Unidirectional Blood Flow Research Articles

A dynamic flow fetal membrane organ-on-a-chip system for modeling the effects of amniotic fluid motion.

Fetal membrane (amniochorion), the innermost lining of the intrauterine cavity, surround the fetus and enclose amniotic fluid. Unlike unidirectional blood flow, amniotic fluid subtly rocks back and forth, and thus, the innermost amnion epithelial cells are continuously exposed to low levels of shear stress from fluid undulation. Here, we tested the impact of fluid motion on amnion epithelial cells (AECs) as a bearer of force impact and their potential vulnerability to cytopathologic changes that can destabilize fetal membrane functions. A previously developed amnion membrane (AM) organ-on-chip (OOC) was utilized but with dynamic flow to culture human fetal amnion membrane cells. The applied flow was modulated to perfuse culture media back and forth for 48h to mimic fluid motion. A static culture condition was used as a negative control, and oxidative stress (OS) condition was used as a positive control representing pathophysiological changes. The impacts of fluidic motion were evaluated by measuring cell viability, cellular transition, and inflammation. Additionally, scanning electron microscopy (SEM) imaging was performed to observe microvilli formation. The results show that regardless of the applied flow rate, AECs and AMCs maintained their viability, morphology, innate meta-state, and low production of pro-inflammatory cytokines. E-cadherin expression and microvilli formation in the AECs were upregulated in a flow rate-dependent fashion; however, this did not impact cellular morphology or cellular transition or inflammation. OS treatment induced a mesenchymal morphology, significantly higher vimentin to cytokeratin 18 (CK-18) ratio, and pro-inflammatory cytokine production in AECs, whereas AMCs did not respond in any significant manner. Fluid motion and shear stress, if any, did not impact AEC cell function and did not cause inflammation. Thus, when using an amnion membrane OOC model, the inclusion of a dynamic flow environment is not necessary to mimic in utero physiologic cellular conditions of an amnion membrane.

Design of chitosan-based drug-loaded laminated materials with superhydrophilic/superhydrophobic properties for simultaneous effective hemostasis and antiadhesion

Hemostatic materials play a crucial role in trauma medicine. However, existing materials have poor hemostatic efficacy and a tendency to adhere to the wound surface, limiting their clinical effectiveness. Herein, a drug-loaded, superhydrophilic/superhydrophobic laminated material (DSLM), consisting of a superhydrophobic inner layer with a micropore array, a superhydrophilic chitosan-based sponge layer loaded with hemostatic/antimicrobial drugs, and a superhydrophobic outer layer, was developed. Furthermore, the DSLM allows unidirectional flow of blood and exudates from the wound bed through the superhydrophobic inner layer while facilitating efficient drug delivery. In addition, it possesses excellent biocompatibility and antiadhesion properties, as confirmed by in vivo and in vitro experiments. Compared with traditional hemostatic materials, the DSLM remarkably increased the survival time by over threefold in the acute femoral transaction wound bleeding model, and simultaneously prevented secondary wound damage by reducing peeling force to one-eighth incomparison to pristine gauze. The DSLM holds promise as a versatile clinical biomaterial for prehospital acute trauma treatment, with its simple structure facilitating manufacturing and expanding applications in biomedicine.

A Dynamic Flow Fetal Membrane Organ-on-a-Chip System for Modeling the Effects of Amniotic Fluid Motion.

Fetal membrane(amniochorion), the innermost lining of the intrauterine cavity, surround the fetus and enclose amniotic fluid. Unlike unidirectional blood flow, amniotic fluid subtly rocks back and forth, and thus, the innermost amnion epithelial cells are continuously exposed to low levels of shear stress from fluid undulation. Here, we tested the impact of fluid motion on amnion epithelial cells (AECs) as a bearer of force impact and their potential vulnerability to cytopathologic changes that can destabilize fetal membrane functions. An amnion membrane (AM) organ-on-chip (OOC) was utilized to culture human fetal amnion membrane cells. The applied flow was modulated to perfuse culture media back and forth for 48 hours flow culture to mimic fluid motion. Static culture condition was used as a negative control, and oxidative stress (OS) condition was used as a positive control for pathophysiological changes. The impacts of fluidic motion were evaluated by measuring cell viability, cellular transition, and inflammation. Additionally, scanning electron microscopy (SEM) imaging was performed to observe microvilli formation. The results show that regardless of the applied flow rate, AECs and AMCs maintained their viability, morphology, innate meta-state, and low production of pro-inflammatory cytokines. E-cadherin expression and microvilli formation in the AECs were upregulated in a flow rate-dependent fashion; however, this did not impact cellular morphology or cellular transition or inflammation. OS treatment induced a mesenchymal morphology, significantly higher vimentin to CK-18 ratio, and pro-inflammatory cytokine production in AECs, whereas AMCs did not respond in any significant manner. Fluid motion and shear stress, if any, did not impact AEC cell function and did not cause inflammation. Thus, when using an amnion membrane OOC model, the inclusion of a flow culture environment is not necessary to mimic any in utero physiologic cellular conditions of fetal membrane-derived cells.

The Influence of Resting Retrograde Shear Rate on Endothelial Function as Assessed by Flow Mediated Dilation

Shear stress profiles are an important determinant of endothelial function. Unidirectional blood flow enhances mean shear and protects endothelial function, whereas increased retrograde and oscillatory shear favors a proatherogenic environment. In this regard, acutely increasing retrograde shear has been shown to impair endothelial function. Also, previous studies have reported an elevation in retrograde shear in older adults that has been suggested to contribute to impaired endothelial function with age. However, the impact of having elevated retrograde shear at rest on endothelial function remains unclear. Therefore, we aimed to assess the associations between resting shear patterns and endothelial function, as measured by flow-mediated dilation (FMD) in a cohort of young and older adults. We hypothesized that higher retrograde shear rate and oscillatory shear index at rest would be related to a lower FMD value. Method: A total of 60 participants, 30 young adults (24 ± 5 years) and 30 older adults (62 ± 9 years), were studied. Resting brachial artery blood flow was measured using duplex Doppler ultrasound and retrograde shear rate and oscillatory shear index were calculated. Brachial artery FMD was used as a measure of endothelial function. Pearson correlations were used to investigate the associations between FMD, resting shear patterns, and age. Result: FMD was significantly lower in older compared to young adults (4.9 ± 2.7% vs. 7.6 ± 3.2%, p < 0.01). Both retrograde shear rate and oscillatory shear index tended to be greater in older adults (-20.7 ± 15.1 s−1 vs. -15.2 ± 17 s−1, p = 0.062, and 10.7 ± 8% vs. 7.9 ± 8.0%, p = 0.056, respectively). FMD was not correlated with retrograde shear rate (r = -0.18, p = 0.17), or oscillatory shear index (r = -0.21, p = 0.11) in the entire cohort or in the young and older group alone. However, FMD, retrograde shear rate, and oscillatory index were moderately correlated with age: FMD (r = -0.45, p < 0.01), retrograde shear rate (r = -0.32, p = 0.012), and oscillatory shear index (r = 0.33, p < 0.01). Conclusion: These preliminary results suggest that resting retrograde shear and oscillatory shear index are not associated with reduced endothelial function in a cohort of young and old adults. Nevertheless, age-associated reductions in endothelial function and elevated retrograde shear were observed. This project was supported by the College of Nursing and Health Innovation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Biomechanical Remodeling of Aortic Valve Interstitial Cells During Calcified Lesion Formation In Vitro.

Healthy aortic heart valves are essential to the regulation of unidirectional blood flow. Calcific aortic valve disease (CAVD) is an actively progressive disease that involves the disorganization of valve cells and accumulation of calcium deposits on the aortic valve leaflets. CAVD involves disruption of cell environment homeostasis that prior cell culture models have found difficult to portray and model. As it is still poorly understood how tissue stiffening associates with lesion formation, here, we implement a novel 3D culture platform to characterize the relationship between mechanical stress and tissue remodeling and analyze how the application of pro-osteogenic stimulation dysregulates the native ability of valve cells to organize its matrix. Through a temporal study of macroscopic remodeling, we determine that aortic valve interstitial neo-tissues undergo varying stiffness and mechanical stress, demonstrate greater myofibroblastic gene expression, and show greater remodeling activity in the outer surface of the neo-tissue in a banding pattern when cultured in osteogenic growth medium. In human aortic valve interstitial cells cultured in osteogenic growth medium, we observed an increase in stress but significant decreases in myofibroblastic gene expression with the addition of growth factors. In summary, we are able to see the interplay of biochemical and biomechanical stimuli in valvular remodeling by using our platform to model dynamic stiffening of valve interstitial neo-tissues under different biochemical conditions.

Comparative Analysis of Morphological and Morphometric Features of Human, Pig, Calf, and Sheep Aortic Valves: A Cross-sectional Study

Introduction: The aortic valve plays a critical role in maintaining unidirectional blood flow from the left ventricle into the aorta, ensuring efficient circulation throughout the body. Comprising three cusps-the left coronary, right coronary, and non-coronary cusps-the intricate anatomy of the aortic valve is essential for its proper function. The scarcity of aortic valve homografts for transplantation has led to increased interest in studying readily available sources for suitable and durable xenografts. Aim: To compare the morphological and morphometric characteristics of the aortic valves in humans with those in pigs, calves, and sheep. Materials and Methods: The present cross-sectional study was conducted over a three-week period in July 2022. Aortic valves were collected from humans, pigs, calves, and sheep. Five human hearts were obtained from the Anatomy Department of Adichunchanagiri Institute of Medical Sciences, BG Nagar. Additionally, five hearts each from calves, pigs, and sheep were obtained from a nearby abattoir. The hearts were then fixed in a 10% formaldehyde solution for approximately 18 hours. All fat and muscle surrounding the aorta were removed, and the aorta with intact valves was dissected. An incision was made between the left coronary and non-coronary aortic cusps to measure the individual cusps. Morphological and morphometric measurements, including annulus diameter, cusp height, commissural distances, and length of the lunula, were taken using a vernier calliper. The obtained values were statistically compared using paired t-test. Results: The mean values of various measurements of human aortic valves were found to be similar to those of pig aortic valves. Both humans and pigs have three aortic cusps, namely the left, right, and non-coronary cusps. The mean diameter of the aortic annulus in humans was 2.18 cm, while in pigs it was 2.28 cm. The height of the left and right cusps in both human and pig aortic valves was approximately 1.6 cm, whereas the height of the non-coronary cusp was 1.64 cm in humans and 1.38 cm in pigs. The external inter-commissural distance of the left cusp was 2.48 cm, and that of the right cusp was 2.58 cm in both humans and pigs. The external inter-commissural distance of the non-coronary cusp was 2.4 cm in humans and 2.36 cm in pigs. The length of the lunula and internal inter-commissural length of the aortic cusps in humans were relatively similar to those in pigs. However, when compared to measurements in cows and sheep, significant variations were observed. Conclusion: The study findings provide valuable insights into the potential suitability of pig aortic valves for xenograft transplantation and their implications for cardiac surgical procedures.

Fluid–structure interaction modeling of bi-leaflet mechanical heart valves using smoothed particle hydrodynamics

Heart valves are essential for maintaining unidirectional blood flow, and their failure can severely affect cardiac functions. The use of artificial heart valves as replacement has proven to be a reliable and effective solution. Computational fluid dynamics has emerged as a powerful numerical tool for investigating the design, performance, and malfunctioning of mechanical heart valves without the need for invasive procedures. In this study, we employed smoothed particle hydrodynamics (SPH) in an open-source code “DualSPHysics,” to study the hemodynamics of a bi-leaflet mechanical heart valve (BMHV). The proposed SPH method was validated against the traditional finite volume method and experimental data, highlighting its suitability for simulating the heart valve function. The Lagrangian description of motion in SPH is particularly advantageous for fluid–structure interaction (FSI), making it well-suited for accurately modeling the heart valve dynamics. Furthermore, the SPH/FSI technique was applied to investigate the hemodynamic abnormalities associated with BMHV dysfunction. This work represents the first attempt to use SPH to model flow through a realistic BMHV by incorporating FSI. The normal and altered flow behavior and the movement dynamics of the BMHV under various blockage scenarios have also been investigated along with the potential risks of the blocked mechanical valve. The findings demonstrate that this SPH/FSI approach provides a unique, effective, and valuable tool for accurately capturing the transient hemodynamic behavior of bi-leaflet heart valves and its versatility enables the application to more complex patient-specific issues related to cardiovascular diseases.

Partial heart transplantation: Growing heart valve implants for children.

Heart valves serve a vital hemodynamic function to ensure unidirectional blood flow. Additionally, native heart valves serve biological functions such as growth and self-repair. Heart valve implants mimic the hemodynamic function of native heart valves, but are unable to fulfill their biological functions. We developed partial heart transplantation to deliver heart valve implants that fulfill all functions of native heart valves. This is particularly advantageous for children, who require growing heart valve implants. This invited review outlines the past, present and future of partial heart transplantation.

Abstract P1029: Abnormal Progenitor Cell Differentiation And Cardiomyocyte Proliferation In Hypoplastic Right Heart Syndrome

Pulmonary atresia with intact ventricular septum (PA-IVS) is a rare (4-8 per 100,000 live births) type of hypoplastic right heart syndrome (HRHS) where the right-sided structures in the heart are malformed. In PA-IVS, the pulmonary valve that acts to regulate the unidirectional flow of blood from the right ventricle (RV) to the lungs does not open, resulting in no connection between the RV and the pulmonary arteries. After surgical or catheter-based intervention, PA-IVS patients have clinical outcomes that range from single-ventricle palliation to a biventricular repair. Mechanisms underlying the spectrum of RV hypoplasia in PA-IVS are difficult to fully ascribe to an atretic pulmonary valve. There are no reliable animal models available for studying disease mechanisms of PA-IVS. In this study, we leverage patient-specific induced pluripotent stem cells (iPSCs) and single-cell RNA sequencing to elucidate cellular etiologies of ventricular hypoplasia in PA-IVS. PA-IVS iPSC-derived cardiomyocytes are less proliferative compared to controls under both static and cyclic stretch, suggesting that genetic factors may contribute to a spectrum of ventricular hypoplasia in PA-IVS. Single-cell transcriptomic analysis reveals that cell lineage determination towards second heart progenitors is suppressed, with enhanced differentiation into first heart field and epicardial lineages during cardiac differentiation. Additionally, biological pathways associated with cell proliferation and cell cycle progression are downregulated whereas mitochondrial activities are elevated in early cardiomyocytes originated from PA-IVS patients. In conclusion, abnormal cell lineage differentiation and cardiomyocyte proliferation may underlie the cellular and developmental etiologies of ventricular hypoplasia in HRHS.

Pancreatic regional blood flow links the endocrine and exocrine diseases.

An increasing number of studies have demonstrated that disease states of the endocrine or exocrine pancreas aggravate one another, which implies bidirectional blood flow between islets and exocrine cells. However, this is inconsistent with the current model of unidirectional blood flow, which is strictly from islets to exocrine tissues. This conventional model was first proposed in 1932, and it has never to our knowledge been revisited to date. Here, large-scale image capture was used to examine the spatial relationship between islets and blood vessels in the following species: human, monkey, pig, rabbit, ferret, and mouse. While some arterioles passed by or traveled through islets, the majority of islets had no association with them. Islets with direct contact with the arteriole were significantly larger in size and fewer in number than those without contact. Unique to the pancreas, capillaries directly branched out from the arterioles and have been labeled as "small arterioles" in past studies. Overall, the arterioles emerged to feed the pancreas regionally, not specifically targeting individual islets. Vascularizing the pancreas in this way may allow an entire downstream region of islets and acinar cells to be simultaneously exposed to changes in the blood levels of glucose, hormones, and other circulating factors.

Morphology and Morphometry of Aortic Valve in Humans and Porcines – A Comparative Study

Background: The aortic valve is a semilunar valve with three leaflets that are in the left ventricle’s outflow tract and only permits unidirectional blood flow away from the ventricle. The valve leaflet can tolerate extremely high mechanical and hemodynamic forces resulting from the great complexity and complicated cellular and molecular functions. Aims: The aim of the study is to provide an add-on to the understanding of the morphological and morphometrical aspects of human and porcine aortic heart valves on comparative grounds so that they can be used as a guide in the construction of three-dimensional (3D)-printed mechanical valve. Materials and Methods: Twenty swine and twenty human hearts were compared and examined in this investigation. The porcine and human hearts weighing in between 300 g and 450 g were considered, and any variation from the normal and any mechanical damage rendered during procurement were all excluded from the study. Results: The length of the attached margin of the right coronary cusp, left coronary cusp, and noncoronary cusp of human and porcine were 45.15 mm, 36.47 mm, and 41.53 mm and 36.55 mm, 43.14 mm, and 36.10 mm, respectively. The length of the free margin and the height of the cusps from nadir to the sinotubular junction and the effective height of the cusp from nadir to the free margin of the cusps of human and porcine have been compared. Conclusion: The human and swine aortic valves share morphological and morphometrical characteristics, which can be used to create 3D valves and tissue engineering procedures with greater biocompatibility and biofunctionality.

On-demand heart valve manufacturing using focused rotary jet spinning

On-demand heart valve manufacturing using focused rotary jet spinning

Large proximal intertwin vascular anastomoses as a rare cause of twin anaemia-polycythaemia sequence (TAPS): case report

Background: Twin anaemia-polycythaemia sequence (TAPS) is a form of chronic twin-to-twin transfusion syndrome (TTTS) secondary to slow unidirectional blood flow across minuscule arteriovenous (AV) anastomoses. We present a case of presumed TAPS secondary to unusual, large, proximal anastomoses. Case report: Monochorionic diamniotic (MCDA) twins were born at 25+6 weeks gestation following intrauterine fetal demise. Ultrasound scan two weeks beforehand showed mild growth discordance (0.7%) with normal amniotic fluid volumes. At post-mortem, Twin 1 (825g) appeared pale and Twin 2 (770g) plethoric. Placental examination revealed side-by-side, fused cord insertions at the extreme placental edge, with one artery-to-artery (AA) anastomosis close to the cord insertion and one umbilical vein-to-umbilical vein (UV-UV) anastomosis within Twin 1's cord. All chorionic veins drained into Twin 1’s UV proximal to the anastomosis. Discussion: TAPS is characterised by anaemia in the donor twin and polycythaemia in the recipient twin without oligohydramnios or polyhydramnios and is typically caused by very small (<1 mm diameter) AV anastomoses. To our knowledge, this is the first reported case of TAPS associated with large AA and UV-UV anastomoses. The possibility of acute exsanguination from Twin 1 into Twin 2 following the demise of Twin 2 cannot be excluded. Reference 1. Tollenaar LSA, Slaghekke F, Lewi L, et al. Spontaneous twin anemia polycythemia sequence: diagnosis, management, and outcome in an international cohort of 249 cases. Am J Obstet Gynecol 2021; 224: 213.

Multiple pkd and piezo gene family members are required for atrioventricular valve formation

Cardiac valves ensure unidirectional blood flow through the heart, and altering their function can result in heart failure. Flow sensing via wall shear stress and wall stretching through the action of mechanosensors can modulate cardiac valve formation. However, the identity and precise role of the key mechanosensors and their effectors remain mostly unknown. Here, we genetically dissect the role of Pkd1a and other mechanosensors in atrioventricular (AV) valve formation in zebrafish and identify a role for several pkd and piezo gene family members in this process. We show that Pkd1a, together with Pkd2, Pkd1l1, and Piezo2a, promotes AV valve elongation and cardiac morphogenesis. Mechanistically, Pkd1a, Pkd2, and Pkd1l1 all repress the expression of klf2a and klf2b, transcription factor genes implicated in AV valve development. Furthermore, we find that the calcium-dependent protein kinase Camk2g is required downstream of Pkd function to repress klf2a expression. Altogether, these data identify, and dissect the role of, several mechanosensors required for AV valve formation, thereby broadening our understanding of cardiac valvulogenesis.

Abstract 13431: Comparative Evaluation of Diastolic Left Heart Dynamics Post-Mitral Valve Interventions

Introduction: Mitral valve (MV) leaflet morphology plays an important role insuring efficient, unidirectional blood flow from the left atrium (LA) to ventricle (LV). When treating severe mitral regurgitation (MR), surgical repair, valve replacement, or transcatheter edge-to-edge (E-2-E) repair all provide valid options depending on anatomy and clinical circumstances. These interventions alter the MV morphology, impacting LV filling dynamics. We used fluid-structure interactions (FSI) to evaluate LV filling dynamics after MV interventions, taking into consideration full left-heart (LH) dynamics. Methods: 3-D MV model of a patient suffering from severe MR was reconstructed from echocardiographic data. A LH wall motion algorithm was developed and applied to CT-derived LA and LV walls to realistically represent LH dynamics. LH wall motion, MV dynamics and blood flow in LA and LV during MV function was simulated using a strongly coupled fluid structure interaction approach. Virtual interventions using a surgical 33mm bioprosthetic valve (BPV) and transcatheter E-2-E repair were performed and evaluated. Results: Our FSI model predicted a physiological vortex ring developing in the LV for the pre-op MV during early diastole. BPV produced complex asymmetrical vortices. Due to its double orifice, the E-2-E clip produced two separate vortex rings with the largest velocity magnitude. Of all the three treatments, BPV had the greatest leaflet deformation rate. Conclusion: This model provides realistic quantitative insights into post-op filling dynamics that can be used to personalize and optimize valve intervention. These methodologies may help clinicians to realistically predict and evaluate patient-specific LV filling dynamics to tailor MV interventions.

Differential requirement for DICER1 activity during the development of mitral and tricuspid valves.

Mitral and tricuspid valves are essential for unidirectional blood flow in the heart. They are derived from similar cell sources, and yet congenital dysplasia affecting both valves is clinically rare, suggesting the presence of differential regulatory mechanisms underlying their development. Here, we specifically inactivated Dicer1 in the endocardium during cardiogenesis and found that Dicer1 deletion caused congenital mitral valve stenosis and regurgitation, whereas it had no impact on other valves. We showed that hyperplastic mitral valves were caused by abnormal condensation and extracellular matrix (ECM) remodeling. Our single-cell RNA sequencing analysis revealed impaired maturation of mesenchymal cells and abnormal expression of ECM genes in mutant mitral valves. Furthermore, expression of a set of miRNAs that target ECM genes was significantly lower in tricuspid valves compared to mitral valves, consistent with the idea that the miRNAs are differentially required for mitral and tricuspid valve development. We thus reveal miRNA-mediated gene regulation as a novel molecular mechanism that differentially regulates mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.

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.

Ex vivo experimental characterizations for understanding the interrelationship between tissue mechanics and collagen microstructure of porcine mitral valve leaflets

Unidirectional blood flow in the left side of the heart is regulated by the mitral valve. To better understand the mitral valve function, researchers have examined the structural and mechanical properties of the mitral valve leaflets; however, limitations of the previous studies include the use of mechanics- and structure-altering tissue modifications (e.g., optical clearing) that limit the ability to quantify the unique load-dependent reorientation and realignment of the collagen fibers as well as their interrelation with the valve tissue mechanics. Herein, we aimed to circumvent these limitations by utilizing an integrated polarized-light imaging and biaxial testing system for understanding the mechanics–microstructure interrelationship for porcine mitral valve leaflets. We further performed constitutive modeling and evaluated the accuracy of the affine fiber kinematics theory. From the tissue mechanics perspective, the posterior leaflet was more extensible in the radial direction than the anterior leaflet (14.2% difference in radial tissue stretch), while exhibiting smaller collagen and elastin moduli based on the determined constitutive model parameters. From the collagen microstructure’s standpoint, the posterior leaflet had smaller increases in optical anisotropy (closely related to the degree of fiber alignment) than the anterior leaflet (32.8±7.7% vs. 50.0±19.7%). Further, the leaflets were found to possess two distinct fiber families – one family oriented along the circumferential tissue direction, and another more disperse family with a 30°–40° offset from the first fiber family. Finally, affine fiber kinematics consistently underpredicted the collagen fiber reorientations Overall, this study improved our understanding of the mitral valve leaflets that is essential for facilitating tissue-emulated valve replacement and cardiac valve modeling frameworks.

Layer Microdissection of Tricuspid Valve Leaflets for Biaxial Mechanical Characterization and Microstructural Quantification.

The tricuspid valve (TV) regulates the unidirectional flow of unoxygenated blood from the right atrium to the right ventricle. The TV consists of three leaflets, each with unique mechanical behaviors. These variations among the three TV leaflets can be further understood by examining their four anatomical layers, which are the atrialis (A), spongiosa (S), fibrosa (F), and ventricularis (V). While these layers are present in all three TV leaflets, there are differences in their thicknesses and microstructural constituents that further influence their respective mechanical behaviors. This protocol includes four steps to elucidate the layer-specific differences: (i) characterize the mechanical and collagen fiber architectural behaviors of the intact TV leaflet, (ii) separate the composite layers (A/S and F/V) of the TV leaflet, (iii) carry out the same characterizations for the composite layers, and (iv) perform post-hoc histology assessment. This experimental framework uniquely allows the direct comparison of the intact TV tissue to each of its composite layers. As a result, detailed information regarding the microstructure and biomechanical function of the TV leaflets can be collected with this protocol. Such information can potentially be used to develop TV computational models that seek to provide guidance for the clinical treatment of TV disease.

Decellularization and Recellularization Methods for Avian Lungs: An Alternative Approach for Use in Pulmonary Therapeutics.

The shortage of compatible allogeneic organs and an increase in the number of patients requiring long-term lung assist devices while waiting for lung transplantation have motivated scientists to explore alternatives to bioengineer new lungs, including through decellularization and recellularization processes. A novel approach for bioengineering an extracorporeal membrane oxygenator is based on the parenchymal structure of avian lungs which utilizes a cross-current unidirectional flow of air and blood rather than bidirectional airflow, and thus eliminates dead-space ventilation. This provides more efficient gas exchange than mammalian lungs. The novel approach utilized is to decellularize avian lungs and then to recellularize with patient-derived human lung epithelial and vascular endothelial cells with the goal of creating a fully functional structure that can be used as a gas-exchange device. Here, we present avian lung decellularization and recellularization methods for chicken and emu lungs, in order to study both small- and large-scale avian lung models. For decellularization, a detergent-based protocol is utilized, and different techniques are used to validate the de- and recellularization of those lungs, including microscopy, mass spectrometry, and immunohistochemical analyses. For recellularization, techniques for seeding different human lung cell types into the decellularized scaffolds are presented.