Crosslinker-free hydrogels

Other novel mixed polymer systems have included glycosaminoglycans (GAGs) modified with multiblock copolymers to form self-assembling, crosslinker free hydrogels. For example, aminooxy pluronic derivatives were coupled with HA to give amphiphilic hydrogels with the ability to bind to hydrophobic surfaces (89). 

Serban and Prestwich synthesised hyaluronic acid bromoacetate (HABA) by using bromoacetic anhydride [43]. The authors used this method to prepare crosslinker-free hydrogels by thiol alkylation using HABA as a polyvalent electrophile and thiol-modified HA (with or without thiol-modified gelatin) as a polyvalent nucleophile. 

Table 1. Swelling of polyacrylamide hydrogels obtained by free-radical crosslinking polymerization...

To determine the crosslinking density from the equilibrium elastic modulus, Eq. (3.5) or some of its modifications are used. For example, this analysis has been performed for the PA Am-based hydrogels, both neutral [18] and polyelectrolyte [19,22,42,120,121]. For gels obtained by free-radical copolymerization, the network densities determined experimentally have been correlated with values calculated from the initial concentration of crosslinker. Figure 1 shows that the experimental molecular weight between crosslinks considerably exceeds the expected value in a wide range of monomer and crosslinker concentrations. These results as well as other data [19, 22, 42] point to various imperfections of the PAAm network structure. 

Hydrogels can be made by a number of methods, but one of the most widely used methods is free radical polymerization of vinyl monomers. Examples of vinyl monomers used in our laboratory are shown in Table 1. Monomers are crosslinked with divalent monomers such as A,A -methyl-enebisacrylamide. Biodegradable crosslinking agents can also be used as long as they have bifunctionality. 

Polymer-based (hydrogel cross-linked with hyaluronic acid) Oxidative damage of crosslinker Antiinflammatory drugs Free radicals 4 /, 48... 

The monomer is completely soluble in water. We would predict that the homopolymer, too (sodium polyacrylate), would dissolve readily in water, because each repeating unit contains an ionic sodium carboxylate group. (Most sodium salts dissolve in water.) If we were to add, say, one gram to 400 to 600 mL of distilled water and stir, the result would be a gel, not the free-flowing solution that we expected. A gel is defined as a chemically or physically crosslinked polymer that is highly swollen by solvent. The solvent is held tightly by the polymer network and does not flow. If the solvent is water it is called a hydrogel. 

Piperidines ( NH, 2 NR, NOH, NOR) bearing polymerizable vinylic or glycidyl moieties, e.g. 182, 183 were proposed for free-radical homo- and copolymerization or grafting of conventional polymers. HAS-functionalized copolymers have a potentially important application in stabilization of hydrogels [285]. Monomer 184 is a crosslinking agent in acrylate hydrogels [286],... 

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