Advanced Methodology and Preliminary Measurements of Molecular and Mechanical Properties of Heart Valves under Dynamic Strain

Abstract

Mammalian heart valves are soft tissue assemblies with multi-scale material properties. This is because they are constructs comprising both muscle and non-contractile extracellular matrix proteins (such as collagens and proteoglycans) and transition regions where one form of tissue structure becomes another, significantly different form. The leaflets of the mitral and tricuspid valves are connected to chordae tendinae which, in turn, bind through papillary muscles to the cardiac wall of the ventricle. The transition regions between these tissue subsets are complex and diffuse. Their material composition and mechanical properties have not been previously described with both micro and nanoscopic data recorded simultaneously, as reported here. Annotating the mechanical characteristics of these tissue transitions will be of great value in developing novel implants, improving the state of the surgical simulators and advancing robot-assisted surgery. We present here developments in multi-scale methodology that produce data that can relate mechanical properties to molecular structure using scanning X-ray diffraction. We correlate these data to corresponding tissue level (macro and microscopic) stress and strain, with particular emphasis on the transition regions and present analyses to indicate points of possible failure in these tissues.

Mechanics and Microstructure of the Atrioventricular Heart Valve Chordae Tendineae: A Review

“…From this unique experimental setting, we observed different chordae mechanics than those reported in previous literature, which may be due to distributions of stress and deformations from the chordae to the leaflet and papillary muscle structures. A similar preliminary study (n = 1 strut chordae for each valve) was recently performed, but in this study the authors bisected the entity such that only a leaflet-chordae segment and a chordae-papillary muscle segment were tested [61]. Reported results from the uniaxial mechanical testing of chordae tendineae are summarized in Table 1.…”

“…They found that along the insertion region the radial extensibility decreased, and the stiffness increased. Another recent preliminary study was published to analyze the leaflet-chordae and papillary muscle-chordae insertion areas using X-ray diffraction [61]. Their preliminary finding was that the leaflet and papillary muscle insertions have a higher molecular strain than the rest of the chordae, suggesting those areas are more rupture vulnerable.…”

Functional Grading of a Transversely Isotropic Hyperelastic Model with Applications in Modeling Tricuspid and Mitral Valve Transition Regions

“…Experimental characterization of the papillary muscle (PM), chordea tendinea (CT) and leaflet (LL) in excised porcine tricuspid valve (TV) and mitral valve (MV) and their transition regions were used to inform the FGM model as well as provide the experimental datasets for model validation. Due to the multiscale and anisotropic nature of these tissues with a primary fiber orientation [44], these anatomical regions are good candidates for development and validation of the proposed FGM model. The experimental protocol, setup and the actual datasets used in this work are presented in detail in our previous work [44].…”

“…We assume that the deformation characteristics of both "pure" tissue and their transition regions display transversely isotropic behavior adequately described by the TI formulation by Weiss et al [38]. Previous experimental studies in our group showed that using a combination of optical microscopy and XRD imaging techniques [44], dissimilar mechanical responses could be observed in CT-LL and CT-PM transition regions in porcine tricuspid valve (TV) and mitral valve (MV) compared to the the "pure" CT, LL and PM tissue under load. In this work, we utilize these experimental results to characterize the CT-LL and CT-PM transition regions by solving the aforementioned two sub-problems (see Figure 1).…”

Polymer- and Hybrid-Based Biomaterials for Interstitial, Connective, Vascular, Nerve, Visceral and Musculoskeletal Tissue Engineering

“…Indeed, human tissues have their own rigidity depending on the type of cells and their structural organization [118]. Peculiarly, mechanical properties of tissues range from kPa to GPa, based on data for arterial walls [119], brain [120], breast [121], bone [121], cartilage [122], cornea [123], heart [124], kidney [125], liver [125], prostate [126], vein [127], skin [127] and tendon [128]). A summary of these data is given in Figure 1.…”