When the hydrogel swelling ratio increased, a higher amount of drug solution was absorbed into the hydrogel network, which should lead to an incremental increase in the drug loading efficiency. Thus, we could conclude that the efficiency of drug loading in the hydrogel was dependent on its swelling ratio. As more CNC was added into the gelatin network, the voids in the gelatin network were gradually filled by CNC, as shown in Fig. 2(B). Void-filling increased as more CNC was added resulting in the formation of a more rigid hydrogel structure as the crystallinity and storage modulus of the hydrogel increased. The increase in rigidity of the hydrogel created a barrier that would prevent a drug solution from “leaking,” which would cause a decrease in the drug loading efficiency. The void formation of hydrogel can be proven by scanning electron microscope (SEM) analysis. Fig. 7 shows the SEM images of hydrogel with 5% CNC (Fig. 7(a)), whereas Fig. 7(b) belongs to the hydrogel with 15% CNC. At the same magnification of 250×, the average pore sizes of the hydrogel with 15% CNC are smaller than the hydrogel with 5% CNC.