One-Pot Synthesis of Gelatin/Gum Arabic Hydrogels Embedding Silver Nanoparticles as Antibacterial Materials

Abstract

High and large-spectrum antibacterial features and ROS scavenging properties are the most important requirements for efficient wound-dressing materials. A composite hydrogel was synthesized herein by a one-pot procedure embedding silver nanoparticles (AgNPs) covered with oxidized gum arabic (OGA) within gelatin (Gel) hydrogel. Small (2-20 nm), round-shaped AgNPs (ζ = -22 mV) were first obtained by green synthesis using OGA as a reducing and capping agent. Composite hydrogels, containing 0.6 and 1.3 wt.% Ag, were obtained by the covalent cross-linking (Schiff base reaction) of amine groups in gelatin with the dialdehyde groups located on the shell of the AgNPs. Thus, the uniform distribution of the AgNPs in the network contributed to the increased physicochemical and hydrolytic stability of the hydrogels. Moreover, the high swelling degree together with the good mechanical properties make them appropriate candidates for wound-healing materials. The hydrogels exhibited 80% scavenging activity of ABTS^●+ free radicals after 6 h of incubation and were effective against E. coli and S. aureus, achieving a 4% survival of bacteria within 3 h (E. coli) and 24 h (S. aureus). These results clearly indicate that the proposed hydrogels have potential in wound-dressing applications.

Keywords: Schiff base reaction; antibacterial; antioxidant; gelatin; oxidized gum arabic; silver nanoparticles.

Scheme 1

Schematic illustration of the OGA-AgNPs synthesis (a) and one-pot preparation process of the composite Gel/OGA-AgNPs hydrogels (b).

Figure 1

FT-IR spectra of GA (a), OGA (b), and OGA-AgNPs (c).

Figure 2

(a) UV–Vis spectra of AgNPs prepared using 1 wt.% aqueous solution of OGA (pH = 7 and 60 °C) at different reaction times. (b) Size distribution of OGA-AgNPs in aqueous solution measured by DLS. (c) TEM images and (d) the size histogram of the nanoparticles obtained after 20 h reaction time.

Figure 3

Scanning electron micrographs of the H1, H2, and H3 hydrogels together with the cross-section of the pore walls (inset).

Figure 4

(a) Schematic representation of the synthesis of composite hydrogels Gel/OGA-AgNPs and (b) optical images of hydrogels without (H3) and with AgNPs (N1 and N2).

Figure 5

Microphotographs (cross-section) of the N1 (a) and N2 (b) hydrogels; EDX spectra of the N1 (c) and N2 (f) hydrogels; SEM image of the mapped zone (d,g) and mapping images for Ag (e,h).

Figure 6

Stress–strain compression curves of the swollen hydrogels (a) and the obtained elastic modulus (b). Results are expressed as means ± standard deviation (S.D.) of three (n = 3) independent experiments; * p < 0.05, ** p < 0.01 among the samples.

Figure 7

Percentage of weight loss (%) after 2 and 4 weeks of incubation in PB (pH = 5.5) at 37 °C of hydrogels without and with AgNPs. Results are expressed as means ± standard deviation (S.D.) of three (n = 3) independent experiments; * p < 0.05, ** p < 0.01 among the samples.

Figure 8

ABTS^●+ radical scavenging activity of different components of the hydrogels in solution (measured after 2 h) (a) and of the hydrogels without and with AgNPs measured in time (b). Photographs of the ABTS solution in the absence and presence of H3 and N2 hydrogels after 5 h of immersion (inset).

Figure 9

In vitro antibacterial activity of the hydrogels after 3 h of incubation with E. coli and S. aureus (a); growth inhibition of the bacterial cells expressed as a percent inhibition vs. incubation time in the case of samples in contact with E. coli (b) and S. aureus (c).