An Interpenetrating Alginate/Gelatin Network for Three-Dimensional (3D) Cell Cultures and Organ Bioprinting

Abstract

Crosslinking is an effective way to improve the physiochemical and biochemical properties of hydrogels. In this study, we describe an interpenetrating polymer network (IPN) of alginate/gelatin hydrogels (i.e., A-G-IPN) in which cells can be encapsulated for in vitro three-dimensional (3D) cultures and organ bioprinting. A double crosslinking model, i.e., using Ca 2+ to crosslink alginate molecules and transglutaminase (TG) to crosslink gelatin molecules, is exploited to improve the physiochemical, such as water holding capacity, hardness and structural integrity, and biochemical properties, such as cytocompatibility, of the alginate/gelatin hydrogels. For the sake of convenience, the individual ionic (i.e., only treatment with Ca 2+ ) or enzymatic (i.e., only treatment with TG) crosslinked alginate/gelatin hydrogels are referred as alginate-semi-IPN (i.e., A-semi-IPN) or gelatin-semi-IPN (i.e., G-semi-IPN), respectively. Tunable physiochemical and biochemical properties of the hydrogels have been obtained by changing the crosslinking sequences and polymer concentrations. Cytocompatibilities of the obtained hydrogels are evaluated through in vitro 3D cell cultures and bioprinting. The double crosslinked A-G-IPN hydrogel is a promising candidate for a wide range of biomedical applications, including bioartificial organ manufacturing, high-throughput drug screening, and pathological mechanism analyses.

A Review on the Adaption of Alginate-Gelatin Hydrogels for 3D Cultures and Bioprinting

“…Cross-linking of hydrosols (liquid polymers) has positive effects on the physico-chemical properties of hydrogels—including their water holding capacity, hardness, and structural integrity, which affect their cytocompatibility—as well as on their biochemical properties [ 94 , 95 ]. In bioprinting, the cells are mixed in hydrosol and the cross-linking of the hydrogel takes place after extrusion from the bioprinter.…”

“…Sodium alginate is most often physically cross-linked through the application of ionic interactions [ 45 , 94 , 95 ]. Cross-linking with divalent or trivalent ions occurs under mild conditions, at room temperature and neutral pH [ 94 , 96 ].…”

“…Cross-linking of sodium alginate occurs through a bond between G blocks (guluronate blocks) and divalent ions. This is an “egg box” cross-linking model [ 45 , 95 ]. Ca 2+ , Ba 2+ , and Zn 2+ are divalent ions, which are usually used in such applications [ 45 , 95 , 96 ].…”

“…A network of isopeptide bonds is formed [ 102 ]. This approach was used in research conducted by Schwarz et al [ 78 ] and Chen et al [ 95 ]. The properties of interpenetrating alginate-gelatin hydrogel have been studied.…”

“…The properties of interpenetrating alginate-gelatin hydrogel have been studied. Sodium alginate has been cross-linked with calcium ions, while gelatin has been cross-linked with transglutaminase [ 95 ]. Another gelatin cross-linking agent could be water-soluble 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), which specifically forms amide or peptide bonds between the carboxylic acid and protein amino groups [ 103 ].…”