Determination of layer-specific mechanical properties of human coronary arteries with nonatherosclerotic intimal thickening and related constitutive modeling

Abstract

Preconditioned prepared strips (n ϭ 78) of segments from the midregion of the left anterior descending coronary artery from the individual layers in axial and circumferential directions were subjected to cyclic quasi-static uniaxial tension tests, and ultimate tensile stresses and stretches were documented. The ratio of outer diameter to total wall thickness was 0.189 Ϯ 0.014; ratios of adventitia, media, and intima thickness to total wall thickness were 0.4 Ϯ 0.03, 0.36 Ϯ 0.03, and 0.27 Ϯ 0.02, respectively; axial in situ stretch of 1.044 Ϯ 0.06 decreased with age. Stress-stretch responses for the individual tissues showed pronounced mechanical heterogeneity. The intima is the stiffest layer over the whole deformation domain, whereas the media in the longitudinal direction is the softest. All specimens exhibited small hysteresis and anisotropic and strong nonlinear behavior in both loading directions. The media and intima showed similar ultimate tensile stresses, which are on average three times smaller than ultimate tensile stresses in the adventitia (1,430 Ϯ 604 kPa circumferential and 1,300 Ϯ 692 kPa longitudinal). The ultimate tensile stretches are similar for all tissue layers. A recently proposed constitutive model was extended and used to represent the deformation behavior for each tissue type over the entire loading range. The study showed the need to model nonstenotic human coronary arteries with nonatherosclerotic intimal thickening as a composite structure composed of three solid mechanically relevant layers with different mechanical properties. The intima showed significant thickness, load-bearing capacity, and mechanical strength compared with the media and adventitia.human left anterior descending coronary artery; elasticity; material model; mechanical properties; ultimate tensile strength ONE CENTRAL AIM IN CARDIOVASCULAR solid mechanics is the investigation of the mechanobiological behavior of arteries in health and disease, which may better explain their function on the basis of their structure and mechanics, i.e., vital information for clinical treatments of artery diseases, for designs of vascular implants such as stents and grafts, and for tissue engineering. For example, 657,000 percutaneous transluminal coronary angioplasty (PTCA) procedures were performed in the United States in 2002 (1). To improve our understanding of the mechanisms involved in PTCA procedures and stent designs, it is fundamental to better explore the mechanical properties and role of the separate arterial layers of coronary arterial walls and to develop efficient computational models.Most of the studies have focused on the mechanical properties of animal coronary arteries (3,11,22,25,26,33,42). In addition to a collagenous adventitia and a medial layer (consisting of smooth muscle, collagen, and some elastin), a coronary arterial wall may consist of a complex intimal layer that develops rapidly in early years and continues to grow gradually throughout life (41). This process is not observed in animals. The intima is a ...

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