Abstract
The aim of the study was to investigate whether a fatigue induced weakening of cortical bone was revealed in microstructure and mechanical competence of demineralized bone matrix. Two types of cortical bone samples (plexiform and Haversian) were use. Bone slabs from the midshaft of bovine femora were subjected to cyclical bending. Fatigued and adjacent control samples were cut into cubes and demineralized in ethylenediaminetetraacetic acid. Demineralized samples were either subjected to microscopic quantitative image analysis, or compressed to failure (in longitudinal or transverse direction) with a simultaneous analysis of acoustic emission (AE). In fatigued samples porosity of organic matrix and average area of pores have risen, along with a change in the pores shape. The effect of fatigue depended on the type of the bone, being more pronounced in the plexiform than in Haversian tissue. Demineralized bone matrix was anisotropic under compressive loads in both types of cortical structure. The main result of fatigue pretreatment on mechanical parameters was a significant decrease of ultimate strain in the transverse direction in plexiform samples. The decrease of strain in this group was accompanied by a considerable increase of the fraction of large pores and a significant change in AE energy.
Highlights
Bone tissue can be considered as a hierarchical composite material consisting mainly of type I collagen, crystals of hydroxyapatite and water
This study focuses on bovine cortical bone, the microstructure of which has been classified into two main types: plexiform and Haversian [2, 3]
For each of twelve fatigued bone slabs the secant modulus obtained from the last complete cycle of bending (Mlast) was compared with the initial modulus (Mfirst) in order to check the assumption that the bending procedure affected mechanical properties of the samples
Summary
Bone tissue can be considered as a hierarchical composite material consisting mainly of type I collagen, crystals of hydroxyapatite and water. To fulfill diverse biological and mechanical functions in bone that basic material is arranged into complex structures at a wide range of length scales. The collagen fibrils (100–200 nm in diameter), with thin elongated mineral platelets of hydroxyapatite inside and between them are arranged into fibril arrays or lamellae (3–7 lm wide) forming the basic structure of bone tissue [1]. Haversian microstructure is made of osteons, which are 150–300 mm wide cylindrical structures made of 3–8 lamellae surrounding the Haversian canal. Their axes are principally aligned parallel to the long axis of the bone [1]
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