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PubMed2006

Influence of the porosity of starch-based fiber mesh scaffolds on the proliferation and osteogenic differentiation of bone marrow stromal cells cultured in a flow perfusion bioreactor.

This study investigates the influence of the porosity of fiber mesh scaffolds obtained from a blend of starch and poly(epsilon-caprolactone) on the proliferation and osteogenic differentiation of marrow stromal cells cultured under static and flow perfusion conditions. For this purpose, biodegradable scaffolds were fabricated by a fiber bonding method into mesh structures with two different porosities-- 50 and 75%. These scaffolds were then seeded with marrow stromal cells harvested from Wistar rats and cultured in a flow perfusion bioreactor or in 6-well plates for up to 15 days. Scaffolds of 75% porosity demonstrated significantly enhanced cell proliferation under both static and flow perfusion culture conditions. The expression of alkaline phosphatase activity was higher in flow cultures, but only for cells cultured onto the higher porosity scaffolds. Calcium deposition patterns were similar for both scaffolds, showing a significant enhancement of calcium deposition on cellscaffold constructs cultured under flow perfusion, as compared to static cultures. Calcium deposition was higher in scaffolds of 75% porosity, but this difference was not statistically significant. Observation by scanning electron microscopy showed the formation of pore-like structures within the extracellular matrix deposited on the higher porosity scaffolds. Fourier transformed infrared spectroscopy with attenuated total reflectance and thin-film X-ray diffraction analysis of the cell-scaffold constructs after 15 days of culture in a flow perfusion bioreactor revealed the presence of a mineralized matrix similar to bone. These findings indicate that starch-based scaffolds, in conjunction with fluid flow bioreactor culture, minimize diffusion constraints and provide mechanical stimulation to the marrow stromal cells, leading to enhancement of differentiation toward development of bone-like mineralized tissue. These results also demonstrate that the scaffold structure, namely, the porosity, influences the sequential development of osteoblastic cells and, in combination with the culture conditions, may affect the functionality of tissues formed in vitro.

Animals↗

PubMed2003

The influence of stem insertion rate on the porosity of the cement mantle of hip joint replacements.

This study investigates the effect of stem insertion rate on the porosity of the cement mantle. An experimental protocol was developed to simulate the surgical technique of cementing a prosthetic stem into the medullary canal of the femur. Cement mantle specimens were produced for three different stem insertion rates. The presence of porosity in the cement mantle was investigated. Additionally, the mechanical strength of the bone cement was assessed. Increasing the stem insertion rate did not have a significant effect on the porosity distribution within the bulk cement mantle. However, for all stem insertion rates investigated, the porosity concentration increased significantly moving from the cement/pseudofemur interface through to the stem/cement interface. In all cases, the presence of porosity significantly decreased the mechanical behaviour of the bone cement. High porosity concentration at the stem/cement interface seems to be attributed also to the rheology of the cement during implant insertion. Nevertheless, the surgeon cannot influence the formation of porosity by changing the stem insertion rate.

Arthroplasty, Replacement, Hip↗

PubMed1990

[The study on surface porosity of die stone. Influence of vinyl polysiloxane impression materials].

In this study, the authors have attempted to discover optimum conditions for eliminating all porosity, except what is caused by manual error, in the surfaces of Die Stone. Five vinyl-porisiloxane impression materials, two other kinds rubber impression materials, and two kinds of die materials were used. Die materials were poured at intervals of 0, 15, 30, 60, and 120 minutes after the impression had been removed. Cast-surface porosity was measured by means of SPICCA II. Results 1. Practically surface porosities were not scarcely observed in casts made from any of the impression materials except vinyl silicone rubber. Among the five vinyl-polysiloxane impression materials, Hydrophilic Exaflex produced the least porosity. 2. Porosity in casts made with Provil tended to decrease definitely as pouring time progressed. This tendency occurred with no other materials. 3. When the die material was mixed at a low water-powder ratio, cast-surface porosity was reduced in the case of all materials except President. 4. Concentration of hydrogen gas, which was released from all vinyl-polysiloxane impression materials, decreased with the passing of time. 5. In the case of Provil, a correlation existed between hydrogen-gas concentration and the degree of cast-surface porosity. But no similar correlation was observed in the case of any other vinyl-polysiloxane impression materials.

Dental Impression Materials↗

PubMedDate not supplied

[Porosity of hard dental tissues].

The examination of the porosity of hard dental tissues and the Zn-phosphate cement was carried out with the mercury-porosimeter (Carlo Erba, Italy mod. 2000) under the atmospheric pressure of 200 MPA. The accuracy of this method does not permit measurements of the porosity of enamel, more precisely the enamel surface cannot be permeated by mercury. The total volume of opened pores of the examined dentin was considerably high (28 cm3/gr); the main characteristics of dentin porosity are: the prevalence of macropores (2R 200 nm) of which 40% with the diameter between 400 and 2000 nm and 40% with the diameter between 6000 and 150,000 nm the presence of pores with diameter between 50 and 400 nm, and over 100,000 nm was minimal. The specific porosity of dentin was found to be 60% greater in relation to the porosity of cement. In the cement the diameter between 4000 and 30,000 nm was found in the majority of pores (about 52%) and the remaining 48% belonged to the macropore groups. The specific porosity of Zn-phosphate cement was found to be five times greater in relation to the specific porosity of dental cement (0.082 to 0.016 cm3/gr). However, the prevalence of these specimens was that of mezo pores.

Dental Cementum↗

PubMed1985

Influence of variations in preparation of dental amalgam on dimensional stability and porosities.

The susceptibility of amalgam to deviations in the preparation procedure produced an overall trend for both the setting dimensional stability and the number of porosities. The dimensional stability of ANA 2000 was the least affected by the deviations, while ANA 68 exhibited low susceptibility to the deviations when porosities are concerned. Lowered condensation pressure usually increased both the setting expansion and the number of porosities, and vice versa. Dispersalloy exhibited an increased number of porosities with both higher and lower condensation pressure. Except for ANA 2000, undertrituration caused increased expansion and porosities, while overtrituration resulted in increased contraction but minor effects on porosities. Lower mercury/alloy ratio increased the setting expansion and the number of porosities, while the response to a higher ratio was relatively small with the exception of a markedly increased setting expansion for ANA 68.

Chemical Phenomena↗

PubMed2005

Spatially resolved measurement of rock core porosity.

Density weighted, centric scan, Conical SPRITE MRI techniques are applied in the current work for local porosity measurements in fluid saturated porous media. The methodology is tested on a series of sandstone core samples. These samples vary in both porosity and degree of local heterogeneity due to bedding plane structure. The MRI porosity measurement is in good agreement with traditional gravimetric measurements of porosity. Spatially resolved porosity measurements reveal significant porosity variation in some samples. This novel MRI technique should have applications to the characterization of local porosity in a wide variety of porous media.

Journal Article↗

PubMed1979

[Oxygen contents and casting porosities in Ag alloys (author's transl)].

Although pure Ag has a large casting porosity near the sprue attachment, Ag-Zn and Ag-Cu alloys have small or no porosities. The casting porosities of Ag-Au alloys are similar to that of pure Ag. These experimental results were discussed using the calculated oxygen contents in molten state and the measured oxygen contents of castings, and related to the capacity for deoxidization of additive elements. In the present study the casting porosities in pure Ag and Ag-Au alloys are considered to be not shrinkage porosities, but porosities due to discharged oxygen gas. In spite of high oxygen contents of molten state and castings, the casting porosity was not observed in pure Cu. This may be due to the fact that the occluded oxygen atoms exist as copper oxide (Cu2O) in solid Cu.

Dental Alloys↗

PubMedDate not supplied

An assay of relative cell wall porosity in Saccharomyces cerevisiae, Kluyveromyces lactis and Schizosaccharomyces pombe.

We have developed a new assay to determine relative cell wall porosity in yeasts, which is based on polycation-induced leakage of UV-absorbing compounds. Polycations with a small hydrodynamic radius as measured by gel filtration (poly-L-lysine) caused cell leakage independent of cell wall porosity whereas polycations with a large hydrodynamic radius (DEAE-dextrans) caused only limited cell leakage due to limited passage through the cell wall. This allowed the ratio between DEAE-dextran- and poly-L-lysine-induced cell leakage to be used as a measure of cell wall porosity in Saccharomyces cerevisiae, Kluyveromyces lactis and Schizosaccharomyces pombe. Using this assay, we found that the composition of the growth medium affected cell wall porosity in S. cerevisiae. In addition, we could show that cell wall porosity is limited by the number of disulphide bridges in the wall and is dependent on cell turgor. It is argued that earlier methods to estimate cell wall porosity in S. cerevisiae resulted in large underestimations.

Cell Wall↗

PubMed2004

Effect of mixing method on the porosity of encapsulated glass ionomer cement.

OBJECTIVE: To observe cement specimens mixed by various methods non-destructively using microfocus computerized tomography (micro-CT) and to evaluate the effect of mixing method on porosity. METHOD: Five glass ionomer cements were used: two were hand-mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Fifteen cylindrical specimens were prepared for each material by each mixing method and stored in distilled water at 37 degrees C until testing. The specimens were observed and analyzed using micro-CT. 201 sliced images were obtained horizontally along the length of the specimens. Three-dimensional reconstructions were made and the sizes, numbers and total volume ratio of bubbles in the specimens were calculated. RESULTS: Mixing method had a significant effect on porosity (P<0.05). For the luting/lining cement, mechanical mixing produced a significantly higher porosity (P<0.05). For the restorative cement, there were only small differences in porosity between specimens mixed by the two methods. More large bubbles were detected in specimens mixed mechanically than by hand for the fluid material. This suggested that for low-viscosity materials bubbles may combine until a certain viscosity is reached during setting. SIGNIFICANCE: The strength of glass ionomer cement is affected by incorporated porosity and this depends on the mixing method. For low-viscosity cements, hand-mixing is favored in order to reduce porosity and increase strength, but this is not generally applicable to high-viscosity cements.

Cementation↗

PubMed2005

Why would cement porosity reduction be clinically irrelevant, while experimental data show the contrary.

Laboratory bench tests have shown that porosity reduction increases the fatigue life of bone cement specimens. Clinically, however, the effect porosity reduction is subject to debate. We hypothesized that the discrepancy between clinical and experimental findings is related to differences in the stress distribution, which is typically uniform in experimental test specimens, while stress concentrations exist in cement around hip implants. We simulated fatigue failure of cement in a finite element model of an experimental test specimen and of a transverse slice of a total hip arthroplasty with a sharp-cornered stem. Four levels of porosity were introduced. In the fatigue test specimen model, the fatigue life clearly was dependent on the level of porosity, while in the transverse slice model, the level of porosity had virtually no effect on failure of the cement mantle. The results of the simulations confirmed our hypothesis. In simulations of laboratory tests, pores clearly acted as crack initiators, while in the simulation of a real total hip reconstruction, crack formation was governed by local stress singularities. This explains why the beneficial effect of cement porosity reduction on the lifetime of total hip reconstructions may be hard to detect clinically.

Arthroplasty, Replacement, Hip↗

PubMed2004

The effect of polymerization cycles on porosity of microwave-processed denture base resin.

STATEMENT OF PROBLEM: Although most of the physical properties of denture base resin polymerized by microwave energy have been shown to be similar to resins polymerized by the conventional heat polymerization method, the presence of porosity is a problem. PURPOSE: This study evaluated the effect of different microwave polymerization cycles on the porosity of a denture base resin designed for microwave polymerization. MATERIAL AND METHODS: Thirty-two rectangular resin specimens (65 x 40 x 5 mm) were divided into 3 experimental groups (A, B, and C; Onda-Cryl, microwave-polymerized resin) and 1 control group (T; Clássico, heat-polymerized resin), according to the following polymerization cycles: (A) 500 W for 3 minutes, (B) 90 W for 13 minutes+500 W for 90 seconds, (C) 320 W for 3 minutes+0 W for 4 minutes+720 W for 3 minutes, and (T) 74 degrees C for 9 hours. Porosity was calculated by measurement of the specimen volume before and after its immersion in water. Data were analyzed using 1-way analysis of variance (alpha=.05). RESULTS: The mean values and SDs of the percent mean porosity were: A=1.05%+/-0.28%, B=0.91%+/-0.15%, C=0.88%+/-0.23%, T=0.93%+/-0.23%. No significant differences were found in mean porosity among the groups evaluated. CONCLUSION: Within the limitations of this study, a denture base resin specifically designed for microwave polymerization tested was not affected by different polymerization cycles. Porosity was similar to the conventional heat-polymerized denture base resin tested.

Acrylic Resins↗

PubMed1997

Comparison of the porosity of hand-mixed and capsulated glass-ionomer luting cements.

The strength of dental glass-ionomer cements will be influenced by defects present within its structure. This study measured the surface area porosity, percentage surface area porosity, and mean surface area of small bubbles (<0.01 mm2) and the surface area porosity, percentage surface area porosity and diameter of large bubbles within 40-microm-thick layers of four cements, using image analysis software. Two hand-mixed cements (Fuji I and KetacCem) and two capsulated cements (Fuji Cap I and KetacCem Maxicap) were viewed under transmitted light at x117.6 magnification. For each selected area (64.75 mm2) of each cement sample, five independent measurements were made of each of these parameters. Analysis of variance (ANOVA) indicated that there were no significant differences between the four cements in the small bubble parameters measured, whilst there were significant differences in the surface area porosity, percentage surface area porosity and diameter of the large bubbles. It was concluded that the hand-mixed cements tested had a greater number of larger diameter bubbles compared with the capsulated cements.

Analysis of Variance↗

PubMed2003

Effect of intragranular porosity on compression behaviour of and drug release from reservoir pellets.

In this study, reservoir pellets were prepared and their compression behaviour as well as the importance of their porosity for compression-induced changes in drug release was investigated. Pellets of three different porosities, consisting of microcrystalline cellulose and salicylic acid, were prepared by extrusion-spheronisation and spray-coated with ethyl cellulose (ethanol solution). Lubricated reservoir pellets were compressed and retrieved by deaggregation of the tablets. The retrieved pellets were analysed regarding porosity, thickness, surface area, shape and drug release. It was found that the coating did not significantly affect their compression behaviour. Compaction of pellets of high original porosity considerably affected densification and degree of deformation, whereas the effect on drug release was minor. For low porosity pellets the influence of compaction on drug release was appreciable, but only slight regarding densification and degree of deformation. In conclusion, the porosity of pellets is a potential factor that the formulator can use to optimize drug release and one that can affect the robustness of a formulation during manufacture. Moreover, the coating may be able to adapt to the densification and deformation of the pellets.

Algorithms↗

PubMedDate not supplied

Air-filled porosity and permeability relationships during solid-state fermentation.

An experimental apparatus was constructed to measure the structural parameters of organic porous media, i.,e. mechanical strength, air-filled porosity, air permeability, and the Ergun particle size. These parameters are critical to the engineering of aerobic bioconversion systems and were measured for a straw--manure mixture before and after 13 days of in-vessel composting. Porosity was measured using air pycnometry at four (day 0) and five (day 13) moisture levels, with each moisture level tested at a range of different densities. Tested wet bulk densities varied with moisture level, but dry bulk densities generally ranged from 100 to 200 kg m(-3). At each moisture/density combination, pressure drop was measured at airflow rates ranging from 0.001 to 0.05 m sec(-1), representing the range of airflow rates found in both intensive and extensive composting. Measured air-filled porosities were accurately predicted from measurements of bulk density, moisture, and organic matter content. Reductions in air-filled porosity at increasing moisture content were accompanied by an increase in permeability, apparently due to aggregations of fines. This aggregation was quantified by calculating an effective particle size from the Ergun permeability relationship, which increased from 0.0002 m at 50% moisture to 0.0021 m at 79% moisture. The range of airflow velocities reported in composting systems requires consideration of the second-order drag force term, particularly at velocities approaching 0.05 m s(-1) for the higher moisture treatments tested. Calculated permeabilities for the matrix ranged from 10(-10) to 10(-7) m2, varying with both air-filled porosity and moisture. Mechanical strength characterization provided a means to predict the effects of compaction on air-filled porosity and permeability of porous media beds. The results of this investigation extend porous media theory to the organic matrices common in solid-state fermentations and help build a framework for quantitative and mechanistic engineering design.

Air↗

PubMed2002

Differences in bone-cement porosity by vacuum mixing, centrifugation, and hand mixing.

The mean pore size and percent porosity of vacuum-mixed cement were compared with centrifuged cement and cement hand mixed by skilled specialized operating room technicians. Centrifuged cement samples had the smallest mean pore size when compared with vacuum-mixed specimens. The mean pore size for the hand-mixed specimens was intermediate and not significantly different from the other 2 mixing techniques. Results were reversed, however, for mean percent porosity. Centrifuged cement had the highest percent porosity; vacuum-mixed cement, the lowest; and hand-mixed cement, intermediate. The porosity of vacuum-mixed Simplex P (Howmedica, Rutherford, NJ) bone-cement was similar from the initial to the remnant cement extruded from the cement gun. There was no reduced cement porosity with vacuum mixing or centrifugation as anticipated. Reversion to hand mixing by highly skilled technicians could result in a significant cost savings without negative effects on cement porosity.

Bone Cements↗

PubMed2000

Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings.

STATEMENT OF PROBLEM: Porosity is a frequently observed casting defect in dental titanium alloys. PURPOSE: This study evaluated the effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium (cp Ti) castings. MATERIAL AND METHODS: Eight groups (A-H) of 16 rectangular wax patterns each (30 mm in length, 3 mm in width, and 1 mm in depth) were prepared. The wax patterns were invested with a magnesia-based material and cast with cp Ti (grade II). Groups A, C, E, and G were cast under a pressure of 1 atm, and groups B, D, F, and H were cast under a pressure of 0.5 atm of He, Ar, Kr, and Xe, respectively. The extent of the porosity of the cast specimens was determined radiographically and quantified by image analysis. Three specimens of each group and 3 cylinders of the as-received cp Ti used as a reference were embedded in resin and studied metallographically after grinding, polishing, and chemical etching. These surfaces were used for determination of the Vickers hardness (VHN) as well. Eight specimens from each group were fractured in the tensile mode, and the 0.2% yield strength, fracture stress, and percentage elongation were calculated. Porosity was analyzed with 2-way ANOVA and the Newman-Keuls multiple range test. VHN measurements and tensile properties for specimen groups were compared with 1-way ANOVA and the Newman-Keuls multiple range test (95% significance level). RESULTS: The porosity levels per group were (%): A = 5.50 +/- 4.34, B = 0.77 +/- 1.27, C = 2.44 +/- 3.68, D = 0.06 +/- 0.12, E-H = 0. Two-way ANOVA showed that there was no detectable interaction (P<.05) between gas type and applied pressure. Metallographic examination revealed no differences in microstructure among the groups studied. A finer grain size was observed in all cast groups compared with the original cp Ti. The VHN of the as-received cp Ti was significantly greater than all the cast groups tested. Groups cast under He showed the highest VHN, yield strength, and fracture stress. No significant differences were found in percentage elongation values among the groups. CONCLUSION: Porosity and mechanical properties of cp Ti castings are dependent on the gas type and pressure, whereas the microstructure remains unaffected.

Analysis of Variance↗

PubMed2001

Effect of unreamed, limited reamed, and standard reamed intramedullary nailing on cortical bone porosity and new bone formation.

OBJECTIVE: To compare the effects of unreamed nail insertion and reamed nail insertion with limited and standard canal reaming on cortical bone porosity and new bone formation. DESIGN: A canine segmental tibial fracture was created in fifteen adult dogs. The tibiae were stabilized with a statically locked 6.5-millimeter intramedullary nail without prior canal reaming (n = 5), after limited reaming to 7.0 millimeters (n = 5), or after standard canal reaming to 9.0 millimeters (n = 5). Porosity, new bone formation, and the mineral apposition rate of cortical bone were directly compared between the three nailing techniques. RESULTS: A significant increase in cortical bone porosity and new bone formation was seen in all three groups of experimental animals compared with the control tibiae. The overall lowest porosity levels were measured in the limited reamed group, with similar porosity levels measured in the unreamed and standard reamed groups. Porosity was lower in the limited reamed group in the entire cortex of the segmental and distal cross sections, as well as the endosteal, anterior, and posterior cortices along the length of the tibia. Overall, there was no difference in the amount of new bone formation or the mineral apposition rate between the three groups of animals at eleven weeks after surgery. DISCUSSION: The results of this study suggest that limited intramedullary reaming is a biologically sound alternative for the treatment of tibial diaphyseal fractures in which the circulation is already compromised.

Analysis of Variance↗

PubMed2005

Dual porosity expanded polytetrafluoroethylene for soft-tissue augmentation.

BACKGROUND: A variety of nondegradable polymers have been evaluated for use as soft-tissue augmentation devices. This study compared a novel dual porosity expanded polytetrafluoroethylene with current, clinically used devices. METHODS: Studies were performed in a porcine model of soft-tissue healing with both histologic evaluations and determination of biomechanical strength of tissue incorporation. Five different samples of expanded polytetrafluoroethylene were used in this study. Control devices were clinically available soft-tissue augmentation devices manufactured by W. L. Gore and Associates (Newark, Del.). Atrium Medical Corporation (Hudson, NH) manufactured three test devices with modified porosities. A total of 12 animals were used with implant evaluations performed after 1, 3, 6, and 12 months. RESULTS: Significant differences in tissue incorporation were observed morphologically with the dual porosity material, including reduced inflammation and increased cellular and extracellular matrix incorporation of the material. Significant increases in both angiogenesis (new vessel formation in the peri-implant tissue) and neovascularization (blood vessel penetration into the interstices of the implants) were observed with the dual porosity expanded polytetrafluoroethylene material. CONCLUSIONS: This novel dual porosity expanded polytetrafluoroethylene is associated with reduced inflammation and more extensive tissue incorporation as compared with the currently available form. These results suggest a dual porosity expanded polytetrafluoroethylene may provide a superior material for soft-tissue augmentation.

Animals↗