Thermosensitive Gels

Chenite et al. reported on thermosensitive chitosan gels for encapsulating living cells and therapeutic proteins they are liquid below room temperature but form monolithic gels at body temperature [220-223]. 

The second example used visible light absorption that increased the temperature locally within the thermosensitive gel [39]. The gel consisted of a covalently cross-linked copolymer network of N-isopropylacrylamide and chloro-phyllin, a combination of a thermo-sensitive gel and a chromophore. In the absence of light, the gel volume changed sharply but continuously as the temperature was varied. Upon illumination the transition temperature was lowered, and beyond a certain irradiation threshold the volume transition became discontinuous. The phase transition was presumably induced by local heating of polymer chains due to the absorption and subsequent thermal dissipation of light energy by the chromophore. The details will be discussed in a later section. 

Finally, we described the permeation characteristics of a thermosensitive gel supported on porous glass. The switch functional ability of the membrane was demonstrated in permeation experiments. It was pointed out that the change in the permeation characteristics resulted from that in the pore structure in the gel. 

Thermosensitive Gels Capable of Regulating Enzyme Reactions.166... 

The first attempt at applying SSPGs in the field of functional immobilized biocatalysts was made by Park and Hoffman [63-65], who demonstrated the capability of thermosensitive gels for enhancing the diffusion of a substrate from the outside to the inside of a gel, which is based upon the possible absorption of the surrounding medium by the gel during a thermally controlled swelling process (see Fig. 2). 

Fig. 2. Schematic illustration of cyclic pumping of surrounding medium (represented by ) by thermosensitive gel during its thermally controlled swelling and collapse...

The present type of thermosensitive gel has been applied in the immobilization of Arthrobacter simplex cells, and the bioconversion of a steroid (hydrocortisone -> prednisolone by 3-ketosteroid-A1-dehydrogenase in A. simplex) was examined using the thermal cycling method [65]. In this case, the thermal cycling was... 

Very recently, Inomata et al. have reported that the Tc of thermosensitive gels consisting of the following /V-substituted acrylamide derivatives varies depending on the species of the substituent groups [69] ... 

This suggests the possibility of various types of thermosensitive gel for use in altering the temperature range in the on/off regulation of immobilized enzyme reactions. Thus, the use of thermosensitive gels in the field of stimulus-sensitive immobilized enzymes is expected to expand. 

As seen in the above, many approaches are now appearing aiming at providing a new driving source like muscles. Responses of thermosensitive gels are mainly governed by thermal diffusivity, and the size of gel as seen from a thermal diffusion equation. In general, the thermal diffusivity of a solvent such as water... 

Chang, J.Y., et al. 2002. Rheological evaluation of thermosensitive and mucoadhesive vaginal gels in physiological conditions. Int J Pharm 241 155. 

Bochot, A., Fattal, E., Gulek, A., and Aonarraze, G. (1998), Liposome dispersed within thermosensitive gel. A new dosage form for ocular delivery of oligonucleotide, Pharm. Res., 15,1364-1369. 

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