A Study on Interaction and Solubility of Acetaminophen with Poly(AM-co-HEA-co-AA) Hydrogels by DSC: Effect on Drug Diffusion Behavior

Abstract

In the present study, acetaminophen solubility and its interaction with poly(AM-co-HEA-co-AA) hydrogels containing acetaminophen (AMP) from 15% to 35% was determined by DSC thermogram; and confirmed by SEM and FTIR analysis. Results obtained by DSC indicated that acetaminophen dissolved up to 16.33% loading, while acetaminophen above the concentration 16.33% existed in crystalline form in matrices, and was responsible for the melting corresponding to the melting of acetaminophen crystals. The heat required to melt the crystalline portion of acetaminophen was theoretically calculated by using an equation, and its validity was confirmed through melting enthalpies observed experimentally. The effect of increasing amount crystalline acetaminophen on the matrix swelling, and simultaneous controlled release of acetaminophen was investigated. The drug diffusion kinetic was analyzed by fitting early-time, late-time and etters diffusion models to the drug release data observed experimentally. By increasing drug loading, values of all drug diffusional coefficients (i.e., early-time, late-time and etters) were decreased, and rank of diffusion coefficients for each hydrogel matrix was followed in the order of etters> late-time >early-time. From model fitting, it was observed that with increasing AMP content in hydrogels matrix, the applicability of early time and late time model were improved; and for 35% AMP containing hydrogel, early time was applicable for first 60% drug diffusion; late-time model was applicable for latter 50% drug diffusion; indicating that diffusion characteristics can be altered by increasing crystalline acetaminophen depending on the% acetaminophen loading in hydrogel. Etters model was best applicable to all type of hydrogel matrices, and followed over entire range of drug diffusion process.