This study reports the current progress in quantitative analysis of the release characteristics of pHEMA spongy hydrogels using prednisolone 21-hemisuccinate sodium salt as a model drug. Extraction of effective diffusion coefficients of the drug from various pHEMA matrices was made using a novel mathematical model that handles both boundary layer and initial burst effects. Drug loading level and entrapment efficiency were also determined. The computed diffusion coefficients and the drug loading capacity in relation to the device porous structure and drug concentration of the loading solution, as well as the size of device are discussed. Mathematical modelling proves to be a powerful tool not only for establishing and interpreting structure and performance relationships but also for handling experimental ambiguity. (c) 2007 Curtin University of Technology and John Wiley & Sons, Ltd.