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Results for “Elastic Modulus”

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PubMedDate not supplied

Scarless skin repair in immunodeficient mice.

Scarring, the end result of the wound healing process in adult mammals, is a problem of significant clinical importance. We observed that athymic nude-nu mice, similar to mammalian fetuses, are able to restore the structure and integrity of injured skin through a process resembling regeneration, where scar formation is absent. Among the postinjured skin tissues collected from athymic nude-nu, wild-type controls (C57BL/6J), severe-combined immunodeficient, Rag (lack of B and T cells), athymic (thymectomized neonates and adult C57BL/6J), and mice treated with an immunosuppressant (cyclosporin A), only athymic nude-nu mice showed: a lack of scar by histological examination (hematoxylin & eosin and Masson's trichrome staining), low levels of collagen (as determined by hydroxyproline content), high levels of hyaluronic acid, a statistically significant increase in elastic modulus for injured samples over unwounded (biomechanical testing) and low levels of the pro-scarring cytokines platelet-derived growth factor-B and transforming growth factor beta1. Additionally, immunohistochemical and Western blot analyses of postinjured tissues as well as flow cytometry analysis of blood samples showed the presence of CD8-positive cells in all studied animals except nude-nu mice. We conclude that scarless skin healing in athymic nude-nu mice provides a new model to study the influence of the immune system on tissue regeneration.

Animals↗

PubMed1992

Influence of tempering method on residual stress in dental porcelain.

The porcelain component of a porcelain-fused-to-metal restoration is strengthened by residual (tempering) stresses which are induced by cooling procedures followed in dental laboratories. The thermophysical properties of materials and cooling rate are the main factors which determine the residual stress. In this paper, the temperatures in the midplane of body-porcelain disks were measured from a heat-soak temperature (1000 degrees C) to room temperature during two different cooling procedures: slow cooling in air and forced-air cooling. Experimental results approximated exponential cooling wherein the cooling rates could be represented by a linear equation of temperature. Residual stresses, as affected by the tempering method and thickness of a porcelain disk, were calculated by computer simulation for regions away from the edges. The following temperature-dependent factors were incorporated into the simulation: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling rate dependencies of the glass transition temperature and the temperature distribution during cooling were also included. The cooling rates used in this simulation were derived from the tempering data. The agreement between development of transient and residual stresses--calculated by computer simulation for various cooling methods, and the tendency toward failures of porcelain disks subjected to the tempering processes--was examined. Simulated residual stresses were also in good agreement with those measured by the indentation fracture method of Marshall and Lawn (1977) and Anusavice et al. (1989).

Computer Simulation↗

PubMed2002

Aortic distensibility after aortic root replacement assessed with cardiovascular magnetic resonance.

BACKGROUND AND AIM OF THE STUDY: The changes in geometry of the aortic root during the cardiac cycle are thought to be essential for optimal valve function, both in terms of leaflet stress and dynamic behavior. Using cardiac magnetic resonance (CMR), the study aim was to determine aortic root distensibility of the homograft (group H) and the Medtronic Freestyle xenograft (group F) after aortic root replacement, from a prospective randomized trial. METHODS: CMR was performed in 15 patients (six homografts, nine Freestyle) at six months and one year after surgery. Percentage change in aortic radius (PCR) and pressure strain elastic modulus (PSEM) were measured as indices of distensibility, and results related to left ventricular mass (LVM). RESULTS: At six months after surgery, mean PCR was 12+/-2.5 in group H and 12.9+/-6.1 in group F (p = NS), and PSEM was 428.5+/-69.8 and 493.5+/-72.7 g/cm2, respectively (p = NS). PCR was reduced to 10+/-1.7% in group H, and by 8.5+/-2.8% in group F (p = NS), while PSEM was increased to 520.5+/-87.3 and 825+/-420.4, respectively (p = NS) at the one-year follow up. Regression analysis showed a correlation between PCR and LVM (r = 0.52, p = 0.08) and LVM index (r = 0.46, p = 0.14), respectively. In addition, there was a relationship between PSEM, LVM and LVM index, suggesting that the stiffer the root wall, the higher the postoperative LVM. CONCLUSION: Up to one year after aortic root replacement, the wall of both the allogenic and xenogenic valves retained near-normal distensibility. For the first time, a correlation was demonstrated between the elastic properties of the aortic root and LVM. The longer-term behavior and clinical implications of these findings require further investigation.

Aged↗

PubMed2004

Hyaluronic-acid-based semi-interpenetrating materials.

In order to enhance the mechanical performances of hyaluronic acid (HA) without compromising its biological activity, HA has been interpenetrating with a fibrillar collagen scaffold. The semi-interpenetrating materials were obtained by mixing HA with different molecular weight and a pepsin-solubilized collagen (atelocollagen) solution, and then by inducing collagen fibrillogenesis. Results indicate that molecular weight of HA significantly influences the mechanical properties of the semi-interpenetrating materials and more specifically stronger material results from the use of low-molecular-weight (LMW) HA. According to the dynamic mechanical data the composite collagen-LMW HA has a higher elastic modulus than collagen, whereas the opposite is true for the high-molecular-weight (HMW) HA. This result highlights the role of specific interactions that occur between collagen and HA during the gel formation in controlling the network mechanical stability. LMW HA may, probably, interact more strongly with collagen during the fibrillogenesis process than HMW HA due to the higher mobility of the chains and the weaker homologous interactions. Moreover, morphological observations showed that LMW HA is intimately interdispersed within the collagen network and completely coated the fibrils, which act as mechanical support.

Biocompatible Materials↗

PubMed1982

Biomechanical study on aging changes and vasospasm of human cerebral arteries.

Mechanical properties of human intracranial arteries were studied with regard to their aging changes as well as cerebral vasospasm. There exists a considerable difference in the development of sclerosis between the intracranial and the extracranial arteries. Intracranial arteries are already stiff at birth and become stiffer with age. Their increase in stiffness is attributable to the marked thickening of their walls, which compensates for the decrease of their elastic modulus with age. The pressure-diameter curve of the intracranial vertebral arteries subjected to subarachnoid hemorrhage is biphasic and has a sharp flexion at the pressure of 180 mmHg when their smooth muscle is activated. Pressure elevation yields little change of diameter in the strongly constricted vessel up to the pressure level at the flexion point, above which the constriction is released abruptly. The existence of flexion point at a high pressure level is an important mechanical feature in considering the development of cerebral ischemia produced by the vasospasm.

Adult↗

PubMedDate not supplied

Quantitative measurement of wound spreading in radial keratotomy.

BACKGROUND: Many studies of radial keratotomy have been performed, however quantitative laboratory evaluation of the biomechanics of this procedure is still incomplete. Furthermore, most measurements of strain in the past have utilized strip testing, thus destroying the normal physiological structure and water balance of the cornea. METHODS: We report on a membrane inflation method of wound spreading in intact human corneas using the Baribeau Micronscope. RESULTS: We measured a secant elastic modulus of 7.58 x 10(6) N/m2 between 25 and 100 mm Hg. The spreading of radial keratotomy incisions as a function of intraocular pressure showed a maximum spreading of approximately 50 mu at 25 mm Hg at a radius of 3.50 mm from the optical center. A slight increase in spreading was observed in proceeding from a single to four radial incisions. CONCLUSIONS: Quantitative measurement of wound spreading is an important parameter of radial keratotomy and can provide important information regarding opposing theories of the biomechanics of this operation.

Biomechanical Phenomena↗

PubMed1990

Biomechanical properties of canine vertebral and internal carotid arteries.

In order to understand the participation of the geometrical and elastic properties of the large cerebral arteries in the maintenance of brain circulatory homeostasis, biomechanical properties of isolated internal carotid artery (extracranial part) and vertebral artery (intrathoracic part) were investigated both in a relaxed and in an activated (3x 10(-6) mol.l-1 norepinephrine) state of the smooth muscle. Quasi-static large deformation mechanical test was carried out by means of changing the intraluminal pressure slowly (2.5 mmHg.sec-1) and cyclicly in a range of 0-250 mmHg at in vivo length while external diameter was recorded continuously as a function of the intraluminal pressure. Maximum active tangential strain was found to be -2.7 +/- 1.6% at 70 mmHg for the internal carotid artery, and -5.9 +/- 1.1% at 100 mmHg for the vertebral artery. Incremental elastic modulus decreased and distensibility increased in both arteries following smooth muscle activation, these alterations, however, were larger in the case of the vertebral artery. A U-shaped characteristic impedance of vertebral artery was found both in relaxed and in constricted states of this vessel. Minimum values for the relaxed and the activated segments were found at 90 mmHg and 120 mmHg, respectively. These results support the hypothesis that certain biomechanical properties of the large arteries, like impedance, can be regarded as controlled variables that may contribute to the optimization of circulatory functions.

Animals↗

PubMed1979

[Mechanical behavior of the subchondral bone in the experimentally induced osteoarthritis].

In order to evaluate the role of the subchondral bone (cancellous bone) in the development and progression of the joint degeneration, osteoarthritis of the knee joint was produced experimentally in the rabbits and viscoelasticity and strength of the subchondral bone from the femoral medial condyle have been investigated along with the pathological, histological study of the joint. The viscoelastic spectrometer and the Instron type testing machine were used. As the first change after operation, osteophyte formation around the joint margin has been observed before the initiation of the degeneration of articular cartilage and there is a possibility that mechanical properties of subchondral bone such as high deformability and low elasticity to the mechanism of osteophyte formation. Subchondral bone softening with marked increase of ultimate strain and phase lag, marked decrease of compressive elastic modulus and ultimate stress precedes or occurs concurrently with the degeneration of the articular cartilage. These facts indicate the relationship between the mechanical properties of the subchondral bone and joint degeneration. Once the joint degeneration starts, degeneration continues progressively while the subchondral bone tends to become brittle. These changes may be considered as a kind of functional adaptation to the damage or denudation of articular cartilage. It is postulated that some architectural changes of the subchondral bone may provide alterations of the mechanical properties. Biomechanical roles of the subchondral bone is suggested as one of the factors in the joint degeneration.

Animals↗

PubMed2003

Effect of atropine on the biomechanical properties of the oesophageal wall in humans.

Recently, we reported a novel ultrasound technique to assess biomechanical properties of the oesophagus in human subjects. In the present study, we use the technique, in combination with atropine, to determine the active and passive biomechanical properties of the oesophagus in normal healthy humans. A manometric catheter equipped with a high-compliance bag and a high-frequency intraluminal ultrasonography probe was used to record pressure and oesophageal geometry. Oesophageal distensions with either isovolumic (5-20 ml water) or with isobaric (10-60 mmHg) technique were performed. Intra-bag pressure and ultrasound images of the oesophagus were recorded simultaneously. Following injection of atropine (15 microg kg-1, I.V.), the oesophageal distensions were repeated. The oesophageal wall compliance, circumferential wall tension, stress, strain and elastic modulus were calculated. Atropine resulted in an increase in the oesophageal wall compliance during isobaric distension, but no change in compliance was observed during isovolumic distension. The stress-strain relationship was found to be linear during both types of distension, before as well as after atropine. The Young's modulus, which is the slope of a linear stress-strain relationship, was significantly higher after atropine in the isovolumic study but not in the isobaric study. The stress-strain relationship of the active component (muscle contraction) was different during isovolumic and isobaric distensions but the passive components were similar. The passive and active stress-strain relationships of the human oesophagus resemble those of other soft biological tissues. Furthermore, the method of oesophageal distension has significant influence on the active but not the passive biomechanical properties due to a strain-rate effect.

Adult↗

PubMed2001

Application of scanning acoustic microscopy for assessing stress distribution in atherosclerotic plaque.

Scanning acoustic microscopy (SAM) was equipped to assess the acoustic properties of normal and atherosclerotic coronary arteries. The SAM image in the atherosclerotic lesion clearly demonstrated that the sound speed was higher than that in the normal intima, and that the variation of elasticity was found within the fibrous cap of the plaque. Young's elastic modulus of each region was calculated and the finite element analysis was applied to derive the stress distribution in these arterial walls. In a case of normal coronary artery, the stress was dominant in the intima and the distribution was rather homogeneous and in a case of atherosclerosis, high stress was concentrated to the relatively soft lesion in the fibrous cap overlying lipid pool. SAM provides information on the physical properties, which cannot be obtained by the optical microscope. The results would help in understanding the pathological features of atherosclerosis.

Acoustics↗

PubMedDate not supplied

Aortic calcification produced by vitamin D3 plus nicotine.

Calcification of the elastic arteries of the young rat by treatment with vitamin D and nicotine (VDN) has been proposed as an animal model of arterial calcification associated with age and age-related vascular pathology in man. The calcium-binding protein, S-100, which is found in human atherosclerotic lesions was associated with medial calcification of the aorta in VDN rats, especially in cases of severe calcification. Calcification (total calcium content: 366 +/- 87, n = 12 in VDN vs. 24 +/- 2 micromol g(-1) aortic dry weight in controls, n = 13) involved elastocalcinosis leading to elastolysis as revealed by a fall in the amount of desmosine and isodesmosine in the aortic wall (266 +/- 17 and 254 +/- 15 in VDN vs. 655 +/- 56 and 588 +/- 30 microg g(-1) aortic dry weight in controls). The decrease in elastin was associated with an increase in the stiffness of the aortic wall (elastic modulus: 15.1 +/- 1.8 in VDN vs. 6.7 +/- 0.5 10(6) dyn cm(-2) in controls), an increase in end-systolic stress (central systolic aortic pressure: 152 +/- 6 in VDN vs. 136 +/- 2 mm Hg in controls) (at a normotensive mean pressure level) and left ventricular hypertrophy (heart weight/body weight 2.51 +/- 0.10 in VDN vs. 2.24 +/- 0.07 g kg(-1) in controls). In conclusion, the mechanisms and consequences of aortic calcification in VDN show several similarities with calcification occurring in human athero- and arteriosclerosis.

Anesthesia↗

PubMedDate not supplied

Effects of secondary curing on indirect posterior composite resins.

This study was designed to compare strength, elastic modulus (stiffness), and hardness for five composite resin materials that are used for laboratory-fabricated posterior composite restorations. Ten specimens of each material were processed according to the manufacturer's instructions. Statistical analysis indicated that there were significant differences in mechanical properties among the materials tested. In addition, materials that are incrementally light cured prior to secondary processing were tested for changes in mechanical properties following secondary processing. It was determined that secondary processing provided improvement in flexural strength (11%) when compared to samples that were only light cured.

Acrylic Resins↗

PubMed1996

Pyridoxine deficiency affects biomechanical properties of chick tibial bone.

The mechanical integrity of bone is dependent on the bone matrix, which is believed to account for the plastic deformation of the tissue, and the mineral, which is believed to account for the elastic deformation. The validity of this model is shown in this study based on analysis of the bones of vitamin B6-deficient and vitamin B6-replete chick bones. In this model, when B6-deficient and control animals are compared, vitamin B6 deficiency has no effect on the mineral content or composition of cortical bone as measured by ash weight (63 +/- 6 vs. 58 +/- 3); mineral to matrix ratio of the FTIR spectra (4.2 +/- 0.6 vs. 4.5 +/- 0.2), line-broadening analyses of the X-ray diffraction 002 peak (beta 002 = 0.50 +/- 0.1 vs. 0.49 +/- 0.01), or other features of the infrared spectra. In contrast, collagen was significantly more extractable from vitamin B6-deficient chick bones (20 +/- 2% of total hydroxyproline extracted vs. 10 +/- 3% p < or = 0.001). The B6-deficient bones also contained an increased amount of the reducible cross-links DHLNL, dehydro-dihydroxylysinonorleucine, (1.03 +/- 0.07 vs. 0.84 +/- 0.13 p < or = 0.001); and a nonsignificant increase in HLNL, dehydro-hydroxylysinonorleucine, (0.51 +/- 0.03 vs. 0.43 +/- 0.03, p < or = 0.10). There were no significant changes in bone length, bone diameter, or area moment of inertia. In four-point bending, no significant changes in elastic modulus, stiffness, offset yield deflection, or fracture deflection were detected. However, fracture load in the B6-deficient animals was decreased from 203 +/- 35 MPa to 151 +/- 23 MPa, p < or = 0.01, and offset yield load was decreased from 165 +/- 9 MPa to 125 +/- 14 MPa, p < or = 0.05. Since earlier histomorphometric studies had demonstrated that the B6-deficient bones were osteopenic, these data suggest that although proper cortical bone mineralization occurred, the alterations of the collagen resulted in changes to bone mechanical performance.

Animals↗

PubMed1999

Mechanical properties of direct core build-up materials.

OBJECTIVE: This work was undertaken to measure mechanical properties of a diverse group of materials used for direct core build-ups, including a high copper amalgam, a silver cermet cement, a VLC resin composite and two composites specifically developed for this application. METHODS: Compressive strength, elastic modulus, diametral tensile strength and flexural strength and modulus were measured for each material as a function of time up to 3 months, using standard specification tests designed for the materials. RESULTS: All the materials were found to meet the minimum specification requirements except in terms of flexural strength for the amalgam after 1 h and the silver cermet at all time intervals. SIGNIFICANCE: There proved to be no obvious superior material in all respects for core build-ups, and the need exists for a specification to be established specifically for this application.

Analysis of Variance↗

PubMed2004

Effect of fluoride addition on the properties of dental alginate impression materials.

Fluoride-containing dental alginate impression materials can exert a considerable reduction in enamel solubility. The objective was to evaluate the effects of fluoride addition in the alginate impression materials on the properties and subsequent release of fluoride. Four experimental alginate impression materials were studied. Materials were mixed with distilled water (control) or 100-ppm fluoride solution. One or two percent NaF, or 1% SnF2 was added to the materials, which were mixed with distilled water. Fluoride release, flexibility, recovery from deformation, setting time, compressive strength and elastic modulus were determined in accordance with the ISO 1563 and ANSI/ADA Spec. 18. Fluoride release increased after addition of fluoride, and the released amount was 0.762-14.761 ppm. Addition of NaF or SnF2 resulted in higher fluoride release than the control group (p < 0.05). After fluoride addition, flexibility was 15.45-20.27%, and the recovery from deformation did not change except one material. Compressive strength after fluoride addition was 0.36-1.12 MPa. Addition of NaF or SnF2 in an alginate impression material may result in effective release of fluoride without deteriorating the properties of material itself.

Alginates↗

PubMed2000

Biomechanical calculation of human TM joint loading with jaw opening.

A three-dimensional, static mathematical calculation of the stomatognathic system was done to predict total temporomandibular joint (TMJ) loading at different levels of jaw opening. The model assumed that muscle forces acting on the mandible could be simulated by a combination of contractile components (CCs) and elastic components (ECs) and that static equilibrium existed within the body of the mandible. The model also imposed the constraint that any generated joint reaction force would act on the centre of the condyle. The results of the model demonstrated that under all conditions of opening and for all values of the elastic modulus selected, the forces between the TMJ condyle and the articular eminence were compressive in nature. The compressive force magnitude increased from 2.7 to 27.6 N incrementally as the jaw opened from 10 to 40 mm. Overall data in this study indicated that the TMJ tissues undergo low levels of compression at open positions up to 40 mm. Finally, the condition of trismus (increased jaw closing activation with opening) was simulated, the joint reaction force at 20 mm opening increased from 7.7 to 64.9 N with only a 20% activation of the closers.

Adult↗

PubMed2005

Normative values for intima-media thickness and distensibility of large arteries in healthy adolescents.

OBJECTIVE: Sonographic evaluation of arterial wall morphology and elasticity is increasingly accepted as a non-invasive tool in cardiovascular assessment. Several studies suggest that intima-media thickness (IMT) and arterial elasticity indices may sensitively reflect different vasculopathic processes in children. However, normative values and the impact of adolescent growth are largely unknown. METHODS: We assessed the IMT of the common carotid (cIMT) and femoral arteries (fIMT), carotid elasticity indices and interacting anthropometric factors in 247 healthy subjects aged 10-20 years. RESULTS: cIMT, fIMT, incremental elastic modulus (Einc) and circumferential wall stress (CWS) were positively, and distensibility coefficient (DC) inversely, correlated with age, height, body mass index (BMI), systolic blood pressure (BP) and brachial pulse pressure (r = 0.56 to -0.45, P < 0.05 to 0.0001). DC (r = -0.29, P < 0.0001) and stiffness index beta (r = 0.25, P < 0.0001), but not Einc, were significantly associated with cIMT independently of age. All vascular parameters showed non-Gaussian distributions. Excessively high IMT was associated with BMI and pulse pressure above the 90th percentile, and elevated Einc with high-normal BMI. Multivariate analysis identified independent positive effects of standardized BMI and brachial pulse pressure on normalized cIMT, negative effects of systolic BP and cIMT on DC, a positive effect of cIMT on stiffness, and positive effects of systolic BP and BMI on Einc and CWS. CONCLUSIONS: Morphological and functional measures of large arteries should be normalized to take account of changes during adolescence and skewed distributions. Relative body mass, systolic blood pressure and/or pulse pressure are determinants of IMT and elasticity.

Adolescent↗

PubMed1992

Noninvasive measurement of diameter changes in the distal abdominal aorta in man.

An ultrasound phase-locked, echo-tracking system was used to determine the dynamic properties of the distal abdominal aorta in 10 Caucasian male subjects (mean age, 25 years). Recordings were made at rest and during the blood pressure increase resulting from isometric exercise. The pressure diameter curve was nonlinear with an inflection at about 90-110 mmHg. Above this pressure range, the vessel was stiffer (less compliant), but the pressure diameter relationship was roughly linear above as well as below the inflection. Individual pressure diameter curves showed hysteresis, i.e., the aorta had a smaller diameter during expansion than during retraction at corresponding pressures. The pressure strain elastic modulus (Ep) and stiffness (beta) were at rest [Mean Arterial Pressure (MAP), 81 mmHg] 0.70 10(5) N/m2 and 6.0, respectively. During isometric exercise (MAP, 122 mmHg), Ep increased significantly by 91% and stiffness (beta) nonsignificantly by 27%. The variability of the compliance determinations was 5% when the ultrasonic system was combined with intra-arterial blood pressure measurements and less than 7% when combined with auscultatory blood pressure measurements. It is concluded that the phase-locked, echo-tracking system fulfills clinical requirements for routine measurements of vascular compliance.

Adult↗