Micrometer-sized Pores Research Articles

Porous Surface Structure Fabricated by Breath Figures that Suppresses Pseudomonas aeruginosa Biofilm Formation

As colonizers of medical-device surfaces, Pseudomonas aeruginosa strains present a serious source of infection and are of major concern. In this study, we fabricated films with porous surfaces by breath figures that disturb mergence by bacterial attachment, thereby impeding biofilm development. Previous studies have shown that microtopography prevents the development of P. aeruginosa biofilms. Accordingly we indented surfaces with patterns of micrometer-sized pores using breath figures at ordinary temperatures and pressures. The antimicrobial effect of surface figures was experimentally investigated by controlling the surface structure. The results suggested that pores of 5-11 μm in diameter effectively inhibit bacterial activity. It appears that biofilm development is precluded by the decreased contact area between the films and bacteria.

Multifunctional polymer scaffolds with adjustable pore size and chemoattractant gradients for studying cell matrix invasion

Transmigrating cells often need to deform cell body and nucleus to pass through micrometer-sized pores in extracellular matrix scaffolds. Furthermore, chemoattractive signals typically guide transmigration, but the precise interplay between mechanical constraints and signaling mechanisms during 3D matrix invasion is incompletely understood and may differ between cell types. Here, we used Direct Laser Writing to fabricate 3D cell culture scaffolds with adjustable pore sizes (2–10 μm) on a microporous carrier membrane for applying diffusible chemical gradients. Mouse embryonic fibroblasts invade 10 μm pore scaffolds even in absence of chemoattractant, but invasion is significantly enhanced by knockout of lamin A/C, a known regulator of cell nucleus stiffness. Nuclear stiffness thus constitutes a major obstacle to matrix invasion for fibroblasts, but chemotaxis signals are not essential. In contrast, epithelial A549 cells do not enter 10 μm pores even when lamin A/C levels are reduced, but readily enter scaffolds with pores down to 7 μm in presence of chemoattractant (serum). Nuclear stiffness is therefore not a prime regulator of matrix invasion in epithelial cells, which instead require chemoattractive signals. Microstructured scaffolds with adjustable pore size and diffusible chemical gradients are thus a valuable tool to dissect cell-type specific mechanical and signaling aspects during matrix invasion.

Preparation and evaluation of porous alginate/ hydroxyapatite composite scaffold coated with a biodegradable triblock copolymer

Background: The scaffolds for bone tissue engineering must meet the functional requirements such as porosity, biocompatibility, and biodegradability. Composite materials could improve mechanical properties compared with polymers, and structural integrity and flexibility compared with brittle ceramics. Objective: The effect of a biodegradable triblock copolymer in the cell attachment into the alginate/hydroxyapatite composite scaffold was evaluated. Methods: Scaffolds were fabricated by freeze-drying method in different alginate/hydroxyapatite weight ratios. Hydroxyapatite was incorporated into the alginate gel solution to improve both the mechanical and cellattachment properties of the scaffolds. The scaffolds were then coated with triblock copolymer (as a surface modifier) and sterilized by ultraviolet light. Then, human mesenchymal stem cells were cultured on the scaffolds, which are an attractive cell source for tissue engineering. Results: Cell adhesion to the scaffolds was observed after three days by 4, 6-diamidino-2-phenylindole (DAPI) fluorescence microscopy. In addition, microstructural observation with SEM suggests the formation of about 50 micrometer size pores and interconnected porosity so that cell adhesion within this structure is well in depth as also observed in DAPI results. Conclusion: These results suggest that the triblock-coated alginate/hydroxyapatite porous scaffolds could provide enhanced cell adhesion and proliferation, which may be a promising approach for tissue-engineering applications. Keywords: Alginate, cell adhesion, freeze-drying, human mesenchymal stem cells, hydroxyapatite, porous scaffold, tissue engineering

Polymer-based microfluidic device for measuring membrane protein activities

Functional assays of membrane proteins are becoming increasingly important, both in research and drug discovery applications. The majority of current assays use the patch-clamp technology to measure the activity of ion channels which are over-expressed in cells. In future, in vitro assay systems will be available, which use reconstituted membrane proteins in free-standing lipid bilayers suspended in nano- or micrometer-sized pores. Such functional assays require (1) expression, purification and reconstitution of the membrane protein of interest, (2) a reliable method for lipid bilayer formation and membrane protein integration, and (3) a sensitive detection system. For practical applications, especially for automation, the reliable and controllable transport of fluids is essential. In order to achieve a stable free-standing lipid bilayer, a pore diameter in the micro- to nanometer range is essential. Novel microfluidic devices were developed by bonding a thick (300 μm) polyether ether ketone foil, bearing a channel structure, to a thin (12 μm) foil with a micropore of about 10 μm diameter and then utilized for the formation of stable, free-standing lipid bilayers within the pore. A bacterial voltage-gated potassium channel is integrated therein by fusion and the ion channel activity detected by voltage clamp.

On chip porous polymer membranes for integration of gastrointestinal tract epithelium with microfluidic ‘body-on-a-chip’ devices

We describe a novel fabrication method that creates microporous, polymeric membranes that are either flat or contain controllable 3-dimensional shapes that, when populated with Caco-2 cells, mimic key aspects of the intestinal epithelium such as intestinal villi and tight junctions. The developed membranes can be integrated with microfluidic, multi-organ cell culture systems, providing access to both sides, apical and basolateral, of the 3D epithelial cell culture. Partial exposure of photoresist (SU-8) spun on silicon substrates creates flat membranes with micrometer-sized pores (0.5-4.0 μm) that--supported by posts--span across 50 μm deep microfluidic chambers that are 8 mm wide and 10 long. To create three-dimensional shapes the membranes were air dried over silicon pillars with aspect ratios of up to 4:1. Space that provides access to the underside of the shaped membranes can be created by isotropically etching the sacrificial silicon pillars with xenon difluoride. Depending on the size of the supporting posts and the pore sizes the overall porosity of the membranes ranged from 4.4 % to 25.3 %. The microfabricated membranes can be used for integrating barrier tissues such as the gastrointestinal tract epithelium, the lung epithelium, or other barrier tissues with multi-organ "body-on-a-chip" devices.

Hierarchically Structured Multifunctional Porous Interfaces through Water Templated Self-Assembly of Ternary Systems

Herein, a facile water-assisted templating approach, the so-called breath figures method, has been employed to prepare multifunctional and hierarchically structured porous patterned films with order at different length scales (nano- and micrometer). Tetrahydrofuran solutions of ternary blends consisting on high molecular weight polystyrene, an amphiphilic block copolymer, polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS(40)-b-P(PEGMA300)(48)), and a fluorinated copolymer, polystyrene-b-poly(2,3,4,5,6-pentafluorostyrene) (P5FS(21)-b-PS(31)), have been used to obtain films varying the proportion of the three components. Confocal micro-Raman spectroscopy and atomic force microscopy demonstrated the preferential location of the different functionalities in the films. Because of the breath figures mechanism, the amphiphilic copolymer yield pores enriched in hydrophilic functionality while the fluorinated copolymer remained mixed with the PS matrix and eventually also forming self-assembled nanostructures at the surface. As a consequence, two levels of order can be observed, i.e., micrometer size pores with nanostructured domains due to the block copolymer self-assembly. In addition, the distribution of the amphiphilic copolymer within the holes is not regular being located principally on the edges of the cavities. This can be attributed to the coffee stain phenomenon occurring in the water droplets as a consequence of the segregation of the block copolymers to the droplets and their self-assembly.

Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores

Matrix-related pore networks in mudrocks are composed of nanometer- to micrometer-size pores. In shale-gas systems, these pores, along with natural fractures, form the flow-path (permeability) network that allows flow of gas from the mudrock to induced fractures during production. A pore classification consisting of three major matrix-related pore types is presented that can be used to quantify matrix-related pores and relate them to pore networks. Two pore types are associated with the mineral matrix; the third pore type is associated with organic matter (OM). Fracture pores are not controlled by individual matrix particles and are not part of this classification. Pores associated with mineral particles can be subdivided into interparticle (interP) pores that are found between particles and crystals and intraparticle (intraP) pores that are located within particles. Organic-matter pores are intraP pores located within OM. Interparticle mineral pores have a higher probability of being part of an effective pore network than intraP mineral pores because they are more likely to be interconnected. Although they are intraP, OM pores are also likely to be part of an interconnected network because of the interconnectivity of OM particles. In unlithifed near-surface muds, pores consist of interP and intraP pores, and as the muds are buried, they compact and lithify. During the compaction process, a large number of interP and intraP pores are destroyed, especially in ductile grain-rich muds. Compaction can decrease the pore volume up to 88% by several kilometers of burial. At the onset of hydrocarbon thermal maturation, OM pores are created in kerogen. At depth, dissolution of chemically unstable particles can create additional moldic intraP pores.

Morphology control and electrochemical properties of LiFePO4/C composite cathode for lithium ion batteries

We developed a novel cathode electrode system composed of ultra highly porous structured LiFePO4/carbon composite for lithium ion batteries by a gelation–freezing (GF) method. This unique technique can be used to provide various shaped components by use of specific molds, and varying the freezing temperature could control the micrometer-sized cylindrical pore size and wall thickness in the porous composite. Film shapes of carbons that originate in the gelatin were found in the porous LiFePO4/carbon composite cathodes. The porous composite cathode shows a good electrochemical performance at a low current density, despite the low carbon content. Charge/discharge capacities for the LiFePO4/carbon composites decreased with decreasing gel-freezing temperature. The template-free GF method for fabricating the porous LiFePO4/carbon composite opens up a new route to develop electrodes with controlled morphologies for applications in high power lithium batteries.

Model calculation of the pore-size and porosity dependences of bulk moduli in nanoporous materials

The bulk moduli of nanoporous materials are studied theoretically on the basis of an interatomic potential. We consider model nanoporous materials in which nanometer-sized cubic-shaped pores are periodically arranged in the fcc lattice. The pore-size and porosity dependences of bulk modulus are calculated exactly for the model nanoporous materials. It is shown that the bulk moduli of model nanoporous materials decrease moderately with increasing porosity. If nanoporous materials of the same porosity are compared, the bulk modulus increases and becomes constant with increasing pore-size. It is suggested from the calculation results that nanoporous materials without defects have higher bulk moduli than materials having micrometer-sized pores.

Surface Morphology Control of Polymer Films by Electron Irradiation and Its Application to Superhydrophobic Surfaces

A simple and controllable one-step method to fabricate superhydrophobic surfaces on poly(tetrafluoroethylene) (PTFE) films is developed on the base of electron irradiation. When the thickness of PTFE films is higher than the penetration depth of electron beams, electrical charging occurs at the surface of the films because of the imbalance between the accumulation of incident electrons and the emission of secondary electrons. Local inhomogeneity of charge distribution due to this electrical charging results in the nonuniform decomposition of PTFE molecular bonds. As electron fluence increases, surface morphology and surface roughness of the films are dramatically changed. An extremely rough surface with micrometer-sized pores is produced on the surface of PTFE films by electron irradiation at a fluence higher than 2.5 × 10(17) cm(-2).Because of high surface roughness, the irradiated PTFE films exhibit superhydrophobic property with a water contact angle (CA) greater than 150° at fluences ranging from 4 × 10(17) to 1 × 10(18) cm(-2). The surface morphology and corresponding water CA can be controlled by simply changing the electron fluence. This electron irradiation method can be applicable to the fabrication of superhydrophobic surfaces using other low-surface-energy materials including various fluoropolymers.

Fabrication of pseudo three-dimensional PADC cell culture substrates for dosimetric studies

Abstract Pseudo three-dimensional (3D) polyallyldiglycol carbonate (PADC) cell culture substrates were fabricated by creating micrometer-size pores on thin PADC films by alpha-particle irradiation and subsequent chemical etching. Our results showed comparatively fewer 53BP1 foci in alpha-particle irradiated as well as bystander HeLa cells cultured on pseudo 3D PADC substrates than in those cultured on two-dimensional substrates.

Zeolite/Polymer Composite Hollow Microspheres Containing Antibiotics and the In Vitro Drug Release

Hemorrhage remains a leading cause of early death after trauma, especially those with infectious complications in combat wounds. The aim of this study was to develop antibiotics-loaded zeolite (Zel)/polymer composites for hemostatic materials. The composite materials were fabricated from zeolite and various biodegradable polymers, including chitosan (CS), gelatin (Gel) and alginate (Alg), using the inversed emulsion method. The morphology of the composites was observed by SEM, and the results showed that the prepared Zel/polymer composites can form hollow microspheres under appropriate conditions. The microspheres contained three sizes of pores, nano-pore of zeolite, micrometer-sized pores between zeolite particles, and void cores having a size of tens of micrometers. It was these pores that made the composites have unexpected water-absorbing capacity. When antibiotics were loaded into the composite microspheres, they exhibited a prolonged drug-releasing period. Thus, we can make full use of the characteristics of chitosan, zeolite and antibiotics to create potential dual-functional hemostatic materials.

Electrochemically Deposited Aluminum in Template of Porous Silicon Film

In this article, we report on the observations that in the aqueous electrolyte of aluminum nitrate, the thin metallic conducting films on both internal and external surface of porous silicon (PS) thin films that emit visible photoluminescence at room temperature prior to electrochemical deposition have been obtained under electrochemical deposition condition. Add to this high surface-to-volume ratio and these make it a good candidate for the catalyst supporter. We have investigated the surface morphology of PS after the interval of about 30 hours of electrochemically deposited aluminum by means of scanning electron microscopy (SEM). It has been shown from SEM images that not only micrometer-sized pores are smoothed by deposition of aluminum microcrystal, but also the presences of semi-sphere aluminum microcrystal which rooted in the tip of micrometer-sized pores are observed. On the one hand, this extremely interesting phenomenon which the micrometer-sized pores are smoothed may be explained in terms of principle of electrochemical deposition; on the other hand, we have laid the formation mechanism of semi-spherical aluminum microcrystal at the door of Gibbs free energy.

Single‐Pore Membranes Gated by Microelectromagnetic Traps

Gating of a single pore with a microelectromagnetic trap consisting of a single-turn gold wire microfabricated on a silicon membrane is described. A single micrometer-sized pore in the center of the microcoil conducts ionic current under the application of an applied transmembrane potential. When energized, the microelectromagnetic trap attracts a droplet of magnetic fluid, bringing the fluid to rest in the center of the trap, blocking the transport of ions through the pore, turning it “off”. Reversal of the current flow through the trap moves the droplet to the periphery of the trap, turning the pore “on”.

Friction reduction by texturing of DLC coatings sliding against steel under oil lubrication

It has been demonstrated that tetrahedral amorphous carbon (ta-C) films provide excellent wear and friction properties in dry sliding. Recently the applications of ta-C coatings in lubricated conditions have become more important. The use of carbon coatings aims at reducing the wear and coefficient of friction under minimum lubrication and without hazardous lubricant additives. For optimum tribological performance, a modification of the ta-C coated surfaces is required. The present paper describes an innovative method of coated surface texturing, by which nanometer and micrometer size pores are processed by various methods. Particle masking was used for processing micrometer size pores and for controlling the coating growth conditions in order to produce nanometer size pores in the ta-C surface. The masking by particles yielded a pore geometry which varied from complex shaped channels to small individual pores. The texturing was performed by distributing metallic powder particles on the surface or by direct chemical deposition of metal particles on the substrate in prior to pulsed vacuum arc deposition. The tribological characterization was carried out by applying reciprocating friction tests with controlled lubricant replenishment, in order to simulate metal forming processes. The friction reducing effect, which was observed in the tribological tests, indicated a microlubrication effect of the textured coating surfaces.

Fabrication and properties of ultra highly porous silicon carbide by the gelation–freezing method

Silicon carbide (SiC) with ultra high porosity and unidirectionally oriented micrometer-sized cylindrical pores was prepared using a novel gelation–freezing (GF) method. Gelatin, water and silicon carbide powder were mixed and cooled at 7 °C. The obtained gels were frozen from −10 to −70 °C, dried using a vacuum freeze drier, degreased at 600 °C and then sintered at 1800 °C for 2 h. The gels could be easily formed into various shapes, such as cylinders, large pipes and honeycombs using molds. Scanning electron microscopy (SEM) observations of the sintered bodies showed a microstructure composed of ordered micrometer-sized cylindrical cells with unidirectional orientation. The cell size ranging from 34 to 147 μm could be modulated by changing the freezing temperatures. The numbers of cells for the samples frozen at −10 and −70 °C were 47 and 900 cells/mm 2, respectively, as determined from cross-sections of the sintered bodies. The resulting porous SiC with a total porosity of 86%, exhibited air permeability from 2.3 × 10 −11 to 1.0 × 10 −10 m 2, which was the same as the calculated ideal permeability, and high compressive strength of 16.6 MPa. The porosity, number of cells, air permeability and strength of the present porous SiC were significantly higher than that reported for other porous SiC ceramics.

Fabrication of Porous Hierarchical Polymer/Ceramic Composites by Electron Irradiation of Organic/Inorganic Polymers: Route to a Highly Durable, Large-Area Superhydrophobic Coating

Polymer/ceramic composite films with micro- and nanocombined hierarchical structures are fabricated by electron irradiation of poly(methyl methacrylate) (PMMA) microspheres/silicone grease. Electron irradiation induces volume contraction of PMMA microspheres and simultaneously transforms silicone grease into a ceramic material of silicon oxycarbide with many nanobumps. As a result, highly porous structures that consist of micrometer-sized pores and microparticles decorated with nanobumps are created. The fabricated films with the porous hierarchical structure exhibit good superhydrophobicity with excellent self-cleaning and antiadhesion properties after surface treatment with fluorosilane. In addition, the porous hierarchical structures are covered with silicon oxycarbide, and thus the superhydrophobic coatings have high hardness and strong adhesion to the substrate. The presented technique provides a straightforward route to producing large-area, mechanically robust superhydrophobic films on various substrate materials.

A simple method for preparation of macroporous polydimethylsiloxane membrane for microfluidic chip-based isoelectric focusing applications

A new, simple method was reported to prepare PDMS membranes with micrometer size pores for microfluidic chip applications. The pores were formed by adding polystyrene and toluene into PDMS prepolymer solution prior to spin-coating and curing. The resulting PDMS membrane has a thickness of around 10 μm and macropores with a diameter ranging from 1 to 2 μm measured using scanning electron microscope (SEM) imaging. This PDMS membrane was validated by integrating it with PDMS microfluidic chips for protein separation using isoelectric focusing mechanism coupled with whole channel imaging detection (IEF-WCID). It has been shown that five standard p I markers and a mixture of two proteins, myoglobin and β-lactoglobulin, can be separated using these chips. The results indicated that this macroporous PDMS membrane can replace the dialysis membrane in PDMS chips for the IEF-WCID technique. The preparation method of macroporous PDMS membrane may be potentially applied in other fields of microfluidic chips.

Induced superhydrophobicity in ZnO nanomaterial

Pronounced variation of wettability from high hydrophilic state to superhydrophobic has been observed in ZnO-nanomaterial irradiated by low energy electrons. It has been found that for electron-treated nanomaterial water does not wet the ZnO-nanoparticles and does not penetrate at all inside the micrometer-size pores between individual nanoparticles and their aggregates. The water droplets fix on individual protrusions of strongly inhomogeneous hydrophobic ZnO-nanomaterial surface leading to the superhydrophobic states. The observed effect is consistent with proposed theoretical description. The developed environmentally clean technology of nanomaterial surface modification is the basis for engineering of other related to wettability surface properties such as hygroscopicity and agglomeration and it may be applied in a number of nanotechnology applications.

Convenient fabrication of three-dimensional cell-culture substrates through introduction of micrometer-size pores on polyallyldiglycol carbonate polymer films

We explored the fabrication of three-dimensional (3D) substrates by creating micrometer-size pores on polyallyldiglycol carbonate (or PADC) polymer films through irradiation of the film by alpha particles and subsequent chemical etching. HeLa cells cultured on these 3D substrates were observed using scanning electron microscope. Multiple directions and multiple layers of HeLa cells were observed to have grown in the pores, with normal nuclei and cell membranes as well as good cell spreading. For the cells cultured in 3D substrates with or without additional small pores, no significant differences were observed between their vinculin expression profiles, which were in contrast to the observation made for cells cultured on 2D substrates showing that small pores could enhance vinculin expression. The presence of the large pores and/or the enhanced biocompatibility of the substrate in the present experiments might be the reasons. The protrusions of cells were confined by the small pores, which was similar to the observation made for cells cultured on 2D substrates.