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Carotid artery diseases, such as atherosclerosis, are a major cause of death in the United States. Wall shear stresses are known to prompt plaque formation, but there is limited understanding of the complex flow structures underlying these stresses and how they differ in a pre-disposed high-risk patient cohort. A ‘healthy’ and a novel ‘pre-disposed’ carotid artery bifurcation model was determined based on patient-averaged clinical data, where the ‘pre-disposed’ model represents a pathological anatomy. Computational fluid dynamic simulations were performed using a physiological flow based on healthy human subjects. A main hairpin vortical structure in the internal carotid artery sinus was observed, which locally increased instantaneous wall shear stress. In the pre-disposed geometry, this vortical structure starts at an earlier instance in the cardiac flow cycle and persists over a much shorter period, where the second half of the cardiac cycle is dominated by perturbed secondary flow structures and vortices. This coincides with weaker favorable axial pressure gradient peaks over the sinus for the ‘pre-disposed’ geometry. The findings reveal a strong correlation between vortical structures and wall shear stress and imply that an intact internal carotid artery sinus hairpin vortical structure has a physiologically beneficial role by increasing local wall shear stresses. The deterioration of this beneficial vortical structure is expected to play a significant role in atherosclerotic plaque formation. 

Hydrogels have emerged as a crucial class of materials within the field of tissue engineering. There is growing interest in matching the mechanical properties of hydrogel scaffolds to tissues in the human body and optimizing these properties for cell growth and differentiation. Gelatin methacrylate (GelMA) is a well-accepted, biocompatible hydrogel with tunable mechanical properties. However, the effects of various formulation parameters on its mechanical properties are not well understood. In this study, an array of GelMA scaffold fabrication parameters is evaluated by varying GelMA concentration and ultraviolet light exposure time. Our overarching goal is to characterize the mechanical properties through ultrasound and rheological measurements, providing a framework for GelMA scaffold selection. Pulse-echo ultrasound techniques were used to non-invasively determine the sound speed and attenuation of the scaffolds, revealing significant dependence on GelMA concentration. Steady shear rate and strain- and frequency-controlled oscillatory shear tests using a rotational rheometer (Model: DHR-2, TA Instruments) revealed a range in the levels of shear-thinning as well as viscoelasticity and showed moduli-dependence on both GelMA concentration and light exposure time. Together, this acoustic and rheological characterization can be used to inform the selection of GelMA scaffolds in tissue engineering applications.