Mechanical Properties of Tissue

This chapter reviews the mechanical properties of tissues, including their densities, moduli of elasticity, and ultimate strengths. The density of tissue may be measured by comparing the mass of a sample in air with the apparent mass measured in water. The density is calculated from the ratio of the apparent masses and knowledge of the density of water at the measurement temperature. Density varies as a function of temperature. The factors affecting elasticity in a tissue can be humidity, tissue composition—either collagen or elastin—and the viscoelasticity of the tissue. Thereafter, the ultimate tensile strength of soft tissue is more amenable to simple numeric evaluation than is the general nonlinear stress–strain relationship. A number of factors may affect this soft tissue property such as age of the tissue, humidity, and the shear and bursting strength of the tissue. The viscosity of a fluid may be measured either by observing its flow along a capillary tube or by the use of a rotational viscometer. The viscometer applies an almost uniform shear rate across the fluid and can be used to investigate the variation of viscosity with velocity gradient. Subsequently, it has been noticed that blood viscosity increases with hematocrit and decreases with temperature.