Three-dimensional culture (3D)

Traditional cell culture conditions like the cultivation of adherent cells on 2D plastic surfaces in a static environment, such as in standard cell culture flasks, well-plates or petri dishes are far from representing the physiologic environment of cells. Transitioning from the 2D flat surface and expanding the culture with a z-axis can greatly improve native-like cell behaviour. A growing body of evidence has suggested that 3D cell culture systems, in contrast to 2D culture, represent the native microenvironment of cells in tissues more closely. Thus, the behavior of 3D-cultured cells is more reflective of in vivo cellular responses as biological, chemical, physical, and mechanical cues in these 3D models can be adjusted in a more controlled manner. As an example, cells grown in 3D using tissue-specific extracellular matrix (ECM) components and architecture, exhibit biochemical and morphological features specific for the in vivo state, but are not or differently expressed in 2D.

Difference of traditional 2D cell culture to 3D culture; in 2D cells (grey) can only form attachments (yellow) to the substrate (teal) on their bottom side and only have very few cell-to-cell contacts, in 3D cultures cells can form attachments to each other and the substrate all over their surface like in vivo

Therefore, to extend cellular growth to the third dimension, supportive structures, called matrices or scaffolds, have been engineered from numerous materials including natural synthetic as well as Hereby, 3D matrices from different materials of different shapes and geometry have been developed together with various bioreactor systems for the application of mechanical forces. Scaffolds for Tissue Engineering (TE) must possess adequate mechanical integrity including structural (macro- and microstructural properties) and mechanical characteristics (mechanical strength, elasticity and stiffness) similar to that of the target tissue and support the physiological load of the body until remodelling process is completed. The combination of cells, biomaterials and dynamic culture conditions have to be in accordance to achieve physiological conditions in vitro in order to mimic the native microenvironment of cells. Each aspect is defined by distinct challenges and needs to be optimized and adapted to the specific application. Nevertheless, the implementation of physiologic conditions is expected to increase the predictability and relevance of in vitro testing for in vivo trials making animal experiment expendable (3R = reduction, refinement, replacement of animal testing).