Hydrogels crosslinking methods

Hennink WE, Van Nostrum CF. Novel crosslinking methods to design hydrogels. Adv Drug Deliv Rev 2002 54 13-36. 

Chang, C. Lue, A. Zhang, L. Effects of crosslinking methods on structure and properties of cellulose/ PVA hydrogels. Macromol. Chem. Phys. 2008, 209 (12), 1266-1273. 

Binetti Valerie R., Fussell Garland W., and Lowman Anthony M. Evaluation of two chemical crosslinking methods of poly(vinyl alcohol) hydrogels for injectable nucleus pulposus replacement. J. Appl. Polym. Sci. 131 no. 19 (2014) 40843-1-40843-8. 

Table 1 Crosslinking methods that are used for encapsulation of cells in hydrogels.

Hydrogel can be prepared from several techniques such as copolymerization [29, 30], suspension copolymerization [31], polymerization by irradiation [32], chemical reaction of complementary groups [33-34] and cross linking using enzymes [35]. Several crosslinking methods such as ionic interaction have also been used for this purpose [36-42]. 

Unfortunately, reliable data on the equilibrium swelling and long-term stability of hydrogels obtained by this method are not available. It should be noted that crosslinking of polymers with metal ions is one of the few reactions which can be carried out directly in the soil medium, which is efficiently used, e.g., in oil recovery [65, 66]. 

This is one of the most universal techniques for obtaining hydrogels from water-soluble polymers. Crosslinked PEO, PVA, PAAm, PAAc and its salts, as well as some polymer blends were obtained by this method. Although all polymers mentioned above have their own specific features, in most cases the gelation doses do not exceed 1-2 Mrad, i.e. they are substantially lower than for the same polymer in bulk. This is due to the fact that in aqueous media crosslinking occurs indirectly, namely because of the OH radical formation and their attack on the macromolecules. There exists a developed theory of these processes [73],... 

The above reviewed techniques permit to obtain hydrogels with a desirable set of properties, primarily swelling, depending on the choice of the starting material. Some of these methods, namely crosslinking polymerization, grafting on bio-... 

Hassan, C. M. and Peppas, N. A. Structure and Applications of Polyfvinyl alcohol) Hydrogels Produced by Conventional Crosslinking or by Freezing/Thawing Methods. Vol. 153, pp. 37-65. 

PMBV and PVA can spontaneously form a hydrogel without using any crosslinkers. Even in cell culture conditions, the gelation can be confirmed. Therefore, it was possible to encapsulate cells in the PMBV/PVA hydrogel. The encapsulation method is illustrated in Fig. 6. 

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