Experimental investigations into the mechanical properties of the collagen fibril-noncollagenous protein (NCP) interface
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Experimental investigations into the mechanical properties of the collagen fibrilnoncollagenous protein (NCP) interface in antler bone Fei Hang1, Asa H. Barber1 1 Centre for Materials Research & School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK. ABSTRACT Antler is an extraordinary bone tissue that displays significant overall toughness when compared to other bone materials. The origin of this toughness is due to the complex interaction between the nanoscale constituents as well as structural hierarchy in the antler material. Of particular interest is the mechanical performance of the interface between the collagen fibrils and considerably smaller volume of non-collagenous protein (NCP) between these fibrils. This paper directly examines the mechanical properties of isolated volumes of antler using combined in situ atomic force microscopy (AFM)-scanning electron microscopy (SEM) experiments. The antler material at the nanoscale is approximated to a fiber reinforced composite, with composite theory used to evaluate the interfacial shear stresses generated between the individual collagen fibrils and NCP during mechanical loading. INTRODUCTION Bones, especially compact bone, is a stiff and tough material having the major functions of providing mechanical support and bearing external load. Bone has a structural organization over different length scales and constituent properties expected to contribute to mechanical performance [1-3]. Collagen fibrils are one such constituent that provide an organic framework and act as a template for the mineralization of carbonated apatite crystals. The irregular shaped apatite crystals are located both within collagen fibrils and extra-fibrilllar regions. These discrete fibrils are organized over different hierarchical length scales to provide optimized mechanical function [1, 4-7]. Importantly, the spaces between the collagen fibrils are filled with predominantly with non-collagen protein (NCP). As with other fiber-reinforced composites, the interface between the fibrous material and surrounding NCP is expected to be critical in defining the overall mechanical properties of the material. Bone can therefore be considered as mineralized collagen fibrils acting as the reinforcement while NCP between fibrils is transfers applied load between the fibrils. Interfacial mechanics between fibers and surrounding polymer matrix has contributed to significant composite theory and is relevant at a number of different length scales [8-14]. The application of composite theory to the mechanical response of the mineralized collagen fibril-NPC interface is therefore critical in understanding the influence of nanoscale structure on the fracture behavior of bone. However, direct testing of this collagen fibril-NCP interface is particularly challenging due to the relatively small volumes considered and has yet to be determined. Measurement of the interfacial mechanical properties within fiber reinforced composite is typically carri
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