A bypass flow model to study endothelial cell mechanotransduction across diverse flow environments.

Disturbed flow is one of the pathological initiators of endothelial dysfunction in intimal hyperplasia (IH) which is commonly seen in vascular bypass grafts, and arteriovenous fistulas. Various in vitro disease models have been designed to simulate the hemodynamic conditions found in the vasculature. Nonetheless, prior investigations have encountered challenges in establishing a robust disturbed flow model, primarily attributed to the complex bifurcated geometries and distinctive flow dynamics. In the present study, we aim to address this gap by introducing an in vitro bypass flow model capable of inducing disturbed flow and other hemodynamics patterns through a pulsatile flow in the same model. To assess the model's validity, we employed computational fluid dynamics (CFD) to simulate hemodynamics and compared the morphology and functions of human umbilical venous endothelial cells (HUVECs) under disturbed flow conditions to those in physiological flow or stagnant conditions. CFD analysis revealed the generation of disturbed flow within the model, pinpointing the specific location in the channel where the effects of disturbed flow were observed. High-content screening, a single-cell morphological profile assessment, demonstrated that HUVECs in the disturbed flow area exhibited random orientation, and morphological features were significantly distinct compared to cells in the physiological flow or stagnant condition after a two days of flow exposure. Furthermore, HUVECs exposed to disturbed flow underwent extensive remodeling of the adherens junctions and expressed higher levels of endothelial cell activation markers compared to other hemodynamic conditions. In conclusion, our in vitro bypass flow model provides a robust platform for investigating the associations between disturbed flow pattern and vascular diseases.

Stem Cell-Secreted Allogeneic Elastin-Rich Matrix with Subsequent Decellularization for the Treatment of Critical Valve Diseases in the Young.

Critical valve diseases in infants have a very poor prognosis for survival. Particularly challenging is for the valve replacement to support somatic growth. From a valve regenerative standpoint, bio-scaffolds have been extensively investigated recently. While bio-scaffold valves facilitate acute valve functionality, their xenogeneic properties eventually induce a hostile immune response. Our goal was to investigate if a bio-scaffold valve could be deposited with tissues derived from allogeneic stem cells, with a specific dynamic culture protocol to enhance the extracellular matrix (ECM) constituents, with subsequent stem cell removal. Porcine small intestinal submucosa (PSIS) tubular-shaped bio-scaffold valves were seeded with human bone marrow-derived mesenchymal stem cells (hBMMSCs), cultured statically for 8 days, and then exposed to oscillatory fluid-induced shear stresses for two weeks. The valves were then safely decellularized to remove the hBMMSCs while retaining their secreted ECM. This de novo ECM was found to include significantly higher (p < 0.05) levels of elastin compared to the ECM produced by the hBMMSCs under standard rotisserie culture. The elastin-rich valves consisted of ~8% elastin compared to the ~10% elastin composition of native heart valves. Allogeneic elastin promotes chemotaxis thereby accelerating regeneration and can support somatic growth by rapidly integrating with the host following implantation. As a proof-of-concept of accelerated regeneration, we found that valve interstitial cells (VICs) secreted significantly more (p < 0.05) collagen on the elastin-rich matrix compared to the raw PSIS bio-scaffold.

Valve Endothelial Cell Exposure to High Levels of Flow Oscillations Exacerbates Valve Interstitial Cell Calcification.

The aortic valve facilitates unidirectional blood flow to the systemic circulation between the left cardiac ventricle and the aorta. The valve's biomechanical function relies on thin leaflets to adequately open and close over the cardiac cycle. A monolayer of valve endothelial cells (VECs) resides on the outer surface of the aortic valve leaflet. Deeper within the leaflet are sublayers of valve interstitial cells (VICs). Valve tissue remodeling involves paracrine signaling between VECs and VICs. Aortic valve calcification can result from abnormal paracrine communication between these two cell types. VECs are known to respond to hemodynamic stimuli, and, specifically, flow abnormalities can induce VEC dysfunction. This dysfunction can subsequently change the phenotype of VICs, leading to aortic valve calcification. However, the relation between VEC-exposed flow oscillations under pulsatile flow to the progression of aortic valve calcification by VICs remains unknown. In this study, we quantified the level of flow oscillations that VECs were exposed to under dynamic culture and then immersed VICs in VEC-conditioned media. We found that VIC-induced calcification was augmented under maximum flow oscillations, wherein the flow was fully forward for half the cardiac cycle period and fully reversed for the other half. We were able to computationally correlate this finding to specific regions of the aortic valve that experience relatively high flow oscillations and that have been shown to be associated with severe calcified deposits. These findings establish a basis for future investigations on engineering calcified human valve tissues and its potential for therapeutic discovery of aortic valve calcification.

Importance of Non-Newtonian Computational Fluid Modeling on Severely Calcified Aortic Valve Geometries-Insights From Quasi-Steady State Simulations.

The Newtonian model has commonly been used to represent the viscosity of blood in the aorta, despite blood itself being a non-Newtonian fluid. This is justified where shear rates tend to be large. However, we hypothesized that using the Newtonian model to predict the hemodynamics on the aortic valve, particularly in those with severe calcifications, is inaccurate owing to valve leaflet geometry irregularities inducing multiple regions of low shear rates, <100 s-1, where a Newtonian model is invalid. We investigated the utility of three fluid viscosity models via quasi-static simulations: Newtonian, Carreau, and Quemada on a severely calcified aortic heart valve and compared their ability to capture important hemodynamic parameters of wall shear stress (WSS) and the oscillatory shear index (OSI). Our findings indicate that when the shear rates were large enough, >100 s-1, the use of a Newtonian model was justified. However, in spatial regions of relatively low shear rates, <100 s-1, specifically on the inner cusps of the fibrosa side of the valve, WSS calculations under a Newtonian model were found to be noticeably different when compared with their non-Newtonian, Carreau and Quemada counterparts. We hereby conclude that to facilitate more accurate computational flow simulations in severe aortic heart valve calcification, which is subjected to relatively large spatial regions of low shear (<100 s-1), a non-Newtonian model should be applied.

Physiologically Relevant Fluid-Induced Oscillatory Shear Stress Stimulation of Mesenchymal Stem Cells Enhances the Engineered Valve Matrix Phenotype.

Support of somatic growth is a fundamental requirement of tissue-engineered valves. However, efforts thus far have been unable to maintain this support long term. A key event that will determine the valve's long-term success is the extent to which healthy host tissue remodeling can occur on the valve soon after implantation. The construct's phenotypic-status plays a critical role in accelerating tissue remodeling and engineered valve integration with the host via chemotaxis. In the current study, human bone-marrow-derived mesenchymal stem cells were utilized to seed synthetic, biodegradable scaffolds for a period of 8 days in rotisserie culture. Subsequently, cell-seeded scaffolds were exposed to physiologically relevant oscillatory shear stresses (overall mean, time-averaged shear stress, ~7.9 dynes/cm2; overall mean, oscillatory shear index, ~0.18) for an additional 2 weeks. The constructs were found to exhibit relatively augmented endothelial cell expression (CD31; compared to static controls) but concomitantly served to restrict the level of the activated smooth muscle phenotype (α-SMA) and also produced very low stem cell secretion levels of fibronectin (p < 0.05 compared to static and rotisserie controls). These findings suggest that fluid-induced oscillatory shear stresses alone are important in regulating a healthy valve phenotype of the engineered tissue matrix. Moreover, as solid stresses could lead to increased α-SMA levels, they should be excluded from conditioning during the culture process owing to their associated potential risks with pathological tissue remodeling. In conclusion, engineered valve tissues derived from mesenchymal stem cells revealed both a relatively robust valvular phenotype after exposure to physiologically relevant scales of oscillatory shear stress and may thereby serve to accelerate healthy valve tissue remodeling in the host post-implantation.

Non-Invasive Plasmonic-Based Real-Time Characterization of Cardiac Drugs on Cardiomyocytes Functional Behavior.

In the fabrication of cardiac tissue, an important factor is continuous measurement of its contraction features. A module that allows for a dynamic system capable of noninvasive and label-free monitoring of the contraction profile under administering chemicals and drugs is highly valuable for understanding accurate tissue mechanobiology. In this research, we have successfully demonstrated the use of surface plasmon resonance (SPR) technology for the first time to characterize the contractility of cardiac cells in response to Blebbistatin and ATP drug exposure in real tme. An optimal flow rate of 10 µL/min was selected for a continuous flow of warm media,and 10 µM drug administration effect was detected with high spatiotemporal sensitivity on contracting cardiomyocytes. Our drug screening has identified the source of the SPR periodic signal to be direct cell contraction rather than action potentials or calcium signaling. Per our results, SPR has high potential in applications in least-interference real-time and label-free tissue characterizations and cellular properties analysis from a functional and structural point of view.

Elastin-Dependent Aortic Heart Valve Leaflet Curvature Changes During Cyclic Flexure.

The progression of calcific aortic valve disease (CAVD) is characterized by extracellular matrix (ECM) remodeling, leading to structural abnormalities and improper valve function. The focus of the present study was to relate aortic valve leaflet axial curvature changes as a function of elastin degradation, which has been associated with CAVD. Circumferential rectangular strips (L × W = 10 × 2.5 mm) of normal and elastin-degraded (via enzymatic digestion) porcine AV leaflets were subjected to cyclic flexure (1 Hz). A significant increase in mean curvature (p < 0.05) was found in elastin-degraded leaflet specimens in comparison to un-degraded controls at both the semi-constrained (50% of maximum flexed state during specimen bending and straightening events) and fully-constrained (maximally-flexed) states. This significance did not occur in all three flexed configurations when measurements were performed using either minimum or maximum curvature. Moreover, the mean curvature increase in the elastin-degraded leaflets was most pronounced at the instance of maximum flexure, compared to un-degraded controls. We conclude that the mean axial curvature metric can detect distinct spatial changes in aortic valve ECM arising from the loss in bulk content and/or structure of elastin, particularly when there is a high degree of tissue bending. Therefore, the instance of maximum leaflet flexure during the cardiac cycle could be targeted for mean curvature measurements and serve as a potential biomarker for elastin degradation in early CAVD remodeling.

Morbilidad inmediata y mortalidad hospitalaria en la sustitución valvular mitral con prótesis mecánica / Immediate morbidity and hospital mortality in the valvular mitral replacement with a mechanical prosthesis

La cirugía valvular mitral representa la cuarta parte de las operaciones realizadas en el Instituto de Cardiología y Cirugía Vascular (ICCCV), el 80 (por ciento) de ellas es de reemplazo valvular mitral y no hay estudios nacionales de morbilidad y mortalidad publicados. Se realizó un estudio prospectivo de los 301 pacientes a los que se les efectuó sustitución valvular mitral, en el ICCCV entre enero de 1996 y mayo de 2001. El objetivo del trabajo fue conocer la morbilidad y mortalidad operatoria. Las complicaciones posoperatorias más frecuentes fueron: fibrilación auricular (78 pacientes, 26,3 (por ciento), bajo gasto cardíaco (53 pacientes, 17,8 (por ciento) y sangrado excesivo (48 pacientes, 16,2 (por ciento). La mortalidad hospitalaria fue del 9,0 ( (27 pacientes). Se concluyó en que la morbilidad y mortalidad operatoria es aceptable, pero se debe insistir en la prevención, diagnóstico y tratamiento precoz de las complicaciones(AU)

Morbilidad inmediata y mortalidad hospitalaria en la sustitución valvular mitral con prótesis mecánica / Immediate morbidity and hospital mortality in the valvular mitral replacement with a mechanical prosthesis

La cirugía valvular mitral representa la cuarta parte de las operaciones realizadas en el Instituto de Cardiología y Cirugía Vascular (ICCCV), el 80 (por ciento) de ellas es de reemplazo valvular mitral y no hay estudios nacionales de morbilidad y mortalidad publicados. Se realizó un estudio prospectivo de los 301 pacientes a los que se les efectuó sustitución valvular mitral, en el ICCCV entre enero de 1996 y mayo de 2001. El objetivo del trabajo fue conocer la morbilidad y mortalidad operatoria. Las complicaciones posoperatorias más frecuentes fueron: fibrilación auricular (78 pacientes, 26,3 (por ciento), bajo gasto cardíaco (53 pacientes, 17,8 (por ciento) y sangrado excesivo (48 pacientes, 16,2 (por ciento). La mortalidad hospitalaria fue del 9,0 ( (27 pacientes). Se concluyó en que la morbilidad y mortalidad operatoria es aceptable, pero se debe insistir en la prevención, diagnóstico y tratamiento precoz de las complicaciones(AU)

Immediate morbidity and hospital mortality in the valvular mitral replacement with a mechanical prosthesis Valvular mitral surgery accounts for the fourth part of the operations performed at the Institute of Cardiology and Vascular Surgery . 80 percent of them correpond to valvular mitral replacement. No national morbidity and mortality studies have been published yet. A prospective study of 301 patients who underwent valvular mitral replacement at this institute from January, 1996, to May, 2001, was conducted. The most frequent postoperative complications were: auricular fibrilation (78 patients, 26.3 percent); low cardiac output (53 patients, 17.8 percent) and excessive bleeding (48 patients, 16.2 percent). Hospital mortlaity was 19.0 percent (27 patients). It was concluded that morbidity and mortlity are acceptable and that emphasis should be made on the prevention, diagnosis and early treatment of the complilcations(AU)