Local Mineral and Matrix Changes Associated with Bone Adaptation and Microdamage
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Local Mineral and Matrix Changes Associated with Bone Adaptation and Microdamage David H. Kohn1,2, Nadder D. Sahar2, Sun Ig Hong3, Kurtulus Golcuk4, Michael D. Morris4 Departments of 1Biologic and Materials Sciences, 2Biomedical Engineering, and 4Chemistry, University of Michigan Ann Arbor, MI 48109-1078, U.S.A. 3 Department of Metallurgical Engineering Chungnam National University, Korea ABSTRACT Skeletal fractures represent a significant medical and economic burden for society. It is generally thought that a high incidence of musculoskeletal fatigue loading results in damage accumulation at too high of a rate to be efficiently remodeled, leading to skeletal fracture. The state of damage in bone at a given time is therefore the net result of damage and repair processes, and is dependent upon extrinsic factors such as mechanical history, but also upon intrinsic factors, such as composition of bone mineral and matrix. In this invited paper, we review investigations on the coupling of Raman spectroscopy with mechanical loading of bone, providing insight into mechanisms of ultrastructural deformation in bone at smaller scales than previously understood. We also present new data showing that in-vivo mechanical loading results in increased resistance to fatigue damage, coupled with an increase in phosphate to amide I ratio and decrease in carbonate to phosphate ratio. Taken together, the data demonstrates the ability to modulate the mechanical and chemical properties of bone via exogenous mechanical stimulation. INTRODUCTION Skeletal fractures result in a significant medical and economic burden for society [1,2]. Agerelated hip, spine, and wrist fractures accounted for more than $17 billion in direct health care costs in the US in 2001, and this annual cost is rising [3]. Skeletal fractures are not restricted to the elderly; stress fractures are also a significant problem in younger people [4]. Skeletal fractures arise when musculoskeletal fatigue loading results in damage accumulation at too high of a rate to be efficiently remodelled [5]. Skeletal integrity and the state of damage in bone at a given time are therefore the net result of damage and repair processes. With age and disease, the ability of bone to self-heal is compromised, cracks accumulate faster than the body can repair them, and bone is more susceptible to fracture. Skeletal integrity is significantly affected by mechanical loading, which modulates tissue quality as well as quantity [6-9]. Mechanical loading, such as in the form of exercise, can strengthen bone and has been hypothesized to increase resistance to damage accumulation [913]. However, excessive mechanical loading may have detrimental effects, leading to increased damage accumulation and reduction in mechanical properties [2,4]. The amount of microstructural damage and overall bone quality are therefore dependent upon extrinsic factors such as mechanical history, but also upon intrinsic factors, such as composition of the mineral and matrix [6-8,14]. It is therefore important to
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