On the effect of calcification volume and configuration on the mechanical behaviour of carotid plaque tissue

Vascular calcification is a complex molecular process that exhibits a number of relatively characteristic morphology patterns in atherosclerotic plaques. Treatment of arterial stenosis by endovascular intervention, involving forceful circumferential expansion of the plaque, can be unpredictable in calcified lesions. The aim of this study was to determine the mechanical stretching mechanisms and define the mechanical limits for circumferentially expanding carotid plaque lesions under the influence of distinct calcification patterns. Mechanical and structural characterisation was performed on 17 human carotid plaques acquired from patients undergoing endarterectomy procedures. The mechanical properties were determined using uniaxial extension tests that stretch the lesions to complete failure along their circumferential axis. Calcification morphology of mechanically ruptured plaque lesions was characterised using high resolution micro computed tomography imaging. Scanning electron microscopy was used to examine the mechanically induced failure sites and to identify the interface boundary conditions between calcified and non-calcified tissue. The mechanical tests produced four distinct trends in mechanical behaviour which corresponded to the calcification patterns that structurally defined each mechanical group. Each calcification pattern produced unique mechanical restraining effects on the plaque tissue stretching properties evidenced by the variation in degree of stretch to failure. Resistance to failure appears to rely on interactions between calcification and non-calcified tissue. Scanning electron microscopy examination revealed structural gradations at interface boundary conditions to facilitate the transfer of stress. This study emphasises the mechanical influence of distinct calcification configurations on plaque expansion properties and highlights the importance of pre-operative lesion characterisation to optimise treatment outcomes.