Description of biomechanical properties of spheroids from human cells

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Spheroids are 3D cell cultures, which reflect the natural physiological situation of cells in tissues better than traditional 2D cell culture approaches due to their 3D arrangement. Therefore, they are very interesting for standardized in vitro approaches but also for clinical applications in terms of a personalized medicine. Spheroids can consist of one cell type (mono-culture) or of several cell types (co-culture) connected by direct cell-cell contacts and proteins of the extracellular matrix (ECM). The number of cells per spheroid can be varied over a wide range. Since spheroids are living systems, cellular organization within the spheroids, expression of the cell adherence protein cadherin and of ECM-proteins as well as the cytoskeleton are not stable and will change over time (maturation), which strongly influence their biomechanical properties. These aging processes are largely unexplored, which makes it difficult to produce spheroids with defined biomechanical properties.This project aims to investigate the relationships between the microstructure and the biomechanical properties of spheroids over time and to describe them with a numerical model using the Discrete Element Method (DEM). To achieve this goal, the biomechanical properties of spheroids from Normal Human Dermal Fibroblasts (NHDF) will be systematically investigated. For this purpose, extensive experimental studies on the mechanical properties of spheroids as well as of 2D cell layers will be performed using the nanoindentation method in a culture medium. The microstructure of the spheroids will be determined by scanning electron microscopic analyses of semi- and ultra-thin sections of spheroids. Furthermore, the cell and molecular biological parameters, expression of cadherin, cytoskeletal proteins as well as proteins of the ECM are determined experimentally. These data will be used to validate the numerical models, which will allow a quantification of the factors influencing the relationships between the microscopic properties (microstructure, interactions of single cells) and macroscopic biomechanical properties of spheroids. A basic understanding of these relevant mechanisms will help to generate spheroids with defined properties for the respective requirements in the context of a personalized medicine, which will significantly improve the clinical success of an application. With the obtained biomechanical properties and developed DEM model, process-related damage to the spheroids in different applications (e.g. tissue engineering, bio-printing, spherox processes) can be predicted in order to optimize these processes.