Viscoelasticity

The Viscoelasticity combines the elastic properties of substances and the viscous properties of fluids and is found in the human body, in addition to the blood, primarily in the soft tissues. In the blood, the viscosity of the substance increases in the context of the hyperviscosity syndrome. In the soft tissues, disorders of the viscoelasticity can occur in the context of neuromuscular diseases.

What is the viscoelasticity?

Material can behave in a number of ways. One possible material behavior is elasticity, which allows fabrics to return to their original position after the application of force. The viscosity describes the viscosity of a fluid and thus corresponds to a measure of the flowability of a liquid.

The viscoelasticity is a mixture of the material behavior of the elasticity and the flowability behavior of the viscosity. Accordingly, viscoelastic materials show both viscous and elastic material behavior. They combine certain material properties of solids with material properties of fluids.

Viscoelastic effects depend on factors such as temperature, time and frequency. Viscoelastic properties of substances play an important role in biophysics. For example, blood has viscoelasticity. The same applies to soft tissue and other cell associations.

In this context, blood is, for example, a non-Newtonian liquid and does not carry its viscosity (blood viscosity) as a material constant, but changes it with the effects of shear. Newtonian fluids, on the other hand, show linearly viscous flow behavior and thus have load-independent viscosity, while viscoelastic fluids like blood react to certain loads with elasticity.

Function & task

Soft tissues are soft tissues such as adipose tissue, muscle tissue, and connective tissue. They consist of collagen, parts of elastin and the basic substance. This structure is called the extracellular matrix of the soft tissue. The basic substance consists to a large extent of water, whereby fibroblasts and chondroblasts produce the fibers and basic substance of the soft tissue.

Viscoelasticity is one of the mechanical properties of soft tissue. With relatively little stress in the form of low stretching, the elastin in the fabric ensures rigidity. The distortion energy is stored in the elastin. The collagen fibers contained in the tissue have a wavy shape when at rest and are relatively elastic. The more the tissue deforms, the more they stretch in the direction of the deformation. After relaxation, the fibers again increase the tissue stiffness.

The fabric behavior is similar to a nylon stocking. The elastin takes on the role of the nylon rubber band and the collagen fulfills the function of the nylon fibers. In this respect, collagen limits the stretching of the tissue and thus protects against injuries.

Human soft tissue can therefore be severely deformed and still return to its original shape.

Physical viscoelasticity can also be observed in relation to the blood. Chemically speaking, blood is a suspension of the Newtonian fluid water and cellular, i.e. material components. Blood is a non-Newtonian liquid and therefore shows different flow properties than water. Because of the erythrocytes it contains, the viscoelasticity of blood is increased compared to plasma. The viscosity increases with the hematocrit value and the flow rate. Due to the deformability of red blood cells (erythrocytes), the flow behavior of blood does not resemble that of a cell suspension when the flow rate increases, but changes to the flow behavior of an emulsion.

Illnesses & ailments

Neuromuscular diseases increase the viscoelasticity in muscle and fascia tissue. This increase in viscoelasticity of the fascia exerts pressure on the myofascial tissue. The increase in viscoelasticity in the myofascial tissue itself has not yet been conclusively researched, but seems to be related to dysfunctions or incorrect regulation by the sympathetic nervous system.

Neuromuscular diseases form an inhomogeneous group of diseases of the muscle cells, neuromuscular transmission or the peripheral nerves. The neuromuscular diseases include, in particular, myopathies and neuropathies. Myopathies are non-neurogenic diseases with structural changes or functional limitations of the affected muscles, which in most cases affect the striated skeletal muscles. Muscular dystrophy is an example of a myopathy.

Neuropathies are diseases of the peripheral nerves without a traumatic origin. Neuropathy can affect single or multiple nerves. Common manifestations are pain or loss of irritation in the affected area. In a late episode, flaccid paralysis of the affected muscles occurs. Myopathies are characterized by weaknesses or degeneration of muscle tissue, which can be traced back to relationships such as genetic mutation or mitochondrial insufficiency.

Viscoelastic disorders can occur not only in the soft tissue of the body. For example, a symptom complex of the blood caused by an increased concentration of paraproteins in the blood plasma is known as hyperviscosity syndrome. Because of the increased viscosity, the flowability of the blood is reduced. The hyperviscosity syndrome occurs in particular in the context of malignant diseases, such as multiple myeloma or Waldenström's disease.

Benign diseases such as Felty's syndrome, lupus erythematosus or rheumatoid arthritis can also be associated with the increase in viscosity. The patients mostly suffer from tiredness, feelings of weakness and shortness of breath.

Anemia (anemia) is caused by mucosal and nosebleeds. It is favored by impaired platelet function. The platelet dysfunction results from an obstruction of the clotting receptors. The platelets are coated with paraproteins and no longer bind to the receptors, but instead interact with the formation of fibrin. The resulting symptoms are similar to those of microangiopathy. The risk of thrombosis and thromboembolism increases significantly.