Effects of Surface Roughness and Maximum Load on the Mechanical Properties of Cancellous Bone Measured by Nanoindentatio
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Effects of Surface Roughness and Maximum Load on the Mechanical Properties of Cancellous Bone Measured by Nanoindentation Eve Donnelly1, Shefford P. Baker2, Adele L. Boskey3,4,5, and Marjolein C. H. van der Meulen1,3 1 Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 2 Department of Materials Science and Engineering, Cornell University, Ithaca, NY 3 Musculoskeletal Integrity Program, Hospital for Special Surgery, New York, NY 4 Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 5 Graduate Program in Physiology, Biophysics, and Systems Biology, Weill Medical College of Cornell University, New York, NY ABSTRACT Nanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250-3000 µN. As the ratio of indentation depth to surface roughness decreased below approximately 3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was approximately 20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that are consistent with microstructural observations of lamellar bone as more mineralized than interlamellar bone.
INTRODUCTION Skeletal function depends critically on bone structural integrity, which is governed by tissue apparent density, architecture, and material properties. While the effect of apparent density on structural behavior is well studied, and microcomputed tomography imaging has lately enabled investigation of the relationship between microarchitecture and structural properties [1], relatively little is known about the local material properties and the effects of their variation on the structural behavior of bone. Mechanical characterization of bone at the microstructural level provides additional insight into the origins of skeletal fragility. The layered microstructure of cancellous bone comprises lamellae consisting of highly oriented mineralized collagen fibers and less-oriented interlamellar regions [2]. Nanoindentation is increasingly being used to assess the mechanical properties of lamellar bone. However, material property data obtained from such studies are often characterized by considerable variability, with maximum standard deviations ranging from 30-60% [3-5]. Additionally, most nanomechanical studies of lamellar bone have used deep indentations relative to lamellar dimensions and have not reported sample surface roughnesses [6-8]. To probe intra-lamellar properties, indentations must be sufficiently shallow that the corresponding indentation volumes lie w
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