Artery buckling analysis using two layered model with collagen dispersion
Artery buckling has been proposed as a possible cause for artery tortuosity associated with various vascular diseases. Since microstructure of arterial wall changes with aging and diseases, it is essential to establish the relationship between microscopic wall structure and artery buckling behavior. The objective of this study was to developed arterial buckling equations to incorporate the two-layered wall with dispersed collagen fiber distribution. Seven porcine carotid arteries were tested for buckling to determine their critical buckling pressures at range of axial stretch ratio (1.0-1.7) which spans the physiological range. The mechanical properties of these intact arteries and their intima-media layer were determined via pressurized inflation test. Collagen alignment was measured from histological sections and modeled by a modified von-Mises distribution. Buckling equations were developed accordingly using microstructure-motivated strain energy function. Our results demonstrated that collagen fibers disperse around two mean orientations symmetrically to the circumferential direction (39.02º±3.04) in the adventitia layer; while aligning closely in the circumferential direction (2.06º±3.88) in the media layer. The microstructure based two-layer model with collagen fiber dispersion described the buckling behavior of arteries well with the model predicted critical pressures match well with the experimental measurement. E.g. the predicted critical buckling pressure at stretch ratio (1.6) using one and two-layer models was 18.24±3.56 kPa and 13.14±3.53 kPa, respectively, compared to 15.38±3.53 kPa obtained from experimental measurement Parametric studies showed that with increasing fiber dispersion parameter, the predicted critical buckling pressure increases. In addition, parametric studies on collagen fiber orientation showed that the critical buckling pressure increases when the main collagen fiber families align toward axial direction. These results validate the microstructure-based model equations for artery buckling and set a base for further studies to predict the stability of arteries due to microstructural changes associated with vascular diseases and aging.