The behaviors of chondrocytes, endothelial cells, and embryonic stem (ES) cells are investigated in vitro by employing specially functionalized polymer hydrogels to facilitate regeneration of tissues and organs. Hydrogels are expected to be used not only as artificial extracellular matrices (ECM) for repairing and regenerating a wide variety of tissues and organs, but also as substitute materials to develop artificial tissues and organs, since their three-dimensional network structure and viscoelasticity are similar to those of the macromolecular-based ECM in biological tissues. Therefore, hydrogels can be used as excellent scaffolds because their properties are similar to those of the in vivo environment. The study of the properties of cells on hydrogel scaffolds will contribute significantly to the design of artificial tissues that can potentially be used in tissue engineering applications in the future.
In vitro two-dimensional (2D) culture of chondrocytes on substrates has been shown to decrease gene expression and production of cartilage-specific proteins such as collagen type II and aggrecan and causes cells to quickly dedifferentiate into a more fibroblastic phenotype. However, hydrogels are expected to be used as scaffolds for repairing and regenerating tissues and organs since their three-dimensional network structure and viscoelasticity are similar to those of the macromolecular-based extracellular matrix (ECM) in biological tissues. In our research, we succeed in culturing chondrocytes on 2D synthetic hydrogels without dedifferentiation of chondrocytes. Furthermore, we found that the properties of chondrocytes cultured on hydrogels were affected by the charge density of the gels.
Usually, cells cannot survive on any hydrogels whose surfaces are not modified with cell adhesive proteins. However, we found that endothelial cells (ECs) could adhere, proliferate, and reach confluence on synthetic anionic hydrogels without any adhesive proteins (Figure 1). Furthermore, the biological and physical properties of endothelial cells cultured on these hydrogels are affected by the properties of these gels, such as their chemical structure and elasticity. The amount of EC-specific glycocalyx secreted by endothelial cells is regulated by the properties of hydrogel scaffolds (Figure 2). Finally, the properties of hydrogels also regulate the blood compatibility and frictional stress of endothelial cells, which depend on the amount of EC-specific glycocalyx secreted.
Overall, endothelial cells cultured on hydrogels exhibit better properties than those cultured on polystyrene (PS) scaffolds. This research may contribute significantly to the design of artificial blood vessels that can potentially be used in tissue engineering in the future.
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