5 - Mechanical behavior of structural tissues

Summary

Inquiry

How does the arrangement of collagen fibers in tendons assist in their function?

The question above represents a fundamental philosophy of this textbook. All materials, natural tissues included, have mechanical properties that reflect the chemical makeup and physical architecture of their microstructures. Tendons are assemblies of bundled collagen fibers arranged on a long axis that connect muscle to bone. Because tendons regularly experience axial tensile stresses with only very rare instances of other types of loading, this alignment optimizes the strength conferred by the collagen fibers by keeping them oriented in the direction of the greatest stress.

Historical perspective and overview

The earliest written records of anatomical study date back to 500 BCE, when Alcmaeon of Crotona asserted that the brain is the organ that governs intelligence. Later experiments by Claudius Galen (129–299 CE) were conducted on monkeys because human dissection was forbidden at that time. His theories on medicine (many of them incorrect, such as the concept that blood vessels were filled with grasping fibers that were responsible for blood flow) remained the basis of medical education for the next 1,400 years. Andreas Vesalius (1514–1564) made the next well-known advance in the understanding of human anatomy. Vesalius sought to recreate several of Galen's findings using human cadavers (by that time, human dissection was more accepted) and ultimately disproved many of them. In 1543, Vesalius published his results in De humani corporis fabrica (Mow and Huiskes, 2005; O’Malley, 1964), where, among other things, he concluded that it was the heart that caused blood to flow through arteries and veins. More recent developments in the study of natural tissues can be attributed to advances in histological techniques (microscopy), biochemical techniques (sample preparation and storage), and understanding of molecular biology (Piesco, 2002). While growth in these fields has led to a dramatic increase in our understanding of natural tissues, there remain aspects of many tissues that are still not fully understood, particularly regarding the relationship between their microstructure and overall physiological performance.