Characterizing the Collagen Fiber Orientation in Pericardial Leaflets Under Mechanical Loading Conditions

Abstract

When implanted inside the body, bioprosthetic heart valve leaflets experience a variety of cyclic mechanical stresses such as shear stress due to blood flow when the valve is open, flexural stress due to cyclic opening and closure of the valve, and tensile stress when the valve is closed. These types of stress lead to a variety of failure modes. In either a natural valve leaflet or a processed pericardial tissue leaflet, collagen fibers reinforce the tissue and provide structural integrity such that the very thin leaflet can stand enormous loads related to cyclic pressure changes. The mechanical response of the leaflet tissue greatly depends on collagen fiber concentration, characteristics, and orientation. Thus, understating the microstructure of pericardial tissue and its response to dynamic loading is crucial for the development of more durable heart valve, and computational models to predict heart valves’ behavior. In this work, we have characterized the 3D collagen fiber arrangement of bovine pericardial tissue leaflets in response to a variety of different loading conditions under Second-Harmonic Generation Microscopy. This real-time visualization method assists in better understanding of the effect of cyclic load on collagen fiber orientation in time and space.

The Effects of Transcatheter Valve Crimping on Pericardial Leaflets

“…Certainly the significant damage to the collagen network induced by crimping will make the tissue less durable and may impair its ability to dampen loads and withstand the constant stresses a heart valve is exposed to [18]. Other important considerations are possible increase in the incidence of prosthetic valve endocarditis and valve thrombosis with transcatheter valves.…”

Non-destructive two-photon excited fluorescence imaging identifies early nodules in calcific aortic-valve disease

“…9,17,22 SHG imaging, which collects signals emitted from non-centrosymmetric structures, such as collagen fibers, has been a powerful tool for characterizing collagen fiber alignment and structure in tissue engineered viable heart valves, 10 and ex vivo animal or human heart valve tissue. 11,12 A recent study reported that CAVD was associated with layer-specific alterations in collagen architecture. 23 They used SHG imaging to quantify organizational changes of collagen fibers in human CAVD valves versus healthy ones, and found that the majority of changes in CAVD, including the fiber number, width, density and alignment, occurred in the layer of spongiosa, in contrast to relatively few changes in the layer of fibrosa.…”

Emerging Trends in Heart Valve Engineering: Part IV. Computational Modeling and Experimental Studies

“…tissue, 3,15,114 making it important to consider in computer simulations of a heart valve. 24,37,135,156 Early modeling of fiber efforts were performed by Peskin and McQueen who generated an array of fibers that functioned as an aortic valve.…”

“…Alavi et al used advanced imaging tools such as SecondHarmonic Generation (SHG) microscopy to characterize the 3D collagen fiber arrangement of native valve leaflets and bovine pericardial tissue leaflets in response to a variety of different loading conditions. 3 They showed that the collagen fibers do not necessarily all align with the load in each layer throughout the depth of tissue. This insight improved our understanding of the pathophysiology of native valves in response to stress and can be used to develop more accurate constitutive and computational models of the heart valves.…”