Abstract

Pluronic hydrogels containing a weakly acidic hydrophobic API, ibuprofen, at concentration of 1% and 5% w/w, were prepared using the cold method over a range of Pluronic F127 concentrations (15%, 20% and 25% w/w) and propylene glycol as a co-solvent. Gels containing 1% w/w ibuprofen were unsaturated whereas gels containing 5% w/w ibuprofen were saturated. Imaging studies of ibuprofen release from the surface of the gels into either stagnant or flowing phosphate buffer (PBS, pH = 7.4) were conducted using the Sirius SDI UV dissolution imaging system at λ = 214 nm. The duration of each run was 60 min and each sample was examined at least in triplicate. The concentration of ibuprofen in the bulk buffer was correlated with the viscosity and the saturation status of the gels. Imaging studies carried at stagnant flow rate (0.0 ml/min) showed that ibuprofen release from gels at constant drug loading was inversely proportional to the viscosity of the gel; thus confirming that diffusion coefficient of ibuprofen molecules was inversely proportional to the viscosity of the matrix (gel). Imaging studies carried at 0.2 ml/min for the first 30 min, followed by 0.0 ml/min for the remaining 30 min of the run, showed a gradual depletion of ibuprofen in the bulk buffer up to 30 min, followed by a gradual increase of ibuprofen concentration from 30 to 60 min. The later imaging studies also demonstrated that at constant Pluronic F127 concentration, drug loading (thus thermodynamic activity) was the determining factor for drug release.