Biocidal effect and durability of nano-TiO₂ coated textiles to combat hospital acquired infections

Abstract

While antimicrobial textiles have received considerable interest and attention from both the scientific community and general consumers, there have been very few studies investigating the durability of such antimicrobial activities. In this study, we describe the modification of the surface of textiles that were modified with commercially available titanium dioxide (TiO₂) powder (P25 Aeroxide®, Degussa™) using a sonochemical technique. The antibacterial activity of TiO₂ can improve textile quality and effectively reduce the rate of infections acquired in hospitals. Medical garments produced from such fabrics may improve the patient's recovery and revolutionize the textile market. This modification imparts biocidal properties to these textiles, which were then optimized to acquire properties of the textile. Samples were washed for 30 cycles at three different temperatures (40 °C, 60 °C and 90 °C) to test the durability of the bonding of the nanoparticles to textiles and the effectiveness was examined with respect to their antimicrobial activity against hospital pathogens: Escherichia coli, MRSA and Candida albicans. Sample's surfaces were examined by a Scanning Electron Microscope equipped with Energy Dispersive X-ray Spectroscopy (SEM/EDS) for surface imaging. Atomic Absorption Spectrometry (AAS) was used as a technique to quantify the Ti present on the fabric. The best durability of TiO₂ on textiles was best retained after washing at 40 °C. From an environmental point of view, the release of nanomaterial from textiles was acceptable against currently available benchmarks. We have investigated the adhesion of nanoparticles (NPs) to the textile surface. Medical garments, bed linens and upholstery produced from such fabrics may improve hospital hygiene against antibiotic resistant superbugs and help reduce hospital acquired infections.

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1. Introduction

Due to antibiotic resistance, common infection type bacteria, nosocomial, or the so called hospital-acquired infections (HAI) are on the rise. It has been reported that 10% of patients are infected in the hospital due to HAI.¹ There are many examples of bacteria species which are the source of HAI, but methicillin resistant Staphylococcus aureus (MRSA) is commonly the most difficult microbe to treat by common antibiotics.² Hygiene practices such as washing hands³ have received only a limited success in restricting the spread of such HAI's, as the reduction of the prevalence of such infections is difficult.⁴ The pathways and risk factors of bacteria transmission include infection via medical devices by catheters, sensors, but also contact between personnel, patients, and contact with contaminated surfaces in the operation theatre (handles, platforms, panels), and transfer by medical garments, bedclothes, and curtains.^5,6 Antibacterial textiles that can kill pathogenic microorganisms will ipso facto reduce the occurrence of hospital acquired infections (HAI).⁷

Antibacterial NPs can be used as active biocidal agents to impart antimicrobial properties in textiles.⁶ NPs are finding applications in fields that range from cosmetics to electronics.⁸ There are several types of NP that can potentially be used as killing agents for microbes: zinc oxide (ZnO), carbon nanotubes (CNT), copper (Cu) and copper oxide (CuO), silver (Ag) materials and titanium dioxide (TiO₂).^9–11 On the other hand, there are several commercially available antimicrobials for textile applications including triclosan, ammonium compounds, zinc pyrithione and, recently, silver and nanosilver.^12,13

Among these possible biocidal agents, the main advantage of nano-TiO₂ is the ability to produce reactive oxygen species (ROS) as a result of photo-activated reactions.^14–17 The ROS produced after absorption of radiation from the UV range give titania its antimicrobial activity.^18–20 This property of titania nanomaterials can be exploited to improve the properties of a textile surface.

In the last decade, there have been many examples of the improvement of quality and potential functions where fabrics benefit from nanotechnology to produce breathable, waterproof, and flame-resistant textiles.^21,22 Various methods have been used to add nanomaterials to textiles, including: dip-coating;^23–25 pad-dry-cure method;^26–28 and methods involving plasma modification.^29–31 Among these methods, it was reported that NP's can be incorporated into textile surfaces through a sonochemical process. Efficiency of this method arises from acoustic cavitation: formation and collapse of bubbles. It has been extensively developed and published by Perelshtein, Abramov and Gedanken.^32–35 It was proven that there was an antibacterial effect of CuO and ZnO against several bacteria species on textiles modified using a sonochemical technique. Ultrasonic modification of textiles was lately published by Montazer³⁶ to photo bleach wool surface.

Here we impart a biocidal activity onto textiles by modifying them with commercially available NPs of titania using a sonochemical technique (dip coating with simultaneous ultrasonic treatment). We then investigated the durability, adhesion and biocidal activity of these fabrics.

Efficient durability of NPs impregnated fabrics is an important characteristic of washable and reusable antimicrobial textile articles.³⁷ Surprisingly, this characteristic of reusable antimicrobial textiles has been overlooked in the literature. The durability and adhesion of NPs to textiles are significant issues related to workers and consumer safety from potential hazards of exposure to NPs.³⁸ Standard methods for testing durability based on colour fastness analysis using appropriate greyscale³⁹ or spectroscopy in UV-Vis spectral range.⁴⁰ As antimicrobial properties of NPs treated textiles originate from the presence of the NPs on the textile surface, the durability of NPs adhesion to textiles also signifies the durability of the antimicrobial properties. Assessing from an environmental standpoint, colour fastness tests using washing procedures can examine the strength of adhesion as well as the potential effluence of NPs in a waste water stream. In this study, we have also tested the adhesion of NPs by using a modified coating adhesion test. The durability and efficacy of the sonochemical treatment of textiles were then tested against Gram positive bacteria, Gram negative bacteria and fungi using standardized antimicrobial test procedures for textiles. Such investigations have allowed us to test the biocidal effect of textiles against a full spectrum of common microbes and were therefore helpful to examine the general broad spectrum antimicrobial activity of these textiles.

2. Materials and methods

2.1. Preparation of TiO₂ nanoparticles with PET textiles

For this study, 100% polyethylene terephthalate (PET) textile was used (50 g m⁻², 130/130 warp/weft density). The SEM pictures of textiles are presented on Fig. 1. A single fibre is of 20 μm diameter and the thread diameter is ∼100 μm. To remove impurities from the textile surface, samples were pre-treated in acetone (acetone pure p.a. 99.5% Polish Chemical Reagents) for 10 min on a magnetic stirrer (3000 rpm) and dried at a temperature of 70 °C in the laboratory oven (Pol-Eko, SLW STP 53).

Fig. 1 SEM pictures of polyester textiles.

Textiles were impregnated in a water sol of TiO₂ (5 g l⁻¹) of commercially available P25 powder (Aeroxide® P25 Degussa Evonik).⁴¹ Solution was mixed for 1 hour using a magnetic stirrer. Textile samples were dip-coated in TiO₂ solution, and then heated to 50 °C and sonicated for 5 min in an ultrasonic washer (InterSonic IS-1K). The samples were then dried at 70 °C (Pol-Eko, SLW STP 53).

2.2. Durability testing method

Standard methods of testing durability of textiles are listed in AATCC Test Method 61-2013 (ref. 39) and ISO 105-C06:2010.⁴² The colorfastness tests are accelerated methods used to evaluate loosing of color of textiles which are expected to withstand frequent laundering. One such test takes about 45 min and the action (detergent solution and abrasive action) represents that of five typical home launderings. In our approach, washing of textiles was performed at washing temperature settings of: 40 °C, 60 °C and 90 °C. A magnetic stirrer was used to agitate the wash water, using a heating setup and thermocouple to provide and monitor the water temperature. A 400 ml volume of distilled water was heated to a set temperature, and the magnetic stirrer motor was set at 3000 rpm, where the textile samples were immersed for 10 min. This washing procedure was a simplified washing method, using laboratory-available equipment, which we have used to study the impact of temperature on NPs retention. This washing is equivalent to one domestic cycle of washing. After this process, the textiles were dried at 70 °C. The washing procedure was performed for a maximum of 30 cycles.

2.3. Atomic absorption spectrometry

The concentration of Ti on textiles was determined by using atomic absorption spectrometry using a modified version of ASTM 4563-02.⁴³ Textiles were analyzed using a Spectra AA 200 Spectrometer fitted with a hallow cathode lamp containing a Ti element with a wavelength of 364.3 nm. Textiles were cut into 16 cm² square-shaped samples, and transferred to 50 ml flasks, where they were dissolved in hydrofluoric acid (HF) 48% AR supplied by Scientific & Chemical Supplies Ltd. and then rinsed in distilled water. The concentration of Ti was quantified by AAS in an airy acetylene and nitrous oxide flame using an aqueous standard calibration curve. The Ti standard used for the examination was purchased from Inorganic Ventures.

2.4. Adhesion assessment

The adhesion of a nanomaterial to a textile surface, and the durability of immobilization of the NPs have been significantly researched as important issues regarding the release of nanomaterials into the environment. The adhesive strength was examined using a modified pull-off method according to ASTM D4541.⁴⁴ The quantity of titania remaining on the sample surfaces was measured using low magnification Energy Dispersive Spectroscopy (EDS).

2.4.1. Coating durability by pull-off test. The adhesive strength of NPs binding to the fibres' surfaces was examined, where the maximum tensile strength applied by a direct load which is perpendicular to the textile surface was assessed.⁴⁵ The tensile load was applied by positioning a pull-head plate that which was adhered to the textile testing area. In the presented standardized method ASTM D4541,⁴⁴ the pull-off stress was measured by a digital PosiTest® AT-A adhesion tester (DeFelsco Company), and by positioning of a dolly that was layered with an adhesive. In this research, the pull-off rate was set at 0.20 MPa s⁻¹. A dolly (d = 20 mm) was first layered with a double-sided adhesive-tape, and then layered with a single-sided adhesive-tape. The dolly was positioned on the textile surface, and the tensile strength was applied to the dolly by an automatic adhesion tester. The recorded data from the PosiTest® AT-A was displayed as stress (MPa), and for the purpose of this analysis the data was converted to force (N). The adhesive-tape that was removed during the pull-off test, and the textile surface from where the dolly was removed, were analyzed using SEM/EDX.

2.4.2. Surface characterization by scanning electron microscopy (SEM). Surface topography of the modified textile was examined using a SEM (Hitachi SU70) fitted with an EDS detector (Joel, Oxford Instruments). Textile samples were positioned on the sample holder by double sided adhesive tape (Agar Scientific). A gold coating (10 nm thickness) was sputtered on the textile surface using a High Vacuum Sputter (Emitech K550), providing optimal conductivity of the sample during analysis. The concentration of compounds was assessed by means of an EDS detector.

2.5. Antimicrobial assay

Antimicrobial tests were performed using clinical strains of methicillin resistant Staphylococcus aureus (MRSA) K 324 and Escherichia coli PA 170, the reference strain of yeasts Candida albicans ATCC 90028 and the fabrics impregnated with TiO₂ NPs, both unwashed and after 30 cycles of washing, at temperature settings of 40, 60 and 90 °C.

The inoculated samples were subjected to UVA irradiation using a Wood's lamp set at λ_max = 365 nm, GP = 1.5 mW cm⁻², and irradiation times set at 20, 40 and 60 min. The selection of 365 nm was dictated by the photocatalytic activity of TiO₂ activity in UV-A range.⁴⁶ The power, 1.5 mW cm⁻² was used to mimic the terrestrial intensity of UVA radiation in typical solar spectra. Analogous systems were stored in a dark environment, with no exposure to any type of light wavelength. Additionally, a benchmark antimicrobial test for an unmodified polyester fabric was washed and illuminated in the aforementioned conditions. After exposure, the cultures were diluted and spread onto Tryptic Soy agar plates. The colony forming units were counted after incubation for 24–48 hours at 37 °C. The percentage reduction of bacteria (R) was calculated as follows:

R = 100(C − A)/C (1)

where, A refers to the number of microorganisms recovered from the inoculated treated fabric samples, that were incubated for 20, 40, 60 min under UVA light or stored in the dark conditions. C is the number of cells recovered from the inoculated, treated, and untreated fabric samples, immediately after inoculation (at ‘0’ time), which was according to AATCC test method 100-2004, in modification.⁴⁷ At least six repetitions of each type of sample were performed.

3. Results and discussion

3.1. Preparation of TiO₂ modified polyester

NPs of TiO₂ were deposited on polyester fabrics. The concentration of Ti on samples was measured by means of AAS and low magnification EDS. The coverage of nanoparticles on textile yarn surfaces at higher magnification of SEM are presented in Fig. 2, which shows that the textiles were successfully covered with NPs of TiO₂ but this coverage is dispersed and does not form a continuous film on the fibre. In the sonochemical deposition process, cavitation microjets and waves can drive particles with sufficiently high velocities so as to cause fusion of NPs onto the textile surface where the particles can adhere strongly to the surface during particle–substrate collision.^48,49 The nanomaterial covered the majority of the outer surface of the yarn, but there were also NPs in the voids between the yarns. The coverage was non-homogenous, and the NPs agglomerated and formed clusters. These agglomerates were typical for P25 powder.⁵⁰ Due to the nature of substrate⁵¹ NPs are bonded to fabric through van der Waals bonding.

Fig. 2 Scanning electron micrographs of the morphology of PET textile fibres after sonochemical modification with nanotitania followed by an accelerated washing for 0, 10 and 30 cycles at 40 °C, 60 °C, 90 °C. For quantitative analysis of the retention of nanoparticles please see Fig. 3.

However the distribution of NPs had an influence on properties and activity of the prepared material. On yarns, there were areas with a dense accumulation of TiO₂ and there were also areas of surface with no visible presence of NPs.

3.2. Durability and washing

3.2.1. Surface characterization. The impact of washing the textile to the surface coverage of TiO₂ was studied. This experiment helped define the optimum temperature to wash the textiles, and provide the minimum release of NPs, aiding the assessment of best optimised NP coating for production of a non-toxic textile product. The distribution of NPs on the surfaces of yarns after 10 and 30 cycles of washing at temperatures of 40 °C, 60 °C and 90 °C was examined by image analysis using a SEM, Fig. 2. There was no assessed visible difference between textiles washed for 10 or 30 cycles, with no effect from the washing temperatures. From imaging, there was no set temperature that presented the greatest release of TiO₂. It was assumed that there was a volume of the nanomaterial that no longer adhered to yarns after 30 cycles of washing, as the amount of NPs after 30 cycles was lower than before washing of textiles. The SEM image for textiles washed 30 times differ from each other, sample washed in 90 °C seems to distinguish itself with higher concentration of NPs on yarn surface. This effect is probably caused by the abrasion process that occurs during washing, where the motion of textile in the washing container alternates (rubbing, dragging, tumbling), so that different areas of textile are subjected to different mechanical forces. Loosening of certain NPs from textile surface depends on the chemical or mechanical forces, due to kinetical energy due to flow of the wash water induced by the tumbling and agitation of textiles.⁵² Because of that qualitative assessment of TiO₂ was necessary to estimate loosening of NPs. Also it was noted that some aggregates of NPs remained adhered to the yarn surface, even after multiple washing cycles. There are several factors that can affect nanoparticles adhesion to textile surface during washing. Washing detergents have different chemistry as they are mixtures of active ingredients (surfactants, builders, corrosion inhibitors, optical brighteners, foam regulators, bleaching agents, enzymes, auxiliary additives). They act synergistically to provide best possible cleaning efficiency.⁵³ The main purpose of using detergents is to remove stains from the surface, but there are several conditions affecting the efficiency of its cleaning properties: temperature and alkaline pH in the presence of inhibitory or deactivating compounds.⁵⁴ Relevant washing conditions are essential to perform effective removal of residuals.

3.2.2. Assessment of Ti concentration by atomic absorption spectrometry. The qualitative characterisation of washed textiles was compared to a quantitative assessment of the NP durability to the textiles. The Ti present on textiles was quantitatively examined by AAS, which were tested after 30 washes at temperatures of 40 °C, 60 °C and 90 °C, as shown in Fig. 3. The 0 W column was the mean value for samples that were unwashed. Fig. 2 shows that the data retrieved for samples washed at 40 °C or 60 °C, does not differ, and also for samples at 0 W. It was assumed that low temperature washing was most suitable for textiles with TiO₂. In comparison, the highest TiO₂ release was obtained when washing at 90 °C. Therefore, for environmental safety it would be suitably better to apply low temperatures for washing textiles coated with TiO₂.

Fig. 3 Content of TiO₂ on modified textiles obtained using AAS, where 0 – sample modified, non-washed, 40 – sample modified and washed 30 times at 40 °C, 60 – sample modified and washed 30 times at 60 °C, 90 – sample modified and washed 30 times at 90 °C.

3.3. Adhesion test

In this research, a conventional test method was used to analyze the long-term adhesion of NPs to textile surfaces. The pull-off test method was used for this assessment, and allows for the examination of the force required to remove an adhered dolly from a textile surface.

3.3.1. Pull-off test on TiO₂ modified textile surface. The results of the pull-off test are presented in Fig. 4. The tests were performed to evaluate the long term adhesion of NPs on to the fabrics. On the application of a threshold force from the textile surface, a number of NPs were removed with the adhesive-tape from the textile surface. There was no recorded difference in the pull-off force measured for both washed and unwashed samples. It was noted that there was a difference in the force required to remove the adhesive-tape for samples washed at 90 °C, when compared to samples washed at 40 °C and 60 °C. The force required to remove the dolly from the textiles that were washed at 90 °C, was lower than that after 30 cycles of washing. This outcome can be attributed to the heterogeneous character of the TiO₂ dispersion over the fibre surface. The T_g of PET is 80 °C approx., and it is assumed that by washing of the PET above T_g for 30 cycles initiated loosening of the woven fibers. The interfacial region between the sticky-tape and the PET fabric was a factor of the loose fibers and the lower pull-off force, than samples washed at lower temperatures and for less cycles of washing.

Fig. 4 Pull-off test results on modified textile samples where 40C – samples washed at 40 °C, 60C – samples washed at 60 °C, 90C – samples washed at 90 °C.

3.3.2. Assessment of surface coverage by EDS. After pull-off testing, the samples were characterized using an EDS detector. A comparison of the quantity of Ti on the textile sample before and after the pull-off test, and on the adhesive tape after pull-off test was measured. Results were referenced to samples before pull-off testing for a greater accuracy of analysis and comparison, so that the Ti content on textile samples before pull-off testing was 100% of the total content, and results for other samples were proportionally calculated, as displayed by results in Fig. 5. A defined quantitative analysis was made of the Ti that was removed from the surface and situated on the adhesive-tape with respect to the initial value present on textiles. Ideally, the magnitude of the Ti content on the adhesive tape, added to the magnitude of the Ti content on the textile sample after pull-off testing should total 100%. Results were grouped in line with the number of wash cycles and temperature of washing procedure.

Fig. 5 Normalized EDS results obtained for textile samples after pull-off test, where 40, 60 and 90 is the temperature of washing, 0 – samples non-washed, 30 – samples after 30 cycles of washing, b – sample before pull-off test, a – sample after pull-off test, ST – adhesive tape sample.

Fig. 5 shows that about 10 to 20% of initial TiO₂ on textiles was removed with the adhesive-tape. Values obtained for samples after 30 cycles of wash, do not differ from the non-washed samples. It is inconclusive if one set of washing conditions affects the adhesion of NPs, as the outcomes were similar for all samples. There is still better retention of NP's after 30 cycles of washing compared to 0 cycles of washing because the washing procedure removes the loosely bound NP's from the fabric. The NP's retained on the fabric after washing are strongly bound NP's. Proportions between the samples before pull-off test and the sum of titania after pull-off testing, and present on the adhesive tape were mostly preserved. This result does not provide a conclusive indication of adhesion of NPs. There was an important aspect to the properties of the adhesive tape and the potential impact on the adhesion test results.

3.4. Microbiological assay

Antibacterial tests were performed for MRSA, Escherichia coli and fungi Candida albicans. Those strains were selected as they were common in nosocomial testing area.^1,5–7 Textile samples were irradiated with UVA and stored in dark conditions for 20, 40 and 60 minutes (Fig. 6).

Fig. 6 Antimicrobial activity test results, control – non-modified textile sample, 0 wash – non-washed TiO₂ modified sample, 40 °C – TiO₂ modified samples after 30 washing cycles at 40 °C, 60 °C – TiO₂ modified samples after 30 washing cycles at 60 °C, 90 °C – TiO₂ modified samples after 30 washing cycles at 90 °C.

It was observed that PET textile has bacteriostatic properties (see control sample in Fig. 6). Moreover, after irradiation with UVA, the antibacterial activity increased. After 20 min of UVA irradiation, approximately 40% of colonies were killed, and for increased irradiation times, the bacterial reduction rate was even larger at 60%.

Antimicrobial activity of TiO₂ modified textiles was obtained for all tested bacteria strains and fungi. The weakest effect was detected for strains of E. coli. For the samples stored in dark conditions, the mean reduction of bacteria was 10%. The best microbial results were obtained for samples washed at 40 °C. The optimal distribution of NPs was assumed to be the major reason for obtaining better antibacterial effect. Textiles impregnated with nano-TiO₂ using a modified ultrasonic method, showed a 20% microbial reduction after 20 min of UVA irradiation, and almost 40% of reduction after 40 min of irradiation. After 1 hour of irradiation, at least 60% of E. coli colonies were killed on unwashed samples. Even after 30 cycles of washing, the antibacterial activity of the textile was maintained. Although nanomaterials were released during the wash process, antibacterial activity of 40% was still achieved. Antimicrobial tests for E. coli and C. albicans clearly indicated reducing biocidal effects with washing. When comparing data obtained for samples washed at three temperature settings, the best results for killing E. coli were obtained for samples washed at 60 °C.

Textiles revealed an inherent antibacterial activity, and when an antimicrobial NPs were added, the activity against microbes was further strengthened. Another way to increase the biocidal activity was to irradiate the textile samples. Improved activity was obtained against C. albicans. The antifungal effect on textiles was better than that assessed against E. coli. A longer incubation time initiated an increased biocidal effect, even when textiles were stored in dark conditions. The effect was slightly decreased after NPs reduction by washing, but remained efficient for microbial activity. In the case of C. albicans incubated in dark conditions, the most effective results were observed after 40 min of incubation. Irradiation of textile samples enhanced the antimicrobial activity. Results show that the irradiation time had no significant influence on the biocidal effect. Here the results obtained for textile samples incubated with C. albicans with the presence of UVA for 20, 40 or 60 min were comparable, and presented 60% reduction on the unwashed sample. After washing, the activity of textiles decreased and the best result remained for the samples washed at 40 °C.

The largest biocidal effect was observed on the MRSA strain, a result which was considered significant to the study. Loading TiO₂ onto a textile surface using an ultrasonic process produced textiles capable of reducing MRSA by 40–60%, where incubation time was a dependent factor. Washing textile samples did not significantly influence the antibacterial activity against MRSA, where results obtained for samples incubated for 20 min decreased, and after 40 min they were significantly similar to those assessed for unwashed textiles. Using 60 min of incubation and UVA irradiation, almost 100% of MRSA was killed. It was noted that washing did not affect the antibacterial activity of textiles. The proposed method enabled significant biocidal activity of pathogenic MRSA from various hospital settings.

4. Discussion

In this paper it was demonstrated that textiles can be coated with NPs of TiO₂ using an ultrasonic surface modification process. This is a novel technique, where efficacy using a sonochemical modification of textiles was presented for other functional oxides.^32–35 The SEM images showed that the obtained NP layer was not continuous over the textile surface and that the TiO₂ formed aggregates. The distribution of NPs was random and non-homogenous, as it has been previously observed and reported.^32–35 There were areas where accumulation of NPs was dense, while some other surfaces had no coverage of NPs. The SEM images showed that NPs were adhered to the yarn surface, and that they were durable to fibres even after 30 cycles of washing. This effect was revealed for three washing temperature settings. The aggregates of TiO₂ remained on textile surfaces even after several washing cycles, they are believed to be less harmful to the environment than NPs that have not been exposed to a light source.^55,56 It was assumed that the NPs released during the washing process have originated from the outer surface of the yarns, while the remaining NPs accumulated in the voids between fibres. Detailed information on the Ti content on PET textiles was assessed using AAS, where it revealed that the highest Ti content on textiles was from samples washed for 30 cycles at a temperature of 40 °C. According to the toxicity of TiO₂ the dislodgement of NPs from a textile surface was lower than 1 ppm per wash cycle, which meets the recommended safety requirements of NP exposure of titania.^57,58 The maximum release of NPs was observed for samples washed at 90 °C (0.17 ppm per cycle).

Standard pull-off testing methods were used to assess the adhesion properties of NP layers to textile surfaces – where a similar application of these tests for the adhesion characterization of TiO₂ coatings has been studied.⁵⁹ However, these testing techniques can also be applied in testing mechanical properties of textiles. Outcomes from the adhesion test in this study showed that there was no significant difference in the pull-off strength between unwashed samples and the samples washed at 10 or 30 cycles at 40 °C, 60 °C, 90 °C. After the pull-off tests, the textile surfaces were examined using an EDX analyzer. The Ti content was studied on samples before and after the pull-off test, and on the adhesive tape used in the test. It was expected that the Ti content on samples before the pull-off test would be equal to the Ti content on the sample after the test, and when added to the Ti content from the adhesive tape. Experimental results were in agreement with the proposed hypothesis. The content of Ti on samples before the pull-off test was marginally different, and proved that this technique of coating allows the loading of fabric with approximately 35–45% of a inhomogeneous layer. Analysis of the adhesive tape revealed that about 20% of the initial Ti was pulled-off from the fabric surface, revealing that the NPs were durable to the fabric. Furthermore after 30 cycles of washing, the content of Ti that was pulled-off from the fabric was lower than the unwashed fabrics.

Antimicrobial test showed that the textiles revealed inherent bactericidal properties. This inherent activity can add to the already instilled biocidal activity from applying a NP surface coating. Adding NPs of TiO₂ to the textiles significantly improved the antimicrobial activity, and also with the addition of UVA irradiation the biocidal effect was further influenced. The highest antimicrobial activity of coated textiles was revealed against strains of MRSA. As reported, the NPs of TiO₂ have the ability to suppress the growth of several bacteria.^{18,28,60–62} The higher effectiveness of TiO₂ against MRSA than compared against Gram-negative bacteria was considered to be a factor of the complexity and differences in the cell walls of different bacteria that that have various resistance to nanomaterials.²⁰ An extension of the antimicrobial activity of modified textiles against a broader spectrum of organisms can be implemented by applying NPs of TiO₂ doped with silver.

5. Conclusions

By conducting several experiments to assess the modification of synthetic textiles with antimicrobial agents at the nano-scale, commercially available TiO₂ was coated to the surfaces of polyester fabrics providing an effectively covered surface using an ultrasonically enhanced process. The durability of the prepared samples was the best after washing in 40 °C, noting that they were below the recommended environmental requirements, the release of the nanomaterial was within the acceptable limits. We have made an attempt to understand the adhesion of NPs to the textile surface, using a normalized testing mechanism, which to date far has only been used for flat surfaces. The photoactive fabrics showed antimicrobial activity against E. coli, C. albicans and MRSA, which are significantly responsible towards hospital infections. Textiles having the listed properties can effectively improve the quality of care in medical-care environments.

Acknowledgements

The BioElectricSurface research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2011) under grant agreement no. 212533. This communication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Notes and references

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