Nanointerfacial strength between non-collagenous protein and collagen fibrils in antler bone

Fei Hang,Himadri S Gupta,Asa H Barber

doi:10.1098/rsif.2013.0993

Abstract

Antler bone displays considerable toughness through the use of a complex nanofibrous structure of mineralized collagen fibrils (MCFs) bound together by non-collagenous proteins (NCPs). While the NCP regions represent a small volume fraction relative to the MCFs, significant surface area is evolved upon failure of the nanointerfaces formed at NCP–collagen fibril boundaries. The mechanical properties of nanointerfaces between the MCFs are investigated directly in this work using an in situ atomic force microscopy technique to pull out individual fibrils from the NCP. Results show that the NCP–fibril interfaces in antler bone are weak, which highlights the propensity for interface failure at the nanoscale in antler bone and extensive fibril pullout observed at antler fracture surfaces. The adhesion between fibrils and NCP is additionally suggested as being rate dependent, with increasing interfacial strength and fracture energy observed when pullout velocity decreases.

Highlights

The failure of interfaces between nanoscale constituents is ubiquitous in tough biological materials, such as bone, shell and their biomimetic equivalents [1 –6]
Recent work has indicated this prominence of non-collagenous proteins (NCPs) by showing a deficiency of specific proteins in NCPs causing a loss in strength for tendon [17] and rat bone [21], suggesting that the transfer of stresses between mineralized collagen fibrils (MCFs) in antler bone is expected to be critically dependent on the mechanical behaviour of the NCP region
The mechanical properties of the NCP interphase region around the MCFs can be calculated by recording the force applied to the MCF by the atomic force microscope (AFM) system

Summary

Introduction

The failure of interfaces between nanoscale constituents is ubiquitous in tough biological materials, such as bone, shell and their biomimetic equivalents [1 –6]. The main structural constituents of antler bone at the nanoscale can be defined as mineralized collagen fibrils (MCFs) bound together by a non-collagenous protein (NCP) region found within the relatively small spaces of 1–2 nm between these collagen fibrils. The NCP region is amorphous and includes a number of proteins, most notably osteopontin [15,16] and proteoglycan tethers between collagen fibrils [17]. These constituents of MCFs and NCPs can be evaluated structurally as a fibrous composite material with a high volume fraction of stiff MCFs acting as a fibre reinforcement within a softer NCP ‘matrix’. Classical mechanical analysis of composites consisting of fibres bound together by a polymer

Methods

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Discussion

Conclusion