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Previous work has addressed the fundamental characteristics of these complexes [350, 351] and has shown preferential complexation of cationic polyelectrolytes with crosslinked carboxymethyl cellulose versus linear CMC [350]. The departure from the 1:1 stoichiometry with the non-neutralized microgels may be due to the collapsed nature of these networks which prevents penetration of water soluble polyelectrolyte. Polyelectrolytes have also been used to regulate drug delivery rates in transdermal devices.

The relation between the force applied during formation of Carbomer 934-based pills and the in vitro release rate was also investigated [334], Novel encapsulation techniques based on polyelectrolyte complexes have been developed and were reviewed by Philipp et al. [335] and Petrak [336], One of the most common examples of encapsulation based upon polyelectrolyte complexes is coacervation, which involves the association of oppositely charged polymers to form an insoluble film or barrier. For example, calcium-gelled sodium alginate capsules reinforced by complex formation between alginate and poly-Z-lysine have been investigated [337], along with haemophilized membranes prepared by the reaction of quaternary polyelectrolyte with anionic materials [338].

In these applications, the polyelectrolytes provide hydrophilicity and pH sensitivity to tablet dosage forms. Acidic polyelectrolytes dissociate and swell (or dissolve) at high pH values whereas basic polyelectrolytes (for instance, polyamines) become protonated and swell at low pH. In either case, swelling results in increased permeability [290], thereby allowing an incorporated drug to be released. Cellulose disintegrants have been studied as insoluble matrices for sustained release tablets. Anionically charged carboxymethyl cellulose (sodium salt) was found to be inferior to methyl cellulose and polyvinyl pyrollidone) as a binding agent for oxyphenbutazone tablets [291].

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