Investigation of the effects of orientation on freeze/thawed Polyvinyl alcohol hydrogel properties

Although hydrogels produced via freeze-thawing (F/T) technique have been thoroughly studied in literature, stretching hydrogels in between freeze-thawing cycles could change its properties for drug delivery systems. The PVA hydrogels and Caffeine-contained PVA hydrogels were created by freezing for 20 min using liquid nitrogen and 4 h thawing at 4 °C. The results revealed that the PVA/CAF hydrogel with two F/T cycles followed by two stretching (S) cycles delivered the best response. Furthermore, this sample had the highest degree of crystallinity and Young's modulus of 36% and 1462 MPa, respectively, which makes this hydrogel very stiff in comparison to all other samples. Moreover, it fits in the Hixson-Crowell drug release model with the highest drug of releasing rate of 15 min, and the highest swelling degree of 470%. Therefore, the study suggests that the number of F/T cycles and stretching cycles influences the properties of the resulting hydrogels and the caffeine release rate.