Nanoindentation of Calcified and Non-calcified Components of Atherosclerotic Tissues

Abstract

Biomechanical models predicting plaque rupture and device-tissue interactions rely on accurate material properties to produce reliable simulation results. However, there is a wide variation in the reported stiffness properties for advanced atherosclerotic lesions. The purpose of this study was to characterise isolated calcified and non-calcified portions of ex vivo carotid atherosclerotic tissues using nanomechanical techniques and compare the results against those from previous studies. Eleven carotid plaque samples were acquired from patients undergoing endarterectomy. Calcification was characterised using traditional instrumented indentation (TII) (n = 06). Micro-Computed Tomography was used to identify areas of calcification. Ferrule-top cantilever nanoindentation (FTC) was conducted on non-calcified tissue regions (n = 05). Adjacent tissue slices were stained with Alizarin Red to select regions of non-calcified tissue for testing. Scanning electron microscopy was employed to qualitatively assess the calcified and non-calcified samples’ surface roughness. The results from this study demonstrate over 6 orders of magnitude difference in stiffness between the elastic moduli of calcified (22.40 [17.70–27.55] GPa) and non-calcified (8.16 [3.85–14.78] kPa) carotid atherosclerotic tissues. Microscopy analysis indicates a larger variation in surface roughness produced with non-calcified tissue cryosectioning than with calcified tissue metallographic preparation, which may account for the increased amount of indent failures with FTC (32%) than with TII (11%). Performing high-resolution imaging and nanomechanical approaches in parallel produce results that clarify the wide range in reported properties for advanced atherosclerotic lesions. Future studies should examine the viscoelastic nature of diseased human arterial tissues.