Using a mild hydrogelation process to confer stable hybrid hydrogels for enzyme immobilization†
In addition to the widely used polymeric hydrogels, molecular hydrogels are also emerging as promising biomaterials. However, molecular hydrogels typically suffer from poor mechanical properties and relatively low in vivo stability. Here we report on the preparation of two hybrid hydrogels (Hgel I and Hgel II) by the combination of two molecular hydrogelators and alginate, respectively. First, the molecular hydrogelator and sodium alginate were dissolved in water, and then a hydrogel was formed upon triggering by enzymes or reductants. Afterward the resulting hydrogel was soaked in calcium ion solution to form the hybrid hydrogel. The preparation process was easy and mild which allowed the resulting hybrid hydrogels to act as carriers for biomacromolecules such as enzymes. Both Hgel I and Hgel II had better stabilities and mechanical properties than the calcium alginate gel (CAgel) alone. Hgel I had exceptional stability compared with Hgel II and CAgel. The reason we propose is that molecular hydrogelators in Hgel I interacted with alginate more strongly than molecular hydrogelators in Hgel II according to the fluorescence results of these gels. Unlike the porous microstructure of molecular hydrogels, the microstructure of two hybrid hydrogels was almost the same as that of CAgel (film-like morphology) except with some nanofibers embedded. We found that Hgel I was an ideal carrier for enzyme immobilization with high recyclable properties and excellent preservation of enzyme activities due to its good mechanical strength. However, Hgel II was not suitable as a carrier for immobilized lactase probably due to poor affinity between Hgel II and the substrate. Combining the advantages of molecular hydrogels and polymeric hydrogels would broaden the applications of both kinds of hydrogels in the future.