Biphasic Structure-Based Modeling of Tissue Equivalent Mechanics

2007 ◽  
Author(s):  
Preethi L. Chandran ◽  
Triantafyllos Stylianopoulos ◽  
Victor H. Barocas
Keyword(s):  
Solid Phase ◽  
Collagen Gel ◽  
Tissue Mechanics ◽  
Soft Tissue Mechanics ◽  
Confined Compression ◽  
Elastic Interactions ◽  
Tissue Equivalents ◽  
Tissue Equivalent ◽  
Vitro Model

The collagen gel has been extensively studied as an in vitro model for soft tissue mechanics, cell-ECM interactions, and as a prototypical bioartificial tissue; a model of gel mechanics from a microstructural perspective is important for all of these [1]. An earlier experimental study recorded the microstructural rearrangements during confined compression by interpreting the evolution of birefringence patterns within the gel [2]. The patterns suggested that strain was transmitted by fiber rotation at interconnections and was non-uniform due to fluid permeation resistance, indicating that macroscopic gel mechanics arise from elastic interactions between the solid phase fibers and viscous interactions with fluid. A structure-based mathematical model to account for both the elastic and viscous response of tissue equivalents was developed.

Hypoxia induces capillary network formation in cultured bovine pulmonary microvessel endothelial cells

1995 ◽  
Vol 268 (5) ◽  
pp. L789-L800 ◽  
Author(s):  
P. G. Phillips ◽  
L. M. Birnby ◽  
A. Narendran
Keyword(s):  
In Vitro Model ◽  
Network Formation ◽  
Collagen Gel ◽  
Coronary Artery Occlusion ◽  
In Vivo Studies ◽  
Hypoxic Exposure ◽  
Vitro Model ◽  
Vessel Networks

The development of new vessels (angiogenesis) is essential to wound healing. The center of a wound space is hypoxic, a condition that has been shown to stimulate angiogenesis in animal models of coronary artery occlusion. Because the mechanisms involved in this complex process are difficult to study in situ, an in vitro model would provide a useful complement to in vivo studies. This laboratory has developed and characterized calf pulmonary microvessel endothelial cell (PMVEC) cultures and an in vitro model system of angiogenesis using collagen three-dimensional gels that permit migration of cells into vessel networks. This system was used to study the direct effect of normoxia (20% O2) or hypoxia (5% O2) on PMVEC ability to undergo angiogenesis in vitro. Major changes leading to formation of capillary-like networks occurred during the first 3 days of hypoxic exposure only and included restructuring of actin filament networks, focal changes in distribution of basic fibroblast growth factor, and orientation and migration of cell tracts into a collagen gel matrix to form vessel networks.

Fibronectin provides a conduit for fibroblast transmigration from collagenous stroma into fibrin clot provisional matrix

1997 ◽  
Vol 110 (7) ◽  
pp. 861-870 ◽  
Author(s):  
D. Greiling ◽  
R.A. Clark
Keyword(s):  
Wound Healing ◽  
In Vitro Model ◽  
Collagen Gel ◽  
Fibrin Clot ◽  
Dependent Manner ◽  
Fibrin Gel ◽  
Concentration Dependent Manner ◽  
Vitro Model ◽  
Early Wound

After injury, the wound space is filled with a fibrin/fibronectin clot containing growth factors released by platelets and monocytes. In response to these factors, fibroblasts migrate into the fibrin clot and contribute to the formation of granulation tissue. The functional mechanisms allowing fibroblasts to leave the collagenous matrix of normal connective tissue and invade the provisional matrix of the fibrin clot have not been fully defined. To investigate these mechanisms we established a new in vitro model which simulates specific aspects of early wound healing, that is, the migration of fibroblasts from a three-dimensional collagen matrix into a fibrin clot. This transmigration could be induced by physiological concentrations of platelet releasate or platelet-derived growth factor BB (PDGF-BB) in a concentration-dependent manner. At 24 hours irradiated fibroblasts invaded the fibrin gel almost as well as non-irradiated cells, indicating that transmigration was independent of proliferation. Plasminogen and its activators appear to be necessary for invasion of the fibrin clot since protease inhibitors decreased the amount of migration. These serine proteases, however, were not necessary for exit from the collagen gel as fibroblasts migrated out of the collagen gel onto a surface coated with fibrin fibrils even in the presence of inhibitors. Removal of fibronectin (FN) from either the collagen gel or the fibrin gel markedly decreased the number of migrating cells, suggesting that FN provides a conduit for transmigration. Cell movement in the in vitro model was inhibited by RGD peptide, and by monoclonal antibodies against the subunits of the alpha5 beta1 and alpha v beta3 integrin receptor. Thus, the functional requirements for fibroblast transmigration from collagen-rich to fibrin-rich matrices, such as occurs in early wound healing, have been partially defined using an in vitro paradigm of this important biologic process.

Retention of acetaminophen in an in vitro model of solid-phase gastric emptying of animals

2007 ◽  
Vol 68 (8) ◽  
pp. 895-898 ◽  
Author(s):  
Cathy A. Wyse ◽  
Will G. Marshall ◽  
Tom Preston ◽  
Philippa S. Yam
Keyword(s):  
Gastric Emptying ◽  
In Vitro Model ◽  
Solid Phase ◽  
Vitro Model

scholarly journals Transforming Growth Factor β Is a Critical Regulator of Adult Human Islet Plasticity

2007 ◽  
Vol 21 (6) ◽  
pp. 1467-1477 ◽  
Author(s):  
Stephen Hanley ◽  
Lawrence Rosenberg
Keyword(s):  
Pancreatic Adenocarcinoma ◽  
Time Course ◽  
Transforming Growth Factor ◽  
Islet Cells ◽  
Collagen Gel ◽  
Transforming Growth Factor Β ◽  
Human Islets ◽  
Tgfβ Signaling ◽  
Vitro Model

Abstract Tissue plasticity is well documented in the context of pancreatic regeneration and carcinogenesis, with recent reports implicating dedifferentiated islet cells both as endocrine progenitors and as the cell(s) of origin in pancreatic adenocarcinoma. Accordingly, it is noteworthy that accumulating evidence suggests that TGFβ signaling is essential to pancreatic endocrine development and maintenance, whereas its loss is associated with the progression to pancreatic adenocarcinoma. The aim of this study was to examine the role of TGFβ in an in vitro model of islet morphogenetic plasticity. Human islets were embedded in a collagen gel and cultured under conditions that induced transformation into duct-like epithelial structures (DLS). Addition of TGFβ caused a dose-dependent decrease in DLS formation. Although it was demonstrated that collagen-embedded islets secrete low levels of TGFβ, antibody-mediated neutralization of this endogenously released TGFβ improved DLS formation rates, suggesting local TGFβ concentrations may in fact be higher. Time course studies indicated that TGFβ signaling was associated with an increase in ERK and p38 MAPK phosphorylation, although inhibitor-based studies were consistent with an islet endocrine-stabilizing effect mediated by p38 alone. Localization of TGFβ signaling molecules suggested that the action of TGFβ is directly on the β-cell to inhibit apoptosis and thus stabilize endocrine phenotype.

Integrin expression and differentiation in transformed human epidermal cells is regulated by fibroblasts

1992 ◽  
Vol 103 (3) ◽  
pp. 755-763 ◽  
Author(s):  
P. Kaur ◽  
W.G. Carter
Keyword(s):  
Human Fibroblasts ◽  
Collagen Gel ◽  
Integrin Expression ◽  
Human Papillomavirus Type 16 ◽  
3T3 Fibroblasts ◽  
Extracellular Matrix Components ◽  
Alternate Mechanism ◽  
Vitro Model ◽  
And Function

Normal human foreskin keratinocytes (HFKs) and transformed HFKs (FEPE1L-8 cells) generated by the introduction of cloned human papillomavirus type 16 sequences were compared for the expression and function of a family of adhesion receptors termed integrins. Initially, cells were examined in conventional monolayer cultures. FEPE1L-8s expressed integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1, alpha 6 beta 4 and beta 1 at comparable levels to HFKs. Further, these receptors were fully functional in mediating specific interactions with exogenously supplied ligands. However, FEPE1L-8s exhibited decreased synthesis of a number of extracellular matrix components, including laminin, fibronectin and epiligrin, compared to normal HFKs, which may be an alternate mechanism for regulating adhesion. Subsequently, organotypic cultures (OCs), which provide a suitable in vitro model system for the ordered stratification and differentiation of keratinocytes, were used to study the regulation of integrins and various epidermal markers in normal and transformed cells. OCs consisted of keratinocytes plated on a collagen gel containing primary human fibroblasts, grown at an air-medium interface. Unlike normal HFKs, the transformed FEPE1L-8 cells exhibited (a) disorganized stratification and limited differentiation capacity, (b) invasion into the collagen gel, and (c) unregulated expression of alpha 3 beta 1 and alpha 2 beta 1, and under-expression of alpha 6 beta 4 integrins. Ordered stratification and spatial regulation of integrin expression could be induced in the FEPE1L-8s by substituting Swiss 3T3 fibroblasts in the collagen gel. Further data indicate that the human fibroblasts induce the transformed HFKs to invade into the collagen gel.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent inhibitory effects of steroids in an in vitro model of angiogenesis

1996 ◽  
Vol 150 (3) ◽  
pp. 457-464 ◽  
Author(s):  
D C Jaggers ◽  
W P Collins ◽  
S R Milligan
Keyword(s):  
In Vitro Model ◽  
Ovarian Follicle ◽  
Collagen Gel ◽  
Rat Aorta ◽  
Significant Inhibition ◽  
Inhibitory Effects ◽  
High Concentrations ◽  
Vitro Model ◽  
Very High

Abstract The regulation of angiogenesis in the ovarian follicle and corpus luteum is unclear. Steroids are produced at very high concentrations in these tissues and we therefore examined the effect of steroids on angiogenesis in vitro. Explants of rat aorta were embedded in collagen gel and cultured in serum-free medium. Capillary-like microvessels were produced from the explants and microvessel number and length were measured in the presence and absence of steroids. At a concentration of 10 μg/ml, cortisol, progesterone, 17α-hydroxyprogesterone and medroxyprogesterone acetate produced degeneration of microvessels after 7 days of steroid treatment (P<0·01). Androstenedione and tetrahydro-S-(11-deoxytetrahydro-cortisol) (tetrahydro S) produced degeneration at a slower rate: androstenedione inhibited microvessel growth after 11 days (P<0·01) and tetrahydro S after 14 days (P<0·05). Oestriol had no effect on microvessels; oestrone had a slow degenerative effect with significant inhibition seen after 14 days (P<0·01). Oestradiol-17β at a concentration of 10 μg/ml completely inhibited microvessel growth from the explant cultures (P<0·01) while at 1 μg/ml it caused degenerative effects on growing microvessels. The effects of oestradiol and cortisol were reversible on removal of steroid-containing medium and replacement with 10% serum. We conclude that oestradiol may modulate angiogenesis in tissues in which the steroid concentration is high. Journal of Endocrinology (1996) 150, 457–464

Formation of new capillary-like tubes in a three-dimensional in vitro model (Aorta/Collagen Gel)

1997 ◽  
Vol 179 (2) ◽  
pp. 137-147 ◽  
Author(s):  
Masumi Akita ◽  
Eiko Murata ◽  
Hans-Joachim Merker ◽  
Katsuji Kaneko
Keyword(s):  
In Vitro Model ◽  
Three Dimensional ◽  
Collagen Gel ◽  
Vitro Model

scholarly journals Streptococcus pneumoniae Choline-Binding Protein E Interaction with Plasminogen/Plasmin Stimulates Migration across the Extracellular Matrix

2007 ◽  
Vol 76 (2) ◽  
pp. 466-476 ◽  
Author(s):  
Cécile Attali ◽  
Cécile Frolet ◽  
Claire Durmort ◽  
Julien Offant ◽  
Thierry Vernet ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Streptococcus Pneumoniae ◽  
Solid Phase ◽  
Binding Protein ◽  
Physiological Role ◽  
Site Directed Mutagenesis ◽  
Binding Assays ◽  
Solid Phase Binding ◽  
Vitro Model

ABSTRACT The virulence mechanisms leading Streptococcus pneumoniae to convert from nasopharyngeal colonization to a tissue-invasive phenotype are still largely unknown. Proliferation of infection requires penetration of the extracellular matrix, which occurs by recruitment of host proteases to the bacterial cell surface. We present evidence supporting the role of choline-binding protein E (CBPE) (a member of the surface-exposed choline-binding protein family) as an important receptor for human plasminogen, the precursor of plasmin. The results of ligand overlay blot analyses, solid-phase binding assays, and surface plasmon resonance experiments support the idea of an interaction between CBPE and plasminogen. We have shown that the phosphorylcholine esterase (Pce) domain of CBPE interacts with the plasminogen kringle domains. Analysis of the crystal structure of the Pce domain, followed by site-directed mutagenesis, allowed the identification of the plasminogen-binding region composed in part by lysine residues, some of which map in a linear fashion on the surface of the Pce domain. The biological relevance of the CBPE-plasminogen interaction is supported by the fact that, compared to the wild-type strain, a mutant of pneumococcus with the cbpE gene deleted (i) displays a reduced level of plasminogen binding and plasmin activation and (ii) shows reduced ability to cross the extracellular matrix in an in vitro model. These results support the idea of a physiological role for the CBPE-plasminogen interaction in pneumococcal dissemination into human tissue.

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