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At least 1,009 records · Page 56Linked to original sources
PubMed2004

In vitro testing of antimicrobial activity of bone cement.

The purpose of this study was to establish a reliable and cost-effective microplate proliferation assay for in vitro antimicrobial testing of bone cement samples. Cement samples devoid of antimicrobial agents, loaded with 2% gentamicin or with different concentrations of high-porosity silver, were incubated in a 96-well microplate with several staphylococcal, Pseudomonas aeruginosa, and Enterococcus faecium isolates exhibiting different susceptibilities to gentamicin. After being rinsed, the samples were brought into a soy medium in which adherent cells on the cement surface either were killed by the antimicrobial surface or started to release clonal counterparts. The medium was monitored in real time by recording a time proliferation curve for each well. Microplate testing revealed no antibacterial effect of plain bone cement. The antibacterial activity of gentamicin-loaded bone cement was shown by the microplate test to depend on the gentamicin susceptibilities of the strains. The effect of high-porosity silver was dose dependent. Bactericidal activity against all tested strains was found for bone cement loaded with 1% high-porosity silver. The accuracy of this new proliferation assay was shown by the high correlation between the types of proliferation curves and antibiotic susceptibility. In contrast to routine agar diffusion testing, it assesses the dynamic response of microorganisms to antimicrobial agents in biomaterials and allows high-throughput screening and detection of antimicrobial properties of poorly water-soluble compounds like silver.

Anti-Bacterial Agents↗
PubMedDate not supplied

In vitro studies of the penetration of adhesive resins into artificial caries-like lesions.

Instead of removing the porous carious tissue at a relatively late stage in the disease process, attempts have been made to 'fill' the microporosities of lesions at a much earlier stage of lesion development. This would not only reduce the porosity and therefore access of acid and egress of dissolved material, but also afford some mechanical support to the tissue and perhaps inhibit further attack. Successful infiltration of materials into lesions has been demonstrated previously using resorcinol-formaldehyde which, however, was clinically unacceptable. The advent of dental adhesives with potentially suitable properties has prompted a re-examination of this concept. Artificial lesions of enamel were generated in extracted human teeth using acidified gels. A range of currently available adhesive materials was then used to infiltrate the porosities. The extent of occlusion of the lesion porosities was determined both qualitatively using light microscopy and quantitatively using a chloronaphthalene imbibition technique. The effect of such treatment upon subsequent exposure to acid gels was also investigated. Results showed that up to 60% of the lesion pore volume had been occluded following infiltration with some of the materials and that this treatment was capable of reducing further acid demineralization. The development of such treatment strategies could offer potential noninvasive means of treating early enamel lesions.

Adhesives↗
PubMed2002

Non-connected versus interconnected macroporosity in poly(2-hydroxyethyl methacrylate) polymers. An X-ray microtomographic and histomorphometric study.

Poly(2-hydroxyethyl methacrylate) (pHEMA) has potentially broad biomedical applications: it is biocompatible and has a hardness comparable to bone when bulk polymerized. Porous biomaterials allow bone integration to be increased, especially when the pores are interconnected. In this study, three types of porogens (sugar fibers, sucrose crystals, and urea beads) have been used to prepare macroporous pHEMA. The pore volume and interconnectivity parameters of the porosity were measured by X-ray microtomography and image analysis. Sucrose crystals, having a high volumetric mass, gave large pores that were located on the block sides. Urea beads and sugar fibers provided pores with the same star volume (2.65 +/- 0.46 mm3 and 2.48 +/- 0.52 mm3, respectively) but which differed in interconnectivity index, fractal dimension, and Euler-Poincarés number. Urea beads caused non-connected porosity, while sugar fibers created a dense labyrinth within the polymer. Interconnectivity was proved by carrying out surface treatment of the pHEMA (carboxymethylation in water), followed by von Kossà staining, which detected the carboxylic groups. Carboxymethylated surfaces were observed on the sides of the blocks and on the opened or interconnected pores. The disconnected pores were unstained. Macroporous polymers can be prepared with water-soluble porogens. X-ray microtomography appears a useful tool to measure porosity and interconnectedness.

Biocompatible Materials↗
PubMed2005

Fabrication and characterization of porous alginate/polyvinyl alcohol hybrid scaffolds for 3D cell culture.

Porous alginate/polyvinyl alcohol (PVA) hybrid scaffolds as bioartificial cell scaffolds were fabricated to improve cell compatibility as well as flexibility of the scaffolds. The alginate/PVA hybrid scaffolds with different PVA compositions up to 50 wt% were fabricated by a modified freeze-drying method including the physical cross-linking of PVA and the following chemical cross-linking of alginate. The prepared alginate/PVA hybrid scaffolds were characterized by morphology observations using scanning electron microscopy (SEM), the measurements of porosity and average pore sizes and the measurements of compressive strength and modulus. The scaffolds exhibited highly porous, open-cellular pore structures with almost the same surface and cross-sectional porosities (total porosities about 85%, regardless of PVA composition) and the pore sizes from about 290 microm to about 190 microm with increasing PVA composition. The alginate/PVA hybrid scaffolds were more soft and elastic than the control alginate scaffold without significant changes of mechanical strength. The scaffolds were examined for their in vitro cell compatibility by the culture of chondrocytes (human chondrocyte cell line) in the scaffolds and the following analyses by MTT assay and SEM observation. It was observed that the alginate/PVA scaffolds had better cell adhesion and faster growth than the control alginate scaffold. It seems that 30 wt% addition of PVA to alginate in the fabrication of the hybrid scaffolds is desirable for improving their flexibility and cell compatibility.

Alginates↗
PubMed1998

Aminated polysaccharides as bile acid sorbents: in vitro study.

Dextran, pullulan, and microcrystalline cellulose were cross-linked with 1-chloro-2,3-epoxypropane and reacted with N-(1-chloroethyl)-N,N-diethylamine or N-glycidyl-N,N,N-trialkylammonium chloride in order to obtain sorbents containing tertiary amino and/or quaternary ammonium groups. In vitro equilibrium sorption of cholic acid on these sorbents was studied in comparison with Cholestyramine, and in vitro dissociation of ionic complexes of cholic acid-sorbents was determined under dynamic conditions. The sorption capacity and the affinity of these sorbents for cholic acid were investigated in relation to the nature of the polymeric support, the swelling porosity of sorbent, the basicity of amino groups, and the nature of the substituents at the nitrogen atom. The maximum sorption capacity increases with the increase in amino group content, their basicity, and the length of alkyl substituents at the nitrogen atom. The affinity for cholic acid of all polysaccharide-based sorbents is higher than that of Cholestyramine. Dextran-based sorbents display the highest sorption affinity. It was found that there exists an optimum swelling porosity for the polysaccharide sorbents to attain the highest affinity for cholic acid. The dissociation rate of ionic complexes depends also on the nature of the polysaccharide and the swelling porosity and its lower for sorbents with higher sorption affinity.

Absorption↗
PubMed2004

Model simulations for describing water transport in a landfill with bottom ash from a municipal solid waste incinerator (MSWI): model validation and scenarios.

In the present study the water movement in a bottom ash landfill from a municipal solid waste incinerator (MSWI) was investigated. The pore regime of such landfills consists of macropores (with diameter > 50 microm), which make up about two-thirds of the total porosity and micropores. The program MACRO, which describes flow through porous media and takes both macro- and micropore flows into account, was applied. The model was calibrated with a time series from the landfill Riet, near Winterthur in Switzerland. In the present study the model was recalibrated at a time series for 1 year. With this scenario the influence of an expected reduction or increase of the porosity on leachate behaviour of such landfills over a long time (> 100 years) was studied ('long-term behaviour'). It has been shown that reliable information about water percolation can only be provided by obtaining more information about the hydraulic structure of such landfills. In particular, the number of macropores and the porosity exert great influence on the water movement.

Calibration↗
PubMed1994

Effects of compression pressure on physical and chemical stability of tablets containing an anticancer drug TAT-59.

(E)-4-[1-[4-[2-(Dimethylamino)ethoxy]phenyl]-2-(4-isopropyl) phenyl]-1-butenyl]phenyl monophosphate (TAT-59) is a new drug for the treatment of breast cancer. Physical and chemical stability of mixtures of TAT-59 and microcrystalline cellulose (1:9) compressed at 0, 300, 600 and 1400 kg/cm2 was evaluated by determination of water content, porosity and the amount of hydrolysis product, DP-TAT-59, formed. The water contents and porosity of these tablets scarcely changed during 57 d at 25-60 degrees C under 50% relative humidity (RH). The degradation rate of TAT-59 increased with increasing compression pressure as well as temperature. The apparent activation energy and frequency factor were determined from an Arrhenius plot of the degradation rate. Activation energy of these tablets was almost the same, while the frequency factor tended to increase with increasing compression pressure. The porosity and pore sizes in TAT-59-containing tablets decreased with increasing compressive force. We speculated from these observations that the increase in compression pressure decreased the distance and increased the contact area between TAT-59 and microcrystalline cellulose. The proximity between TAT-59 and moisture presented at the surface of microcrystalline cellulose by compression was considered to enhance the degradation of TAT-59.

Antineoplastic Agents↗
PubMed1994

Long-term changes in the haversian systems following high-dose irradiation. An ultrastructural and quantitative histomorphological study.

The effects of high-dose irradiation on the morphology of haversian bone were studied, over a fifty-two-week period, in seventy-seven adult rabbits, after the administration of a single dose of radiation (therapeutic x-ray; twenty-five, fifty, or 100 gray) to one knee joint. The specimens of bone were examined with microangiography, light and transmission electron microscopy, and histomorphometry. Analysis was performed on the haversian bone in the subchondral bone plate of weight-bearing portions of the femoral condyles. Microangiography demonstrated dilatation of the microvasculature four weeks after irradiation. Beginning at twelve weeks, there was a marked decrease in vascularity; no obvious recovery of the subchondral bone had occurred by fifty-two weeks. At four weeks, morphological analysis revealed two changes in the haversian canals: simple occlusion of the haversian vessels with loss of cells in the canal, and dilatation of the capillaries with abnormal resorption of the perivascular bone matrix by osteoclasts. The abnormal bone resorption was not coupled with subsequent new-bone formation, resulting in increased porosity. Beginning at four weeks, a progressive decrease in the number of haversian vessels and in cellularity became prominent. The decrease in cellularity involved all types of cells, including endothelial cells, pericytes, perivascular mesenchymal cells, osteoblasts, osteocytes, and osteoclasts. The loss of perivascular cells was often but not always associated with occlusion of the haversian vessels. Histomorphometry revealed both time-dependent and dose-dependent decreases in capillary density (the number of intraosseous capillaries per unit area) and in the number of osteocytes in the subchondral bone plate. The porosity of the same areas showed a significant increase by four weeks (p < 0.001 after administration of twenty-five gray and p < 0.01 after administration of both fifty and 100 gray), but between twelve and fifty-two weeks, there was only a slight additional increase. Statistical analysis revealed significant correlations between capillary density and osteocyte survival (p < 0.001) and between capillary density and porosity (p < 0.001). The portion of the subchondral bone plate that was located farthest from the non-irradiated normal bone showed progressive damage and no sign of recovery at fifty-two weeks.

Animals↗
PubMed1993

Castability and surface hardness of titanium cast plates obtained from experimental phosphate-bonded silica investment molds.

The effect of 12 different experimental compositions of phosphate-bonded SiO2 investments was examined on cast pure titanium. The mold temperature was 600 degrees C and the casting was conducted with an argon-arc melting and pressure casting machine. Castability was evaluated by the volume of casting porosity, which was calculated from the volume of wax pattern (15 mm x 15 mm x 1.5 mm), the weight of cast plate and the specific density of pure titanium. The existence of inner casting porosities was confirmed by an X-ray non-destructive inspection instrument. Cast plates made in molds with cristobalite had significantly lower castability and higher surface hardness than those in molds with quartz as a refractory material. Cast plates in molds (quartz-cristobalite mixtures) with 20% binder had lower surface hardness and fewer casting porosities than those in molds with 10% binder.

Analysis of Variance↗
PubMed2001

Combustion synthesis of porous glasses and ceramics for bone repair.

Porous bioactive materials with constituents such as CaO, P2O5, SiO2, MgO, K2O, Na2O implanted in bone can activate a biologic response to enhance bone healing. These biomaterials are currently formed utilizing wet chemistry, plasma spray, D-gun, sintering, and diffusion bond techniques. This work investigates the use of self propagating high temperature combustion synthesis (SHS) in the creation of porous bioactive glasses for bone repair. The use of combustion synthesis has many advantages over the methods mentioned previously. The primary advantages are the ability to control the process to provide specified porosity (% porosity, pore size distribution, interconnected pores, functionally grading of porosity), structural mechanical properties, together with rapid production of the material. The focus of this project is the investigation of combustion synthesis reactions based on the reaction system 3CaO + P2O5==>Ca3(PO4)2 and incorporating other known biocompatible constituents into the reaction.

Alloys↗
PubMedDate not supplied

Experimental study on the cement mantle in hip arthroplasty: effect of defects on the property of the materials used.

The study simulated implantation of a hip prosthesis stem in the femur. The cement mantle produced in vitro was observed under an optic microscope. A higher concentration of porosity in the cement mantle at the stem-cement interface was observed. By heating the stem to 45 degrees C and 55 degrees C the authors observed a reduction in porosity in the three surfaces examined: stem-cement interface, internal surface, and cement-pseudofemur interface. Heating of the stem causes a reduction in polymerization time and an increase in maximum temperature achieved during the polymerization process. A reduction in porosity at the stem-cement interface influenced bending strength of the specimens extracted from the mantle. A significant difference between resistance to flexion in the specimens produced with the stem at 55 degrees, and in those with the stem at 23 degrees C was observed.

Arthroplasty, Replacement, Hip↗
PubMed1992

Morphometric and physical investigations of segmental cortical bone autografts and allografts in canine ulnar defects.

Cortical bone grafts were implanted for six months in mature dogs using an osteoperiosteal 3-cm defect in the ulna to evaluate their respective morphometric and physical values compared with autografts. The bone-grafting material included fresh auto- and allografts, frozen and thimerosal preserved allografts, and partially demineralized bone allografts. The grafts were evaluated by roentgenograms, microradiograms, photon absorptiometry, porosity, fluorescence labeling measurements, and torsional loading at failure. Autografts achieved a better union score than the allografts, but intracortical bone porosity, percentage of cumulative new bone, and mineral apposition rate were not variables with statistical significance. Lamellar bone was found earlier and in greater quantity in autografts. Within the graft, new bone was deposited at a slower rate than in the recipient bone. Autografts showed less peripheral resorption and a greater torsional resistance than allografts. Photon absorptiometry demonstrated that nondemineralized allografts underwent a substantial loss of peripheral bone. This marked reduction in the outer diameter of the graft had more influence on torsional resistance than did the intracortical porosity of the graft. Demineralized allografts were osteoinductive in only 28% of the cases and appeared to respond in an all-or-nothing pattern. Frozen and thimerosal preserved allografts were the most acceptable substitutes to autografts.

Absorptiometry, Photon↗
PubMed1992

Characterization of hemophan hemodialysis membranes by thermoporometry.

A new wet-state membrane characterization method, thermoporometry, was used to study the effect on membrane structure of commonly used sterilization methods for artificial kidney membranes. The porosity and pore size distribution of differently sterilized hollow fiber Hemophan hemodialysis membranes were determined. Also the effect of a glycerol treatment (before sterilization) on porosity and pore size distribution after sterilization was studied. Hemophan was found to have a pore size distribution of pores with radii between 1.5 and 12 nm. Most of the samples had a maximum pore volume at a pore radius of 2.5 nm, only the steam sterilized and non glycerol treated sample had a maximum pore volume at 1.5 nm. The porosity was found to vary between 14 and 31% and was dependent on the applied treatment.

Biocompatible Materials↗
PubMed2004

[Configuration of pyrolytic chars from waste tires in fluidized bed reactor].

With the fluidized bed as main reactor, the configuration of chars of waste tire was investigated. The change of specific surface area, porosity and specific pore volume of chars received at various temperature, diameter of bed materials and superficial fluidization number was mainly researched. The specific surface area and porosity of chars had the peak value at 650 degrees C or 750 degrees C, which showed there exists the best pyrolysis temperature from the angle of char quality and it will decrease with smaller diameter of bed materials, 0.135-0.304mm. The porosity of chars decreases with the fluidization number increasing. The change tendency of the specific surface area of chars with the fluidization number is correlated with the pyrolysis temperature. At 550 degrees C the specific surface area of chars decreases with the fluidization number increasing, while at 650 degrees C the other way round. The change tendency of the specific pore volume of chars with the temperature is correlated with the diameter of bed materials. With larger bed materials (0.304-0.4mm), the specific pore volume of chars rises at fisrt, then decreases with the temperature increasing, and with smaller bed materials, it decreases with the temperature increasing.

Bioreactors↗
PubMed2005

[Experimental study on gelatin-chondroitin sulfate-sodium hyaluronate tri-copolymer as novel scaffolds for cartilage tissue engineering].

OBJECTIVE: To fabricate a novel gelatin-chondroitin sulfate-sodium hyaluronate tri-copolymer scaffold and to confirm the feasibility of serving as a scaffold for cartilage tissue engineering. METHODS: Different scaffolds was prepared with gelatin-chondroitin sulfate-sodium hyaluronate tri-copolymer by varying the freezing temperatures (-20 degrees C, - 80 degrees C and liquid nitrogen). Pore size, porosity, inter pores and density were observed with light microscopy and scanning electron microscopy (SEM). The load-stiffness curves were compared between different scaffolds and normal cartilage. The number of MSCs attaching to different scaffolds and the function of cells were also detected with MTT colorimetric microassay. RESULTS: The pore size was 300 +/- 45, 230 +/- 30 and 45 +/- 10 microm; the porosity was 81%, 79% and 56%; the density was 9.41+/-0.25, 11.50 +/- 0. 36 and 29.50 +/- 0. 61 microg/mm3 respectively in different scaffolds fabricated at - 20 degrees C, - 80 degrees C and liquid nitrogen; the latter two scaffolds had nearly the same mechanical property with normal cartilage; the cell adhesion rates were 85.0%, 87.5% and 56.3% respectively in different scaffolds and the scaffolds can mildly promote the proliferation of MSCs. CONCLUSION: Gelatin-chondroitin sulfate-sodium hyaluronate tri-copolymer scaffold fabricated at -80 degrees C had proper pore size, porosity and mechanical property. It is a novel potential scaffold for cartilage tissue engineering.

Animals↗
PubMedDate not supplied

[Late changes in a recipient's tissues after implantation of synthetic hydroxyapatite of varying density: an experimental morphological study].

The synthetic hydroxyapatite made in Russia was applied as an insert-implant to 4 rabbits (6 eyes, 6 eviscerations). These included 2 implants having a porosity of 40% and a pore size of 0.03-1.5 microm and 2 with a porosity of 63% and a pore size of 0.05-3.0 microm. The hydroxyapatite that is made in Russian and that has preferably a porosity of 40% and a pore size of 0.03-1.5 microm can be successfully used to make a locomotor stump after removal of the eyeball. The hydroxyapatite having these parameters more rapidly intergrows around the periphery with fibrovascular tissue and its vascular components mainly reduce by month 8. Our data suggest that the synthetic hydroxyapatite made in Russia may be used in ophthalmological care.

Animals↗
PubMed2006

Design variables for mechanical properties of bone tissue scaffolds.

The reconstruction of segmental defect in long bone is a clinical challenge. Multiple surgeries are typically required to restore the structure and function of the affected defect site. In order to overcome this defect a biodegradable bone tissue engineering scaffold is used. This scaffold acts as a carrier of proteins and growth factors, while also supporting the load that the bone would normally sustain, until the natural bone can regenerate in its place. Work was done to optimize an existing solid free-form scaffold design. The goal of the optimization was to increase the porosity of the scaffold while maintaining the strength of a previously-tested prototype design. With this in mind, eight new designs were created. These designs were drawn using CAD software and then through the use of finite element analysis the theoretical ultimate compressive strength of each design was obtained. Each scaffold design was constructed by casting a thermal-curable poly(propylene fumarate)/tricalcium phosphate (PPF/TCP) suspension into wax molds fabricated on inkjet printing rapid prototyping machine. The constructs were then experimentally tested by applying a uniaxial compressive load. The theoretical and experimental values of ultimate compressive strength and specific strength of each design were compared. Theoretically, the best scaffold design produced from this work improved upon the current design by increasing the porosity by 46% and also increasing the ultimate compressive strength by 27%. The experimental data was found to match the theoretical strength in four designs, but deviate from the theoretical strength in five designs. The reasons for the deviations and their relation to the rapid prototyping manufacturing technique were discussed. The results of this work show that it is possible to increase the porosity and strength of a bone tissue engineering scaffold through simple iterations in architectural design.

Biocompatible Materials↗
PubMed2006

Bovine albumin release and degradation analysis of dicalcium phosphate dihydrate cement.

Dicalcium phosphate dihydrate (DCPD) cement was effective in our prior study as a bone morphogenetic protein-2 (BMP-2) delivery vehicle in a rat segmental defect regeneration study. In this study, we investigated the effects of liquid-to-powder (L/P) ratio on the in vitro degradation and protein release behavior of this material. The L/P ratios used in this study ranged from 0.50 to 0.83. DCPD cylinders were formed with a diameter of 1/4" and a height of 1/4". The effect of L/P on the initial compressive strength was found to be related to the porosity of the material at different L/P level. The strength of the material in phosphate buffered solution was found to degrade roughly 20% in 14 days. The relation between the final porosity and the compressive strength after degradation was modeled with Ryshkewitch equation. A liquid-to-powder ratio of 0.55, 0.7, and 0.8 was then used to fabricate samples for the protein release kinetic study. The low porosity (L/P = 0.55) group was found to have the fastest release rate, while the L/P = 0.8 group had the lowest. More then 60% of the loaded protein was released after 10 hours in all three groups with a final total release ranging between 75% and 93%. The findings suggested that the protein release profile of DCPD cements can be adjusted by the L/P ratio.

Absorbable Implants↗