In situ synthesised silver nanoparticle-infused L-lysine-based injectable hydrogel: Development of a biocompatible, antibacterial, soft nanocomposite

The synthesis of l-lysine-based amphiphilic hydrogelator consisting of a naphthalene moiety at the N termini and an ethyleneoxy unit with free primary amine at the C terminus is reported. The amphiphile showed good gelation ability with minimum gelation concentration 0.6% w/v in binary mixtures of dimethyl sulfoxide/phosphate buffer (1:4 v/v, pH 7.4). The hydrogel was characterised by spectroscopic and microscopic studies to delineate the role of non-covalent interactions in self-assembly gelation. Subsequently, Ag nanoparticles were synthesised within the hydrogel by in situ photo-reduction of AgNO₃ under sunlight, in which the gelators act as reducing/stabilising agents. The nanocomposites were characterised by transmission electron microscopy, UV/Vis and X-ray diffraction spectroscopy and thermogravimetric analysis. Rheology of the soft nanocomposite showed significant mechanical strength and thixotropic self-recovery properties, which made the composite suitable for use as a syringe-injectable hydrogel. These soft nanocomposites exhibited excellent antibacterial activity against both Gram-positive and Gram-negative bacteria. They showed low haemolytic activity and high biocompatibility to mammalian (Chinese hamster ovarian) cells. In addition, agar-gelatin film infused with these nanocomposites allowed normal growth of mammalian cells on its surface while being lethal towards bacteria.