Polyelectrolytes in Novel Responsive Delivery Systems

Two similar approaches were adopted by Ishihara et al. [364-368]. Membranes based on hydroxyethyl acrylate, dimethylaminoethyl methacrylate and trimethyl silyl styrene were solvent cast, and capsules containing insulin and glucose oxidase were prepared by interfacial precipitations. The authors reported dramatic changes in permeability in response to pH changes between 6.1 and 6.2. Moreover, addition of glucose induced an increase in the permeation rate of insulin, and upon removal of the glucose the permeability rates returned to their original levels. However, the conclusions were criticized [361] due to 

Kwon and coworkers described solid polyelectrolyte complex systems which dissolve rapidly in response to small electric currents. The solid doses were based on poly(ethyl oxazoline) and poly(methacrylic acid) with a repeating unit stoichiometry of 1 1. Insulin was released in response to slight electric currents due to electrically induced polymer dissolution [380]. In similar work Kwon and coworkers [381] studied release of edrophonium chloride and hydrocortisone from poly(2-acrylamido-2-methylpropane sulfonate-co-n-butyl methacrylate). An on/oflf mechanism of the edrophonium chloride release was observed and was attributed to ion exchange of solute and hydroxonium ion. The cationic solute release was assisted by electrostatic forces, whereas release of the neutral hydrocortisone solute was only affected by swelling and deswelling. 

Novel responsive controlled release systems based upon polyelectrolyte-grafted membranes have also been reported. Iwata and Matsuda prepared novel environmentally sensitive membranes by grafting poly(acrylic acid) onto poly(vinylidene fluoride) membranes [382, 383]. Under basic conditions, the 

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