THE TENSILE BEHAVIOR OF DEMINERALIZED BOVINE CORTICAL BONE

Bone is frequently modeled as a two-phase composite of hydroxyapatite mineral crystals dispersed throughout an organic collagen matrix. Howe ver, because of the numerous limitations (e.g. small sample size, poor strain measuring techniques, rapid demineralization with acids) of pr evious mechanical tests of bone with its hydroxyapatite chemically rem oved, we have determined new, accurate data on the material properties of the demineralized bone matrix for use in these composite models. W e performed tensile tests on waisted specimens of demineralized bovine cortical bone from six humeral diaphyses. Specimens were demineralize d over 14 days with a 0.5 M disodium EDTA solution that was replaced d aily. Atomic absorption spectrophotometry was used to track the demine ralization process and to determine the effectiveness of our demineral ization protocol. Mechanical tests were performed at room temperature under displacement control at an approximate strain rate of 0.5% per s . We imposed nine preconditioning cycles before a final ramp to failur e, and measured gauge length displacements using a non-invasive optica l technique. The resulting stress-strain curves were similar to the te nsile behavior observed in mechanical tests of other collagenous tissu es, exhibiting an initial non-linear 'toe' region, followed by a linea r region and subsequent failure without evidence of yielding. We found an average modulus, ultimate stress, and ultimate strain of 613 MPa ( S.D. = 113 MPa), 61.5 MPa (S.D. = 13.1 MPa), and 12.3% (S.D. = 0.5%), respectively. Our average modulus is approximately half the value freq uently used in current composite bone analyses. These data should also have clinical relevance because the early strength of healing fractur ed bone depends largely on the material properties of the collagen mat rix. Copyright (C) 1996 Elsevier Science Ltd.