Poloxamer and Pluronic gels

Aqueous solutions of Poloxamer or Pluronic undergo sol-to-gel transition as the temperature increases (Fig. 13.4). However, the implanted gel of Poloxamer is quickly eroded and does not persist for more than a few days at most. To improve the system, end-group modified Poloxamers, and multiblock copolymers consisting of Poloxamer and biodegradable polymers have been developed. In addition, random multibloek eopolymers consisting of PEG, PPG, and a biodegradable polymer were reported. 

Polyphosphazene is prepared by ring-opening polymerization of hexachloro-cyclotriphosphazene to make a poly(dichlorophosphazene), followed by nucleo-philie substitution reactions to poly(dichlorophosphazene) (Fig. 13.5). Biodegradability and hydrophihc/hydrophobic balance can be controlled by 

Aqueous solutions of chitosan-g-PEG and hyamlonic acid-g-Poloxamer undergoing thermal gelation were reported. Aqueous solutions of hydroxy-propyl methylcellulose or methyl cellulose also show thermal gelation. The hydrophobic interactions were suggested as the sol-to-gel transition mechanism. Aqueous solutions of the inclusion complexes between methylated a- 

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