Gelatin network structure

Figure 4-19) viscosity was reached depending on whether (1) the temperature was maintained at 92°C for about 2.5 min or at 95°C for about 5.5 min, or (2) the temperature was increased upto 95°C continuously after the peak viscosity temperature. The former was characterized by a slower rate of decrease in tj after the temperature was held constant and the latter by a rapid rate of decrease in tj upto the final temperature (95°C) suggesting that the network structure formed during gelatinization was drastically weakened by increase in the temperature. 

Kurisawa M and Yui N. Dual-stimuli-responsive drug release from interpenetrating polymer network-structured hydrogels of gelatin and dextran. J. Control. Rel. 1998 54 191-200. 

Any formal definition of a gel has been avoided, because its formulation would be difficult on the basis of external properties. By any criterion, a 1 % aqueous solution of agar does form a gel when it is cooled from 95 to 20°, whereas a 1 % solution of sucrose does not but properties may be so continuous between these extremes that any dividing line would be arbitrary. Most of this Chapter is concerned with fairly permanent network structures formed from polymer solutions. As a definition of gels, this description is incomplete. Some cellulose gels, and pastes of gelatinized, starch granules, would be excluded, because they are formed by limited dispersion of solids. In other words, an arbitrary choice will be made to focus on those gels that are dilute with respect to polymer, because the information available about them at the molecular level is more precise than for others. 

In the network structure of Fig. V. 1 the crosslinks need not be produced by chemical reaction. Any physical process which favors association between certain (but not all) points on different chains may also lead to gels. Many examples of this are found with biological molecules, such as gelatin" or certain polysaccharides. In many of these sterns the association process is still disputed. There are three main posabilities ... 

Scheme 1. Proposed network structure of tyrosinase-catalyzed gelatin-chitosan gels and possible explanation for their transient nature.

The formation of condensation structures is the main cause for the gelling of solutions of various natural and synthetic polymers. Gel formation may be accompanied by conformational changes of the polymer molecules, as is the case with gelatin and other biopolymers, or by various chemical interactions. Such is the acid-catalyzed synthesis of synthetic leather by the partial acetylation of polyvinyl alcohol with formaldehyde. Under supersaturation conditions, the fibers of the polyvinyl formal form in this system and develop into the network structure of synthetic leather. 

Whereas in gelatin gels the network structure appears to involve associations of specific loci spaced far apart on the rodlike parent molecule and in denatured proteins the associations appear to be nonspecific, occurring anywhere along the polypeptide cluun in the fibrin structure both types of associations seem to be involved. The specific linkages differ from those of gelatin in that they are irreverdble and are probably primary chemical bonds. 

Fig. 42 Photocurable gelatin for application to femtosecond laser microfabrication, a Chemical structures of styrene-derived gelatin, b photogelation mechanism by formation of cross-linked gelatin networks via intermolecular crosslinking and intramolecular polymerization...

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