A series of poly(vinylalcohol-co-ethylene-graft-acetylsalicylic acid) hydrogel (H i ) of different acetylsalicylic acid (AcSa) contents were prepared by grafting of AcSa groups to poly(vinylalcohol-co-ethylene) in an esterification reaction and then crosslinking with oxalic acid. The H i was characterized by the solubility test, DSC, NMR, and SEM analyses. The AcSa released by retroesterification of H i at 37 C and at different pHs during 92 h. The results revealed that the amount of AcSa released from H i depended on the initial content of AcSa in H i and the pH of the media. In general, the results revealed that the PEVA-graft-AcSa (H 2 ), which contained initially 1.59 mg of AcSa, released at pH 1 a lower amount of AcSa (0.08 6 0.02 wt % of AcSa/h), stable during the longest period (85 h). On the reverse H 3 which contained 2.05 mg of AcSa presented a highly efficient release rate at pH 7. This hydrogel was able to release 0.80 6 0.05 wt % of AcSa/h, stable for about 60 h. From the first view, this finding seemed to be very important in the drug-release domain, because the hydrogel prepared in this work was able to release a greatest amount of aspirin directly into the intestines (neutral pH).

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