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Dentin, the main tissue of the tooth, is made of tubules surrounded by peri-tubular dentin (PTD), embedded in a matrix of inter-tubular dentin (ITD). The PTD and the ITD have different relative fractions of collagen and hydroxyapatite crystals. The ITD is typically less rigid than the PTD, which can be seen as a set of parallel hollow cylindrical reinforcements in the ITD matrix. In this paper, we extend Hashin and Rozen's homogenization scheme to a nonuniform distribution of hollow PTD cylinders, determined from image analysis. We relate the transverse isotropic elastic coefficients of a Representative Elementary Volume (REV) of dentin to the elastic and topological properties of PTD and ITD. The model is calibrated against experimental data. Each sample tested is consistently characterized by Environmental Scanning Electron Microscopy (ESEM), nanoindentation and Resonant Ultrasound Spectroscopy (RUS), which ensures that macroscopic mechanical properties measured are correlated with microstructure observations. Despite the high variability of microstructure descriptors and mechanical properties, statistical analyses show that Hashin's bounds converge and that the proposed model can be used for back-calculating the microscopic Poisson's ratios of dentin constituents. Three-point bending tests conducted in the laboratory were simulated with the Finite Element Method (FEM). Elements were assigned transverse isotropic elastic parameters calculated by homogenization. The tubule orientation and the pdf of the ratio inner/outer tubule radius were determined in several zones of the beams before testing. The remainder of the micro-mechanical parameters were taken equal to those calibrated by RUS. The horizontal strains found experimentally by Digital Image Correlation (DIC) were compared to those found by FEM. The DIC and FEM horizontal strain fields showed a very good agreement in trend and order of magnitude, which verifies the calibration of the homogenization model. By contrast with previous studies of dentin, we fully calibrated a closed form mechanical model against experimental data and we explained the testing procedures. In elastic conditions, the proposed homogenization scheme gives a better account of microstructure variability than micro–macro dentin models with periodic microstructure. [ABSTRACT FROM AUTHOR]

The goal of this paper is to examine the trapezius muscle tone by measuring simultaneously using Myoton-2 myometer i.e., the natural oscillation frequency, stiffness and the elasticity of the trapezius muscle. With this method, the mechanical response of the muscle, to a short applied mechanical impulse, is registered by an acceleration probe. From the acquired damped natural oscillation waveform, the frequency (Hz), the stiffness (N/m) and the logarithmic decrement of damping (characterizing tissue's elasticity) are calculated, quantifying the functional state of the muscle. The trapezius muscle on both sides of the body was tested in twenty adult women by two investigators using the Myoton-2 myometer. During the measurements, the subjects were in a relaxed sitting position. The Bland and Altman graphical test, comparing the differences of the measurements of two investigators, was used for assessing the inter-observer repeatability. The registered values for the trapezius muscle tension, stiffness and elasticity are varying between the tested subjects, but the intra-class correlation coefficient (ICC) was near 1 for three muscular properties, showing that the variation within the subject (due to the investigator) is negligible, compared with the variation between the subjects. [ABSTRACT FROM AUTHOR]

Chiral growth is ubiquitous in nature and has always been of great interest in the field of biomimetic and man-made materials, but its formation mechanism is complex. In order to clarify this mechanism, with the help of the plate theory and the theory from differential geometry, we established a new theoretical model that can be used to describe the interaction between anisotropic elasticity and anisotropic residual stress of slender biomaterials and provide additional insight onto the mechanical mechanism of biomaterial's morphological chiral growth. Based on these results, it appears that misfit of material properties and residual stresses may create various chiral morphologies, like helices and twisting belts. It is found here that the cooperative and competitive interactions between anisotropic elasticity and anisotropic residual stress can also give rise to chiral morphologies, and macro shapes, sizes, and handedness of chiral morphologies can be designed by residual stresses orientation angles and elastic parameters of biomaterials. This theoretical model is in good agreement with the recent experiments and can provide theoretical guidance for the design of medical-assisted soft robots. [ABSTRACT FROM AUTHOR]

Understanding the deformation of arterial walls under loading is essential for the definition of some new therapeutic protocols. This requires the modeling of the mechanical behavior of the artery wall. In this work, in order to account for the microstructure, each of the conventional three layers of the artery is assumed to behave like a dilatation elastic solid. The resulting compound is then submitted to various loads and the response analyzed in order to highlight the contribution of the microstructure. Finally, the impact of a localized zone of microstructure modification on the overall deformation is investigated. [ABSTRACT FROM AUTHOR]

The low-intensity ultrasound effects on MCF7 (human breast adenocarcinoma) and MCF10A (healthy breast cells) have been investigated at different sonication protocol to probe the effectiveness and the selectivity of the ultrasound (US) treatment and to understand the implications between cell mortality, biomechanical interactions and cell elastic modulus. Experiments performed at fixed and variable frequency demonstrated the effectiveness of some protocols in killing carcinogenic cells and the healthy cells insensitivity. Variation of elastic properties of MCF7 cells exposed to US under varying sonication conditions was examined. Sonication was carried out at fixed frequency (as it is usually done in therapy protocols), between 400 kHz and 620 kHz, following two protocols: (i) at fixed power output; (ii) at fixed voltage of the US generator. Evolution of cell stiffness during the US treatment was monitored via atomic force spectroscopy (AFS). It was found that cell mortality has a similar trend of variation with respect to sonication frequency regardless of the way specimens are exposed to US. Mechanical properties do not show a uniform trend with respect to frequency, but variations of Young's modulus are more marked near the very low (400–480) kHz or very high frequencies (580–620) kHz. The observed variations may be related to mechanical interactions occurring in the cell culture, suggesting a primacy of the environment on other factors. [ABSTRACT FROM AUTHOR]

Helices are ubiquitous building blocks in natural systems, and have since become major sources of inspiration for engineering design of helical devices with a range of applications in sensors, transducers, transistors and micro-robotics devices. In this work, we illustrate the mechanical self-assembly principle in spontaneous helical structures, and perform finite element simulations to model such large deformation of thin structures in three dimensions. Our work can facilitate designs of tunable helical structures at both macroscopic and microscopic scales with desirable geometric parameters for engineering applications such as in nanoelectromechanical systems (NEMS), drug delivery, sensors, acturators, optoelectronics and microbotics. [ABSTRACT FROM AUTHOR]

A novel recursive algorithm was proposed to calculate the input impedance of human systemic arterial tree, and to simulate the human systemic arterial hemodynamics with an 55 segment transmission line model. In calculation of input impedance, the structure of the arterial tree was expressed as a single linked list. An infinitesimal constant was used to replace 0 Hz frequency to calculate the DC and AC part of input impedance simultaneously. The input impedance at any point of the arterial tree can obtain easily by the proposed recursive algorithm. The results of input impedance are in accord with experimental data and other models' results. In addition, some comparisons were conducted about the effects of arterial compliance, length, internal radius and wall thickness on the input impedance of ascending aorta. The results showed input impedances of ascending aorta displayed significantly different characteristics for different kinds of parameters. Finally, the blood pressure and flow waveforms of all arterial segments were calculated and displayed in 3D. The arterial elasticity and viscosity were discussed by changing the Young's modulus and the phase difference, respectively. The simulation results showed that the blood pressure and flow waveforms of the arterial tree reflected accurately the main characteristic features of physiopathological changes, which demonstrated the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Wrist pulse diagnosis has been used in traditional Chinese medicine (TCM) for thousands of years, because pulse pressure signal contains a large number of physiological and pathological information of people. In this research, a systematic approach was proposed to analyze the computerized radial pressure waveform, with the focus placed on the power spectrum. We gained the power spectrum by using a modified fast Fourier transform, and the power-spectral characteristics were analyzed and compared. The analyzing program calculated the first peak frequency (F1) and the second peak (F2) automatically, and gained the time of phase shift between two frequencies. They could provide a simple noninvasive means for studying changes in the elastic properties of the vascular system depending on the age and the disease. Namely, the frequency analysis of radial pressure waveform gives new insight into the dynamics of cardiovascular system. [ABSTRACT FROM AUTHOR]

Young's modulus and structural stiffness were determined for chordae tendineae of the mitral valve from young (18-26 weeks) and old (over 2 years) porcine hearts. For chordae from the posterior leaflet of the valve, the Young's modulus values were significantly higher (p < 0.05) for the thinner marginal chordae (59 ± 31 MPa young; 88 ± 21 MPa old) than for the thicker basal chordae (31 ± 4 MPa young; 28 ± 9 MPa old). Marginal chordae (both anterior and posterior) had significantly higher (p < 0.05) value for their Young's modulus in old (88 ± 21 MPa anterior and posterior) than in young (62 ± 17 MPa anterior, 59 ± 18 MPa posterior) pig hearts. There was no significant difference in structural stiffness between marginal and basal (anterior and posterior leaflets) or between strut chordae (that are associated with anterior the leaflet only) and marginal and basal chordae. However, the value of structural stiffness of chordae was significantly higher (p < 0.05) for old (2.2 ± 0.2 kN/m) than for young (2.0 ± 0.4 kN/m) chordae. These results show that aging affects the properties of chordae and that all chordae need to be included in finite element models of valve function. [ABSTRACT FROM AUTHOR]

The mechanical properties of bone extracellular matrix have become of increasing interest for the understanding of vertebral fracture risk. Depth-sensing indentation techniques allow the measurement of directional elastic properties of trabecular bone ex vivo with a high spatial resolution. Transverse isotropic elastic properties of vertebral trabecular bone obtained from two orthogonal directions were investigated using microindentation under dry conditions focusing on the influence of microanatomical location, age, gender, vertebral level, and anatomic direction on these properties. Biopsies were obtained from 104 human vertebrae (T1–L3) with a median age of 65 (21–94) years. Significantly, higher indentation moduli were found for indentations on axial than on transverse cross-sections of trabeculae (p < 0.01). Indentation moduli in the core were 1.05 to 1.12 times higher than in the periphery (p < 0.01). No difference in stiffness could be detected between males and females (p > 0.05) and different ages (p > 0.5). Vertebral level showed a weak correlation (p = 0.073, r2 ≈ 0.17). These results provide insights in the transverse isotropic properties of trabecular bone matrix related to age, gender, microanatomical location, and anatomic direction for a broad spectrum of human vertebrae. [ABSTRACT FROM AUTHOR]