Nanocomposite hydrogels reinforced with vinyl functionalised silica nanoparticles.

This work reports double network hydrogel/silica nanocomposites with increased mechanical toughness and strength compared to their soft polymer-only counterparts. Applications are in tissue repair, such as cartilage, soft robotics and motion sensing. Covalent coupling of the sol-gel silica nanoparticles and the gel is vital because the gel swells on contact with water. Here, coupling was achieved through vinyl functionalisation of the silica nanoparticles (VSNPs) that enabled cross-linking to the network using photopolymerisation. The double network gel was an interpenetrating network hydrogel (IPNG) with 2-acrylamido-2-methylpropane-sulfonic acid (AMPS) as the first network, and acrylamide (AAm) as the second network. The effect of vinyl silica nanoparticle size and loading concentration were investigated on swelling behaviour, microstructure, compressive properties and nanoparticle retention. Increased size and loading concentration of VSNPs allowed for tailorability of swelling properties; nanocomposite IPNGs swelled less (88%) compared to control gels (97%). The nanocomposite IPNGs, with 20Wt% VSNPs, exhibited a max compressive strength of 810 ± 80 kPa at a strain of 75 ± 6%, similar to the lower range of articular cartilage, and an order of magnitude higher strength than control gels (90 ± 20 kPa, at a strain of 40 ± 3). SEM images show VSNP-polymer integration, with nanoparticles within the mesh walls. The nanocomposite structure provides reinforcement and toughness to soft IPNGs, making them suitable candidates for soft material repair.