Molecular basis of the elastic properties of biological objects

MOLECULAR 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: 885