Atherosclerotic plaque rupture is a major cause of myocardial infarction, coronary thrombosis and stroke. In a previous study, we proposed a new plaque rupture mechanism, plaque separation at the shoulder, and developed a novel quantitative mechanical test to measure the adhesive strength between the atherosclerotic plaque and the underlying vascular wall in mouse models using the local energy release rate, G, as a quantifiable metric for direct comparison of plaque separation strengths (1). We have now investigated structure-function relationships between the local energy release rate and local plaque composition. We hypothesize that adhesive strength varies with plaque composition in mice of different genotypes, and that it correlates with collagen deposition and macrophage content in lesions. Mice which are genetically deficient in matrix metalloproteinase 12 (MMP12), have previously been shown to demonstrate altered lesion composition (2). Therefore, we used apoE knockout (KO) and apoE MMP-12 double knockout (DKO) mice for our experiments and expected to see a difference in local energy release rates between strains.