136 Chapter 6 Table 5: Comparison of 2- and 3-dimensinoal culture systems. 2D 3D Adhesion One plane Three dimensional Polarity Basal-apical No forced polarity Stiffness High stiffness (mega- to gigapascal range) Variable stiffness (kilopascal range) Soluble gradients Absent Present Access to nutrients, GF, oxygen Very accessible More complicated with increasing thickness, similar to in vivo ECM One layer of matrix (coating) Surrounded by matrix Motion Unconstrained spreading and migration spreading and migration is hindered due to surrounding Matrix Culturing Cost Cheap Expensive Throughput High Low Visualization Easy Difficult Interactions 2D cell interaction, basolateral ECM interactions, no niches 2D and 3D cell interactions, cell-ECM/ scaffold, niches Culture protocols Simple, methods are known, various kits are available, easy to reproduce Complex methods that are not standardized, not easy to reproduce, more difficult to maintain the culture Reproduction of key aspects of the tissue Stiffness ~100 MPa (stiffer than fibrotic tissue), cells change behavior (gene, RNA, protein expression, adhere more strongly, proliferation is higher) Stiffness comparable to tissue and highly adaptable, cells behavior is closer to the behavior in vivo 2D: 2-dimensional, 3D: 3-dimensional, ECM: extracellular matrix, GF: growth factors 2D cell culture models have provided a wealth of knowledge and insight over the past decades into some of the physiological and pathophysiological mechanisms of human biology and disease [77-79]. Nevertheless, the lung, as well as all other organs, is a 3D tissue structure in vivo. The 3D structure of every tissue is highly reliant on its native ECM, which is specialized for that tissue and the mechanical stresses it must endure in situ. The cells residing in the lung naturally experience physical interactions with their relative ECM in either 2- or 3-D. The endothelial cells, as well as the alveolar and airway epithelium experience a 2D interaction with the basement membrane that lies beneath their basal surfaces, whereas the mesenchymal cells that reside in the interstitium experience 3D interactions with their surrounding ECM. When put together the whole model is a complex 3D structure with intricate interactions between the resident cells and the ECM. The inflow of transient immune cells is an element that is not within the scope of the models discussed in this chapter.
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