviors of butterfly's wing, liquid‐infused “slippery” surface of the pitcher plant, and the motile microcilia of micro‐organisms. Anisotropic wettability, lubricated surfaces, and magnetoresponsive microstructures are assembled into one unified system. The as‐prepared surface covered by tilted microcilia achieves significant unidirectional droplet adhesion and sliding. Regulating by external magnet field, the directionality of ferromagnetic microcilia can be synergistically switched, which facilitates a continuous and omnidirectional‐controllable water delivery. This work opens an avenue for applications of anisotropic wetting surfaces, such as complex‐flow distribution and liquid delivery, and extend the design approach of multi‐bioinspiration integration.     

Various fates of neuronal progenitor cells observed on several different chemical functional groups

Neuronal progenitor cells cultured on gold-coated glass surfaces modified by different chemical functional groups, including hydroxyl (-OH), carboxyl (-COOH), amino (-NH₂), bromo (-Br), mercapto (-SH), -Phenyl and methyl (-CH₃), were studied here to investigate the influence of surface chemistry on the cells’ adhesion, morphology, proliferation and functional gene expression. Focal adhesion staining indicated in the initial culture stage cells exhibited morphological changes in response to different chemical functional groups. Cells cultured on -NH₂ grafted surface displayed focal adhesion plaque and flattened morphology and had the largest contact area. However, their counter parts on -CH₃ grafted surface displayed no focal adhesion and rounded morphology and had the smallest contact area. After 6 days culture, the proliferation trend was as follows: -NH₂>-SH>-COOH>-Phenyl>-Br>-OH>-CH₃. To determine the neural functional properties of the cells affected by surface chemistry, the expression of glutamate decarboxylase (GAD67), nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were characterized. An increase of GAD67 expression was observed on -NH₂, -COOH and -SH grafted surfaces, while no increase in NGF and BDNF expression was observed on any chemical surfaces. These results highlight the importance of surface chemistry in the fate determination of neuronal progenitor cells, and suggest that surface chemistry must be considered in the design of biomaterials for neural tissue engineering.     

Surface modification of polymers by ion-assisted reaction

This paper deals with a new surface modification technique of polymers, the so-called ion-assisted reaction (IAR) to improve the surface properties of polymers and provides outstanding experimental results regarding wettability and adhesion of various polymers. In the IAR, polymer surfaces were subjected to low energy ion irradiation at different dosage in reactive gas environment. Dramatic improvements in wettability and surface energy are observed for the IAR-treated polymer surfaces and can be explained by the addition of functional groups, responsible for the increase of polar component in surface energy. The formation of functional groups results from the interaction among ion, reactive gas and polymer chain involved in IAR treatment, depending on the reactive ion species, the flow rate of the reactive gas and the irradiating ion fluence. The improvement in adhesion between the IAR-treated polymers and coating materials was explained in terms of the increased surface energy as well as surface roughness in the polymers modified by the IAR and possible adhesion enhancement mechanism is to be discussed.     

Anisotropic wetting of microstructured surfaces as a function of surface chemistry

In order to study the influence of surface chemistry on the wetting of structured surfaces, microstructures consisting of grooves or squares were produced via hot embossing of poly(ethylene-alt-tetrafluoroethylene) ETFE substrates. The structured substrates were modified with polymer brushes, thereby changing their surface functionality and wettability. Water droplets were most strongly pinned to the structure when the surface was moderately hydrophilic, as in the case of poly(4-vinylpyridine) (P4VP) or poly(vinyl(N-methyl-2-pyridone) (PVMP) brush-modified substrates. As a result, the droplet shape was determined by the features of the microstructure. The water contact angles (CA) were considerably higher than on flat surfaces and differed, in the most extreme case, by 37° when measured on grooved substrates, parallel and perpendicular to the grooves. On hydrophobic substrates (pristine ETFE), the same effects were observed but were much less pronounced. On very hydrophilic sampes (those modified with poly(N-methyl-vinylpyridinium) (QP4VP)), the microstructure had no influence on the drop shape. These findings are explained by significant differences in apparent and real contact angles at the relatively smooth edges of the embossed structures. Finally, the highly anisotropic grooved microstructure was combined with a gradient in polymer brush composition and wettability. In the case of a parallel alignment of the gradient direction to the grooves, the directed spreading of water droplets could be observed.     

Patterned cell culture substrates created by hot embossing of tissue culture treated polystyrene

Patterning materials such that they elicit a different cell response in different regions would have significant implications in fields such as implantable biomaterials, in vitro cell culture and tissue engineering and regenerative medicine. Moreover, the ability to pattern polymers using inexpensive, currently available processes, without the need for adding proteins or other biochemical agents could lead to new opportunities in biomaterials research. The research reported here demonstrates that by combining the plasma surface treatments used to create commercial grade tissue culture treated polystyrene, with controlled hot embossing processes, that distinct regions can be created on a substrate that result in spatial control of endothelial cell adhesion and proliferation. As well as the topographical changes that result from hot embossing, significant changes in surface chemistry and wettability have been observed and characterised and the resultant effects on endothelial cell responses evaluated. By spatially controlling endothelial cell adhesion, proliferation and subsequent angiogenesis, the processes outlined here have the potential to be used to create a range of different substrates, with applications in the development of assays for high throughput screening, the patterning of implantable biomaterials or the development of smart scaffolds for tissue engineering.     

Fabrication and characterization of transparent superhydrophilic/superhydrophobic silica nanoparticulate thin films

The realization of transparent and superhydrophilic/superhydrophobic surfaces by silica nanoparticulate thin films was exploited in this work. An aqueous electrostatic layer-by-layer assembly process was utilized to fabricate nanoparticulate thin films with adhesion/body/top layer structure on glass substrates by using SiO₂ nanoparticles and polyelectrolytes. The effects of volume ratio of differently sized silica nanoparticle solutions for the body layer deposition on transmittance in visible light region and surface wettability of the nanoparticulate thin films were systematically studied. The experimental results revealed that both optical transparency and superhydrophobicity/superhydrophilicity can be achieved on the same SiO₂ nanoparticulate thin film by using appropriate volume ratios of differently sized silica nanoparticle solutions for body layer deposition, and with and without silane treatment in the fabrication process. The high contrast of wettability that can be achieved by this way suggests the possibility of the creation of superhydrophilic/superhydrophobic patterning and superhydrophilic-superhydrophobic gradient on the same surfaces.