Influence of preservation in two kinds of formaldehyde solutions on the fracture characteristics of bovine femoral compact bones

Abstract

For the evaluation of the physical properties of bones, specimens are often either deep-frozen or chemically fixed with reagents such as formaldehyde (formalin) or ethanol for antisepsis and sterilization. However, formalin contains formic acid, which dissolves bone minerals such as Ca and P. To suppress this bone mineral elution, we tested neutral buffered formalin as a fixative. In this study, we investigated the influence of formalin and the neutral buffered formalin fixation on the fracture characteristics of bovine femoral compact bones over a relatively long-term preservation period. In both the formalin and the neutral buffered formalin fixation, bone minerals migrated rapidly into the fixatives. Thus, some aqueous solutions such as a normal saline solution may also dissolve bone minerals. In the neutral buffered formalin fixation, fine calcium phosphate grains precipitated on the surface of the soft tissues of blood vessels in the Haversian canal, as observed by scanning electron microscopy. An element analysis with energy-dispersive X-ray spectroscopy also demonstrated the presence of Ca and P. Thus, the precipitated grains are assumed to be hydroxyapatite. In this study we evaluated the influence of formalin preservation, which reduces the fracture toughness of bovine femoral compact bones, and concluded that due to the formation of chemical bridges from the reaction of formaldehyde with the collagen fibers in the bones, the collagen fibers are cured and hardened, resulting in a reduction in the fracture toughness of the bovine femoral compact bones. © 2007 The Japan Institute of Metals.