In-Situ Deformation of the Aortic Valve Interstitial Cell Nucleus Under Diastolic Loading

2007 ◽  
Vol 129 (6) ◽  
pp. 880-889 ◽  
Author(s):  
Hsiao-Ying Shadow Huang ◽  
Jun Liao ◽  
Michael S. Sacks
Keyword(s):  
Aortic Valve ◽  
Collagen Fiber ◽  
Structural Integrity ◽  
Tissue Level ◽  
Fe Model ◽  
Mechanical Stimuli ◽  
Fiber Alignment ◽  
Collagen Fiber Alignment

Within the aortic valve (AV) leaflet resides a population of interstitial cells (AVICs), which serve to maintain tissue structural integrity via protein synthesis and enzymatic degradation. AVICs are typically characterized as myofibroblasts, exhibit phenotypic plasticity, and may play an important role in valve pathophysiology. While it is known that AVICs can respond to mechanical stimuli in vitro, the level of in vivo AVIC deformation and its relation to local collagen fiber reorientation during the cardiac cycle remain unknown. In the present study, the deformation of AVICs was investigated using porcine AV glutaraldehyde fixed under 0–90mmHg transvalvular pressures. The resulting change in nuclear aspect ratio (NAR) was used as an index of overall cellular strain, and dependencies on spatial location and pressure loading levels quantified. Local collagen fiber alignment in the same valves was also quantified using small angle light scattering. A tissue-level finite element (FE) model of an AVIC embedded in the AV extracellular matrix was also used explore the relation between AV tissue- and cellular-level deformations. Results indicated large, consistent increases in AVIC NAR with transvalvular pressure (e.g., from mean of 1.8 at 0mmHg to a mean of 4.8 at 90mmHg), as well as pronounced layer specific dependencies. Associated changes in collagen fiber alignment indicated that little AVIC deformation occurs with the large amount of fiber straightening for pressures below ∼1mmHg, followed by substantial increases in AVIC NAR from 4mmHgto90mmHg. While the tissue-level FE model was able to capture the qualitative response, it also underpredicted the extent of AVIC deformation. This result suggested that additional micromechanical and fiber-compaction effects occur at high pressure levels. The results of this study form the basis of understanding transvalvular pressure-mediated mechanotransduction within the native AV and first time quantitative data correlating AVIC nuclei deformation with AV tissue microstructure and deformation.

Collagen Fiber Re-Alignment and Mechanical Properties in a Mouse Supraspinatus Tendon Model: Examining Changes With Age and Location

2012 ◽  
Author(s):  
Kristin S. Miller ◽  
Brianne K. Connizzo ◽  
Elizabeth Feeney ◽  
Louis J. Soslowsky
Keyword(s):  
Mechanical Properties ◽  
Collagen Fiber ◽  
Mechanical Load ◽  
Mechanical Test ◽  
Insertion Site ◽  
Supraspinatus Tendon ◽  
Tissue Response ◽  
Mechanical Stimuli ◽  
Fiber Alignment ◽  
Collagen Fiber Alignment

One postulated mechanism of tendon structural response to mechanical load is collagen fiber re-alignment. Recently, where collagen fiber re-alignment occurs during a tensile mechanical test has been shown to vary by tendon age and location in a postnatal developmental mouse supraspinatus tendon (SST) model [1]. It is thought that as the tendon matures and its collagen fibril network, collagen cross-links and collagen-matrix interactions develop, its ability to respond quickly to mechanical stimuli hastens [1]. Additionally, the insertion site and midsubstance of postnatal SST may develop differently and at different rates, providing a potential explanation for differences in fiber re-alignment behaviors at the insertion site and midsubstance at postnatal developmental time points [1]. However, collagen fiber re-alignment behavior, in response to mechanical load at a mature age and in comparison to developmental ages, have not been examined. Therefore, the objectives of this study are to locally measure: 1) fiber re-alignment during preconditioning and tensile mechanical testing and 2) to compare local differences in collagen fiber alignment and corresponding mechanical properties to address tissue response to mechanical load in the mature and postnatal developmental mouse SST. We hypothesize that 1) 90 day tendons will demonstrate the largest shift in fiber re-alignment during preconditioning, but will also re-align during the toe- and linear-regions. Additionally, we hypothesize that 2) mechanical properties and initial collagen fiber alignment will be greater in the midsubstance of the tendon compared to the tendon-to-bone insertion site at 90 days, 3) that mechanical properties will increase with age, and that 4) collagen fiber organization at the insertion site will decrease with age.

Mechanical properties of tissue formed in vivo are affected by 3D-bioplotted scaffold microarchitecture and correlate with ECM collagen fiber alignment

2019 ◽  
Vol 61 (2) ◽  
pp. 190-204 ◽  
Author(s):  
Pedro Huebner ◽  
Paul B. Warren ◽  
Daniel Chester ◽  
Jeffrey T. Spang ◽  
Ashley C. Brown ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Collagen Fiber ◽  
Fiber Alignment ◽  
Collagen Fiber Alignment

scholarly journals An in vitro assay of collagen fiber alignment by acupuncture needle rotation

2008 ◽  
Vol 7 (1) ◽  
pp. 19 ◽  
Author(s):  
Margaret Julias ◽  
Lowell T Edgar ◽  
Helen M Buettner ◽  
David I Shreiber
Keyword(s):  
Collagen Fiber ◽  
In Vitro Assay ◽  
Vitro Assay ◽  
Fiber Alignment ◽  
Acupuncture Needle ◽  
Collagen Fiber Alignment

Abstract P351: Grayscale Texture Feature Angular Second Moment Correlates With Collagen Alignment in Carotid Artery Plaques

Stroke ◽  
2021 ◽  
Vol 52 (Suppl_1) ◽  
Author(s):  
Carol Mitchell ◽  
Stephanie M Wilbrand ◽  
M.Shahriar Salamat ◽  
Jens Eickhoff ◽  
Nirvedh H Meshram ◽  
...  
Keyword(s):  
Collagen Fiber ◽  
Texture Feature ◽  
Texture Features ◽  
Fiber Alignment ◽  
Vulnerable Plaques ◽  
The Mean ◽  
Collagen Alignment ◽  
Collagen Fiber Alignment ◽  
Multiscale Imaging

Introduction: Grayscale (GS) texture features that examine homogeneity and echogenicity have been used to identify vulnerable plaques with in vivo ultrasound imaging have been shown to correlate with plaque tissue composition. However, the relationship of collagen fiber organization to GS texture features extracted from in vivo images is a novel idea to provide additional information about plaque structure. We hypothesize that collagen fiber alignment is clinically relevant to identify vulnerable plaques. The objective of this feasibility study was to use multiscale imaging (in vivo ultrasound and high resolution optical microscopy) to determine how GS texture features are related to plaque collagen structure. Methods: Participants (n=6) scheduled for clinically indicated carotid endarterectomy underwent in vivo carotid ultrasound imaging with texture feature extraction (spatial gray level dependence matrices method for calculating angular second moment [SGLDM-ASM] and grayscale median value [GSM]). Plaque specimens were sent to histopathology and stained with H&E. The collagen fibers in the fibrous cap of the plaque histopathology slides were imaged with liquid crystal based polarization microscopy and quantified using an established software tool (CurveAlign). Correlations between collagen alignment coefficient (range 0-1, 1 represents perfectly aligned fibers) and the texture feature SGLDM-ASM (a measure of homogeneity, higher values are more homogenous) and GSM (a measure of echogenicity higher values are more echogenic) were examined. Results: Participants were mean (SD) 72.5 (6.1) years of age, had 71.67 (8.16) percent stenosis. The mean SGLDM-ASM was 0.0017 (0.0023), the mean SD GSM was 73.13 (30.98). SGLDM-ASM was significantly correlated to collagen alignment (r=0.83; p=0.028). There was no significant correlation detected between GSM and collagen alignment (r=-0.43;p=0.38). Conclusion: Results of this study indicate the potential role for using high resolution optical microscopy with ultrasound to characterize collagen fiber alignment in plaques with measures of homogeneity. Future studies are needed to see how multiscale imaging can be used to inform in vivo imaging for identification of vulnerable plaque features.

scholarly journals A Novel Bioreactor for the Mechanical Stimulation of Clinically Relevant Scaffolds for Muscle Tissue Engineering Purposes

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 474
Author(s):  
Silvia Todros ◽  
Silvia Spadoni ◽  
Edoardo Maghin ◽  
Martina Piccoli ◽  
Piero G. Pavan
Keyword(s):  
Mechanical Stimulation ◽  
Strain Range ◽  
Tensile Tests ◽  
Muscular Tissue ◽  
Fe Model ◽  
Mechanical Stimuli ◽  
Physiological Strain ◽  
Cellular Alignment ◽  
Stimulation Of

Muscular tissue regeneration may be enhanced in vitro by means of mechanical stimulation, inducing cellular alignment and the growth of functional fibers. In this work, a novel bioreactor is designed for the radial stimulation of porcine-derived diaphragmatic scaffolds aiming at the development of clinically relevant tissue patches. A Finite Element (FE) model of the bioreactor membrane is developed, considering two different methods for gripping muscular tissue patch during the stimulation, i.e., suturing and clamping with pliers. Tensile tests are carried out on fresh and decellularized samples of porcine diaphragmatic tissue, and a fiber-reinforced hyperelastic constitutive model is assumed to describe the mechanical behavior of tissue patches. Numerical analyses are carried out by applying pressure to the bioreactor membrane and evaluating tissue strain during the stimulation phase. The bioreactor designed in this work allows one to mechanically stimulate tissue patches in a radial direction by uniformly applying up to 30% strain. This can be achieved by adopting pliers for tissue clamping. Contrarily, the use of sutures is not advisable, since high strain levels are reached in suturing points, exceeding the physiological strain range and possibly leading to tissue laceration. FE analysis allows the optimization of the bioreactor configuration in order to ensure an efficient transduction of mechanical stimuli while preventing tissue damage.

STRETCHABLE Lab-on-Chip Device With Impedance Spectroscopy Capability for Mammalian Cell Studies

2016 ◽  
Author(s):  
Xudong Zhang ◽  
Anis Nurashikin Nordin ◽  
Fang Li ◽  
Ioana Voiculescu
Keyword(s):  
Impedance Spectroscopy ◽  
Mammalian Cells ◽  
Dynamic Environment ◽  
Cyclic Strain ◽  
Cyclic Stretch ◽  
Mechanical Stimuli ◽  
Aortic Endothelial Cells ◽  
Lab On Chip

This paper presents the fabrication and testing of electric cell-substrate impedance spectroscopy (ECIS) electrodes on a stretchable membrane. This is the first time when ECIS electrodes were fabricated on a stretchable substrate and ECIS measurements on mammalian cells exposed to cyclic strain of 10% were successfully demonstrated. A chemical was used to form strong chemical bond between gold electrodes of ECIS sensor and polymer membrane, which enable the electrodes keep good conductive ability during cyclic stretch. The stretchable membrane integrated with the ECIS sensor can simulate and replicate the dynamic environment of organism and enable the analysis of the cells activity involved in cells attachment and proliferation in vitro. Bovine aortic endothelial cells (BAEC) were used to evaluate the endothelial function influenced by mechanical stimuli in this research because they undergo in vivo cyclic physiologic elongation produced by the blood circulation in the arteries.

scholarly journals Modelling human skull growth: a validated computational model

2017 ◽  
Vol 14 (130) ◽  
pp. 20170202 ◽  
Author(s):  
Joseph Libby ◽  
Arsalan Marghoub ◽  
David Johnson ◽  
Roman H. Khonsari ◽  
Michael J. Fagan ◽  
...  
Keyword(s):  
Computational Model ◽  
Three Dimensional ◽  
Basic Knowledge ◽  
Fe Model ◽  
Adult Size ◽  
Fe Method ◽  
Percentage Difference ◽  
Skull Growth

During the first year of life, the brain grows rapidly and the neurocranium increases to about 65% of its adult size. Our understanding of the relationship between the biomechanical forces, especially from the growing brain, the craniofacial soft tissue structures and the individual bone plates of the skull vault is still limited. This basic knowledge could help in the future planning of craniofacial surgical operations. The aim of this study was to develop a validated computational model of skull growth, based on the finite-element (FE) method, to help understand the biomechanics of skull growth. To do this, a two-step validation study was carried out. First, an in vitro physical three-dimensional printed model and an in silico FE model were created from the same micro-CT scan of an infant skull and loaded with forces from the growing brain from zero to two months of age. The results from the in vitro model validated the FE model before it was further developed to expand from 0 to 12 months of age. This second FE model was compared directly with in vivo clinical CT scans of infants without craniofacial conditions ( n = 56). The various models were compared in terms of predicted skull width, length and circumference, while the overall shape was quantified using three-dimensional distance plots. Statistical analysis yielded no significant differences between the male skull models. All size measurements from the FE model versus the in vitro physical model were within 5%, with one exception showing a 7.6% difference. The FE model and in vivo data also correlated well, with the largest percentage difference in size being 8.3%. Overall, the FE model results matched well with both the in vitro and in vivo data. With further development and model refinement, this modelling method could be used to assist in preoperative planning of craniofacial surgery procedures and could help to reduce reoperation rates.

Tracings of Behavior of Myoblasts Cultured Under Couette Type of Shear Flow Between Parallel Disks

2021 ◽  
Author(s):  
Shigehiro Hashimoto ◽  
Hiroki Yonezawa
Keyword(s):  
Shear Stress ◽  
Shear Flow ◽  
Rotating Disk ◽  
Time Lapse ◽  
Mechanical Stimuli ◽  
Parallel Disks ◽  
Before And After ◽  
A Cell

Abstract A cell deforms and migrates on the scaffold under mechanical stimuli in vivo. In this study, a cell with division during shear stress stimulation has been observed in vitro. Before and after division, both migration and deformation of each cell were analyzed. To make a Couette-type shear flow, the medium was sandwiched between parallel disks (the lower stationary culture-disc and the upper rotating disk) with a constant gap. The wall shear stress (1.5 Pa < τ < 2 Pa) on the surface of the lower culture plate was controlled by the rotational speed of the upper disc. Myoblasts (C2C12: mouse myoblast cell line) were used in the test. After cultivation without flow for 24 hours for adhesion of the cells to the lower disk, constant τ was applied to the cells in the incubator for 7 days. The behavior of each cell during shear was tracked by time-lapse images observed by an inverted phase contrast microscope placed in the incubator. Experimental results show that each cell tends to divide after higher activities: deformation and migration. The tendency is remarkable at the shear stress of 1.5 Pa.

scholarly journals Functional Organization of the Yeast SAGA Complex: Distinct Components Involved in Structural Integrity, Nucleosome Acetylation, and TATA-Binding Protein Interaction

1999 ◽  
Vol 19 (1) ◽  
pp. 86-98 ◽  
Author(s):  
David E. Sterner ◽  
Patrick A. Grant ◽  
Shannon M. Roberts ◽  
Laura J. Duggan ◽  
Rimma Belotserkovskaya ◽  
...  
Keyword(s):  
Histone Acetylation ◽  
Structural Integrity ◽  
Functional Organization ◽  
Binding Protein ◽  
Tata Binding Protein ◽  
Saga Complex ◽  
Specific Domain ◽  
Nucleosomal Histone

ABSTRACT SAGA, a recently described protein complex in Saccharomyces cerevisiae, is important for transcription in vivo and possesses histone acetylation function. Here we report both biochemical and genetic analyses of members of three classes of transcription regulatory factors contained within the SAGA complex. We demonstrate a correlation between the phenotypic severity of SAGA mutants and SAGA structural integrity. Specifically, null mutations in the Gcn5/Ada2/Ada3 or Spt3/Spt8 classes cause moderate phenotypes and subtle structural alterations, while mutations in a third subgroup, Spt7/Spt20, as well as Ada1, disrupt the complex and cause severe phenotypes. Interestingly, double mutants (gcn5Δ spt3Δand gcn5Δ spt8Δ) causing loss of a member of each of the moderate classes have severe phenotypes, similar tospt7Δ, spt20Δ, or ada1Δmutants. In addition, we have investigated biochemical functions suggested by the moderate phenotypic classes and find that first, normal nucleosomal acetylation by SAGA requires a specific domain of Gcn5, termed the bromodomain. Deletion of this domain also causes specific transcriptional defects at the HIS3 promoter in vivo. Second, SAGA interacts with TBP, the TATA-binding protein, and this interaction requires Spt8 in vitro. Overall, our data demonstrate that SAGA harbors multiple, distinct transcription-related functions, including direct TBP interaction and nucleosomal histone acetylation. Loss of either of these causes slight impairment in vivo, but loss of both is highly detrimental to growth and transcription.

scholarly journals Microfluidic and Lab-on-a-Chip Systems for Cutaneous Wound Healing Studies

2021 ◽  
Author(s):  
Ghazal Shabestani Monfared ◽  
Peter Ertl ◽  
Mario Rothbauer
Keyword(s):  
Wound Healing ◽  
Molecular Mechanisms ◽  
Chronic Wounds ◽  
Cell Communication ◽  
Lab On A Chip ◽  
Tissue Level ◽  
Cutaneous Wound Healing ◽  
Cutaneous Wound

Cutaneous wound healing is a complex multi-stage process involving direct and indirect cell communication events with the aim of efficiently restoring the barrier function of the skin. One key aspect in cutaneous wound healing is associated with cell movement and migration into the physically, chemically and biologically injured area resulting in wound closure. Understanding the conditions under which cell migration is impaired and elucidating the cellular and molecular mechanisms that improve healing dynamics is therefore crucial in devising novel therapeutic strategies to elevate patient suffering, reduce scaring and eliminate chronic wounds. Following the global trend towards automation, miniaturization and integration of cell-based assays into microphysiological systems, conventional wound healing assays such as the scratch assay or cell exclusion assay have recently been translated and improved using microfluidics and lab-on-a-chip technologies. These miniaturized cell analysis systems allow precise spatial and temporal control over a range of dynamic microenvironmental factors including shear stress, biochemical and oxygen gradients to create more reliable in vitro models that resemble the in vivo microenvironment of a wound more closely on a molecular, cellular, and tissue level. The current review provides (a) an overview on the main molecular and cellular processes that take place during wound healing, (b) a brief introduction into conventional in vitro wound healing assays, and (c) a perspective on future cutaneous and vascular wound healing research using microfluidic technology.

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