Salicylic acid-based pH-sensitive hydrogels as potential oral insulin delivery systems

Salicylic acid (SA)-based physically crosslinked pH-sensitive hydrogels were developed for oral insulin delivery using various ratios of salicylate-based poly(anhydride-ester) and poly(acrylic acid) (PAA). Pore size, swelling behavior, insulin loading, insulin and SA release rates of the gels were varied by changing PAA concentration. About 50% of insulin was incorporated within all of the hydrogels, with about 4-8% of insulin released in acidic conditions (pH 1.2) over 2 h. In pH simulating the intestine (pH 6.8), 90% of the insulin and 70% of SA were released within 24 h from the hydrogel system. These results suggest that hydrogels enable pH-dependent protein delivery and can be used for oral insulin and SA delivery to benefit diabetes patients.