Temperature-Dependent Structure of Alginate/PEO–PPO–PEO/Nanoclay Composite Hydrogels

Formation of alginate-based interpenetrating networks and addition of nanoparticles into these gels are widely used strategies to enhance the mechanical properties of alginate gels used for delivery and biomedical applications. Our previous work demonstrated that alginate-clay nanocomposite hydrogels containing poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) copolymers exhibited significant enhancement of elasticity and temperature-dependent rheology. However, the behavior of PEO–PPO–PEO copolymers within an alginate network remains unclear. In this study, we use small-angle neutron scattering (SANS) to investigate the interactions between the alginate network and PEO–PPO–PEO triblock chains. Our fitting results revealed that the triblock chains can form micelles integrated into the alginate gel “egg box” structure at higher temperatures. The presence of the alginate network influences the formation of PEO–PPO–PEO micelles in our gels, leading to elongated ellipsoidal micelles rather than spherical micelles. Interestingly, as the temperature increased, these micelles did not expand in all three dimensions, as observed for pure PEO–PPO–PEO solutions. Rather, the total size increased only in one direction while remaining the same in the other two directions, suggesting that the alginate networks restrict the growth of micelles. Furthermore, we did not observe the distinct higher-order peaks that are typical of cubic PEO–PPO–PEO hydrogels; rather, relatively weak secondary peaks were observed. These results demonstrate that the presence of the alginate network significantly influences micelle formation and assembly in composite hydrogel systems.