Evaluation of poly(acrylic acid-co-ethylhexyl acrylate) films for mucoadhesive transbuccal drug delivery: factors affecting the force of mucoadhesion

Based on the premise that similar surface properties between the adhesive a nd the substrate would yield a strong adhesive bond, copolymers of acrylic acid (AA) and 2-ethylhexyl acrylate (EHA), P(AA-co-EHA), were designed and synthesized for buccal mucoadhesion. A series of linear copolymers with var ying feed ratios of the two monomers (AA and EHA) were synthesized through free radical copolymerization at 69+/-0.5 degrees C using azobis(isobutyron itrile) (AIBN) as initiator. The reactions were carried out in THF under ni trogen for 24 h. The glass transition temperatures, T-g, of the copolymers were determined using DSC. The adhesion studies were conducted to determine the effects of copolymer composition, contact time between the substrate a nd the adhesive, and crosshead speed on mucoadhesive performance of the cop olymer films using a computer interfaced Instron material testing system. T he glass transition temperature of the copolymers decreased with increasing EHA content. Wet glass surface as substrate was shown not to be a good sub strate model for adhesion determination studies. The copolymer composed of 46:54 mol.% AA:EHA (an almost 1:1 ratio in the repeat units) yielded the hi ghest mucoadhesive force in contact with porcine buccal mucosa which was si gnificantly greater (P<0.05) than that of poly(acrylic acid) (PAA) (used as positive control). The mucoadhesive force for all copolymers studied was s ignificantly (P<0.05) greater than that of the negative control (backing ma terial without copolymer film) except for the EHA homopolymer. Crosshead sp eed increased mucoadhesive force linearly and had a more pronounced effect on the mucoadhesive performance than time of contact between the adhesive a nd the substrate. (C) 2000 Elsevier Science B.V. All rights reserved.