Effect of the Medium Composition on the Zn2+ Lixiviation and the Antifouling Properties of a Glass with a High ZnO Content

Abstract

The dissolution of an antimicrobial ZnO-glass in the form of powder and in the form of sintered pellets were studied in water, artificial seawater, biological complex media such as common bacterial/yeast growth media (Luria Bertani (LB), yeast extract, tryptone), and human serum. It has been established that the media containing amino acids and proteins produce a high lixiviation of Zn²⁺ from the glass due to the ability of zinc and zinc oxide to react with amino acids and proteins to form complex organic compounds. The process of Zn²⁺ lixiviation from the glass network has been studied by X-ray photoelectron spectroscopy (XPS). From these results we can state that the process of lixiviation of Zn²⁺ from the glass network is similar to the one observed in sodalime glasses, where Na⁺ is lixiviated to the media first and the fraction of Zn that acts as modifiers (~2/3) is lixiviated in second place. After the subsequent collapse of the outer surface glass layer (about 200-300 nm thick layer) the dissolution process starts again. Antifouling properties against different bacteria (S. epidermidis, S. aureus, P. aeruginosa, E. coli, and M. lutea) have also been established for the glass pellets.

Keywords: Zn dispenser; amino acids; antimicrobial glass; biofilm.

Figure 1

XRD patterns of the starting glass powders of ZnO35 and the obtained ZnO35 sintered pellets at 630 °C (insert photograph of ZnO35 pellet).

Figure 2

Zinc released from the ZnO35 pellet after 24 h in different concentrations of l-Glutamine.

Figure 3

X-ray photoelectron spectroscopy (XPS) spectra in the Si2p, Zn3p, Al2p, and Na2s region of the ZnO35 pellet and the ZnO35 pellet after being immersed for 40 days in LB (labelled as BIO). (A) XPS signals upon background subtraction; (B) signals normalized to the Si2p peak upon background subtraction.

Figure 4

Evolution of viable cells within biofilms developed for 24 h, 48 h, or 5 days on control G1 pellets.

Figure 5

Effect of ZnO35 on the viability of bacterial and yeast biofilms. NR; no reduction. * p < 0.05, ** p < 0.01.

Figure 6

Scanning electron micrographs of S. epidermidis (A–D) and E. coli (E–H) grown on glass pellets. (A,B) panels show S. epidermidis biofilm formation on the surface of control G1 at day 5; (C,D) show colonization of ZnO35 pellets by S. epidermidis after 24 h (C) and 5 days (D); (E,F) show growth of E. coli on ZnO35 surfaces after 24 h, and (G,H) after 5 days.