Wettability changes of TiO2 nanotube surfaces

This study examines the effect of environmental and experimental conditions, such as temperature and time, on the wettability properties of titania nanotube (TNT) surfaces fabricated by anodization. The fabricated TNTs are 60-130 nm inner diameter and 7-10 μm height. One-microliter water droplets were used to define the wettability of the TNT surfaces by measuring the contact angles. A digital image analysis algorithm was developed to obtain contact angles, contact radii and center heights of the droplets on the TNT surfaces. Bare titanium foil is inherently less hydrophilic with approximately 60°-80° contact angle. The as-anodized TNT surfaces are more hydrophilic and annealing further increases this hydrophilic property. Furthermore, it was found that the TNT surface became more hydrophobic when aged in air over a period of three months. It is believed that the surface wettability can be changed due to alkane contamination and organic contaminants in an ambient atmosphere. This work can provide guidelines to better specify the environmental conditions that changes surface properties of TNT surfaces and therefore affect their desirable function in specific applications such as orthopedic implants.     

Guided transport of water droplets on superhydrophobic-hydrophilic patterned Si nanowires

We present a facile method to fabricate hydrophilic patterns in superhydrophobic Si nanowire (NW) arrays for guiding water droplets. The superhydrophobic Si NW arrays were obtained by simple dip-coating of dodecyltrichlorosilane (DTS). The water contact angles (CAs) of DTS-coated Si NW arrays drastically increased and saturated at the superhydrophobic regime (water CA ≥ 150°) as the lengths of NWs increased. The demonstrated superhydrophobic surfaces show an extreme water repellent property and small CA hysteresis of less than 7°, which enable the water droplets to easily roll off. The wettability of the DTS-coated Si NW arrays can be converted from superhydrophobic to hydrophilic via UV-enhanced photodecomposition of the DTS, and such wettability conversion was reproducible on the same surfaces by repeating the DTS coating and photodecomposition processes. The resulting water guiding tracks were successfully demonstrated via selective patterning of the hydrophilic region on superhydrophobic Si NW arrays, which could enable water droplets to move along defined trajectories.     

Flow behavior in surface-modified microchannels with polymer nanosheets

The paper describes water flow behavior in surface-modified microchannels. We prepared straight-type microchannels which had rectangular cross sections with four different combinations of microchannel surface wettability; cleaned glass substrates served as hydrophilic microchannel walls and the microchannel walls coated with polymer Langmuir–Blodgett (LB) films were used as hydrophobic surfaces. The polymer LB films were successfully transferred onto glass substrates by vertical dipping method. The flow rates and the water meniscus shape strongly depended on the microchannel surface wettability. The decrease in flow rate with the increasing number of hydrophobic (polymer LB film) surface was attributed to the higher adhesion energy of hydrophobic surface. The Reynolds number was also characterized to be in the order of 10^− 1, implying a specific feature of microchannel; laminar flow.     

Micropatterning functional groups on polymer surfaces via masked vapor-phase photografting

Controlling cell behavior on biomaterial surface is the ultimate goal of cell and tissue engineering. Fabrication of biomaterials with alternatively hydrophilic/hydrophobic surface of parallel nanopatterned groves can provide biomaterial surfaces for the study of cell-surface interactions. In the present communication, masked vapor-phase photografting was used in patterning functional groups on flat polymeric substrates using poly (dimethylsiloxane) (PDMS) channels. Surface patterns were fabricated by UV-initiated photografting in the presence of a patterned PDMS mask. The approach is exemplified by patterning maleic anhydride (MAH) and acrylamide (AAm) onto poly (methyl methacrylate) (PMMA). The method offers another means to chemically functionalize and pattern polymer surface at the same time.     

Achieving One‐Step Surface Coating of Highly Hydrophilic Poly(Carboxybetaine Methacrylate) Polymers on Hydrophobic and Hydrophilic Surfaces

It is highly desirable to develop a universal nonfouling coating via a simple one‐step dip‐coating method. Developing such a universal coating method for a hydrophilic polymer onto a variety of surfaces with hydrophobic and hydrophilic properties is very challenging. This work demonstrates a versatile and simple method to attach zwitterionic poly(carboxybetaine methacrylate) (PCB), one of the most hydrophilic polymers, onto both hydrophobic and hydrophilic surfaces to render them nonfouling. This is achieved by the coating of a catechol chain end carboxybetaine methacrylate polymer (DOPA‐PCB) assisted by dopamine. The coating process was carried out in water. Water miscible solvents such as methanol and tetrahydrofuran (THF) are added to the coatings if surface wettability is an issue, as for certain hydrophobic surfaces. This versatile coating method was applied to several types of surfaces such as polypropylene (PP), polydimethyl siloxane (PDMS), Teflon, polystyrene (PS), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC) and also on metal oxides such as silicon dioxide.     

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.     

羟基磷灰石陶瓷表面微沟槽的制备及其对成骨细胞早期行为的影响

利用超声探针在铝合金圆片上雕刻微米沟槽图案作为模板, 并成功地将此沟槽图案转移到羟基磷灰石(HAP)陶瓷表面上。扫描电子显微镜(SEM)表征结果显示3种沟槽宽度分别为20、40和60 μm, 与预先设计沟槽的尺寸一致; 接触角测量结果表明, 沟槽化HAP表面的纯水润湿性随沟槽宽度的减小而明显提高。对体外培养在三种沟槽尺寸HAP表面成骨细胞(MC3T3-E1)的形态观察、细胞核染色计数以及细胞取向角测量统计分析的结果表明, 沟槽化的HAP表面具有引导成骨细胞沿沟槽方向铺展的作用, 而且这种引导作用随着沟槽变窄而显著增强, 但这种引导作用并没有对成骨细胞的早期(30 h)增殖行为产生影响。     

Superhydrophobicity of natural and artificial surfaces under controlled condensation conditions

In this paper, we have comparatively investigated the stability of superhydrophobic behaviors of fresh and biomimetic lotus leaf surfaces under controlled water condensation conditions. The binary micro/nano structures of the superhydrophobic surfaces are observed with electron micrographs. Contact and sliding angles are evaluated by syringing water droplets on the substrates with surface temperatures and humidity precisely controlled between -10 and 30 °C, and RH = 10, 30, 60, and 90%. According to the calculations on the solid-liquid contact area fraction in different environmental conditions based on a micro/nano binary structure model, the effects of condensed water on superhydrophobic surfaces are assessed quantitatively. Both the calculated and experimental results indicate that the temperature difference between surface temperature and the dew point during measurement is essential to the occurrence of water condensation while the effect of condensation on the surface wettability also depends on the topology of hierarchical structured surfaces. The loss of water repellency that usually appears on the artificial superhydrophobic surface under low temperature and high humidity conditions is proved to be reversible, showing a bidirectional transition of the equilibrium state between Wenzel and Cassie-Baxter.     

Effect of ultrasonic vibration-assisted laser surface melting and texturing of Ti-6Al-4V ELI alloy on surface properties

Ultrasonic vibration-assisted laser surface processing that involves application of vertical ultrasonic vibrations to the Ti-6 Al-4 V alloy substrates while being irradiated with a CO_2 laser was performed for the development of laser melted and textured surfaces with potential applications in biomedical implants.The laser processing resulted in very consistent repeating undulating grooved surfaces, and the undulations were significantly more pronounced in the samples processed with higher ultrasonic power outputs.The phase evolution, studied by x-ray diffraction, confirmed that the laser processing triggered transformation of globular α→ acicular α and martensitic α' as well as increased amounts of retained α phases,which were also reflected in the microscopic analysis. The surface texture developed by laser processing resulted in increased surface wettability with increasing ultrasonic power output. The textured surfaces exhibited marked decrease in coefficients of friction during sliding wear testing performed under simulated body fluid due to lubricant entrainment within the textured grooves. The texturing also resulted in significant reduction in surface contact area during the wear process, which considerably reduced the overall wear rates due to abrasive wear.     

The determination of the morphology of melanocytes by laser-generated periodic surface structures

We generated self-organized, grating-like structures on the surface of polyethylene-terephthalate by ArF excimer laser ablation. Tilting the polymer films with angles larger than 60°, we got parallel grooves. The surface changes caused by the laser illumination were qualified by AFM. The period of the structures was approximately 1 μm, which is commensurable with the characteristic size of melanocytes. We examined the cell shape of normal epidermal melanocytes (M-C) and of melanocytes from the skin of one neurofibromatosis 1 patient (M-NFS) in vitro. The number of dendrites per cell, the length of dendrites and the orientation of several hundred cells were evaluated by an image-processing program. It was proven that the cell morphology and orientation is determined by the topography of the structured polymer substrate. All cells are aligned parallel to the grooves and show the typical bipolar shape. In contrast, on the untreated part of the substrate, the cells are randomly oriented, and the NF cells have more dendrites.     

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 μm and a depth of 1.5–2 μm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 μm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 μm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.     

Surface characterization of poly(N-isopropylacrylamide) grafted tissue culture polystyrene by electron beam irradiation, using atomic force microscopy, and X-ray photoelectron spectroscopy

To understand features of polymers grafted by electron beam (EB) irradiation method, we investigated topology of poly(N-isopropylacrylamide) (PIPAAm) grafted tissue culture polystyrene (TCPS) (PIPAAm-TCPS) prepared by EB irradiation, using atomic force microscopy (AFM) in air and under aqueous conditions. Furthermore, surfaces properties of PIPAAm-TCPS surfaces before and after cell culture were also examined for evaluation of functionality of the surface as biomaterials, using XPS analysis. Three types of PIPAAm-TCPSs with different graft densities (1.0+/-0.1, 1.6+/-0.1, and 2.0+/-0.1 microg/cm2 of the grafted) were obtained (abbreviated as 11PIPAAm-, 16PIPAAm-, and 20PIPAAm-TCPS) by using different initial monomer concentration (20, 55, and 65 wt%). Contact angles (costheta value) of the surfaces increased with an increase in density of the grafted polymer. AFM observation in air clearly revealed that original TCPS surface possesses scratched and grooved topology (ca. 10 nm height of the scratch), while PIPAAm-TCPSs surfaces exhibited nanoordered PIPAAm particle-like domains. The size of the particles also increased proportionally initial IPAAm monomer concentration. The 11PIPAAm-and 16PIPAAm-TCPS surfaces having ca. 10-30 nm and ca. 40-50 nm size of the particles also displayed scratched and grooved topology featured in basal TCPS. However, the larger sizes of the particles (ca. 40-100 nm) formed on 20PIPAAm-TCPS surfaces adequately conceals the topological feature of the basal TCPS surfaces. The AFM images indicate that the graft polymer is as ultra thin as the scratch and grooves featured on basal TCPS are discernible, and the grafted PIPAAm layer become thicker with an increase of the monomer concentration. For 16PIPAAm-TCPS surfaces, the nanoordered particles were also observable in aqueous conditions at 20 degrees C and 37 degrees C. Comparison between the images obtained at 20 degrees C and 37 degrees C suggest that the domains are not likely to exhibit significant swelling and shrinking by temperature change, although the topology of PIPAAm grafted onto clover glass surface (50 microm thickness of the gel layer) were dramatically changed by temperature change in early reports. This difference should be due to ultra thin thickness of the grafted PIPAAm, which is subject to more restricted molecular motion by basal hydrophobic TCPS interfaces, as we reported previously. XPS C1s and N1s spectra of 16PIPAAm-TCPS surface after removal of cells suggest that proteins and/or peptides components possibly remained on the surfaces. Based on results from XPS analysis, we further discuss surface properties of 16PIPAAm-TCPS as biomaterials, comparing those of PIPAAm grafted polystyrene prepared by a radio frequency plasma method used in recent reports.     

Micro-structural geometry of thin films intended for the inner lumen of nerve conduits affects nerve repair

Damage to peripheral nerves can cause significant motor or sensory injuries. In serious cases, a nerve is sacrificed from another part of the body to repair a damaged nerve (autograft). The development of biodegradable polymer conduits may offer an alternative to autografts. This study investigated the surface topography and mechanical properties of smooth, pitted and grooved structures of ultra-thin poly (ε-caprolactone)/poly lactic acid blended, solvent-cast films. We have investigated the effect of the groove shape on cell morphology and alignment. Photolithography and dry/wet etching was used to develop patterned silicon substrates with grooves with accurate geometries (V shaped, sloped walls and square shaped). Using a neural cell line (NG108-15), in vitro experiments confirmed good cell attachment and proliferation on all the polymer scaffolds. Imaging techniques demonstrated that there was different cellular responses and morphology according to the shape of the groove. Studies showed that the geometry, particularly the angle of the slope and the space between grooves, affected cellular responses. In addition, biomechanical studies showed that the patterned films had excellent mechanical properties and were stronger than the natural nerve. The conduit tubes were made by rolling the films around a mandrel and using a thermal welding technique to join the edges. The promising biomechanical and in vitro results demonstrate that nerve cell responses are affected by the shape of longitudinal grooves, and particularly by the angle of the slope of the groove walls.     

Modulation of human dermal microvascular endothelial cell and human gingival fibroblast behavior by micropatterned silica coating surfaces for zirconia dental implant applications

Dental ceramic implants have shown superior esthetic behavior and the absence of induced allergic disorders when compared to titanium implants. Zirconia may become a potential candidate to be used as an alternative to titanium dental implants if surface modifications are introduced. In this work, bioactive micropatterned silica coatings were produced on zirconia substrates, using a combined methodology of sol–gel processing and soft lithography. The aim of the work was to compare the in vitro behavior of human gingival fibroblasts (HGFs) and human dermal microvascular endothelial cells (HDMECs) on three types of silica-coated zirconia surfaces: flat and micropatterned (with pillars and with parallel grooves). Our results showed that cells had a higher metabolic activity (HGF, HDMEC) and increased gene expression levels of fibroblast-specific protein-1 (FSP-1) and collagen type I (COL I) on surfaces with pillars. Nevertheless, parallel grooved surfaces were able to guide cell growth. Even capillary tube-like networks of HDMEC were oriented according to the surface geometry. Zirconia and silica with different topographies have shown to be blood compatible and silica coating reduced bacteria adhesion. All together, the results indicated that microstructured bioactive coating seems to be an efficient strategy to improve soft tissue integration on zirconia implants, protecting implants from peri-implant inflammation and improving long-term implant stabilization. This new approach of micropatterned silica coating on zirconia substrates can generate promising novel dental implants, with surfaces that provide physical cues to guide cells and enhance their behavior.     

Polymer films with surfaces unmodified and modified by non-thermal plasma as new substrates for cell adhesion

The surface properties of biomaterials, such as wettability, polar group distribution, and topography, play important roles in the behavior of cell adhesion and proliferation. Gaseous plasma discharges are among the most common means to modify the surface of a polymer without affecting its properties. Herein, we describe the surface modification of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) films using atmospheric pressure plasma processing through exposure to a dielectric barrier discharge (DBD). After treatment the film surface showed significant changes from hydrophobic to hydrophilic as the water contact angle decreasing from 95° to 37°. All plasma-treated films developed more hydrophilic surfaces compared to untreated films, although the reasons for the change in the surface properties of PS and PMMA differed, that is, the PS showed chemical changes and in the case of PMMA they were topographical. Excellent adhesion and cell proliferation were observed in all films. In vitro studies employing flow cytometry showed that the proliferation of L929 cells was higher in the film formed by a 1:1 mixture of PS/PMMA, which is consistent with the results of a previous study. These findings suggest better adhesion of L929 onto the 1:1 PS/PMMA modified film, indicating that this system is a new candidate biomaterial for tissue engineering.     

Tribological behaviors of plasma-treated carbon composite grooved surfaces

The tribological behavior of carbon epoxy composites whose surfaces have many small grooves of 100 μm width were compared with respect to plasma treatment duration under dry sliding conditions. The surface coating material on the grooved surface was high-density polyethylene (HDPE) and suitable plasma treatment time for grooved composite surface for atmospheric pressure plasma system was experimentally investigated by measuring the friction coefficient and wear volume. The wear morphology of the composites observed with a scanning electron microscopic (SEM) revealed that the surface coating layer on the grooved surface significantly improved the wear resistance and the plasma treatment can improve the durability of the coating layer.     

A general mathematical form and description of contact angles

A general mathematical form for contact angles on surfaces is suggested, offering fundamental new insights into describing wettability phenomena, which may be of considerable relevance to many fields of science. It was found that the Young equation – although physically well understood on ideal surfaces – is not unique, but a special case of a more general fundamental equation based on complex contact angles, comprising wettability on both ideal and non‐ideal surfaces. The novel mathematical form predicts the existence of imaginary contact angles on all non‐ideal surfaces, implying two dimensions of wettabilty and necessitating the experimental determination of real and imaginary contact angles. It could be demonstrated that the new equation can be successfully applied to experimental physical and biomedical data in the hydrophilic and hydrophobic range, with novel information gained on non‐ideality in the form of complex and imaginary contact angles.     

Solidification contact angles of molten droplets deposited on solid surfaces

Droplet impact and equilibrium contact angle have been extensively studied. However, solidification contact angle, which is the final contact angle formed by molten droplets impacting on cold surfaces, has never been a study focus. The formation of this type of contact angle was investigated by experimentally studying the deposition of micro-size droplets (∼39 μm in diameter) of molten wax ink on cold solid surfaces. Scanning Electron Microscope (SEM) was used to visualize dots formed by droplets impacted under various impact conditions, and parameters varied included droplet initial temperature, substrate temperature, flight distance of droplet, and type of substrate surface. It was found that the solidification contact angle was not single-valued for given droplet and substrate materials and substrate temperature, but was strongly dependent on the impact history of droplet. The angle decreased with increasing substrate and droplet temperatures. Smaller angles were formed on the surface with high wettability, and this wetting effect increased with increasing substrate temperature. Applying oil lubricant to solid surfaces could change solidification contact angle by affecting the local fluid dynamics near the contact line of spreading droplets. Assuming final shape as hemispheres did not give correct data of contact angles, since the final shape of deposited droplets significantly differs from a hemispherical shape.     

利用银镜反应制备梯度润湿性表面

利用工艺简单的银镜反应制备了润湿性均一的纳米银表面.该表面具有一定的粗糙度,随着与低表面能的正十二烷基硫醇自组装时间的延长,银表面的接触角逐步增大,并达到超疏水性.通过调节正十二烷基硫醇溶液的浓度或滴加速度,能在同一银表面的不同位置实现从疏水性到超疏水性的梯度润湿性调控.     

Surface characterization of laser-ablated polymers used for microfluidics

Fabrication of microfluidic devices by excimer laser ablation under different atmospheres may provide variations in polymer microchannel surface characteristics. The surface chemistry and electroosmotic (EO) mobility of polymer microchannels laser ablated under different atmospheres were studied by X-ray photoelectron spectroscopy and current monitoring mobility measurements, respectively. The ablated surfaces of PMMA were very similar to the native material, regardless of ablation atmospheres due to the negligible absorption of 248-nm light by that polymer. The substrates studied that exhibit nonnegligible absorption at this energy, namely, poly(ethylene terephthalate glycol), poly(vinyl chloride), and poly(carbonate), showed significant changes in surface chemistry and EO mobility when the ablation atmospheres were varied. Ablation of these three polymer substrates under nitrogen or argon resulted in low EO mobilities with a loss of the well-defined chemical structures of the native surfaces, while ablation under oxygen yielded surfaces that retained native chemical structures and supported higher EO mobilities.