Multi-responsive hydrogels based on magneto-plasmonic nanoparticles in a thermo-responsive polymer matrix

• Magneto-plasmonic nanoparticles with different morphologies are synthesized. • Nanoparticles are functionalized with double thermo-responsive-graft copolymers. • Hybrid material exhibits optical, magnetic, and thermo-responsive properties. • Multi-responsive hybrid hydrogels with three different swelling states are obtained. • NIR irradiation remotely triggers a deswelling of the hydrogel via plasmonic heating. Due to their unique combination of magnetic and plasmonic properties, magneto-plasmonic nanoparticles (MP-NPs) are engaging platforms for multi-responsive materials. While the magnetic and plasmonic properties can be tuned by different synthesis methods that yield different particle compositions and morphologies, the possibilities of adding responsive properties by embedding MP-NPs in smart polymer matrices have not been extensively explored. This work presents the synthesis and characterization of a magneto-plasmonic CoFe 2 O 4 @Au@Polymer hybrid material using a double thermo-responsive graft copolymer. The polymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, using their trithiocarbonate (TTC) end group as an anchoring group on the particles’ surface. The colloidal hybrid material was crosslinked to prepare multi-responsive hydrogels, and the presence of the MP-NPs' magnetic and optical properties and the gel's temperature-dependent swelling behavior were explored. To show the synergy of the components, photothermal heating with near-infrared (NIR) irradiation was investigated to reveal that significant amounts of water can be expelled from the hydrogel. Furthermore, the approach of using MP-NPs and TTC-terminated polymers as bases for multi-responsive materials can be adapted to obtain materials with different polymer structures to tailor transition temperatures and surface functionalization. This versatility of the properties, in combination with the heat generation capabilities and the possibility to release water and additional substances dispersed in the water phase, make such hybrid materials interesting for various applications like delivery or targeted release applications.