Effects of cellulose nanocrystal polymorphs and initial state of hydrogels on swelling and drug release behavior of alginate-based hydrogels

In this work, composite hydrogels composed of sodium alginate (SA) and two crystal structures of cellulose nanocrystals (CNCs) I and II were prepared, respectively. Impacts of CNC polymorphs and initial state of the hydrogels on the swelling kinetics were analyzed on the basis of power law and Schott's second-order kinetic equation. It was found that the swelling ratio of SA/1 CNC II was the largest, and it showed the non-Fickian diffusion behavior, while SA and SA/1 CNC I exhibited the Fickian diffusion behavior. And the swelling ratio of soaked hydrogels was great larger than that of the rinsed ones, but the swelling mechanism of the two situations was almost the same, that is, the Fickian diffusion behavior. In addition, drug release tests were performed in deionized water using chloramphenicol as a model drug. The results indicated that for the soaked hydrogels, the drug loading was high, while the release rate was slow. The reason for the higher loading but slower release rate was also discussed based on the morphology of hydrogels. On the other hand, the addition of CNC II into SA brought the high drug loading and slow release rate. It resulted from the strong hydrophilicity of CNC II and the strong interaction between drug and SA/CNC II hydrogels. This work could give a new promise for tuning the swelling and drug release behavior of hydrogels by varying the initial state of hydrogels or the crystal form of CNCs.