In situ synthesized Ag nanoparticle in self-assemblies of amino acid based amphiphilic hydrogelators: development of antibacterial soft nanocomposites

The present work reports the development of a new class of antibacterial soft-nanocomposites by in situ synthesis of silver nanoparticle (AgNP) within the supramolecular self-assemblies of amino acid (tryptophan/tyrosine) based amphiphilic hydrogelators. Interestingly, the nanoparticle synthesis does not require the use of any external reducing/stabilizing agents. The nanocomposites were characterized by UV-vis spectra, transmission electron microscopy (TEM) images, X-ray diffraction spectroscopy (XRD) and thermo gravimetric analysis (TGA). Encouragingly, these soft nanocomposites showed excellent antibacterial activity against both Gram-positive and Gram-negative bacteria whereas the amphiphiles alone were lethal only toward Gram-positive bacteria. Judicious combination of bactericidal AgNP within the self-assemblies of inherently antibacterial amphiphilic gelators led to the development of soft nanocomposites effective against both type of bacteria. The head group charge and structure of the amphiphiles were altered to investigate their important role on the synthesis and stabilization of AgNP and also in modulating the antibacterial activity of the nanocomposites. The antibacterial activities of soft nanocomposites comprising amphiphiles with cationic head group were found to be more efficient than the anionic soft nanocomposites. Interestingly, these nanocomposites have shown considerable biocompatibility to mammalian cell, NIH3T3. Furthermore, the well-known tissue engineering scaffold, agar-gelatin film infused with these soft nanocomposites allowed normal growth of mammalian cells on its surface while being lethal toward both Gram-positive and Gram-negative bacteria.