The oP@ALG was obtained by thoroughly mixing ALG with oH2 and PT-100. Similarly, the oH@ALG was conducted by thoroughly mixing ALG with oH2 and the PT@ALG was prepared by thoroughly mixing ALG with PT-100. The formation of hydrogel
in vitro was first confirmed. The oH2-Cy5.5@ALG solution rapidly formed a hydrogel upon extrusion from the needle tip into the surrounding fluids with intratumoral calcium concentration, exhibiting no morphological changes within 3 h (Figs. S1A and S2 in Supporting information). On the contrary, free oH2-Cy5.5 dispersed quickly throughout the beaker when injected into the Ca
2+-containing solution. This result suggests that the cross-linking of ALG with Ca
2+ shows an effective ability to immobilize the drug in the hydrogel. In addition, we explored the effect of different concentrations of ALG on the formation of hydrogels from oP@ALG. As shown in Fig. S1B (Supporting information), hydrogel formation depended on the concentration of ALG. When the concentration of ALG was only 1 or 2 mg/mL, the mixture diffused rapidly at the bottom of the cup due to its weak gelation. When the ALG concentration was raised to 5, 10, and 20 mg/mL, the oH2-Cy5.5@ALG quickly turned into the hydrogels in the Ca
2+ solution. It is worth noting that when the concentration of ALG was >5 mg/mL, the viscosity was too large and not conducive to injection. Additionally, 5 mg/mL of ALG was added to the Ca
2+ solution to form a hydrogel with weaker mechanical intensity and variable morphology. Based on the above results, ALG concentration of 5 mg/mL was selected for subsequent experiments. To further investigate the properties of the hydrogels, rheometers were employed to examine the rheology and viscosity of hydrogels. In rheological analysis experiments, when the elastic modulus (G') is greater than the viscosity modulus (G''), the sample is defined as a solid rather than a liquid [
17,
18]. As shown in Fig. S3A (Supporting information), G' was significantly larger than G'', indicating that ALG could form hydrogels by chelation with Ca
2+. Besides, we also explored the relationship between the viscosity of the hydrogel and the shear rate. As shown in Fig. S3B (Supporting information), the viscosity of the oP@ALG hydrogel gradually decreased with the increase of the shear rate, signifying the presence of shear thinning behavior within the hydrogel, while the viscosity of the oP@ALG solution did not exhibit significant changes. The formation of oP@ALG hydrogel was then examined by confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscope (cryo-SEM). As presented in Fig. S4 (Supporting information), the distribution of Cy5.5-labeled oH2 within the FITC-labeled ALG hydrogel was observed to be uniform. Additionally, surface aggregation of oH2 particles on the hydrogel was evident, accompanied by the formation of a cross-linked mesh structure inside the hydrogel (
Fig. 1B). The differential release capability of oP@ALG was further validated by quantifying the release of each component at different time intervals. The release of PT-100 exhibited a rapid increase up to 4 h, accounting for approximately 40% of the total release (
Fig. 1C and Fig. S5 in Supporting information). The release rate of oH2 was significantly reduced compared to PT-100, with only a 10% release observed over a period of 4 h. This disparity can be attributed to the larger particle size of the oH2 viral particles, which function as nanoparticles rather than free drug. The aforementioned statement is in complete alignment with the differential release strategy employed for hydrogel-loaded drugs in this study. Specifically, the rapid-release PT-100 functions as an anti-CAFs agent to normalize CAFs and alleviate mesenchymal pressure at the tumor site. Subsequently, the slow-release oH2 effectively infects and eradicates tumor cells.