Mineralised turkey tendons may hold the key to understanding how, when and why human bones fail, according to scientists in the School of Engineering and Physical Sciences.
Dr Uwe Wolfram, Assistant Professor in Biomechanics, and Alexander Groetsch, a PhD student, extracted an individual mineralised collagen fibre, one millionth of a metre wide, from a mineralised turkey leg tendon and ‘compressed it until failure’, while simultaneously testing it with high brilliance x-rays.
The breakthrough means that, for the first time, it is possible to see exactly how bones react to compression at the molecular level while excluding possible effects of coarser features on their mechanical behaviour.
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Dr Uwe Wolfram, added: “We use mineralised turkey tendons because they show similar composition to human bone with respect to the mineralised collagen fibril, but feature a much simpler arrangement of these fibrils.
“This makes it an attractive model system to study the mechanical behaviour by means of strength tests at these small length scales.”
“Before this experiment, we understood how bone behaved at the organ level, but the mechanical properties of bones’ fundamental building blocks, the mineralised collagen fibres, were something of a mystery.”
Dr Wolfram believes his team’s findings could help to improve how bone diseases are diagnosed and treated.
“We have now captured exactly how these fibres respond to stress. This could lead to far more effective prediction of bone fracture risk and even the development of patient-specific implants to mitigate that risk.”
Currently, medical professionals diagnose osteoporosis and calculate the likelihood of fractures using a variety of tests and procedures, such as bone density scans. However, none of the tests account for loads under patient specific day-to-day activities. This could be included in the assessment of bone strength by using computational tools. These tools, however, critically depend on the used material properties which, in turn, are defined by bone’s hierarchical structure.
Dr Uwe Wolfram and PhD student Alexander Groetsch, both from the university’s Institute of Mechanical, Process and Energy Engineering, prepared the micron-sized specimens on the individual fibre by a novel preparation protocol combining dissection, ultra-milling, ultra-short pulsed laser ablation, and focused ion beam milling.
Once prepared, the fibre was tested until failure during a micropillar compression test, which measured its reaction to an applied load. At the same time, the fibre was hit by high-energy x-rays for small angle x-ray scattering or x-ray diffraction techniques, which gave simultaneous and quantifiable information about the mechanical behaviour of the fibre’s main components.
Alexander Groetsch said: “Micropillar compression and simultaneous x-ray diffraction represents a novel tool to understand the non-linear mechanical behaviour of bone. Eventually, such a combination helps us to understand why and when tissue fails.”
“This means we now have an idea of how the tissue reacts to external loading at the level of an individual fibre. This allows us to better understand scale effects of bone’s material properties which eventually may help to optimise the prediction of bone fracture risk.”
Wolfram and Groetsch are now investigating how their set-up can be extended to testing under quasi-physiological conditions. In addition, ultra-high resolution computed-tomography imaging with a resolution of one millionth of a millimetre will be used to link the mechanical properties to the structure of the mineralised collagen fibre.
This research is part of a joint international research project bringing together five scientific institutes from three European countries: Heriot-Watt University in Edinburgh, UK; the Swiss Federal Laboratories for Materials Science and Technology in Thun, Switzerland, the University of Bern in Switzerland; the Université Grenoble Alpes, France and the European Synchrotron Radiation Facility in Grenoble, France.
The research is supported by the Engineering and Physical Sciences Research Council and the European Synchrotron Radiation Facility. The study and its results were presented at the 23rd Congress of the European Society of Biomechanics.