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