Silver (Ag) has broad-spectrum antibacterial properties and is widely used in various fields, including in antibacterial coatings for orthopedic implants. For reasons of cost and cytotoxicity, improvement of the antibacterial efficiency of Ag is necessary. The scientific community has also shown a strong enthusiasm in this research area. In this paper, ZnO nanorod arrays were prepared on a titanium (Ti) substrate by seed-assisted hydrothermal method and Ag nanoparticles were deposited by magnetron sputtering to obtain Ag nanoparticle-decorated ZnO nanorod arrays (ZnO nanorods/Ag nanoparticles). The antibacterial properties of ZnO nanorods/Ag nanoparticles against Pseudomonas aeruginosa were systematically studied by agar diffusion method and were compared with other samples such as ZnO nanorod arrays and ZnO seed layer/Ag nanoparticles. The experimental results showed that ZnO nanorods/Ag nanoparticles displayed significantly higher antibacterial properties against Pseudomonas aeruginosa than other samples, including ZnO nanorod arrays and ZnO seed layer/Ag nanoparticles. These superior antibacterial properties originated predominantly from the morphological structure of ZnO nanorods, which optimized the particle size and distribution of Ag nanoparticles, greatly improving their antimicrobial efficiency. The synergistic antibacterial properties of Ag nanoparticles and ZnO nanorods make Ag nanoparticle-decorated ZnO nanorod arrays a promising candidate for antibacterial coating of orthopedic implants.
In orthopedics, implant-related postoperative infection is a serious complication with a high incidence rate of 1%-4% [
Silver (Ag) nanoparticles have broad-spectrum antibacterial activities and good inhibitory effects on Gram-positive and Gram-negative bacteria, fungi, virus, and cancer cells [
In this study, ZnO nanorod arrays were fabricated on Ti wafer by a modified seed-assisted hydrothermal method [
The ZnO seed layer was fabricated on
Two types of ZnO nanorods were hydrothermally prepared on the ZnO seed layer with zinc nitrate (Zn(NO3)2)·(6H2O, 99%, Sinopharm) and hexamethylenetetramine (HMT) (C6H12N4, 99%, Aladdin) as precursors. The first type of nanorods was synthesized by warming 50 mL each of 0.1 M Zn(NO3)2 and HMT at 90°C for 0.5 h and mixing the two solutions in a 130 mL glass bottle. The Ti/seed layer sample was immersed in this mixture, and the glass bottle was sealed. After reacting for 3 h at 90°C, the sample was washed with deionized water and anhydrous ethanol. This Ti/ZnO nanorod sample was named “SG,” in which the amount of ZnO was approximately 500
Ag nanoparticles were deposited on the two types of ZnO nanorod arrays by radio frequency (RF) magnetron sputtering at room temperature. An RF power of 70 W was used for deposition. The deposition process took place at an argon flow rate of 40 sccm and working pressure of 1 Pa for 30 s. The amount of silver deposited was about 13
The structural properties of the resultant samples were investigated using an X-ray diffractometer (XRD) (PANalytical, X’Pert Pro) with Cu K
To study in depth the antibacterial properties of ZnO nanorods/Ag nanoparticles, tests were also performed on Ti wafer, hereafter referred to as SA, Ti/Ag nanoparticles (SB), Ti/ZnO seed layer (SC), Ti/ZnO seed layer/Ag nanoparticles (SD), and Ti/ZnO nanorods (SG). The ZnO seed layers and Ag nanoparticles were prepared in the same manner in all samples.
Our antibacterial activity test has been approved by the ISO15189 procedure. The antibacterial effectiveness of the samples was studied by agar diffusion [
The crystal structure of the samples was first characterized by XRD to prove the successful preparation of ZnO nanorods/Ag nanoparticles. Highly similar XRD spectra were obtained on the ZnO nanorods/Ag nanoparticles samples. As shown in the XRD spectrum of the SF sample in Figure
X-ray diffraction spectrum of the ZnO nanorod/Ag nanoparticle (SF) sample. The peaks marked with an asterisk are associated with the titanium alloy plate.
In addition, additional flat and broad peaks appeared at
The SEM images of ZnO nanorod/Ag nanoparticle samples are displayed in Figure
Scanning electron microscopy images of the SF (a, b) and SE (c, d) samples.
Figure
Atomic force microscopy image of the SD sample.
The antimicrobial activity of the samples was determined by the size of the Pseudomonas aeruginosa inhibition zone formed. Figure
The size of the inhibition zone of Pseudomonas aeruginosa after 24 h of culture.
In the N2 medium, noticeable bacterial inhibition zones were formed around the SE, SF, and SG samples. The inhibition zone formed by SG (ZnO nanorods) was smaller and had a diameter of 11.5 mm, while those by SE and SF (two ZnO nanorod/Ag nanoparticle samples) were larger and had diameters of 13.1 mm and 13.2 mm, respectively. The antibacterial properties of ZnO and Ag were then studied in depth by comparing the antibacterial actions of different samples. First, the antibacterial properties of SG (ZnO nanorods) were similar to those of SD (ZnO seed layer/Ag nanoparticles). The amount of ZnO in the SG sample was about 500
Figure
The inhibition zone test of the SD, SE, SF, and SG samples at different times.
In summary, ZnO nanorods/Ag nanoparticles were prepared on a Ti substrate using both gas- and liquid-phase methods. Their excellent synergic antibacterial properties were confirmed with Pseudomonas aeruginosa as the target. Comparison with other samples was also carried out as verification. Although ZnO nanorods alone also have some antibacterial effects, the superiority of ZnO nanorods/Ag nanoparticles in this respect was mainly derived from the morphological structure of ZnO nanorods, which optimized the size and distribution of Ag nanoparticles and greatly enhanced their antibacterial efficacy. Improving the antibacterial efficiency of Ag nanoparticles reduces the cytotoxicity induced by high dosage of Ag and lowers the cost of antibacterial coating. Because of its synergic antibacterial activity, this type of ZnO nanorod/Ag nanoparticle material will have broad usage prospects as antibacterial coatings on orthopedic implants. In addition, this work provides a novel route for the synthesis of Ag-based coatings with higher antibacterial efficiency.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
This work was financially supported by the Science and Technology Research Project of Heilongjiang Provincial Education Department (12541344).