A facile strategy for the construction of TiO₂/Ag nanohybrid-based polyethylene nanocomposite for antimicrobial applications

Highlights

• TiO${}_2$ and Ag nanoparticles were used to prepare TiO${}_2$/Ag nanohybrid.

• The PE–TiO${}_2$/Ag nanocomposite was successfully constructed by facile melt mixing strategy.

• The results showed that the TiO2/Ag nanohybrid completely dispersed into the PE-matrix.

• Strong antimicrobial activities were investigated by PE–TiO${}_2$/Ag nanocomposite.

Abstract

This work aims to explore the antibacterial activity of PE–TiO₂/Ag nanocomposites. Rutil-TiO₂/Ag hybrid nanoparticles (the content of 0.2–0.6 wt%) were introduced into the PE matrix under melt mixing process. The TEM images for the ultra-thin section (about 80 nm thick) of nanocomposite showed that TiO₂/Ag hybrid nanoparticles were well dispersed into the PE matrix. Moreover, mechanical tests indicated that the tensile property of PE was slightly reduced in the presence of hybrid nanoparticles due to the low contents of nanofillers. Besides, the antibacterial tests revealed that the nanocomposites displayed a potent bactericidal efficiency against both E. coli and S. aureus bacteria (i.e. 1.83 log and 1.9 log after 24 h, respectively). The developed fabrication technique and delivered results of the TiO₂/Ag nanohybrid-based PE nanocomposite enable a promising avenue to design and construct the advanced nanostructured hybrid materials for potential antimicrobial applications.

Introduction

Incorporation of antibacterial agents into neat materials is a common approach to produce antibacterial nanoplatforms with novel and multifunctional properties. Recently, nanoparticles have been regarded as the most effective and promising alternatives to antibiotics against antibiotic-resistant bacteria and viruses [1], [2], [3], [4], as compared to traditional antibiotics. Due to their higher surface area to volume ratio, the metal nanoparticles offer improved antimicrobial activity [5], [6] and employed in various fields i.e. food packaging and bioimplants [7], [8]. Several types of nanoparticles such as AlNPs [9], [10], ZnNPs [11], [12], [13], [14], MnNPs [15], TiNPs [16], [17], [18], AgNPs [19], [20], [21], [22], CuNPs [23], [24], [25], and AuNPs [26], [27], etc have been used as antimicrobial and antibacterial agents. Among the current nanoparticles for antibacterial application, nano-titanium dioxide (TiO₂) and silver nanoparticles (AgNPs) are one of the most typical and efficient nanostructured materials [7], [8], [28]. To destroy the bacteria, nano-TiO${}_2$ reacts mainly by the photocatalytic mechanism (formation of reactive oxygen species — ROS) under UV or visible light irradiation [29], [30], [31], [32]. Their anatase form exhibited much higher antibacterial activity than the rutile counterpart due to the superior photocatalytic activity through the more elevated surface adsorption capacity and lower charge carrier recombination rate [33], [34], [35]. On the other hand, AgNPs have been widely used for antibacterial applications in many commercial products, such as plastic, textile, cosmetics, painting, air filter, etc. These nanoparticles could inhibit the growth of broad-spectrum bacterial pathogens by destroying via various mechanisms, such as ROS production (deterioration of DNA/RNA/proteins), direct contact (destruction of cell wall/peptidoglycan layer), the release of toxic ions, destruction of protons efflux bombs and reduction of adenosine triphosphate production [36], [37], [38].

Hybridization of two typical nanoparticles is a new approach to engineer hybrid nanosystems at a lower quantity of nanoparticles under both visible light radiation and darkness [39]. In this direction, we have successfully synthesized the AgNPs decorated TiO₂- and ZnO nanohybrid system ($\sim$60 nm/$\sim$5 nm TiO₂/Ag nanohybrids) [39]. The antibacterial test indicated that nanohybrids could destroy Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) effectively in dark or under visible light irradiation. At the low quantity (40 mg/mL), these nanohybrids showed higher inhibition zones under light irradiation than that in the dark. Hybridization with AgNPs enhanced the photocatalytic activity of TiO₂, especially in the visible light. To control the solubility and toxicity of AgNPs, TiO₂ could also act as the supporting material for AgNPs for reducing their aggregation and required effective amount [3].

Regarding antibacterial, the polyethylene (PE) is generally been used due to its resistance to various chemicals and fatigue, excellent sealing and hydrophobic nature, as well as low friction coefficient. Furthermore, as compared to other polymers, PE is relatively inexpensive and typically known as a medical polymer. However, PE usually shows insufficient biocompatibility and bioactivity, as well as prone to infections, therefore, its additional treatment and/or modification is imperative to make it microbial with the addition of nanoparticles [40], [41], [42]. In addition, with the help of PE and nanoparticles, the active protective packaging films are produced, which could completely overcome or inhibit the growth of microorganisms [43], [44]. Recently, our group has fabricated antibacterial PE/Ag [45], [46], and PE–Ag/Fe₃O₄ nanocomposites for various biological activities [47]. Various other works also been reported the antibacterial PE/TiO₂ nanocomposites using both the TiO₂ rutile phase [48] and the TiO₂ anatase phase [49]. Besides, the photo-degradation of PE/anatase-TiO₂ nanocomposites under solar irradiation has also been reported elsewhere [50]. Herein, the current study aims to fabricate the effective antibacterial PE–TiO₂/AgNPs nanocomposite by cost-effective and large-scale strategy, using nano-TiO₂ (rutile)/Ag based hybrid nanoparticles as the new substantial antibacterial agents. We believe our strategy will open a new avenue to design advanced type of nanostructured materials for variety of antimicrobial and bio-related applications.