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PubMed2005

Evaluation of biopolymer-modified concrete systems for disposal of cathode ray tube glass.

Cathode ray tubes (CRTs) from computer monitors and television sets, which contain significantly high percentage of lead (Pb) by weight, represent an enormous and growing hazardous waste problem in the United States and worldwide. As a result, new technologies are needed to cope with current CRT waste stream and increased hazard and build new markets for its recycled components, developing commercially viable concrete composites, as well as minimizing CRT disposal problems. In this study, commercially available biopolymers, such as xanthan gum, guar gum, and chitosan, were used to encapsulate CRT glass waste, reducing the Pb leachability. The biopolymers utilized contain a number of useful functional groups, such as carboxyl (xanthan), hydroxyl (guar), and amino groups (chitosan), which play important roles in binding and stabilizing Pb onto concrete structures. The use of biopolymers in concrete systems can create a stable interpenetrating cross-linking composite that will last for many years. Results from these new composites show 30% higher compressive strength than standard concrete and a sharp decrease in lead leachability from several thousand milligrams per liter initially to an amount of three-tenths milligrams per liter or lower values (much lower than the U.S. Environment Protection Agency standard for hazardous waste of 5 mg/L by the toxicity characteristic leaching procedure test), and for some of the composites leachability is below even the standard for drinking water. This efficient and cost-effective CRT-biopolymer-concrete composite is a new class of biopolymer-modified material that can potentially perform a significant role in relieving the current CRT issue.

Biopolymers↗

PubMed2005

Immune response and effect of adenovirus-mediated human BMP-2 gene transfer on the repair of segmental tibial bone defects in goats.

BACKGROUND: Tissue-engineered bone may be used for filling bone defects. There are, however, no reports on this technique used in large animals. METHODS: We evaluated the effectiveness of, and immune response in repairing diaphyseal bone defects by gene transfer using bone morphogenetic proteins (BMPs). We used adenovirus-mediated human BMP-2 (Adv-hBMP-2) gene-transduced bone marrow stromal cells (BMSCs) to repair 2.1-cm segmental tibial bone defects in goats (group I, n = 7). An Adv-ssgal-transduced BMSC group (group II, n = 5), a non-transduced BMSC group (group III, n = 5), and an untreated group (group IV, n = 2) were used as controls. Self-secreted extracellular matrix was used as cellular carrier. RESULTS: Radiographic and histomorphometric examination demonstrated more callus in the bone defects of group I compared to other groups. Week 24 after implantation, the defect healing rates of groups I, II, III, and IV were 6/7, 1/5, 2/5, and 0/2, respectively. The maximum compressive strength of new tissue in the bone defects of group I was higher than those of groups II and III. Temporary cellular and persistent humoral immune responses against adenovirus were detected after hBMP-2 gene transfer. INTERPRETATION: We found that Adv-hBMP-2 genetransduced BMSCs had superior osteoinductivity in the repair of tibial bone defects in goats, but it could cause temporary cellular and persistent humoral immune responses against adenovirus.

Adenoviridae↗

PubMed2005

Stabilization and solidification of waste phosphate sludge using portland cement and fly ash as cement substitute.

Stabilization and solidification of the waste phosphate sludge (WPS) using Portland cement (PC) and fly ash (FA) were studied in the present work. The WPS content in the cement mortars varied from 5% to 15%. Setting times were measured, and unconfined compressive strengths (UCS) were determined for the mortars cured in water for 3, 7, 28, 56, and 90 days. Zinc and nickel leaching of the solidified products were measured according to the Toxicity Characteristic Leaching Procedure. Setting times were extended as the WPS content in the paste samples increased. The UCS values of the mortar containing 5% WPS solidified by using 95% PC were similar to the reference sample. Use of 10% FA as cement substitute increased the UCS values by 10% at the end of curing period of 56 days. The WPS contained initially 130.2 mg L(-1) of zinc and 22.7 mg L(-1) of nickel. The zinc and nickel leached from the 5% WPS solidified by using 95% PC were measured as 3.8 mg L(-1) and 0.4 mg L(-1), respectively. These metal concentrations were below the limits given by the U.S. Environmental Protection Agency for landfilling the solidified wastes.

Carbon↗

PubMed2003

Fabrication and biocompatibility of collagen sponge reinforced with poly(glycolic acid) fiber.

This article describes an investigation of collagen sponge mechanically reinforced through the incorporation of poly(glycolic acid) (PGA) fiber. A collagen solution with PGA fiber homogeneously dispersed at collagen:PGA weight ratios of 1.5, 0.8, 0.4, and 0.2 was freeze-dried, followed by dehydrothermal cross-linking to obtain collagen sponges incorporating PGA fiber to various extents. By scanning electron microscopy observation, the collagen sponges exhibited isotropic and interconnected pore structures with an average size of 180 microm, irrespective of PGA fiber incorporation. As expected, PGA fiber incorporation enabled the collagen sponges to significantly enhance their compression strength. In vitro cell culture studies revealed that the number of L929 fibroblasts initially attached was significantly greater for any collagen sponge incorporating PGA fiber than for collagen sponge. The shrinkage of sponge after cell seeding was suppressed by fiber incorporation. It is possible that shrinkage suppression results in the superior cell attachment of sponge incorporating PGA fiber. After subcutaneous implantation into the backs of mice, the residual volume of collagen sponge incorporating PGA fiber was significant compared with that of collagen sponge and increased with a decrease in the collagen:PGA ratio. The greater number of cells infiltrated and deeper infiltration were observed for collagen sponge incorporating PGA fiber implanted subcutaneously. We conclude that the incorporation of PGA fiber is a simple and promising way to reinforce collagen sponge without impairing biocompatibility.

Animals↗

PubMedDate not supplied

Novel starch-based scaffolds for bone tissue engineering: cytotoxicity, cell culture, and protein expression.

Starch-based biomaterials and scaffolds have been proposed for several biomedical applications. In the present work new scaffolds based on a 50/50 (wt%) blend of corn starch/ethylene-vinyl alcohol (SEVA-C) were studied. These scaffolds were processed by a melt-based technology, which has been used before with other starch-based materials but never with SEVA-C. Scanning electron microscopy (SEM) observation showed that the developed porous structures were 60% porous with pore size between 200 and 900 microm and a reasonable degree of interconnectivity. Moreover, scaffolds presented a compressive modulus of 117.50 +/- 3.7 MPa and a compressive strength of 20.8 +/- 2.4 MPa. Cytotoxicity evaluation was performed according to ISO/EN 10993 part 5 guidelines, and revealed that the developed scaffolds were nontoxic and did not inhibit cell growth. Direct contact assays were also carried out by use of a cell line of human osteoblast-like cells (SaOS-2). Cells were seeded (3 x 10(5) per scaffold) and allowed to grow for 4 weeks at 37 degrees C, in a humidified atmosphere containing 5% CO(2). Total protein assay showed that the cells were able to grow for the 4 weeks of the experiment. These data were further confirmed by SEM. Moreover, a cell viability assay (MTS test) demonstrated that cells were perfectly viable after the 4 weeks of culture, showing the adequacy of the developed structure in supporting them. Finally, Western blot analysis revealed that osteopontin was being actively expressed by the cells, which, in association with collagen deposition observed by SEM, seems to indicate that bone extracellular matrix was being deposited. Consequently it is believed that starch-based scaffolds should be considered as an alternative for bone tissue-engineering applications in the near future.

Animals↗

PubMedDate not supplied

Intramuscular bone induction by the simultaneous administration of recombinant human bone morphogenetic protein 2 and bisphosphonate for autobone graft.

An ideal substitute for bone graft is autobone tissue, of which there is an ample supply of the required form and with vascularity. Our strategy is to generate intramuscular autogenous bone by administering recombinant human bone morphogenetic protein 2 (rhBMP-2) with beta-tricalcium phosphate (beta-TCP) as a carrier, and to transplant this bone as a muscle-pedicled autograft. However, in a previous study (Jingushi et al., J. Orthop. Sci. 7, 490, 2002), bone resorption occurred early after bone induction. This study was conducted to determine whether rhBMP-2-induced bone tissue could be maintained by simultaneous administration of bisphosphonate, and to investigate whether the induced bone could be used for bone grafting. In this study, we first applied rhBMP-2 alone to a beta-TCP disk and inoculated it into rat quadriceps muscle. Bone area and the number of tartrate-resistant acid phosphatase (TRAP)-positive cells in the induced bone disk peaked at 2 weeks, and induced bone resorption occurred later. Bisphosphonate and rhBMP-2 were then simultaneously applied to a beta-TCP disk and inoculated as in the first experiment. The addition of bisphosphonate decreased the number of TRAP-positive cells and increased the bone area and compression strength at 4 weeks. In the last experiment, a rhBMP-2 applied beta-TCP disk treated with or without bisphosphonate was free-grafted to parietal bone 4 weeks after inoculation. Both bone disks united similarly. We concluded that the concurrent use of bisphosphonate prevented bone absorption attributed to osteoclast activity after bone induction by rhBMP-2. The bisphosphonate application did not disturb the union of induced bone to host bone.

Animals↗

PubMed2004

Low-level exposure to cadmium during the lifetime increases the risk of osteoporosis and fractures of the lumbar spine in the elderly: studies on a rat model of human environmental exposure.

In this study, based on a rat model of human environmental exposure to cadmium (Cd), it has been examined whether low-level lifetime Cd exposure increases the risk of vertebral osteoporosis and vertebrae fractures in the elderly. For this purpose, the lumbar vertebral bodies (L4 or L3) of control and Cd-exposed (1 mg Cd/l in drinking water for 24 months) female Wistar rats were assigned to densitometric, radiographic, biomechanical (compression test), and biochemical studies, as well as to assess their dimensions and chemical composition. The exposure to Cd affected the mineral status of the L4. The decreased mineral content, density (BMD) and bone mineral area of the vertebral body together with the unchanged ratio of non-organic and organic components indicate osteoporotic nature of the Cd-induced changes. The activity of alkaline phosphatase in the L3 decreased. Cd also influenced the mechanical properties of the L4. The yield load and ultimate load decreased indicating a weakness in the vertebral body compression strength. Stiffness of the L4 decreased and the displacement at ultimate increased suggesting its enhanced susceptibility to deformities. Indeed, in the Cd group vertebral deformities (in 30% of females) or even fractures (in 40% of females), including those with disruption of bone continuity were evident. Z-score values for the L4 BMD revealed vertebral osteopenia in 30% and osteoporosis in 70% of the Cd-exposed females. The results allow for the conclusion that low lifetime exposure to Cd may become an important factor increasing the risk of lumbar spine osteoporosis with vertebral deformities and fractures in the elderly.

Alkaline Phosphatase↗

PubMed2002

Use of injectable calcium phosphate cement for fracture fixation: a review.

Injectable osteoconductive calcium phosphate cements have been introduced as an adjunct to internal fixation for treating selected fractures. These cements harden without producing much heat, develop compressive strength, and are remodeled slowly in vivo. The main purpose of the cement is to fill voids in metaphyseal bone, thereby reducing the need for bone graft, but cements also may improve the holding strength around metal devices in osteoporotic bone. Several bioactive cements are being developed. One of these cements, Skeletal Repair System, is available in Europe and has been approved by the United States Food and Drug Administration for use in selected distal radius fractures. Cadaveric studies have shown that using Skeletal Repair System cement with conventional metal fixation in certain fractures of the distal radius, tibial plateau, proximal femur, and calcaneus can produce better stability, stiffness, and strength than metal fixation alone. Early clinical results have shown reduced time to full weightbearing when cement has been used for augmentation of tibial plateau and calcaneal fractures, more rapid gain of strength and range of motion when used in distal radius fractures, and improved stability in certain hip fractures. Bioactive cements in general also may prove useful in vertebroplasty.

Animals↗

PubMed1990

Outer hair cell electromotility and otoacoustic emissions.

Outer hair cell electromotility is a rapid, force generating, length change in response to electrical stimulation. DC electrical pulses either elongate or shorten the cell and sinusoidal electrical stimulation results in mechanical oscillations at acoustic frequencies. The mechanism underlying outer hair cell electromotility is thought to be the origin of spontaneous otoacoustic emissions. The ability of the cell to change its length requires that it be mechanically flexible. At the same time the structural integrity of the organ of Corti requires that the cell possess considerable compressive rigidity along its major axis. Evolution appears to have arrived at novel solutions to the mechanical requirements imposed on the outer hair cell. Segregation of cytoskeletal elements in specific intracellular domains facilitates the rapid movements. Compressive strength is provided by a unique hydraulic skeleton in which a positive hydrostatic pressure in the cytoplasm stabilizes a flexible elastic cortex with circumferential tensile strength. Cell turgor is required in order that the pressure gradients associated with the electromotile response can be communicated to the ends of the cell. A loss in turgor leads to loss of outer hair cell electromotility. Concentrations of salicylate equivalent to those that abolish spontaneous otoacoustic emissions in patients weaken the outer hair cell's hydraulic skeleton. There is a significant diminution in the electromotile response associated with the loss in cell turgor. Aspirin's effect on outer hair cell electromotility attests to the role of the outer hair cell in generating otoacoustic emissions and demonstrates how their physiology can influence the propagation of otoacoustic emissions.

Animals↗

PubMed1991

Incorporation of simulated waste raffinates containing 134Cs into cement-clay matrices.

Simulated waste solutions containing 134Cs were incorporated into cement matrices at varying compositions and in the presence and absence of various additive materials. Montmorillonite and kaolinite clay minerals, in addition to sand, were added for improving the properties of the cement composites. The leachability of 134Cs was measured for different cement-clay mixtures. The effect of the presence of ions, such as borates, sulphate, and nitrates commonly found in waste raffinates, was also investigated. The results for compressive strength and leachability were explained in light of the effect of the presence of clay additives on cement matrices.

Aluminum Silicates↗

PubMedDate not supplied

The relation between bone mineral content, experimental compression fractures, and disc degeneration in lumbar vertebrae.

The bone mineral content and the ultimate compressive strength were determined in 109 fresh lumbar vertebrae from 36 different subjects, 31 to 79 years of age. The degree of macroscopic disc degeneration and the types of fracture were determined. Three types of fracture-central, wedge and transverse-were found, but only under magnification and at simultaneous movements of the fracture segment. The central type of fracture was found predominantly in specimens with high bone mineral content surrounded by normal discs. The wedge type of fracture was consistent with lower bone mineral content and more severe disc degeneration.

Adult↗

PubMedDate not supplied

Can the lumbar spine be crushed in heavy lifting?

Cadaveric lumbar intervertebral joints were wedged to simulate forward flexion and then compressed to failure. The compressive strengths of the young male specimens tested were compared with the forces calculated to act when average young men perform maximum lifts from the flexed posture. It is concluded that the spine has a considerable margin of safety when such lifts are performed.

Adult↗

PubMed1989

Regional variations in the compressive properties of lumbar vertebral trabeculae. Effects of disc degeneration.

The compressive mechanical properties of human lumbar vertebral trabeculae were examined on the basis of anatomic origin, bone density, and intervertebral disc properties. Trabecular bone compressive strength and stiffness increased with increasing bone density, the latter proportional to strength and stiffness to the one-half power. Regional variations within each segment were found, the most prevalent differences occurring in regions of bone overlying the disc nucleus in comparison with bone overlying the disc anulus. For normal discs, the ratio of strength of bone overlying the disc nucleus to bone overlying the disc anulus was 1.25, decreasing to 1.0 for moderately degenerated discs. These results suggest that an interdependency of trabecular bone properties and intervertebral disc properties may exist.

Aged↗

PubMed1994

A comprehensive study of physical parameters, biomechanical properties, and statistical correlations of iliac crest bone wedges used in spinal fusion surgery. II. Mechanical properties and correlation with physical parameters.

Iliac crest wedges have been the most frequently used bone graft in spinal fusion procedures since the 1970s. Physical parameters and correlations among physical parameters of allogeneic iliac crest wedges have been described in part I of this series. This article discusses the mechanical properties, as well as their correlations with physical parameters, of iliac crest wedges. A total of 250 frozen-thawed, freeze-dried, and rehydrated iliac crest wedges were used in this study. The axial load-bearing capacities for wedges in the three subgroups showed no statistically significant differences, however, rehydrated wedges appeared to have the greatest load bearing capacity and compressive strength. In addition, rehydrated wedges were more deformable than either the frozen-thawed or freeze-dried wedges. Based on biomechanical properties, it is suggested that rehydrated (1 hour in vacuo), or frozen-thawed iliac crest wedge should be used in spinal fusion procedures, and the direct clinical application of nonrehydrated freeze-dried wedges should be avoided.

Aging↗

PubMed1995

Evaluation of porous biphasic calcium phosphate ceramics for anterior cervical interbody fusion in a caprine model.

STUDY DESIGN: This study compared the efficacy of characterized 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics of 30%, 50%, and 70% porosity and autograft to promote interbody spinal fusion at C2-C3 and C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months. OBJECTIVES: Radiographs, histology, dual energy x-ray absorptiometry analysis, and biomechanical testing were used to evaluate the ability of the 30%, 50%, and 70% porous 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics and autograft to promote cervical interbody fusion. SUMMARY OF BACKGROUND DATA: The conundrum in the use of calcium phosphates for interbody fusion is what porosity is most effective to promote ingrowth yet strong enough to resist compressive stresses found in the spine? It is known that the ability for bone ingrowth increases and the compressive strength decreases as porosity of the ceramic is increased. Dense ceramics remain intact but may be surrounded by fibrous tissue. Porous ceramics have good ingrowth but may fracture. METHODS: Radiographs were evaluated for fusion and fracture or collapse of the ceramics or autograft. Dual energy x-ray absorptiometry was used to evaluate the fusion mass. Treated motion segments underwent biomechanical testing to quantify the flexibility of the segment. Undecalcified and decalcified histologic analysis were performed to evaluate the presence or absence of a bony union. RESULTS: Thirty percent, 50%, and 70% porous ceramics had better radiographic fusion scores than the autograft at 3 and 6 months. Incidence of ceramic fracture did not increase with porosity and was equivalent to the collapse of autograft, although ceramics maintained disc height when fracture occurred. No statistically significant differences were found between autograft and the porous ceramics with biomechanical testing and peri-implant bone mineral density values as measured by dual energy x-ray absorptiometry. At 3 months, histologic analysis showed a union rate of 0% for autograft and 30% porous ceramic, 67% for 50% porous ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate was 67% for the 30%, 50%, and 70% porous ceramics and 50% for autograft. CONCLUSIONS: Thirty percent, 50%, and 70% porous ceramics performed equal to or better than autogenous bone after 3 and 6 months. There may be promise for the use of 50/50 hydroxyapatite/beta-tricalcium phosphate in spine surgery as the need to harvest autograft from the iliac crest is obviated, and complications and cost associated with the harvest are avoided.

Animals↗

PubMed1997

Biomechanics of osteoporosis and vertebral fracture.

The ability of the spine to carry load depends on the structural capacity of the vertebrae and on the loading conditions that arise from activities of daily living or trauma. The ratio of the load on the spine to the failure load of the bone is called the factor of risk, a value that indicates whether fracture is likely during a given activity. A high factor of risk can result from weak bone that has a low failure load or from a risk activity that generates a large force. The failure load of the vertebral body depends on the density and architecture of the trabecular bone and on the shape, size, and organization of the vertebral body. Spine bone mineral density determined by dual-energy x-ray absorptiometry correlates strongly with the compressive failure load and therefore should be a convenient and specific indicator of the compressive strength of the vertebrae in vivo. The magnitude of a load applied to the spine depends on the specific activity. Bending and lifting activities generate loads on the spine that exceed the failure load of vertebrae with very low bone mineral density. Biomechanical indications for prevention of age-related fractures point to the need to strengthen bone by maintaining or increasing density and the need to lower the magnitude of forces applied to the spine in the elderly by avoiding such risk activities as lifting.

Aged↗

PubMed2001

Structural features and thickness of the vertebral cortex in the thoracolumbar spine.

STUDY DESIGN: The thickness and structure of the vertebral body cortex were examined from sections of human cadaveric vertebrae. OBJECTIVES: The objectives were to identify the principal structural features of the cortex, to directly measure the minimum and maximum thicknesses of the cortex in the thoracolumbar spine, and to compare regional variations in the structure of the cortex. SUMMARY OF BACKGROUND DATA: The thickness of the vertebral cortical shell contributes to the compressive strength of the vertebral body. There is little consensus concerning the thickness and morphology of vertebral shell and endplate along the spine in existing data. METHODS: Human T1, T5, T9, L1, and L5 vertebral bodies (mean age 70.4 years) from 20 cadaveric spines were sectioned and photographed. The minimum and maximum cortical thickness of the shells and endplates in the midsagittal plane were measured from magnified images. RESULTS: The anterior shell thickness was significantly greater than the posterior shell and both endplates. Endplate thickness was greatest in the lower lumbar vertebrae. There was a significant decrease in cortex thickness over the central portion of endplates and shells, with a mean minimum thickness of 0.40 mm and a mean maximum thickness of 0.86 mm, with an overall mean of 0.64 +/- 0.41 mm. Increased porosity was also observed along the central regions of the cortical shells. In the lower thoracic and lumbar spine, a double-layered endplate structure was observed. CONCLUSIONS: Invasive techniques provide the only means to directly resolve the thickness and distribution of bone in the vertebral cortex. The cortex thickness and structure varies along the endplates and the anterior and posterior surfaces of the vertebral body. The implications of the so called double-layered endplate structure are unknown, but indicate the need for further study.

Aged↗

PubMed2001

Evaluation of the effect of the residual bone angulation on implant-supported fixed prosthesis in mandibular posterior edentulism. Part II: 3-D finite element stress analysis.

Buccolingual angulation of the mandibular posterior edentulous region may affect the prosthetic load conditions, so as to cause high stress concentrated areas that may easily lead to failure. The aim of this study was to evaluate the effect of various predetermined buccolingual angulation values on stress distribution in the mandibular posterior edentulous region restored with implant-supported fixed partial dentures, using three-dimensional finite element analysis. Stress analyses were performed applying 400N oblique force to implant-supported fixed prosthesis. Stress analyses indicated tensile stress values on the buccal surface and compressive stress values on the lingual surface of cortical bone were increased as the angulation of the edentulous bone increased (especially corresponding to the cervical region of the implants). Compressive stress values, observed where two implants were placed at the second premolar and second molar regions (5-7 design) and first and second molar regions (6-7 design), respectively, were very close to or even exceeded the ultimate compressive strength of bone. It is concluded that when a definite buccolingual angulation is added to other existing risk factors such as bruxism, placing an implant for every missing tooth might reduce the high stress concentration areas.

Bicuspid↗