There are two major scientific challenges to address if the PEP-GAG gels are to be successfully translated to clinic. Challenge 1: To develop methods to effectively visualise the location of the gel, and identify if/where it disperses to over a period of time. In order to assess the long term efficacy of the treatment, it is necessary to be able to quantify the degree to which the gel disperses out of the nucleus over time, in both in vitro laboratory tests and in vivo. We have successfully used clinical radio-opaque agents to visualise the immediate location of the injected gel under x-ray/CT, but longer term, the agent and gel will not necessarily diffuse at the same rate. There have been some initial attempts to chemically bond markers to the gel, but further investigation is needed to examine if this affects their performance. Recent work has also examined the use of histological methods to identify the peptides which have shown some promise. In parallel, we are continuing to develop in vitro testing methods to examine the performance of the PEP-GAG gel under cyclic loading in the laboratory and have a planned in vivo study due to commence next year. If successful methods for visualising the gel can be developed, then greater evidence can be generated on the efficacy of the treatment and its likely longevity. If the gel can be seen long-term in vivo, then this will also reassure clinicians on how patients could be monitored. These aspects are critical if the PEP-GAG gel is to be successfully commercialised and adopted. Challenge 2: To identify the most suitable patient characteristics for the treatment to be successful and the optimum volume of PEP-GAG gel to inject. Different levels of disc degeneration cause changes to both the annulus and nucleus of the disc, and it is not yet known what stage of degeneration the treatment would be most effective, or what the important contra-indications would be. Our early laboratory findings have shown variance from specimen-to-specimen, likely due to the differences in the volumes of PEP-GAG injected compared to the degree of degeneration. Due to the large number of unknowns, this challenge is best addressed using computational models in which different variables can be systematically altered to evaluate their effect. We have developed finite element (FE) models of the disc to assess the mechanical performance, but the models do not yet have the sufficient sophistication in terms of representing the biphasic behaviour and gel-disc interactions to fully answer these questions. Addressing this challenge will provide underpinning evidence necessary for the PEP-GAG gel to progress successfully through clinical trials, where it will be essential to be able to identify exactly which patients will benefit and carefully regulate the procedure to avoid the risk of complication. These challenges require a multidisciplinary approach encompassing aspects of mechanical engineering and simulation alongside chemistry, biology, imaging and image processing The aim of this project is to optimise aspects of the PEP-GAG hydrogel nucleus augmentation procedure so that it can be more effectively translated to clinical practice.