Zinc-triggered hydrogelation of self-assembled small molecules to inhibit bacterial growth

Abstract

There is a significant need to develop antibacterial materials that could be applied locally and directly to the places surrounded by large amount of bacteria, in order to address the problems of bacterial antibiotic-resistance or irreversible biofilm formation. Hydrogels are thought to be suitable candidates due to their versatile applications in biomedical field. Among them, small molecular hydrogels have been paid lots of attention because they are easy to design and fabricate and often sensitive to external stimuli. Meanwhile, the antibacterial activity of metal ions are attracting more and more attention because resistance to them are not yet found within bacteria. We therefore designed the zinc ion binding peptide of Nap-GFFYGGGHGRGD, who can self-assemble into hydrogels after binds Zn(2+) and inhibit the growth of bacteria due to the excellent antibacterial activity of Zn(2+). Upon the addition of zinc ions, solutions containing Nap-GFFYGGGHGRGD transformed into supramolecular hydrogels composed of network of long nano-fibers. Bacterial tests revealed an antibacterial effect of the zinc triggered hydrogels on E. coli. The studied small molecular hydrogel shows great potential in locally addressing bacterial infections.

Figure 1. Chemical structure of Zn²⁺ binding peptide and schematic diagram of it binding with Zn²⁺ and self-assembling into hydrogel.

Blue ribbon and green ribbon stand for peptide before and after binding with Zn²⁺, respectively.

Figure 2. Optical images of solutions and hydrogels and the rheology test results.

A)Solution containing 1.0 wt% of compound and hydrogels formed after adding B)0.3, C)0.7 and D)1.0 equiv. of Zn²⁺. E) Oscillatory rheological dynamic frequency sweeps of 1 wt% peptide in pH 7.4 buffer at 25°C with addition of different equiv. of Zn²⁺: 0, 0.1, 0.2, 0.3 0.5, 0.7 and 1.0, respectively. G’ is the storage modulus in units of Pa.

Figure 3. TEM images of (A) solution of Nap-GFFYGGGHGRGD (1.0 wt% in PBS), hydrogels of Nap-GFFYGGGHGRGD (1.0 wt% in PBS) with addition of (B) 0.3, (C) 0.7 and (D) 1.0 equiv. of Zn²⁺.

Figure 4. Growth inhibition of E. coli by zinc ion binding hydrogels (1.0 wt% in LB buffer, pH 7.4) and zinc ion solutions (LB buffer, pH 7.4).

The data is presented as the absorbance at 600 nm following 6 hours of growth divided by the absorbance at 600 nm just after the mixing of bacteria with hydrogels. Each bar represents standard error of the mean of three technical replicates.

Figure 5. Cell viability assay for Hela cells.

A) Relative cell viability with respect to control group (untreated cells) is plotted against increasing peptide concentrations. B) Cell viability against different amount of zinc ion in the triggered hydrogels (Concentration of peptide is 1.0 wt%).