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PubMed1999

The deformation behavior and mechanical properties of chondrocytes in articular cartilage.

INTRODUCTION: Chondrocytes in articular cartilage utilize mechanical signals to regulate their metabolic activity. A fundamental step in determining the role of various biophysical factors in this process is to characterize the local mechanical environment of the chondrocyte under physiological loading. METHODS: A combined experimental and theoretical approach was used to quantify the in-situ mechanical environment of the chondrocyte. The mechanical properties of enzymatically-isolated chondrocytes and their pericellular matrix (PCM) were determined using micropipette aspiration. The values were used in a finite element model of the chondron (the chondrocyte and its PCM) within articular cartilage to predict the stress-strain and fluid flow microenvironment of the cell. The theoretical predictions were validated using three-dimensional confocal microscopy of chondrocyte deformation in situ. RESULTS: Chondrocytes were found to behave as a viscoelastic solid material with a Young's modulus of approximately 0.6 kPa. The elastic modulus of the PCM was significantly higher than that of the chondrocyte, but several orders of magnitude lower than that of the extracellular matrix. Theoretical modeling of cell-matrix interactions suggests the mechanical environment of the chondrocyte is highly non-uniform and is dependent on the viscoelastic properties of the PCM. Excellent agreement was observed between the theoretical predictions and the direct measurements of chondrocyte deformation, but only if the model incorporated the PCM. CONCLUSIONS: These findings imply that the PCM plays a functional biomechanical role in articular cartilage, and alterations in PCM properties with aging or disease will significantly affect the biophysical environment of the chondrocyte.

Biomechanical Phenomena↗

PubMed1978

Osmotic adjustment in leaves of sorghum in response to water deficits.

The relationships among the total water potential, osmotic potential, turgor potential, and relative water content were determined for leaves of sorghum (Sorghum bicolor [L.] Moench cvs. ;RS 610' and ;Shallu') with three different histories of water stress. Plants were adequately watered (control), or the soil was allowed to dry slowly until the predawn leaf water potential reached either -0.4 megapascal (MPa) (treatment A) or -1.6 MPa (treatment B). Severe soil and plant water deficits developed sooner after cessation of watering in ;Shallu' than in ;RS 610', but no significant differences in osmotic adjustment or tissue water relations were observed between the two cultivars. In both cultivars, the stress treatments altered the relationship between leaf water potential and relative water content, resulting in the previously stressed plants maintaining higher tissue water contents than control plants at the same leaf water potential. The osmotic potential at full turgor in the control sorghum was -0.7 MPa: stress pretreatment significantly lowered the osmotic potential to -1.1 and -1.6 MPa in stress treatments A and B, respectively. As a result of this osmotic adjustment, leaf turgor potentials at a given value of leaf water potential exceeded those of the control plants by 0.15 to 0.30 MPa in treatment A and by 0.5 to 0.65 MPa in treatment B. However, zero turgor potential occurred at approximately the same value of relative water content (94%) irrespective of previous stress history. From the relationship between turgor potential and relative water content there was an approximate doubling of the volumetric elastic modulus, i.e. a halving of tissue elasticity, as a result of stress preconditioning. The influence of stress preconditioning on the moisture release curve is discussed.

Journal Article↗

PubMed1999

Extract of wine phenolics improves aortic biomechanical properties in stroke-prone spontaneously hypertensive rats (SHRSP).

We studied the effect of the extract of wine phenolics (EWP) on blood pressure, vasorelaxing activity and aortic biomechanical properties in stroke-prone hypertensive rats (SHRSP). Thirty-six 4-week-old male SHRSP/Izm rats were divided into 6 equal groups fed one of the following 6 diets: A control diet (plain laboratory diet), the control diet substituted with 0.5 or 1.0% polyphenolic compounds derived from the extract of apple phenolics (EAP), the control diet substituted with 0.5 or 1.0% polyphenolic compounds derived from the extract of tea phenolics (ETP), or the control diet along with drinking water containing 1.0% polyphenolic compounds derived from EWP. Systolic blood pressure (SBP) and body weight (BW) were checked once a week. At the end of the 8th week of feeding, all of the rats were sacrificed and the heart weight and aortic biomechanical properties were measured. The relaxation effect of the addition of EWP on endothelium-intact aortic rings precontracted with prostaglandin (PG) F2 alpha was also measured. Only EWP, not EAP or ETP, significantly lowered the SBP values a compared with the control group at the 4th, 7th and 8th weeks of feeding (p < 0.05). The heart weight and ventricular weight, expressed as the percentage of BW, were significantly lower in the EWP group than in the control group (p < 0.05). The aortic maximum stress was significantly increased (p < 0.05), and the aortic incremental elastic modulus was significantly reduced (meaning higher elasticity) (p < 0.001) in the EWP group as compared with the control group. The aortic rings showed concentration-dependent relaxation induced by EWP, and the relaxation was significantly greater than that induced by a commercial red wine preparation. In conclusion, EWP attenuated the elevation of blood pressure in SHRSP possibly by increasing the vasorelaxation activity. The aortic fragility and elasticity were also improved in EWP-fed SHRSP.

Animals↗

PubMed1991

Relationship between dynamic viscoelasticity and biochemical parameters in whole sputum from patients with hypersecretory respiratory diseases.

To obtain suitable biochemical parameters for measuring the dynamic viscoelasticity of sputum, we examined the relationships of the dynamic viscoelasticity with the dry weight (DW) and the contents of fucose, a parameter of airway mucous glycoprotein (AMG), and total protein (TP) and major proteins in whole sputum. The DW and TP, albumin and IgG concentrations and elastase activity were higher in purulent sputum than in mucoid-mucopurulent sputum, but there was no significant difference in the concentrations of airway wall-derived substances, such as fucose and S-IgA in the two. In mucoid-mucopurulent sputum, the dynamic viscosity (eta') and elastic modulus (G'), an indicator of dynamic elasticity, were most closely correlated with the fucose concentration (r = +0.75, and +0.74, p < 0.005 at 1 Hz) and slightly correlated with the DW, TP and S-IgA, but not with the other parameters tested. In the purulent sputum, the eta' and G' correlated with the DW and concentration of TP (r = +0.70-0.80, p < 0.005), but not with any concentrations of fucose, S-IgA or albumin. The results indicate that as parameters for estimating the dynamic viscosity and elasticity of whole sputum, fucose is useful for mucoid-mucopurulent sputum whereas DW and TP are useful for purulent sputum.

Adult↗

PubMed2001

A simple method of determining the modulus of orthopedic bone cement.

Accurate determination of the elastic modulus of surgical bone cements is of primary importance, when evaluating the stresses within the cement mantle in Total Joint Arthroplasty. This article presents a new method of determining the modulus of surgical bone cements from the biaxial flexural test. The biaxial flexural test is not currently employed in mainstream orthopedic mechanical testing, which is surprising because most loading in orthopedic applications is biaxial in nature. Nor has this method been utilized for dental materials, even though the biaxial flexure test has been used for many years in this field. It has been demonstrated that the modulus of surgical bone cements can be determined from the biaxial flexural test, and these results are in agreement with results from compressive and bending tests.

Bone Cements↗

PubMed2004

Gas in stems: abundance and potential consequences for tree biomechanics.

Secondary xylem of woody plants has a large volumetric proportion of gas occupying spaces that would otherwise be filled with water. We examined whether these gas-filled voids have a mechanical role by either decreasing the fresh mass the tree must support (by replacing some of the water with gas) or by providing inexpensive filler to increase stem diameter (thereby increasing the second moment of area at the expense of the modulus of elasticity and modulus of rupture). Calculations from published data show that temperate softwood species (n = 26) average 18 and 50% gas by volume for sapwood and heartwood, respectively; temperate hardwood species (n = 31) average 26% gas by volume in both the sapwood and heartwood; and tropical species (n = 52) with mixed sapwood and heartwood have 18% gas by volume. In this paper, we develop equations to show how gas affects the mechanical behavior of tree stems, and describe model results to show how gas affects mechanical stability, based on mass and stem diameters for six 34-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. For the same applied load, modeled stems in which the gas space was filled with water differed in their surface stresses by < 2% from modeled stems in the native state (partially gas-filled), indicating no practical benefit from a reduction in stem mass due to gas. A second modeling scenario compared the native state to stems in which gas was removed and stem diameters decreased (and material properties adjusted to concur with the increased wood density) to conserve mass. Removal of the gas-filled voids resulted in up to 41% higher surface stress for the same applied load, caused by a decrease in the second moment of area greater than the increase in modulus of elasticity. Trees with gas removed had higher modulus of rupture, but could withstand up to 14% lower maximum wind forces than trees in their native state, suggesting a biomechanical role for the gas if the model assumptions are valid. The gas content may, however, have evolved in response to pressures unrelated to biomechanics. We discuss some of its potential effects on sapwood physiology.

Biomechanical Phenomena↗

PubMed2006

Fine needle aspiration of the vocal fold lamina propria in an animal model.

OBJECTIVES: The development of a minimally invasive fine needle aspiration (FNA) technique for vocal fold (VF) biopsy would have far-reaching implications and applicability in laryngology. The objective of this study was to determine whether FNA of the VF lamina propria is feasible and whether it causes injury to the VF. METHODS: Unilateral VF FNA was performed with a 26-gauge needle on 20 rabbits. The FNA cell collection of the lamina propria was confirmed by cytology. Four weeks after the FNA, the rabbits were painlessly sacrificed and the larynges were harvested. Histologic analysis of the VF lamina propria included Masson's trichrome and elastin-van Gieson stains. The linear viscoelastic shear properties, elastic modulus, and viscous modulus of the tissue were measured. RESULTS: Compared to the contralateral normal VFs, those VFs that underwent FNA demonstrated no significant differences in levels of collagen (p = .17) and elastin (p = .94). Rheologically, the elastic shear modulus and viscous modulus did not significantly differ between the normal and FNA VFs (p = .9380 and p = .9359, respectively). CONCLUSIONS: Fine needle aspiration of the VF lamina propria is feasible without injury and offers a potentially promising, less invasive alternative to be developed for future diagnostic and therapeutic management of VF lesions.

Animals↗

PubMed1998

[Changes of the deformability of neutrophil and the influence of anisodamine on neutrophil deformability during endotoxin-induced acute lung injury in rats].

OBJECTIVE: To explore the mechanisms of change of deformability of polymorphonuclear leukocytes (PMN) and influence of anisodamine on deformability of PMN during endotoxin-induced acute lung injury (ALI) in rat. To explore the role of PMN in ALI. METHOD: The model of ALI in rat was reproduced by intravenous injection of E Coli endotoxin. The deformability of PMN was measured by micropipette aspiration technique. RESULT: The elastic modulus K1 of PMN at the 1st hour (33 +/- 12 Pa), 4th hours (37 +/- 12 Pa, 1 Pa = 0.0075 mmHg) and 6th hours (38 +/- 13 Pa) after injection of E Coli endotoxin are all significantly higher than that in the control group (26 +/- 9 Pa P < 0.01). The viscosity modulus (mu) of PMN at the 4th hours (5 +/- 3 Pa.s) and 6th hours (6 +/- 3 Pa.s) after injection of E Coli endotoxin are all significantly higher than the control group (3.1 +/- 2.6 Pa.s, P < 0.01). The elastic shear modulus (G) of PMN at the 4th hours (54 +/- 20 Pa) and the 6th hours (56 +/- 21 Pa) after injection of E Coli endotoxin are all significantly higher than the control group (47 +/- 17 Pa, P < 0.05). The K1(33 +/- 12 Pa) and mu(4 +/- 3 Pa.s) in anisodamine group are all significantly lower than endotoxin group in the same time phases (P < 0.05). CONCLUSION: The deformability of PMN decrease remarkably during ALI, which will enhance PMN sequestration in lungs, lead to ALI. It may be one of important pathogenic mechanism of ALI. The anisodamine can inhibit the decrease of deformability of PMN effectively and may have some therapeutic effect on ALI.

Animals↗

PubMed1999

Inexpensive, semi-automated system for measuring mechanical properties of soft tissues.

Stiffness and strength are important properties of many tissues, but standard material-testing equipment is expensive, often ill-suited for testing soft tissues, and rarely accessible to biologists. We describe a system built around a microcomputer and an electronic balance which is particularly well-suited for measuring stress and strain in small samples of soft tissue. We use a discarded floppy disk drive as a linear actuator to strain the sample, while an electronic balance measures the tension (used to calculate stress). We give an algorithm for a program to drive a microcomputer which controls the floppy disk drive via its parallel port and records the balance measurements via its serial port. We used this system to obtain stress-strain curves from a sample of latex rubber and a sample of soft insect cuticle. Three tests of the rubber sample gave nearly identical results, with smooth, J-shaped stress-strain curves. The stress-strain curves gave a modulus elasticity value of 1.72 Mpa over the steep, straight region, well within the range for natural latex rubber. We also tested a sample of abdominal cuticle from a caterpillar (Manduca sexta). The caterpillar cuticle had a J-shaped stress-strain curve with a modulus of elasticity of 2.11 Mpa over the steep part of the curve. J. Exp. Zool. 284:374-378, 1999.

Animals↗

PubMed2006

Microstructure and deformation behavior of biocompatible TiO2 nanotubes on titanium substrate.

Titanium oxide coatings have been shown to exhibit desirable properties as biocompatible coatings. We report on the quantitative microstructure characterization and deformation behavior of TiO(2) nanotubes on Ti substrate. Nanotubes were processed using anodic oxidation of Ti in a NaF electrolyte solution. Characterization of the as-processed coatings was conducted using scanning electron microscopy and focused ion beam milling. Increases in anodization time had no significant effect on tube diameter or tube wall thickness. Coating thickness, however, increased with time up to 2h of anodization, at which point an equilibrium thickness was established. Nanoindentation was used to probe the mechanical response in terms of Young's modulus and hardness. Progressively higher values of elastic modulus were obtained for thinner films consistent with increasing effects of the Ti substrate. A possible deformation mechanism of densification of the porous oxide and wear of the dense surface is suggested and discussed.

Biomechanical Phenomena↗

PubMed2003

Trabecular bone modulus-density relationships depend on anatomic site.

One outstanding issue regarding the relationship between elastic modulus and density for trabecular bone is whether the relationship depends on anatomic site. To address this, on-axis elastic moduli and apparent densities were measured for 142 specimens of human trabecular bone from the vertebra (n=61), proximal tibia (n=31), femoral greater trochanter (n=23), and femoral neck (n=27). Specimens were obtained from 61 cadavers (mean+/-SD age=67+/-15 years). Experimental protocols were used that minimized end-artifact errors and controlled for specimen orientation. Tissue moduli were computed for a subset of 18 specimens using high-resolution linear finite element analyses and also using two previously developed theoretical relationships (Bone 25 (1999) 481; J. Elasticity 53 (1999) 125). Resultant power law regressions between modulus and density did depend on anatomic site, as determined via an analysis of covariance. The inter-site differences were among the leading coefficients (p<0.02), but not the exponents (p>0.08), which ranged 1.49-2.18. At a given density, specimens from the tibia had higher moduli than those from the vertebra (p=0.01) and femoral neck (p=0.002); those from the trochanter had higher moduli than the vertebra (p=0.02). These differences could be as large as almost 50%, and errors in predicted values of modulus increased by up to 65% when site-dependence was ignored. These results indicate that there is no universal modulus-density relationship for on-axis loading. Tissue moduli computed using methods that account for inter-site architectural variations did not differ across site (p>0.15), suggesting that the site-specificity in apparent modulus-density relationships may be attributed to differences in architecture.

Aged↗

PubMed1984

Alterations in the mechanical properties of peripheral nerve following crush injury.

The mechanical properties of injured nerves have been studied. At specific times following unilateral nerve crush, the sciatic nerves of mice were tested mechanically. Photographs and longitudinal force measurements were obtained as nerve segments were elongated to mechanical failure. Stress and strain at the proportional limit and apparent elastic modulus were used as indicators of strength, elasticity and stiffness. Injury led to time-dependent increases in strength and stiffness and decreases in elasticity. These changes were apparent in both damaged and contralateral, undamaged nerves. Many of the changes appear to be related to the epineurium. Some mechanical changes in nerve could have important consequences for the integrity and function of nerves and mechanically interfaced structures.

Animals↗

PubMed1994

Morphology-mechanical property relations in trabecular bone of the osteoarthritic proximal tibia.

Alteration of morphologic and mechanical properties of trabecular bone in the osteoarthritic proximal tibia may be a contributing factor in tibial component loosening. To explore this issue, the authors performed tissue property measurements, morphologic analysis, and mechanical testing of subchondral, epiphyseal, and metaphyseal trabecular bone specimens retrieved from six human proximal tibias exhibiting a range of medial unicondylar osteoarthritic degeneration. Apparent density in the proximal tibia was altered according to varus misalignment and medial subluxation associated with medial osteoarthritis of the knee. In subchondral bone, a decrease in tissue mineralization contributed to a significant reduction in axial mechanical properties with degenerative disease (P < .0005). In epiphyseal and metaphyseal bone, trabecular thickness and the number of trabeculae increased linearly with volume fraction, providing a power law relationship between axial elastic modulus and apparent density (R2 = .84). Average elastic properties of the tibial epiphysis and metaphysis were not reduced by degenerative disease (P < .05). The results suggest that absolute minimization of tibial resection might not be an optimal strategy for tibial component fixation and that mechanical properties of the tibial resection surface are more homogeneous in planes parallel to the joint surface than in a plane normal to the longitudinal axis of the tibia.

Aged↗

PubMed1992

Effect of lipid A on the deformability, membrane rigidity and geometry of human adult red blood cells.

Lipid A is responsible for the activities of endotoxin and may cause circulatory failure and haemolysis. This study evaluated the effects of different lipid A concentrations on red blood cell (RBC) deformation (rheoscope), the aspiration pressure required to aspirate RBC into 3.3 microns pipettes, the membrane shear elastic modulus (i.e. membrane rigidity) and cellular geometry (micropipette system) after 15 min of incubation. Lipid A concentrations of 10 and 100 micrograms ml-1 of RBCs decreased RBC deformability by 26% and 39%, respectively. The aspiration pressure for RBCs into a 3.3 microns micropipette increased by 235% at a lipid A concentration of 10 micrograms ml-1 and by 586% at a concentration of 100 micrograms ml-1. The elastic shear modulus almost doubled at a lipid A concentration of 10 micrograms ml-1 and tripled at 100 micrograms ml-1. At a lipid A concentration of 100 micrograms ml-1, 37% of RBCs showed spicules. These echinocytes were less deformable than discocytes. Mean corpuscular volume, RBC volume and surface area were not affected by lipid A. We conclude that lipid A causes marked reduction of RBC deformability due to increasing membrane rigidity.

Adult↗

PubMedDate not supplied

Mechanics of porcine coronary arteries ex vivo employing impedance planimetry: a new intravascular technique.

Our objective was to evaluate methodological aspects of impedance planimetry, a new balloon catheter-based technique, for the investigation of coronary artery mechanical wall properties. We used a four ring-electrode electrical impedance measuring system that was located inside a balloon. Two of the electrodes were used for excitation and connected to a generator producing a constant alternating current of 250 mA at 5 kHz. The other two electrodes for detection were placed midway between the excitation electrodes. The balloon was distended with electrically conducting fluid through an infusion channel. The vessel cross-sectional area (CSA) was measured according to the field gradient principle by measuring the impedance of the fluid inside the balloon. Impedance planimetry was applied in the three major branches of the coronary arteries of seven extracted porcine hearts to assess luminal CSAs in response to internal pressurization. The biomechanical wall properties were evaluated by computing the strain [(r - r0) x r0(-1), where r is the vessels inner radius computed as (CSA x pi-1)1/2 and r0 is the radius of the vessel at a minimal distension pressure], the tension [(r x dP), where dP is the transmural pressure difference], and the pressure elastic modulus (delta P x r x delta r-1). We found that in vitro testing demonstrated that impedance planimetry was accurate and reproducible. The technique has controllable sources of error. Measurements were performed with consecutively increasing pressures in the range 1-25 kPa (8-188 mmHg, 0.01-0.25 atm). The CSAs increased nonlinearly and were significantly larger in the left anterior descendent coronary artery (LAD) (1 kPa, mean 5.0 mm2; 25 kPa, mean 21.8 mm2) than in both the left circumflex (Cx) (4.5-16.0 mm2) and the right coronary artery (RCA) (2.8-15.6 mm2) (analysis of variance, P < 0.001 for both). The circumferential wall tension-strain relation showed exponential behavior. For a given strain, tension values for LAD were significantly lower than those of Cx (P < 0.01). The pressure elastic modulus-strain relation also was exponential, and values for Cx were significantly lower than values for LAD (P < 0.001) and RCA (P < 0.05). Impedance planimetry was applied to the study of coronary artery biomechanics ex vivo. The LAD had the largest CSA, and the Cx was the least compliant. Methodological aspects of an in vivo introduction of the method require additional evaluation.

Analysis of Variance↗

PubMed2005

[Experimental study on viscoelastic properties of human cornea].

The biomechanical properties of eight human corneas from four normal Chinese fresh corpses were investigated by use of one dimension tensile test, tensile stress relaxation and creep test. The destructive load, stretchy ratio, spreading stress, spreading strain and elastic modulus were determined. Also obtained were the stress relaxation and creep data and curves. After reduction of data, the reduced stress relaxation and creep data and curves were worked out. The regression method was used to get the regression coefficient. The least square method was employed to fit the data of stress and strain; then the stress-strain formula was expressed and the curves of human cornea were plotted. The constitutive equation is K (lambda,t) = G(t) T(e) (lambda) and some conclusions are drawn.

Biomechanical Phenomena↗

PubMed2005

Quantitative shear wave magnetic resonance elastography: comparison to a dynamic shear material test.

Magnetic resonance elastography (MRE), a phase contrast MRI technique, images the propagation of applied mechanical waves in tissue, allowing shear stiffness to be quantified in vivo. This MRE technique has been validated with static mechanical compression tests. Dynamic mechanical analysis (DMA) may be a more appropriate comparison to MRE because it directly measures the shear modulus dynamically, while compression tests convert the measured elastic modulus to shear modulus with an assumed Poisson ratio. This study compared the shear stiffness estimated with various MRE inversion algorithms (i.e., manual calculation, local frequency estimate, phase gradient, direct inversion, and matched filter) to the dynamic mechanical test. The shear stiffness of five agarose gels with concentrations ranging from 1.5 to 3.5% were measured using MRE and DMA. The phase gradient inversion algorithm overestimated the shear modulus at higher concentrations (i.e., 3-3.5% agar), while the results from the other techniques correlated well with the dynamic mechanical test.

Agar↗

PubMed2004

Linked mechanical and biological aspects of remodeling in mouse pulmonary arteries with hypoxia-induced hypertension.

Right heart failure due to pulmonary hypertension causes significant morbidity and mortality. To study the linked vascular mechanical and biological changes that are induced by pulmonary hypertension, we mechanically tested isolated left main pulmonary arteries from mice exposed to chronic hypobaric hypoxia and performed histological assays on contralateral vessels. In isolated vessel tests, hypoxic vessels stretched less in response to pressure than controls at all pressure levels. Given the short length and large diameter of the pulmonary artery, the tangent Young's modulus could not be measured; instead, an effective elastic modulus was calculated that increased significantly with hypoxia [(280 kPa (SD 53) and 296 kPa (SD 50) for 10 and 15 days, respectively, vs. 222 kPa (SD 35) for control; P < 0.02)]. Hypoxic vessels also had higher damping coefficients [(0.063 (SD 0.017) and 0.054 (SD 0.014) for 10 and 15 days, respectively, vs. 0.033 (SD 0.016) for control; P < 0.002)], indicating increased energy dissipation. The increased stiffness with hypoxia correlated with an increase in collagen thickness (percent collagen multiplied by wall thickness) as well as the sum of elastin and collagen thicknesses measured histologically in the artery wall. These results highlight the mechanobiological changes in the pulmonary vasculature that occur in response to hypoxia-induced pulmonary hypertension. Furthermore, they demonstrate significant vascular mechanical and biological changes that would increase pulmonary vascular impedance, leading to right heart failure.

Animals↗