Design and properties of alginate/gelatin/cellulose nanocrystals interpenetrating polymer network composite hydrogels based on in situ cross-linking

Alginate (Alg) hydrogels have attracted extensive attention in the biomedical field due to their biocompatibility. However, single Alg hydrogels exhibit weak mechanical strength, poor stability and cell adhesion, which severely restricts their biomedical application. For this reason, we designed alginate/gelatin/cellulose nano-crystals (Alg/G/CNCs) composite hydrogels by combining interpenetrating network (IPN) technology, cellulose nanocrystals (CNCs) reinforcement and in situ cross-linking method to improve the functional defects of Alg hydrogels. The structure and properties of the resultant Alg/G/CNCs composite hydrogels were comprehensively evaluated by FT-IR, TGA, XRD, swelling and degradability measurements, and cytocompatibility experiments. Alg/G/CNCs composite hydrogels with regular three-dimensional porous network (3D) structures was success-fully fabricated through the ionic cross-linking of alginate and the covalent cross-linking of gelatin, followed by the reinforcement of colloidal cellulose nanocrystals (CNCs) that were prepared by sulfuric acid hydrolysis of microcrystalline cellulose (MCC). The addition of CNCs could generate interaction force with the polymer in the IPN matrix, which was able to regulate the physicochemical properties of the composite hydrogel to a certain extent. Moreover, with the increase of gelatin (G) content, the compressive strength of Alg/G/CNCs composite hydrogels gradually increased, while the swelling property decreased gradually. Meanwhile, Alg/G/CNCs composite hydrogels exhibited good cell adhesion, proliferation and differentiation properties. In particular, Alg/ 0.5G/CNCs composite hydrogels displayed the best cell proliferation effect, while Alg/2G/CNCs composite hydrogels revealedthe most significant cell differentiation effect. Therefore, Alg/G/CNCs composite hydrogels could exhibit good mechanical properties and biocompatibility, which possessed great application potential in the field of tissue engineering.