Aqueous two-phase system enabled dual-layered hydrogels with tunable nanoparticle localization

Abstract

Hydrogels are cross-linked polymeric networks capable of absorbing large amounts of water and have been widely explored for applications in drug delivery, tissue engineering, biosensing, and environmental remediation. The recent development of dual-layered hydrogels (DLHs) has expanded their potential, enabling spatial control over their mechanical and chemical properties. Furthermore, incorporating nanoparticles into each of these layers introduces unique optical, electronic, or catalytic properties, expanding the scope of these materials. However, complex processes often hinder the fabrication of DLHs, requiring precise control over the reaction conditions. This poses challenges in achieving a uniform nanoparticle distribution without aggregation. This work presents an approach for synthesizing DLHs with an aqueous two-phase system (ATPS), integrating phase separation and selective nanoparticle localization, followed by subsequent polymerization. Using a model system of poly(ethylene glycol) (PEG) and dextran (DEX) to generate the ATPS, we combined acrylamide, bis(acrylamide), and Irgacure (photoinitiator) to fabricate DLHs. Rheological studies provided insights into the viscoelastic behavior of DLHs, while mercury porosimetry was employed to analyze the pore size distribution. We illustrate that citrate-capped gold nanoparticles can be localized within the PEG-rich layer, while bovine serum albumin (BSA)-capped silver nanoparticles can be localized within the DEX-rich layer. We performed molecular dynamics simulations to investigate the factors contributing to the preferential partitioning. Finally, we exploit the fabricated DLHs with localized nanoparticles to catalyze the conversion of p-nitrophenol to p-aminophenol in the presence of gold nanoparticles. Upon laser irradiation at 450 nm, the reaction rate is further enhanced due to photothermal heating induced by the silver nanoparticles. We anticipate that this process offers a fabrication route toward multifunctional DLHs with spatially organized nanoparticles, opening avenues for advanced catalytic and responsive materials.