Passive biaxial mechanical behavior of newborn mouse aorta with and without elastin

A comparative study of storage solutions on the biomechanical preservation of human saphenous veins

Storage solutions have a significant impact on the physiological properties of saphenous veins (SV), yet their effects on the biomechanics remained unclear. This study investigated how different storage solutions affect the biomechanical properties of SV. The goal was to find a solution that minimally impacts SV biomechanics, providing an effective method for SV preservation. A total of 108 SV samples (54 axial, 54 circumferential) were randomly divided into four groups: Baseline (tested within 24 h after surgical removal), and three stored for 72 h-sodium lactated ringer's solution (SLR), physiological saline (PS), and Air. Uniaxial tensile experiments were performed, and differences in elastic modulus, maximum stress, and average stress-strain curves were evaluated. In the axial direction, the elastic modulus of SVs stored in SLR was significantly higher than in PS (7.21 ± 2.78 MPa vs. 3.90 ± 1.54 MPa, p = 0.009) and similar to Baseline (vs. 8.52 ± 3.43 MPa), while the PS group did not differ significantly from the Air group (3.90 ± 1.54 MPa vs. 2.50 ± 1.34 MPa, p > 0.99). The maximum stress in SLR was similar to Baseline (1.92 ± 0.82 MPa vs. 1.91 ± 0.58 MPa) and significantly higher than in PS (vs. 1.05 ± 0.56 MPa, p = 0.002). Similar trends could also be observed in the circumferential direction. PS significantly impairs the mechanical performance of SVs, while short-term storage in SLR can effectively preserve the biomechanical characteristics of SVs. SLR may be considered as an effective short-term storage solution for SV.

Transcriptional regulation of postnatal aortic development

The aorta exhibits tremendous changes in geometry, composition, and mechanical properties during postnatal development. These changes are necessarily driven by transcriptional changes, both genetically programmed and mechano-responsive, but there has not been a careful comparison of time-course changes in the transcriptional profile and biomechanical phenotype. Here, we show that the greatest period of differential gene expression in the normal postnatal mouse aorta occurs prior to weaning at three weeks of age though with important evolution of many transcripts thereafter. We identify six general temporal patterns, including transcripts that monotonically decrease to lower or increase to higher steady state values as well as those that either peak or dip prior to or near weaning. We show that diverse transcripts within individual groupings correlate well over time, and that sub-sets of these groups correlate well with the developmental progression of different biomechanical metrics that are expected to be involved in mechano-sensing. In particular, expression of genes for elastin and elastin-associated glycoproteins tend to correlate well with the ratio of systolic-to-diastolic stress whereas genes for collagen fibers correlate well with the daily rate of change of systolic stress and genes for mechano-sensing proteins tend to correlate well with the systolic stress itself. We conclude that different groupings of genes having different temporal expression patterns correlate well with different measures of the wall mechanics, hence emphasizing a need for age-dependent, gene-specific computational modeling of postnatal development.

Experimental Protocols to Test Aortic Soft Tissues: A Systematic Review

Experimental protocols are fundamental for quantifying the mechanical behaviour of soft tissue. These data are crucial for advancing the understanding of soft tissue mechanics, developing and calibrating constitutive models, and informing the development of more accurate and predictive computational simulations and artificial intelligence tools. This paper offers a comprehensive review of experimental tests conducted on soft aortic tissues, employing the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology, based on the Scopus, Web of Science, IEEE, Google Scholar and PubMed databases. This study includes a detailed overview of the test method protocols, providing insights into practical methodologies, specimen preparation and full-field measurements. The review also briefly discusses the post-processing methods applied to extract material parameters from experimental data. In particular, the results are analysed and discussed providing representative domains of stress-strain curves for both uniaxial and biaxial tests on human aortic tissue.

Constitutive Modeling of Mouse Arteries Suggests Changes in Directional Coupling and Extracellular Matrix Remodeling That Depend on Artery Type, Age, Sex, and Elastin Amounts

Arterial stiffening occurs during natural aging, is associated with an increased risk of adverse cardiovascular events, and can follow different timelines in males and females. One mechanism of arterial stiffening includes remodeling of the extracellular matrix (ECM), which alters the wall material properties. We used elastin haploinsufficient (Eln+/-) and wildtype (Eln+/+) mice to investigate how material properties of two different arteries (ascending aorta and carotid artery) change with age, sex, and ECM composition. We used a constitutive model by Dong and Sun that is based on the Holzapfel-Gasser-Ogden (HGO) type, but does not require a discrete number of fibrous ECM families and allows varied deformation coupling. We find that the amount of deformation coupling for the best fit model depends on the artery type. We also find that remodeling to maintain homeostatic (i.e., young, wildtype) values of biomechanical parameters with age, sex, and ECM composition depends on the artery type, with ascending aorta being more adaptable than carotid artery. Fitted material constants indicate sex-dependent remodeling that may be important for determining the time course of arterial stiffening in males and females. We correlated fitted material constants with ECM composition measured by biochemical (ascending aorta) or histological (carotid artery) methods. We show significant correlations between ECM composition and material parameters for the mean values for each group, with biochemical measurements correlating more strongly than histological measurements. Understanding how arterial stiffening depends on age, sex, ECM composition, and artery type may help design effective, personalized clinical treatment strategies.

Elastic fibers define embryonic tissue stiffness to enable buckling morphogenesis of the small intestine

During embryonic development, tissues must possess precise material properties to ensure that cell-generated forces give rise to the stereotyped morphologies of developing organs. However, the question of how material properties are established and regulated during development remains understudied. Here, we aim to address these broader questions through the study of intestinal looping, a process by which the initially straight intestinal tube buckles into loops, permitting ordered packing within the body cavity. Looping results from elongation of the tube against the constraint of an attached tissue, the dorsal mesentery, which is elastically stretched by the elongating tube to nearly triple its length. This elastic energy storage allows the mesentery to provide stable compressive forces that ultimately buckle the tube into loops. Beginning with a transcriptomic analysis of the mesentery, we identified widespread upregulation of extracellular matrix related genes during looping, including genes related to elastic fiber deposition. Combining molecular and mechanical analyses, we conclude that elastin confers tensile stiffness to the mesentery, enabling its mechanical role in organizing the developing small intestine. These results shed light on the role of elastin as a driver of morphogenesis that extends beyond its more established role in resisting cyclic deformation in adult tissues.

ELASTIC FIBERS DEFINE EMBRYONIC TISSUE STIFFNESS TO ENABLE BUCKLING MORPHOGENESIS OF THE SMALL INTESTINE

During embryonic development, tissues must possess precise material properties to ensure that cell-generated forces give rise to the stereotyped morphologies of developing organs. However, the question of how material properties are established and regulated during development remains understudied. Here, we aim to address these broader questions through the study of intestinal looping, a process by which the initially straight intestinal tube buckles into loops, permitting ordered packing within the body cavity. Looping results from elongation of the tube against the constraint of an attached tissue, the dorsal mesentery, which is elastically stretched by the elongating tube to nearly triple its length. This elastic energy storage allows the mesentery to provide stable compressive forces that ultimately buckle the tube into loops. Beginning with a transcriptomic analysis of the mesentery, we identified widespread upregulation of extracellular matrix related genes during looping, including genes related to elastic fiber deposition. Combining molecular and mechanical analyses, we conclude that elastin confers tensile stiffness to the mesentery, enabling its mechanical role in organizing the developing small intestine. These results shed light on the role of elastin as a driver of morphogenesis that extends beyond its more established role in resisting cyclic deformation in adult tissues.

Elastin, arterial mechanics, and stenosis

Elastin is a long-lived extracellular matrix protein that is organized into elastic fibers that provide elasticity to the arterial wall, allowing stretch and recoil with each cardiac cycle. By forming lamellar units with smooth muscle cells, elastic fibers transduce tissue-level mechanics to cell-level changes through mechanobiological signaling. Altered amounts or assembly of elastic fibers leads to changes in arterial structure and mechanical behavior that compromise cardiovascular function. In particular, genetic mutations in the elastin gene (ELN) that reduce elastin protein levels are associated with focal arterial stenosis, or narrowing of the arterial lumen, such as that seen in supravalvular aortic stenosis and Williams-Beuren syndrome. Global reduction of Eln levels in mice allows investigation of the tissue- and cell-level arterial mechanical changes and associated alterations in smooth muscle cell phenotype that may contribute to stenosis formation. A loxP-floxed Eln allele in mice highlights cell type- and developmental origin-specific mechanobiological effects of reduced elastin amounts. Eln production is required in distinct cell types for elastic layer formation in different parts of the mouse vasculature. Eln deletion in smooth muscle cells from different developmental origins in the ascending aorta leads to characteristic patterns of vascular stenosis and neointima. Dissecting the mechanobiological signaling associated with local Eln depletion and subsequent smooth muscle cell response may help develop new therapeutic interventions for elastin-related diseases.