1,721,069 research outputs found
A simulation model for the growth of engineered cartilage on polymeric scaffolds
No full textA mathematical model to simulate the growth of engineered cartilage on polymeric scaffold performed in rotating bioreactors has been developed. The model, based upon the material balance for the nutrient species (oxygen) and the primary extra-cellular matrix product (GAG), accounts for population balances to simulate cell proliferation and its distribution within the polymeric scaffold. A comparison between model results and literature experimental data in terms of GAG contents and its distribution within the tissue construct has been performed. All model parameters are taken from the literature except for the constant of the time rate of mass change appearing in the proposed population balance which has been adjusted to reproduce the experimental data concerning the tissue culture performed at 80 mm Hg of oxygen partial pressure. The predictive capability of the model has been also demonstrated by comparison with experimental data obtained for a different value of oxygen partial pressure (40 mm Hg)
Modelling breakage and reagglomeration during fine dry grinding in ball milling devices
No full textModelling of grinding of fine powders in ball milling devices is addressed. The model quantitatively describes breakage and agglomeration phenomena by considering two populations, i.e. primary particles and porous aggregates. The population balance approach takes into account breakage and aggregation kernels which are considered functions of the size of the two populations. The proposed model is able to properly simulate the inversion from the breakage to the agglomerative regime typical of fragile material powder system undergoing ball milling. A suitable fitting procedure is performed for separately determining the adjustable parameters of the model. Model reliability is tested against experimental data, while the proposed breakage/agglomeration kernels are related to the quantitative description of ball milling apparatus dynamics
A population balance approach for the description of water osmosis and intracellular ice formation during cryopreservation
No full textA novel model capable of quantitatively describing and predicting Intracellular Ice Formation (IIF) as a function of temperature in a cell population during the cooling stage of a cryopreservation protocol, without Cryo-Protective Agent (CPA) is proposed. The model accounts for water osmosis and IIF occurrence during freezing of the cell population, whose size distribution dynamics is simulated by means of a suitable population balance approach. It is found that IIF temperature depends upon the cell size, i.e. it is higher for larger cells. Correspondingly, the Probability of IIF (PIIF) results to be dependent on the initial size distribution of the cell population. Model reliability is successfully verified by predicting experimental data available in the literature of PIIF at different, constant cooling rates with better accuracy as compared to previous theoretical approaches
Thermally and catalytically induced coarsening of nanoporous Au
No full textThis study focuses on the structural stability of nanoporous Au foams fabricated by chemical dealloying. Thermal annealing and catalytic transformations are shown to activate coarsening processes exhibiting same overall kinetics and comparable rate. Data support the hypothesis of a mechanistic scenario dominated by surface diffusion and suggest for catalytic runs local temperatures higher than nominal ones
A population balance model to investigate the effect of microgravity on the kinetics of in vitro cell proliferation
No full textIn this work a mathematical model helpful to investigate the effects of microgravity on the kinetics of in vitro proliferation of adherent cells is proposed. The model is based on a Population Balance (PB) approach that allows to describe cell cycle progression through the different phases experienced by any cell of the entire population during its own life. Specifically, the proposed model has been developed as a multi-staged 2-D PB, by considering a different sub-population of cells for any single phase of the cell cycle. These sub-populations composing the entire population of cells of the cultivation system are discriminated through cellular volume and DNA content, that both increase during the mitotic cycle. A series of numerical simulations related to the in vitro proliferation kinetics of adherent cells is here reported for illustrating model capabilities. It is found that, the change of one adjustable parameter related to cell volume growth rate in response to a change of gravity is able to mimic cell culture behaviour under microgravity conditions, as reported in the technical literature
HMSCs from UCB: isolation, characterization and determination of osmotic properties for optimal cryopreservation
Full text linkIn tissue engineering, storing of biological material represents a fundamental step to bring cell-based medical devices to market on demand - Karlsson and Toner (2000) and more recently Fadda et al. (2009). Compared to other methods, freezing to cryogenic temperatures allows long shelf lives and genetic stability (Karlsson and Toner, 2000). Unfortunately, cryopreserved cells are damaged by the cryopreservation process itself (Mazur, 2004). This loss (up to 50 %) can be tolerated for some cell lineages, but it's unacceptable for others, as the human Mesenchymal Stem Cells (hMSCs) from Umbilical Cord Blood (UCB), whose collection and isolation is known to be difficult (Bieback et al., 2004). In this case, an optimal cryopreservation protocol is mandatory. Due to the high number of trials actually required for experimental optimization, mathematical modelling is considered a practical solution. To this aim, the osmotic properties need to be first estimated in order to determine the volume of residual intra-cellular water left by osmosis to form lethal ice or glass. In this work, the hMSCs from UCB of three different donors, after informed consent, have been isolated by a density gradient centrifugation method. The successful isolation has been verified through phenotypic cytofluorimetric analysis, and adipogenesis/osteogenesis capability differentiations. Osmotic properties, namely inactive cell volume, water and CPA (DMSO) permeabilities, have been determined by means of experimental runs carried out under hypertonic conditions (obtained with the addition of sucrose or DMSO), at three different temperatures. Cells volumes excursions have been measured by a potenziometric device (Coulter Counter) under equilibrium and dynamic conditions. Linear and non-linear regression analyses have been carried out to determine the adjustable parameters by means of the two parameters bi-compartimental model by Kleinahns (1998), as applied to a single-sized cell population (i.e. identical cells with size equal to the average). It is found that, the inactive volume fraction of hMSC from UCB apparently changes (increase) when DMSO is used instead of sucrose, thus limiting cell volume excursion during swelling. It is hypothesized that, a cell volume control system is activated during swelling, probably due to the action of ion pumps
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