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PubMed1995

Porosity in composite resins.

Porosity in the pastes of composite resins before and after polymerization has been measured. The influence of the diameter of the extrusion orifices and the spatulation of the chemically-activated pastes has been evaluated. Considering that thin layers of these materials are transparent, the investigation has been carried out mainly by analysis of approximately 300 microns or lower thickness layers, that are still transparent under the microscope. Generally, there was a significant dependence of the porosity on the orifice diameter. However, this rule showed some exceptions. As far as the chemically-activated pastes were concerned, in all examined cases the number of small size (10-40 microns) porosities increased after spatulation.

Biocompatible Materials↗
PubMed1996

Effects of different osteopromotive membrane porosities on experimental bone neogenesis in rats.

Biologically inert expanded polytetrafluorethylene (e-PTFE) membranes (GORE-TEX) have earlier been shown to improve healing of different types of bone defects, to be able to restore earlier existing bone, and to produce bone neogenesis. This study was performed to investigate the influence of membrane porosity on the osteopromotive efficacy and to determine bone neogenesis times in the rat. Three different e-PTFE membrane qualities with different porosities (internodal distances < 8, 20-25 and 100 microns) and four healing periods (6, 12, 18 weeks and 6 months) were studied. Dome-shaped e-PTFE membranes (5 mm inner diameter) were placed on denuded rat calvaria and covered with the periosteum and skin. After the respective time intervals, specimens were prepared for histology, and the bone obtained within the domes was quantified by an image analysis system. The results confirmed that it is possible to produce new bone by the use of the osteopromotion technique. The rate of bone neogenesis depended on the quality of membrane used; the membranes with the smallest internodal distance were less efficient than the others in that osteogenesis was somewhat delayed. The amount of new bone achievable was essentially already obtained after 6 weeks with the two most porous membranes, whereas the least porous one lagged behind. After 12 weeks there was no difference in the amount of newly formed bone. There was an obvious time sequence, in that the newly formed bone showed an increased maturity with longer observation periods. The material with the smallest internodal distance did not integrate well with the surrounding soft tissue, leading to a lack of stabilization of the membrane and more soft tissue ingrowth from the side. It is concluded that there is a porosity range within which osteogenesis beneath the membranes is optimal, tissue integration for stability is adequate enough, and soft connective tissue ingrowth is avoided.

Analysis of Variance↗
PubMed2004

Novel approach to fabricate keratin sponge scaffolds with controlled pore size and porosity.

A compression-molding/particulate-leaching (CM/PL) method was developed to fabricate S-sulfo keratin sponges with the controlled pore size and porosity. The S-sulfo keratin was extracted from wool and was then spray-dried to give S-sulfo keratin powder. The S-sulfo keratin powder mixed with urea in advance was compression-molded together with the sieved NaCl particulates above the melting temperature of urea. The following removal of the salts and urea in water created the sponges composed of interconnected pores and the continuous S-sulfo keratin matrix. The S-sulfo keratin sponges were strong enough to handle and water-insoluble. By contrast, the sponges prepared without urea were very fragile and readily collapsed, because most of S-sulfo keratin matrix remained powdery. The pore size was in good accordance with the size of the salts, indicating that the pores were formed by leaching-out the salts. The S-sulfo keratin sponges with the regulated sizes of pores (<100, 100-300 and 300-500 microm) were fabricated, all of which had more than 90% of the porosity. Thus, CM/PL method is able to give the S-sulfo keratin sponge with the desired pore size and porosity, which might be a good scaffold for the cells in tissue engineering.

Biocompatible Materials↗
PubMed2004

Bending properties, porosity, and ash fraction of black bear (Ursus americanus) cortical bone are not compromised with aging despite annual periods of disuse.

In many species, including humans, disuse causes an imbalance in bone remodeling that leads to increased bone porosity as a result of increased bone resorption and decreased bone formation. However, black bears (Ursus americanus) may not develop disuse osteopenia, to the extent that other animals do, during long periods of disuse (i.e. hibernation) because they maintain osteoblastic bone formation during hibernation, even though bone resorption is increased during hibernation. Black bears may also have a mechanism to rapidly and completely recover the bone lost (by increased resorption during hibernation) during their remobilization period. Our findings suggest that cortical bone bending strength (211-328 MPa), bending modulus (16.0-29.5 MPa), fracture energy (0.0118-0.0205 J mm(-2)), porosity (2.3-7.1%), and ash fraction (0.638-0.672) are not compromised with age in black bears, despite annual periods of disuse. In fact, the ultimate strength (p=0.01), modulus (p=0.04), and ash fraction (p=0.03) of cortical bone were shown to significantly increase with age (2-14 yrs). Female bears give birth and nurse during hibernation; however, we found no significant (p>0.16) differences between male and female bone properties. Other animals require remobilization periods 2-3 times longer than the immobilization period to recover the bone lost during disuse. Our findings support the idea that black bears, which hibernate 5-7 months annually, have evolved a biological mechanism to mitigate the adverse effects of disuse on bone porosity and mechanical behavior.

Adaptation, Physiological↗
PubMed2006

Use of high-resolution MRI for investigation of fluid flow and global permeability in a material with interconnected porosity.

We present a multi-scale experimental approach designed to improve the investigation of both localized and global fluid flow in biomaterials with randomly interconnected porosity. Coralline hydroxyapatite (ProOsteon 500 from Interpore-Cross), having a relatively well-defined porosity, was used as an in vitro model of typical bone architecture. Axial fluid velocity profiles within the pores of a cylindrical hydroxyapatite sample were characterized using high-resolution MRI in conjunction with the measurement of global flow and associated permeability based on the Darcy-type relationship. Assuming Newtonian fluid behaviour, image analysis permitted computation of local porosity, intra-pore fluid shear, and visualization of flow heterogeneity within the sample. These results may benefit applications in biomaterials for the evaluation of factors influencing bony incorporation in porous scaffolds and on porous implant and bone surfaces. Normal and diseased biological tissues are also clinical relevant applications.

Bone Substitutes↗
PubMed2005

Surface and porosity of nanocrystalline boehmite xerogels.

Boehmite xerogels are prepared by hydrolysis of Al(OC4H9)3 followed by peptization with HNO3 (H+/Al = 0, 0.07, 0.2). XRD and TEM show that these gels are made of nanosized crystals (5-9 nm in width and 3 nm thick). According to the amount of acid, no significant differences are found in size and shape, but only in the spatial arrangement of the crystallites. Nitrogen adsorption-desorption isotherms of nonpeptized gels are of type IV, whereas isotherms of peptized gels are of type I. These isotherms are analyzed by the t-plot method. The majority of pore volume results from intercrystalline mesopores, but the peptized gels also contain intercrystalline micropores. The particle packing is very dense for the gel peptized with H+/Al = 0.2 (porosity = 0.26), but it is less dense in non-peptized gel (porosity = 0.44). Heating these gels under vacuum creates, from 250 degrees C onwards, an intracrystalline microporosity resulting from the conversion of boehmite into transition alumina. But heating also causes intercrystalline micropores collapsing. The specific surface area increases up to a limit temperature (300 degrees C for nonpeptized gels and 400 degrees C for peptized) beyond which sintering of the particles begins and the surface decreases. The PSD are calculated assuming a cylindrical pore geometry and using the corrected Kelvin equation proposed by Kruk et al. Peptized xerogels give a monomodal distribution with a maximum near 2 nm and no pores are larger than 6 nm. Nonpeptized gels have a bimodal distribution with a narrow peak near to 2 nm and a broad unsymmetrical peak with a maximum at 4 nm. Heating in air above 400 degrees C has a strong effect on the porosity. As the temperature increases, there is a broadening of the distribution and a marked decrease of small pores (below 3 nm). However, even after treatment at 800 degrees C, micropores are still present.

Aluminum Hydroxide↗
PubMed2005

Effect of porosity on the release kinetics of propafenone-loaded PEG-g-PLA nanoparticles.

Nanoparticle preparation by the emulsification-solvent evaporation method is a complex phenomenon. Various formulation factors can affect the internal structure and release of drug from nanoparticles (NPs). The aim of the present study is to optimize NPs of PEG-g-PLA polymer and study the effect of various factors on the porosity as well as release profile of drug-loaded NPs. Propafenone hydrochloride (Prop.HCl), a model drug, was encapsulated in NPs using different amounts of triethylamine (TEA) and initial drug loading levels. NPs were also prepared without TEA by using propafenone base (Prop). All the formulations were characterized for surface morphology, size and size distribution, encapsulation efficiency, thermal analysis, porosimetry and in vitro release studies. Encapsulation efficiency of Prop ranged between 10% and 43% and was dependent on initial drug loading as well as amount of TEA added. Porosity studies revealed different pore size distribution (PSD) for formulations with and without TEA. Formulations with higher drug loading showed greater volume contribution of small pores, higher fractal dimension suggesting more complex pore structure and slower drug release, probably due to decrease in the effective diffusion coefficient of Prop. Results suggest that formulation factors play an important role affecting the porosity and release rate of NPs. Also, fractal dimension could be one of the most important factors in determining the release behavior of NPs.

Anti-Arrhythmia Agents↗
PubMed2001

Macro-porosity is necessary for the reduction of neointimal and medial thickening by external stenting of porcine saphenous vein bypass grafts.

BACKGROUND: placing external non-restrictive macro-porous stents around porcine vein grafts prevents neointima formation and medial thickening in both the short and long term. Whether the porosity of the stent material influences this effect, however, has not been determined. Therefore, the effect on neointimal and medial thickening of external macro-porous (polyester) and micro-porous (polytetrafluorethylene) stents of equal diameter were compared. The effect on expression of platelet-derived growth factor (PDGF), a potent mediator of vascular smooth muscle cell migration and proliferation and its receptors was also investigated. METHODS AND RESULTS: saphenous vein-carotid artery interposition grafting was performed in Landrace pigs with external placement of 8 mm diameter macro- and micro-porous stents contralaterally. One month after surgery, graft wall dimensions, PDGF and PDGF receptor expression and cell proliferation using proliferating cell nuclear antigen (PCNA) were measured on histological sections. Macro-porous stents significantly reduced neointimal and medial thickening compared with micro-porous stents (0.1+/-0.02 vs. 0.25+/-0.03 mm, P<0.002, and 0.10+/-0.02 vs. 0.17+/-0.02 mm, P<0.014, respectively). Macro-porous stents significantly reduced the percentage of cells expressing PDGF and PCNA, compared with micro-porous stents (36+/-9 vs. 80+/-7, P < 0.002, and 11+/-3 vs. 21+/-2, P < 0.02, respectively). The percentage of cells expressing PDGF receptors was similar with both the stent types. Adventitial microvessel formation occurred across macro-porous stents but was markedly suppressed by micro-porous stents. CONCLUSIONS: porosity is crucial to the efficacy of external stents in reducing neointima formation in porcine vein grafts. Decreases in PDGF expression and cell proliferation accompany the reduction in neointima formation. In addition, macro-porous stents allow adventitial microvessels to connect with the vasculature outside the stent, thereby potentially improving oxygenation. Although external stenting is highly effective in reducing neointima formation after vein grafting, the properties of the stent material necessary for this effect have not been defined. This study establishes that macro-porosity is one essential feature required to reduce PDGF expression cell proliferation and neointima formation.

Animals↗
PubMed1991

Porosity of denture resin cured by microwave energy.

This study compared porosity of denture resin cured by microwave energy to denture resin cured by the conventional heat method. Seven groups of 10 samples each were tested. The control samples of methyl methacrylate monomer were cured in a curing tank at 165 degrees F for 9 hours. Four of the six experimental groups, consisting of samples made from Micro Liquid monomer (H.D. Justi Co., Oxnard, Calif.), were cured by microwave energy at varying wattages and times. The other two experimental groups contained samples of methyl methacrylate monomer cured by microwave energy. No significant differences were found in mean porosity between the control group and the four groups of microwave-processed samples that used Micro Liquid monomer. The two groups of microwave-processed samples of methyl methacrylate monomer showed a significantly higher mean porosity.

Acrylic Resins↗
PubMed2002

Porosities and voids in Class I restorations placed by six operators using a packable or syringable composite.

OBJECTIVES: The aim of the study was to investigate the influence of two resin composites with different handling properties and application techniques on the homogeneity of a restoration placed in small and large cavities. Furthermore, the operator-effect on the restorative procedure was studied. METHODS: Standardized Class I cavities of two sizes were prepared in artificial lower first molars. The cavities were restored with two resin composites (Surefil and Ecusit) using either a packing or an injection technique. Six operators were involved in the study, five general practitioners and one final-year dental student. Each operator restored 40 preparations, ten in each group. After finishing, the restorations were sectioned and inspected for the presence of voids and porosities. RESULTS: 240 restorations were placed and 480 sections were available for evaluation. Only 143 sections were totally free of porosities. For both the small and large preparation design the Ecusit composite used with the injection technique resulted in significantly less porosities in the restoration. Differences between operators were evident, but none of the operators achieved significantly better results with the packing technique than with the injection technique. SIGNIFICANCE: The use of a syringable resin composite results in a better adaptation of the restoration compared to a packable resin composite.

Composite Resins↗
PubMed1998

Computer aided prediction and control of shrinkage porosity in titanium dental castings.

OBJECTIVES: The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS: A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS: The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE: It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.

Computer Simulation↗
PubMed1999

Mineral precipitation and porosity losses in granular iron columns.

As permeable reactive barriers containing zero-valent iron are becoming more widely used to remediate contaminated groundwaters, there remains much uncertainty in predicting their long-term performance. This study focuses on two factors affecting performance and lifetime of the granular iron media: plugging at the treatment zone entrance and precipitation in the bulk iron media. Plugging at the system entrance is due principally to mineral precipitation promoted by dissolved oxygen in the influent groundwater and is an issue in aerobic aquifers or in above-ground canister tests. Designs to minimize plugging in field applications where the groundwater is oxygenated include the use of larger iron particles and admixing sand of comparable size with the iron particles. Beyond the entrance zone, the groundwater in anaerobic and mineral precipitation leads to porosity losses in the bulk iron media, potentially reducing flow through the treatment zone. The nature of the mineral precipitation and the factors that affect extent of mineral precipitation have been examined by a variety of tools, including tracer tests, aqueous inorganic profiles, and surface analytical techniques. At short treatment times, porosity losses as measured by tracer tests are due mainly to Fe(OH)(2) precipitates and possible entrapment of a film of hydrogen gas on the iron surfaces. Over longer treatment times, precipitation of Fe(OH)(2) and FeCO(3) in low carbonate waters and of Fe(OH)(2), FeCO(3) and CaCO(3) in higher carbonate waters begin to dominate porosity losses. The control of pH within the iron media by addition of ferrous sulfide was shown not to reduce significantly calcium and carbonate precipitates, indicating that mineral precipitation is controlled by more than simple carbonate equilibrium considerations.

Chemical Precipitation↗
PubMed1998

A comparison of porosity, fabric and fractal dimension as predictors of the Young's modulus of equine cancellous bone.

The purpose of this study was to compare the structural parameters of fabric and fractal dimension as predictors of the Young's modulus of equine cancellous bone. Eight 15 mm cubes of cancellous bone were obtained from three equine third metacarpal bones. Young's modulus was determined for the three orthogonal directions. The fabric and fractal dimension were calculated for each of the six exposed faces of each cube. Fractal dimension plus porosity provided a higher explanatory power for Young's modulus (R2 = 78.7%. P < 0.0001) than fabric plus porosity (R2 = 69.2%, P < 0.0001). Fractal dimension was also significantly correlated with fabric (R2 = 53.8%, P < 0.0001). Although this novel method for combining fractal dimension data into a pseudo-directionally dependent predictor of Young's modulus requires further validation over a greater range of porosities and differing cancellous bone tissues, its potential has been demonstrated.

Animals↗
PubMed2005

Modeling of porous filter penneability via image-based stochastic reconstruction of spatial porosity correlations.

A methodology for producing a pore-scale, 3D computational model of porous filter permeability is developed that is based on the analysis of 2D images of the filter matrix and first principles. The computationally reconstructed porous filter model retains statistical details of porosity and the spatial correlations of porosity within the filter and can be used to calculate permeability for either isotropic or 1D anisotropic porous filters. In the isotropic case, validation of the methodology was conducted using 0.2 and 0.8 microm ceramic membrane filters,forwhich it is shown that the image-based computational models provide a viable statistical reproduction of actual porosity characteristics. It is also shown that these models can predict water flux directly from first principles with deviations from experimental measurements in the range of experimental error. In the anisotropic case, validation of the methodology was conducted using a natural river sand filter. For this case, it is shown that the methodology yields predictions of filtration velocity that are similar or better than predictions offered by existing filtration models. It was found for the sand filter that the deviation between observation and prediction was mostly due to swelling during the preparation of the sand filter for imaging and can be reduced significantly using alternative methods reported in the literature. On the basis of these results, it is concluded that the computational reconstruction methodology is valid for porous filter modeling, and given that it captures pore-scale details, it has potential application to the investigation of permeability decline underthe influence of pore-scale fouling mechanisms.

Engineering↗
PubMed1999

Numerical simulation of porosity-free titanium dental castings.

The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.

Chemical Phenomena↗
PubMed2003

Influence of number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin.

Simultaneous irradiation of multiple flasks may have deleterious effects on the polymerization of microwave cured-acrylic resins. This study evaluated the effect of the number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin. Samples were made of Acron MC(R) (AMC, GC Dent. Ind. Corp.) processed at 500 W. The following associations of the number and position of the flasks were tested: one simple flask centrally placed on the turning plate (I, control); two flasks, one in the centre (IIa) and the other peripherally placed in the plate (IIb); two flasks centrally, one above (IIIa) and the other below (IIIb). The processing time varied according to the number of flasks: 3 or 4.5 min for one or two flasks, respectively. For monomer release, each specimen (n = 12) was put in an assay glass tube containing 6 mL of deionized water that was changed daily. Monomer levels were obtained by spectrophotometry at 206 nm. For hardness test (n = 10), 12 indentations were made in the surface of each specimen. Immersing the polished specimens in permanent ink and counting the porous in a stereo light microscope verified the porosity. Monomer release was significant before 24 h: GI = 263.1(153.3)a, GIIa = 236.9(180.2)a, GIIb = 441.5(446.2)a, GIIIa = 1216.6(857.9)b. Tukey test showed no statistically significant differences among the groups for porosity and hardness. Monomer release was affected by the position of the flask (P < 0.05).

Acrylic Resins↗
PubMed1998

Better increase in fibrin gel porosity by low dose than intermediate dose acetylsalicylic acid.

AIM: To investigate the influence on plasma fibrin gel structure of low and intermediate doses of acetylsalicylic acid in healthy individuals. The influence of acetylsalicylic acid on thrombin formation, fibrinolytic capacity and plasminogen inhibitor-1 in plasma was also investigated. METHODS: Nineteen subjects were treated with 75 mg and 11 with 320 mg acetylsalicylic acid daily; eight subjects received both doses. Fibrin gel structure was determined by a permeability technique yielding a porosity constant (Ks), and the thromboxane metabolite 11-dehydro-thromboxane B2 (TxM) was determined by an ELISA. RESULTS: Acetylsalicylic acid increased fibrin porosity by 65% at 75 mg (P<0.001, n=19), whereas lower increases were found at 320 mg (+22%, P<0.05, n=11). One week after withdrawal Ks had essentially returned to baseline (ns). Urinary thromboxane metabolites were suppressed during treatment (-61%, P<0.001 at 75 mg, n=19; -46%, P<0.01 at 320 mg, n=11). The intra-individual comparison showed similar results (Ks +92%, TxM -62% at 75 mg; Ks +5%, TxM -52% at 320 mg). Fibrinolytic capacity, plasminogen inhibitor-1 levels and thrombin generation (in platelet-poor citrated plasma) were not influenced. CONCLUSION: Low dose acetylsalicylic acid causes the greatest increase in fibrin gel porosity; this may well be of therapeutic importance.

Adult↗
PubMed2000

Tablet and capsule hydrophilic matrices based on heterodisperse polysaccharides having porosity-independent in vitro release profiles.

The purpose of the study was to investigate the release-controlling action of a swellable hydrophilic material based on heterodisperse polysaccharides (HP) in relation to the initial pore structure of the formulations. HP-based granules were produced under carefully controlled conditions and compacted into matrix tablets having equivalent tablet thickness. Quantification of pore structure using mercury porosimetry showed that the tablets had substantially different pore volumes and pore size distributions. Dissolution studies demonstrated that release of a water-soluble model compound, benzamide, from swollen matrices was affected neither by total porosity nor median pore diameter of the initial dry matrix. To extend the concept of porosity-independent release further, HP-based formulations containing either diclofenac sodium or propranolol HCl were contained within hard gelatin capsules in the form of uncompacted granules. This produced a dosage form with a high intraparticulate porosity in the dry state. Equivalent weights of the same formulations were also compacted into tablets. The in vitro release profiles from matrix tablets compacted from any of the formulations did not differ significantly from release profiles obtained when the same materials were contained uncompacted in hard gelatin capsules.

Benzamides↗