Gelation chemical cross-linking

The ways in which a covalently linked gel network can form, in principle, are outlined below. Some examples are given in the subsection on Chemical Cross-Linking Gelation (pp. 256-8). 

The formation of chemically cross-linked gels from synthetic polymers has been comprehensively reported, including comparison with theoretical predictions and study of the thermodynamic behaviour of such systems after gelation. Therefore, the examples described here are in a different vein and are based on a cross-linking mechanism which occurs in biological gel-network formation in both animals and plants and also forms the basis of a potential industrial process. As described in the subsection on Covalent Junctions (pp. 240-1), there are two basic methods by which chemically cross-linked gelation can occur (1) copolymerization of monomers, some fraction of which are... 

Physically cross-linked hydrogels can degrade by processes that reverse the gelation mechanism or disturb the noncovalent interactions of the cross-links. Chemically cross-linked hydrogels can be degraded via several mechanisms (Fig. 10.17) and include cleavage of the backbone chain, cross-linker, or pendant groups. 

Kjoniksen, A. L. Nystrbrn, B. (1996) Effects of Polymer Concentration and Crosslinking Density on Rheology of Chemically Cross-Linked Poly(vinyl alcohol) near the Gelation Threshold, Macromolecules (19%), Vol.29(15), 5215-5222. 

Chemically cross-linked networks provide higher cross-linking densities to the polymer network, are more favorable for the sustained release of therapeutics, and allow for the fabrication of scaffolds with enhanced mechanical properties. However, the toxicity of the chemical cross-linking agents used may adversely affect cell behavior and the incorporated bioactive molecules. On the other hand, physical gelation of the network may avoid the use of cross-linking agents, but shows a limited performance in their physical properties. In the next sections, we will discuss the mechanisms involved in the solidification of injectable materials. 

Matricardi P, Dentini M, Crescenzi V, Ross-Murphy SB (1995) Gelation of chemically cross-linked polygalacturonic acid derivatives. Carbohydr Polym 27(3) 215... 

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