THE DISTRIBUTION OF COLLAGEN-APATITE ORIENTATION IN BONE MICROSTRUCTURES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This work characterizes a fundamental aspect of human bone micro-structure, pertinent to fracture initiation and arrest. It addresses whether orientation of elementary components proximate to osteocyte lacunae influences secondary osteon micro-biomechanics. New data at the perilacunar region concerning orientation of collagen-apatite, and prior data on collagen orientation away from the perilacunar region, were incorporated in a novel simulation of secondary osteon to investigate how orientation relates to strains and stresses during mechanical testing. We have created a series of finite element models, using Abaqus software on Datastar, of so-called secondary osteons, basic units of human skeleton which .measure up to 0.5 mm in length. The models include ellipsoids that simulate osteocyte lacunae. The number of the simulated lacunae ranges between 7 and 70. The positions of lacunae can be chosen by the operator or assigned to follow experimentally observed distributions in the osteon. The mechanical properties of the elements adjacent to the ellipsoids simulate the collagen-apatite orientation that we have observed in isolated lamellar specimens under confocal microscopy. We have completed the simulation of the experimental mechanical behavior of osteon specimens under tension and compression in relation to collagen-apatite orientation and presence of porosity during the elastic phase. The current algorithm for collagen orientation distribution will be improved to avoid step-functions and allow continuity of collagen orientation in three-dimension. This is to increase adherence of simulation to experimental observations. This is a particular important point because discontinuities in the orientation distribution may create erroneous strains. Maple software will be used on PC's to prepare the input files for Abaqus software to run on Datastar.