Bacterial infections and their related complications can even lead to the death of patients. With the aim to outstrip the limitations that take place due to drug-resistant pathogens, worldwide researchers focused on the development of unconventional antibacterial strategies [9,19]. Amongst them, nanomaterial-based formulations represent a feasible choice for modern antibacterial agents.
Silver nanoparticles are one of the most promising metal-based bactericidal that have been used in medicine [12]. Silver endows high antibactericidal action even with small dose usage and it is not harmful to human being. Most scientists have attributed inhibition of bacterial cell due to the presence of Ag+ ions upon dissolution of Ag NPs inside or outside the bacterium [12].
There are several application techniques that have recently been used for coating Ag NPs on cotton fabrics. However, it has been recognized that the deposition on textiles is not permanent particularly due to washing processes. Application of binders, cross-linkable polymers and agents have been adopted.
The synthesis of Ag graphed textile via pad coating impregnation method (pad-dry-cure) has been used by many researches via wet chemical or biomass filtrate. Ag NPs are first prepared before padding the textile into NPs colloidal solution, drying and finally curing. The green syntheses of nanoparticles using actinomycetes, fungi, bacteria, algae and plants have better advantages as they are environmentally safe. In 2016, it was reported that cotton fabrics could be treated with a solution containing Tragacanth gum, as a natural polysaccharide polymer, silver nitrate, citric acid (cross-linker) and sodium hypophosphite (catalyst) to prepare a Tragacanth gum/nanosilver hydrogel on cotton fabric [20]. Antibacterial activities were observed, reducing the number of colonies against E. coli and S. aureus ( , run 1).
Searching for advanced functionalization of cotton textiles, Ag NPs were prepared from silver nitrate using the biopolymer dextran as reducing and stabilizing agent and then added to a tetraethoxysilane (TEOS) solution that, after aging, formed a solid Ag@SiO2. These Ag@SiO2 were modified with other silane compounds (vinyltriethoxysilane (VTEOS) or (3-aminopropyl)triethoxysilane (APTEOS). Ag@SiO2 and Ag@SiO2/APTEOS were applied to cotton fabrics using 1,2,3,4-butantetracarboxylic acid (BTCA) as a cross-linking agent and a laboratory paddler as the technique of coating. In addition, the functionalized fabric with Ag@SiO2/VTEOS was treated, using UV irradiation, with 4-benzoyl(benzyl)trimethylammonium chloride (BTC) as initiation for polymerization. The in vitro antibacterial activity of treated cotton fabrics was quantitatively determined against two types of bacteria E. coli and S. aureus. Treated cotton fabrics with Ag NPs have an excellent antibacterial activity. However, the bacterial reduction was decreased with increasing the washing cycle. It has been found that the antibacterial activities of the fabrics treated with Ag@SiO2/VTEOS and with Ag@SiO2/APTEOS have the same values for both E. coli and S. aureus, however Ag@SiO2/VTEOS is the most resistant to washing cycles (Scheme 1, , run 2) [21].
Ibrahim and collaborators have published the treatment of cotton fabrics with a prepared sol by a padded process. Dimethylol dihydroxyethylene (DMDHEU) was added as a cross-linker that reacted with the cotton hydroxylic groups forming cotton-DMDHEU. Simultaneously, a silica sol form was prepared from 3-glicidyloxytrimethoxysilane (GPTMS), which was covalently linked to cotton-DMDHEU by reaction of hydroxylic groups with the epoxides in acid media. Ag NPs were prepared from silver nitrate and carboxymethyl cellulose as reducing and stabilizing agent (Scheme 2). Fabrics were padded twice. Sometimes a fluorinated finishing water repellent agent was added. Then, Ag NPs were added [22]. Antibacterial activity was successfully evaluated against S. aureus and E. coli ( , run 3).
Another process of deposition consisted in immersion of textiles in silver containing solutions. As an example, the group of Seino in 2016, irradiated with a high-energy electron beam an AgNO3-soaked textile. This process induces a reducing reaction forming Ag NPs [23] due to the species generated by radiolysis of water and by the irradiated fabric. The Ag NPs immobilized on the support textiles fabrics exhibited an excellent antibacterial activity across a wide antibacterial spectrum (S. aureus, Klebsiella pneumoniae, MRSA, E. coli, P. aeruginosa, Salmonella enterica and Vibrio parahaemolyticus) ( , run 4).
Recently, there has been an increasing interest in implementing plasma technology, as an eco-friendly physical tool, to modify and activate the surface properties creating new active sites. Conductive polymers can produce conductive surfaces by plasma-assisted coating in the presence of silver nanoparticles introducing antibacterial activity and electrical conductivity. A pre-surface modification of the cotton fabric using N2-plama to create new active binding sites (-NH2 groups) followed by subsequent loading of biosynthesized Ag NPs has been described by Ibrahim [24]. The cellulosic substrate was pre-activated through placing it between the two electrodes of dielectric barrier discharge plasma, using N2 gas. Then, the N2-plasma treated fabric was post-treated with the Ag NPs dispersion, biosynthesized using AgNO3 as precursor and marine bacterial as reductant (Bacillus sp.). Subsequent loading with certain antibiotics was also assayed, such as Ciprofloxacin® and Cefobib®. This post-treatment step was accompanied by a remarkable improvement in the imparted antibacterial activity against S. aureus and E. coli pathogens regardless of the used antibiotic type, which reflects the synergy between Ag NPs and the antibiotic ( , run 5). Moreover, the imparted antibacterial activity against S. aureus and E. coli pathogens was still retained even after 15 washings. Another recent example based on plasma activation of the surface was described by Ahmed and Rehan [25]. The plasma treated cotton fabric samples (glow discharge plasma under atmospheric pressure) were activated and then soaked in a solution of aromatic amine, ammonium acetate and silver nitrate. They report polymerization of the aniline to afford thin films of conductive polymers. Silver nitrate was simultaneously reduced by the aromatic amine to Ag NPs. As expected, polyaniline conductive polymer/AgNPs coated onto plasma cotton fabrics demonstrated improved antibacterial activity compared to polyaniline conductive polymer/cotton samples against E. coli and S. aureus ( , run 6).
We have used functionalized antibiotics derived from Eugenol (Eu), diaminotriarylmethane (TAM) and fluoroquinolone (FQ) as stabilizers to protect Ag NPs (Ag@Antibio). These nanoparticles were prepared mixing a solution of AgNO3 and NaBH4 as reducing agent in the presence of the different selected antibiotics derivatives as stabilizers. Microbicidal activity studies of fabricated cotton textiles coated by impregnation with these Ag@Antibio were performed. Protective ligand layers of Ag NPs resulted to be a deterministic factor in their properties. The best bactericidal activity was obtained for fabric coated with Ag NPs with diaminotriarylmethane derivates (Ag@TAMSH) in surface against S. aureus strain. Intrinsic antibiotic activity and partial positive charge of the ammonium salts of the TAMSH in the surface of the NPs probably enhanced their antimicrobial effects. Fabric coated with Ag NPs with eugenol derivates in surface (Ag@EugenolSH), and fabric coated with Ag NPs embedded in PEG-fluoroquinolone derivatives in surface (Ag@FQPEG), displayed antibacterial activity for both S. aureus and P. aeruginosa strains [26] (Scheme 3, , run 7).
Another interesting example of impregnation of Ag NPs onto a fabric surface by dipping is due to He’s group [27]. The cotton fabric was first padded with a solution of carboxymethylchitosan and then soaked in a solution of silver nitrate and black rice extracts (reductant). The Ag(I) is coordinated with the donating groups of chitosan (-OH and -NH2) and anthocyanines metabolites reduce this Ag(I) to Ag(0). This novel method imparted cotton fabric with excellent antibacterial ability against E. coli and S. aureus (Scheme 4, , run 8).
Sonochemical preparation provides a facile approach to produce spherical metal nanoparticles. Ultrasonic irradiation of water generates highly reactive H and OH radicals, which are responsible for redox chemistry. Baytekin’s group prepared cotton Ag NPs composites via ultrasonication. Fabric-metal composites were prepared dipping cellulose samples on AgNO3 solutions in water. The formation of radicals from water during the sonication of cellulose has been determined by ESR studies. Ag NPs loaded on the fabrics inhibited the growth of E. coli and B. subtilis, yet they were more potent against E. coli in comparison to B. subtilis [28] ( , run 9).
Aerosols of silver nanoparticles were produced by means of electrical discharges between two electrodes in nitrogen and passed through fabrics were particles are retained. High purity silver electrodes were used. The antibacterial activity of the fabrics coated with silver nanoparticles were studied with success against S. aureus and Klebsiella pneumoniae [29] ( , run 10).
In addition to silver, there are other metals of interest that have been studied. Among them, copper. Aerosols of copper were produced by means of electrical discharge in nitrogen and passed through fabrics were particles are retained, in the same conditions that Ag NPs. The antibacterial activity of cotton samples with copper NPs was assessed against S. aureus and Klebsiella pneumoniae in compliance, obtaining only acceptable antibacterial results [29].
In addition, gold has attracted special interest due to the Zheng et al. [30] suggestion that Au NPs coated on fabric possess UV protection and antibacterial properties. A greener synthesis of gold nanoparticles was successfully done by reducing HAuCl4.3H2O using Coleus aromaticus leaf extract. These stabilized Au NPs were coated on pre-treated cotton fabrics by simple pad-dry-cure method. The Au NPs coated fabrics exhibited remarkable antibacterial sensivity against S. aureus and E. coli. Further they showed cytotoxicity against human liver cancer (HEpG2) cell line [31]. More recently, the same group of research have synthesized phyto-engineered Au NPs from the aqueous extract of Acalypha indica. An equal quantity of Acalypha indica leaf extract and of HAuCl4.3H2O buffer solution (pH 7) were taken in an Erlenmeyer flask. The intact extract was appropriately coated to the cotton fabric employing a pad-dry-cure procedure. The gold nanoparticle-coated cotton fabric was evaluated for the antibacterial activity against S. epidermidis and E. coli bacterial strains, which revealed remarkable inhibition [32].
To enhance the properties of individual M NPs the generation and study of binary and tertiary nanoparticles has been developed. In 2018, bimetallic nanoparticles were generated in cotton fabrics using Aloe vera extract as reducing agent. Aqueous solutions of mixtures of AgNO3 and CuSO4.5H2O were first prepared and then the cotton fabrics with infused Aloe vera leaf extracts (matrix) were kept in these metallic source solutions and stirred. The nanocomposite cotton fabrics show good antibacterial activity for E. coli, Pseudomonas, Bacillus, Klebsiella and Staphylococcus cultures [33]. In addition, Mahesh [34] described the reduction of CuSO4.5H2O and AgNO3 with red sand extracts. The flavonoids and sugars of these extracts act as reducing agents and other constituents as capping agents. The cotton fabrics were dipped in the solution of the red sanders extracts and these matrices were then used to generate nanoparticles. Silver and copper nanoparticles and silver-copper bimetallic nanoparticles were prepared for comparison of antibacterial activity. Bimetallic nanoparticles generated in cotton fabrics exhibited higher activity against Gram negative (E. coli and P. aeruginosa) and Gram-positive (S. aureus and B. lichinomonas) strains.
Recently, hyperbranched poly(amide-amine) (HBPAA) was used to encapsulate M NPs showing a good protective ability to prevent agglomeration and oxidation. AgNO3, HAuCl4 and H2PtCl6 were reduced by NaBH4 to metal NPs in the presence of the mentioned polymer. Then fibers of cotton were impregnated to produce monolayered Ag-Au-Pt coated fabrics probably due to electrostatic repulsion among positively charged NPs. Furthermore, the combination of Ag, Au, Pt nanoparticles ( ) yields a positive potential and could aid in the self-assembly to cotton upon surface capping with HBPAA. Moreover, the authors [35] infer that different metal NPs capped with the same functional polymer may inherit the chemical characteristics of the latter. High antibacterial activities were found against E. coli and P. aeruginosa.
Open in a separate windowThe antibacterial activity of metal oxides is believed to be a consequence of their dissolution into metal ions, which can be cytotoxic to bacteria. Furthermore, as we have seen for M NPs the growth of metal oxide nanoparticles in an eco-friendly manner by plant materials has attracted significant attention.
In 2017, ZnO NPs were prepared from Zn(AcO)2.2H2O using aqueous leaf extract of Cardiospermum halicacabum. The antimicrobial properties of ZnO nanoparticles coated on cotton fabrics against clinical isolates E. coli and S. aureus were evaluated [36]. Losego’s group, in 2019, examined the atomic layer deposition (ALD) of ZnO films onto cotton fabrics to control bacteria spread. ALD is a well-known technique for thin-film deposition in which vapor phase-precursors are sequentially delivered to a substrate and undergo self-limiting surface reactions, depositing a film ‘‘atomic-layer-by-atomic-layer’’. Curiously enough, at low ZnO loading, bacteria could metabolize Zn2+ ions and reproduced more rapidly. However, they found that increasing the thickness of the ZnO film, the nanocoating became an effective biocide material with a complete eradication of all E. coli bacteria present [37].
Moreover, aiming the preparation of bleached cotton khadi fabrics (handloom woven from handspun yarns) with UV protection and antimicrobial properties, different amounts of ZnO NPs were dispersed in poly-hydroxy-amino methyl silicone (PHAMS) and applied to these fabrics using the pad-dry-cure method [38]. This method will give rise to this modified cotton by a single-step treatment. First, the ZnO NPs were prepared by a co-precipitation method and then dispersed in poly-hydroxy-amino methyl silicone. By varying dosages of ZnO NPs (1–5%) dispersed in the PHAMS binder media (2–10%), the authors found that with 1% of ZnO NPs and 4% of PHAMS the modified materials led to an UV protection factor of 10 and 93–95% of microbial reduction (against S. aureus and K. pneumoniae). This metal combination did not provide antifungal properties. Better UV protection (factor of 20) and microbial reduction (99%) were obtained keeping the amount of PHAMS and increasing the amount of ZnO NPs up to 5%. The microbicide activity is reduced upon 96% and UV protection factor is reduced at 15 after five cycle washes. Finally, this modified bleached cotton khadi fabric is in consonance with the commercially available UV absorber 2-hydroxy-benzotriazole in terms of UV protection.
Another approach, reported by Belay, to prepare zinc oxide nanoparticles used ZnCl2 and NaOH aqueous solution. The particles were peptized with 2-propanol at room temperature to disrupt microagglomerates. Finally, the prepared particles were treated thermally in the oven for 5 h at 250 °C, which leads to the formation of ZnO NPs. For the application of NPs on cotton fabrics, the cotton sample was immersed into the dispersion of ZnO NPs. Another preparation reported in the same article consisted on the in situ deposition immersing the fabric in a solution of Zn(NO3)2.6H2O. Afterwards, NH4Cl, urea and ammonia solution were added to the reaction vessel. The system was heated to 90 °C and kept for 60 m. After the reaction was completed, the fabric was rinsed several times using distilled water and finally, it was kept in the oven at 150 °C to ensure particles’ adhesion to the fibers’ surface. The ZnO NPs synthesized by the two methods possess very good bacteriostatic activity against S. aureus and E. coli bacteria [39].
Recently, copper oxide nanoparticles have gained significant importance due to their distinctive properties (applications in batteries, catalysis, gas sensors and in electrical, optical and solar energy exchange tools), including that they are cheaper than other metal oxides. To reduce the risk of toxicity, Ruellia tuberosa aqueous extract was used for the synthesis of CuO NPs in a study reported in 2019 [40]. The fabrics were then treated with green synthesized CuO NPs and were allowed to dry at 50 °C for 30 min. Cotton fabrics showed bactericidal activity against clinical pathogens such as S. aureus, E. coli and Klebsiella pneumoniae.
In a 2016 paper, Gedanken described the simultaneous deposition on cotton fabrics of Reactive Orange 16 (RO16) or Reactive Black 5 (RB5) with antibacterial CuO or ZnO nanoparticles from an aqueous solution. The solution contained both the dye and the corresponding M(OAc)2 (M = Zn or Cu) precursor, which undergoes hydrolysis under alkaline conditions (ammonia) to form ZnO or CuO. The cotton was colored with the dye and showed good antibacterial properties [41].
In addition, Manteccas’s group reported the coating of ZnO or CuO NPs on fabric surfaces using the roll to roll sonochemical installation. They observed solvent as one of the factors that influenced the shape and size of the sonochemically produced metal oxide NPs. The synthesis of NPs and the coating of textiles were carried out with water, which is the safer solvent in industry, as well as with a mixture of ethanol/water. Ethanol/water mixture gave less NPs leaching. Copper/zinc acetates solutions were first heated by the ultrasonic transducers, and after a temperature of 60 °C was reached, an aqueous solution of ammonium hydroxide was injected into the reaction cell to adjust the pH to ∼8.0. At the end of the reaction, a change of the color of the fabric from white to brown was observed in the case of CuO NPs, whereas, for ZnO NPs, it remained white (ZnO NPs are a white solid). Antibacterial tests revealed that, in the case of CuO NPs coated bandages in both water and ethanol, the complete killing of both S. aureus and E. coli bacteria was observed, ZnO NPs-coated bandages in water or ethanol were less effective [42].
With the goal of preparing multifunctional fabrics Ibrahim et al. searched appropriate finishing formulations. The fabrics were paddled with 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU) as crosslinking agent, MgCl2/citric acid as catalyst, silicone softener, UV-absorber, flame retardant and a commercial antibacterial cationic agent based on a silver compound (HEIQ®, Huntsman, city, Maple Shade, NJ, USA). Then embedding of the MO NPs (nano-metal oxides were of commercial grades) gave the next descending order results regarding antibacterial function: ZnO–NPs > TiO2–NPs > ZrO–NPs > control >> untreated [43]. Other finishing dispersions were prepared by the same group of research. In this case Chitosan (Cs) and various metal oxide nanoparticles namely ZnO, TiO2 and SiO2 were paddled onto fabric surface using citric acid/sodium hypophosphite for ester–crosslinking and creating new anchoring and binding sites, COOH groups, onto the ester-crosslinked fabrics surface. On the other hand, the extent of improvement in the aforementioned functional properties is governed by the type of nano metal oxide and follows the descending order: Cs/TiO2 NPs > Cs-ZnO NPs > Cs/SiO2 NPs > Cs alone. As a conclusion, among the used Cs/MO’sNPs hybrids, Cs/TiO2 NPs composite showed the highest photocatalytic and antibacterial activity [44] ( ).
Open in a separate windowIn 2019, fabrics were coated with commercial ZnO NPs, ZrO2 NPs, antibiotics namely doxymycin, cefadroxil and ciprofloxacin, individually and combined, in the presence of citric acid and sodium hypophosphite as a crosslinking agent and a catalyst, respectively. The results obtained signified that the antibacterial activity improved significantly and followed the decreasing order: antibiotic/MO NPs > antibiotic > MO NPs Among the used composites, doxymycin/ZnO NPs showed the highest antibacterial efficiency [45].
Among the metal oxides, titanium dioxide has become the benchmark for promising applications such as antibacterial agent [43]. The coating dispersion treated on textile fibers based on TiO2 NPs and ZnO NPs were prepared through uniform dispersion of nanoparticles in binder MTP acrylate solution by ultrasonication. It was observed the superiority of TiO2 NPs as antibacterial agent over ZnO NPs (against S. aureus bacteria). Interestingly, when equal mass ratio of TiO2 NPs and ZnO NPs was used, the antagonistic effect was observed in the antibacterial effect as the inhibition zone was recorded [46].
Inorganic bacterial agents are usually photocatalytic metal oxides that generally belong to semiconductor compounds. Among them, ZnO attract the most attention because its excellent biocompatibility. However, the photocatalytic antibacterial performance of ZnO can be reduced because of the high recombination rate of electron-hole pair. Moreover, the excitation light of ZnO is in ultraviolet region, which means the low utilization of daylight. One of the ways to overcome these problems and promote the photocatalytic antibacterial activity of ZnO, is doping with noble metal. On the other hand, Ag NPs are a gold standard bacteriostatic agent. Thus, El-Naggar and collaborators enhance the antibacterial activity of ZnO due to synergic charge transfer. Tri-component nanoparticles, silver, copper and zinc oxide, have been deposited onto the cotton textile surface imparting durable antibacterial activity, UV protection and conductivity properties. The chemical synthesis of these metal and metal oxide nanoparticles has been performed using a polymethylol and functionalized polyethylenimine compounds (Scheme 5) [47].
Quaternary ammonium salts are widely used in cationic polymers-based antibacterial textiles; thus, they can kill bacteria by contact mechanism [3]. In a 2020 report from Gao, Ag/ZnO nanoparticles were prepared from commercial ZnO NPs in the presence of 3-aminopropyltriethoxysilane, AgNO3 and trisodium citrate solution as reductant and stabilizer. Then an organic-inorganic hybrid was synthetized by radical polymerization of diallyldimethyl ammonium chloride and an acyloxy silane as coupling agent to form a pyrrolidinium based polymer. Ag/ZnO nanoparticles were incorporated to this mixture. The cotton samples were immersed in the dispersion solution for paddling. Antibacterial activity (S. aureus and E. coli), durability, hydrophilicity and air permeability were studied [48].
Recently cotton fabrics were coated with Ag, TiO2 and ZnO nanoparticles. Ag NPs were synthesized from AgNO3 with trisodium citrate, whereas TiO2 nanoparticles were prepared mixing TiCl4 and ammonium carbonate. Finally, ZnO NPs were obtained from ZnCl2 and sodium hydroxide. In order to decorate the cotton fabrics with the synthesized nanoparticles, the cotton fabrics were first immersed in the beaker containing a polyurethane solution. After that, the fabrics were immediately immersed in the solution containing ZnO nanoparticles and then in the beaker containing TiO2 nanoparticles. This process was repeated with the beaker containing Ag NPs solution. The optimum photocatalytic and antibacterial activities (Salmonella typhi and Shigella) were observed in the decorated fabrics with Ag, ZnO and TiO2 [49].
Another approach to obtain antibacterial cotton fabrics was the anchoring of metallic silver nanoparticles decorated with bismuth oxybromide (BiOBr) nanosheets on carboxymethyl cotton fabric. To facilitate the nucleation of BiOBr, cotton fabric was modified through SN2 reaction of hydroxylic groups with chloroacetic acid using NaOH as base to yield the sodium carboxylates (caboxymethyl cotton fabrics, CCF). When this fabric was immersed in a Bi(NO3)3 solution, Bi2O2+ ions were absorbed by the carboxyl groups. Immersion in a KBr solution induced bromide ions to react with Bi2O2+ forming BiOBr-CCF. Silver ions from AgNO3 were absorbed by BiOBr-CCF and reduced via exposure to ultraviolet irradiation. This Ag/BiOBr-CCF can effectively photodegradate rhodamine B and herbicide isoproturon in response to irradiation when placing them into solutions of these organic pollutants. Furthermore, they showed bacteriostatic effects against E coli and S. aureus [50].
Ibrahim and coworkers reported the use of Streptomices sp, a marine bacterial, as reducing and stabilizing agent for the biosynthesis of Au NPs. After modification of cotton fabrics with O2-plasma the fabrics were coated with Au NPs/ZnO NPs combination. This combination gave high antibacterial activity (S. aureus and E. coli) and durability (textiles were active after 15 washings) [51].
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