Supervisor

Associate Professor John Costi
Costi, John (Associate Professor)
john.costi@flinders.edu.au
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Project description

Description: The disc can be damaged during mechanical (sudden) overload in bending, however the majority of disc injuries occur after a relatively minor lifting event, where fatigue loading and damage accumulation play a significant role in weakening the disc structure. A recent PhD study found that simulated repetitive lifting during flexion and axial rotation lead to clinically relevant disc protrusions and herniations. In this study, the internal disc deformations and strains were measured, as well as the 6DOF translations, rotations, forces and moments of the lumbar segment over 20,000 fatigue loading cycles. Analysis of the fatigue data is required to determine whether changes in the 6DOF mechanical properties with increasing cycles could indicate impending failure of the disc.

Supervisors research focus

My program of research aims to understand the fundamental multiscale properties of normal, degenerated and injured spinal discs, and their mechanisms of failure, and to develop medical devices to treat these problems. Low back pain is ranked globally as the greatest contributor to the number of years lived with disability and is the number one contributor to the non-fatal health burden in Australia. Injury to the disc can occur through awkward lifting postures or propagate over many years of repetitive lifting. In both cases, the disc can herniate (aka 'slipped disc') causing radiating nerve pain and disability. We use a range of equipment including a unique, world-leading six axis hexapod robot, a single axis materials fatigue testing system and a biaxial system for testing microscale portions of biological tissues. We also use scanning electron microscopy to visualise the micro-/nano-scale structure of disc tissue to understand mechanisms of failure. Collaborations can be developed with researchers across Flinders, or across Australia and internationally. My programs of research bring together both experimental, computational and theoretical approaches to understanding the complex behaviour of composite biological materials across the nano-, micro- and macro-scopic scales. Current computational models of spinal discs, for example, are unable to account for the complex, non-linear, time-dependent, multi-phasic (solid, fluid, ionic, chemical-electric) properties of the disc tissue. These models employ a mix of both micro- and macro-scopic disc tissue properties, although data at the micro scale is lacking. It is believed that the disc tissue behaviour needs to be understood across each scale in order to understand the whole. The novelty of my program of research lies in developing an understanding of how these tissues function across the hierarchical scales, specifically from nano-micro, micro-macro and nano-macro. This important understanding is not presently available and poses many challenges for researchers. This leads to many important, unanswered research questions such as: 1. At what scale does an understanding of biological tissue need to be quantified in order to describe the macro-scopic behaviour? 2. How does a multi-scale understanding correlate to macro-scopic behaviour. 3. What specific hierarchical information is required in order to create more-realistic computational models that are able to better predict macro-scopic behaviour? 4. What effect does tissue degeneration have on their multi-scale structural and functional properties and how can these be computationally modelled to provide a greater understanding of the disease process? 5. What tissue engineering approaches could be employed to repair diseased/damaged tissues based on this knowledge?


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