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At least 523 records · Page 29Linked to original sources

PubMed1994

Effects of pretwist on biomechanical properties of canine patellar tendon.

The purpose of this study was to measure the effect produced on canine patellar tendon of a 90 degree pretwist on the following mechanical properties: failure stress, failure strain, average elastic modulus, and strain energy density. Forty adult mongrel dog cadavers, killed for other studies, were used. Paired patellar tendons were isolated with patellar and tibial bone and the central 4.0-4.6 mm of tendon used for testing. Specimens were elongated to failure using a Materials Testing System (MTS). Only those paired specimens both failing in substance were analyzed. Eight paired specimens were analyzed, both with 0 degree twist, for right-left reproducibility. Thirty-two paired specimens were randomly assigned to four groups: right 0 degree/left 90 degree clockwise pretwist; right 0 degree/left 90 degree counterclockwise; left 0 degree/right 90 degree clockwise; left 0 degree/right 90 degree counterclockwise. No statistically significant differences were present between the paired untwisted specimens in any mechanical property. In the pretwisted specimens, there were statistically significant differences between the group left/clockwise and right/counterclockwise and the group left/counterclockwise and right/clockwise with respect to the mechanical properties failure stress, average elastic modulus, and strain energy density. No statistically significant differences were observed between the two groups for failure strain. For the canine patella-patellar tendon-tibia complex (PPTTC), the mechanical properties failure stress, average elastic modulus, and strain energy density are sensitive to both side (left/right) of PPTTC and direction (clockwise/counterclockwise) of pretwist. Pretwist of patellar tendon grafts in anterior cruciate ligament reconstruction may produce significant changes in their mechanical properties that vary with the direction of twist.

Animals↗

PubMed2003

A novel Doppler echocardiographic method of measuring the biophysical properties of the aorta in pediatric patients.

BACKGROUND: This study was performed to: (1) assess the feasibility of measuring pulse wave velocity (PWV) from aortic (AO) Doppler flow and deriving AO input and characteristic impedances and the arterial pressure strain elastic modulus; and (2) compare these indices in pediatric patients with arterial disease to control (C) patients. METHODS: There were 14 healthy children in the C group, 9 with inflammatory connective tissue diseases (ICTD), and 6 with Marfan syndrome (M). Using standard echocardiographic equipment, the AO annulus, AO root diameter in systole (AO(S)) and diastole (AO(D)), and AO length (L) were measured. The time taken for the Doppler signal to travel from the ascending to descending aorta was measured. AO peak flow was calculated from AO annulus cross-sectional area x peak aortic velocity (AoV); PWV = L/time taken for the Doppler signal to travel from the ascending to descending aorta; input impedance = (systolic - diastolic blood pressure)/(AO cross-sectional area x AoV); characteristic impedance = (PWV x rho)/Ao cross-sectional area (where rho = 1.06); and pressure strain elastic modulus = (systolic - diastolic blood pressure)/[(AO(S) - AO(D))/AO(D)]; beta index = ln (systolic/diastolic blood pressure)/[(AO(S) - AO(D))/AO(D)]. RESULTS: Results for PWV were ICTD = M > C (533, 496, 362 cm/s; P <.02); for input impedance were ICTD > M = C (245, 120, 116; P <.03); for characteristic impedance were ICTD < M = C (249, 107, 142; P <.05); for pressure strain elastic modulus were M > ICTD = C (262, 447, 187; P <.003); and for beta index were M > ICTD > C (2.91, 2.51, 2.13; P <.0006). CONCLUSIONS: This novel, relatively simple method of assessing the biophysical properties of the aorta shows abnormal function in patients with M and ICTD. This technique may be helpful in the long-term follow up of patients with arterial disease.

Adolescent↗

PubMed2001

Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain.

AIM: The aim of this study was to test the null hypothesis that sodium hypochlorite irrigation of root canals does not alter the properties of dentine and contribute to the weakening of root-treated teeth. METHODOLOGY: The effect of two concentrations (0.5%, 5.25%) of sodium hypochlorite (NaOCl) and saline on (i) the elastic modulus and flexural strength of machined dentine bars, and (ii) changes in strain of 'whole' extracted human teeth were evaluated. One hundred standardized plano-parallel dentine bars (> 11.7 x 0.8 x 0.8 mm) were randomly divided into the three groups, immersed for 2 h in the respective solutions and then subjected to a three-point bend test. Changes in strain of each of 10 teeth on cyclical nondestructive occlusal loading were measured using electrical resistance strain gauges bonded to the cervical aspects. Each tooth had its crown and enamel reduced and root canal prepared. These were irrigated sequentially in a series of four separate, 30-minute regimes; initial-saline, 0.5% NaOCl, 5.25% NaOCl and final-saline. The changes in strains after each irrigation regime were compared. RESULTS: There was a significant decrease in elastic modulus of the dentine bars immersed in 5.25% NaOCl compared with the saline group (P < 0.01). There was also a significant decrease in flexural strength of the dentine bars in the 5.25% NaOCl group compared to both the saline and 0.5% NaOCl groups (P < 0.01). The strain data from the nondestructive tooth loading tests revealed significant increases in tensile strain between the initial-saline and the final-saline stages (P < 0.01). Significant increases in compressive strains were also found between initial-saline and 5.25% NaOCl; and between 0.5% NaOCl and 5.25% NaOCl stages (P < 0.01). CONCLUSIONS: The null hypothesis was rejected, 5.25% NaOCl reduced the elastic modulus and flexural strength of dentine. Irrigation of root canals of single, mature rooted premolars with 5.25% NaOCl affected their properties sufficiently to alter their strain characteristics when no enamel was present.

Analysis of Variance↗

PubMed2006

Apparent Young's modulus of human radius using inverse finite-element method.

The ability to assess the elastic and failure properties of cortical bone at the radial diaphysis has a clinical importance. A new generation of quantitative ultrasound (QUS) devices and peripheral quantitative computed tomography (p-QCT) has been developed to assess non-invasively bone material and structural properties at the distal radius. This anatomical site is characterized by a thin cortical thickness that complicates traditional mechanical testing methods on specimens. Until now, mechanical properties of cortical bone at distal radius (e.g., elastic modulus, yield stress and strain) remain rarely studied probably due to experimental difficulties. The present study introduces an inverse finite-element method strategy to measure the elastic modulus and yield properties of human cortical specimens of the radial diaphysis. Twenty millimeter-thick portions of diaphysis were cut from 40 human radii (ages 45-90) for biomechanical test. Subsequently the same portion was modeled in order to obtain a specimen-specific three dimensional finite-element model (3D-FEM). Longitudinal elastic constants at the apparent level and stress characterizations were performed by coupling mechanical parameters with isotropic linear-elastic simulations. The results indicated that the mean apparent Young's modulus for radial cortical bone was 16 GPa (SD 1.8) and the yield stress was 153 MPa (SD 33). Breaking load was 12,946 N (SD 3644), cortical thickness 2.9 mm (SD 0.6), structural effective strain at the yield (epsilon(y)=0.0097) and failure (epsilon(u)=0.0154) load were also calculated. The 3D-FEM strategy described here may help to investigate bone mechanical properties when some difficulties arise from machining mechanical sample.

Aged↗

PubMed2006

Influence of elasticity on gap formation in a lining technique with flowable composite.

The purpose of this study was to investigate the effect of flowable composites as liners for direct composite restorations, with key focus on the elastic moduli of flowable and condensable composites. After treating the composite mold cavity surface with an adhesive system, one of the flowable composites was placed as a 1 mm-thick layer on the cavity floor and irradiated for 20 seconds. The rest of cavity was subsequently filled with a condensable composite and irradiated for 40 seconds. Gap formation at both interfaces--between the cavity floor and flowable composite, and between the flowable and condensable composites--was examined. No gaps were detected at the interface between the cavity floor and flowable composite. Gap percentage at the interface between the flowable and condensable composites was dependent on the difference in elastic modulus. It was concluded that flowable composite with high elastic modulus could inhibit gap formation between flowable and condensable composites.

Acrylic Resins↗

PubMed2003

Juniper wood as a possible implant material.

Natural materials, such as wood and bone, possess structures fulfilling the requirements of support and transport of nutrients. Similarity in function and properties provides inspiration for investigating the possible use of wood as an implant material. Juniperus communis wood is dense, durable, and strong and has naturally impregnated essential oils that display antiseptic properties. This study investigated the toxicity of the oil, the effect of sterilization on the mechanical properties of the wood, and bone attachment with animal studies. The possible toxicity of the oil was determined orally and by intravenous injection. At low concentrations, the dose that would be released by the wood in the body could be tolerated without any detrimental effects. Sterilization of the wood in boiling water lowered the elastic modulus and modulus of rupture to a level at which the elastic modulus could be better matched to bone. Wood shaped into the form of femoral implants were implanted into rabbits and displayed good acceptance by the body up to a period of 3 years, indicating bone apposition, abutment into pores, and growth into drilled cavities.

Animals↗

PubMed1983

Quantitative microradiography of cortical bone in disuse osteoporosis following fracture fixation.

Stainless steel (elastic modulus 210 GN/m2) and carbon fibre reinforced epoxy resin (elastic modulus 65 GN/m2) plates have been attached to intact femora in cats and the development of disuse osteoporosis assessed by microdensitometric methods after 8 months. The bone adjacent to the stainless steel plate showed evidence of considerable demineralization, both uniformly throughout a section and especially at certain focal points. A noticeable, but much smaller amount of osteoporosis developed adjacent to the composite plate. Various methods of presenting quantitative micro-densitometric data are used.

Animals↗

PubMed2000

A screening technique to study the mechanical strength of gelatin formulations.

A semiquantitative method for measuring the mechanical strength of gelatin ribbons was demonstrated using a universal tensile testing machine (Instron, model 1122). Molten gelatin formulations comprised of acid-bone gelatin, limed-hide gelatin, or their combinations were made, pored as gelatin films, and aged at 50% relative humidity (RH). Viscoelastic properties (mechanical strength) of five gelatin formulations were evaluated by determining elastic modulus, tensile strength, and ratio of tensile strength to elastic modulus of gelatin ribbons. This study demonstrated that a 3:1 ratio of acid-bone to limed-hide gelatin combination showed better viscoelastic properties than the other formulations studied.

Chemistry, Pharmaceutical↗

PubMed1994

[Cardiovascular physiology. Elasticity and viscoelasticity of the circulatory system. I. Physical basis. II. Arteries].

The vascular walls and the myocardium have the mechanical behaviour of viscoelastic materials. This paper consists in the first two parts of a review on elasticity and viscoelasticity in the circulatory system. The main elastic and viscoelastic properties of the arterial walls and some of its consequences are studied and some of its quantification theories are exposed, proceeded by the Physical and Biophysical basis necessary to the understanding of phenomena concerned in the totality of the work. Arterial stress and strain are analysed and the notions of arterial static elastic modulus, stiffness or elastance and compliance or capacitance such as the concepts of dynamic or viscoelastic modulus and stiffness are developed. Creep, stress relaxation, histeresis and pulse waves dispersion and atenuation effects are described.

Arteries↗

PubMed1982

Experimental determination of whole long bone sectional properties.

A strain gage based experimental method is presented which provides an alternative to use of area sectional properties for obtaining the cross sectional centroids, flexural rigidities and axial stiffness of whole bone specimens. While area sectional property computations require detailed records on the geometry of cross sections, the experimental method presented here requires only gage locations plus the applied loads and recorded strains. Both techniques are used to analyze the midshaft sectional properties of canine radii. The results demonstrate the advantage of the experimental method for the analysis of heterogeneous cross sections with an unknown distribution of bone elastic modulus. By applying the experimental and area methods together, effective elastic modulus values for the sections were obtained.

Animals↗

PubMed2002

Quantitative elasticity imaging: what can and cannot be inferred from strain images.

We examine the inverse problem associated with quantitative elastic modulus imaging: given the equilibrium strain field in a 2D incompressible elastic material, determine the elastic stiffness (shear modulus). We show analytically that a direct formulation of the inverse problem has no unique solution unless stiffness information is known a priori on a sufficient portion of the boundary. This implies that relative stiffness images constructed on the assumption of constant boundary stiffness are in error, unless the stiffness is truly constant on the boundary. We show further that using displacement boundary conditions in the forward incompressible elasticity problem leads to a nonunique inverse problem. Indeed, we give examples in which exactly the same strain field results from different elastic modulus distributions under displacement boundary conditions. We also show that knowing the stress on the boundary can, in certain configurations, lead to a well-posed inverse problem for the elastic stiffness. These results indicate what data must be taken if the elastic modulus is to be reconstructed reliably and quantitatively from a strain image.

Computer Simulation↗

PubMed1995

Effect of lipopolysaccharide, leukocytes, and monoclonal anti-lipid A antibodies on erythrocyte membrane elastance.

The micropipette aspiration technique was used to quantify membrane deformability of individual red blood cells (RBCs) before and after exposing whole blood and blood free of leukocytes to lipopolysaccharide (LPS). The ability of an anti-lipid A monoclonal antibody (E5) to inhibit the effects of LPS was also investigated. In the LPS/whole blood studies, a significant increase in elasticity modulus was observed following incubation with LPS. An increase in elasticity modulus indicates a decrease in RBC membrane deformability. The effect depended on the incubation time but was not concentration-dependent in the range studied (25, 40, or 170 micrograms/mL). When incubating blood free of leukocytes with LPS, the elasticity moduli of erythrocytes did not change. Results also showed that preincubation of the LPS with E5 prior to incubation with whole blood partially inhibited the effect of LPS, suggesting a possible mechanism of the beneficial actions of monoclonal antibodies in septic shock.

Animals↗

PubMed1986

The ciliary body in accommodation.

The ciliary muscle ring contracts about 0.8 mm in radius during maximum accommodation and this change in radius does not significantly alter as the eye ages between 15 and 45 years. Despite this constant movement of the ciliary muscle ring, the force of contraction steadily increases over the same age period from 0.8 to 1.2 gms. The force of contraction of the ciliary muscle per dioptre--the myodioptre--changes both during the act of accommodation and as the eye ages. In the first case as the amplitude of accommodation increases, the myodioptre also increases in direct proportion to the amplitude. In the second case, as the eye ages an additional increase occurs at all amplitudes of accommodation. This increase is initially quite small but between the ages of 40 and 45 it becomes very much greater. As age advances this increased force of contraction is matched by a decrease in movement of the equator of the lens so that the zonule which is attached to both the ciliary body and the lens becomes increasingly stretched during accommodation and so can transmit the increased force of contraction. The zonular fibres between the ages of 15 and 45 do not appear to change in their extensile properties so the elasticity modulus remains constant with a value of 3.5 X 10(5)Nm-2. This Young's modulus is some 10 to 900 times less than the elasticity modulus respectively of lens capsule or tendon collagen but almost the same as aortic elastin.

Accommodation, Ocular↗

PubMed1992

The effect of elastic compression on the venous tone in patients with varicose veins.

The long term effect of elastic compression, with an emphasis on the changes in venous wall elasticity, was studied in 10 limbs with varicose veins. By simultaneously measuring venous volume, using the air plethysmograph (APG), and venous pressure, while the venous outflow was occluded, the pressure/volume (P/V) relationship of the venous system of the leg could be studied and the elastic modulus calculated. These measurements were performed prior to the application of elastic stockings and 6 weeks later, one day after the stockings had been removed. Statistically significant improvements were noted in the APG parameters studied and in the P/V curve derived elastic modulus calculations. The limbs could be divided into two groups based on the response of the P/V curves to elastic stockings and the severity of disease. Those limbs with milder disease tended to shift their P/V curves downward and to the right after compression (giving them a more normal pattern). Limbs with more severe disease showed evidence of a similar pattern of improvement at low but not at high venous pressures.

Bandages↗

PubMed1997

Microstructure and micromechanical properties of the mid-diaphyses of human fetal femurs.

The microstructure, composition and the micromechanical properties across the thickness of femoral mid-diaphyses from 14 to 26 week human fetuses have been investigated. Scanning electron microscopy and transmission electron microscopy were employed to examine structural changes with maturation. The fetal bones consist of layers of woven bone. From young to old fetuses and from outer to inner bone layers, the collagen fibrils become more cross-linked, densely packed and change from disordered to an ordered arrangement. The collagen fibril bundles are also more preferentially oriented and change from a chiefly circumferential to longitudinal direction. The sizes of the apatite crystals also increase with age. The Ca/P ratio remains constant around 1.55 for all the bone layers except the outmost layer which is lower than 1.2. An nano-indenter was used to evaluate the microhardness and elastic modulus of each bone layer. The increase of microhardness and elastic modulus correlates with the maturation of bone. The mechanical properties of the mid-diaphyses of human fetal femurs are anisotropic, which is due to the preferential orientation of collagen fibrils.

Collagen↗

PubMed1976

Elastic behavior of brain tissue in vivo.

A measurement system and a test sequence have been developed to determine the in vivo elastic response of brain tissue in terms of a pressure-depth ratio. This parameter appears sensitive to changes in the tissue environment that may occur due to the influence of, e.g., anesthetic agents, hyperventilation, etc., and thus may be useful in evaluating such influences. The measurements are made with the dura-arachnoid membranes intact, thus maintaining the influence of the cerebrospinal fluid compartment on the response behavior of the brain tissue that comprises the subpial region. As an integral part of the test, the procedure also serves to determine the depth or position of the subpial region and thus assures that the subsequent pressure-depth measurements invole brain tissue response. Finally, some discussion is given to relating the measured pressure-depth ratio to the classical elastic modulus. Values of the pressure-depth ratio and the corresponding elastic modulus for seven dogs are given.

Animals↗

PubMed2003

Influence of regular exercise on age-related changes in arterial elasticity: mechanistic insights from wall compositions in rat aorta.

Arterial stiffness increases with age in healthy sedentary adults. We previously reported that the age-related increases in arterial stiffness are absent or attenuated in regularly exercising adults. However, the mechanism underlying this training effect is unknown. One possibility is that regular exercise minimizes age-related changes in the arterial wall composition of elastin and collagen. To gain insight into this issue, we studied four groups of rats (N = 23): young (42-46 wks) and old (80-84 wks), sedentary and exercise-trained. The exercise group swam 1 hr.d-1, 6 d.wk-1 for 17-21 weeks. There was no significant difference in the incremental elastic modulus between young sedentary and exercise-trained rats. The elastic moduli of the old exercise-trained rats were 31% lower than in the old sedentary controls. As such, the magnitude of age-related increase in the elastic modulus was smaller in the exercise-trained (110%) vs. the sedentary group (151%) (p < 0.05). In both activity groups, elastin content was lower and collagen content was higher in old vs. young rats (p < 0.05). However, there were no significant differences between the two activity groups. These results are not consistent with the hypothesis that regular physical exercise minimizes age-related compositional changes in the arterial wall and attenuates the age-related increase in arterial stiffness.

Animals↗

PubMed2004

Correlates of carotid artery stiffness in young adults: The Bogalusa Heart Study.

Decreased arterial elasticity, an independent risk factor for cardiovascular (C-V) disease, is associated with C-V risk factors in middle-aged and older individuals. However, information is limited in this regard in young adults. This aspect was examined in a community-based sample of 516 black and white subjects aged 25-38 years (71% white, 39% male). The common carotid artery elasticity was measured from M-mode ultrasonography as Peterson's elastic modulus (Ep) and relative wall thickness-adjusted Young's elastic modulus (YEM). Blacks and males had higher Ep (P < 0.05); males had higher YEM (P < 0.0001); and blacks had higher wall thickness (P < 0.01). For the entire sample adjusted for race and gender both Ep and YEM correlated significantly (P < 0.05-0.0001) with age, BMI, waist, systolic and diastolic blood pressures, heart rate, product of heart rate and pulse pressure, triglycerides, total cholesterol to HDL cholesterol ratio, insulin and glucose. In a multivariate regression model that included hemodynamic variables, systolic blood pressure, product of heart rate and pulse pressure, age, triglycerides, BMI, and male gender (for YEM only) were independent correlates of Ep (R2 = 0.38) and YEM (R2 = 0.25). When the hemodynamic variables were excluded from the model, age, triglycerides, BMI, black race (Ep only), male gender, parental history of hypertension, HDL cholesterol (inverse association), and insulin (marginal significance) remained independent correlates of Ep (R2 = 0.20) and YEM (R2 = 16). Both Ep and YEM increased (P for trend P < 0.0001) with increasing number of independent continuous risk factors (defined as values above or below the age, race, and gender-specific extreme quintiles) that were retained in the regression models. The observed increasing arterial stiffness (or decreased elasticity) with increasing number of risk factors related to insulin resistance syndrome in free-living, asymptomatic young adults has important implications for prevention.

Adult↗