Bone is a complex fibrous biological nanocomposite material optimized to avoid catastrophic failure and to perform a variety of mechanical functions, most notably load bearing. The fracture behaviour of bone is expected to be controlled by the various structural features present across the many existing hierarchical length scales. Micron sized bone lamellae present the simplest composite unit in bone consisting of mineralized collagen fibrils within a protein matrix, with some work suggesting that this length scale dominates the fracture of whole bone. However, the synergy between the bone components even at these relatively small length scales is poorly understood. The aim of this work is to therefore examine the mechanical properties of bone at length scales where the bone material itself can be considered as a composite material. To achieve this, discrete volumes of bone corresponding to the sub-lamellar unit were mechanically tested using an in situ Atomic Force Microscope (AFM) while monitoring using Scanning Electron Microscope (SEM). The elastic modulus of sub-lamellar bone units mechanically tested by the AFM in a bending configuration within the SEM was shown to be similar in both wet and SEM vacuum conditions, indicating that the SEM vacuum is insufficiently strong to drive off water from hydrated bone samples at lamellae length scales. AFM-SEM mechanical testing was extended to determine the structural effects of collagen fibril orientation in bone sub-lamellar units on both elastic modulus and fracture. Final experiments examined small scale mechanical properties of osteoporotic Mechanical Properties of Bone at the Sub-lamellar Level Queen Mary University of London 3 bone, with results highlighting how osteoporosis has little effect on the strength of the bone material but lowers the elastic modulus. This work therefore highlights the use of small scale mechanical testing using AFM and SEM to determine the influence of structural organization, specifically collagen fibril orientation, and compositional changes induced by osteoporosis on resultant bone material behaviour.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:667060 |
| Date | January 2012 |
| Creators | Jimenez Palomar, Ines |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://qmro.qmul.ac.uk/xmlui/handle/123456789/8471 |
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