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At least 487 records · Page 27Linked to original sources
PubMed1993

Mold filling and porosity in castings of titanium.

The present study focused on the effects of argon pressure, mold venting, and investment permeability on the mold filling of titanium and the soundness of titanium castings. Casting soundness was determined by density measurement and x-ray radiography. To achieve complete filling of molds made from a relatively impermeable investment, the molds were vented. Regardless of the presence or absence of vents, all of the molds made from a highly permeable refractory material filled completely. The soundness of castings made under an argon pressure of 50 torr was significantly greater than that of castings made under a pressure of 400 torr. The non-vented molds of the highly permeable refractory material yielded the soundest castings (mean density = 4.45 g/cm3).

Dental Casting Investment↗
PubMed2005

Modulation of porosity in apatitic cements by the use of alpha-tricalcium phosphate-calcium sulphate dihydrate mixtures.

Calcium phosphate bone cements are injectable biomaterials that are being used in dental and orthopaedic applications through minimally invasive surgery techniques. Nowadays, apatitic bone cements based on alpha-tricalcium phosphate (alpha-TCP) are of special interest due to their self-setting behaviour when mixed with an aqueous liquid phase. In this study, a new method to improve osteointegration of alpha-TCP-based cements is presented. This method consists in the modification of the cement's powder phase with different amounts of calcium sulphate dihydrate (CSD). The resulting hardening properties of the new biphasic cements are a combination between the progressive hardening due to the main alpha-TCP reactant and the progressive dissolution of the CSD phase, which render a porous material. It was observed that the maximum compressive strength of Biocement-H (45 MPa) decreased as the amount of CSD increased in the cement powder mixture ( approximately 30 MPa for 25 wt% of CSD). It was also observed that after complete dissolution of the CSD phase a porous apatitic structure appears with a mechanical compressive strength suitable for cancellous bone applications (10 MPa).

Apatites↗
PubMed2005

The influence of surface porosity on gap-healing around intra-articular implants in the presence of migrating particles.

The aim of the present study was to compare the effect of two different porous coatings on bone ongrowth and on the peri-implant migration of polyethylene (PE) particles. Porous-coated cylindrical implants with an either plasma-sprayed closed-pore coating (Pl) or titanium fiber metal open-pore coating (Fi) were inserted intra-articular in exact fit or with a 0.75 mm peri-implant gap. A weight-loaded implant device in the distal femur was used. We used a randomized paired design in eight dogs. PE particles were injected repeatedly intra-articular in the knee until the dogs were killed after 8 weeks. Fi implants had significantly more bone ongrowth 8 (0-21)% compared with Pl implants 0 (0-0)% in gap situations and reduced the number of peri-implant PE particles significantly. Among exact-fitted implants we found that peri-implant tissue around Pl implants consisted of significantly more fibrous tissue than around Fi implants. A sealing effect against the migration of PE particles was found for both Fi and Pl implants in exact fit.

Alloys↗
PubMed2005

Macroporous interconnected dextran scaffolds of controlled porosity for tissue-engineering applications.

Dextran hydrogels have been studied as drug delivery vehicles but not as scaffolds for tissue-engineering likely because previously synthesized dextran hydrogels had pores too small for cell penetration. Our goal was to create macroporous, interconnected dextran scaffolds. To this end, we took advantage of the liquid-liquid immiscibility of poly(ethylene glycol) and methacrylated dextran during radical crosslinking of the methacrylated moieties. By controlling the degree of methacrylate substitution on dextran, dextran molar mass and PEG concentration, macroporous hydrogels were created. The presence of PEG in solution had a significant effect on the final morphology of the dextran hydrogel leading to the formation of different types of structures, from microporous gel to macroporous gel-wall to a macroporous interconnected-beaded structure. A series of formulation diagrams were prepared which allowed us to determine which conditions led to the formation of macroporous interconnected-beaded scaffolds. Dextran macroporous interconnected-beaded gels had a high water content, between 89% and 94%, a homogeneous morphology, determined by scanning electron microscopy, with interconnected macroporous pores, as determined by protein diffusivity where the effective diffusion coefficients of BSA were calculated to be 3.1 x 10(-7)cm2/s for Dex-MA 40 kDa DS 5 and 1 x 10(-7)cm2/s for Dex-MA 6 kDa DS10, which are similar to that of BSA in water, 5.9 x 10(-7)cm2/s. Mercury intrusion porosimetry showed that the macroporous interconnected-beaded scaffolds had a bimodal distribution of macropores, with a median diameter of 41 microm, interconnected by throats, which had a median diameter of 11 microm. Together, these data suggest that the dextran scaffolds will be advantageous in applications that require an interconnected macroporous geometry, such as those of tissue engineering where cell penetration and nutrient diffusion are necessary for tissue regeneration.

Acrylates↗
PubMed2006

Mesoporous carbide-derived carbon with porosity tuned for efficient adsorption of cytokines.

Porous carbons can be used for the purification of various bio-fluids, including the cleansing blood of inflammatory mediators in conditions such as sepsis or auto-immune diseases. Here we show that the control of pore size in carbons is a key factor to achieving efficient removal of cytokines. In particular, the surface area accessible by the protein governs the rate and effectiveness of the adsorption process. We demonstrate that novel mesoporous carbon materials synthesized from ternary MAX-phase carbides can be optimized for efficient adsorption of large inflammatory proteins. The synthesized carbons, having tunable pore size with a large volume of slit-shaped mesopores, outperformed all other materials or methods in terms of efficiency of TNF-alpha removal and the results are comparable only with highly specific antibody-antigen interactions.

Adsorption↗
PubMed2006

Chitosan-based controlled porosity osmotic pump for colon-specific delivery system: screening of formulation variables and in vitro investigation.

A microbially triggered colon-targeted osmotic pump (MTCT-OP) has been studied. The gelable property at acid condition and colon-specific biodegradation of chitosan were used to: (1) produce the osmotic pressure, (2) form the drug suspension and (3) form the in situ delivery pores for colon-specific drug release, respectively. The scanning electron microscopy (SEM) study and the calculation of membrane permeability were applied to elucidate the mechanism of MTCT-OP. The effects of different formulation variables, including the level of pH-regulating excipient (citric acid) and the amount of chitosan in the core, the weight gain of semipermeable membrane and enteric-coating membrane, and the level of pore former (chitosan) in the semipermeable membrane, have been studied. Results of SEM showed that the in situ delivery pores could be formed in predetermined time after coming into contact with dissolution medium, and the number of pore was dependent on the initial level of pore former in the membrane. The amount of budesonide release was directly proportional to the initial level of pore former, but inversely related to the weight of semipermeable membrane. The effects of variations in the level of citric acid and chitosan in the core formulation on drug release were studied. The different levels of enteric-coating membrane could prevent cellulose acetate membrane (containing chitosan as pore former) from forming pore or rupture before contact with simulated colonic fluid, but had no effect on the drug release. Budesonide release from the developed formulation was inversely proportional to the osmotic pressure of the release medium, confirming that osmotic pumping was the major mechanism of drug release. These results showed that MTCT-OP based on osmotic technology and microbially triggered mechanism had a high potential for colon-specific drug delivery.

Animals↗
PubMed2005

Unidirectional gas flow in soil porosity resulting from barometric pressure cycles.

During numerical simulation of air flow in the vadose zone, it was noticed that a small sinusoidal pressure would cause a gradual one-way migration of the pore gas. This was found to be a physical phenomenon, not a numerical artifact of the finite element simulation. The one-way migration occurs because the atmospheric pressure, and hence the air density, is slightly greater when air is flowing into the ground than when air is flowing out of the ground. A simple analytic theory of the phenomenon is presented, together with analytic calculations using actual barometric pressure data. In soil of one Darcy permeability, the one-way migration is of the order of a few tenths of a meter per year for either plane flow from ground surface or for radial flow from an open borehole. The migration is sufficiently small that it will have no practical consequences in most circumstances; however, investigators who conduct detailed numerical modeling should recognize that this phenomenon is not a numerical artifact in an apparently linear system.

Air Pressure↗
PubMed2005

Influence of the experimental conditions on porosity and structure of adsorbents elaborated from Moroccan oil shale of Timahdit by chemical activation.

This study records experiments undertaken to determine the suitable conditions for the use of the oil shale of Timahdit, as an adsorbent for water treatment. A simple process was proposed based on chemical activation. The preparation has been carried out by carbonization after impregnation of the precursor with phosphoric acid. The effect of different conditions of preparation on the specific surface area is discussed. These parameters are H3PO4/shale weight ratio, carbonization temperature, carbonization time and concentration of H3PO4. The properties and surface structure of the adsorbent were investigated by XPS and FT-IR. Their total surface acidity and basicity were also determined. The retention process of methylene blue (MB) by adsorbents has been studied. It was found that MHP2 and MHP7 have relatively high retention ability as compared to activated carbons.

Adsorption↗
PubMed2004

Ultrasound-induced cell membrane porosity.

Recent studies of ultrasound (US) methods for targeted drug delivery and nonviral gene transfection revealed new, advantageous possibilities. These studies utilized US contrast agents, commonly stabilized microbubbles, to facilitate delivery and suggested that US delivery resulted from cell sonoporation, the formation of temporary pores in the cell membrane induced by US. Using voltage clamp techniques, we obtained real-time measurements of sonoporation of single Xenopus oocyte in the presence of Optison trade mark, an agent consisting of albumin-shelled C(3)F(8) gas bubbles (mean diameter 3.2 microm). Ultrasound increased the transmembrane current as a direct result of decreased membrane resistance due to pore formation. We observed a distinct delay of sonoporation following US activation and characteristic stepwise increases of transmembrane current throughout US duration. We discovered that the resealing of cell membrane following US exposure required Ca(2+) entering the cell through US-induced pores.

Albumins↗
PubMed2003

NMR applications to low porosity carbonate stones.

The purpose of this paper is to investigate NMR applications to porous materials widely employed in artistic and historical monuments and largely studied in the Cultural Heritage conservation field. Carrara marble, Candoglia marble and travertine samples were studied and data from relaxation times measurements were compared. Very interesting results from treated samples are reported and explained under the structure related spin lattice relaxation time point of view. Images of Carrara marble aged sample (XIX century), coming from the Florence Cathedral obtained for short absorption time of water by capillary rise and for relatively small thickness slices together show the fluid's spatial distribution within the stone. Comparative images showing untreated sample with the treated ones were obtained suggesting very useful applications for the determination of treatment effectiveness.

Carbonates↗
PubMed1994

The effect of different porosities in coral implants: an experimental study.

Goniopora lobata and polyphyllia talpina were tested in 10 sheep with a follow-up of 12 months. The reference material was a glass ceramic CAP 42. Different implantation sites are used: craniofacial and orthopaedic. A macro and microscopic postoperative study was performed at 3, 6, 9 and 12 months. The results show: (1) biocompatibility with bone and soft tissues; (2) disappearance, without colonisation, of Goniopora Lobata associated with complete bone regeneration at 12 months and (3) later resorption of polyphyllia talpina with a fibrous colonisation, without osseous transformation. The possibility of using these materials in cranio-maxillo facial surgery is discussed.

Aluminum Compounds↗
PubMed2000

Comparison of two stent-grafts with different porosity: in vivo studies in a sheep model.

PURPOSE: To compare two stent-grafts with a polyurethane-carbonate (PUC) polymer lining of different pore size and water permeability in the iliac arteries of sheep. MATERIALS AND METHODS: Two stent-grafts with an inner PUC-lining of normal and low water permeability (normal, 1,200 mL/min/cm2; low, 280 mL/min/cm2; pressure gradient, 20 mm Hg) were implanted in each of 16 sheep. Hoop strength was two times higher in low-permeable than in normal-permeable stent-grafts. Patency was monitored with use of angiography and intravascular ultrasound (IVUS) after 1, 3, and 6 months. The sheep were killed after 1 or 6 months. Specimens were studied histologically. IVUS and histologic data were analyzed statistically. RESULTS: IVUS measurements showed a wider patent lumen of the low- compared to the normal-permeable prostheses at all time points (P < .03). This is likely due to the greater hoop strength of the low-permeable stent-graft. After 1 month, both types of prostheses demonstrated complete transprosthetic tissue penetration and were covered with neointima and endothelium. The neointimal area was greater in low- than in normal-permeable stent-grafts (1 month, P < .005; 6 months, P < .03). CONCLUSIONS: Presumably, the higher permeability of the normal-permeable stent-grafts led to the reduced neointimal area by improving transprosthetic capillary ingrowth and endothelialization.

Angiography↗
PubMedDate not supplied

Effect of adsorbent porosity on performance of expanded bed chromatography of proteins.

Expanded bed or fluidized bed adsorption has emerged as an important unit operation in downstream processing of proteins. A number of specifically designed commercial adsorbents are available today for expanded bed purification of proteins. Protein purification essentially requires adsorbent matrices that have large pore size. Very large pore size or macroporous adsorbents can provide high efficiency in packed beds even at high flow rates on account of reduced pore diffusion resistance resulting from finite intraparticle flow in the macropores. This is reflected in leveling off of HETP (height equivalent to theoretical plate) versus flow curve after a threshold velocity. Expanded bed operation, on the other hand, can also show plateauing of the HETP curve, but not necessarily on account of macroporosity of adsorbent. It is shown in this article how any adsorbent intended for protein adsorption in expanded bed mode can give plateauing HETP curve, regardless of pore size. As a result, RTD measurements on an expanded bed can give equal, and at times better, performance than a corresponding packed bed. Large pore size, on the other hand, can result in lesser retention of biomass and easy flushing of the adsorbent to obtain an entirely particulate-free adsorbent prior to the product elution step. Adsorbent with larger pores is also shown to provide faster and more efficient elution both in packed and expanded bed modes.

Adsorption↗
PubMed2006

Impact of natural organic matter on monochloramine reduction by granular activated carbon: the role of porosity and electrostatic surface properties.

Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters-one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity.

Carbon↗
PubMed2002

Coordination-driven self-assembly: solids with bidirectional porosity.

Coordination-driven self-assembly reactions have been used in the preparation of a variety of discrete supramolecular species, some of which have shown promise as synthetic receptors. Many highly ordered coordination polymers and porous networks have been prepared in a similar fashion. While a few of these solids are capable of the uptake of small organic molecules in the resultant molecular channels, the formation of truly porous structures has frequently been thwarted by lattice interpenetration. A strategy for the formation of porous solids that may circumvent this problem is based on the covalent construction of nanoscale macrocycles which, when eclipsed in the solid state, may lead to porous, tubular assemblies. We have incorporated these concepts toward the realization of a bidirectionally porous solid. The metal-directed, self-assembly of a conjugated, macrocyclic ligand provides a discrete, supramolecular entity in solution and the solid state. X-ray crystallographic analysis establishes that this assembly packs such that bidirectional channels are realized, and the incorporation of only ClCH2CH2Cl into the crystal lattice demonstrates that these channels are potentially suitable for the selective uptake of small organic guests.

Crystallography, X-Ray↗