Application of an Antibacterial Coating Layer via Amine-Terminated Hyperbranched Zirconium-Polysiloxane for Stainless Steel Orthodontic Brackets

Abstract

The massive growth of various microorganisms on the orthodontic bracket can form plaques and cause diseases. A novel amine-terminated hyperbranched zirconium-polysiloxane (HPZP) antimicrobial coating was developed for an orthodontic stainless steel tank (SST). After synthesizing HPZP and HPZP-Ag coatings, their structures were characterized by nuclear magnetic resonance spectroscopy, scanning electron microscopy, thickness measurement, contact angle detection, mechanical stability testing, and corrosion testing. The cell toxicity of the two coatings to human gingival fibroblasts (hGFs) and human oral keratinocytes (hOKs) was detected by cell counting kit eight assays, and SST, HPZP@SST, and HPZP-Ag@SST were cocultured with Staphylococcus aureus, Escherichia coli, and Streptococcus mutans for 24 hr to detect the antibacterial properties of the coatings, respectively. The results show that the coatings are about 10 μm, and the water contact angle of HPZP coating is significantly higher than that of HPZP-Ag coating (P < 0.01). Both coatings can be uniformly and densely distributed on SST and have good mechanical stability and corrosion resistance. The cell counting test showed that HPZP coating and HPZP-Ag coating were less toxic to cells compared with SST, and the toxicity of HPZP-Ag coating was greater than that of HPZP coating, with the cell survival rate greater than 80% after 72 hr cocultured with hGFs and hOKs. The antibacterial test showed that the number of bacteria on the surface of different materials was ranked from small to large: HPZP@SST < HPZP-Ag@SST < SST and 800 μg/mL HPZP@SST showed a better bactericidal ability than 400 μg/mL after cocultured with S. aureus, E. coli, and S. mutans, respectively (all P < 0.05). The results showed that HPZP coating had a better effect than HPZP-Ag coating, with effective antibacterial and biocompatible properties, which had the potential to be applied in orthodontic process management.

Figure 1

(a) 1H NMR spectrum of SBSi; (b) 1H NMR spectrum of HPSi; (c) SEM images. The coating thickness gradually increases from left to right. The scale was shown in the pictures; (d) WCA of SST, HPZP@SST, and HPZP-Ag@SST. n = 3, each sample is tested three times.

Figure 2

(a) Flowchart of HPZP@SST sample preparation based on tetrahedral wet film preparation process by coating method; (b) SST sample picture; (c) HPZP@SST sample picture.

Figure 3

(a) SEM pictures of HPZP@SST before and after 100 cycles of brushing (100 min in total); (b) SEM pictures of HPZP@SST before and after 9 days of immersion in artificial saliva. The scale was shown in the pictures.

Figure 4

The cytocompatibility of HPZP@SST and HPZP-Ag@SST: (a) cell viability of hGFs treated with different concentrations of HPZP@SST for 24, 48, and 72 hr. n = 5; (b) cell viability of hOKs treated with different concentrations of HPZP@SST for 24, 48, and 72 hr. n = 5; (c) cell viability of hGFs treated with different concentrations of HPZP-Ag@SST for 24, 48, and 72 hr. n = 5; (d) cell viability of hOKs treated with different concentrations of HPZP-Ag@SST for 24, 48, and 72 hr. n = 5. Data are presented as the mean ± SD.  ^∗P < 0.1,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001,  ^∗∗∗∗P < 0.0001 vs. control group.

Figure 5

SEM pictures of HPZP@SST and HPZP-Ag@SST after cocultured with S. aureus, E. coli, and S. mutans for 24 hr. The scale was shown in the pictures.

Figure 6

The antibacterial properties of HPZP@SST: (a) effect of colony formation on S. aureus, E. coli, and S. mutans in plate after treating with different concentrations of HPZP@SST for 24 hr; (b) the bactericidal rate of the HPZP@SST on S. aureus, E. coli, and S. mutans. n = 3. Data are presented as the mean ± SD.  ^∗∗∗P < 0.001,  ^∗∗∗∗P < 0.0001, 800 vs. 400 μg/mL group.