In vitro release behavior and stability of insulin in complexation hydrogels as oral drug delivery carriers

Novel pH-responsive complexation hydrogels containing pendent glucose (P(MAA-co-MEG)) or grafted PEG chains (P(MAA-g-EG)) were synthesized by photopolymerization. The feasibility of these hydrogels as oral protein delivery carriers was evaluated. The pH-responsive release behavior of insulin was analyzed from both P(MAA-co-MEG) and P(MAA-g-EG) hydrogels. In acidic media (pH 2.2), insulin release from the hydrogels was very slow. However, as the pH of the medium was changed to 6.5, a rapid release of insulin occurred. In both cases, the biological activity of insulin was retained. For P(MAA-co-MEG) hydrogels, the biological activity of insulin decreased when the pendent glucose content increased. In P(MAA-g-EG) hydrogels, when the grafted PEG molecular weight increased, the insulin biological activity decreased. Finally, hydrogels of P(MAA-co-MEG) prepared with an initial ratio of 1:4 MEG:MAA and P(MAA-g-EG) hydrogels containing PEG chains of molecular weights of 200 showed the greatest change in insulin release rate from acidic to basic pH solutions and the greatest protective effect for insulin in simulated GI tract conditions.