Adequate Pore Size Research Articles

Intrinsic porosity of calcium phosphate cements and its significance for drug delivery and tissue engineering applications

One key point in the field of tissue engineering and drug delivery is to provide materials with an adequate porosity. Many events, including nutrient and waste exchange in scaffolds for tissue engineering, as well as the drug-loading capacity and control of the release rate in drug delivery systems, are controlled by the size, shape and distribution of the pores in the material. Calcium phosphate cements (CPCs) possess an intrinsic porosity that is highly suited for these applications, and this porosity can be controlled by modifying some processing parameters. The objective of this work was to characterize and control the intrinsic porosity of α-tricalcium phosphate (α-TCP) cements, and to investigate its role against adsorption of bovine serum albumin (BSA). Cements with different percentages of open porosity (35–55%) were prepared by modifying the liquid-to-powder ratio. In addition, two different TCP particles were used to yield cements with specific surface areas of ∼20 and ∼37 m 2 g −1. Mercury porosimetry analysis on the set cements showed in most cases a bimodal pore size distribution which varied with the processing parameters and affected differently the adsorption and penetration of BSA. The peak occurring at larger pore dimensions controlled the penetration of BSA and was ascribed to the voids generated in between crystal aggregates, while the peak appearing at lower pore sizes was believed to be due to the intercrystallite voids within aggregates. It was found that, at the concentrations studied, the high intrinsic porosity in CPC does not ensure protein penetration unless there is an adequate pore size distribution.

Effect of pore size on in vitro cartilage formation using chitosan‐based hyaluronic acid hybrid polymer fibers

In this study, we successfully developed three-dimensional scaffolds fabricated from the chitosan-based hyaluronic acid hybrid polymer fibers, which can control the porous structure. To determine the adequate pore size for enhancing the chondrogenesis of cultured cells, we compared the behaviors of rabbit chondrocytes in scaffolds comprising different pore sizes (100, 200, and 400 microm pore size). Regarding the cell proliferation, there was no significant difference among the three groups. On the other hand, glycosaminoglycan contents in the 400 microm group significantly increased during the culture period, compared with those in the other groups. The ratio of type II to type I collagen mRNA level was also significantly higher in the 400 microm group than in the other groups. These results indicate that our scaffold with 400 microm pore size significantly enhances the extracellular matrix synthesis by chondrocytes. Additionally, the current scaffolds showed high mechanical properties, compared with liquid and gel materials. The data derived from this study suggest great promise for the future of a novel fabricated material with relatively large pore size as a scaffold for cartilage regeneration. The biological and mechanical advantages presented here will make it possible to apply our scaffold to relatively wide cartilaginous lesions.

Relationship between the nanoporous texture of activated carbons and their capacitance properties in different electrolytes

A series of activated carbons (ACs) with progressively changing nanotextural characteristics was obtained by heat-treatment of a bituminous coal at temperatures ranging from 520 to 1000 °C, and subsequent activation by KOH at 700 °C or 800 °C. As the pre-treatment temperature increases, the total pore volume V T decreases from 1.28 to 0.30 cm 3 g −1, and the BET specific surface area from 3000 to 800 m 2 g −1. The specific capacitance determined for each series of ACs using symmetric two electrode cells in 6 mol L −1 KOH varies almost linearly with the BET surface area, suggesting that the charge accumulation is controlled primarily by the surface area development. A further analysis of the electrochemical behaviour in different electrolytic media—aqueous and organic—shows that an adequate pore size is more important than a high surface area in order to obtain high values of capacitance. Theoretical values of volumetric capacitance could be evaluated without considering the size of ions, which is always uncertain in solution, and compared with the experimental data as a function of the pore width. The efficiency of pore filling, i.e., of double layer formation, is optimal when the pore size is around 0.7 nm in aqueous media and 0.8 nm in organic electrolyte. A study of the performance of the positive and negative electrodes during the charge/discharge of the capacitor, reveals an additional pseudo-faradaic contribution due to oxygenated functionalities within the working potential window of the negative electrode. This effect is more pronounced for the ACs series obtained at 700 °C, because of their higher oxygen content.

Preparation of porous hydroxyapatite scaffolds

In this work, the sintering and grain growth of hydroxyapatite green bodies are analyzed in order to identify the optimum heat treatments for the preparation of porous hydroxyapatite scaffolds. Sintering in air at temperatures ranging between 1100 and 1200 °C yields dense materials with narrow grain-size distributions. The scaffolds are formed by the infiltration of polymer foams with hydroxyapatite slurries or by robocasting, a novel rapid-prototyping technique. Examples of the microstructures achieved with each approach are presented. It is observed that both techniques can be used to fabricate scaffolds with adequate pore size to promote bone ingrowth.

Surface properties of granular activated carbons from agricultural by-products and their effects on raw sugar decolorization

Granular activated carbons (GACs) were produced from sugarcane bagasse combined with one of two binders (corn syrup, coal tar) by physical activation and from pecan shells by physical and chemical activation. GACs were evaluated for their physical (hardness, bulk density), chemical (ash, pH), surface (surface area, pore size distribution, surface chemistry), and adsorption properties (molasses color removal, sugar decolorization) and compared with two commercial reference carbons. Results showed that larger surface area, a well-developed macro- and mesoporosity, and a minimal surface charge were desirable in GACs designed for sugar decolorization. Steam activation of pecan shells carbon was the only by-product-activation combination that produced GAC with all the above three desirable characteristics of a good sugar decolorizer. Chemical activation of pecan shells yielded GACs with high surface area and adequate pore size distribution but with large surface charge. In contrast, sugarcane bagasse-based GACs exhibited low surface areas and unsatisfactory physical/chemical properties.

Nanofiltration in the utilization of coal-mine brines

The utilization of saline coal mine waters is considered to be the most adequate method of solving ecological problems caused by this kind of water in Poland. In the case of most concentrated waters, the so-called coal-mine brines, the method of concentrating by evaporation in a twelve-stage expansion installation or vapour compression is applied, after which sodium chloride is manufactured. A considerable restriction in the utilization of coal mine brines is the high energy consumption in these methods of evaporation. An obstacle in the application of low energy evaporation processes, e.g. multi-stage flash, is the high concentration of calcium and sulfate ions in the coal mine brines. The present paper deals with the application of nanofiltration in the pretreatment of the brine. The application of nanofiltration membranes with an adequate pore size, including charged membranes, makes it possible to decrease the concentration of divalent ions in the permeate practically without any changes in the concentration of sodium chloride. Then the permeate may be concentrated in a multi-stage evaporation process, e.g. MSF, without any risk of the crystallization of gypsum. A combination of NF and MSF ought to set down the unit costs of the concentration of coal mine brines below those of mere evaporation.

Performance of wide-pore silica- and polymer-based packing materials in polypeptide separation: effect of pore size and alkyl chain length

The effects of pore size and alkyl chain length of silica- and polymer-based packing materials in the elution of polypeptides with an acetonitrile gradient in the presence of trifluoroacetic acid were studied. Considerable differences were found in the performance of alkylsilylated phases prepared from various wide-pore silica particles assumed to have 30–50-nm pores. The pore size of such silica gels was found to be the critical factor in determining the efficiency for high-molecular-weight polypeptides. Silica C 18 phases having small pore volumes below 20 nm pore diameter showed comparable performances to C 4 and C 8 phases for polypeptides with molecular weights of up to 80 000, and were more stable. Polymer-based packing materials with adequate pore size provided excellent column efficiencies and recoveries for polypeptides with higher chemical stabilities than silica-based materials.

Gel Permeation Chromatography of Polymers from Wood

Abstract Polymers from wood, including cellulose via the methylol derivative, are soluble in dimethyl sulfoxide (DMSO). To perform gel permeation chromatography of these high polymers, a packing material was sought which combined adequate pore size with stability in DMSO. Contrary to recommended practice, it was discovered that gel permeation chromatography in DMSO can be performed on prepacked, high-performance columns of μ-Styragel without adverse effects from bead swelling. When using the methylol derivative of cellulose, it is necessary to freeze dry the reaction mixture to obtain a product which gives reproducible results from gel permeation chromatography.

Die Ermittlung Der Porengrössenverteilung Eines Tonbodens Über Entwässerung Und Auf Rasterelektronenmikriskopischem Wege Ein Vergleich

The variation of the relation between the soil moisture content (volume base) and the soil water suction (cm water column) of a clay soil has been investigated in dependence of the intensity of the first drainage. The calculatable pore sizes have been compared with the directly measured pore sizes got by the scanning electron microscope. The pattern of the ψ/θ curve of the differently prepared clay soils samples as well as the photos of the scanning electron microscope of the same samples show no significant relation between the water content and the soil water tension on the one side and the to that soil suction adequate pore size on the other side. The reason is the lost of water by diminishing the pore volume and not by the drainage of the stable pores. An einem Tonboden wird die Veränderung der Beziehung zwischen Wasserspannung und Wassergehalt (pF-Kurve) in Abhängigkeit von der Intensität der primären Entwässerung untersucht und die daraus errechenbare Porengröße mit auf direktem Wege mittels rasterelektronenmikroskopischer Aufnahmen gemessenen Porengrößen verglichen. Sowohl die Verläufe der pF-Kurven der unterschiedlich behandelten Tonproben als auch die rasterelektronenmikroskopischen Aufnahmen der entsprechenden Proben zeigen keine eindeutige Beziehung zwischen dem Wassergehalt und der Wasserspannung einerseits und der daraus errechenbaren Porengröße andererseits. Als eine Ursache wird der Wasserverlust durch die Verkleinerung des Porenvolumens und nicht durch die Entleerung der Poren angesehen.

Bone growth into porous carbon, polyethylene, and polypropylene prostheses.

Using rats as a model, porous discs of RPG carbon and polypropylene and polyethylene were localized subperiosteally and supraperiosteally in the skull. Bone and blood vessels grew into the discs, which had adequate pore size, when placed in direct contact with bone. No bone was generated from the periosteum. Both plastic materials were estimated to be better than carbon for use in osseous reconstructive work. More long term material-tissue stability and reaction studies should be performed.

Plant Viruses with a Multipartite Genome

If a viral genome consists of two or more nucleic acid molecules of different length, which are separately encapsidated, the resulting particles are likely to differ in sedimentation rate but will not necessarily differ in size and buoyant density. The different classes of particles, which are called the components of the virus, can be separated by physical means. This chapter summarizes the different modes of particle heterogeneity that have been described and the methods suited for the detection and separation. If the size of the capsid is adapted to the size of the genome parts, the particles can be separated by electrophoresis in sieving media provided that an adequate pore size can be found and by sedimentation in density gradients. Since the RNA:protein ratio, and thus the buoyant density, does not differ appreciably, the particles cannot be separated by banding in equilibrium gradients. Tubular (tobraviruses) and bacilliform viruses (alfalfa mosaic virus) as well as spherical viruses (tobacco streak virus, pea enation mosaic virus) belong to this class. The particles of como- and nepoviruses do not differ in size, and thus cannot be separated by electrophoresis in sieving media, but they sediment and band differently. Separation of the parts of the genome can only be accomplished after the extraction of the RNA's. It is conceivable that viruses exist that have genome parts of the same length. The nepovirus tomato ring-spot virus approaches this situation. In the animal DNA virus, adeno-associated virus the complementary strands are present in different particles. In preparations of bromo- and cucumoviruses, a similar RNA is found encapsidated together with the smallest part of the genome.