Fracture Toughness Evaluation of Cortical Bone Preserved by Different Methods

Bone specimens used for evaluating the mechanical properties of bone have not necessarily been preserved by the same method before they become available. However, the mechanical properties of bone may be influenced by freezing, a common preservation method, as well as by formalin and other preservation solutions. In this study, bone specimens were preserved by different methods (freezing, physiological saline solution, ethanol, formalin and neutral buffered formalin) to examine the effects of preservation method on the fracture characteristics of bovine femoral cortical bone. Regarding the crack extension behavior in the fracture toughness test, microcracks accumulated at the top of the slit in the low load region before the maximum load was reached. When such accumulated microcracks grew to a visible size, a crack was formed from the top of the slit, and then grew with subsequent expansion of the processing zone. The fracture toughness values of the groups preserved in formalin and neutral buffered formalin were significantly lower than those of other preservation groups. As the fracture surface by SEM observations was smoother with a loading rate of 20 mm/min than 1 mm/min, cracks were considered to develop easily, resulting in a lower fracture toughness value. SEM observations of a test section subjected to a low loading rate showed that the fracture surface of the groups preserved in formalin or neutral buffered formalin was flat and smooth. In the other preservation groups, the lamellae adjacent to the top of the slit had undulating fracture surface, with plastic deformation produced.