Passive mechanical properties of biological tissues

Passive mechanical properties of biological tissues

Plan:

1. Introduction

• Mechanical properties of biological tissues

II.   The main part

• Version of mechanical properties of biological fabrics.
• Passive mechanical properties biological bodies.
• Deformation. Kinds of deformation.
• Mechanical properties of muscles and bones.
• Fabric of blood vessels.

III. Conclusion

Mechanical properties of biological tissues

The mechanical properties of biological tissues and organs are shown in their response to mechanical stress. A measure of the interaction of physical bodies is power. The force acting on a unit surface of the body, called the surface force, or surface load (s):

It is this physical quantity is usually characterized in biomechanics mechanical effects on living tissues and organs.

Version of mechanical properties of biological fabrics.

Due to the most important mechanical properties of biological tissues, through a variety of mechanical phenomena - such as the functioning of the musculoskeletal system, the process of deformation of tissues and cells, and propagation of elastic deformation of contraction and relaxation of muscles, movement of liquid and gaseous biological environments.

Among these properties are distinguished:

Resilience - the ability to renew the body dimensions (shape or volume) after removal of the load;

Rigidity - the ability of a material to oppose the external load;

Flexibility - the ability to change the size of the material under the influence of external forces;

Density - the ability to resist the destruction of bodies under the action of external forces;

Plasticity - the ability to store phone (fully or partially) change size after removal of the load;

Fragility - the ability of the material to break down non-significant residual strain;

Viscosity - dynamic properties that characterize the properties of the body to counteract the change in its form under the action of tangential stresses.;

Fluidity - Dynamic Property Protection, which describes the ability of its individual layers are mixed, with some speed in space relative to other sectors of the environment.

So under the mechanical properties of biological tissues understand two varieties:

• Passive mechanical properties of biological bodies
• The mechanical properties of the muscles and bones

 

Passive mechanical properties biological bodies.

Biological tissues have a complex anisotropic structure, depending on the functions for which they are intended. This amazing optimum structure can be seen in the design of the bones of the lower limbs or in the myocardium, which are reinforced with high-fiber in the district and spiral intersecting directions. Biological tissues have usually large deformation.

The relationship between the strength and elongation, respectively, between stress and strain is established experimental way and are non-linear.

Deformation. Kinds of deformation.

All real bodies can be deformed.

Deformation is a change in the relative position of the points of the body, which is accompanied by a change in its shape and size, due to the action of external forces on the body.

WAVE - disappears completely after the cessation of external forces.

Plastic (residual) - is the termination of the external forces.

Elastic-Plastic - incomplete disappearance of deformation.

Visco-elastic - a combination of viscous flow and elasticity.

The elastic strains are of the following types:

a) The tensile or compressive deformation occurs under the action of forces acting in the direction of the axis of the body:

b) bending strain:

c) deformation of the fold:

d) twisting deformation:

f) deformation of the cutting:

The main characteristics of deformation

Tensile strain (compression) occurs in the body by the action of a force directed along its axis.

where l₀ - initial linear dimension.

Δl - elongation of the body

Deformation ε (elongation) is given by

ε= Δl /l₀

ε - a dimensionless quantity

Elastic deformations obey Hooke's law, according to which the voltage is proportional to the strain:

 

where E - modulus of elasticity, it is equal to the tension created by the strain equal to one. In unilateral strain  E is also called Young's modulus.

If living tissues is low warp, then they are not appropriate to determine the Young's modulus and stiffness. Rigidity characterizes the ability of the physical environment to resist the formation of deformation.

Elasticity inherent polymer is called elasticity.

Biological structures, such as muscles, tendons, blood vessels, lung tissue, and others, are viscoelastic or viscoelastic system. Their passive mechanical properties, i.e. properties that appear in the action of an external force, it is possible to model a combination of elastic and viscous elements.

An example of a purely elastic element is perfectly elastic spring in which the deformation process is "instantly" and obeys Hooke's law:

 

Voltage

f - elastic force equal to the external force (load), which is attached perpendicular to the cross section with an area of ​​"S";

E - modulus of elasticity;

x and Dх - original length and its change during deformation.

   relative deformation

 

Mechanical properties of muscles and bones.

Almost all soft human tissue exhibit properties of viscoelasticity and viscoplastic. Mechanical properties of biological tissues have individual and depend on many factors - age, the feeding, environment, etc. Established, for example, that the strength of tissues and organs is increased to 20 years and then begins to decrease, and the strength of the teeth and the skin is increased to 50 years of age.

Muscles have a fibrous structure. Under the ordinary microscope easily observed striated muscle fiber structure. Individual muscle fiber has a diameter of 0.02-0.08 mm. It is surrounded by a membrane with a thickness of about 10 mm. Fiber consists of 1000-2000 finer fiber myofibril diameter of 1-2 mm. Fibrils have a shell formed tubules and vesicles of sarcoplasmic reticulum. Muscle contains mitochondria, located between the fibrils. Myofibril in turn consists of a number of protein fibers - thick and thin.

When excited by muscle changes its mechanical condition, and these changes are called reduction. It manifests itself in a change in muscle length and tension, as well as its other mechanical properties (elasticity, hardness, etc.).

Mechanical properties of muscles are complex and depend on the mechanical properties of the elements forming the muscle (muscle fibers, connective education, etc.), and the state of the muscle (excitation, fatigue, etc.).

Understand many of the mechanical properties of muscles helps simplified model of its structure - in the form of a combination of elastic and contractile components.

Elastic components on the mechanical properties similar to spring: to stretch them, you need to apply a force. The work force is equal to the elastic energy, which may in the next phase of the movement to go into mechanical work.

distinguish:

a) parallel elastic components (PARC) - a connective tissue formation, membrane components of muscle fibers and their bundles.

b) serial elastic components (POSCO) - tendon, place of transition myofibrils in the connective tissue, as well as some parts of the sarcomere, the exact location of which is currently unknown.

Contractile (contractile) components correspond to those parts of the muscle sarcomere, where actin and myosin myofilaments overlap. In these areas the muscles are excited by mechanical interaction between the actin and myosin filaments, leading to a change in muscle length and tension.

Resting muscle has elastic properties to its end when an external force, the muscle is stretched (the length is increased), and after removal of the external load recovers its original length.

Length, which tends to take the muscle, being delivered from all the load is called the equilibrium (or free). With such a long muscles of her elastic forces are zero.

For the muscles is also characterized by the property as relaxation - Reduces the elastic deformation over time.

Bone - the basic material of the musculoskeletal system. Strength of bone depends on the chemical composition, the general framework of the internal reinforcement, the number and strength of components, the main orientation of the components in relation to the longitudinal axis of the bone, age, density, individual growth conditions, etc.

Compact bone is an environment with five structural levels.

When the deformation of bone in it there is the piezoelectric effect. If you cut a strip of bone, secure it with one hand and subject to bending strain, it appears on the convex side of the "+" charge on the concave "-" charge, ie a potential difference.

There is evidence that the generation of piezoelectricity have a place in the mechanical load of bones in the body and an electric current can stimulate growth or resorption of bone.

Fabric of blood vessels.

Fabric - a system of cells and intercellular substance, united by a common origin, structure and function. The structure of the tissues of living organisms, studying science histology. Collection of different and interacting tissues form organs.

In humans, four main groups of tissues:

• epithelial
• connective
• nervous
• muscle

Epithelial tissue - are on the outer surface of the skin. In addition, they line the blood vessels, airways. They are:

the inner surface of blood vessels;

the inner surface of the airways.

  Connective tissue - have different functions: transportation, shifting, stretching. By connective tissues include:

  supporting tissue - cartilage and bone

liquid tissue - blood

adipose tissue, etc.

  Muscle tissue has contractility and excitability. Divided into:

smooth muscle that powers the blood vessels and internal organs.

striated muscle tissue

cardiac muscle tissue