Wetting properties of polystyrene/divinylbenzene crosslinked porous polymers obtained using W/O highly concentrated emulsions as templates

Macroporous polystyrene/divinylbenzene (PS‐DVB) monoliths were obtained using highly concentrated W/O emulsions as templates. These monoliths are of interest due to the high potential applications for catalysis, scaffolds for tissue engineering, filters, membranes, or drug delivery systems. Dynamic wetting behavior through the polymer monolith is directly related to contact angle. For this reason, in this paper we investigate the relationship between contact angle, morphology, and chemical composition of the dense skin layer and the highly porous interior surface of PS‐DVB porous monoliths. Whereas the dense skin layer exhibits a Wenzel regime using water as wetting liquid, the highly porous interior surface exhibits a Cassie–Baxter regime. This behavior is correlated with the roughness observed by scanning electron microscopy (SEM). However, the observed contact angle hysteresis seems to indicate that factors other than surface roughness should be taken into account. For this reason, chemical composition was also studied by elemental microanalysis and X‐ray photoelectron spectroscopy (XPS). The differences in chemical composition observed between the dense skin layer and the highly porous interior surface, according to the wetting model for a heterogeneous surface proposed by Johnson and Dettre, seems also to contribute to the wetting hysteresis. The different wetting between the dense skin layer and the highly porous interior surface results in a dual wettability phenomenon, in which a liquid wets the dense skin layer and does not penetrate into the highly porous interior of the PS‐DVB monoliths. This phenomenon can be of relevance in absorption or desorption processes such as in drug delivery processes. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication and characterization of plasma processed surfaces with tuned wettability

Engineered surfaces with controlled hydrophilic/ hydrophobic character have been fabricated by tailoring the substrate topography and chemistry. In this method, the substrate to be treated was first coated by a photoresist, which was then surface-roughened using SF6 plasma etching. The resulting rough texture was then transferred to the underlying silicon surface by over-etching of the photoresist. At this point, the topographically modified surface was modified chemically by controlled deposition of a thin polymer layer using plasma processing. In this way, both the surface texture and the surface chemistry could be varied independently, producing surfaces with variable wetting character, including super-hydrophilicity and super-hydrophobicity, depending on the choice of plasma polymer deposited. Chemical characterization demonstrates a correlation between the surface chemistry and the wettability of the samples after etching. The surface elementary composition contained more C-F groups as the measured contact angle increased, indicating that the change of wettability is due to both the roughness and the surface energy of the deposited photoresist. In the case of materials deposited on the plasma-treated rough surfaces, the strengthening of the wetting character is only due to the created surface roughness, as XPS analyses showed no significant chemical difference as compared to the flat polymer.     

Particle-collision and porogen-leaching technique to fabricate polymeric porous scaffolds with microscale roughness of interior surfaces

A facile technique is herein reported to fabricate three-dimensional(3D) polymeric porous scaffolds with interior surfaces of a topographic microstructure favorable for cell adhesion.As demonstration,a well-known biodegradable polymer poly(lactide-co-glycolide)(PLGA) was employed as matrix.Under the porogen-leaching strategy,the large and soft porogens of paraffin were modified by colliding with small and hard salt particles,which generated micropits on the surfaces of paraffin spheres.The eventual PLGA scaffolds after leaching the modified porogens had thus interior surfaces of microscale roughness imprinted by those micropits.The microrough scaffolds were confirmed to benefit adhesion of bone marrow stromal cells(BMSCs) of rats and meanwhile not to hamper the proliferation and osteogenic differentiation of the cells.The insight and technique might be helpful for biomaterial designing in tissue engineering and regenerative medicine.     

Confinement effects on the morphology of photopatterned porous polymer monoliths for capillary and microchip electrophoresis of proteins

We find that the morphology of porous polymer monoliths photopatterned within capillaries and microchannels is substantially influenced by the dimensions of confinement. Porous polymer monoliths were prepared by UV-initiated free-radical polymerization using either the hydrophilic or hydrophobic monomers 2-hydroxyethyl methacrylate or butyl methacrylate, cross-linker ethylene dimethacrylate and different porogenic solvents to produce bulk pore diameters between 3.2 and 0.4 microm. The extent of deformation from the bulk porous structure under confinement strongly depends on the ratio of characteristic length of the confined space to the monolith pore size. The effects are similar in cylindrical capillaries and D-shaped microfluidic channels. Bulk-like porosity is observed for a confinement dimension to pore size ratio >10, and significant deviation is observed for a ratio <5. At the extreme limit of deformation a smooth polymer layer 300 nm thick is formed on the surface of the capillary or microchannel. Surface tension or wetting also plays a role, with greater wetting enhancing deformation of the bulk structure. The films created by extreme deformation provide a rapid and effective strategy to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. This approach is demonstrated through cationic films used for electroosmotic flow control and neutral hydrophilic coatings for electrophoresis of proteins.     

Tunable morphology of 2D honeycomb-patterned films and the hydrophobicity of a ferrocenyl-based oligomer

Honeycomb-patterned polymer films with tunable pore size and regularity of ordered two- or three-dimensional hexagonal arrays have met with widespread interest in recent years in different areas, for instance as separation and superhydrophobic materials. Herein, 2D honeycomb-patterned films of amphiphilic ferrocenyl-based oligomer with cholesterol as side chains were prepared by the breath-figure method on solid surfaces and their surface-wetting behavior were tested. These films can be simply prepared by spreading a mixture of polymer and organic solvents on a solid surface under moist airflow and at an air/water interface without any extra moist airflow. An ordered 2D hexagonal array of pores with monodisperse size distribution can be obtained over a large area by changing various influencing factors, including humidity, wet volume, concentration, selective solvent, and spreading method, which provides a facile route to regulate the morphology of patterned porous films. The surface-wetting behavior indicates that a higher hydrophobicity of the ferrocenyl-based oligomer honeycomb films can be obtained by modulating the pore size and regularity. It is expected that this could promote the potential application of ordered porous polymer films in hydrophobic materials and biochemistry.     

Microfluidic chip-based fabrication of PLGA microfiber scaffolds for tissue engineering

In this paper, we have developed a method to produce poly(lactic- co-glycolic acid) (PLGA) microfibers within a microfluidic chip for the generation of 3D tissue engineering scaffolds. The synthesis of PLGA fibers was achieved by using a polydimethylsiloxane (PDMS)-based microfluidic spinning device in which linear streams of PLGA dissolved in dimethyl sulfoxide (DMSO) were precipitated in a glycerol-containing water solution. By changing the flow rate of PLGA solution from 1 to 50 microL/min with a sheath flow rate of 250 or 1000 microL/min, fibers were formed with diameters that ranged from 20 to 230 microm. The PLGA fibers were comprised of a dense outer surface and a highly porous interior. To evaluate the applicability of PLGA microfibers generated in this process as a cell culture scaffold, L929 fibroblasts were seeded on the PLGA fibers either as-fabricated or coated with fibronectin. L929 fibroblasts showed no significant difference in proliferation on both PLGA microfibers after 5 days of culture. As a test for application as nerve guide, neural progenitor cells were cultured and the neural axons elongated along the PLGA microfibers. Thus our experiments suggest that microfluidic chip-based PLGA microfiber fabrication may be useful for 3D cell culture tissue engineering applications.     

Special wetting behavior of a graphitic nanofiber-modified epoxy generalized for rough textured fabric surfaces

Wetting behavior of a polymer resin used as matrix on fabric surfaces is one of the key attributes for making high quality structural composites. Though incorporation of various functionalized nanoparticles can stimulate improvements to many properties of epoxy resins, there has not been any report on wettability of any nano-modified epoxy on rough inclined fabric surfaces. In this research work, wetting behavior of a previously developed nano-epoxy resin modified by a type of reactive graphitic nanofibers (r-GNFs) was investigated. The observation results revealed that a unique wetting behavior was discovered from the nano-epoxy on rough fabric surfaces due to the contribution of the r-GNFs. Based on this dramatically improved wettability of the epoxy, a concept of dry–wet contact model was proposed to interpret the different wetting phenomenon observed from the nano-epoxy and that of the pure epoxy. The improved wetting characteristics of the nano-epoxy system will be essential for enabling future energy efficient infusion processing for manufacturing high quality and high-performance structural composite applications.     

与胶原特异性结合的BMP2模拟肽/PLGA 3D打印复合支架的制备及成骨诱导活性

将胶原绑定结构域(CBD)多肽序列与骨形态发生蛋白2模拟肽(BMP2-MP)序列连接制备具有胶原绑定能力的CBD-BMP2-MP, 再将CBD-BMP2-MP与聚丙交酯-乙交酯/胶原(PLGA/COL)3D打印支架相结合, 以支架表面的胶原成分为媒介, 将CBD-BMP2-MP更有效地固定于骨修复材料上, 达到对其进行改性的目的. 利用扫描电子显微镜(SEM)、 电子万能试验机和接触角测量仪对复合支架表面形貌、 力学强度和亲水性等材料学性能进行评价. 用荧光成像法评测 CBD-BMP2-MP及BMP2-MP与支架材料的结合能力. 在各组支架材料表面接种MC3T3-E1细胞进行体外培养, 采用CCK-8、 鬼笔环肽荧光染色、 茜素红染色及qPCR综合评价细胞在材料表面的黏附、 增殖和成骨分化等细胞行为, 研究CBD-BMP2-MP修饰的3D多孔PLGA/COL复合支架的生物学性能. 研究结果表明, 利用3D打印技术制备的多孔支架具有形貌可控的孔隙结构, 为细胞生长创造更有利的细胞微环境, 支架表面胶原成分的加入提高了支架材料的亲水性, 同时对支架材料本身的力学性能无任何影响, 提高了复合支架本身的生物相容性. 与普通BMP2-MP相比, CBD-BMP2-MP具有更好的胶原绑定能力, 与复合支架的结合更稳定, 提高了PLGA/COL复合支架对BMP2-MP的负载能力. 支架表面负载CBD-BMP2-MP后具有极强的促细胞成骨分化能力. MC3T3-E1细胞表现出更高的钙沉积能力, 并且成骨分化相关基因Runx2, ALP, COL-I及OPN等水平也有了明显提升. 表明CBD-BMP2-MP多孔复合支架具有良好的生物相容性和成骨诱导活性, 在骨组织修复领域具有良好的应用前景.     

CO2‐Responsive Nanofibrous Membranes with Switchable Oil/Water Wettability

Responsive polymer interfacial materials are ideal candidates for controlling surface wetting behavior. Here we developed smart nanostructured electrospun polymer membranes which are capable of switching oil/water wettability using CO₂ as the trigger. In particular, the combination of CO₂‐responsiveness and porous nanostructure enables the as‐prepared membranes to be used as a novel oil/water on–off switch. We anticipate that the promising versatility and simplicity of this system would not only open up a new way of surface wettability change regulation by gas, but also have obvious advantages in terms of highly controlled oil/water separation and CO₂ applications.     

Wetting on nanoporous alumina surface: transition between Wenzel and Cassie states controlled by surface structure

This paper reports a systematic study on the relationship between surface structure and wetting state of ordered nanoporous alumina surface. The wettability of the porous alumina is dramatically changed from hydrophilicity to hydrophobicity by increasing the hole diameter, while maintaining the hole interval and depth. This phenomenon is attributed to the gradual transition between Wenzel and Cassie states which was proved experimentally by comparing the wetting behavior on these porous alumina surfaces. Furthermore, the relationship between surface wettability and hole depth at a fixed hole interval and diameter was investigated. For those porous alumina with relatively larger holes in diameter, transition between Wenzel and Cassie states was also achieved with increasing hole depth. A capillary-pressure balance model was proposed to elucidate the unique structure-induced transition, and the criteria for the design and construction of a Cassie wetting surface was discussed. These structure-induced transitions between Wenzel and Cassie states could provide further insight into the wetting mechanism of roughness-induced wettability and practical guides for the design of variable surfaces with controllable wettability.     

Fabrication of flexible gold films with periodic sub-micrometer roughness and their wettability control by modification of SAM

Flexible honeycomb gold films supported by polymer sheets are fabricated by using polystyrene particle monolayers. The surfaces of the flexible gold films are covered with self-assembled monolayers (SAMs) of hydrophobic or hydrophilic thiol compounds, and the wettability of the modified surface is evaluated by measurements of the contact angles of water droplets. The contact angle of the film covered with hydrophobic SAM is ca. 150 degrees, which is greater than the value of 112 degrees for a flat gold surface, while the values for hydrophilic SAM are below 10 degrees.     

Diffusive flux of nanoparticles through chemically modified alumina membranes

Surface chemistry plays an important role in determining flux through porous media such as in the environment. In this paper diffusive flux of nanoparticles through alkylsilane modified porous alumina is measured as a model for understanding transport in porous media of differing surface chemistries. Experiments are performed as a function of particle size, pore diameter, attached hydrocarbon chain length and chain terminus, and solvent. Particle fluxes are monitored by the change in absorbance of the solution in the receiving side of a diffusion cell. In general, flux increases when the membranes are modified with alkylsilanes compared to untreated membranes, which is attributed to the hydrophobic nature of the porous membranes and differences in wettability. We find that flux decreases, in both hexane and aqueous solutions, when the hydrocarbon chain lining the interior pore wall increases in length. The rate and selectivity of transport across these membranes is related to the partition coefficient (K(p)) and the diffusion coefficient (D) of the permeating species. By conducting experiments as a function of initial particle concentration, we find that K(p)D increases with increasing particle size, is greater in alkylsilane-modified pores, and larger in hexane solution than water. The impact of the alkylsilane terminus (-CH(3), -Br, -NH(2), -COOH) on permeation in water is also examined. In water, the highest K(p)D is observed when the membranes are modified with carboxylic acid terminated silanes and lowest with amine terminated silanes as a result of electrostatic effects during translocation.     

Wetting properties of flat and porous silicon surfaces coated with a spiropyran

We report the immobilization and characterization of a spiropyran (SP) derivative (1) on smooth Si(100) and porous H-terminated silicon surfaces through a thermal hydrosilylation protocol. Under visible light exposure the SP is in a closed, hydrophobic form, whereas under UV irradiation it converts to a polar, hydrophilic open form named merocyanine (MC). The SP-MC photoinduced isomerization gives a small contact angle (CA) change of 9 degrees for smooth Si(100) samples under sequential irradiation cycles with white and UV light. Irradiation of porous silicon (PS) surfaces, under the same conditions, gave a CA change of 11 degrees. Treatment of PS surfaces, bearing the MC form of chromophore 1, with cobalt(II) ions enhances the wettability switching of the PS surface to a much larger extent, giving rise to a CA variation as high as 32 degrees.     

Polyester scaffolds with bimodal pore size distribution for tissue engineering

This paper presents a method for the preparation of porous poly(L-lactide)/poly[(L-lactide)-co-glycolide] scaffolds for tissue engineering. Scaffolds were prepared by a mold pressing-salt leaching technique from structured microparticles. The total porosity was in the range 70-85%. The pore size distribution was bimodal. Large pores, susceptible for osteoblasts growth and proliferation had the dimensions 50-400 microm. Small pores, dedicated to the diffusion of nutrients or/and metabolites of bone forming cells, as well as the products of hydrolysis of polyesters from the walls of the scaffold, had sizes in the range 2 nm-5 microm. The scaffolds had good mechanical strength (compressive modulus equal to 41 MPa and a strength of 1.64 MPa for 74% porosity). Scaffolds were tested in vitro with human osteoblast-like cells (MG-63). It was found that the viability of cells seeded within the scaffolds obtained using the mold pressing-salt leaching technique from structured microparticles was better when compared to cells cultured in scaffolds obtained by traditional methods. After 34 d of culture, cells within the tested scaffolds were organized in a tissue-like structure. Photos of section of macro- and mesoporous PLLA/PLGA scaffold containing 50 wt.-% of PLGA microspheres after 34 d of culture. Dark spots mark MG-63 cells, white areas belong to the scaffold. The specimen was stained with haematoxylin/eosin. Bar = 100 microm.     

Biomimetic polymer/apatite composite scaffolds for mineralized tissue engineering

The material surface must be considered in the design of scaffolds for bone tissue engineering so that it supports bone cells adhesion, proliferation and differentiation. A biomimetic approach has been developed as a 3D surface modification technique to grow partially carbonated hydroxyapatite (the bonelike mineral) in prefabricated, porous, polymer scaffolds using a simulated body fluid in our lab. For the rational design of scaffolding materials and optimization of the biomimetic process, this work focused on various materials and processing parameters in relation to apatite formation on 3D polymer scaffolds. The apatite nucleation and growth in the internal pores of poly(L-lactide) and poly(D,L-lactide) scaffolds were significantly faster than in those of poly(lactide-co-glycolide) scaffolds in simulated body fluids. The apatite distribution was significantly more uniform in the poly(L-lactide) scaffolds than in the poly(lactide-co-glycolide) scaffolds. After incubation in a simulated body fluid for 30 d, the mass of poly(L-lactide) scaffolds increased approximately 40%, whereas the mass of the poly(lactide-co-glycolide) scaffolds increased by about 15% (see Figure). A higher ionic concentration and higher pH value of the simulated body fluid enhanced apatite formation. The effects of surface functional groups on apatite nucleation and growth were found to be more complex in 3D scaffolds than on 2D films. Surprisingly enough, it was found that carboxyl groups significantly reduced the apatite formation, especially on the internal pore surfaces of 3D scaffolds. These findings are critically important in the rational selection of materials and surface design of 3D scaffolds for mineralized tissue engineering and may contribute to the understanding of biomineralization as well.SEM micrograph of a poly(L-lactide) scaffold.     

Porous scaffolds based on cross-linking of poly(L-glutamic acid)

Porous scaffolds based on water-soluble PLGA and CS were prepared. The pores were verified to be alveolate, uniform and continuous. The effects of freezing temperature, freeze-drying time, solid content and molecular weight of reactants on the pore structure of the scaffolds were studied. The scaffold morphology could be adjusted by changing the freezing temperature and solid content of reacting polymer. Their degradation rate can be adjusted by changing the proportion of PLGA and CS. The porosity of scaffolds was higher than 90% and the high swelling ratio showed that these scaffolds had excellent hydrophilic performance. The in vitro culture of chondrocytes indicates that the obtained PLGA/CS porous scaffolds are very promising biomaterials for tissue engineering applications.     

High-fidelity solvent-resistant replica molding of hydrophobic polymer surfaces produced by femtosecond laser nanofabrication

We demonstrate that hydrophobic areas formed by femtosecond laser irradiation on poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymer substrates can be faithfully replicated on samples of the same material via a solvent-resistant perfluoropolyether (PFPE) elastomer mold. The replicated PMMA and PS samples show nearly identical micro-nanoscale topography and hydrophobic wetting characteristics as the laser-patterned master substrates. This work combines the femtosecond laser capability of spatially tailoring the wettability with a high-resolution parallel replication method, offering the potential for the efficient production of microfluidic devices with selectively tailored flow behavior.     

Biomimetic Fabrication of Polymer Film with High Adhesive Superhydrophobicity by Duplicating Locust Wing Surface

Locust is a common flying insect. Locust wings were used as biomimetic templates to fabricate multi-functional polymer(polydimethylsiloxane, PDMS) films by soft lithography. The microstructure and wettability of the natural and artificial locust wing surfaces were investigated by means of a scanning electron microscope(SEM) and a video-based contact angle meter. The natural locust wing surface exhibits complicated hierarchical structures and high adhesive superhydrophobicity(contact angle 152°). The prepared polymer film faithfully reproduces the surface microstructures of the bio-template, and displays a good hydrophobicity and high adhesion(contact angle 144°). The complex wettability of the natural and artificial locust wing surfaces ascribes to the cooperative effect of hydrophobic composition and multi-dimensional rough microstructures. This work not only promotes our understanding of the wetting mechanism on bio-surfaces, but offers an inexpensive and effective approach for biomimetic fabrication of multi-functional interfacial materials.     

Observing capillarity in hydrophobic silica nanotubes

The development of template-synthesized silica nanotubes has created a unique opportunity for studying confined fluids by providing nanometer-scale containers in which the inner diameter (i.d.) and surface chemistry can be systematically and independently varied. An interesting question to be answered is the following: do solvents wet nanometer-scale tubes in the same way they wet ordinary capillaries? To answer this question, we have conducted studies to explore the wettability of the hydrophobic interiors of individual nanotubes. In these studies, single nanotubes with i.d.'s of either 30 or 170 nm were investigated over a range of water/methanol mixtures. These studies provide a direct route for comparing wetting phenomena in nanotubes with conventional macroscopic theories of capillarity. Our observations reveal four important aspects of capillary wetting in the 30-170 nm regime, a size range where the application of the Young-Laplace theory has not been experimentally investigated for hydrophobic pores. They are (i) a sharp transition between wetting and nonwetting conditions induced by addition of a cosolvent, (ii) invariance of this transition between nanotubes of 30 and 170 nm pore diameter, (iii) failure of the Young-Laplace equation to accurately predict the cosolvent's (methanol) mol fraction where the transition occurs, and (iv) reversibility of the observed wetting. The first two aspects conform to conventional capillarity (Young-Laplace), but the latter two do not. These measurements were complemented with ensemble experiments. The difference between theory and experiment is likely due to reliance on macroscopic values of contact angles or to liquid-phase instability within the hydrophobic pore.     

Modification of porous silica particles with poly(acrylic acid)

The surface of porous silica particles was modified with poly(acrylic acid) by reacting the carboxyl groups on poly(acrylic acid) with the amino groups of pregrafted aminopropyltriethoxysilane (APS). The chemical modifications by APS and polymer were characterized by infrared spectroscopy and the amount of APS and poly(acrylic acid) grafted to the surface were determined by thermal gravimetric analyses. The wettability of the modified silica particles, based on the rate of water penetration, was pH‐dependent with PAA; at pH 1.5 the wettability increased but at pH 5.5 it decreased dramatically. The pore size and size distribution of the silica particles decreased with APS and polymer grafting. Copyright © 2000 John Wiley & Sons, Ltd.