Virtual Fruit tissue Generation Based on Cell Growth Modeling

The fact that production of pome fruits is both season and location dependent calls for preservation methods to maintain the quality of the produce after harvest. The principal method to preserve pome fruit is postharvest storage in cool rooms under Controlled Atmosphere (CA) or Ultra Low Oxygen (ULO) conditions. These methods are based on empirical trials to determine optimum storage conditions for a specific cultivar in terms of temperature, oxygen and carbon dioxide concentration and relative humidity. Improved understanding of the underlying fruit physiology in relation to the gas and water exchange processes during storage will assist in improving postharvest quality and reducing the occurrence of storage disorders. Both experimental and modeling approaches have been followed to investigate the relationship between the gas concentration, gas diffusion, respiration and physiological disorders in apple and pear. Experimental approaches are, however, costly, tiresome and time consuming. Moreover, it is difficult to investigate the time course of the physiological disorders experimentally because of the lack of non-destructive techniques to measure the internal gas concentration in the fruit. Alternatively, mathematical models can be used to study gas and water exchange. They are usually based on the continuum hypothesis where the fruit is considered as a material with transport properties that are independent of the spatial scale. However, unlike the traditional engineering materials fruit tissue has a complex fine structure. The cellular architecture is believed to determine to a large extent the biophysical processes in the fruit. The continuum hypothesis does not hold in this case and a multiscale approach is required in which the model parameters of the model that operates at the macroscale the scale of interest are obtained from simulations with a microscale model that incorporates the actual microstructure of the fruit. For the latter, microscale geometric models of the fruit are required. Pome fruit tissue microscale geometry generators exist today but are based on digitized 2D or 3D images of the cellular architecture. Therefore, although these algorithms generate representative geometries of the tissues, they require experimental input in terms of microscopic images. These approaches need complex image acquisition procedures and expensive infrastructures such as synchrotron radiation sources. Also, they do not allow to parameterize the microscale geometry to, for example, investigate the effect of cell size or shape on the transport properties in a systematic way. The main objective of this dissertation was to develop virtual microscale fruit tissue generators (algorithms) that generate statistically and spatially equivalent virtual tissue microstructures resolving the cell symplast, cell wall and intercellular air spaces in both 2D and 3D and interface them to finite element and/or finite volume codes. To achieve this, we have developed virtual tissue generators that are based on cell growth modeling bytaking into account cell biomechanics. The generators are initiated from a random Voronoi tessellation and growth biomechanics is applied to the tessellation which results in a virtual tissue that has equivalent geometrical properties as that of real tissues obtained from microscopic or synchrotron microtomography images. In a further extension we have also developed a cell division algorithm which is based on cell biomechanics and that is capable of mimicking both symmetric cell division and asymmetric cell division with different degree of anisotropic growth. The cell division algorithm can be used instead of the Voronoi tessellation as an input for the expansive growth models. Initial tessellations obtained from the cell division algorithm will have more realistic representation of the cells than the Voronoi tessellations. The geometric models can be used to carry out in silico simulations to determine transport properties to be used in multiscale framework of gas and moisture exchange studies in pome fruits. This approach helps to include more geometrical details and fewer assumptions than the classical continuum modeling approach, while requiring less computer time compared to solving governing model equations at the resolution of the microscale.

Publication year:2014

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