1,099,418 research outputs found
The role of topology and mechanics in uniaxially growing cell networks
In biological systems, the growth of cells, tissues, and organs is influenced
by mechanical cues. Locally, cell growth leads to a mechanically heterogeneous
environment as cells pull and push their neighbors in a cell network. Despite
this local heterogeneity, at the tissue level, the cell network is remarkably
robust, as it is not easily perturbed by changes in the mechanical environment
or the network connectivity. Through a network model, we relate global tissue
structure (i.e. the cell network topology) and local growth mechanisms (growth
laws) to the overall tissue response. Within this framework, we investigate the
two main mechanical growth laws that have been proposed: stress-driven or
strain-driven growth. We show that in order to create a robust and stable
tissue environment, networks with predominantly series connections are
naturally driven by stress-driven growth, whereas networks with predominantly
parallel connections are associated with strain-driven growth
Growth regulation in Hydra. Relationship between epithelial cell cycle length and growth rate
The relationship between epithelial cell production and growth rate was investigated in Hydra attenuata under different feeding regimes. The increase of epithelial cell number was compared to the duration of the epithelial cell cycle using standard methods of cell cycle analysis. The results indicate that cell cycle changes accompanying changes in feeding regime are not sufficient to explain the altered growth rate. Under heavy feeding regimes, epithelial cell production equals tissue growth rate. At low feeding level or under starvation conditions the epithelial cell cycle lengthens and growth rate of epithelial cell population is slowed. However, the cell cycle changes are insufficient to account for the reduction in tissue growth and thus there is an effective overproduction of epithelial cells amounting to 10% per day. Evidence suggests that these excess cells are phagocytized by neighboring cells in the tissue. Thus phagocytosis is directly or indirectly involved in regulating the growth of hydra tissue
A multiple scale model for tumor growth
We present a physiologically structured lattice model for vascular tumor growth which accounts for blood flow and structural adaptation of the vasculature, transport of oxygen, interaction between cancerous and normal tissue, cell division, apoptosis, vascular endothelial growth factor release, and the coupling between these processes. Simulations of the model are used to investigate the effects of nutrient heterogeneity, growth and invasion of cancerous tissue, and emergent growth laws
A level-set method for the evolution of cells and tissue during curvature-controlled growth
Most biological tissues grow by the synthesis of new material close to the
tissue's interface, where spatial interactions can exert strong geometric
influences on the local rate of growth. These geometric influences may be
mechanistic, or cell behavioural in nature. The control of geometry on tissue
growth has been evidenced in many in-vivo and in-vitro experiments, including
bone remodelling, wound healing, and tissue engineering scaffolds. In this
paper, we propose a generalisation of a mathematical model that captures the
mechanistic influence of curvature on the joint evolution of cell density and
tissue shape during tissue growth. This generalisation allows us to simulate
abrupt topological changes such as tissue fragmentation and tissue fusion, as
well as three dimensional cases, through a level-set-based method. The
level-set method developed introduces another Eulerian field than the level-set
function. This additional field represents the surface density of tissue
synthesising cells, anticipated at future locations of the interface. Numerical
tests performed with this level-set-based method show that numerical
conservation of cells is a good indicator of simulation accuracy, particularly
when cusps develop in the tissue's interface. We apply this new model to
several situations of curvature-controlled tissue evolutions that include
fragmentation and fusion.Comment: 15 pages, 10 figures, 3 supplementary figure
Critical Point in Self-Organized Tissue Growth
We present a theory of pattern formation in growing domains inspired by
biological examples of tissue development. Gradients of signaling molecules
regulate growth, while growth changes these graded chemical patterns by
dilution and advection. We identify a critical point of this feedback dynamics,
which is characterized by spatially homogeneous growth and proportional scaling
of patterns with tissue length. We apply this theory to the biological model
system of the developing wing of the fruit fly \textit{Drosophila melanogaster}
and quantitatively identify signatures of the critical point.Comment: 5 pages, 3 figure
The interplay between tissue growth and scaffold degradation in engineered tissue constructs
In vitro tissue engineering is emerging as a potential tool to meet the high demand for replacement tissue, caused by the increased incidence of tissue degeneration and damage. A key challenge in this field is ensuring that the mechanical properties of the engineered tissue are appropriate for the in vivo environment. Achieving this goal will require detailed understanding of the interplay between cell proliferation, extracellular matrix (ECM) deposition and scaffold degradation.\ud
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In this paper, we use a mathematical model (based upon a multiphase continuum framework) to investigate the interplay between tissue growth and scaffold degradation during tissue construct evolution in vitro. Our model accommodates a cell population and culture medium, modelled as viscous fluids, together with a porous scaffold and ECM deposited by the cells, represented as rigid porous materials. We focus on tissue growth within a perfusion bioreactor system, and investigate how the predicted tissue composition is altered under the influence of (i) differential interactions between cells and the supporting scaffold and their associated ECM, (ii) scaffold degradation, and (iii) mechanotransduction-regulated cell proliferation and ECM deposition.\ud
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Numerical simulation of the model equations reveals that scaffold heterogeneity typical of that obtained from ÎĽCT scans of tissue engineering scaffolds can lead to significant variation in the flow-induced mechanical stimuli experienced by cells seeded in the scaffold. This leads to strong heterogeneity in the deposition of ECM. Furthermore, preferential adherence of cells to the ECM in favour of the artificial scaffold appears to have no significant influence on the eventual construct composition; adherence of cells to these supporting structures does, however, lead to cell and ECM distributions which mimic and exaggerate the heterogeneity of the underlying scaffold. Such phenomena have important ramifications for the mechanical integrity of engineered tissue constructs and their suitability for implantation in vivo
Growth factor releasing scaffolds for cartilage tissue engineering
Over the last century, life expectancy has increased at a rapid pace resulting in an increase of articular cartilage disorders. To solve this problem, extensive research is currently performed using tissue engineering approaches. Cartilage tissue engineering aims to reconstruct this tissue both structurally and functionally by combining cells and biomaterials mimicking extracellular matrix (scaffolds). Although significant progress has been achieved over the last decade, the complete regeneration of cartilage is not yet at hand. The opportunity to release growth factors from porous scaffolds in a controlled way might allow to further enhance cartilage tissue engineering. However, from the literature reviewed in Chapter 2, it can be concluded that many hurdles still have to be overcome to allow the safe incorporation of labile proteins such as growth factors to scaffolds. As a result, the attempts to release growth factors from scaffolds are often restricted to surface adsorption, which only\ud
allows a limited control on the release rates. In addition, important knowledge is still lacking regarding the most effective rate at which relevant growth factors should be delivered. Therefore, the aim of this thesis was to design polymeric scaffolds containing and releasing\ud
growth factors in a safe and controlled way to further study the relations between release rate and cartilage formation
Role of growth factors in the pathogenesis of tissue fibrosis in systemic sclerosis.
The most severe clinical and pathologic manifestations of systemic sclerosis (SSc) are the result of a fibrotic process characterized by the excessive and often progressive deposition of collagen and other connective tissue macromolecules in skin and numerous internal organs. The mechanisms involved in the initiation and progression of the remarkable fibrotic process in SSc remain largely unknown. Extensive recent studies have indicated that a variety of polypeptide growth factors play a crucial role in this process. The most commonly implicated growth factors include transforming growth factor beta (TGF-β), connective tissue growth factor (CTGF), platelet derived growth factor (PDGF), and vascular endothelial growth factor (VEGF). Here, the experimental evidence supporting the participation of various growth factors in the pathogenesis of the fibrotic process in SSc and the molecular mechanisms involved will be reviewed
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