Evaluation of pH- responsive poly(styrene-co-maleic acid) copolymer nanoparticles for the encapsulation and pH- dependent release of ketoprofen and tocopherol model drugs

Abstract

The pH- induced intelligent drug release ability of poly(styrene-co-maleic acid) copolymer nanoparticles (SMA NPs; d = 22.4 ± 3.1 nm) is presented using poorly water soluble ketoprofen (KETO) and α-Tocopherol (TP) model drugs. Increasing styrene content of the copolymer led to lower surface charge (from −28.4 to −15.0 meq/100 g) and the different styrene/maleic acid ratio (SMA#1: 1:2; SMA#2: 2:1 and SMA#3: 3:1) influences the pH- dependent solubility properties. Because of the polyanionic nature, homogeneous polymer solution was obtained at higher pH, while at lower pH nanoparticles were formed. The corresponding cut- off pH values showed increasing tendency with increasing hydrophobicity (pH = 3.12, 4.22 and 5.44 for SMA#1, 2 and 3, respectively).Next the hydrophobic, non- water soluble KETO and TP drug cores were coated with SMA#2 shell. The polymer-stabilized drug particles provided stable dispersion in aqueous environment, i.e. the prepared polymer shell increased the water dispersibility of the initial hydrophobic drugs. According to the experiments the release of low crystallinity KETO drug was almost complete at physiological pH (=7.40), while at acidic pH the released amount of model drug was only about 30%. Similar kinetic release profile was obtained in the case of more hydrophobic TP drug without charged groups and it indicates that the drug release was primarily controlled by the pH- responsive polymer particles instead of the pH- dependent solubility of the model drug. The prepared NPs could be useful in all areas where the alkaline pH value causes problems, for example in the case of female genital diseases of fungal origin.