Morphology and transverse stiffness of Drosophila myofibrils measured by atomic force microscopy

Atomic force microscopy was used to investigate the surface morphology and transverse stiffness of myofibrils from Drosophila indirect flight muscle exposed to different physiologic solutions. I- and A-bands were clearly observed, and thick filaments were resolved along the periphery of the myofibril. Interfilament spacings correlated well with estimates from previous x-ray diffraction studies. Transverse stiffness was measured by using a blunt tip to indent a small section of the myofibrillar surface in the region of myofilament overlap. At 10 nm indention, the effective transverse stiffness (K( perpendicular)) of myofibrils in rigor solution (ATP-free, pCa 4.5) was 10.3 +/- 5.0 pN nm(-1) (mean +/- SEM, n = 8); in activating solution (pCa 4.5), 5.9 +/- 3.1 pN nm(-1); and in relaxing solution (pCa 8), 4.4 +/- 2.0 pN nm(-1). The apparent transverse Young's modulus (E( perpendicular)) was 94 +/- 41 kPa in the rigor state and 40 +/- 17 kPa in the relaxed state. The value of E( perpendicular) for calcium-activated myofibrils (55 +/- 29 kPa) was approximately a tenth that of Young's modulus in the longitudinal direction, a difference that at least partly reflects the transverse flexibility of the myosin molecule.     

Microtensile measurements of single trabeculae stiffness in human femur

In this paper, the authors perform microtensile tests of single trabeculae excised from a human femur head. One of the main issues of this work is to establish some experimental procedures for preparing and testing the specimens. The use of a well-characterized microtensile apparatus allows for a low intraspecimen dispersion of the measured stiffness. Tensile/compressive tests were chosen because they appear less sensitive to errors in the cross-sectional area measurements with respect to bending tests. By these considerations, some tensile/compressive tests of plate-like trabecular specimens have been carried out. Typical stiffness values are 74.2+/-0.7Nmm(-1) for tensile tests, and 58.9+/-0.6Nmm(-1) for compressive test. Another compressive test performed on a shorter specimen yielded a stiffness value of 148.3+/-5.3Nmm(-1). The maximum applied load was about 0.5N. Rough measurements of specimens sizes yielded a Young's modulus value ranging from 1.41 to 1.89GPa.     

Magnetic phagosome motion in J774A.1 macrophages: influence of cytoskeletal drugs

The role of the different cytoskeletal structures like microfilaments (MF), microtubuli (MT), and intermediate filaments (IF) in phagosome motion is unclear. These cytoskeletal units play an important role in macrophage function (migration, phagocytosis, phagosome transport). We investigated ferromagnetic phagosome motions by cell magnetometry. J774A.1 macrophages were incubated with 1.3-microm spherical magnetite particles for 24 h, after which more than 90% of the particles had been phagocytized. Phagosome motions can be caused either by the cell itself (relaxation) or by applying magnetic twisting forces, yielding cell stiffness and viscoelastic properties of the cytoskeleton. Apparent viscosity of the cytoplasm was non-Newtonian and showed a shear-rate-dependent power law behavior. Elastically stored energy does not force the magnetic phagosomes back to their initial orientation: 57% of the twisting shear was not recoverable. Cytoskeletal drugs, like Cytochalasin D (CyD, 2 - 4 microM), Colchicine (CoL, 10 microM), or Acrylamide (AcL, 40 mM) were added in order to disturb the different cytoskeletal structures. AcL disintegrates IF, but affected neither stochastic (relaxation) nor directed phagosome motions. CyD disrupts MF, resulting in a retarded stochastic phagosome motion (relative decay 0.53 +/- 0.01 after 5 min versus 0.34 +/- 0.01 in control), whereas phagosome twisting shows only a small response with a 9% increase of stiffness and a small reduction of recoverable strain. CoL depolymerizes the MT, inducing a moderately accelerated relaxation (relative decay 0.28 +/- 0.01 after 5 min) and a 10% increase of cell stiffness, where the pure viscous shear is increased and the viscoelastic recoil is inhibited by 40%. Combining the two drugs conserves both effects. After disintegrating either MF or MT, phagosome motion and cytoskeletal stiffness reflect the behavior of either MT or MF, respectively. The results verify that the dominant phagosome transport mechanism is MF-associated. MT depolymerization by CoL induces an activation of the F-actin synthesis, which may induce an accelerated relaxation and an increase of stiffness. Cell mechanical properties are not modulated by MF depolymerization, whereas MT depolymerization causes a loss of viscous resistance and a loss of cell elasticity. The mean energy for stochastic phagosome transport is 5*10(-18) Joules and corresponds to a force of 7 pN on a single 1.3-microm phagosome.     

Anisotropic Poisson's ratio and compression modulus of cortical bone determined by speckle interferometry

Young's modulus and Poisson's ratios of 6mm-sized cubes of equine cortical bone were measured in compression using a micro-mechanical loading device. Surface displacements were determined by electronic speckle pattern-correlation interferometry. This method allows for non-destructive testing of very small samples in water. Analyses of standard materials showed that the method is accurate and precise for determining both Young's modulus and Poisson's ratio. Material properties were determined concurrently in three orthogonal anatomic directions (axial, radial and transverse). Young's modulus values were found to be anisotropic and consistent with values of equine cortical bone reported in the literature. Poisson's ratios were also found to be anisotropic, but lower than those previously reported. Poisson's ratios for the radial-transverse and transverse-radial directions were 0.15+/-0.02, for the axial-transverse and axial-radial directions 0.19+/-0.04, and for the transverse-axial and radial-axial direction 0.09+/-0.02 (mean+/-SD). Cubes located only millimetres apart had significantly different elastic properties, showing that significant spatial variation occurs in equine cortical bone.     

Precision of nanoindentation protocols for measurement of viscoelasticity in cortical and trabecular bone

Nanoindentation has recently gained attention as a characterization technique for mechanical properties of biological tissues, such as bone, on the sub-micron level. However, optimal methods to characterize viscoelastic properties of bones are yet to be established. This study aimed to compare the time-dependent viscoelastic properties of bone tissue obtained with different nanoindentation methods. Bovine cortical and trabecular bone samples (n=8) from the distal femur and proximal tibia were dehydrated, embedded and polished. The material properties determined using nanoindentation were hardness and reduced modulus, as well as time-dependent parameters based on creep, loading-rate, dissipated energy and semi-dynamic testing under load control. Each loading protocol was repeated 160 times and the reproducibility was assessed based on the coefficient of variation (CV). Additionally, three well-characterized polymers were tested and CV values were calculated for reference.The employed methods were able to characterize time-dependent viscoelastic properties of bone. However, their reproducibility varied highly (CV 9–40%). The creep constant increased with increasing dwell time. The reproducibility was best with a 30 s creep period (CV 18%). The dissipated energy was stable after three repeated load cycles, and the reproducibility improved with each cycle (CV 23%). The viscoelastic properties determined with semi-dynamic test increased with increase in frequency. These measurements were most reproducible at high frequencies (CV 9–10%). Our results indicate that several methods are feasible for the determination of viscoelastic properties of bone material. The high frequency semi-dynamic test showed the highest precision within the tested nanoindentation protocols.     

Material characterization of human medial collateral ligament.

The objectives of this study were to determine the longitudinal and transverse material properties of the human medial collateral ligament (MCL) and to evaluate the ability of three existing constitutive models to describe the material behavior of MCL. Uniaxial test specimens were punched from ten human cadaveric MCLs and tensile tested along and transverse to the collagen fiber direction. Using load and optical strain analysis information, the tangent modulus, tensile strength and ultimate strain were determined. The material coefficients for each constitutive model were determined using nonlinear regression. All specimens failed within the substance of the tissue. Specimens tested along the collagen fiber direction exhibited the typical nonlinear behavior reported for ligaments. This behavior was absent from the stress-strain curves of the transverse specimens. The average tensile strength, ultimate strain, and tangent modulus for the longitudinal specimens was 38.6 +/- 4.8 MPa, 17.1 +/- 1.5 percent, and 332.2 +/- 58.3 MPa, respectively. The average tensile strength, ultimate strain, and tangent modulus for the transverse specimens was 1.7 +/- 0.5 MPa, 11.7 +/- 0.9 percent, and 11.0 +/- 3.6 MPa, respectively. All three constitutive models described the longitudinal behavior of the ligament equally well. However, the ability of the models to describe the transverse behavior of the ligament varied.     

Impact of body composition on performance in fitness tests among personnel of the Croatian navy

The purpose of this study was to determine the impact of body weight on fitness tests among the personnel of the Croatian navy. Forty two naval personnel (age 27 +/- 4.1 years; body mass 86.2 +/- 4.9 kg; height 184.6 +/- 7.4 cm; body fat percentage 17.3 +/- 5.2) participated in this study. In order to evaluate the fitness of the naval servicemen, we applied a testing procedure that included measurements of 7 fitness tests and 15 body anthropometric tests. A negative correlation was found between the body fat percentage and all the analyzed sprint tests and three anaerobic power tests (r), SP5 (r = -0.42), SP10 (r = -0.51), SP20 (r = -0.53), SJ (r = -0.45), CM (r = -0.57), SLJ (r = -0.67). Also a negative correlation was found between the body fat percentage and VO2(max) (r = -0.44). A positive correlation was found between the sprint test and the power performance test and thigh and calf girth. Spiriting ability is influenced by the strength of a person. This is one of the reasons why we found a positive correlation between the sprint test (SP5, SP10 and SP20) and thigh and calf girth. In this study we found a negative correlation between body fat percentages and all the sprint tests and three anaerobic power tests and VO2(max). The ectomorph somatotypes have positive correlations with all variables. The mesomorph somatotypes have the greatest positive correlations with all variables. The endomorph somatotypes have negative correlations with all variables. According to the body composition of Croatian naval servicemen we can conclude that they need a sufficient level of strength and endurance for everyday tasks. The effectiveness of a weight-management program is determined by the success of the participants in losing the necessary amount of weight and being able to maintain that weight loss. This requires long-term tracking of these individuals in a naval environment.     

Tissue softening of guinea pig oesophagus tested by the tri-axial test machine

Tissue softening is commonly reported during mechanical testing of biological tissues in vitro. The loss of stiffness may be due to viscoelasticity-induced softening (the time-history of load-caused softening) and strain-induced stress softening (the maximum previous load-caused softening). However, the knowledge about tissue softening behaviour is presently poor. The aims of this study were to distinguish whether the loss of the stiffness during preconditioning was due to strain softening or viscoelasticity and to test the tissue softening in circumferential and longitudinal direction in the guinea pig oesophagus. Eight repeated pressure controlled ramp distensions and eight uniaxial tensile-release ramp stretches in three series were done on eight guinea pig oesophagi. The stress–strain curves were used to display the time-dependency (viscoelasticity) and the maximum previous load-caused softening (strain softening) in circumferential and longitudinal directions. For both the longitudinal and the circumferential softening, the peak stress and stiffness produced during the first loading were bigger than those produced in the remaining loadings. The stress loss due to strain softening was about three times more than that due to viscoelasticity in the longitudinal direction. The strain increased more than two times between the strain softening and viscoelastic softening in the circumferential direction. With a stress level of 20 kPa, the stiffness in the circumferential direction lost more than that in the longitudinal direction (P<0.05), indicating the anisotropic softening properties in the oesophagus. In conclusion, the stiffness loss during preconditioning is mainly attributed to strain softening, appears irreversible and is anisotropic.     

Minimizing errors during in vitro testing of multisegmental spine specimens: considerations for component selection and kinematic measurement

Apparatus-induced artifacts may invalidate standard spine testing protocols. Kinematic measurements may be compromised by the configuration of motion capture equipment. This study has determined: (1) the influence of machine design (component friction) on in vitro spinal kinetics; (2) the sensitivity of kinematic measurements to variations in the placement of motion capture markers. A spinal loading simulator has been developed to dynamically apply pure bending moments (three axes) with or without a simultaneous compressive preload. Two linear slider types with different friction coefficients, one with caged ball bearings and one with high-precision roller bearings on rails, were mounted and specimen response compared in sequential tests. Three different optoelectronic marker cluster configurations were mounted on the specimen and motion data was captured simultaneously from all clusters during testing. A polymer tube with a uniform bending stiffness approximately equivalent to a polysegmental lumbar spine specimen was selected to allow reproducible behavior over multiple tests. The selection of sliders for linear degrees of freedom had a marked influence on parasitic shear forces. Higher shear forces were recorded with the caged-bearing design than with the high-precision rollers and consequently a higher moment was required to achieve a given rotation. Kinematic accuracy varied with each marker configuration, but in general higher accuracy was achieved with larger marker spacings and situations where markers moved predominantly parallel to the camera's imaging plane. Relatively common alternatives in the mechanical components used in an apparatus for in vitro spine testing can have a significant influence on the measured kinematic and kinetics. Low-magnitude parasitic shear forces due to friction in sliders induces a linearly increasing moment along the length of the specimen, precluding the ideal of pure moment application. This effect is compounded in polysegmental specimens. Kinematic measurements are highly sensitive to marker design and placement, despite equivalent absolute precision of individual marker measurements, however marker configurations can be designed to minimize errors related to spatial distribution and system bias.     

The use of surface strain data and a neural networks solution method to determine lumbar facet joint loads during in vitro spine testing

A new method for determining facet loads during in vitro spine loading using strain gauges and a neural networks solution method was investigated. A test showed that the new solution method was more robust than and as accurate as a previously presented graphical solution method for computing facet loads using surface strain. The technique was subsequently utilized to assess facet loads at L1-L2 during flexibility testing [7.5Nm pure moments in flexion (FL), extension (EX), right and left axial rotation (AR), and right and left lateral bending (LB)], and stiffness testing (FL-EX with 400N compressive follower load) of six human lumbar spine segments (T12-L2). In contrast to other techniques, such as thin film sensors or pressure-sensitive film, the strain-gauge method leaves the facet joint capsule intact during data collection, presumably allowing more natural load transmission. During flexibility tests, the mean (+/-standard deviation) calculated facet loads (in N) were 46.1+/-41.3 (FL), 51.5+/-39.0 (EX), 70.3+/-43.2 (AR-contralateral side), 31.3+/-33.4 (AR-ipsilateral side), 30.6+/-29.1 (LB-contralateral side), and 32.0+/-44.4 (LB-ipsilateral side). During stiffness tests, the calculated facet loads were 45.5+/-40.4 (upright), 46.6+/-41.9 (full FL), and 75.4+/-39.0 (full EX), corresponding to an equivalent of 11.4%, 11.6%, and 18.8% of the compressive follower load (upright, full FL and EX, respectively). The error associated with this technique, which was below 11N for loads up to 125N, is comparable to that reported with other techniques. The new method shows promise for assessing facet load during in vitro spine testing, an important parameter when evaluating new implant systems and surgical techniques.     

A comparison of healthy human and swine articular cartilage dynamic indentation mechanics

Articular cartilage is a multicomponent, poroviscoelastic tissue with nonlinear mechanical properties vital to its function. A consequent goal of repair or replacement of injured cartilage is to achieve mechanical properties in the repair tissue similar to healthy native cartilage. Since fresh healthy human articular cartilage (HC) is not readily available, we tested whether swine cartilage (SC) could serve as a suitable substitute for mechanical comparisons. To a first approximation, cartilage tissue and surgical substitutes can be evaluated mechanically as viscoelastic materials. Stiffness measurements (dynamic modulus, loss angle) are vital to function and are also a non-destructive means of evaluation. Since viscoelastic material stiffness is strongly strain rate dependent, stiffness was tested under different loading conditions related to function. Stiffness of healthy HC and SC specimens was determined and compared using two non-destructive, mm-scale indentation test modes: fast impact and slow sinusoidal deformation. Deformation resistance (dynamic modulus) and energy handling (loss angle) were determined. For equivalent anatomic locations, there was no difference in dynamic modulus. However, the HC loss angle was ~35% lower in fast impact and ~12% higher in slow sinusoidal mode. Differences seem attributable to age (young SC, older HC) but also to species anatomy and biology. Test mode-related differences in human-swine loss angle support use of multiple function-related test modes. Keeping loss angle differences in mind, swine specimens could serve as a standard of comparison for mechanical evaluation of e.g. engineered cartilage or synthetic repair materials.     

The compressive material properties of the plantar soft tissue

The plantar soft tissue is the primary means of physical interaction between a person and the ground during locomotion. Dynamic loads greater than body weight are borne across the entire plantar surface during each step. However, most testing of these tissues has concentrated on the structural properties of the heel pad. The purpose of this study was to determine the material properties of the plantar soft tissue from six locations beneath: the great toe (subhallucal), the 1st, 3rd and 5th metatarsal heads (submetatarsal), the lateral midfoot (lateral submidfoot) and the heel (subcalcaneal). We obtained specimens from these locations from 11 young, non-diabetic donors; the tissue was cut into 2 cm x 2 cm blocks and the skin was removed. Stress relaxation experiments were conducted and the data were fit using the quasi-linear viscoelastic (QLV) theory. To determine tissue modulus, energy loss and the effect of test frequency, we also conducted displacement controlled triangle waves at five frequencies ranging from 0.005 to 10 Hz. The subcalcaneal tissue was found to have an increased relaxation time compared to the other areas. The subcalcaneal tissue was also found to have an increased modulus and decreased energy loss compared to the other areas. Across all areas, the modulus and energy loss increased for the 1 and 10 Hz tests compared to the other testing frequencies. This study is the first to generate material properties for all areas of the plantar soft tissue, demonstrating that the subcalcaneal tissue is different than the other plantar soft tissue areas. These data will have implications for foot computational modeling efforts and potentially for orthotic pressure reduction devices.     

Methodological and physiological variability within the ventilatory response to hypoxia in humans.

Measurement of the acute hypoxic ventilatory response (AHVR) requires careful choice of the hypoxic stimulus. If the stimulus is too brief, the response may be incomplete; if the stimulus is too long, hypoxic ventilatory depression may ensue. The purpose of this study was to compare three different techniques for assessing AHVR, using different hypoxic stimuli, and also to examine the between-day variability in AHVR. Ten subjects were studied, each on six different occasions, which were >/=1 wk apart. On each occasion, AHVR was assessed using three different protocols: 1) protocol SW, which uses square waves of hypoxia; 2) protocol IS, which uses incremental steps of hypoxia; and 3) protocol RB, which simulates an isocapnic rebreathing test. Mean values for hypoxic sensitivity were 1.02 +/- 0.48, 1.15 +/- 0.55, and 0.93 +/- 0.60 (SD) l. min(-1). %(-1) for protocols SW, IS, and RB, respectively. These differed significantly (P < 0.01). The coefficients of variation for measurement of AHVR were 20, 23, and 36% for the three protocols, respectively. These were not significantly different. There was a significant physiological variation in AHVR (F (50,100) = 3.9, P < 0. 001), with a coefficient of variation of 26%. We conclude that there was relatively little systematic variation between the three protocols but that AHVR varies physiologically over time.     

The effects of refreezing on the viscoelastic and tensile properties of ligaments

Biomechanical testing protocols for ligaments can be extensive and span two or more days. During this time, a specimen may have to undergo more than one cycle of freezing and thawing. Thus, the objective of this study was to evaluate the effects of refreezing on the viscoelastic and tensile properties of ligaments. The femur-medial collateral ligament-tibia complexes (FMTC) from six pairs of rabbit knees were used for this study. Following sacrifice, one leg in each pair was assigned to the fresh group and the FMTC was immediately dissected and prepared for testing. The contralateral knees were fresh-frozen at -20 degrees C for 3 weeks, thawed, dissected and then refrozen for one additional week before being tested as the refrozen group. The cross-sectional area and shape of the medial collateral ligament (MCL) was measured using a laser micrometer system. Stress relaxation and cyclic stress-relaxation tests in uniaxial tension were performed followed by a load to failure test. When the viscoelastic behavior of the MCL was described by the quasi-linear viscoelastic (QLV) theory, no statistically significant differences could be detected for the five constants (A, B, C, tau1, and tau2) between the fresh and refrozen groups (p > or = 0.07) based on our sample size. In addition, the structural properties of the FMTCs and the mechanical properties of the MCLs were also found to be similar between the two groups (p > or = 0.68). These results suggest that careful refreezing of the specimens had little or no effect on the biomechanical properties measured.     

Determination of Poisson's ratio of articular cartilage by indentation using different-sized indenters

Articular cartilage is often characterized as an isotropic elastic material with no interstitial fluid flow during instantaneous and equilibrium conditions, and indentation testing commonly used to deduce material properties of Young's modulus and Poisson's ratio. Since only one elastic parameter can be deduced from a single indentation test, some other test method is often used to allow separate measurement of both parameters. In this study, a new method is introduced by which the two material parameters can be obtained using indentation tests alone, without requiring a secondary different type of test. This feature makes the method more suitable for testing small samples in situ. The method takes advantages of the finite layer effect. By indenting the sample twice with different-sized indenters, a nonlinear equation with the Poisson's ratio as the only unknown can be formed and Poisson's ratio obtained by solving the nonlinear equation. The method was validated by comparing the predicted Poisson's ratio for urethane rubber with the manufacturer's supplied value, and comparing the predicted Young's modulus for urethane rubber and an elastic foam material with modulii measured by unconfined compression. Anisotropic and nonhomogeneous finite-element (FE) models of the indentation were developed to aid in data interpretation. Applying the method to bovine patellar cartilage, the tissue Young's modulus was found to be 1.79 +/- 0.59 MPa in instantaneous response and 0.45 +/- 0.26 MPa in equilibrium, and the Poisson's ratio 0.503 +/- 0.028 and 0.463 +/- 0.073 in instantaneous and equilibrium, respectively. The equilibrium Poisson's ratio obtained in our work was substantially higher than those derived from biphasic indentation theory and those optically measured in an unconfined compression test. The finite element model results and examination of viscoelastic-biphasic models suggest this could be due to viscoelastic, inhomogeneity, and anisotropy effects.     

Bi-directional mechanical properties of the axillary pouch of the glenohumeral capsule: implications for modeling and surgical repair

The objective of this study was to determine the mechanical properties of the axillary pouch of the inferior glenohumeral ligament in the directions perpendicular (transverse) and parallel (longitudinal) to the longitudinal axis of the anterior band of the inferior glenohumeral ligament. A punch was used to excise one transverse and one longitudinal tissue sample from the axillary pouch of each cadaveric shoulder (n = 10). Each tissue sample was preconditioned and then a load-to-failure test was performed. All tissue samples exhibited the typical nonlinear behavior reported for ligaments and tendons. Significant differences (p < 0.05) were detected between the transverse and longitudinal tissue samples for ultimate stress (0.8 +/- 0.4 MPa and 2.0 +/- 1.0 MPa, respectively) and tangent modulus (5.4 +/- 2.9 MPa and 14.8 +/- 13.1 MPa, respectively). No significant differences (p > 0.05) were observed between the ultimate strain (transverse: 23.5 +/- 11.5%, longitudinal: 33.3 +/- 23.6%) and strain energy density (transverse: 10.8 +/- 8.5 MPa, longitudinal: 21.1 +/- 15.4 MPa) of the transverse and longitudinal tissue samples. The ultimate stress determined for the longitudinal axillary pouch tissue samples was comparable to a previous study that reported it to be 5.5 +/- 2.0 MPa. The ratio of the longitudinal to transverse moduli (3.3 +/- 2.8) is considerably less than that of the medial collateral ligament of the knee (30) and interosseous ligament of the forearm (385), suggesting that the axillary pouch functions to stabilize the joint in more than just one direction. Future models of the glenohumeral joint and surgical repair procedures should consider the properties of the axillary pouch in its transverse and longitudinal directions to fully describe the behavior of the inferior glenohumeral ligament.     

A method for measuring linearly viscoelastic properties of human tympanic membrane using nanoindentation

A viscoelastic nanoindentation technique was developed to measure both in-plane and through-thickness viscoelastic properties of human tympanic membrane (TM). For measurement of in-plane Young's relaxation modulus, the TM sample was clamped on a circular hole and a nanoindenter tip was used to apply a concentrated force at the center of the TM sample. In this setup, the resistance to nanoindentation displacement can be considered due primarily to the in-plane stiffness. The load-displacement curve obtained was used along with finite element analysis to determine the in-plane viscoelastic properties of TM. For measurements of Young's relaxation modulus in the through-thickness (out-of-plane) direction, the TM sample was placed on a relatively rigid solid substrate and nanoindentation was made on the sample surface. In this latter setup, the resistance to nanoindentation displacement arises primarily due to out-of-plane stiffness. The load-displacement curve obtained in this manner was used to determine the out-of-plane relaxation modulus using the method appropriate for viscoelastic materials. From our sample tests, we obtained the steady-state values for in-plane moduli as approximately 17.4 MPa and approximately 19.0 MPa for posterior and anterior portions of TM samples, respectively, and the value for through-thickness modulus as approximately 6.0 MPa for both posterior and anterior TM samples. Using this technique, the local out-of-plane viscoelastic modulus can be determined for different locations over the entire TM, and the in-plane properties can be determined for different quadrants of the TM.     

Quantifying the effectiveness of the sustained muscle stretching treatments in stroke patients with ankle hypertonia.

Sustained muscle stretch (SMS) is commonly used to reduce hypertonia. The present study evaluates the effectiveness of three different SMS protocols, namely constant-angle, cyclic, and constant-torque stretching, in the immediate reducing of ankle hypertonia. Forty-seven hemiplegic subjects, 53.7+/-10.3 years old and 22.4+/-16.0 months after stroke, with hypertonic ankle joints were recruited to undergo three SMS applied to protocols treatment their hypertonic ankle joints using an integrated treatment/assessment system. The immediate post-treatment effectiveness of each stretching protocol was assessed by reference to the pre-treatment Modified Ashworth Scale (MAS), passive range of motion (ROM), and reactive torque measurement, from which the viscous-elastic components of the ankle joint were derived. All three SMS protocols successfully reduced MAS grade. Additionally, each stretching method yielded an increase in ankle ROM, from 9.7 degrees to 16 degrees , 9.6 degrees to 14.8 degrees , and 9.2 degrees to 18.3 degrees for the constant-angle, cyclic-stretching, constant-torque protocols, respectively, and reduction of the elastic and viscous properties of the ankle joint dorsiflexion (p<0.05). The changes in the ROM, elasticity, and viscosity were most pronounced in the case of the constant-torque stretching protocol. In addition to clinical scales, current biomechanical assessments indicate that three SMS protocols are all effective in reducing the immediate viscoelastic components of hypertonic ankle joints. Our quantitative analysis further shows that of the three treatment protocols, the constant-torque treatment is the most effective.     

Measuring the transverse Young’s modulus of maize rind and pith tissues

Wind-induced bending loads frequently cause failure of maize (corn) stalks. When failure occurs, it usually manifests as transverse buckling. Because this failure mode is closely related to transverse tissue stiffness, the purpose of this study was to develop a method for measuring the transverse Young’s modulus of maize stalk rind and pith tissues. Short, disc-shaped stalk segments were used for this purpose. X-ray computed tomography was used to obtain the geometry of each specimen prior to testing. Each specimen was tested in two different configurations. Computed tomography data was used to create a specimen-specific finite element model of each test specimen. Data from the first testing configuration was used in conjunction with the finite element model to determine the Young’s Modulus values for each specimen. The specimen-specific finite element models provided estimates of the stress states in the stem under transverse loading, and these stress states accurately predicted the location of failure in transverse test specimens. The entire testing method was validated using data from one test configuration to predict the structural response of each specimen during the second test configuration.     

A biomechanical study of the human periodontal ligament

The mechanical properties of the normal human periodontal ligament (PDL) were investigated at eight different root levels. One millimetre transverse sections of teeth, PDL and alveolar bone of mandibular premolars were examined in a materials testing machine. During testing bone was supported by metal rings and teeth by metal cylinders of individually adjusted sizes. Having corrected for differences of size and width of the PDL the influence of root level was estimated using a multivariate analysis of variance. The shear strength was almost constant at the upper part of the root, diminishing in apical direction. The shear extensibility and the relative failure energy in shear were higher at the middle of the root, diminishing coronally and apically. Only the elastic stiffness did not vary significantly along the root. These results demonstrate that in order to compare the mechanical properties of PDL care should be taken to compare areas at the same root level.