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At least 613 records · Page 34Linked to original sources
PubMed2004

High-porosity activated carbon as a possible matrix for native DNA and dextran-sulfate immobilization.

In this study, specific and nonspecific activity of calf thymus DNA and Dextran-Sulfate (DS)-containing synthetic carbonic adsorbents (0.7-7mg of each ligands per 1 cm3 of activated carbonic beads, 0.3-0.6mm diameter, bulk density gamma=0.1-0.2g/cm3) have been compared in stir-bath and micro-column in vitro tests. DS coating as well as DNA coating does not demonstrate deep influence on the unspecific adsorptive activity of carbonic matrix toward creatinine, vitamin B12, and unconjugated bilirubin. No essential difference has been found in the specific activity of DNA and DS containing adsorbents toward anti-ds- and anti-ss-DNA-antibodies, as well as antibodies against DNA-protein complexes (anti-DNP-antibodies): in both cases the percentage of decrease of appropriate antibody concentration varied between 35 and 51% for single-pass microcolumn experiments with moderate enhancement of extraction efficacy (up to 60-75%) due to additional recirculation (2 h) or preliminary plasma dilution in 2-5 times. In the micro-column experiments with the proinflammatory cytokines DNA or DS-coating did not diminish TNF-alpha, IL-1beta, and IL-6 adsorption from 3% BSA solution, but even improves to some extent its removal compared with uncoated matrix.

Animals↗
PubMed1975

A small arterial substitute: expanded microporous polytetrafluoroethylene: patency versus porosity.

Eighty-nine grafts of expanded microporous polytetrafluoroethylene (PTFE) with a diameter of 4 mm, were placed in the carotid and femoral arteries of dogs. The animals were sacrificed at varying intervals beginning three days after operation. Four animals remain alive with patent grafts 10 months post-operatively. Twenty-four of 89 grafts were occluded, an overall patency of 73%. Fibril length (pore size) of the graft material was varied from 4 to 110 microns. Average pore size ranged from 9 to 65 microns. Wall thickness varied from 0.3 to 0.75 mm. Density ranged from 0.24 to 0.35 g/ml. Tissue ingrowth, neointimization and patency rate as compared to pore size, wall-thickness and density of expanded PTFE were observed. Pore size is the primary determinant of tissue ingrowth, neointimization and patency. Of 51 grafts with an average pore size of 22 microns or less, there were 6 occlusions, an 88% patency rate. There were 38 grafts with an average pore size of 34 microns or greater. In these 38 grafts, 18 occlusions were observed, a 53% patency rate. Patent grafts demonstrated tissue ingrowth, capillary formation an a thin neointima. Using small pore grafts, patency rates of 90% can be anticipated in the dog. Expanded microporous PTFE with its ease of handling, strength and pliability may be the vascular prosthesis of choice in man.

Animals↗
PubMedDate not supplied

The effect of porosity and biomaterial on the healing and long-term mechanical properties of vascular prostheses.

Continuing efforts in vascular prosthetic design are focused on understanding the characteristics required for function of small internal diameter and low-flow prostheses. The pioneers of vascular surgery developed large diameter textile prostheses for successful reconstruction of the aortoiliac vessels, but fabric grafts function poorly in diameters less than six millimeters. Major advances in small vessel reconstruction include the use of autogenous vessels for coronary artery lesions and microvascular surgery of digital and cerebral vessels. The author believes that future advances in graft design will enable prosthetic repair of two to four millimeter arteries and reconstruction of veins. This manuscript discusses the development of improved synthetic blood compatible surfaces with detailed consideration of prosthetic design factors such as pore size, biomaterial mechanical properties and thrombogenicity of the blood flow surface.

Biocompatible Materials↗
PubMed1994

A comparison of stress-induced porosity due to conventional and a modified spinal fixation device.

A hypothesis that device-related osteopenia can be reduced by decreasing the rigidity of a fixation device was tested through a canine study. Polymer washers were interposed between the integral nut and plate of the variable spinal plating (VSP) system to reduce its rigidity. A solid fusion was observed 6 months postoperatively in all of the animals using VSP or modified systems. The stabilized segment using both systems showed similar load-displacement behaviors immediately after surgery and 6 months postoperatively. Although not significant, 5.6 and 1.8% decreases in volumetric density of mineralized bone were found in the stabilized segments due to VSP and modified systems, respectively. The modified system also increased bone growth around screws. The new concept of using polymer washers, to decrease rigidity of the fixation device over time, may reduce device-related osteopenia.

Animals↗
PubMed1980

The porosity of the cell wall of Candida albicans.

Polyethylene glycols of different molecular sizes have been used to study the penetrability of the cell wall of Candida albicans harvested at the end of the growth phase and after prolonged incubation in the stationary phase. No differences were found which could account for the greater resistance of cells from stationary phase cultures of C. albicans to the antimycotic agents amphotericin B methyl ester and miconazole.

Amphotericin B↗
PubMed1986

Factors enhancing genetic transformation of intact yeast cells modify cell wall porosity.

Genetic transformation of intact cells of Saccharomyces cerevisiae, achieved by incubating the cells with plasmid DNA in the presence of PEG, could be enhanced, not only by pretreatment of the cells with Li+ and 2-mercaptoethanol, as has been reported previously, but also by pretreatment with proteolytic enzymes. The efficiency of transformation with 2-mercaptoethanol rose dramatically when the pretreated cells had been handled in osmotically stabilized media. Following all the pretreatments the cells became leaky for nucleic acids as detected by the presence of endogenous RNAs in the medium. The pretreatments evidently facilitated the passage of transforming DNA across the cell wall.

Cell Survival↗
PubMed2003

Linear dynamics of double-porosity dual-permeability materials. I. Governing equations and acoustic attenuation.

The equations governing the linear acoustics of composites with two isotropic porous constituents are derived from first principles using volume-averaging arguments. The theory is designed for modeling acoustic propagation through heterogeneous porous structures. The only restriction placed on the geometry of the two porous phases is that the overall composite remains isotropic. The theory determines the macroscopic fluid response in each porous phase in addition to the combined bulk response of the grains and fluid in the composite. The complex frequency-dependent macroscopic compressibility laws that are obtained allow for fluid transfer between the porous constituents. Such mesoscopic fluid transport between constituents within each averaging volume provides a distinct attenuation mechanism from the losses associated with the net Darcy flux within individual constituents as is quantified in the examples.

Journal Article↗
PubMed2004

Structure and mechanical properties of high-porosity macroscopic agglomerates formed by random ballistic deposition.

We present experimental results on the mechanical properties of macroscopic agglomerates formed by ballistic hit-and-stick deposition. The agglomerates, produced with a new experimental method, consist of monodisperse SiO2 spheres with 1.5 microm diameter and have a volume filling factor of phi=0.15, matching very closely the theoretical value for random ballistic deposition. They are mechanically stable against unidirectional compression of up to 500 Pa. For pressures above that value, the volume filling factor increases to a maximum of phi=0.33 for pressures above 10(5) Pa. The tensile strength of slightly compressed samples (phi=0.2) is 1000 Pa.

Journal Article↗
PubMed2004

Porosity variation in hydroxyapatite and osteoblast morphology: a scanning electron microscopy study.

The biocompatibility of hydroxyapatite has been demonstrated by previous studies, with enhancement of osteointegration through the use of porous hydroxyapatite (pHA). Emphasis has been focused on the use of coralline hydroxyapatite or the introduction of macroporosity into synthetic hydroxyapatite. The current study investigates the role of macro- and microporosities in synthetic phase-pure porous hydroxyapatite on the morphological aspects of human osteoblast-like cells using scanning electron microscopy. Cells were seeded on four different types of porous hydroxyapatite (HA1, HA2, HA3 and HA4) and examined following 1, 2, 14 and 30 days of incubation in vitro. The results indicated that the cells had an affinity to micropores through filopodia extensions, at initial stage of attachment. Cellular proliferation and colonization was evident on all materials with cells forming cellular bridges across the macropores at day 14 with cellular canopy formation covering entire macropores observed by day 30. This study demonstrates that while the introduction of microporosity has no evident effect on cellular morphology at later time points, it seems to play a role in initial cellular anchorage and attachment.

Bone and Bones↗
PubMedDate not supplied

Laboratory and field-based studies of abundances, small-scale patchiness, and diversity of gymnamoebae in soils of varying porosity and organic content: evidence of microbiocoenoses.

Soil samples (varying in granularity) from four natural sites were cultured in microcosms to determine small-scale patchiness in abundance and diversity of gymnamoebae. Eighty grams of the same thoroughly mixed soil, either moistened with distilled water (- nutrients) or supplemented with an equivalent vol. of organically enriched water (+ nutrients), were placed in covered glass jars and incubated for 14 d (25 degrees C). Abundances (number/gram soil) were assessed in each of 3 core samples (5-10 mm apart). Assay precision was estimated to be +/- 4%. Abundances were similar in the 3 closely-spaced samples, but occasional samples had higher abundances, probably representing localized enriched sites ("nutrient hot spots"). Diversity within the triplicate, closely spaced samples varied substantially. Mean abundance and diversity of amoebae were consistently higher in organically enriched soil and in soil of increasing granularity. Field samples collected directly from two of the sites showed similar patterns of abundance and diversity as found in the experimental studies, indicating substantial small-scale compartmentalization of soil protist communities. These data provide evidence of soil eukaryotic microbiocoenoses and indicate that soil microfauna may encounter wide variations in resources and prey communities as they migrate within small distances of several millimeters or less.

Amoebida↗