Читать книгу The Rheology Handbook - Thomas Mezger - Страница 230

Life itself could not have developed in all its diversity, were it not for the complex interplay of natural VE liquids and VE solids.

Examples: Blood (if the elastic portion of this VE liquid is too high, there is the risk of a stroke; haemo-rheology, i. e., blood-rheology), mucus, the synovial fluid (to lubricate the knee joint), the vitreous body of the eyes (the water content of this gel-like material is more than 98 %); soft, flexible, swellable, taut or firm tissues (such as skin, cornea, cartilages, body fat); arteries and veins (if they are becoming too inflexible, this may lead to arteriosclerosis, which means artery hardening), leaves, twigs, tendons, barks, bones, wood, tree trunks.

The spine is a complex natural composite material consisting of disks (fibers with a gelatinous core), vertebrae (spongy bone containing bone marrow), ligaments, joints and connecting tissue. Its task is to give stability to the body, to absorb impacts, to show elasticity and also to enable us to make bending, stretching and torsional motions [5.25] [5.26] [5.27].

These areas of medical technology/biotechnology are opening up new opportunities for designers and engineers who work on the modification and development of natural and artificial tissues, cartilages, bone cements and implants (such as TEMPs, tissue engineered medical products [5.18]). By the way, this is also a working field of tribology (see Chapter 10.8.4.3).

When performing rheological tests on biological materials, it is important to take into consideration that these kinds of materials usually cannot be deformed evenly in the entire shear gap due to their mostly inhomogeneous and anisotropic structures and superstructures, related to the size of the macroscopic structures in the range of around 0.1 mm to 1 mm. This may lead to conditions at which the reproducibility of test results will be poor, and therefore, these kinds of materials often cannot be analyzed scientifically in terms of absolute values (see also Chapter 3.3.4.2c: inhomogeneous, “plastic” behavior).