Investigations into Demineralized Cortical Bone
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Investigations into Demineralized Cortical Bone Ekaterina Novitskaya1, Ana Castro-Ceseña2, Po-Yu Chen1, Joshua Vasquez1, Robert Urbaniak1, Steve Lee1, Gustavo Hirata3, and Joanna McKittrick1 1 University of California, San Diego, La Jolla, CA 92093, USA 2 Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada, México 3 Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, México ABSTRACT Partially demineralized (DM) bone is of interest due to its promising osteointegrative properties for advanced bone grafts. Structural features of partially DM (35 vol.%, 45 vol.% and 55 vol.% reduction), and untreated cortical bone samples were studied by scanning electron microscopy. Mechanical properties were investigated by compression testing in three anatomical directions at different stages of DM. The radial direction appears to be the stiffest and strongest bone direction for the all DM stages. INTRODUCTION Partially demineralized bone is of interest due to the excellent osteointegrative properties for advanced bone grafts [1-4]. Bone is a hierarchically structured composite material consisting mainly of a biopolymer (type-I collagen) and a mineral phase (carbonated hydroxyapatite). Additionally, there is water and some amount of non-collagen proteins [5]. A major structural component in cortical bone is the osteon that consists of thin (about 5-10 m) lamellar sheets composed of mineralized collagen fibers. Osteons have a cylindrical shape (150-250 m in diameter) and align parallel with the long axis of the bone. Bone loss (osteoporosis) and demineralization occur as bones age and are a major cause of bone fractures. The mineral/collagen interaction is important in understanding how this affects bone fractures. Demineralization (DM) studies have been carried by several groups [6-9]. Broz et al. [6] investigated properties of partially DM (by ethylenediamine-tetraacetic acid) bone samples in three-point bending. They showed that specimens became less brittle with the increasing demineralization time. Lewandrowski et al. [7] provided an electron microscopy study of the DM process. They found that the DM process is described by advancing reaction front theory. Kotha et al. [8] summarized different techniques, which affect the bone mineral content, and found that sodium chloride solutions (NaCl) do not affect the mechanical properties of bone, while fluoride treatments (NaF) reduced the mechanical strength by converting some amount of bone mineral into calcium fluoride. The kinetics of cortical bone DM in 0.6N HCl was discussed in detail by Castro-Ceseña et al. [9]. The steady state DM reaction was found to be a first order reaction and kinetic parameters (activation energy and rate constant) were calculated. Since there are no systematic studies on mechanical properties of partially DM cortical bone, the main goal of this research is to find a correlation between mineral content during demineralization and the corresponding mechanical response.
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