Functional nanofibers embedded into textiles for durable antibacterial properties

Journal Pre-proofs Functional nanofibers embedded into textiles for durable antibacterial properties Qiaohua Qiu, Siyuan Chen, Yuanping Li, Yuchen Yang, Hongnan Zhang, Zhenzhen Quan, Xiaohong Qin, Rongwu Wang, Jianyong Yu PII: DOI: Reference:

S1385-8947(19)32653-1 https://doi.org/10.1016/j.cej.2019.123241 CEJ 123241

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Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

26 June 2019 17 October 2019 18 October 2019

Please cite this article as: Q. Qiu, S. Chen, Y. Li, Y. Yang, H. Zhang, Z. Quan, X. Qin, R. Wang, J. Yu, Functional nanofibers embedded into textiles for durable antibacterial properties, Chemical Engineering Journal (2019), doi: https://doi.org/10.1016/j.cej.2019.123241

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Functional nanofibers embedded into textiles for durable antibacterial properties

Qiaohua Qiu 1, Siyuan Chen 1, Yuanping Li 1, Yuchen Yang 1, Hongnan Zhang 1, Zhenzhen Quan 1, 2, Xiaohong Qin 1, *, Rongwu Wang 1, Jianyong Yu 2

1. Key Laboratory of Textile Science & Technology of Ministry of Education, College of Textiles, Donghua University, Shanghai 201620, China; 2. Innovation Center for Textile Science and Technology, Donghua University, Shanghai 201620, China.

*

Corresponding author. Xiaohong Qin, Ph.D., Professor E-mail address: [email protected]

Abstract: While antibacterial textile materials play an important role in preventing transmission of infectious diseases, poor antibacterial durability limits their applications. As one kind of the well-known additives for functional textiles, nanofibers might be a feasible solution. In this study, nanofibers embedded-textiles (NFs-embedded textiles) with durable antibacterial activity are demonstrated by depositing antibacterial electrospun nanofibers into fiber-mesh of cotton fibers and then spinning the mesh into functional textiles. The as-prepared NFs-embedded textiles exhibited strong antibacterial properties. The inhibition rate was 99.99% for both E. coli and S. aureus. In addition, the cytotoxicity experiment of the prepared textiles revealed that the NFs-embedded textiles had a low cytotoxic response to the seeded cells in vitro. On the basis of these features, sportswear based on the antibacterial textiles was fabricated and presented excellent antibacterial durability, still more than 95% against E. coli and S. aureus after 35 cycles of washing. The NFs-embedded textiles reported in the present article would provide a novel methodology for the durably functional textiles. Keywords: Cotton fibers; Nanofibers; Antibacterial; Release behavior; Sportswear; Durability. 1. Introduction Public health occurrence driven by emerging infectious diseases has become the forefront of global safety concerns [1]. Antibacterial fabrics could prevent the growth of the microorganisms or even kill them, thus reducing the transmission of infectious diseases [2]. To endow fabrics with antibacterial properties, either antibacterial finishing or blending with antibacterial chemical fibers has been extensively adopted. Antibacterial finishing incorporate some antibacterial moieties (such as Ag [3-5], TiO2 [6, 7], Cu2O [8], organic quaternary ammonium salts [9, 10], N-Halamine [11, 12] and chitosan [13, 14] and so on) into fabrics based on chemical crosslinking or pad-dry-cure processes,

which generally require chemical reactions in a liquid medium, and the excess solution from the padded procedure is detrimental to the environment [15]. In addition, the comfort and texture properties of the fabrics may be altered. Another shortcoming is that the antibacterial ability of the textiles may be gradually decreased during the use, resulting in the formation of biofilm on the material surface [16-18]. Alternatively, antibacterial active protective technologies developed by blending antibacterial fibers into textiles could be another strategy of integrating antibacterial properties into textiles. Various antibacterial fibers, such as hemp fibers and metal fibers, have recently been incorporated for antibacterial applications [19, 20]. However, their high blending ratio and limited loading capacity of antibacterial agents hinder the applications. The advancement of antibacterial textiles not only requires higher antibacterial efficiency activity but also the durable and eco-friendly viability. Electrospinning technology has been extensively used in the production of ultrafine fibers with diameters in micro- to nanometer scale that has notable applications in protective clothing [21, 22, 23], drug delivery [24-26], wound dressings [27, 28], and filtration [29, 30]. In drug delivery applications, electrospun nanofibers offer higher loading capabilities, greater flexibility of polymers and drugs, and better encapsulation efficiency making them a powerful and excellent choice for loading antibacterial agents [31]. In this regard, nanofibers offer a great promise as an exceptional additive for antibacterial applications. Despite this huge potential, the major challenge is the means by which they can be incorporated into substrate materials. To date, using nanofibers by different methods has garnered attention as a useful means for introducing new and improved functionalities into textiles [32-34]. For example, Dariush et.al made the cotton/polyester fabric as the substrate for drug-loaded nanofibers and investigated the performance of drug release [35]. Zhou et.al coated the PEO nanofibers onto the PET multifilament and monofilament [36]. In addition,

some researchers have applied different methods for enhancing adhesion between nanofibrous membranes and their textile substrates. Varesano et al. treated a cotton fabric with alkali solution and a nylon fabric with ethanol to improve their adhesion with nanofibers [37]. Vitchuli et al. applied the hybrid process of plasma electrospinning to form active chemical surface groups, resulting in the improvement of the bonding strength [38]. Tang et al. mixed the electrospinning solution with hot melt adhesive powder to trigger and enhance the adhesion between nanofibers and substrates [39]. In another research, Golchehr et al. improved the adhesion between nanofibrous membranes and the supporting substrate by blending nylon 66 nanofibers with PVAc nanofibers as a hot melt adhesive [40]. However, the problem of durability still greatly limits their applications because the nanofibers as a coating mainly distribute on the surface of the fabrics. In this work, a sustainable and facile technology is proposed for producing weavable antibacterial yarns by depositing the antibacterial electrospun nanofibers onto the surface of cotton fibers. Then they were together spun into yarns. The scheme is illustrated in Figure 1 and the process proposed here is amenable to upscaling. It is suitable to spin functional yarns in which a high content of strong host-cotton fibers enables weavability and mechanical strength, while a low guest content of functional nanofibers endows functions. Herein, nanofibers loaded with antibacterial agent were made to develop antibacterial textiles. The textiles displayed great antibacterial activity and sustained antibacterial agent release performance. Moreover, they also had low cytotoxicity and good hydrophilicity. Considering these features, the antibacterial sportswear was fabricated with this kind of fabric to demonstrate its potential application in functional textiles. After the functional nanofibers were embedded into fabrics, the antibacterial activity of the sportswear became more durable.

Figure 1. Fabrication of antibacterial NFs-embedded textiles. (a) Schematic illustration of the fabrication of antibacterial NFs-embedded textiles and their application in sportswear. (b) SEM image of fiber-mesh. (c) SEM image of the NFs-embedded yarn and (d) NFs-embedded fabric.

2. Materials and Methods

2.1 Preparation of NFs-embedded yarns

Due to the ease of detection and characterization, during the preparation of NFs-embedded yarns, triclosan (TR) was adopted as the model drug. PAN (Mw 85,000, Shanghai Chemical Fibers Institute, China) of 10 g was dissolved in DMF (99.8%, Sigma-Aldrich) solvent to prepare a 10 wt% solution and the TR (97%, Macklin) of different contents (2~10 wt%) was added to the polymer solution. After stirring for 8 h at room temperature, the solution was electrospun into nanofibers by using a modified electrospinning setup fabricated from the authors' laboratory. The electrospun antibacterial nanofibers were deposited onto the fiber-mesh of cotton fibers which moved forward, and then spun into NFs-embedded hybrid yarns.

2.2 Characterizations of NFs-embedded yarns

The morphology of nanofibers was observed by scanning electron microscope (SEM, Hitachi TM300). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray powder diffraction (XRD) were used to evaluate the relationship and properties of TR and PAN nanofibers. DSC was performed from 30 to 400℃ at a heating rate of 20℃/min under a N2 atmosphere. TGA was then performed from 25 to 500℃ at a heating rate of 10℃/min under a N2 atmosphere. XRD data were obtained by using Cu Ka radiation in a range of 2θ=5-60o. The 1H NMR spectra of TR and released TR were recorded on a Bruker Avance-400 spectrometer at 400 MHz by using CDCl3 as solvent. The surface and cross-sectional morphologies of NFs-embedded yarns and fabrics were observed by SEM. In order to observe the distribution states of nanofibers, rhodamine was added to the electrospinning solution, and the obtained yarns and fabrics were observed under an inverted fluorescence microscope (Leica DMi8-M).

2.3 Efficiency of nanofibers

Efficiency (which we define as the weight of nanofibers divided by weight of NFs-embedded textiles in unit time) of nanofibers can be obtained by testing the weight of TR in the antibacterial textiles. The test method was investigated as detailed in Supporting Information 1.

2.4 Antibacterial evaluation of functional NFs-embedded fabrics

The colony count method and inhibition zone test were used to determine the antibacterial activity of fabrics. The Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus) were cultivated in an oven at 37 ℃ for 24 hours. After this bacterial activation process, raw cotton fabrics (0.75 g) as control sample and NFs-embedded fabrics (0.75 g) were cut into pieces and added in a flask with 5 mL

of diluted bacterial suspension and 70 mL PBS, respectively. After that, the flasks were incubated in a shaking bed at 120 rpm and 37 °C for 24 h, and then, 100 µL of the resulting diluted mixture was plated onto LB agar plates for bacteria counts. Inhibition activity was assessed by diffusion method on agar plate. 100 µL of diluted bacterial suspension (concentration of ~105 CFU mL-1) was plated onto solidified LB agar plate. The square fabric samples with a dimension of (1 × 1) cm2 were sterilized under UV light for 1h, which were then placed onto the surface of agar plate and incubated at 37 ℃ for 18 h. The surface antibacterial ability of NFs-embedded fabrics was estimated against E. coli according to the reported literature [41]. The relevant fabrics were cut into patches (2×2 cm2) and put onto the solidified LB agar plates, and then 0.5mL bacterial suspension was dropped on fabric patches. After that, the patches were covered by a piece of coverslip and incubated at 37 ℃ for 18 h. Repetition for each test was three.

2.5 Release behavior evaluation of NFs-embedded fabrics

The durability of the antibacterial was evaluated by the release behavior of the antibacterial agent in the release medium. Drug release from the fabrics was measured as follows, NFs-embedded fabrics, sectioned into 2×2 cm2 squares, were soaked in 50 mL of 0.01M phosphate buffer saline (PBS, PH 7.4) solution at 37 ℃ with mild shaking and observed for 25 days. Since TR was slightly soluble in PBS, 0.5% w/v sodium lauryl sulfate (SLS) was added to increase the solubility. At predetermined time intervals, 1 mL of the medium/soaking solution was replaced with 1 mL of fresh PBS (with 0.5% w/v SLS) for measuring the TR concentration by ultraviolet spectrophotometer at 281 nm (UV, PerkinElmer- Lambda 35).

2.6 Contact angle measurement of NFs-embedded fabrics

In order to verify that nanofibers had no effect on the performance of cotton fabrics, the wettability of NFs-embedded fabrics was measured with contact angle θ by captive bubble method. During tests, the NFs-embedded fabrics were pasted onto a glass slide and immersed into deionized water. Then, 5 µL of air bubble was introduced to attach onto the surface of the fabric. After an air bubble was attached to the fabric surface, the bubble profile was recorded by CCD camera for contact angle θ calculation.

2.7 Cell culture and cytotoxicity measurement of NFs-embedded fabrics

The cytotoxicity of the NFs-embedded fabrics was evaluated with mouse embryonic 3T3 fibroblast cells, which were inoculated in a 24-well plate (3×104 cells per well) and cultured in DMEM/HIGH GLUCOSE (HyClone) supplemented with 10% fetal bovine serum (FBS, HyClone) and 1% penicillin-streptomycin (HyClone) in a humidified atmosphere of 5% CO2 at 37 ℃. After 24 h, culture media in each well was changed with 2 ml fresh one. Then, 0.02 g cotton fabrics and NFs-embedded fabrics, as the control and experimental group, respectively, were added and cultured for 72 h. Each group included three parallel samples. Subsequently, 100 µL DMEM/HIGH GLUCOSE and 20 µL MTS (Promega) were added to each well and further incubated at 37 ℃ for 4 h. The cell morphologies were observed under an optical microscope. The supernatant was measured at 490 nm using a microplate reader (BIO-RAD, USA). The relative growth rate (RGR) was calculated as follows: RGR (%) = (𝑂𝐷𝑠𝑎𝑚𝑝𝑙𝑒/𝑂𝐷𝑐𝑜𝑛𝑡𝑟𝑜𝑙) × 100, where 𝑂𝐷𝑠𝑎𝑚𝑝𝑙𝑒 and 𝑂𝐷𝑐𝑜𝑛𝑡𝑟𝑜𝑙 represent the optical densities of the experimental sample and control groups, respectively. 2.8 Washing procedure of the sportswear

The washing procedure was conducted according to the AATCC test method 61-2007. The fabrics were washed in 500 mL water with 0.93% soap at 40 ℃ for 45 min, with ten steel balls applying mechanical stress. The samples were washed for different washing cycles [42]. Then they were dried in ambient. To further demonstrate the structural and functional stability of the NFs-embedded fabrics, its surface and cross-sectional morphologies were observed by SEM and inverted fluorescence microscope after 35 washing cycles. The effect of washing on moisture absorption properties was also measured.

3. Results and Discussions

3.1 Characterization of NFs-embedded textiles

The SEM images of nanofibers presented in Figure S2 (Supporting Information) revealed randomly oriented three-dimensional nonwoven morphologies with fiber diameters in the range of 250 to 400 nm. The interaction between TR and PAN nanofibers were evaluated using DSC, TGA and XRD (see detail in Figure S3, Supporting Information). 1H-NMR and UV-VIS measurements were also carried out to confirm that electrospinning process had no adverse effects on antibacterial agent, and the results suggested that the chemical structure of the TR has not been affected during the electrospinning process (Figure S4, Supporting Information). The distribution of nanofibers in the NFs-embedded yarns and fabrics was observed by SEM and inverted fluorescence microscope as shown in Figure 2. From the SEM images, it can be seen that the nanofibers were distributed on both the surface and inner part of the NFs-embedded yarns. As shown in Figure 2a and 2c, nanofibers were distributed among the cotton fibers in a dispersion or aggregation form. This was further demonstrated by the fluorescent photographs in Figure 2b and 2d. The nanofibers loaded with rhodamine that showed red under the fluorescence microscope from excitation

with green light demonstrating that nanofibers were evenly distributed in the yarns. The similar phenomenon can be observed in the SEM and fluorescence microscopy images of the fabrics (Figure 2e and 2f). The fiber-mesh of cotton fibers was very thin and porous (Figure 1b), which resulted in nanofibers radiating through this pore network to entangle with cotton fibers. Furthermore, the solvent used in dissolving the nanofiber polymer did not fully evaporate in time, resulting in nanofibers tightly combining with the cotton fiber-mesh under wet conditions during the fabrication process. It has to be noted that the nature of adhesion between nanofibers and cotton fibers needs further investigation.

Figure 2. SEM micrograph (a) and fluorescent photographs (b) of NFs-embedded yarn. Inset depicts the magnified view of the NFs-embedded yarn. SEM micrograph (c) and fluorescent photographs (d) of cross-sectional view of NFs-embedded yarn. SEM micrograph (e) and fluorescent photographs (f) of NFs-embedded fabric.

3.2 Efficiency of nanofibers

The efficiency of nanofibers in NFs-embedded textiles can be obtained by calculating the weight of TR in the NFs-embedded textiles. When the mass fraction of TR was 10%, its content determined by

the ultraviolet spectrophotometer was 425 mg/kg (Figure S1, Supporting Information), and thus the obtained efficiency of PAN nanofibers was 4250 mg/kg (0.4 wt%). In addition, there is no guarantee that all of the TR is released from the nanofibers when calculating the weight of TR, so the obtained value could have been smaller than the real one.

3.3 Antibacterial properties of NFs-embedded fabrics

TR has been widely shown to possess antibacterial properties. Its growth-inhibitory qualities result from blocking lipid synthesis by specifically inhibiting an NADH-dependent enoyl-acyl carrier protein (ACP) reductase or inhibiting of enoyl reductase [43, 44]. TR released from nanofibers led to the bacteria inactivation and in this case E. coli and S. aureus were selected as the model bacteria. As shown in Figure 3a, almost no reduction in bacteria was detected for raw cotton fabrics. In contrast, the NFs-embedded fabrics showed effective killing of E. coli and S. aureus, even when the TR content was only at 2%, affirming the favorable antibacterial efficiency of NFs-embedded fabrics. To qualitatively evaluate the antimicrobial activity of NFs-embedded fabrics, the inhibition zone assay was carried out using E. coli as the representative bacteria. With the increase in TR content, the diameter of the inhibition zone was increased, i.e., more drugs diffused from nanofibers which enhanced their ability to inhibit bacterial growth (Figure 3c). Figure 3d-e show the agar plates of the surface antibacterial experiment. The bacterial growth in the NFs-embedded fabrics with 0% TR was robust. In contrast, the NFs-embedded fabrics loaded with 2~10% TR inhibited the bacterial growth significantly, indicating that even a TR content as low as 2% enriched the fabrics with excellent surface antibacterial properties. In contrast to antibacterial agents that act on the surface of the fibers (Figure 3f), NFs-embedded textiles were loaded antibacterial agents not only on the textile surfaces but also within the textiles, enabling the immediate release of antibacterial agents around and throughout the

textiles and, thus, facilitating the kill of bacteria both on the textile surfaces and inside the fabrics (Figure 3g).

Figure 3. Antibacterial efficiency of NFs-embedded fabrics. (a, b) Antibacterial kinetics of NFs-embedded fabrics toward E. coli and S. aureus, respectively. (c) The zone of inhibition images of NFs-embedded fabrics with different TR content against E. coli. (d) Schematic illustration of surface antibacterial examination. (e) The results of the surface antibacterial examination of NFs-embedded fabrics with different TR content against E. coli. (f-g) Simulating fabric into a cuboid. Antibacterial schematic illustration of traditional surface antibacterial fabrics and NFs-embedded fabrics, respectively.

3.4 Release behavior evaluation of NFs-embedded textiles

To further confirm the release behavior of antibacterial agent, the cumulative release of TR from the NFs-embedded fabrics is illustrated in Figure 4a. The release curve could be divided into three stages. During the first stage (≤50 h), the drug was released rapidly, which was due to the direct release of the TR away from the surface of the nanofibers located on the fabric surface. In addition, the increasing TR contents led to more drug on the surface of the nanofibers, causing burst release at the initial stage. The second stage lasted longer (50~480 h), during which TR released sustainably into PBS. In the final stage (＞480 h), TR inside the nanofibers took very long to be released due to the non-degradable of PAN nanofibers. Two theoretical models were adopted to describe the TR release from the fabrics. At the early stage (𝑀𝑡 𝑀∞ ≤ 0.6), the Higuchi model (Equation (1)) was utilized to describe the rapid release of the drugs. When 𝑀𝑡 𝑀∞ ≥ 0.4, first-order equation (Equation (2)) was applied to fit the subsequent release of the drugs [45]. 𝑀𝑡 𝑀 = 𝑘 𝑡1 2 , 0 ≤ 𝑀𝑡 𝑀 ≤ 0.6 0 0 1

(1)

𝑀𝑡 𝑀 = 1 ― 8 𝜋2exp ( ― 𝑘 𝑡), 0.4 ≤ 𝑀𝑡 𝑀 ≤ 1.0 0 0 2

(2)

Where k1 and k2 are the Higuchi and first-order release constants, respectively, and Mt and M∞ are the cumulative amounts of drug released at time t and infinite time ∞. The fitted theory curves are given in Figure 4b, which are in good agreement with the experimental results (symbols). These phenomena suggested that TR contents had almost no influence on the drug diffusion mechanisms, but have an effect on the cumulative release of the drug. TR had a relatively fast release in the early stage, resulting in a desired instant antibacterial effect. However, the initial release rate was lower than the pure drug-loaded nanofiber assembly. Then, the drug release curves moved into a first-order release behavior, slowing the release rate and prolonging the release time. After the TR was released from the NFs-embedded fabrics, the drug had three diffusion paths: diffusing away from the surface of the nanofibers (Figure 4c-I), diffusing through the inter-fiber spaces (Figure 4c-II) and diffusing across the fibers’ “wall” (Figure 4c-III). At the second stage which lasted longer (50~480 h), TR had two main diffusion paths, with some diffusing through the inter-fiber spaces and the others diffusing across the fibers’ “wall”, which constituted an additional barrier that prolonged the diffusion path and diffusion time. Diffusion of TR through fibrous media became the main mechanism that governed the release profile. We did not consider the release of drugs from the fibers. The Fick’s second law of diffusion was utilized to describe the diffusion of drugs between fibers. ∂𝑐 ∂𝑡 = 𝐷(∂2𝑐 ∂𝑥2 + ∂2𝑐 ∂𝑦2)

（3）

where c represents the drug concentration evolving with time and position, D is the drug diffusion coefficient, t is the time and x, y is the position. For the diffusion coefficient, we used the semi-empirical equation proposed Clague and Phillips

[46]: 𝐷 𝐷 = 𝐹𝑆(𝑓) = exp ( ― 𝑎∅𝑏)exp ( ―0.84𝑓1.09) 0

（4）

where 𝐷 𝐷0 is the ration of diffusivity in a fluid with and without the presence of the fibers, F expresses the hydrodynamic effects and S is steric effects. 𝑓 is an adjusted volume fraction and is given by: 𝑓 = (1 ― 𝜀)(1 + 𝑟𝑑 𝑟𝑓)

2

（5）

Where ε is the porosity of the material. 𝑟𝑑 and 𝑟𝑓 are the radius of the drug and fiber, respectively. a and b are the constants, which can be determined by equation S6 and S7 given in the Supporting Information. 𝜆 is the ration of fiber radius to the drug radius, 𝜆 = 𝛾𝑓 𝛾𝑑. Combining Eq. (4) and (5), then MATLAB was used to yield the result of the relationship between 𝐷, 𝜆 and 𝜀 (Figure 4d). Here, both the fiber diameter and the drug diameter have been fixed, so only the change of porosity is considered. As the porosity decreases, the diffusion coefficient decreases. When the NFs-embedded textiles were placed in the release medium, the cotton fibers swelled, making the fabrics more compact and less porous, thereby reducing the diffusion rate of the drug. In addition, since the drug is only present in the nanofibers, the cotton fibers were used as a physical barrier and in the prolonged-action form to decreased the rate of the drug release. NFs-embedded fabrics had a novel hybrid structure that allowed the drug to release slowly under the action of a fibrous barrier, resulting in a durable antibacterial activity.

Figure 4 (a) Release behavior of NFs-embedded textiles with different TR contents. (b) Experimental results and fitted curve of NFs-embedded textiles. (c) Mechanisms of transport of drug from yarns to PBS: release from nanofibers to the PBS (I), diffusion through the inter-fiber spaces (II), diffusion across the fibers’ wall (III). (d) Calculated diffusion coefficient D/D0 as a function of porosity ε and fiber to molecule ration λ.

3.5 Contact angle measurement and cytotoxicity of NFs-embedded textiles

The moisture absorption and cytotoxicity are critical to guaranteeing the comfort and safety [47]. Figure 5a-b describe the results of contact angle measurements of cotton fabric and NFs-embedded fabric by the captive bubble method. The measured contact angles were 29.8° and 29.9°, respectively. None significant influence on the wettability of fabrics was induced by nanofibers, which might be due to the fact that most of them were distributed within the NFs-embedded yarns and fabrics. In addition,

the diameter of nanofibers was much smaller than that of cotton fibers and did not make a big difference. Mouse embryonic 3T3 fibroblast cells were used to evaluate the possibility of cytotoxicity of the fabrics and OD ration of the cells was measured at 490 nm by MTS assay. Figure 5c-f present the cell viability and microscopy images of the 3T3 cells cultured in fabrics for 72 h. As shown in Figure 5c, the cell viability of NFs-embedded fabric was 81%, indicating absence of obvious cytotoxic effect for the 3T3 cells. Figure 5d-f show the representative images of 3T3 cells cultured for 72 h. After 72 h culture, the cells near the NFs-embedded fabrics grew well and no abnormal morphology was found, implying the low cytotoxicity of the fabrics.

Figure 5. Contact angle θ of pure cotton fabrics (a) and NFs-embedded fabrics (b). (c) Cell viability of fibroblast 3T3 cells cultured with cotton fabrics and NFs-embedded fabrics. Representative microscopy images of fibroblast cell 3T3 cultured with blank (d), cotton fabrics (e) and NFs-embedded fabrics (f).

3.6 Applications potential of NFs-embedded textiles

Given their good antibacterial activity and low cytotoxicity, the NFs-embedded textiles can be used in functional sportswear (Figure S5, Supporting Information). The laundering durability is important for their use. A mechanical washing test was carried out to evaluate the NFs-embedded

fabric’s washing durability. As shown in Figure 6a-b, the antibacterial rate of textiles (PAN-6% TR and PAN-10% TR) remained over 95.00% even after 35 washing cycles, suggesting good durability of antibacterial activity. In addition, the result of PAN-2% TR fabrics became unsatisfactory after 35 times of mechanical washing, likely because the TR content was too low to release enough antibacterial agent. However, the antibacterial rate still remained over 80.00%, especially for S. aureus, retained over 85.00%, implying that a lower amount of TR would be sufficient to achieve a good antibacterial activity. The photographs of colonies of E. coli and S. aureus after different washing cycles are given in Figure S6 (Supporting Information). In order to explore the laundering durability, we tested the TR content after different washing cycles. In addition, the minimum inhibitory concentration (MIC) of TR against E. coli and S. aureus was also evaluated. As shown in Figure 6c, a high TR release was observed in 5-25 washing cycles (ca. 35%), which could be ascribed to the immediate desorption of TR distributed on the surface of nanofibers, while less TR was released in 30-35 cycles (ca. 3%). The minimum inhibitory concentration (MIC) values of E. coli and S. aureus were evaluated by broth dilution method (Figure S7 and S8, Supporting Information). They were about 0.25 µg/mL and 0.0625 µg/mL for E. coli and S. aureus, respectively. The values of MIC were low which might explain why the antibacterial effect remained good after 35 washing cycles. Furthermore, the release behavior of TR, the distribution of nanofibers in the NFs-embedded fabrics, and the unique properties of nanofibers all ensured excellent antibacterial durability of NFs-embedded textiles. SEM images and fluorescent photographs of NFs-embedded textiles after washing were also taken to evaluate its structural and functional stability. As shown in Figure S9 (Supporting Information), the nanofibers were still embedded inside the textiles or well coated on their surface after 35 washing cycles. However, the diminishing intensity of fluorescent in Figure S9b, 9d and 9f (Supporting

Information) attributed to the general effect of nanofiber and fluorescent dyes loss in the washing cycles. Despite the lost part, the NFs-embedded textiles showed great continuous antibacterial stability towards repeated washing. Besides, as shown in Figure S10 (Supporting Information), the washing had little effect on the contact angle of NFs-embedded fabrics.

Figure 6. (a-b) Antibacterial rate of E. coli and S. aureus after different washing cycles, respectively. (c) TR content in the NFs-embedded fabrics after different washing cycles. (d) The minimum inhibitory concentration (MIC) of the triclosan (TR) against E. coli and S. aureus.

4. Conclusions

In the present work, a novel method for one-step fabrication of functional textiles was presented by depositing antibacterial nanofibers onto a web of cotton fibers, which were together spun into antibacterial yarns. Great antibacterial activity and low cytotoxicity were demonstrated for the resulting NFs-embedded textiles, and then based on these textiles, the prepared antibacterial sportswear showed good antibacterial durability of over 95.00% after 35 washing cycles. Although this work only

demonstrated the antibacterial properties of the NFs-embedded fabrics only, the concept can be extended to different functional nanofibers for the preparation of multifunctional textiles and the types of nanofibers and substrate fibers can also be changed, which would enable more functionalities and applications.

Notes There are no conflicts to declare.

Acknowledgments This work was partly supported by the Chang Jiang Youth Scholars Program of China and grants (51773037) from the National Natural Science Foundation of China to Prof. Xiaohong Qin as well as the “Innovation Program of Shanghai Municipal Education Commission”, “Fundamental Research Funds for the Central Universities” and “DHU Distinguished Young Professor Program” to her. This work has also been supported by grant (51803023, 61771123) from the National Natural Science Foundation of China to Dr. Hongnan Zhang and Prof. Rongwu Wang and the Shanghai Sailing Program (18YF 1400400), the Project funded by China Postdoctoral Science Foundation (2018M640317) and the Fundamental Research Funds for the Central Universities (2232018A3-11) to Dr. Zhenzhen Quan and the Fundamental Research Funds for the Central Universities and Graduate Student Innovation Fund of Donghua University (CUSF-DH-D-2018043) to Ms. Qiaohua Qiu.

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Declaration of interests

☒

The authors declare that they have no known competing financial interests or

personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:



The durable antibacterial textiles are fabricated by embedding functional nanofibers into textiles.



The nanofibers embedded-textiles exhibit strong antibacterial property and favorable biocompatibility.



Sportswear based on the antibacterial textiles are fabricated.

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The sportswear presents an excellent antibacterial durability after washing.