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PubMed1988

Effect of the porosity of the filler aggregates on the setting expansion of investment material.

Twenty experimental phosphate-bonded investments were prepared by the mixing of two types of fillers (spherical glass beads and irregularly shaped silica particles) with five types of filler aggregates of different porosities, and two different ratios of MgO to NH4H2PO4. These investments were mixed with three different liquids, and their setting expansion, time until setting expansion began (induction time), and fluidity were measured under constant experimental conditions. The following results were obtained: (1) The setting expansion was significantly related to bulk porosity of filler aggregates, not to packed porosity, despite variations in type of filler, ratio of MgO to NH4H2PO4 or type of liquid; and (2) the fluidity and the time until setting expansion began were also related to the bulk porosity of the filler aggregates.

Chemical Phenomena↗
PubMed1992

Control of prolonged drug release and compression properties of ibuprofen microspheres with acrylic polymer, eudragit RS, by changing their intraparticle porosity [corrected].

Prolonged-release spherical micro-matrices of ibuprofen with Eudragit RS were prepared using a novel emulsion-solvent diffusion method. Those particles were termed "microspheres" due to their characteristic sponge-like texture and unique dissolution and compression properties unlike conventional microcapsules or microspheres. The internal porosity of microspheres could be easily controlled by changing the concentration of the drug and the polymer in the emulsion droplet (ethanol). With lower concentration of ibuprofen in the ethanol, the resultant microspheres had a higher porosity, about 50%. The drug release rate from the microspheres was interpreted by the Higuchi model of spherical matrices, which depended only on their internal porosity of the microspheres when size distribution and drug content were the same. The tortuosities in the microspheres were found to be almost constant (3-4) irrespective of porosity, suggesting the same internal texture. Microsphere compressibility was much improved over the physical mixture of the drug and polymer owing to the plastic deformation of their sponge-like structure. The more porous microspheres produced stronger tablets [corrected].

Acrylic Resins↗
PubMed1999

An automated analysis of intracortical porosity in human femoral bone across age.

The matrix of human cortical bone is arranged around a network of vascular spaces (hereafter referred to as "pores"). Our aim was to investigate age-related differences in human cortical porosity (total pore area divided by cortical bone area), pore size and number, and surface to volume ratios, while adjusting for sex, height, and weight. Ninety-six specimens of entire transverse sections of human femoral diaphysis, from subjects aged 21-92 years, were examined. We used our established automated image acquisition and analysis system which measures pores from entire sections of multiple specimens of bone. Over 400,000 pores were recorded. Results showed a greater porosity in older bone (p < 0.01) but marked variation in porosity for any given age. The cohort median, of the specimen medians, of pore cross-sectional area was 2050 microns 2. Older specimens did not have more pores than younger specimens but had a greater proportion of larger pores (p < 0.05) and greater intraspecimen variation in pore size (p < 0.001). The pore surface to bone matrix volume ratio was a median 2.3 mm2/mm3. This varied more than 4-fold between individuals but did not relate to age. No simple relationships were found between any of the measured parameters and either sex, height, or weight, even after adjustment for age. We conclude that the greater porosity in older specimens is due to greater pore size rather than a larger number of pores. Age, however, explains little of the inter-individual variation in the parameters studied.

Adult↗
PubMed2003

Cervical laminoplasty: evaluation of bone bonding of a high porosity hydroxyapatite spacer.

OBJECT: The purpose of this study was to evaluate the usefulness of a high-porosity hydroxyapatite (HA) spacer in cervical laminoplasty. Bone-spacer bonding rates, complications associated with the implant, and factors related to bone bonding were examined. METHODS: The authors evaluated 33 consecutive patients with cervical myelopathy who underwent high-porosity HA spacer-assisted laminoplasty and were followed for at least 1 year (mean 30 months). The results of bone-spacer bonding of the 147 implants were evaluated using computerized tomography (CT) scanning. The symptoms significantly improved in 30 patients. No difference in results was detected between patients with cervical spondylosis and those with ossification of posterior longitudinal ligament. Breakage of seven spacers occurred in four patients without causing neck pain or neurological deficits. There were no other HA spacer-related complications. The spacers became rigidly bound to bone in 61% of the cases, and bone regrowth developed around the spacer in 91%. The rate of bone-spacer bonding increased over time, and the CT-documented attenuation value (Hounsfield unit) of the spacer adjacent to the bone-spacer junction in the group in which union occurred was significantly higher than in the nonunion group. CONCLUSIONS: High-porosity HA spacer-augmented laminoplasty produced good bonding-related results. Bone bonding continued to progress 1 year after surgery, indicating the good osteoconductive capability of high-porosity HA. To avoid breakage of a spacer, a minimum 7-mm distance between spacers is necessary.

Biocompatible Materials↗
PubMed1992

Comparison of parachute landing injury incidence between standard and low porosity parachutes.

Deployment of personnel by parachute is a common practice in many types of operations, both in and out of the military. Such operations are not without hazard and are associated with injuries which commonly occur during the landing phase of deployment. Environmental factors (i.e., wind and terrain) together with parachute sink rate are thought to influence the incidence of landing injuries. This study compared the incidence of overall landing injury and landing injury by parachute type in 8,706 jumps over 3 years between 1988 and 1990 between a standard porosity round canopy and a lower sink rate low porosity round canopy. In all cases the low porosity parachute group experienced significantly (p = 0.007) fewer overall injuries and fewer injuries of every type (reductions of 77% in 1988, 81% in 1989, and 94% in 1990). Reduction of sink rate by even small amounts correlates with significant (p less than 0.001) injury incidence reductions on the basis of reduced kinetic energy dissipation. Low porosity parachutes should be adopted where appropriate to reduce sink rate and hence landing injuries. Flight surgeons associated with airborne operations and who are familiar with these data can play a significant role in reducing parachute landing injuries.

Aerospace Medicine↗
PubMed1991

[The bioavailability of paracetamol II. The effect of porosity and mechanical properties of the dosage form on solubility].

The authors attempt to explain differences observed in dissolution rate of twelve different brands of paracetamol (nine tablets and three capsules) in terms of pore structure and tensile strength; the pore structure of both tablets and capsules is investigated by mercury porosimetry. Brands (tablets) which liberate paracetamol rapidly are characterized by a higher porosity value. Higher mean pore diameter signifies less t50 and higher porosity. An increase in tensile strength results in an increase in t50 and a decrease in porosity. Porosity alone cannot dictate the dissolution behaviour of capsules.

Acetaminophen↗
PubMed1989

[Influence of the sprue casting design on the surface porosity of the silver-palladium dental alloys].

The purpose of this work is to investigate and find out the best "design" of the casting sprues on the area and the number of the surface porosity when we cast silver-palladium dental alloys for metalloacrylics fixed partial dentures. Our observation and research have been done on 216 external surfaces from 72 M.O.D. specimens, which were casted using four different designs of casting sprues and three types of silver-palladium dental alloys (Panag, Pangold and Palliag M.). The evaluation of our findings and statistical analysis have been done. The findings of our study are the following. 1. It has been found that the "alloy" factor doesn't influence the area and the number of the surface porosity we examined, on the contrary it has been found that the "design" factor has great influence on the area and the number of the dental alloys. 2. The use of chill-sets and the securing of sprue button alloy decrease the area and the number of the surface porosity when we cast silver-palladium dental alloys. 3. The straight sprues and the placing of the specimens near the heat-center of the mold created much better conditions for decreasing the number and the area of the surface porosity than when we use the preci-roto system.

Dental Alloys↗
PubMed1988

Porosity in manually mixed bone cement.

Forty-six samples of acrylic cement mixed by seven nurses were analyzed for porosity by correlated roentgenograms and microscopy studies. Mean porosity was 26.7 vol % +/- 9.21 vol % with large variations among specimens. There was also a gross variation of the pore size. The pore size exceeded 300 micron in 23% of the specimens, with a wide scatter of percentage porosity produced by each nurse. A manual mixing technique lacks reproducibility and produces cements with uncontrollable porosity.

Air↗
PubMed1977

[Origination of casting porosity on high fused dental alloys by use of Bio-X X-ray unit (MRO-10R) (author's transl)].

Experiments were carried out clarify internal defects in dental casting with high fused dental alloys, as cobalt-chromium alloy or nickel-chromium alloy by use of Bio-X X-ray unit (MRO-10R for dental castings), exploited by KAWAHARA and TSK international corporation. Satisfactory radiographic observations were obtained with the following results; 1. In any of castings, a large amount of porosity was found on X-ray clearly. 2. On the castings in this experiment, porosity, round and bubble like in shape was markedly observed in the location right below the sprue attachment and its neighborhood. But in regions far from sprue, porosity was decreased, it came gradually to be present on the surface of castings. 3. Radiographically some defects were of a clack type and a shrinkage type in castings, although castings seemed to be quite sound in appearance. These types of defects were considered to become a weak point when external force was applied. 4. In regard to the completeness of castings, especially large round shape, clack type and shrinkage porosity can be prevented by a rapid removal of the air or gas from a mold and by improving the casting system to obtain better efficiency.

Chromium Alloys↗
PubMed1986

Investigations into the function and chemical compositions of the porose areas secretion of Rhipicephalus evertsi evertsi during oviposition.

Major differences were observed in hexane, ethanol and butanol extracts of eggs obtained from Rhipicephalus evertsi evertsi females in which the porose areas functioned normally (AP+ eggs) and from R. evertsi evertsi in which the porose areas were selectively destroyed by electrocautery (AP- eggs). Mass yields and UV spectra of the hexane extracts were similar for AP+ and AP- eggs. The UV spectra changed only slightly in the 294-320 nm range with respect to time and temperature. High performance liquid chromatography revealed 2 components which originate from the porose areas. Mass spectroscopy of these components indicated the presence of aliphatic and phenolic groups. The ethanol and butanol extracts showed quantitative but no qualitative differences with respect to AP+ and AP- eggs. Electrophoretic fractionation of the butanol extracts revealed the presence of proteins in the secretion of the porose areas. Apart from this information on the chemical composition of the secretion, no indication was obtained of their function during oviposition of R. evertsi evertsi.

Animals↗
PubMedDate not supplied

Dual-porosity expanded polytetrafluoroethylene implants for lip, nasolabial groove, and melolabial groove augmentation.

OBJECTIVE: To evaluate the clinical outcomes with the use of a dual-porosity expanded polytetrafluoroethylene implant for midfacial rejuvenation. DESIGN: An institutional review board-approved retrospective chart review was conducted of all patients who underwent implantation with the dual-porosity expanded polytetrafluoroethylene implant between 2001 and 2005. RESULTS: A total of 170 patients, with 612 implants, were evaluated. Only 8 patients had minor complications, 3 of which necessitated implant removal. The overall results of independent observer analysis of outcomes were favorable in the majority of cases. CONCLUSION: The dual-porosity expanded polytetrafluoroethylene implant is safe and reliable to use for midfacial implantation.

Face↗
PubMed1996

Is there any difference between vacuum mixing systems in reducing bone cement porosity?

Six vacuum mixing systems, Cemvac, Merck, Mitvac, Optivac, Osteobond, and Stryker, were tested using prechilled Palacos R bone cement to investigate the reduction of porosity compared to mixing at atmospheric pressure. In addition the Optivac, Osteobond, and Stryker were tested using Simplex P bone cement to find out if they were effective in reducing the porosity of a middle viscosity bone cement. All vacuum mixing systems reduced the number of macropores (> 1 mm) and micropores (0.1 mm < voids < 1 mm) and increased the density of both Palacos R and Simplex P. But only the Optivac, Stryker, and Merck systems reduced the area percentage of macropores with more than 50% compared to the control. When using Simplex P bone cement, all three mixing systems tested reduced the numbers and the area percentage of macropores compared to the control. The results show that vacuum mixing is effective in reducing the porosity in both a high viscosity cement such as Palacos R and a middle viscosity cement such as Simplex P. Not all systems tested were effective in reducing the number and size of large voids.

Absorptiometry, Photon↗
PubMed2000

Evolution of porosity during in vitro hydroxycarbonate apatite growth in sol-gel glasses.

A bioactive glass of composition (mol %) SiO(2) 58, CaO 36, P(2)O(5) 6 was obtained using the sol-gel method. Changes in porosity during the growth of a hydroxycarbonate apatite (HCA) phase were studied at different stages of the process. The high Ca (II) content led to a higher degree of porosity and enhancement of Ca(2+) released from surface and bulk when the glass was soaked into simulated body fluid (SBF). Saturation of the media (SBF) together with the porosity of the material led to fast growth of HCA on the surface and into the pores.

Apatites↗
PubMed1995

The resorption of bone-implanted corals varies with porosity but also with the host reaction.

Three different exoskeletons of coral species Porites asteroides (P), Montastrea annularis (M), and Dichocoenia stokesi (D) were implanted for 2-20 weeks in rabbits. At 2, 4, 8, or 20 weeks, the exoskeletons presented variations in their resorptions depending on the species. To understand the variations in the decreasing speed of the implants despite their similar chemical composition, a study of the surface and architecture of the coral was carried out using scanning electronic microscopy, porosity was evaluated, and growth and differentiation of osteogenic cells cultured in vitro were observed for more than 1 month. At the cellular level, the surface of the implants was identical. Three-dimensional structures of the implants were variable, but the porosity values [P = 42.7%, M = 40.7%, and D = 17.4%] could not completely account for the differences in the resorbing process of the species. Standard histologic studies performed at 2, 4, 8, and 20 weeks after implantation produced the same pattern with P or M, showing aspects of rapid resorption; however, with D there were images resembling those of a foreign-body reaction. It seems that when resorption is not quick enough, a foreign body reaction develops which further slows down the process. This work focuses on the importance of porosity when using coral as bone substitute.

Animals↗
PubMed2005

Effect of porosity on the fluid flow characteristics and mechanical properties of tantalum scaffolds.

In many cases of traumatic bone injury, bone grafting is required. The primary source of graft material is either autograft or allograft. The use of both material sources are well established, however, both suffer limitations. In response, many grafting alternatives are being explored. This article specifically focuses on a porous tantalum metal grafting material (Trabecular Metaltrade mark) marketed by Zimmer. Twenty-one cylindrical scaffolds were manufactured (66% to 88% porous) and tested for porosity, intrinsic permeability, tangent elastic modulus, and for yield stress and strain behavior. Scaffold microstructural geometries were also measured. Tantalum scaffold intrinsic permeability ranged from 2.1 x 10(-10) to 4.8 x 10(-10) m(2) and tangent elastic modulus ranged from 373 MPa to 2.2 GPa. Both intrinsic permeability and tangent elastic modulus closely matched porosity-matched cancellous bone specimens from a variety of species and anatomic locations. Scaffold yield stress ranged from 4 to 12.7 MPa and was comparable to bovine and human cancellous bone. Yield strain was unaffected by scaffold porosity (average = 0.010 mm/mm). Understanding these structure-function relationships will help complete the basic physical characterization of this new material and will aid in the development of realistic mathematical models, ultimately enhancing future implant designs utilizing this material.

Biocompatible Materials↗
PubMed2005

Novel approach for quantification of porosity for biomaterial implants using microcomputed tomography (microCT).

Porous bioceramics have been widely investigated in orthopaedic tissue engineering. Attention has been given to manufacturing of a porous bioceramic that mimics the trabecular bone structure for proper bone regeneration. With the advance of biomedical imaging through microcomputed tomography (microCT), this study attempted to quantify the pore structure of different bioceramics. Two bioceramic blocks (BSC and ChronOS) were synthesized by two methods. The specification claimed the porosity of the bioceramic ranged from 40% to 70%. Six blocks of each bioceramic were evaluated by conventional water immersion method and microCT. The pore size and connectivity were evaluated with standardized protocols. By the water immersion method, the porosity of BSC and ChronOS was 60.4% and 74.7%, respectively. The three-dimensional results of microCT showed that BSC porosity was 26.2% and ChronOS was 60.0%. The pore connectivity was evaluated to be 2.6 for BSC and 39.7 for ChronOS. ChronOS had functional pores with 200 microm to 400 microm in diameter (87.8%+/-0.5%), which is significantly more than 52.8%+/-11.5% of pores in BSC (p<0.05). Providing information on the functional pores objectively, the microCT evaluation serves as a good standard for specification of the bioceramic-related implants.

Coated Materials, Biocompatible↗
PubMed2001

VEGF can act as vascular permeability factor in the hepatic sinusoids through upregulation of porosity of endothelial cells.

VEGF is shown to be a vascular permeability factor (VPF) as well as a growth stimulatory factor on endothelial cells. In the hepatic sinusoids, endothelial cells express flt-1 and KDR/flk-1, receptors for VEGF. These cells, in primary culture, proliferate in response to VEGF stimulation. However, the role of VEGF as VPF in the hepatic sinusoids is to be elucidated. The effect of VEGF on the porosity of sinusoidal endothelial cells was studied. Sinusoidal endothelial cells were isolated from rats and cultured in DMEM containing 10% FCS on plastic dishes coated with type I collagen for 16 and 48 h for morphological examination and cell-number measurement, respectively. When the cells were cultured without VEGF addition, their number was decreased at 48 h compared to that at 16 h. However, the number was unchanged in the cells cultured with VEGF at 10 ng/mL and increased with addition of VEGF at 100 ng/mL. Scanning electron microscopic examination revealed that sieve-plate appearance of the cells was impaired in culture with no VEGF addition, but the appearance was maintained in culture with VEGF at 10 ng/mL or more. The cells cultured with VEGF at 100 ng/mL showed significantly increased number and size of pores compared to the cells cultured with VEGF at 10 ng/mL, suggesting that sinusoidal endothelial cells proliferating in response to VEGF may increase their porosity. It is concluded that VEGF can act as VPF in the hepatic sinusoids through regulation of endothelial cell porosity.

Animals↗
PubMedDate not supplied

Alteration of hemodynamics in aneurysm models by stenting: influence of stent porosity.

Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow apparatus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/-30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explain in vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.

Fluorescent Dyes↗