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PubMed2003

Controlled porosity osmotic pump-based controlled release systems of pseudoephedrine. I. Cellulose acetate as a semipermeable membrane.

A controlled porosity osmotic pump-based drug delivery system has been described in this study. Unlike the elementary osmotic pump (EOP) which consists of an osmotic core with the drug surrounded by a semipermeable membrane drilled with a delivery orifice, controlled porosity of the membrane is accomplished by the use of different channeling agents in the coating. The usual dose of pseudoephedrine is 60 mg to be taken three or four times daily. It has a short plasma half life of 5-8 h. Hence, pseudoephedrine was chosen as a model drug with an aim to develop a controlled release system for a period of 12 h. Sodium bicarbonate was used as the osmogent. The effect of different ratios of drug:osmogent on the in-vitro release was studied. Cellulose acetate (CA) was used as the semipermeable membrane. Different channeling agents tried were diethylphthalate (DEP), dibutylphthalate (DBP), dibutylsebacate (DBS) and polyethyleneglycol 400 (PEG 400). The effect of polymer loading on in-vitro drug release was studied. It was found that drug release rate increased with the amount of osmogent due to the increased water uptake, and hence increased driving force for drug release. This could be retarded by the proper choice of channeling agent in order to achieve the desired zero order release profile. Also the lag time seen with tablets coated using diethylphthalate as channeling agent was reduced by using a hydrophilic plasticizer like polyethyleneglycol 400 in combination with diethylphthalate. This system was found to deliver pseudoephedrine at a zero order rate for 12 h. The effect of pH on drug release was also studied. The optimized formulations were subjected to stability studies as per ICH guidelines at different temperature and humidity conditions.

Administration, Oral↗
PubMed2003

Effect of filler fraction on strength, viscosity and porosity of experimental compomer materials.

OBJECTIVE: The primary goal is to develop a self-cured polyacid-modified resin composite with good mechanical and rheological properties. To achieve such a goal, the aim of this study is to determine how volume filler fraction (VFF) affects mechanical properties and viscosities of such materials containing different filler volumes. METHODS: A series of self-cured polyacid-modified composites made from polyacid modified resins and TEGDMA, mixed with filler particles, were evaluated regarding compressive strength (CS), diametral compressive strength (DCS) and viscosity. The maximum filler content, which could be incorporated into the materials, was calculated from CS tests as well as from viscosity measurements using Mooney's equation. Porosity contents were also determined in an attempt to explain different failure behaviours. RESULTS: The CS values peaked at 18.9 vol.% filler particles and declined afterwards for self-cured polyacid-modified resin composites cured in air. Using photopolymerisation and barium filler in the polyacid-modified resin composites resulted in the highest CS and DCS values. The viscosity increased continuously with increased VFF. VFF results determined experimentally and with Mooney's equation at shear rates of 0.01, 0.1, 1.0, and 10.0 s(-1) revealed that the maximal filler fraction values were 54.9+/-1.8, 55.9+/-1.3, 56.3+/-0.9, and 56.8+/-0.8 vol.%, respectively. The largest porosity content occurred at a VFF value of 53 vol.% CONCLUSIONS: We conclude that an increase in filler fraction of the investigated experimental polyacid-modified resin composite materials above a certain value (20-30 vol.%) does not result in improved mechanical properties.

Analysis of Variance↗
PubMed1999

Effect of magnesium stearate on bonding and porosity expansion of tablets produced from materials with different consolidation properties.

The negative effect of magnesium stearate on tablet strength is widely known. This strength reduction is always considered to be the result of reduction of interparticle bonding. It is also known that interparticle bonding affects relaxation of tablets. Relaxation increases with decreasing bonding. Microcrystalline cellulose is an example of a material with a high lubricant sensitivity, which effect is caused by its plastic deformation behavior during compression. This paper shows for microcrystalline cellulose that the porosity under pressure was equal for unlubricated tablets and for tablets containing 0.5% magnesium stearate. This points to equal densification properties. The lubricated tablets show, however, a much larger relaxation than the tablets without magnesium stearate. This difference can be ascribed to the reduction of interparticle bonding by the lubricant, because a strong interparticle bonding counteracts tablet relaxation. In contrast to microcrystalline cellulose, aggregated gamma-sorbitol (Karion Instant) has a low lubricant sensitivity. Both porosity under pressure and tablet relaxation were found to be equal for lubricated and unlubricated sorbitol tablets. This phenomenon is caused by the particle structure of gamma-sorbitol. During compression, a lubricant film will be destroyed by fragmentation of the sorbitol aggregates. For this reason, magnesium stearate will hardly affect the interparticle bonding between sorbitol particles and hence have only a small or no effect on tablet relaxation.

Elasticity↗
PubMed1996

Quantitative porosity profiles and wettability contrast visualisation in sandstone by CPMG imaging.

CPMG imaging is applied to the visualisation of porosity and wetting heterogeneities in water saturated sandstone samples at 0.1 T. Porosity profiles from NMR imaging are in agreement within 1% with the standard core analysis. T2 calculated profiles show a factor greater than two between water-wet and oil-wet samples; thus, wettability contrast can be easily visualised.

Magnetic Resonance Imaging↗
PubMed1996

The degree of porosity influences the release of growth factors by healing polytetrafluoroethylene (PTFE) grafts.

OBJECTIVES: The aim of this study was to determine the influence of the degree of porosity on the release of growth factors (PDGF AA, PDGF BB, bFGF) by healing PTFE grafts. DESIGN AND SETTING: Laboratory animal study. MATERIALS: 1 cm long segments of non-reinforced PTFE grafts (30 microns fibril length, 2 mm internal diameter, 0.39 mm thick) were placed as an abdominal aortic interposition in Lewis rats. Fifteen grafts served as control (Group A; porous grafts); in eight rats (Group B; non porous grafts) the PTFE graft was completely wrapped by a non-porous plastic envelope. Animals were killed 4 weeks after surgery. OUTCOME MEASURES: The release of PDGF AA, PDGF BB and bFGF was assessed by Enzyme Linked Immunosorbent Assay (ELISA). RESULTS: The release of PDGF AA, PDGF BB and bFGF was statistically higher in porous grafts. The only histological difference between the two groups was that porous PTFE grafts were invaded by many tufts of capillaries from the surrounding tissue, whereas this phenomenon was absent in non porous PTFE grafts. CONCLUSIONS: The degree of porosity influences the release of growth factors by healing PTFE grafts. This fact may have implication in the endothelisation of PTFE grafts and in myointimal hyperplasia formation as well.

Animals↗
PubMed1998

Changes in the fracture toughness of bone may not be reflected in its mineral density, porosity, and tensile properties.

Age-related changes in the skeleton often lead to an increase in the susceptibility of bone to fracture. Such changes most likely occur in the constituents of bone, namely, the mineral and organic phases, and in their spatial arrangement manifested as orientation and microstructure. In the past, however, bone loss or decline in bone mineral density has been considered to be the major contributing factor for the increased risk of bone fractures, and elastic modulus and ultimate strength have been commonly used to assess bone quality and strength. However, whether these properties provide sufficient information regarding the likelihood of bone to fracture remains debatable. Using a novel fracture toughness test, which measures the energy or stress intensity required to propagate a crack within a material, the objective of this study was to investigate if the mineral density and mechanical properties of bone can accurately predict bone fragility as measured by fracture toughness. Changes in fracture toughness (K(IC)), bone mineral density (BMD), elastic modulus (E), yield and ultimate strength (sigma y and sigma s), porosity (P0), and microhardness (Hv) of bone were examined as a function of age in a baboon model. With increasing age, the fracture toughness of bone decreased, and its microhardness increased. However, no significant changes were found in BMD, E, P0, sigma y, and sigma s as a function of age. In addition, simple regression analyses revealed no significant correlation between bone fracture toughness and the other parameters, except for microhardness of bone. The results of this study indicate that changes in bone fracture toughness may not be necessarily reflected in its mineral density, porosity, elastic modulus, yield strength, and ultimate strength.

Aging↗
PubMed2000

Analysis of the compression mechanics of pharmaceutical agglomerates of different porosity and composition using the Adams and Kawakita equations.

PURPOSE: To analyze the mechanics of some pharmaceutical agglomerates during uniaxial confined compression by using compression parameters derived from the Heckel, Kawakita and Adams equations, and to study the influence of these compression parameters on the tablet-forming ability of agglomerates. METHODS: Force and displacement data sampled during in-die compression of agglomerates was used to calculate compression parameters according to the Heckel (sigmay), Kawakita (1/b and a), and Adams (tau0') equations. Mechanical strength of single agglomerates as well as the air permeability and tensile strength of tablets prepared from them were also determined. RESULTS: Sigmay- from the Heckel equation did not differ between agglomerates of different porosity. Both 1/b and tau0' varied with agglomerate porosity and composition. These two compression parameters were linearly related to each other. No general correlation was found between 1/b and tau0' and the strength of single agglomerates. The two parameters were related to the intergranular pore structure and tensile strength of tablets formed from the agglomerates. CONCLUSIONS: 1/b and tau0' may be interpreted as measures of the agglomerate shear strength during uniaxial confined compression, and as such they may be used as indicators of the tabletting performance of the agglomerates.

Algorithms↗
PubMed2004

Gradient surface porosity in titanium dental implants: relation between processing parameters and microstructure.

To be successful, an implant should be biocompatible, strong and contain surface pores to promote osseointegration. A one-step microwave sintering procedure of titanium powders was attempted in this work. The idea was to take advantage of the peculiar way microwave couple with metallic powders, i.e. generating heat in the interior of the sample and dissipating it away through the surface. This non-conventional heating of titanium powder produced a dense core with surface porosity. The dense core provides the strength while the surface pores promote bone growth. The experiments were carried out in a semi-industrial grade microwave cavity using a alpha-SiC susceptor. Power levels of 1-1.5 kW, and soaking periods of approximately 30 min were used. Microstructural characterization was carried out by a scanning electron microscope. The sintered titanium had gradient porosity on the surface with a thickness of about 100-200 microm depending on the microwave power. The pores were interconnected with size ranging from 30 to 100 microm. This kind of microstructure is favorable for cell growth. Tensile strength values as high as 400 MPa were obtained for these samples.

Dental Implants↗
PubMed2004

Development of porous ceramics with well-controlled porosities and pore sizes from apatite fibers and their evaluations.

Porous hydroxyapatite (HAp) ceramics possessing well-controlled porosities and pore sizes were developed by firing apatite-fiber compacts mixed with carbon beads and agar. The total porosities could be controlled in the range from 40 to 85% by varying compaction pressure (20-40 MPa), firing temperature (1000-1300 degrees C) and carbon/HAp ratio (0/10-10/10 (w/w)). Most of the pores were regarded as open pores. The pore sizes were mainly affected by the carbon-bead diameter (5, 20 or 150 microm) and partly by the compaction pressure and the firing temperature. The pore sizes of the porous HAp ceramics derived from the carbon beads of 150 microm in diameter were distributed in the two separate ranges of several micrometers and more than 100 microm.

Ceramics↗
PubMed2002

Light microscopy evaluation of polyurethane vascular grafts porosity by Sudan Black B staining.

In small-diameter vascular grafts, the porosity of the internal surface plays an important role because it affects initial thrombus deposition and therefore the graft's patency. As well as many other studies reported in the literature we have carried out a study of the relationship between porosity and the manufacturing parameters of polyurethane (PU) grafts by standard scanning electron microscopy (SEM) analysis. However, SEM was not completely satisfactory for evaluating the 'sponge-like' uptake of water by the graft due to the unavoidable water loss and metal coating during preparation. In fact this preparation produces artefacts of the three-dimensional porous structure. To avoid this problem we investigated the possibility of observing the graft's internal surface through a stereomicroscope after it had absorbed water. We looked into a simple staining procedure which preferentially colours the PU graft fibres with respect to the void areas. After testing different kinds of stains, we eventually found that Sudan Black B, which usually stains for all kinds of lipid, turned out to be an excellent stain for the water-loaded PU grafts when diluted with ethanol. This staining procedure, coupled with a computerized image analysis system, allowed us to evaluate the degree of void and average void size of the graft internal surface and to correlate these data with graft density and manufacturing parameters.

Azo Compounds↗
PubMed1997

Age-related changes in cortical porosity of the midshaft of the human femur.

Complete cross-sections from the femoral midshaft of 180 individuals of known height and weight, aged 21-97 y, from a modern Australian population were examined using automatic video image analysis to quantify total subperiosteal porosity (TSPP). More specifically, the aim was to investigate whether age changes were similar in both sexes in (1) total subperiosteal area (TSPA), cortical area (CA) and medullary area (MA), (2) intracortical porosity (ICP), and (3) the respective contributions to TSPP made by MA and intracortical void area (ICVA). Our findings indicated that both sexes showed a significantly greater height normalised TSPA in the 70s as compared with the 20s. Males had consistently larger bones with a greater height normalised CA. In both sexes CA showed a tendency to increase till the 7th decade and then to decline, more so in females. MA approximately trebled in females and doubled in males over the age range studied. Although ICP also increased, from 4-6% in young adults to over 9% in the elderly, it showed a significant difference between the sexes only in the 3rd decade, being greater in males at this stage. By contrast, TSPP became significantly greater in females (from that recorded in the 3rd decade) by the time they reached the 50s, while in males this did not occur till the 80s. It increased from approximately 25% in young adults of both sexes to approximately 50% in females and approximately 37% in males in their 80s. However, in the elderly there was great variability in both sexes in the appearance of bones from individuals of similar chronological age. Some bones differed little from those in younger subjects, others showed greatly increased ICP, still others displayed reduced cortical widths with low ICP. The femoral midshaft resembles other skeletal sites in that age changes in TSPP are more marked in females than males.

Adult↗
PubMed2003

Biomass and porosity profiles in microbial granules used for aerobic wastewater treatment.

AIMS: To obtain biomass and porosity profiles for aerobically grown granules of different diameters and to determine a suitable range of granule diameters for application in wastewater treatment. METHODS AND RESULTS: Microbial granules were cultivated in an aerobic granulated sludge reactor with model wastewaters containing acetate, or ethanol plus acetate, or glucose as the main carbon source. Granules were formed by retaining microbial aggregates using a settling time of 2 min. Sampled granules had diameters ranging from 0.45 to 3 mm. Microbial biomass in the granules was detected with the nucleic acid stain SYTO 9 and confocal laser scanning microscopy. The thickness of the microbial biomass layer was proportional to the granule diameter, and had a maximum value of 0.8 mm. The thickness of the microbial biomass layer correlated with the penetration depth of 0.1 microm fluorescent beads into the granule. CONCLUSIONS: The microbial biomass and porosity studies suggest that aerobically grown microbial granules should have diameters less than a critical diameter of 0.5 mm, if deployed for wastewater treatment applications. This critical diameter is based on the assumption that whole granules should have a porous biomass-filled matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: This work could contribute to the development of aerobic granulation technology for effective biological wastewater treatment.

Aerobiosis↗
PubMed2003

Increased plasma fibrin gel porosity in patients with Type I diabetes during continuous subcutaneous insulin infusion.

BACKGROUND: Patients with Type 1 diabetes have a tighter plasma fibrin gel structure, to which impaired glycemic control might contribute. Improved glycemic control can be achieved with continuous subcutaneous insulin infusion (CSII). OBJECTIVES: The aim of the present study was to investigate the effect of CSII on plasma fibrin gel properties and circulating markers of inflammatory activity in patients with Type 1 diabetes. PATIENTS AND METHODS: Twenty-eight patients were investigated before and after 4-6 months' treatment with CSII. Fibrin gel structure formed in vitro from plasma samples was investigated by liquid permeation of hydrated fibrin gel networks. P-fibrinogen was analyzed by a syneresis method. Comparisons were made between patients with improved (> 0.5%) and unchanged (< 0.5%) glucosylated hemoglobin (HbA1c) during CSII. RESULTS: Eighteen patients showed improved and 10 patients unchanged HbA1c during CSII. P-fibrinogen, high sensitive C-reactive protein and serum amyloid A-antigen were not significantly changed, while fibrin gel permeability (Ks) and fiber mass-length ratio ( micro ) increased in both groups (P < 0.02). P-insulin and triglycerides decreased (P < 0.05) in both groups, while reductions of total cholesterol and intercellular adhesion molecule-1 were seen only in patients with improved HbA(1c) (P < 0.05). Absolute changes in Ks were inversely correlated to changes in plasma fibrinogen (r = 0.50; P < 0.01) and in LDL-cholesterol (r = 0.46; P < 0.05). CONCLUSIONS: Treatment with CSII in patients with Type 1 diabetes is associated with increased plasma fibrin gel porosity. Slight attenuation of the inflammatory activity was also observed. The changes in fibrin gel porosity seem to be mainly mediated by changes in plasma fibrinogen and blood lipids, and are probably secondary to improved insulin sensitivity.

Adolescent↗
PubMedDate not supplied

Hair analysis for cocaine: the requirement for effective wash procedures and effects of drug concentration and hair porosity in contamination and decontamination.

It has been proposed that issues of external contamination of hair can be resolved by the presence of metabolites. This is true for some drugs in some circumstances. However, even if some metabolites such as cocaethylene are sufficiently definitive to indicate certainty of use, others such as benzoylecgonine can occur as contaminants. In addition, for phencyclidine, only the parent compound is determined. Therefore, effective washing procedures are needed to rule out contamination as the source of the parent or metabolite. The protection provided by cutoffs is also dependent on washing to remove surface contamination, which can range from very little to greater than 20 times the amount in the hair. In cocaine-positive head hair samples from 67 subjects with cocaine-positive urine tests, contamination of positive hair samples ranged from 0.7 to 8009 ng/10 mg hair, demonstrating that analyses of such samples to determine use is meaningless without removal of contamination. Wash procedures have been a focus of this laboratory for many years. In this paper, the effectiveness of our wash procedure was further challenged by application to negative hair (blonde, auburn, brown, and black) contaminated by soaking for 1 h in 1000, 10,000, and 50,000 ng cocaine/mL water. The uptake of the cocaine was approximately linear with increasing concentrations of cocaine in the soaking solutions. By application of the wash criterion, all samples were clearly identified as contaminated (i.e., negative). The effects of hair porosity on uptake of cocaine were also studied with 10 hair samples of all colors. Permed and unpermed samples were soaked in 10,000 ng cocaine/mL for 1 hour. All hair responded to the perm with increased uptake, and all were decontaminated or identified as contaminated (i.e., negative for cocaine use). Porosity, not hair color, determined the rate of penetration of hair by cocaine in solution, and, likewise, washing characteristics were unrelated to hair color.

Cocaine↗
PubMed2003

Mineral trioxide aggregate (MTA) solubility and porosity with different water-to-powder ratios.

This study tested mineral trioxide aggregate (MTA) solubility and porosity with different water-to-powder proportions. The study also determined the chemical composition of the salts dissolved by MTA. Four sets of specimens using the following water-to-powder proportions were prepared: 0.26, 0.28, 0.30, and 0.33 grams of water per gram of cement. The latter is the ratio recommended by the manufacturer. It was determined that the degree of solubility and porosity increased as the water-to-powder ratio increased. Significant differences were found among the sets of specimens. The chemical analyses of the salts dissolved by MTA in the water identified the presence of calcium as the main chemical compound. The pH level of the solution was highly alkaline, ranging between 11.94 and 11.99. It can be stated that the calcium found in the solution should be in its hydroxide state at this high pH level. This ability to release calcium hydroxide could be of clinical significance because it could be related to the proven capacity of MTA to induce mineralization.

Aluminum Compounds↗
PubMed1995

Clinical use of low porosity woven ultrafine polyester fiber grafts.

A woven fabric graft made of ultrafine polyester fibers (UFPF) (Toray Graft, water porosity: 100 ml/min/cm2:120 mm Hg H2O) was clinically applied in 81 cases (28 thoracic aortic aneurysms, 6 thoracoabdominal aortic aneurysms, 42 abdominal aortic aneurysms, and 5 atherosclerotic obstructions of the peripheral arteries). Eight patients died after surgery due to causes unrelated to the graft. The other 73 patients were in good condition after surgery. For operations requiring extracorporeal circulation, the graft was presealed with human albumin. For the abdominal aortic aneurysms, the graft was preclotted in situ with nonheparinized autoblood after the completion of the proximal anastomosis. It took about 2 min to complete the preclotting. A nonsealed graft was used for the reconstruction of peripheral arteries for the intraaortic balloon pumping procedure. The graft was easy to handle. There was no cut edge fraying problem with the graft in any direction of cutting. Even after presealing, the graft was soft and pliable enough to enable easy adaptation and anastomosis. Just after implantation, bleeding was minimal from the graft wall, anastomotic sites, and suture pores, and it stopped spontaneously. These clinical data showed that the woven UFPF graft exhibited both easy handling despite in spite of low porosity and safe application in the reconstruction of arterial systems even under totally heparinized conditions during extracorporeal circulation.

Aortic Aneurysm↗
PubMedDate not supplied

Modeling fracture porosity development using simple growth laws.

A model of porosity development has been developed to investigate general relationships between simple fracture aperture growth laws and fracture porosity in evolved fracture arrays in aquifers. The growth of fracture apertures in two-dimensional orthogonal arrays with initially spatially uncorrelated lognormal aperture distributions has been studied, where aperture growth rate is proportional to an exponent of the flow rate through each fracture. The evolved arrays show geometrical phase changes as a function of the aperture growth rate exponent, e, and the standard deviation of the initial aperture distribution, sigma(z). Low values of e and sigma(z) lead to bimodal aperture distributions, where apertures parallel to flow are preferentially enlarged. At moderate values of e and sigma(z), there is a transition to a regime of more complex geometries consisting of networks of channel-like structures of preferentially enlarged apertures. At larger values of e, array-spanning channel-like paths of preferentially enlarged apertures develop, where the tortuosity of the channel-like paths is a linear function of sigma(z). Following an initial growth phase, during which dynamically stable aperture configurations develop, arrays undergo simple amplification. The geometry of the evolved aperture fields is diverse and they can be highly complex; consequently, parameterization and prediction of their evolution in terms of the initial aperture distributions and growth rate laws is not trivial.

Forecasting↗
PubMed1964

POROSITY OF ISOLATED CELL WALLS OF SACCHAROMYCES CEREVISIAE AND BACILLUS MEGATERIUM.

Gerhardt, Philipp (The University of Michigan, Ann Arbor), and Jean A. Judge. Porosity of isolated cell walls of a yeast and a bacillus. J. Bacteriol. 87:945-951. 1964.-Decagram masses of cell walls were isolated from Saccharomyces cerevisiae and Bacillus megaterium; their porosity was examined by measuring the extent of uptake with polyethylene glycols and dextrans varying in molecular weight from 62 to 2,000,000. The results indicated that both walls are heteroporous. The near equality of extrapolated water-uptake values and determined moisture contents suggested that water in the cell walls is mainly free for distribution of solutes. Polymers with molecular weights of 4,500 and above were excluded by the yeast walls, and those with molecular weights of 57,000 were excluded by the bacillus walls; from these results, maximal openings of 36 and 107 A, respectively, were calculated. Electron micrographs of shadowed, stained, and sectioned walls revealed fine structure not inconsistent with heteroporosity, but the predicted openings were not seen. Altogether, in structure and permeability behavior, the cell walls were like a random meshwork of cross-linked macromolecular strands.

Bacillus↗