title: Strain-induced optical changes in demineralized bone.
abstract: Bone "stress-whitens," becoming visibly white during mechanical loading, immediately prior to failure. Stress-whitening is known to make materials tougher by dissipating mechanical energy. A greater understanding of stress-whitening, both an optical and mechanical phenomenon, may help explain age-related increases in fracture risk that occur without changes in bone mineralization. In this work, we directly measure the optical properties of demineralized bone as a function of deformation and immersing fluid (with different hydrogen-bonding potentials, water, and ethanol). The change in refractive index of demineralized bone was linear: with deformation and not applied force. Changes in refractive index were likely due to pushing low-refractive-index fluid out of specimens and secondarily due to changes in the refractive index of the collagenous phase. Results were consistent with stress-whitening of demineralized bone previously observed. In ethanol, the refractive index values were lower and less sensitive to deformation compared with deionized water, corroborating the sensitivity to fluid hydration. Differences in refractive index were consistent with structural changes in the collagenous phase such as densification that may also occur under mechanical loading. Understanding bone quality, particularly stress-whitening investigated here, may lead to new therapeutic targets and noninvasive methods to assess bone quality.
authors.affiliation: University of California-Davis, School of Medicine, Lawrence J. Ellison Musculoskeletal Research Laboratory, Department of Orthopaedic Surgery, Sacramento, California, 95817bUniversity of California-Davis, Biomedical Engineering Graduate Group, Davis, Cal.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hardisty
authors.affiliation: University of California-Davis, Department of Chemical Engineering and Materials Science, Biomedical Engineering Graduate Group, Davis, California, 95616.
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Kienle
authors.affiliation: University of California-Davis, Biomedical Engineering Graduate Group, Davis, California, 95616cUniversity of California-Davis, Department of Chemical Engineering and Materials Science, Biomedical Engineering Graduate Group, Davis, California, 95616.
authors.forename: Tonya L
authors.initials: TL
authors.lastname: Kuhl
authors.affiliation: University of California-Davis, Biomedical Engineering Graduate Group, Davis, California, 95616dUniversity of California-Davis, School of Veterinary Medicine, JD Wheat Veterinary Orthopedic Research Laboratory, Biomedical Engineering Graduate Group, Davis.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Stover
authors.affiliation: University of California-Davis, Biomedical Engineering Graduate Group, Davis, California, 95616eUniversity of California-Davis, Department of Biomedical Engineering, Davis, California, 95616.
authors.forename: David P
authors.initials: DP
authors.lastname: Fyhrie
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology*; D018488:Bone Demineralization, Pathologic / Q000503:physiopathology*; D001842:Bone and Bones / Q000503:physiopathology*; D003094:Collagen; D006736:Horses; D016014:Linear Models; D008954:Models, Biological; D012031:Refractometry / Q000379:methods*; D013314:Stress, Mechanical
chemical_list: D003094:Collagen