PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Porosity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1975

Evaluation of prosthetic grafts of different porosity for arterial reconstruction.

Autogenous jugular veins and Dacron grafts of different porosities were implanted as short bypass grafts around ligated femoral arteries in the dog. Patency rates for periods up to eight months were: vein, 79 per cent; DeBakey Dacron (lowest porosity), 39 per cent; Wesolowski Weavenit (imtermediate porosity), 56 per cent; high porosity Dacron, 8 per cent. The failure of sixteen of the twenty-four high porosity grafts was related to perigraft hematomas that occurred two to seven days after operation and later thrombosis. The higher the porosity of the graft, the better the healing pattern as evidenced by fibrous bonding of the inner and outer linings of the grafts through the interstices. In the spectrum of grafts with increasing porosity there is apparently an optimal porosity beyond which late bleeding counterbalances the better healing properties of the higher porosity graft.

Animals↗
PubMed1978

The measurement of the adhesion of film coatings to tablet surfaces: the effect of tablet porosity, surface roughness and film thickness.

The effect of tablet porosity, surface roughness and film thickness on the adhesion of hydroxypropyl methyl cellulose films to placebo tablet substrates have been studied using a specially designed tensile tester (Fisher & Rowe, 4976). There were direct relations between measured adhesion and tablet porosity and also surface roughness and tablet porosity. The effect of film thickness on the measured adhesion is complex with an initial decrease with thicknesses up to 35 micron and then a gradual increase with thicknesses up to 140 micron dut to differences in the strees distribution within the film during testing. A knowledge of these effects is necessary if results from various sources are to be compared. The findings illustrate the potential capability of the extrapolation of measured adhesion results to zero porosity and zero thickness values in order to obtain a measure of the true or intrinsic adhesion at any film/tablet interface without the confusing elements of tablet porosity, surface roughness and residual stresses in the film.

Adhesiveness↗
PubMed1975

Permeability and porosity of dental casting investments.

Permeability of various gypsum- and phosphate-bonded investments was measured during conventional burn-out procedures. Porosity determinations were made on specimens cooled to room temperature after burn-out. As a group, the gypsum-bonded investments were found to be more permeable than the phosphate-bonded investments. Two phosphate-bonded investments were determined to be relatively impermeable to gas flow, while another exhibited permeability comparable to that of the gypsum-bonded investments. In spite of differences in permeability, the porosity of each type of investment was nearly constant. The porosity of the phosphate-bonded investment was approximately three-fourths that of the gypsum investments. These investments were modified by the addition of varying amounts of acrylic polymer for the purpose of altering permeability. The addition of acrylic polymer increased porosity and permeability of all of the materials included in this investigation. The acrylic additives, however, had no effect on the permeability of relatively impermeable investments unless used in high concentration. The results of this investigation would tend to substantiate the need for special spruing and venting procedures.

Acrylic Resins↗
PubMed1977

Determination of porosity and pore-size distribution of aspirin tablets relevant to drug stability.

Total porosity and pore-size distribution of aspirin tablets prepared from aspirin, starch USP, and precipitated colloidal silicon dioxide were determined using mercury porosimetry. The model represented a hydrolyzable drug substance in combination with simple excipients. The role of starch and silicon dioxide on the microstructure of the tablets was investigated, as was the chemical stability of various systems. In general, the porosity of tablets containing a constant quantity of starch increased linearly with silicon dioxide concentration. Examination of the pore-size distribution, however, revealed that a low concentrations silicon dioxide functioned primarily to reduce the size and volume of coarse pores representing the spaces between the agglomerates of starch and aspirin particles. This effect was optimum at 3%. A further increase in silicon dioxide concentration produced tablets with relatively larger pore sizes. Studies of changes in the porosity characteristics of tablets as influenced by water vapor over time showed distinct differences in this complex parameter. A unique trend in the change of the pore-size distribution was noted with tablets containing 3% silicon dioxide. These observations are discussed relative to the stability of aspirin tablets in which this concentration of silicon dioxide produced a maximum stabilizing effect.

Aspirin↗
PubMed1975

Estimates of the porosity of Bacillus licheniformis and Bacillus subtilis cell walls.

The maximum porosity of Bacillus subtilis and Bacillus licheniformis cell walls was estimated by two independent and relatively simple methods. Peptidoglycan was isolated from Bacillus subtilis cell wall preparations and used as an insoluble support for exclusion chromatography of dextrans of known average molecular size. In an alternative approach the leakage of radioactively labelled proteins from Bacillus licheniformis cells incubated in butanol-saline mixtures was measured and their size estimated by exclusion chromatography on Sephadex G-100. Under these conditions the permeability barrier of the cytoplasmic membrane was destroyed with preservation of the structural integrity of the outer cell wall. The apparent exclusion threshold of the cell wall of either organism as determined by these means corresponded to molecules with a diffusional radius of not more than 2.5 nm.

Alanine↗
PubMed1979

Activity staining for glutamate and alanine dehydrogenases in polyacrylamide gels of varying porosity. A study of bovine placental enzyme forms.

A procedure has been developed for characterizing the various molecular forms of placental and liver glutamate dehydrogenases through a combination of activity staining and varying gel pore size in electrophoresis. At a concentration of 2 mg/ml, the bovine liver GDH remained associated in a very high molecular weight form, while the placental enzyme was substantially dissociated to a molecular species of near 240,000 molecular weight and several charge isomeric species of near 160,000 molecular weight. The general approach outlined here provides a means of definitely correlating the electrophoretic behavior of various dehydrogenase isozymes with both glutamate and alanine dehydrogenase activities and molecular size and should be applicable, even in crude extracts to other dehydrogenase enzymes which exhibit multiple forms or states of association.

Alanine↗
PubMed1975

Porosity and surface area of anionic resins: limitations in the employment of model substrates for the colloidal iron reaction.

Quantitative evaluations of the uptake of an acid ferric hydroxide sol revealed the iron binding of model substrates unrelated to their ion binding capacity. Electron microscopy showed iron particles bound exclusively or mainly to the surfaces of model substrates. Morphometric estimations resulted in a good agreement of the surface/volume ratio with the amount of bound iron. The results are discussed with regard to the steric hindrance of the colloidal iron reaction resulting in a nonstoichiometric interaction.

Anion Exchange Resins↗
PubMed1976

Oxytetracyline tablet formulations: effect of variations in binder concentration and volume on granule and tablet properties.

Formulation studies have been conducted on an oxytetracycline dihydrate tablet formulation containing microcrystalline cellulose and alginic acid, wet granulated with polyvinylpyrrolidone (PVP) solution. A range of granule properties including size, strength packing and porosity, and tablet properties including breaking load, porosity, disintegration and dissolution have been measured. Increased compaction pressure decreased tablet porosity. The reproducibility of the above properties was determined by tests on nine standard batches of granules and tablets. An increased concentration of PVP in the binder solution decreased the rate of tablet dissolution. Although the volume of granulating solution apparently controlled the granule size, it did not significantly alter the tablet dissolution, when the amount of PVP was constant.

Excipients↗
PubMed2011

Mice lacking Nf1 in osteochondroprogenitor cells display skeletal dysplasia similar to patients with neurofibromatosis type I.

Mutations in NF1 cause neurofibromatosis type I (NF1), a disorder characterized, among other clinical manifestations, by generalized and focal bony lesions. Dystrophic scoliosis and tibial pseudoarthrosis are the most severe skeletal manifestations for which treatment is not satisfactory, emphasizing the dearth of knowledge related to the biology of NF1 in bone cells. Using reporter mice, we report here that the mouse Col2α1-Cre promoter (collagen, type II, alpha 1) is active not only in chondrocytes but also in adult bone marrow osteoprogenitors giving rise to osteoblasts. Based on this finding, we crossed the Col2α1-Cre transgenic and Nf1(flox/flox) mice to determine whether loss of Nf1 in axial and appendicular osteochondroprogenitors recapitulates the skeletal abnormalities of NF1 patients. By microtomographic and X-rays studies, we show that Nf1(Col2)(-/-) mice display progressive scoliosis and kyphosis, tibial bowing and abnormalities in skull and anterior chest wall formation. These defects were accompanied by a low bone mass phenotype, high bone cortical porosity, osteoidosis, increased osteoclastogenesis and decreased osteoblast number, as quantified by histomorphometry and 3D-microtomography. Loss of Nf1 in osteochondroprogenitors also caused severe short stature and intervertebral disc defects. Blockade of the RAS/ERK activation characteristic of Nf1(-/-) osteoprogenitors by lovastatin during embryonic development could attenuate the increased cortical porosity observed in mutant pups. These data and the skeletal similarities between this mouse model and NF1 patients thus suggest that activation of the RAS/ERK pathway by Nf1 loss-of-function in osteochondroprogenitors is responsible for the vertebral and tibia lesions in NF1 patients, and that this molecular signature may represent a good therapeutic target.

Animals↗
PubMed1979

Seeding endothelium onto canine arterial prostheses. The effects of graft design.

To identify prosthetic characteristics that support the proliferation of an endothelial lining, 14 different graft designs were studied in dogs. The grafts were prepared by the use of a technique of endothelial seeding that we described previously. They were studied two and four weeks after their implantation. Weft-knit Dacron grafts (water porosity from 1,400 to 1,650 mL/min/sq cm) were the most successful. A velour index (velour stitch frequency times velour loop height) was computed. When the internal velour index (IVI) was greater than 60,000 loop-mu/sq cm, the percentage of clot-free surface was 17.2 +/- 14.5%, compared with 62.0 +/- 26.9% when the IVI less than 60,000 loop-mu/sq cm. Endothelium could be detected on 61.5% of the grafts when the IVI less than 60,00 loop-mu/sq cm, compared with 0% when the IVI greater than 60,000 loop-mu/sq cm. The cells that formed the outer capsule were better organized and more adherent to the graft when an external velour was present, but external velour did not affect the inner lining. We conclude that weft-knit Dacron grafts with water porosities from 1,400 to 1,650 mL/min/sq cm and with limited internal velour (IVI less than 60,000 loop-mu/sq cm) are suitable substrates for single-staged endothelial-cell seeding.

Animals↗
PubMed1979

Enzyme immobilization by radiation-induced polymerization of 2-hydroxyethyl methacrylate at low temperatures.

Enzyme immobilization by radiation-induced polymerization of hydrophilic glass-forming monomers, such as 2-hydroxyethyl methacrylate, was studied. Enzyme radiation damage could be sufficiently retarded at low temperatures. The immobilized enzyme activity yield was markedly higher at low temperature than at higher temperature polymerization. At low temperatures the polymerized composite had a porous structure owing to ice crystallization which depends on the monomer concentration. It was deduced that the enzyme was partially trapped on the polymer surface, partially isolated in the pore, and partially occluded inside the polymer matrix. A decrease in activity caused by enzyme leakage was observed with repeated use in enzyme reactions where the composites had a large porosity. The activity yield showed a maximum at certain optimum porosities, i.e., at optimum monomer concentrations. Continuous enzyme reaction was preferably carried out using immobilized enzyme columns.

Acrylates↗
PubMed1979

Porous titanium endosseous dental implants in Rhesus monkeys: microradiography and histological evaluation.

Artificial tooth roots with porous surface coatings were fabricated by sintering spherical powder of titanium alloy to solid cylindrical cores. The tooth roots were implanted subgingivally in healed mandibular premolar extraction sites of fifteen Rhesus monkeys. Supracrestal abutments were screwed into pretapped holes in the superior aspect of the primary subgingival stage four to eight weeks after implantation of the root. Clinical evaluations were performed monthly. Ten animals were sacrificed for histological evaluation of the functioning free standing implants. Of twenty-nine implants placed, three were lost and four were rated failures on the basis of histological evaluation. Postmortem evaluations revealed bone growth into the porous surface coating of the primary stage of all the implants. The most characteristic features which could be used to describe differences in the implant histology were the buccal and lingual crestal bone heights measured in relation to the root porosity. Twelve of sixteen implants had crestal bone heights within one millimeter of the superior aspect of the root. Four other implants displayed excessive bone recession, revealing as much as one half of the root porosity supracrestally. The four implant failures could be related to unfavorable features of recipient bone sites. The results demonstrate that the bone growth into the porous surface coatings of artificial tooth roots is an efficacious method of dental implant fixation.

Alloys↗
PubMedDate not supplied

Development and evaluation of porous dental implants in miniature swine.

Organized bone ingrowth in endosteal porous implants fabricated from VMC titanium alloy and surgically implanted with a tight interference fit, securely anchored the implants in fresh and healed mandibular premolar sites of miniature swine. This bone-implant union retained its integrity under high as well as slight masticatory stresses up to one-year after implantation. Bone invasion of the alumina porcelain implants was impeded by the lack of adequate interconnecting porosity; when the porosity was increased, insufficient ceramic strength prohibited a tight initial bone-implant fit. As a consequence, inadequate initial implant stability resulted in a soft tissue encapsulation of the majority of the ceramic implants. Histological examination and mechanical testing results were similar for bone-ingrown implants exposed to different experimental stresses for 4, 5, 8, and 12 months. Bone ingrowth and interface shear strengths were also similar in the different VMC pore sizes and shapes investigated. The design of intraoral attachments appeared critical, at least in swine where no postoperative treatment was administered. Gingival inflammation and alveolar bone resorption caused by calculus were severe around truncated cone-shaped devices. Slender transgingival posts, occlusal caps, and crown restorations were less susceptible to calculus accumulation, resulting in a more satisfactory gingival and subgingival response. Excessive epithelial invagination was a problem only in implants with transgingival truncated cones. Good adherence of soft tissue to metal under the gingival mucosa prevented epithelial migration around implants with other transgingival devices. Alveolar bone resportion around the tops of bone-ingrown implants was minimal at the time intervals examined (up to one year); however, a definite conclusion should be delayed until longer-term implants under full occlusion are evaluated.

Aluminum↗
PubMed2026

A correction factor for bridging compaction simulator and different roller compactors.

Roller compaction (RC) is an important dry granulation technique. Since pilot and commercial scale roller compactors, which operate continuously on a large scale, usually require kilograms of material per run, formulation and process development directly on such roller compactors is not practical. In contrast, a compaction simulator (CS) can produce ribblets, also known as "slugs", using only a few grams of material with sinusoidal displacement profile replicating the motion of a specific point on the roll surface. Thus, it is possible to develop RC formulation and process in laboratory using a CS-based material-sparing approach. However, because of the inherently different configurations for applying pressure between die compression and roll compression, translating uniaxial pressure from CS experiments to roll pressure during RC is often unreliable, leading to significant uncertainties in the critical quality attributes of ribbons, such as ribbon solid fraction (or porosity) and mechanical strength. The objective of this study was to identify a correction factor (Kp = uniaxial die compression pressure/roll pressure), by correlating the compressibility profiles from CS and a roller compactor of interest, to enable more reliable process translation from CS to roller compactor. In this study, a Kp value of 0.5 was determined for Alexanderwerk WP120 and validated for Gerteis Mini-Pactor and Bepex Pharmapactor. This value may serve as a starting point for translating the optimal compaction pressure identified based on CS investigation to common roller compactors, requiring only minor adjustments to attain optimal RC process parameters (i.e., roll force and roll gap) for a chosen roller compactor.

Drug Compounding↗
PubMed2026

Transforming Curcuma longa leaf waste into cellulose scaffolds.

The constant dearth of transplantable tissues and organs in India required the development of substitute biomaterials for tissue engineering. Plant-based decellularized scaffolds have become attractive options because of their abundance, ethical acceptability, architectural diversity, and lower risks of zoonotic transmission. Curcuma longa leaves were investigated in this study as a possible source of cellulose-based scaffolding for use in biomedical applications. After cuticle removal, an immersion decellularization technique utilizing sodium dodecyl sulphate (SDS) and triton-X-100 was developed to successfully remove cellular and nuclear material while maintaining leaf parenchyma architecture. Histology, DAPI staining, scanning electron microscopy, and a notable decrease in leftover DNA content all demonstrated efficient decellularization. When contrasted with native leaves, the resultant decellularized C. longa leaf scaffolds showed significant increase in porosity, water vapor transmission rate and swelling percent, and significantly lower contact angle with an optimum surface roughness promoting cell adhesion. Mechanical test manifest higher tensile strength with decreased stiffness. Fourier transform infrared spectra of leaf scaffold reveals persistence of different components except cuticle but the intensity of different peaks was decreased. The leaf scaffolds showed superior hemocompatibility and excellent compatibility with Madin-Darby canine kidney cells (MDCK) which is demonstrated by cell attachment and proliferation. MTT assay of seeded scaffold showed significantly higher metabolically active cell. In vivo subcutaneous implantation of decellularized scaffolds showed host tissue incorporation, accumulation of collagen, and neovascularization. C. longa leaf scaffolds can be utilized as cost effective and sustainable biomaterials for soft tissue engineering and regenerative medicine.

Curcuma↗