Effect of starch oxidation degree on the properties of hydrogels from dialdehyde starch and polyvinyl alcohol

Starches have been applied as biomaterials due to their wide availability and biocompatibility. These have also been modified by oxidation, resulting in dialdehyde starch (DAS), to improve their stability in water and mechanical properties. Cassava starch with a low oxidation degree has been introduced into hydrogels based on polyvinyl alcohol (PVA) to improve their properties. However, the behavior of these materials with starch at different oxidation levels has not been previously explored. In the present work, the effect of the oxidation degree of cassava starch on the physical and chemical properties of DAS-PVA hydrogels was evaluated. To modify the degree of oxidation, different concentrations of H2O2 were used, and a high degree of oxidation was achieved by incorporating copper sulfate II as a catalyst. Oxidation was confirmed by quantification of carbonyl groups and Fourier Transformed Infrared Spectroscopy. Hydrogels with low and medium oxidation DAS displayed greater swelling, but also lower stability over time. Similarly, scanning electron microscopy confirmed greater porosity in them. On the other hand, hydrogels with high oxidation DAS had lower water absorption capacity, but greater stability over time. Regarding the controlled release of ibuprofen, as a model drug, hydrogels formulated with low and medium oxidation DAS presented a greater and faster release, compared to the formulations with high oxidation DAS. These results showed that the degree of starch oxidation, for the PVA-DAS hydrogel synthesis has a significant effect on the behavior of the polymeric network.