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PubMed2007

Environmental degradation of glass-ionomer cements: a depth-sensing microindentation study.

This study investigated the effects of various environmental conditions on the hardness and elastic modulus of restorative glass-ionomer cements (GICs). Two resin-modified GICs (RMGICs) (Fuji II LC [FL]; Photac-Fil Quick [PQ]) and three highly viscous GICs (HVGICs) (Fuji IX Fast [FN]; KetacMolar [KM]; KetacMolar Quick [KQ]) were evaluated in this study. Specimens were fabricated according to the manufacturers' instructions and stored under a variety of conditions (n = 7): 100% humidity, distilled water, pH 5 demineralization solution, and pH 7 remineralization solution. The hardness and elastic modulus were measured using a depth-sensing microindentation test after 4 weeks. The results were analyzed using the independent samples T-test and ANOVA/Scheffe's post hoc test (p < 0.05). HVGICs showed significantly higher hardness and elastic modulus than RMGICs under all storage conditions. Storage in distilled water significantly increased the hardness and elastic modulus of FN, but decreased that of PQ. All HVGICs and RMGICs stored in remineralization solution had hardness values and elastic moduli comparable to those stored in water. Compared to remineralization solution, demineralization solution had no significant effects on the modified GICs with the exception of KQ. The results suggest that the mechanical properties of glass-ionomer restoratives are material-type and storage condition dependent. Therefore, the clinical selection of a glass-ionomer material should be based on the oral environment to which it will be subjected.

Biodegradation, Environmental↗
PubMed2005

Firmness evaluation of melon using its vibration characteristic and finite element analysis.

The "Huang gua" melons were measured for their physical properties including firmness and static elastic modulus. The vibrational characteristics of fruits and vegetables are governed by their elastic modulus (firmness), mass, and geometry. Therefore, it is possible to evaluate firmness of fruits and vegetables based on their vibrational characteristics. Analysis of the vibration responses of a fruit is suggested for measuring elastic properties (Firmness) non-destructively. The impulse response method is often used to measure firmness of fruits. The fruit was excited using three types of balls (wooden, steel and rubber) and the vibration is detected by an accelerometer. The Instron device was used to measure the static elastic modulus of the inner, middle and outer portions of melon flesh. Finite element (FE) technique was used to determine the optimum excitation location of the chosen measurement sensor and to analyze the mode shape fruits. Four types of mode shapes (torsional or flexural mode shape, first-type, second-type spherical mode and breathing mode shape) were found. Finite element simulation results agreed well with experimental results. Correlation between the firmness and resonant frequency (r2=0.91) and between the resonant frequency and stiffness factor (r2=0.74) existed. The optimum location and suitable direction for excitation and response measurement on the fruit were suggested.

Cucurbitaceae↗
PubMed1999

Mechanical and morphological variation of the human lumbar vertebral cortical and trabecular bone.

The nanoindentation technique was used to characterize the variation in the elastic modulus and hardness of human lumbar vertebral cortical and trabecular bone. The elastic modulus (and in most cases, the hardness as well) of axially aligned trabeculae cut in the transverse direction was significantly greater than in other orientations of vertebral cortical and trabecular bone. In all cases, the elastic modulus and hardness of bone in the load-bearing direction was greater than in corresponding bone types cut in the other directions. Scanning electron micrographs of cortical shell revealed the Haversian-like canal systems expected in secondary cortical bone, but it was difficult to differentiate by morphology cortical from trabecular bone in the human lumbar vertebrae.

Aged↗
PubMed1981

Effect of beta-aminopropionitrile on the static elastic properties and blood pressure of spontaneously hypertensive rats.

The static elastic properties of the aorta ad systolic blood pressure in the caudal artery have been measured in 55 spontaneously hypertensive rats of the AS strain. Animals were divided into five groups and treated from the age of 4 to 12 weeks as follows: (1) 0.25 mm silver clip positioned around the right renal artery; (2) renal artery clipped as group (1) followed by daily injection of beta-aminopropionitrile fumarate (beta-APN); (3) daly injection of beta-APN without clipping; (4) daily injection of 0.09% saline; (5) untreated. Mean systolic blood pressures at 12 weeks of age were Group (1) 21.8; Group (2) 16.2; Group (3) 17.0; Group (4) 18.0; Group (5) 17.5 (units kPa). Thus, administration of beta-APN prevents the development of renal hypertension in clipped animals while producing no significant alteration in animals with intact renal arteries. At pressures within the physiological range the functional distensibility of all the treated animals was greater than that of the controls (pressure strain elastic modulus significantly lower). Similar changes were observed in the variation of structural distensibility (incremental elastic modulus) with pressure. At any level of total strain greater than 0.7 the incremental elastic modulus of both groups of animals treated with beta-APN was significantly less than control values. These observations are consistent with reports in the literature that administration of beta-APN causes a reduction in either the amount of cross-linked or normal scleroprotein in the aorta.

Aminopropionitrile↗
PubMed1995

The effect of two types of cross-linking on some mechanical properties of collagen.

Samples of collagen were cross-linked by two different methods: (a) glutaraldehyde and (b) a combination of dehydrothermal treatment and cyanamide. The elastic modulus, the ultimate tensile strength (fracture stress), strain to failure, work of fracture, and fracture toughness were measured before and after cross-linking in ambient laboratory conditions, and during immersion in water. These tests were all performed over a range of strain rates. For collagen tested in the wet condition, it was found that cross-linking increased the elastic modulus from approximately 25-30 MPa, to between 55 and 60 MPa, but there was little effect on fracture stress, and strain to failure was reduced. The work of fracture of the collagen decreased on cross-linking. Cross-linking had the same effect on the elastic modulus, fracture stress, and strain to failure of dry collagen, but the work of fracture was unaffected. In conclusion, cross-linking increased the elastic modulus, reduced the strain to failure, and had little effect on the fracture stress of collagen under the present experimental conditions.

Biocompatible Materials↗
PubMed1994

Load transmission through the callus site with external fixation systems: theoretical and experimental analysis.

The fracture callus contribution to the total rigidity of external fixator-fractured bone element was analysed. This study was achieved from both theoretical and experimental perspectives. The theoretical study was done using the finite element method with a three-dimensional model. In this model, both the callus and the development of its elastic characteristics were considered. A series of 38 New Zealand-California white rabbits with tibial fractures treated with some external fixation system was used in this study. Such devices could reproduce either rigid or elastic features. The frame dynamization can be obtained at different fracture healing stages. Animals were classified into four series: (1) rigid fixators, (2) dynamized fixators two weeks after surgery, (3) three weeks after surgery and (4) four weeks after surgery. Tension tests were performed to evaluate callus strength. Theoretical results showed significant levels of callus load transmission (85.5%) when the callus elastic modulus is 1/100 of the elastic modulus of intact bone in an external fixator with rigid features. Experimental analysis of the callus obtained with different external fixator systems did not show differences among them. This fact implies that the immature callus theoretically modelled (E = 100 N mm-2) appears early in the rabbit fracture model (before two weeks, when first dynamization was made), for this reason no differences were found between the two types of treatment (rigid and dynamized systems). This fact questions the reliability of the dynamization process in external fixation of fractures and it implies accurate investigations in the clinical field.

Animals↗
PubMed1995

Non-insulin-dependent diabetes mellitus and fasting glucose and insulin concentrations are associated with arterial stiffness indexes. The ARIC Study. Atherosclerosis Risk in Communities Study.

BACKGROUND: Cardiovascular diseases are the most common cause of disability and death among subjects with non-insulin-dependent diabetes mellitus (NIDDM). The atherosclerotic process begins during the prediabetic phase characterized by impaired glucose tolerance, hyperinsulinemia, and insulin resistance. In vitro studies have suggested that glucose and insulin can substantially alter the structure and function of the arterial wall and affect the development of atherosclerosis. METHODS AND RESULTS: We performed a cross-sectional study of the relation of arterial stiffness indexes with glucose tolerance and serum insulin concentrations. Several indexes of common carotid artery stiffness were assessed with noninvasive ultrasound methods in a biracial sample of 4701 men and women 45 to 64 years of age in the Atherosclerosis Risk in Communities (ARIC) Study. Arterial compliance (AC), stiffness index (SI), pressure-strain elastic modulus (Ep), and Young's elastic modulus (YEM) were calculated. YEM includes wall (intima-media) thickness and thus gives an estimate of arterial stiffness controlling for wall thickness. All indexes of arterial stiffness were higher with increasing concentrations of fasting glucose. This finding was consistent in both black and white examines and in both sexes. A 25% increase in fasting glucose (approximately 1 SD) was associated in nondiabetic white men with a 5.8% (95% CI, -9.6% to -1.9%; P = .004) decrease in AC and increases of 5.8% (95% CI, 2.0% to 9.7%; P = .002) in SI, 11.3% (95% CI, 6.9% to 15.9%; P < .001) in Ep, and 11.2% (95% CI, 6.2% to 16.6%; P < .001) in YEM. In nondiabetic white women, the corresponding predicted changes were a decrease of 15.0% (95% CI, -18.2% to -11.7%; P < .001) in AC and increases of 16.6% (95% CI, 12.5% to 20.8%; P < .001) in SI, 23.2% (95% CI, 18.4% to 28.2%; P < .001) in Ep, and 19.2% (95% CI, 14.0% to 24.7%; P < .001) in YEM. Glucose and insulin contributed synergistically to the increase in stiffness indexes. Insulin and triglycerides also had a synergistic association with stiffness indexes. CONCLUSIONS: Our findings are compatible with the view that persons with NIDDM or borderline glucose intolerance have stiffer arteries than their counterparts with normal glucose tolerance and that the decreased elasticity is independent of artery wall thickness. The joint effect of elevated glucose, insulin, and triglycerides can have a considerable impact on arterial stiffness and play an important role in the early pathophysiology of macrovascular disease in NIDDM.

Arteriosclerosis↗
PubMed2000

The effect of glass fibre-reinforcement on the transverse strength, deflection and modulus of elasticity of repaired acrylic resins.

AIM: To test the effect of reinforcement qualities of glass fibre in the repair of acrylic fractures. METHODS: Four types of heat-curing acrylic resin test specimens were fabricated. The bottom and sides of the specimens were placed in stone to form a repair template. Lines were drawn 3.5 mm on each side of the centring mark. The 45 degree-bevel joint margins were cut at these lines to simulate fracture and the centre section was discarded. A 1 mm gap was created between the margins before repair with autopolymerising acrylic resin with and without glass fibre. OUTCOME MEASURES: A three-point loading test was used to measure transverse strength, deflection and the modulus of elasticity of repaired acrylic resin joints. RESULTS: The transverse strength of acrylic resins was increased with fibres. CONCLUSION: Glass fibre-reinforcement significantly increased resistance to deflection and increased the modulus of elasticity.

Acrylic Resins↗
PubMed1993

Staging of patellar tendon autograft healing after posterior cruciate ligament reconstruction. A biomechanical and histological study in a sheep model.

The prerequisite for adequate rehabilitation after cruciate ligament reconstruction with a patellar tendon autograft is a thorough knowledge of the biologic healing processes. It is of interest to determine whether distinct phases similar to those in wound healing can be differentiated. It is also important to assess the magnitude of the biomechanical loading capacity and the duration of the healing processes. One posterior cruciate ligament in each of 48 skeletally mature sheep was replaced with a free patellar tendon autograft. Immediate rehabilitation without immobilization followed. Four phases of healing were demonstrated using the histologic condition of the autograft as a guide. The biomechanical data were correlated with the morphologic data. During the necrotic phase, a maximum of necrotic tissue was seen two weeks postoperatively. The strength of the graft is initially limited by the surgical fixation strength; however, later the intraarticular portion becomes the strength-limiting factor. During the revitalization phase, which is characterized by revascularization and proliferation of fibroblasts, and during the following phase, collagen formation, an increase in maximum stress is seen while the elastic modulus remains constant. Only in the remodeling phase is an increase in elastic modulus seen, owing to longitudinal alignment of the collagen bundles. One year after implantation, the autograft achieves approximately 50% of the material properties of the control. Even after two years, the autograft reaches only a maximum stress of 60% and an elastic modulus of 70% of the control. Ligamentization of the autograft could not be demonstrated in this study, but degeneration was seen in the core region of the graft during late remodeling.

Animals↗
PubMed2005

Preparation and characterization of ibuprofen pellets based on Eudragit RS PO and RL PO or their combination.

The aim of this study was to assess the application of Eudragit RL PO and RS PO and their combination for production of ibuprofen pellets by extrusion-spheronization. The pellets were prepared based on full factorial design. Independent variables were % ibuprofen (40, 60, 80), the ratio of Eudragit RS to Eudragit RL (1:0, 1:1, 0:1) and % PVP (1, 3, 5). The evaluated responses were mean dissolution time (MDT), crushing strength and elastic modulus of pellets. Surface characteristics, sphericity and aspect ratio of pellets were also evaluated. Linear regression and response surface modeling was used for analyzing results. It was shown that the amount of water required to prepare a proper wet mass was affected by composition of formulations. The required amount of water decreased with increasing drug load and percent of PVP. It was also shown that formulations containing Eudragit RL need more water. Increasing percent of PVP slightly decreased MDT and elastic modulus but had negligible effect on crushing strength. Increasing the percent of ibuprofen up to 60% decreased MDT but beyond that increased MDT. Increasing the percent of ibuprofen also decreased elastic modulus of pellets. Eudragit RL PO compare with Eudragit RS PO resulted in pellets with high crushing strength; however, Eudragit type did not have a significant effect on elastic modulus.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2004

Mechanical properties and function of the spinal pia mater.

OBJECT: The pia mater has received little attention regarding its function in the deformation of the spinal cord under compression. In this study the mechanical properties and function of the spinal pia mater were investigated using three methods. METHODS: Spinal cord segments were excised from rabbits. The elastic modulus of the pia mater was measured by performing a tensile test using specimens with the pia mater intact and ones with the pia mater stripped off. The stiffness of the spinal cord was examined by performing a compression test with specimens containing an intact pia mater and ones with a pia mater that was incised at both sides. The cross-sectional area and circumference of the spinal cord were measured on axial views of magnetic resonance images in patients with cervical disc herniations before and after surgery. The pia mater had an elastic modulus of 2300 kPa, which was 460 times higher than that of spinal cord parenchyma. By covering the parenchyma, it tripled the overall elastic modulus of the spinal cord. The pia mater increased the stiffness of the spinal cord and enhanced its shape recovery after removal of the compression. The cross-sectional area of the spinal cord increased after surgery, whereas the circumference of the spinal cord changed little. CONCLUSIONS: The pia mater firmly covers the spinal cord and has a high elastic modulus; it therefore provides a constraint on the spinal cord surface. It prevents elongation of the circumference and produces a large strain energy that is responsible for shape restoration following decompression.

Adult↗
PubMed1993

The effects of collagen fiber orientation, porosity, density, and mineralization on bovine cortical bone bending properties.

The relationship between the mechanical properties of bone in three-point bending and eight histocompositional variables was studied. Ultimate stress, ultimate strain, and elastic modulus were measured in 35 beams of cortical bone from bovine tibias using standard ASTM methods. Four elements of porosity were determined by point counting, mineralization by ashing, and wet and dry apparent density from weight and volume. Collagen fiber orientation was estimated using polarized light, and specimens were categorized as plexiform, mixed, or osteonal. Analysis of variance showed that ultimate stress was similar in the plexiform and osteonal specimens, but elastic modulus was reduced in the latter (18.6 +/- 1.2 vs 21.0 +/- 1.9 GPa), which were significantly less porous (by 24%) and less mineralized (by 3%) than the plexiform group. Stepwise multiple regression analysis showed that collagen fiber orientation ranked highly as a predictor of bending properties. The next best predictors were density and mineralization. In the plexiform group, 77% of the variability in elastic modulus was accounted for by wet and dry density and collagen fiber orientation. In the osteonal group, 88% of modulus variability was accounted for by percentage mineralization and collagen fiber orientation. When all the specimens were pooled, 62% of the variability in elastic modulus was attributable to variations in collagen fiber orientation, density, and porosity due to Haversian canals.

Animals↗
PubMed1991

Effect of stem modulus in a total hip arthroplasty model.

The purpose of this study was to determine the biological effects of the elastic modulus of the femoral stem in canine hip arthroplasty. Cementless total hip arthroplasty was performed in 12 dogs, six had a low elastic modulus polyacetal resin stem and six had a high modulus stainless steel stem. The components were otherwise similar. At six and 12 months after operation, radiographic and histomorphometric analysis showed that those with steel implants had more cortical porosity than did the other group (p less than 0.01). We suggest that the elastic modulus of the implant is an important factor in controlling cortical bone resorption. A low modulus femoral prosthesis can significantly decrease bone resorption which might otherwise eventually lead to implant failure.

Animals↗
PubMed1997

The characterization of broadband ultrasound attenuation and fractal analysis by biomechanical properties.

The purpose of this study was to show how the difference in structure affects the mechanical properties of bone and if BUA or fractal analysis is able to detect these changes in mechanical properties. A total of 38 cancellous bone cubes were obtained from seven bovine tibiae (32 specimens) and one human tibia (6 specimens). BUA was measured in the superior/inferior (SI), medial/lateral (ML), and anterior/posterior (AP) directions for each specimen. The fractal dimension was estimated by using the continuous alternating sequential filter (CASF) pyramid approach to handle fractal dimension estimation of small images. Nondestructive compressive tests were also performed in the three orthogonal directions for each sample. The correlations between BUA and density were statistically significant for all three directions. The correlation between BUA and elastic modulus varied depending on the direction in which the two parameters were measured. The best correlation was in the AP directions (r = 0.75, p < 0.0001), followed by the ML direction (r = 0.52, p = 0.0006), and finally the SI direction (r = 0.18, p = 0.28). The only significant correlation between fractal dimension and density was in the SI direction (r = 0.39, p = 0.015). There was significant correlation between fractal dimension and elastic modulus in all three directions, but the direction that exhibited the best correlation was the SI direction (r = 0.61, p < 0.0001). The correlation coefficients for the AP and ML directions were 0.45 (p = 0.0046) and 0.34 (p = 0.0377), respectively. A multivariate model, carried out to predict the elastic modulus from the BUA or fractal dimension including density, demonstrated that the correlation coefficient significantly increased in all three directions for BUA and fractal dimension. After adjustment for density, significant relationships between elastic modulus and BUA or fractal dimension were still found (p < 0.05).

Animals↗
PubMed2002

Experimental evaluation of a new layered prosthesis exhibiting a low tensile modulus of elasticity: long-term integration response within the rat abdominal wall.

The use of a new type of prosthesis, Bard Composix (BC), constructed of two layers of polypropylene mesh (PP) and one layer of expanded polytetrafluoroethylene (ePTFE), could provide a good solution for hernia repair when both minimal adhesions and maximum collagenous infiltration are necessary. We experimentally evaluated long-term stability of this composite. In 15 Sprague-Dawley rats, a full thickness defect was created in the anterior abdominal wall and repaired with BC. Studies were performed over implantation intervals of 2, 4, and 6 months in strips obtained from the prosthesis-host tissue interfaces. Light microscopy, environmental scanning electron microscopy (ESEM), immunohistochemistry, and tensiometry were used. Overall findings provide evidence that PP and ePTFE association renders the alloy well suited for hernia repair, promoting a robust and durable alloplast-soft tissue union. At all points studied, the patch was well tolerated and meshes did not shrink, come loose, or migrate. Neovascularization continued 6 months after implantation. Ex vivo mechanical characterization demonstrated that the primary advantage of the new device stems from a low modulus of elasticity, a property that can be exploited to enhance mechanical load transfer from prosthetic materials to the relatively frail surrounding tissues. After implantation, adequate tensile strength and a low modulus of elasticity were detected in the restored zone, conferring great adaptability to the abdominal wall. In conclusion, the BC layered prosthesis proved suitable for implantation in abdominal wall defects, exhibiting favorable biocompatibility and integration with minimal side effects.

Animals↗
PubMed1999

Inulin hydrogels as carriers for colonic drug targeting. Rheological characterization of the hydrogel formation and the hydrogel network.

Free radical polymerization converts aqueous solutions of methacrylated inulin into cross-linked hydrogels. The purpose of this work was to study the hydrogel formation and to characterize the fully cured hydrogels. The gelation process of aqueous solutions of methacrylated inulin was monitored as a function of time by means of linear oscillatory shear measurements, at a fixed frequency and amplitude. The fully cured inulin hydrogels were characterized by measurement of the frequency-dependency of the linear elastic modulus G'. The effects of the degree of substitution and feed concentration of methacrylated inulin on both the gelation kinetics and the rigidity of the obtained hydrogels were determined. The effect of the concentration of the initiators of the radical polymerization reaction has been studied as well. The weight fraction of polymer which was not incorporated in the hydrogel networks was determined using the anthrone reaction, and physical chain entanglements were determined by solution viscosity measurements. The gelation kinetics and the elastic modulus were proportional to the degree of substitution and feed concentration of methacrylated inulin. Increasing concentrations of radical-forming compounds also accelerated the hydrogel formation, but lowered the elastic modulus of the obtained hydrogels. The amount of polymer chains incorporated in the hydrogel network seemed to be especially influenced by the degree of substitution of the derivatized inulin, and for a feed concentration of 27% w/w of methacrylated inulin, entanglements have to be accounted for. The gelation kinetics and the elastic modulus of inulin hydrogels are not only affected by the degree of substitution and the feed concentration of methacrylated inulin, but also by the concentration of the initiators of the free radical polymerization reaction.

Algorithms↗
PubMed2001

Assessing modulus of elasticity of wood-fiber cement (WFC) sheets using nondestructive evaluation (NDE).

This study evaluates whether the mechanical properties of modulus of rupture (MOR) and modulus of elasticity (MOE) of wood-fiber cement (WFC) sheets are correlated with the nondestructive parameters of stress wave velocity and density of the material. Longitudinal stress wave technique was used to evaluate WFC nondestructively using a total of 117 specimens (measuring each 241 x 51 mm) obtained from 39 WFC sheets. The aim was to establish the correlation between dynamic versus static MOE of the material for predicting the actual mechanical property. Even though short dimension specimens were used, results obtained were encouraging. A correlation coefficient (R) of 0.828 was found when the static MOE of the material was used as a function of nondestructive parameters. A multivariate linear regression analysis using the specimen's density, wave velocity, and dynamic MOE provided the strongest correlation to the static MOE. The correlation observed for MOR as a function of static MOE is within the normal range obtained for wood composites. A nondestructive evaluation (NDE) using full size WFC sheets is recommended and can probably improve the relationship between the static and the predicted MOE.

Conservation of Natural Resources↗