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PubMed2003

Solidification of stainless steel slag by accelerated carbonation.

On exposure to carbon dioxide (CO2) at a pressure of 3 bars, compacts formed from pressed ground slag, and 12.5 weight percent water, were found to react with approximately 18% of their own weight of CO2. The reaction product formed was calcium carbonate causing the slag to self-cement. Unconfined compressive strengths of 9MPa were recorded in carbonated compacts whereas strengths of < 1 MPa were recorded in non-carbonated slag compacts. As molten stainless steel slag containing dicalcium silicate (C2S) cools it can undergo several phase transitions. The final transformation from the beta-polymorph to gamma-C2S is accompanied by a volume change that causes the slag to self-pulverise or 'dust'. As a consequence of this the fine grained portion of the slag contains more of this phase whilst the coarser particles of the slag contain more of the calcium magnesium silicates that contribute the bulk of the waste. The fine fraction (< 125 microm) of the slag when ground is found to react to the same extent as the ground bulk slag and produces compacts with equivalent strength. A coarser fraction (4-8 mm) when ground to a similar grading does not react as extensively and produces a weaker product. Additions of ordinary Portland cement (OPC) at 5 and 10 percent by weight did not alter the degree of reaction during carbonation of the bulk slag or ground fine fraction, however the strength of the 4-8 mm fraction was increased by this change.

Calcium Carbonate↗

PubMed2003

Mechanically stable implants of synthetic bone mineral by cold isostatic pressing.

A calcium phosphate phase that is equivalent in composition (carbonate content) and crystallinity (nanocrystals) to the mineral phase of bone was prepared by a continuous precipitation method. The powder was compacted by cold isostatic pressing into desired shapes with high compressive strength (range of 20-50 MPa, depending on the geometry). It is concluded that such implant materials can be prepared with a fine-tuned biodegradability in combination with a high mechanical strength. The high mechanical strength of the objects also permits further mechanical shaping procedures like drilling or cutting.

Biocompatible Materials↗

PubMed2005

A three-dimensional nonlinear finite element analysis of the mechanical behavior of tissue engineered intervertebral discs under complex loads.

The use of tissue-engineering method holds great promise for treating degenerative disc disease [Gan JC, Ducheyne P, Vresilovic E, Shapiro IM. J Biomed Mater Res 2000; 51(4): 596-604]. This concept typically implies that nucleus pulposus (NP) cells are seeded on a scaffold, while the NP tissue is regenerated. Such hybrid implant is inserted into the host intervertebral disc. Because the success of a tissue engineering approach depends on maintenance or restoration of the mechanical function of the intervertebral disc, it is useful to study the initial mechanical performance of the disc after implantation of the hybrid. A three-dimensional finite element model (FEM) of the L2-L3 disc-vertebrae unit has been analyzed. The model took into account the material nonlinearities and it imposed different and complex loading conditions. In this study, we validated the model by comparison of its predictions with several sets of experimental data; we determined the optimal Young's modulus as well as the failure strength for the tissue-engineered scaffold under different loading conditions; and we analyzed the effects of implanted scaffold on the mechanical behavior of the intervertebral disc. The results of this study suggest that a well-designed tissue-engineered scaffold preferably has a modulus in the range of 5-10 MPa and a compressive strength exceeding 1.67 MPa. Implanted scaffolds with such properties can then achieve the goal of restoring the disc height and distributing stress under different loading conditions.

Biomechanical Phenomena↗

PubMed2000

Influence of glass composition on the properties of glass polyalkenoate cements. Part III: influence of fluorite content.

The influence of fluorite content of the glass on the formation and properties of glass polyalkenoate cements was investigated. A series of glass powders based on 1.5SiO2 x 0.5P2O5 x Al2O3 x CaO x XCaF2 were synthesised. The glass transition temperature of the glass fell with increasing fluorite content. Setting and working times of the cement pastes decreased with increasing fluorite content of the glass. Compressive strength and un-notched fracture strength increased with increasing fluorite content of the glass. Fracture toughness and toughness of the cements were relatively insensitive to fluorite content.

Calcium Fluoride↗

PubMed2006

Synthesis and preparation of novel 4-arm star-shape poly(carboxylic acid)s for improved light-cured glass-ionomer cements.

OBJECTIVE: The objective of this study was to synthesize and characterize novel 4-arm star-shape poly(acrylic acid)s (poly(AA)s) via atom-transfer radical polymerization (ATRP) technique, tether in situ light-curable methacrylate functionalities onto the poly(AA) backbone, use these star-shape poly(AA)s to formulate the light-cured glass-ionomer cements (LCGICs), and evaluate the mechanical strengths of the formed cements. MATERIALS AND METHODS: The 4-arm poly(AA)s were synthesized using ATRP and tethered with either 2-isocyanatoethyl methacrylate (IEM) or glycidyl methacrylate (GM). The polymers were formulated with 2-hydroxyethyl methacrylte (HEMA) or methacryloyl beta-alanine (MBA), water, initiators, and Fuji II LC filler. Compressive strength (CS) was used as a tool to evaluate the formed cements. The specimens were conditioned in distilled water at 37 degrees C for 24h prior to testing. RESULTS: The 4-arm poly(AA) showed a lower viscosity as compared to its linear counterpart. Both IEM-tethered and GM-tethered 4-arm poly(AA) constructed LCGICs showed significantly high mechanical strengths. Both types of co-monomer and grafting agent dramatically affected the mechanical strengths. The MBA-containing poly(AA) cements exhibited much higher CS than the HEMA-containing cements. The IEM-tethered poly(AA) cements showed much higher CS and DTS than the GM-tethered cements. CONCLUSIONS: This study developed a novel light-curable 4-arm star-shape poly(AA) system. The system was 13% in CS, 178% in DTS and 123% in FS, compared to Fuji II LC.

Acrylic Resins↗

PubMed2002

Kinetic study of citric acid influence on calcium phosphate bone cements as water-reducing agent.

Most of the research performed on calcium phosphate bone cements (CPBCs) has dealt with the improvement of bone cement formulations for new, demanding bone-filling applications. In particular, the development of injectable bone cements is of real interest for the biomedical community. The aim of this work was to study the effect of citric acid on the injectability and the setting properties of alpha-tricalcium phosphate-based cements. A comparative kinetic study was performed on cements with and without citric acid relating the hardening curves and the hydration rates using a mathematical approach. Citric acid behaved as a fluidificant during the first stages of the cement mixing. The dissolution-precipitation reactions of the alpha-tricalcium phosphate were retarded with the addition of citric acid and the compressive strength at saturation increased. In conclusion, citric acid can behave as a water-reducing admixture.

Bone Cements↗

PubMed2002

Performance study of cementitious systems containing zeolite and silica fume: effects of four metal nitrates on the setting time, strength and leaching characteristics.

The aim of this study is to investigate the effect of four metal nitrate contaminants, namely chromium, manganese, lead and zinc on the mechanical and leaching characteristics of cement-based materials. For this purpose, three different matrices made of: (i) Portland cement, (ii) Portland cement and silica fume, and (iii) Portland cement and natural zeolite were studied. The effects of metals on the stabilised/solidified (S/S) product characteristics were monitored by measuring: (i) setting time, (ii) compressive strength, (iii) acid neutralisation capacity (ANC), and (iv) solubility of the metal contaminants as a function of pH. The results of both mechanical and leaching tests showed the importance of the contaminant/matrix couple considered. Setting time was accelerated in presence of chromium, while in presence of manganese, lead and zinc it was delayed. However, for the last two contaminants, a 10% replacement of cement by silica fume and zeolite, markedly accelerated the setting time compared to the cement-only matrix. Although the early strength development was adversely affected in presence of all four contaminants, the long-term strength was less affected compared to the control materials. Although the ANC of the materials was not markedly affected by the presence of contaminants, the nature of the matrix did modify the ANC behaviour of the solidified materials. The increased strength and reduced ANC observed in the presence of silica fume are both due to pozzolanic reaction. The type of matrix used for solidification did not affect the solubility of the four metal contaminants. Overall, the results showed that the use of blended cements must be carried out with care and the performance assessment of waste-containing cement-based materials must take into consideration both the mechanical and leaching characteristics of the systems.

Compressive Strength↗

PubMed2005

Effective use of optimized, high-dose (50 kGy) gamma irradiation for pathogen inactivation of human bone allografts.

The safety of tissue allografts has come under increased scrutiny due to recent reports of allograft-associated bacterial and viral infections in tissue recipients. We report that 50 kGy of gamma irradiation, nearly three times the dose currently used, is an effective pathogen inactivation method when used under optimized conditions that minimize damage to the tissue. Cancellous bone dowels treated with a radioprotectant solution and 50 kGy of optimized irradiation had an ultimate compressive strength and modulus of elasticity equal to conventionally irradiated (18 kGy) and non-irradiated control bone grafts. We subjected bone dowels treated with this pathogen inactivation method to an in vitro cytotoxicity test using three different mammalian cell lines and concluded that the treated grafts were not cytotoxic. The log reduction of nine pathogens spiked into radioprotectant-treated bone irradiated to 50 kGy was also tested. We achieved 4.9 logs of inactivation of a model virus for HIV and hepatitis C and 5 logs inactivation of a model virus for human parvovirus B-19. Complete inactivation (6.0-9.2 logs) of seven clinically relevant microorganisms was demonstrated. The results show that a combination of radioprotectants and optimized, high-dose gamma irradiation is a viable method for producing safer cancellous bone grafts that have the mechanical strength of existing grafts.

Bacteria↗

PubMed1999

The effects of extreme temperatures on composite, compomer and ionomer restorations.

The composite resin, compomer and glass ionomer restorative materials used in modern dental practice are fire resistant and remain radiopaque. They shrink significantly and are likely to fall out of the cavities after being burnt, but they remain extremely important for identification purposes and it may be possible to identify the white filling materials used to restore teeth by their radiopacity and morphology. The radiographic density of these filling materials do not change significantly when exposed to heat and although they may be difficult to see with the naked eye, they will remain visible when radiographed. Furthermore, special care has to be taken when handling heated materials as their compressive strengths decrease significantly depending on temperature and time of exposure and damage is possible.

Analysis of Variance↗

PubMed2005

Effects of incorporation of HA/ZrO(2) into glass ionomer cement (GIC).

Glass ionomer cements (GICs) are a class of bioactive cements that bond directly to bone. In this paper, a new bioactive hydroxyapatite (HA)/zirconia (ZrO(2))-filled GIC composite was developed to improve the biocompatibility and bioactivity of the GICs with the surrounding bone and connective tissues. Nano-sized HA/30 wt% ZrO(2) powders were heat treated at 700 degrees Celsius and 800 degrees Celsius for 3 h to elucidate the influence of the crystallinity of composite powders on the performance of HA/ZrO(2)-GICs. The effects of different volume percentages of HA/ZrO(2) powders (4, 12, 28 and 40 vol%) substituted within GICs were investigated based on their microhardness, compressive strength and diametral tensile strength. The HA/ZrO(2)-GICs composite was soaked in distilled water for 1 day and 1 week before subjecting the samples to mechanical testing. Results showed that the glass and HA/ZrO(2) particles were distributed uniformly in the GIC matrix. The substitution of highly crystalline HA/ZrO(2) improved the mechanical properties of the HA/ZrO(2)-GICs due to the slow resorption rate for highly crystalline powders in distilled water. The mechanical properties of HA/ZrO(2)-GICs increased with increasing soak time due to the continuous formation of aluminium salt bridges, which improved the final strength of the cements. The compositions 4 and 12 vol% HA/ZrO(2)-GICs exhibited superior mechanical properties than the original GICs. The mechanical properties of HA/ZrO(2)-GICs were found to be much better than those of HA-GICs because ZrO(2) has the attributes of high strength, high modulus, and is significantly harder than glass and HA particles. Furthermore, ZrO(2) does not dissolve with increasing soaking time.

Bone Cements↗

PubMed2001

[Comparative biomechanical compression trials with a new vertebral prosthetic implant].

UNLABELLED: The authors present a new titanium implant for replacement of the vertebral body (Synex). Possible indications would be fractures or dislocations with destruction of the anterior column, posttraumatic kyphosis as well as tumors in the throracolumbar spine. The construction has to be completed by a stabilizing implant. For best fit and contact to adjacent end-plates Synex is distractable in situ. The possibility of secondary dislocation or loss of correction should thereby be minimised. OBJECTIVES: We performed comparative compression tests with Synex and MOSS ("Harms mesh cage") on human cadaveric specimens of intact vertebrae (L1). The aim of the study was to measure the compressive strength of the vertebral body end-plate in uniaxial loading via both implants to exclude a caving of Synex in vivo. METHODS: 12 human cadaveric specimens of intact vertebrae (L1) were divided in 2 similar groups (matched pairs) according to bone mineral density (BMD), determined using DE-QCT. The specimens were loaded with axial compression force at a constant speed of 5 mm/min to failure and the displacement was recorded with a continuous load-displacement curve. RESULTS: The mean ultimate compression force (Fmax) showed a tendency towards a higher result testing Synex with 3396 N versus 2719 N (non significant). The displacement until Fmax was 2.9 mm in group S (Synex), which was half as long as in group M (5.8 mm). The difference was significant (p < 0.001). The compression force was twice as high and significantly (p < 0.05) higher with Synex at a displacement of 1 mm, 1.5 mm and 2 mm. A significant (p < 0.001) correlation (R = 0.89) between Fmax and BMD was found. CONCLUSIONS: Synex was found to be at least comparable to MOSS for suspensory replacement of the vertebral body at the thoracolumbar spine. A possible consequence of the significantly higher mean compression forces between 1 and 2 mm displacement might be a decreased segmental deformation or loss of correction.

Adult↗

PubMed2006

Increasing sex difference in bone strength in old age: The Age, Gene/Environment Susceptibility-Reykjavik study (AGES-REYKJAVIK).

INTRODUCTION: It is important to identify possible pathological mechanisms that underlie the known sexual dimorphism in bone fragility in old age. In this cross-sectional population-based study, we use data from three different skeletal sites to examine sex differences in volumetric bone density, geometry and strength indices and determine whether sex differences in these bone strength measures continue to increase into very old age. MATERIALS AND METHODS: A total of 1715 elderly individuals (807 men and 908 women) age 67-93 years, participants in a population-based study, the Age, Gene/Environment Susceptibility-Reykjavik Study (AGES-REYKJAVIK) and not taking medications affecting bone metabolism, were studied. Quantitative computed tomography (QCT) was performed in the lumbar spine, hip and mid-femoral shaft to estimate volumetric trabecular, cortical and integral BMD, bone geometry and bone strength indices. Regression models were used to assess the effects of age and gender-adjustment for standing midlife height and current weight. RESULTS: At age 67-69 years, men had 24.9-31.7% larger cross-sectional bone size at measured sites than women. At all bone sites, women had two- to fivefold diminution in net bone mass with age compared to men but had comparable increments in bone size (1.8-6.0% per 10 years). This was reflected in significantly worse (more than twofold) bone strength measures with age in women, including compressive strength indices at the spine, femoral neck and trochanter and bending strength indices at the femoral neck. CONCLUSION: With the limitations of a cross-sectional study, our data support the hypothesis that sex differences in bone strength continue into old age. These sex differences appear to be due to greater net bone loss in women rather than due to greater bone gain in men.

Age Distribution↗

PubMed2001

Calcite precipitation induced by polyurethane-immobilized Bacillus pasteurii.

Polyurethane (PU) foam was used to immobilize the whole cell of Bacillus pasteurii. The immobilized cells exhibited the rates of calcite precipitation and ammonia production as high as those of the free cells. Scanning electron micrographs identified the cells embedded in calcite crystals throughout PU matrices. Calcite in PU showed little effect on the elastic modulus and tensile strength of the polymer, but increased the compressive strengths of concrete cubes, whose cracks were remediated with PU-immobilized cells. These observations led us to believe that the calcite might remain as a form of precipitation, not as a bonding material within the matrices.

Journal Article↗

PubMed2004

The effect of particle size distribution on an experimental glass-ionomer cement.

OBJECTIVES: The role of particle size and size distribution of glass powders in glass-ionomer cements (GICs) has been largely overlooked, being limited to demonstrations of the classical inverse size-strength relationship. This study investigated variation in properties of an experimental glass-ionomer cement when a combination of large ('Powder A') and small ('Powder B') particles was used. METHODS: Large- (mean size 9.60mum) and small-particle (3.34mum) glass powders were blended in various proportions and mixed with powdered polyacrylic acid to make a range of glass-ionomer powders. These powders were mixed with a glass-ionomer liquid (SDI Ltd, Australia) at powder to liquid ratios of 2:1, 2.5:1, and 3:1, and the resultant cements evaluated for working time, setting time, clinical handling, and compressive strength. Results were analysed by ANOVA. RESULTS: An increased proportion of smaller particles corresponded to higher strengths, and an increased proportion of larger particles with a decrease in viscosity of the unset cement. When 20-30% by weight of small particles was used, the paste demonstrated a peak in cohesion and working time, with a viscosity similar to commercial restorative GICs. SIGNIFICANCE: Optimisation of particle sizing and distribution may thus lead to glass-ionomer cements with improved clinical handling characteristics and greater strength, which may increase the longevity of the restoration.

Analysis of Variance↗

PubMed2005

Jarosite characteristics and its utilisation potentials.

During metallic zinc extraction from zinc sulphide or sulphide ore, huge quantity of jarosite is being released universally as solid residues. The jarosite mainly contains iron, sulphur, zinc, calcium, lead, cadmium and aluminium. Jarosite released from such industrial process is complex and its quality and quantity make the task more complex for safe disposal. Apart from water contamination, jarosite already accumulated and its increasing annual production is a major source of pollution for surrounding environment including soil, vegetation and aquatic life and hence its disposal leads to major concern because of the stringent environmental protection regulations. An attempt was made to evaluate the characteristics of Indian jarosite with an objectives to understand its potentials for recycling and utilising as raw materials for developing value added products. Sand and Coal Combustion Residues (CCRs) was used as an admixture to attain good workability and detoxify the toxic substance in the jarosite. Result revealed that jarosite is silty clay loam in texture having 63.48% silt sized and 32.35% clay sized particles. The particle size of jarosite (D90=16.21+/-0.20 microm) is finer than the CCRs (D90=19.72+/-0.18 microm). The jarosite is nonuniform in structure and shape as compared to the CCRs having spherical, hollow shaped and some of them are cenosphere in nature. The major mineral phase of jarosite is Potassium Iron Sulphate Hydroxide {KFe3(SO4)2(OH)6}and Iron Sulphate Hydrate {2 Fe2O3SO3 x 5 H2O}. In CCRs the dominant phases are quartz {SiO2}, mullite {3 Al2O3 x 2 SiO2} and hematite {Fe2O3}. The high electrical conductivity of jarosite (13.26+/-0.437 dS/m) indicates that the presence of cations and anions are predominant over CCRs (0.498+/-0.007 dS/m). The major portion of jarosite consists of iron (23.66+/-0.18%), sulphur (12.23+/-0.2%) and zinc (8.243+/-0.075%). But CCRs main constituents are silicon (27.41+/-0.74%), aluminium (15.167+/-0.376%) and iron (4.447+/-0.69%). The other constituents such as calcium, aluminium, silicon, lead, and manganese are also present in the range of 0.5 to 5%. Heavy metals such as copper, chromium, and cadmium are found higher in jarosite as compared to the CCRs. The statistically designed experimental trials revealed that the density, water absorption capacity and compressive strength of fired jarosite bricks are 1.51 gm/cm3, 17.46% and 43.4 kg/cm2 respectively with jarosite sand mixture in the ratio of 3:1 indicating the potentials in developing building materials.

Coal↗

PubMed2000

Osteoconduction at porous hydroxyapatite with various pore configurations.

To assess the histological response and the reinforcing effects of bone ingrowth within porous hydroxyapatite (HA) implants depending on pore geometry, four kinds of cylindrical-type with parallel linear pores phi50, 100, 300, 500 microm), one kind of sponge-type with irregular interconnecting pores (phi250 microm) and one cross-type with crossing linear pores (phi100 x 120 microm) of porous HA were prepared. Eighty-four rabbits were divided into six groups, and a 5 x 5 x 7 mm sized porous HA block was inserted through the medial cortical window of the proximal tibia. Histomorphological changes were examined using light and scanning electron microscopy. A biomechanical compression test was performed using material test machines. After implantation, the implants showed different histological changes depending on pore geometry. Active osteoconduction was also found in the phi50 microm sized cylindrical-type porous HA. Evidence of remodeling of new bone and bone marrow formation within porous HA was found in the larger cylindrical-types (phi300, 500 microm), and the sponge- and cross-types. The biomechanical test showed that the ultimate compressive strength increased significantly in the phi300 microm sized cylindrical-type, and in the sponge- and cross-types eight weeks after implantation. Porous HA with cylindrical pores could be a useful graft material due to its strength, osteoconductivity and the ease with which its pore geometry can be controlled.

Animals↗

PubMed2004

Effect of incadronate on corticosteroid-induced osteopenia in rats.

The effect of incadronate, a third-generation bisphosphonate, was evaluated in rats with corticosteroid-induced osteopenia. Male Wistar rats were treated with methylprednisolone acetate (1 mg/kg, s.c.) once daily, 3 days a week for 12 weeks. Other groups received simultaneous treatment with methylprednisolone acetate and incadronate (0.03, 0.3 or 3 mg/kg, p.o.); incadronate was given once daily, 6 days a week for 12 weeks. Bone mineral densities (BMDs) of the second lumbar (L2) vertebra as well as the ultimate compressive strength of the fifth lumbar (L5) vertebra decreased. Incadronate dose-dependently inhibited the loss of L2 BMDs and the decrease in strength of the L5 vertebrae. These results suggest that incadronate may be effective in treating osteopenia accompanying corticosteroid therapy.

Administration, Oral↗

PubMed2001

[Biomechanical evaluation of osteosynthesis with cannulated screws for Ponteau-Colles fractures in a bird model].

INTRODUCTION: The use of cannulated screw without protrusive head in Colles fractures could avoid some of the drawbacks of conventional pinning. In order to compare the mechanical resistance of Kirshner wires versus cannulated screws we designed a animal model of Colles fractures and tested three types of osteosynthesis: A: K-wires, B: Herbert cannulated screw, C: specific cannulated screws. METHOD: After creating a 10 mm defect in three sets of 10 fresh turkey tibia, 3 types of osteosynthesis were done and tested in compression with an Adamel Lhomargy machine: set A: K-wire fixation, set B: Herbert screws fixation and set C: specifics screws fixation. RESULTS: The compression strength needed for failure of the fixations were: for the K-wires (set A): 52 N +/- 17; for the Herbert screws (set B): 93 N +/- 39; for the specifics screws (set C): 160 N +/- 48; (p < 0.0001). DISCUSSION: The use of an animal model makes the experimentation easier and the sampling more homogeneous. In this model, resistance to compression of the cannulated screw was better than K-wires and the specific cannulated screw better than Herbert screw. Therefore clinical trial of osteosynthesis with cannulated screw in Colles fracture could be considered.

Animals↗