Amphiphilic Peptide-Based Supramolecular, Noncytotoxic, Stimuli-Responsive Hydrogels with Antibacterial Activity

Abstract

A series of peptides with a long fatty acyl chain covalently attached to the C-terminal part and a free amine (–NH2) group at the N-terminus have been designed, so that these molecules can be assembled in aqueous medium by using various non-covalent interactions. Five different peptide amphiphiles with a general chemical formula [H2N-(CH2)nCONH-Phe-CONHC12 (n=1-5, C12= dodecylamine)] have been synthesized, characterized and examined for self-assembly and hydrogelation. All of these molecules [P1 (n= 1), P2 (n= 2), P3 (n= 3), P4 (n= 4), P5 (n= 5)] form thermo-responsive hydrogels in water (pH 6.6) with nano-fibrillar network structure. Interestingly, the hydrogels obtained from compound P4 and P5 exhibit potential anti-microbial activity against Gram positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram negative bacteria (Escherichia coli). Dose dependent cell-viability studies using MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) by taking human lung carcinoma (A549) cells vividly demonstrates the non-cytotoxic nature of these gelator molecules in vitro. Haemolytic studies show non-significant or little haemolysis of human erythrocyte cells at minimum inhibitory concentration (MIC) of these tested bacteria. Interestingly, it has been found that these antibacterial non-cytotoxic hydrogels exhibit proteolytic resistance towards the enzymes proteinase K and chymotrypsin. Moreover, the gel strength and gel recovery time have been successfully modulated by varying the alkyl chain length of the N-terminally located amino acid residues. Similarly, the thermal stability of these hydrogels has been nicely tuned by altering the alkyl chain length of the N-terminally located amino acid residues. In the era of antibiotic resistant strain of bacteria, the discovery of this new class of peptide-based antibacterial, proteolytically stable, injectable and non-cytotoxic soft-materials hold future promise for the development of new antibiotics.