Mend the gap

Bone is a tough substance, but exactly how it resists cracks and breaks has been difficult to determine. In the March of Nature Materials, Nalla et al. take on this question. One way that bones stay tough is by bridging gaps using structures such as collagen fibrils) (shown in this scanning electron micrograph). An even more important contributor to bone toughness is deflection of cracks along so-called cement lines, the boundaries between osteons (cylinder-like bone structures). The authors made notches on the edges of bones and found that the cracks developed similiarly to those seen in ductile substances such as certain metal alloys—at the site of the notch, instead of ahead of it. The investigators are eager to examine bone properties in people of different ages and with diseases such as osteoporosis. Some osteoporosis drugs can inhibit bone remodeling, a process that counterbalances bone consumption with bone formation. Such treatments could result in disrepair and the accumulation of 'micro-cracks' as the body ages.