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Molecular basis of the elastic properties of biological objectsMOLECULAR BASIS OF ELASTIC PROPERTIES bioobject The elastic properties and strength of tissues except bone, mainly determined by the elastin and collagen fibers and their complexes. Higher strength and modulus of elasticity of bone caused by the presence "fiberglass" structures built of collagen and crystals hydroxyapatite. Proteins elastin and collagen are part of precisely those tissues that continuously subjected to mechanical stresses. For example, in the lung Collagen and elastin are respectively 12-20 and 5-10% by dry weight. In wall of large blood vessels on these proteins may account for about 50% by dry weight. The ratio of elastin and collagen in arterial wall changes in the course of the circulatory system. In the wall Thoracic aortic elastin x 1/2 times as much as the abdominal aorta and other large arteries is about 3 times less than collagen. since mechanical properties of elastin and collagen fibers are not the same, the difference in their contents, but also in the spatial arrangement within the vascular the wall causes that the elastic properties of different vessels strongly differ. Elastin filaments have a relatively high elongation, ie. E. low modulus of elasticity in tension along the fiber: (0,4-1,0) • 10e N / m2. Collagen threads have an order of magnitude higher modulus (0,5-1,0) • 107 N / m 2 m. Ie. Characterized by a low ability to stretching. It is believed that in the tissues of elastin fibers are under voltage even at moderate tension. Collagen fibers alone are currently in a state of tension only when a strong deformation Fabric: With a high modulus of elasticity and strength, these fibers prevent rupture of tendons, blood vessel walls and other fabrics with large mechanical loads, and provide light alveolar tissue stabilization at high volumes. With a weak strain tissue collagen strands are not stretched, but it deforms their network. The most detailed nature of the deformation of tissue at various elongations studied in skeletal muscle by thermodynamic methods. We will consider muscle deformation under constant volume and its unchanged temperature. According to the laws of thermodynamics (refer. Ch. One) change muscle free energy during deformation by external force f is the mechanical work / A / done on the muscle by its elongation of A /. On the basis of the equation (1.2), in which the Academy of Sciences = AU due to a constant volume, we get: f = - TA [SIAl & [U / Al, (10.22) where the subscript I denotes the dependence on the length. From this equation, it is clear that the resulting tensile elastic muscle force (right-hand side equation) is determined by the change in the entropy change in the internal and AtS energy AtU. Of interest are the two extreme cases. If AtU - 0, the elastic force is described by only the first term on the right side of equation (10.22), and its occurrence is associated with a decrease in entropy, as this term is positive in sign at AtS • <0. The reduction in entropy indicates that the process should be released elongation heat. This thermal effect is observed in the experiment on the muscle when it is sprains, relevant section A in Fig. 78 Consequently, the deformation is associated with a decrease in entropy, and its mechanism is orientation of the moving parts of the protein molecules responsible for the elastic muscle properties along the direction of the force /. Thus there is an ordering the molecular structure of the muscles, reduces the number of possible conformations (states) of proteins. Component - TAtS / Al in equation (10.22) is often called thermokinetic elastic force.
Literature which was used: Wikipedia- free encyclopedia which contain general information about mechanical properties of biological tissues. Biophysics - Yuri Vladimirov- this book gives correct and true information information about mechanical properties of biological tissues.
Date: 2016-01-03; view: 995
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