The glue distorts and reduces the concentration of the stress, and the adjacent fibers consequently are not exposed to the same high stress. In effect, the epoxy glue acts to spread the stress over many fibers. Bone is constructed in a similar manner. Within bone, the collagen is laid down along the lines of stress. No crack can penetrate far into bone without encountering myriad hydroxyapatite crystals in a collagenous matrix.
Bone is more rigid than collagen, just as fiberglass is more rigid than epoxy glue.
The ends and interiors of long bones are composed of an open lattice of bone called spongy bone tissue or marrow. Within this lattice framework, most of the body's red blood cells are formed. Surrounding the spongy bone tissue at the core of bones are concentric layers of compact bone tissue in which the collagen fibrils are laid down in a pattern that is far denser than marrow. The compact bone tissue gives the bone the strength to withstand mechanical forces. New bone is formed by cells called osteoblasts, which secrete collagen fibers on which calcium subsequently is deposited.