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PubMed1992

The effect of porosity of articular cartilage on the lubrication of a normal human hip joint.

The effect of porosity of articular cartilage on the lubrication of a normal human hip joint has been studied. The poroelasticity equation of articular cartilage and the modified Reynolds equation for the synovial fluid lubricant have been successfully solved under squeeze-film motion and for the conditions experienced in a normal human hip joint. It has been shown that porosity of the articular cartilage depletes the lubricant film thickness, rather than increasing it, particularly when the lubricant film thickness becomes small. Furthermore, it has been shown that articular cartilage can be treated as a single-phase incompressible elastic material in the lubrication modelling under physiological walking conditions.

Cartilage, Articular↗
PubMed2006

Controlled porosity osmotic pump for the delivery of flurbiprofen.

Controlled porosity osmotic pump contains water-soluble additives in the coating membrane, which in contact with aqueous environment dissolves and results in formation of micro porous membrane. The resulting membrane is substantially permeable to both water and dissolved drug. The drug release from this type of system is independent of pH and follows zero order kinetics. In the present investigation, effort has been made to study release mechanism of drug having low water solubility by means of controlled porosity osmotic pump. The capsule membrane was prepared by phase inversion technique. The phase inversion was carried by dipping the stainless steel mould in a 15% solution of cellulose acetate containing varying amounts of pore-forming agent, glycerol (50% to 70% w/w), followed by quenching in an aqueous solution (10% w/v glycerol), which resulted in the formation of the asymmetric membrane. The delivery orifices so formed were confirmed by release of an encapsulated dye from the capsule and scanning electron microscope (SEM). The drug selected for this study, Flurbiprofen, has low water solubility and hence is unable to create osmotic pressure to cause drug release. To enhance the solubility and its osmotic pressure, this study was conducted with a solubility enhancer sodium lauryl sulfate (SLS). The quantity of SLS was predetermined by conducting a solubility study of flurbiprofen with SLS. Release rate studies revealed that less than 10% of drug was released from the system without SLS, while about 75% release was observed from systems containing SLS. The release rate increased as the concentration of pore forming agent increased.

Delayed-Action Preparations↗
PubMedDate not supplied

Gradation of microcapsule wall porosity by deposition of polymer mixtures (Eudragit RL and Eudragit RS). Phase separation of polymer mixtures and effects of external media and conditions on release.

With the aim of increasing flexibility in controlling release from microcapsules, mixtures of wall polymers varying in porosity were investigated by phase separation. Eudragit RL and RS (polymethylmethacrylate linear backbone polymers) mixtures differing in polar substituent content and porosity were used as the wall material and were deposited using a non-solvent addition method. Release rates increased with polar group content of the mixtures, using theophylline, potassium dichromate or sodium chloride as model core materials. Theophylline release rate had the same relationship to polar group content as found earlier for urea permeation of cast mixed-polymer films. Release was generally accelerated in these systems when the external medium contained sodium lauryl sulphate as a wetting agent but not consistently, decreasing unexpectedly for RL-theophylline microcapsules. Localized dissolution of core substance was visible microscopically during release from single microcapsules. The release rate was sensitive to agitation intensity only at low wall to core ratios. Temperature change revealed only a single release mechanism for sodium chloride by Arrhenius equation treatment. Buffer ions penetrated coatings readily, changing theophylline release rates and providing clear evidence of diffusion via a pore-capillary mechanism.

Acrylic Resins↗
PubMed1993

Porosity of bone cement reduced by mixing and collecting under vacuum.

Palacos R bone cement was mixed in a commercial vacuum mixing system (MITAB), and in an experimental system allowing evacuating air from the powder before mixing and collecting the cement under partial vacuum. The effect on the porosity of mixing at different pressure levels was tested. The effect of evacuating air from the powder before mixing was also analyzed. The numbers and sizes of the voids in the cement samples were measured in radiographs and under the microscope. Also, the density of the cement was measured. Vacuum mixed samples had a substantial reduction of voids, as well as an increase in density compared to mixing at atmospheric pressure. After vacuum mixing and collection, a further reduction of the porosity and increased density were seen; all the large voids within the cement were eliminated at 0.05 bar absolute pressure.

Bone Cements↗
PubMed1994

Relationship between shell porosity, shell thickness, egg weight loss, and embryonic development in Japanese quail eggs.

Japanese quail eggs that hatched (H) or pipped (PIP) exhibited less weight loss through 15 d of incubation than did eggs that died late (LD), whereas eggs containing early dead (ED) embryos exhibited the greatest weight loss. The pore concentration at the large end of each egg was greatest in H eggs when compared with all other types. The pore concentration at the equator was greatest in H eggs and least in the eggs of the ED embryos. All other egg types lay statistically between these two types with regard to equator porosity. The small end pore concentration was similar in H, INF, and LD eggs and in the LD, PIP, and ED eggs. The least number was exhibited by the ED eggs and most by the H eggs. The thinnest shells at the small end were exhibited by H eggs, whereas thicker small end shells were exhibited by ED, LD, and PIP egg types. No differences were observed at the large end or equator. The data suggest that ED eggs exhibit excessive weight loss even though shell porosity was lower and shell thickness was similar to other egg types. This suggests that some functional component of the egg such as the shell membrane or albumen may contribute to this excessive weight loss. A similar statement can be made for LD eggs, which experienced greater weight loss through 15 d than did PIP or H eggs.

Animals↗
PubMed2003

Influence of porosity and composition of porous carriers on the uptake of nutrients.

The current paper assesses the potential of industrial solid wastes utilization such as blast furnace slag (BFS) and zeolite synthesized from fly ash (ZFA), which are effective as well as economically attractive for the uptake of phosphate and ammonium from polluted seawater. The solidification of BFS and ZFA has been developed in different proportions of BFS/ZFA (30/70, 50/50 and 70/30 (w/w)) with different porosities (25%, 40% and 52%, respectively) to cylindrical porous carriers using a Hydrothermal Hot-Pressing (HHP) method. The concentrations of heavy metals in ZFA and BFS were too low to affect the aquatic environment. The main finding is that the high rate of BFS (70%) in porous carriers enhanced phosphate uptake explained by the higher percentage of calcium (35.7%) in porous carriers and high pH conditions. The efficient ammonium uptake was observed with high rate of ZFA (70%) in porous carriers. Results found through this experimental work imply that porous carriers with BFS/ZFA proportion of 70/30 are suitable for potential practical application in the aquatic environment due to their efficient uptake of phosphate and ammonium. The choice was made upon their porosity (40%) and their compressive strength (56 kgf/cm2) which are relatively higher than those with BFS/ZFA proportion of 30/70 and 50/50.

Ammonia↗
PubMed2006

Experimental study on stability of a high-porosity expanded polytetrafluoroethylene graft in dogs.

PURPOSE: The purpose of the present study was to evaluate the stability of a high-porosity expanded polytetrafluoroethylene (ePTFE) graft, which has been shown to possess excellent biocompatibility and tissue integration. METHODS: The graft used in the present study was a high-porosity ePTFE graft , which had an average internodal distance of approximately 60 microm and a random node architecture with tortuous path channels extending from the outer to the inner surface. Eleven beagle dogs (each group n = 3 or 4) weighing 10-12 kg were used. The graft, with a 6 mm inside diameter and a 30-40 mm length, was implanted into the canine abdominal aorta and retrieved after 2-80 weeks. The deformation of the graft was evaluated by conventional computed tomography (CT). The radial tensile strength, longitudinal tensile strength, and suture retention strength of the graft were measured after 2-80 weeks. RESULTS: CT studies showed no anastomotic aneurysm or deformation of the graft. Physical tests demonstrated no significant deterioration in suture retention strength, radial tensile strength or longitudinal tensile strength for periods ranging from 2-80 weeks compared to pre-implantation grafts. CONCLUSION: The graft possesses adequate stability that ensures safe and effective clinical use.

Animals↗
PubMed1990

[Comparison of investment expansion methods aspect of porosity].

Currently, the use of non-precious metal alloys in fixed prosthetic restorations has warranted review of the work done sofar using precious metal alloys. One of the parameters exhibiting the success of castings done using non-precious metal alloys is porosity, which is evaluated through such methods as rod forms, waxing heat, to investing and other castability methods. The porosity ratios of cats similarly done employing different investment expansion methods have been evaluated. While there is no statistical difference due to different methods, the hygroscopic expansion method noted successful results.

Dental Alloys↗
PubMed1994

Evaluation of an adhesive system for amalgam repair: bond strength and porosity.

This study compared the shear bond strengths and the porosity at the bond sites of a spherical amalgam alloy to those of an admixed amalgam alloy, when they were bonded to like and unlike alloy specimens with or without a resin bonding material. The spherical alloy had higher bond strength and less porosity than did the admixed alloy, whether bonded to spherical or admixed alloy. The results suggest that use of a spherical alloy should be strongly considered when an amalgam restoration is to be repaired with an amalgam alloy, regardless of the type of alloy used in the original restoration. Use of a resin bonding agent did not increase bond strengths of amalgam to amalgam.

Analysis of Variance↗
PubMedDate not supplied

Microhardness and porosity of Class 2 light-cured composite restorations cured with a transparent cone attached to the light-curing wand.

A new technique for curing class 2 composite fillings was investigated with respect to microhardness and porosity in the cervical part of the restorations. The technique is based on a plastic transparent cone that is attached to the curing wand. Before polymerizing the cervical portion, the cone is pressed down into the material in the direction of the floor of the approximal box. When the light is activated, it concentrates in the tip of the cone, from where it is distributed into the composite material. In order to compare this technique with conventional curing, standardized class 2 cavity preparations were made in brass blocks. Four different composite materials were used for 20 restorations each: Heliomolar, Herculite XR, Occlusin, and P-50. Ten restorations of each material were cured using the conventional technique (in two portions), and in the remaining 10 restorations the cervical portion was cured with the transparent cone. The irradiation time was 60 seconds in all instances. The Vickers hardness of the cervical approximal surfaces was measured after one and 24 hours. The surfaces were photographed in a stereomicroscope, and the numbers of porosities were counted on black-and-white prints.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1996

Porosity reduction in bone cement at the cement-stem interface.

The fatigue failure of bone cement, leading to loosening of the stem, is likely to be one mode of failure of cemented total hip replacements. There is strong evidence that cracks in the cement are initiated at voids which act as stress risers, particularly at the cement-stem interface. The preferential formation of voids at this site results from shrinkage during polymerisation and the initiation of this process at the warmer cement-bone interface, which causes bone cement to shrink away from the stem. A reversal of the direction of polymerisation would shrink the cement on to the stem and reduce or eliminate the formation of voids at this interface. We have investigated this by implanting hip prostheses, at room temperature or preheated to 44 degrees C, into human cadaver femora kept at 37 degrees C. Two types of bone cement were either hand-mixed or vacuum-mixed before implantation. We found that the area of porosity at the cement-stem interface was dramatically reduced by preheating the stem and that the preheating temperature of 44 degrees C determined by computer analysis of transient heat transfer was the minimum required to induce initial polymerisation at the cement-stem interface. Temperature measurements taken during these experiments in vitro showed that preheating of the stem caused a negligible increase in the temperature of the bone. Reduction of porosity at the cement-stem interface could significantly increase the life of hip arthroplasties.

Bone Cements↗
PubMed1997

[Tricalcium phosphate, vector of antibiotics: gentamycin and vancomycin. In vitro physicochemical characterization, study of biomaterial porosity and gentamycin and vancomycin elution].

We have investigated a Vancomycin and Gentamycin loaded macroporous tri-calcium phosphate-type beta-ceramic, Calciresorbr. Elution kinetics of Vancomycin and Gentamycin from spheric implants was studied by varying porosity and initial concentrations; then, the other following parameters, that can be modulated and are likely to be involved in this elution process, were analysed: Antibiotic charge: quantitative analysis (titration). qualitative analysis by scanning electron microscopy. Material's porosity: qualitative analysis: optical and scanning electron microscopy. quantitative analysis by stereology and treatment. This physicochemical characterization would favour correct manufacturing of new macroporous synthetic bioceramics in order to achieve satisfactory elution kinetics and homogenous materials.

Biocompatible Materials↗
PubMed1998

Fibrinogen Caracas I: a dysfibrinogenemia with a hemorrhagic diathesis associated with diminished fibrin fiber diameter and reduced fibrin gel porosity.

Fibrinogen Caracas I is a dysfibrinogenemia with a mild bleeding diathesis and a defective wound healing. We have characterized this abnormal fibrinogen using transmission electron microscopy (TEM) in combination with turbidity and permeation studies. Turbidometric and permeability analysis showed that the abnormal fibrin had a significantly decreased mass:length ratio and fiber diameter. In addition, the permeability studies of plasma fibrin clots showed that the gel porosity of the abnormal fibrinogen was reduced. Images of the abnormal fibrin structure obtained using TEM showed that the fibers were thinner, much less branched and less ordered than normal fibers. Diminished fibrin fiber diameter and reduced fibrin gel porosity have been taken as hallmarks of thrombophilic dysfibrinogenemias. The results of the present study show that these features are not necessarily predictive of thrombophilia. Further studies performed on a larger number of dysfibrinogenemias need to be conducted in order to establish the implications of these parameters on the clinical outcome.

Coagulation Protein Disorders↗
PubMed1997

Significance of porosity and compliance of microporous, polyurethane-based microarterial vessel on neoarterial wall regeneration.

The microporous structure of artificial vascular grafts, which increases compliance and porosity simultaneously, may enhance neoarterial regeneration. In order to differentiate these effects, three models of segmented polyurethane grafts (inner diameter, 1.5 mm; wall thickness, 100 microns) with or without micropores fabricated using an excimer laser ablation technique, were prepared, and their neoarterial regenerative potentials were studied upon implantation: Model I (microporous, permeable, compliant); Model II (smooth-surfaced, impermeable, compliant); and Model III (smooth-surfaced, impermeable, noncompliant). In Models I and II, the pore or groove size (diameter, 100 microns) and pore or groove arrangement were fixed, and consequently their compliances were almost identical. Irrespective of model, the luminal surfaces were coated with benzophenone-derivatized gelatin and subsequently photocured. Twenty grafts (length, 20 mm) of each model were implanted in the aortas of rats. Predetermined implantation periods were 4, 12, and 24 weeks. Total patency rate decreased in the order Model I (100%), II (87%), and III (59%) grafts. All patent grafts were completely endothelialized after 12 weeks of implantation, irrespective of model. After 12- and 24-week implantations, in Model I grafts, the neoarterial wall was thin, and smooth muscle cells (SMCs) were of the contractile phenotype. In Model II grafts, the neoarterial wall exhibited considerable thickening. In Model III grafts, the neoarterial wall exhibited marked thickening, and SMCs were of the synthetic phenotype. The neoarterial wall thickness at the midportion of the grafts after 24 weeks of implantation increased in the order Model I (48 +/- 8 microns), II (146 +/- 87 microns), and III (385 +/- 21 microns) grafts. These results strongly suggest that compliance matching and porosity synergistically resulted in neoarterial wall restoration without appreciable thickening.

Animals↗
PubMed2000

A theoretical and experimental analysis of polymerization shrinkage of bone cement: A potential major source of porosity.

A theoretical basis for understanding polymerization shrinkage of bone cement is presented based on density changes in converting monomer to polymer. Also, an experimental method, based on dilatometry and the Archimedes' principle is presented for highly precise and accurate measurement of unconstrained volumetric shrinkage of bone cement. Furthermore, a theoretical and experimental analysis of polymerization shrinkage in a constrained deformational state is presented to demonstrate that porosity can develop due to shrinkage. Six bone-cement conditions (Simplex-Ptrade mark vacuum and hand mixed, Endurancetrade mark vacuum mixed, and three two-solution experimental bone cements with higher initial monomer levels) were tested for volumetric shrinkage. It was found that shrinkage varied statistically (p< or = 0.05) from 5.1% (hand-mixed Simplex-Ptrade mark) to 6.7% (vacuum-mixed Simplex-Ptrade mark) to 10.5% for a 0.6:1 (polymer g/monomer mL) two-solution bone cement. Shrinkage was highly correlated with initial monomer content (R(2) = 0.912) but with a lower than theoretically expected rate. This discrepancy was due to the presence of residual monomer after polymerization. Using previously determined residual monomer levels, the theoretic shrinkage analysis was shown to be predictive of the shrinkage results with some residual monomer left after polymerization. Polymerization of a two-solution bone cement in a constrained state resulted in pores developing with volumes predicted by the theory that they are the result of shrinkage. The results of this study show that shrinkage of bone cement under certain constrained conditions may result in the development of porosity at the implant-bone cement interface and elsewhere in the polymerizing cement mantle.

Animals↗
PubMed1987

Alternative techniques of seeding cultured endothelial cells to ePTFE grafts of different diameters, porosities, and surfaces.

Attachment of 111Indium-oxine labeled cultured canine venous endothelial cells to expanded polytetrafluorethylene (ePTFE) grafts was evaluated in vitro. Three alternative seeding techniques were studied in grafts having different diameters, porosities, and surfaces, including: (I) manual milking of blood containing endothelial cells within the graft; (II) a two-step procedure of incubating grafts initially with blood and then with an endothelial cell suspension; and (III) mechanical spinning of grafts filled with blood containing endothelium. Method II had significantly higher cell attachment to the graft (11.6%) than did Method I (1.5%) or III (4.7%). A somewhat higher seeding efficiency was noted in 10-mm-I.D. grafts (11.6%) compared to 6-mm-I.D. grafts (6.3%). Different graft porosity, created by altering internodal distances, did not cause significant changes in cell attachment (10 microns, 13.4%; 30 microns, 6.3%; 90 microns, 16.0%). Fibronectin-coated surfaces, which should have enhanced cell adhesion, demonstrated a 6.0% cell attachment, a lower efficiency than the 11.6% observed with a blood coating alone. Acetone-soaked surfaces, which should have predictably exhibited less hydrophobicity, produced quite variable attachments (range 3.4 to 59.7%, mean 23.4%). In the present investigation the best seeding technique was method II, the two-step incubation procedure. Consistent differences were not noted with various ePTFE graft configurations or surfaces.

Animals↗
PubMed1989

Comparison of coral resorption and bone apposition with two natural corals of different porosities.

Previous studies showed that natural coral implanted into bone tissue was gradually resorbed and progressively replaced by newly formed bone. The objectives of this study were to compare the fate of two Madreporian corals, Porites and Acropora, after implantation during 1 and 2 months into sheep and pig long bones. These materials are identical in composition (CaCo3) but differ in volume (49 +/- 2%, 12 +/- 4%, respectively) and mean size (250 vs. 500 microns) of porosities. The non-decalcified histological slices were observed under light microscopy. Implant resorption and new bone formation were quantified through an automatic image analysis system. Quantitative results showed that the larger the porosity volume, the greater was the coral resorption as well as the new bone apposition. Large differences were found between the two animal species. Histological findings were identical to those previously reported: implants were resorbed and progressively replaced by newly formed bone. Coral was found to be an osteoconductive biomaterial which acted as a scaffold for a direct osteoblastic apposition and consequently could be an interesting alternative to bone auto-, allo-, or xenografts.

Animals↗
PubMed1982

Quantitative evaluation of pharmaceutical effervescent systems II: Stability monitoring by reactivity and porosity measurements.

The stability of selected effervescent tablet systems was monitored by means of mercury intrusion porosimetry and by a cantilever beam/proximity transducer balance. The porosity measurements proved to be useful in elucidating tablet pore structure changes over time. The measured parameter, percent pores greater than the experimental range, was a useful measure of porosity for statistical evaluations. The study showed that compression pressure and manufacturing conditions are not significant factors in the stability of an effervescent tablet system when nonhygroscopic materials are used.

Bicarbonates↗