Silica Nanoparticle-Reinforced Bioactive Oxidized Alginate/Polyacrylamide–Gelatin Interpenetrating Polymer Network Composite Hydrogels

Alginate hydrogels are promising tissue engineering biomaterials due to their biocompatibility and structural similarity to the extracellular matrix, but their poor mechanical strength, rapid degradation, and lack of bioactivity limit applications. To address this, a novel oxidized alginate/polyacrylamide/silica nanoparticle–gelatin (OA/PAAm/SiO2-GT) composite hydrogel was developed using an interpenetrating polymer network (IPN) strategy, reinforced with silica nanoparticles and coated with gelatin. The influence of SiO2 content on the microstructure, mechanical properties, swelling behavior, biodegradability, biomineralization, and cytocompatibility of the composite hydrogel was systematically investigated. Experimental results revealed that SiO2 nanoparticles interacted with the polymer matrix within the composite hydrogel. With increasing content of SiO2, the porosity of the OA/PAAm/SiO2-GT composite hydrogel gradually decreased, while the mechanical properties exhibited a trend of initial enhancement followed by reduction, with maximum compressive strength at a SiO2 content of 1.0% (w/v). Moreover, the incorporation of SiO2 nanoparticles effectively modulated the swelling behavior, biodegradability, and biomineralization capacity of the composite hydrogel under in vitro conditions. Meanwhile, the OA/PAAm/SiO2-GT composite hydrogel supported favorable cell adhesion and proliferation, optimal at a SiO2 content of 0.5% (w/v). Furthermore, with increasing concentration of SiO2 nanoparticles, the intracellular alkaline phosphatase (ALP) activity progressively increased, suggesting a promotive effect of SiO2 nanoparticles on the osteogenic differentiation of MG63 cells. Therefore, the incorporation of SiO2 nanoparticles into the OA/PAAm IPN matrices provides an effective means to tailor its biological properties, rendering it great potential for biomedical applications such as tissue engineering.