Microstructure of early embryonic aortic arch and its reversibility following mechanically altered hemodynamic load release.

In the embryonic heart, blood flow is distributed through a bilaterally paired artery system composed of the aortic arches (AAs). The purpose of this study is to establish an understanding of the governing mechanism of microstructural maturation of the AA matrix and its reversibility, toward the desired macroscopic vessel lumen diameter and thickness for healthy, abnormal, and in ovo repaired abnormal mechanical loading. While matrix-remodeling mechanisms were significantly different for normal versus conotruncal banding (CTB), both led to an increase in vessel lumen. Correlated with right-sided flow increase at Hamburger & Hamilton stages 21, intermittent load switching between collagen I and III with elastin and collagen-IV defines the normal process. However, decreases in collagen I, elastin, vascular endothelial growth factor-A, and fibrillin-1 in CTB were recovered almost fully following the CTB-release model, primarily because of the pressure load changes. The complex temporal changes in matrix proteins are illustrated through a predictive finite-element model based on elastin and collagen load-sharing mechanism to achieve lumen area increase and thickness increase resulting from wall shear stress and tissue strain, respectively. The effect of embryonic timing in cardiac interventions on AA microstructure was established where abnormal mechanical loading was selectively restored at the key stage of development. Recovery of the normal mechanical loading via early fetal intervention resulted in delayed microstructural maturation. Temporal elastin increase, correlated with wall shear stress, is required for continuous lumen area growth.NEW & NOTEWORTHY The present study undertakes comparative analyses of the mechanistic differences of the arterial matrix microstructure and dynamics in the three fundamental processes of control, conotruncal banded, and released conotruncal band in avian embryo. Among other findings, this study provides specific evidence on the restorative role of elastin during the early lumen growth process. During vascular development, a novel intermittent load-switching mechanism between elastin and collagen, triggered by a step increase in wall shear stress, governs the chronic vessel lumen cross-sectional area increase. Mimicking the fetal cardiovascular interventions currently performed in humans, the early release of the abnormal mechanical load rescues the arterial microstructure with time lag.

Asymmetry in Mechanosensitive Gene Expression during Aortic Arch Morphogenesis.

Embryonic aortic arches (AA) are initially bilaterally paired, transitional vessels and failures in remodeling based on hemodynamic and growth-related adaptations cause a spectrum of congenital heart disease (CHD) anatomies. Identifying regulatory mechanisms and cross-talk between the genetic elements of these vessels are critical to understand the ethiology of CHD and refine predictive computational models. This study aims to screen expression profiles of fundamental biological pathways in AA at early stages of chick embryo morphogenesis and correlate them with our current understanding of growth and mechanical loading. Reverse transcription-quantitative PCR (RT-qPCR) was followed by correlation and novel peak expression analyses to compare the behaviour and activation period of the genes. Available protein networks were also integrated to investigate the interactions between molecules and highlight major hierarchies. Only wall shear stress (WSS) and growth-correlated expression patterns were investigated. Effect of WSS was seen directly on angiogenesis as well on structural and apoptosis-related genes. Our time-resolved network suggested that WSS-correlated genes coordinate the activity of critical growth factors. Moreover, differential gene expression of left and right AA might be an indicator of subsequent asymmetric morphogenesis. These findings may further our understanding of the complex processes of cardiac morphogenesis and errors resulting in CHD.

Haemodynamic Recovery Properties of the Torsioned Testicular Artery Lumen.

Testicular artery torsion (twisting) is one such severe vascular condition that leads spermatic cord injury. In this study, we investigate the recovery response of a torsioned ram testicular artery in an isolated organ-culture flow loop with clinically relevant twisting modes (90°, 180°, 270° and 360° angles). Quantitative optical coherence tomography technique was employed to track changes in the lumen diameter, wall thickness and the three-dimensional shape of the vessel in the physiological pressure range (10-50 mmHg). As a control, pressure-flow characteristics of the untwisted arteries were studied when subjected to augmented blood flow conditions with physiological flow rates up to 36 ml/min. Both twist and C-shaped buckling modes were observed. Acute increase in pressure levels opened the narrowed lumen of the twisted arteries noninvasively at all twist angles (at ∼22 mmHg and ∼35 mmHg for 360°-twisted vessels during static and dynamic flow experiments, respectively). The association between the twist-opening flow rate and the vessel diameter was greatly influenced by the initial twist angle. The biomechanical characteristics of the normal (untwisted) and torsioned testicular arteries supported the utilization of blood flow augmentation as an effective therapeutic approach to modulate the vessel lumen and recover organ reperfusion.

Time-Series Interactions of Gene Expression, Vascular Growth and Hemodynamics during Early Embryonic Arterial Development.

The role of hemodynamic forces within the embryo as biomechanical regulators for cardiovascular morphogenesis, growth, and remodeling is well supported through the experimental studies. Furthermore, clinical experience suggests that perturbed flow disrupts the normal vascular growth process as one etiology for congenital heart diseases (CHD) and for fetal adaptation to CHD. However, the relationships between hemodynamics, gene expression and embryonic vascular growth are poorly defined due to the lack of concurrent, sequential in vivo data. In this study, a long-term, time-lapse optical coherence tomography (OCT) imaging campaign was conducted to acquire simultaneous blood velocity, pulsatile micro-pressure and morphometric data for 3 consecutive early embryonic stages in the chick embryo. In conjunction with the in vivo growth and hemodynamics data, in vitro reverse transcription polymerase chain reaction (RT-PCR) analysis was performed to track changes in transcript expression relevant to histogenesis and remodeling of the embryonic arterial wall. Our non-invasive extended OCT imaging technique for the microstructural data showed continuous vessel growth. OCT data coupled with the PIV technique revealed significant but intermitted increases in wall shear stress (WSS) between first and second assigned stages and a noticeable decrease afterwards. Growth rate, however, did not vary significantly throughout the embryonic period. Among all the genes studied, only the MMP-2 and CASP-3 expression levels remained unchanged during the time course. Concurrent relationships were obtained among the transcriptional modulation of the genes, vascular growth and hemodynamics-related changes. Further studies are indicated to determine cause and effect relationships and reversibility between mechanical and molecular regulation of vasculogenesis.

Hemodynamic flow visualization of early embryonic great vessels using µPIV.

Microparticle image velocimetry (µPIV) is an evolving quantitative methodology to closely and accurately monitor the cardiac flow dynamics and mechanotransduction during vascular morphogenesis. While PIV technique has a long history, contemporary developments in advanced microscopy have significantly expanded its power. This chapter includes three new methods for µPIV acquisition in selected embryonic structures achieved through advanced optical imaging: (1) high-speed confocal scanning of transgenic zebrafish embryos, where the transgenic erythrocytes act as the tracing particles; (2) microinjection of artificial seeding particles in chick embryos visualized with stereomicroscopy; and (3) real-time, time-resolved optical coherence tomography acquisition of vitelline vessel flow profiles in chick embryos, tracking the erythrocytes.

Decellularization method influences early remodeling of an allogenic tissue scaffold.

Extracellular matrix-based biomaterials are currently pursued as an alternative to autologous transplants for the treatment of gingival recession and periodontal disease. These grafts offer improved tissue regeneration without the need for a second operative procedure used in current treatments to remove nonresorbable synthetic biomaterials. However, while decellularization is necessary to minimize the potential immunological impact, it can significantly modify the materials architectural and biochemical properties. By understanding cellular responses, it is possible to more specifically target varying clinical situations. These investigations assess a novel allogenic scaffold derived from the human umbilical vein and determine the effects of two decellularization approaches (osmotic lysis and the surfactant Triton X-100) on the biological and mechanical properties during early remodeling events. Results show Triton X-100 to be significantly more effective at extracting lipids, while the extraction of the scaffolds bulk protein, GAG and DNA similar between the two treatments. Once seeded, scaffolds prepared with osmotic lysis displayed increased cellular proliferation and reduced metabolic activity compared to scaffolds treated with surfactant. Biomechanical properties were largely preserved and similar between the two treatments. These results suggest that by optimizing scaffold processing conditions, biological events associated with remodeling can be modulated to tailor scaffold function for specific clinical applications.

Biomechanical behavior of oral soft tissues.

BACKGROUND: Little attention has been given to understanding the variation in biomechanical behavior of oral soft tissues, and this represents an obstacle for the development of biomaterials that perform with appropriate biomechanical characteristics. With this as our motivation, a uniaxial mechanical analysis was performed on lingual and buccal aspects of the attached gingiva, alveolar mucosa, and buccal mucosa to gain insight into human tissue performance and site-specific mechanical variation. METHODS: A discrete quantitative mechanical evaluation of each soft tissue region using tensile, dynamic compression, and stress relaxation analysis was conducted to correlate tissue structure with function as assessed histologically. RESULTS: Results confirm the keratinized gingiva to have increased tensile strength (3.94 ± 1.19 MPa) and stiffness (Young modulus of 19.75 ± 6.20 MPa) relative to non-keratinized mucosal regions, where densely arranged elastin fibers contribute to a tissue with increased viscoelastic properties. Dynamic compression analysis indicated the instantaneous modulus (E(int)), steady modulus (E(s)), and peak stress increased with loading frequency and strain amplitude, with the highest values found in the buccal attached gingiva. CONCLUSION: These investigations quantify the biomechanical properties of oral soft tissues and show region-to-region variation that details structure-function relationships and provides key parameters to aid development of biomaterials that perform with appropriate biomechanical properties.

Cellular interactions and biomechanical properties of a unique vascular-derived scaffold for periodontal tissue regeneration.

These investigations describe the development of a novel ex vivo three-dimensional scaffold derived from the human umbilical vein (HUV), and its potential as a regenerative matrix for tissue regeneration. Unique properties associated with the vascular wall have shown potential to function as a surgical barrier for guided tissue regeneration, particularly with the regeneration of periodontal tissues. HUV was isolated from umbilical cords using a semiautomated machining technology, decellularized using 1% sodium dodecyl sulfate, and then opened longitudinally to form tissue sheets. Uniaxial tensile testing, stress relaxation, and suture retention tests were performed on the acellular matrix to evaluate the HUV's biomechanical properties, followed by an evaluation of cellular interactions by seeding human gingival fibroblasts to assess adhesion, metabolic function, and proliferation on the scaffold. The scaffold's biomechanical properties were shown to display anisotropic behavior, which is attributed to the ex vivo material's composite structure. Detailed results indicated that the ultimate tensile strength of the longitudinal strips was significantly higher than that of the circumferential strips (p < 0.001). The HUV also exhibited significantly higher stress relaxation response in the longitudinal direction than in the circumferential orientation (p < 0.05). The ablumenal and lumenal surfaces of the material were also shown to differentially influence cell proliferation and metabolic activity, with both cellular functions significantly increased on the ablumenal surface (p < 0.05). Human gingival fibroblast migration into the scaffold was also influenced by the organization of extracellular matrix components, where the lumenal surface inhibits cell migration, acting as a barrier, while the ablumenal surface, which is proposed to interface with the wound site, promotes cellular invasion. These results show the HUV bioscaffold to be a promising naturally derived surgical barrier that may function well as a resorbable guided tissue regeneration membrane as well as in other clinical applications.