Abstract
This review compiles information regarding the use of alginate, and in particular alginate hydrogels, in culturing cells in 3D. Knowledge of alginate chemical structure and functionality are shown to be important parameters in design of alginate-based matrices for cell culture. Gel elasticity as well as hydrogel stability can be impacted by the type of alginate used, its concentration, the choice of gelation technique (ionic or covalent), and divalent cation chosen as the gel inducing ion. The use of peptide-coupled alginate can control cell–matrix interactions. Gelation of alginate with concomitant immobilization of cells can take various forms. Droplets or beads have been utilized since the 1980s for immobilizing cells. Newer matrices such as macroporous scaffolds are now entering the 3D cell culture product market. Finally, delayed gelling, injectable, alginate systems show utility in the translation of in vitro cell culture to in vivo tissue engineering applications. Alginate has a history and a future in 3D cell culture. Historically, cells were encapsulated in alginate droplets cross-linked with calcium for the development of artificial organs. Now, several commercial products based on alginate are being used as 3D cell culture systems that also demonstrate the possibility of replacing or regenerating tissue.
Highlights
The world around us, including the human body, is constructed in three dimensions
One approach for tuning degradation of alginate hydrogels includes the use of covalently cross-linked methacrylated alginates where the linkages are hydrolytically degradable [43,44], or inclusion of linkages that can be cleavable by matrix metalloproteinases (MMP) [45]
The presentation of the RGD peptide sequence has been shown to be an important cue regulating cellular behavior. This was demonstrated by, for example, Hsiong et al [63] who compared the behavior of MC3T3-E1 preosteoblasts, human bone marrow stromal cells and D1 stem cells encapsulated in alginate hydrogels containing either linear G4RGDSP or cyclic G4CRGDSPC
Summary
The world around us, including the human body, is constructed in three dimensions. Since the 1940s, cells have been cultured, often attached to glass or plastic surfaces, essentially in two dimensions. We will focus on the “physical” differently shaped hydrogel formats like beads, moldable gels, injectable gels and macroporous structures Other technologies such as hanging drop, low-binding plastic, pyramid plates, etc., are available for culturing cells in 3D. Some macroporous scaffolds such as meshes, fibrous patches or foams, enable cell seeding throughout the thickness of the matrix and cells may be spatially organized Such systems are, considered semi-3D or 2.5D [1,8] as the initial cell–matrix interaction will be more similar to what is found in 2D with cells spreading on the surface of fibers or pore walls. This is especially true for polystyrene-based 3D cell culture materials. We will focus on 3D cell culture techniques and present aspects of immobilization of cells in alginate beads and new alginate-based 3D cell culture kits commercially available for use with standard cell culture well plates
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