Interpolymer complexes of poly(acrylic acid) and chitosan: influence of the ionic hydrogel-forming medium

Non-covalent polyionic complexes were developed for localized antibiotic delivery in the stomach. Freeze-dried interpolymer complexes based on polyacrylic acid (PAA) and chitosan (CS) were prepared in a wide range of copolymer compositions by dissolving both polymers in acidic conditions. The influence of hydrogel-forming medium on the swelling and drug release was evaluated. The properties of these complexes were investigated by using scanning electron microscopy, dynamic swelling/eroding and release experiments in enzyme-free simulated gastric fluid (SGF). The electrostatic polymer/polymer interactions generate polyionic complexes with different porous structures. In a low pH environment, the separation of both polymer chains augmented as the amount of cationic and carboxilic groups increased within the network. However, the presence of higher amount of ions in the hydrogel-forming medium produced a network collapse, decreasing the maximum swelling ratio in SGF. PAA:CS:A (1:2.5:2)-1.75 M complexes released around 54% and 71% of the amoxicillin in 1 and 2 h, respectively, in acidic conditions. A faster drug release from this interpolymer complex was observed when the ionic strength of the hydrogel-forming medium increased. Complexes with a high amount of both polymer chains within the network, PAA:CS:A(2.5:5:2), showed a suitable amoxicillin release without being affected by an increased amount of ions in the hydrogel-forming medium. These freeze-dried interpolymer complexes could serve as potential candidates for amoxicillin delivery in an acidic enviroment.