Natural gels

Transformations with immobilized enzymes or cells Often the stability of the biocatalyst can be increased by immobilization and many different enzymes and cells have been immobilized by a variety of different methods. The most popular method for the fixation of whole cells is entrapment or encapsulation with calcium alginate. Other natural gels e.g., carrageenan, collagen, chemically-modified natural polymers e.g., cellulose acetate and synthetic gels and polymers e.g., polyacrylamide or polyhydroxyethylmethacrylate can also be used for this type of immobilization. 

The observed I-V characteristics for the developed gels are shown in Figure 12.24. The linear nature was found for HjPO gel complex. The other two gel complexes exhibit nonlinear I-V characteristics, which are probably due to the formation of ion channels by the d-band metallic ligands of submicron dimensions. The observed characteristics may be due to formation of ion channels within the bulk gel. The same characteristic has been observed for natural gels [43]. 

Chevallier T, Woignier, T, Toucet J, Blanchart E, Dieudonne P (2008) Fractal structure in natural gels effect on carbon sequestration in volcanic soils J Sol-Gel Sci Techno 48 231-238... 

Woignier, T., Braudeau, E., Doumenc, H. and Rangon, L (2005) Supercritical drying applied to natural gels ... 

For pharmacy preparations the (half) synthetic gel forming agents are generally preferred. Caution should be exercised with natural gel forming agents due to the varying quality and the presence of micro-organisms. 

Table 23.14 gives an overview of the main groups of viscosity enhancers. In this section the following groups are discussed in detail natural gel formers, cellulose derivatives, povidone, carbomers, mineral viscosity enhancers. 

Polymer gels can be of both natural and synthetic origin. Examples of natural gels are the cornea, the vitreous, and the connective tissues in our body. Examples of synthetic gels are sodium polyaaylate gels used in diapers and poly-(2-hydroxyethyl methacrylate) gels used in soft contact lenses. ... 

Synthetic gels, based on cross-linked soluble polymers, are mostly too weak to be used in any stmctural application. Many natural gel stmetures, such as are found in marine organisms, seem to be quite strong. As discussed next, possibly this difference arises from the microstmeture of natural gels, which most synthetic gels lack. 

Coordination bonding Natural gels, frozen gels... 

Structural polymers Natural gels Food, protein, polysaccharides, tissues living in the natural world... 

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