tannic acid bilayers layer-by-layer deposited cellulose nanofibrous mats for antibacterial application

Journal Pre-proof Chitosan/tannic acid bilayers layer-by-layer deposited cellulose nanofibrous mats for antibacterial application

Jing Huang, Yanxiang Cheng, Yang Wu, Xiaowen Shi, Yumin Du, Hongbing Deng PII:

S0141-8130(19)32256-1

DOI:

https://doi.org/10.1016/j.ijbiomac.2019.07.185

Reference:

BIOMAC 12937

To appear in:

International Journal of Biological Macromolecules

Received date:

28 March 2019

Revised date:

1 July 2019

Accepted date:

26 July 2019

Please cite this article as: J. Huang, Y. Cheng, Y. Wu, et al., Chitosan/tannic acid bilayers layer-by-layer deposited cellulose nanofibrous mats for antibacterial application, International Journal of Biological Macromolecules(2019), https://doi.org/10.1016/ j.ijbiomac.2019.07.185

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© 2019 Published by Elsevier.

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Chitosan/tannic acid bilayers layer-by-layer deposited cellulose nanofibrous mats for antibacterial application Jing Huang

a,1

, Yanxiang Cheng

b,1

, Yang Wu a, Xiaowen Shi a, Yumin Du

a

and

Hongbing Deng a,* a

Hubei International Scientific and Technological Cooperation Base of Sustainable

of

Resource and Energy, Hubei Key Laboratory of Biomass Resource Chemistry and

ro

Environmental Biotechnology, Hubei Engineering Center of Natural Polymers-based

Department of Obstetrics and Gynecology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, China

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b

re

University, Wuhan 430079, China

-p

Medical Materials, School of Resource and Environmental Science, Wuhan

Contributed equally to this work.

*

Corresponding author. Tel.: +86 27 68778501; Fax: +86 27 68778501

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na

1

E-mail address: [email protected] (H. Deng)

1

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Abstract The research and development of environmentally friendly and nontoxic biomass products has become an important topic of worldwide concern. In this study, natural materials were used for producing a kind of antibacterial mats. Cellulose acetate (CA) mats prepared by electrospinning technology were converted to cellulose mats via

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alkali hydrolysis. Chitosan (CS) and tannic acid (TA) were used to fabricate the

ro

composite mats by suing layer-by-layer (LBL) self-assembly technology. The

-p

cellulose mats exhibited great fibrous structure, three-dimensional network and small

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average fiber diameter ranging from 300 to 400 nm. Besides, the results of

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mechanical properties testing and water contact angle measurements of these LBL-structured mats demonstrated that the LBL technology was able to improve their

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surface characteristics, hydrophilicity and mechanical properties. The analysis of

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antibacterial activity of the mats revealed over 86% antibacterial activity against Escherichia coli and up to 99% antibacterial activity against Staphylococcus aureus. Hence, the LBL-structured cellulose mats have excellent antibacterial activity and mechanical properties. Therefore, these nano-cellulose mats can be expected to have considerable development prospects for food packaging or wound dressing. Key Words: Chitosan; Tannic acid; LBL; Cellulose nanofibrous mats; Antibacterial mats

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1. Introduction To transform the current mode of production, the research and development of biomass products has gradually become a hot spot. Plant phenolic compounds are an example of a natural substance containing one or more aromatic rings with hydroxyl substituents. They exist in large amounts in edible plants and are highly polymeric

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with molecular weights ranging from 300 to 3000 Da [1, 2]. Tannin is the most

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abundant plant phenolic substances other than lignin [3]. Tannic acid (TA), a special

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kind of tannins [4], has a cyclic glucose and five digalloyl groups, whose chemical

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structure is shown in Scheme 1 [5]. TA possesses weak acidity because of its large

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number of phenolic hydroxyl groups, the pKa of which is approximately 6 [6]. TA ionizes at a pH value higher than 4.5, and it will possess negative charges in aqueous

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solution after ionization [7]. TA can be considered as a good membrane modifier to

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improve the surface properties, because it is negatively charged in solution, high adhesiveness and antibacterial ability [8, 9]. Besides, TA possesses adhesive properties due to the aromatic components in its structure, which enables TA to form coatings on various nonporous or porous substrates [9, 10]. In addition, Lim et al. [11] reported that TA was able to inhibit bacterial growth including Gram-positive bacteria and Gram-negative bacteria. There are several bactericidal mechanisms that TA can destroy the integrity of the cell wall [12], inhibit the formation of the biofilm [13] and inhibit some enzymes activity [14]. Chitosan

(CS),

a

natural

antibacterial 3

agent

with

biodegradability,

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biocompatibility, low cytotoxicity and antibacterial activity [15-19], can be prepared by the deacetylation of chitin [20, 21]. CS is capable of dissolving in acetic acid solution if the degree of deacetylation exceeds 50% [22]. The structure of CS is shown in Scheme 1. When the pH value is lower than 6.3, the amino group carries positive charge, which contributes to electrostatic interactions with negatively charged

of

substances [23].

ro

Therefore, in this study, CS and TA were assembled alternately on cellulose

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nanofibrous mats by using layer-by-layer (LBL) self-assembly technology to form an

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antibacterial material with multilayers as shown in Scheme 1 [24]. The multilayers of

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the material are CS and TA, respectively. The electrostatic interaction between the positively charged CS and negatively charged TA is the main force behind the

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multilayers forming process. Besides, LBL technology has been successfully applied

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to preparing nanocellulose multilayers. Dai et al. [25] prepared multilayer films using negatively charged cellulose nanofibrils and positively charged guar gum via LBL technology. Hamedi et al. [26] fabricated nanocellulose aerogels with multilayers through the LBL assembly of nanoparticles and polymers. In addition, the combination of electrospinning and LBL technology has been used to prepare multilayers nanofibrous mats in previous reports. Zhou et al. [27] fabricated a multilayers electrospun nanofibrous film with poly(ethylene glycol) and TA using LBL assembly. Liang et al. [28] obtained a multilayered electrospun nanofibrous film, which was structured with TA and phosvitin via LBL assembly. However, there is no 4

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report about tannic acid/chitosan multilayers on cellulose nanofibrous mats. The cellulose nanofibrous mats were made of cellulose acetate (CA) via electrospinning [29], which was deacetylated to cellulose by alkali hydrolase [30]. CA is a derivative of natural polymers, which can be obtained from rice husk, coconut shells and other biomass resources [31, 32]. It is able to be processed into nanofibers

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with bead-free uniformity by electrospinning [33]. This nanofibers not only have the

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chemical resistance and biodegradability of CA but also possess high specific surface

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area, high porosity and quantum effects, wettability and adsorption of nanomaterials

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[30, 34]. Therefore, the cellulose mats are ideal substrates for LBL.

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In this study, the effects of the assembly of TA and CS on the mechanical properties, hydrophilicity and wettability of the mats were investigated. The

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antibacterial properties of the assembled nanofibers were evaluated as well.

2.1 Materials

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2. Materials and methods

Cellulose acetate (CA, average Mn ∼ 30,000, Aldrich Co., USA), tannic acid (TA, Mw 1701.2, Shengen Chemical Technology (Shanghai) Co., Ltd.) and chitosan (CS, Mw 2.1×105 KD, DD 92%, Yuhuan Ocean Biochemical Co., China) were the raw materials used to make the mats. Hydrogen chloride, N, N-dimethylacetamide (DMAC), sodium chloride, sodium hydroxide, acetone and acetic acid used in present work were all purchased from Aladdin Chemical Reagent Co., China. In addition, China Center for Type Culture Collection, Wuhan University (Wuhan, China) 5

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provided bacterial strains, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), for the antibacterial activity test. The resistance of the purified water was18.2 MΩ cm. 2.2 Fabrication of cellulose nanofibrous mats Based on the previous report [35], CA nanofibrous mats were prepared via

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electrospinning as shown in Scheme 1. CA powder was added to a mixture of DMAC

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and acetone (the weight ratio was 1:2) with stirring to obtain a 16 wt% CA solution. A

-p

plastic syringe loaded with 10 mL prepared solution was driven by a syringe pump

syringe

was

connected

with

a

high

voltage

power

supply

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the

re

(LSP02-1B, Baoding Longer Precision Pump Co., td, China), and the metal needle on

(DW-P303-1ACD8,Tianjin Dong wen Co., China). The distance between the collector

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and the tip, applied voltage and velocity of syringe pump were set to 20 cm, 16 kV

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and 100 m/min, respectively. During electrospinning, the relative humidity was 45% and the temperature was 25℃. After electrospinning, the obtained CA mats were put into a vacuum drying oven for 24 hours to remove the trace remaining solvents. Ultimately, the desired mats were obtained by hydrolyzing the dried mats with 0.05 mol/L NaOH solution at ambient temperature for 7 days. 2.3 Fabrication of LBL-structured nanofibrous mats The cellulose nanofibrous mats were modified with CS solution and TA solution by LBL technology. CS powder was dissolved in 2 wt% acetic acid to obtain a 1 mg/mL CS solution, the pH of which was adjusted at 3.4 by adding NaOH (1 mol/mL) and 6

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HCl (1 mol/mL) solutions. TA powder was added into purified water to prepare a 1 mg/mL solution, the pH of which was maintained at 5.0. The ionic strength of CS solution and TA solution was maintained at 0.1 mg/mL by adding NaCl. Previous literature has introduced the process of forming LBL-structured multilayers on cellulose nanofibrous mats, which is shown in Scheme 1 [35]. Initially, the cellulose

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nanofibrous mats were placed in the CS solution. After 20 minutes of immersion, the

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mats were washed with a 0.1 mol/mL NaCl solution for 2 minutes, and the washing

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process was repeated three times. Afterwards, the washed mats were put into the TA

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solution. After 20 minutes, the mats were washed three times with the NaCl solution

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to get a bilayer. The desired number of LBL-assembled bilayers was achieved by repeating the immersing and washing procedures. In this study, Cellulose-(CS/TA)n

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was used for labeling the LBL-structured materials, where n was equal to the numbers

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of the CS/TA bilayers. When the outermost layer was CS, n was 0.5, 5.5 and 10.5. Before further characterizations, all structured mats were dried at ambient temperature.

2.4 Characterizations of cellulose nanofibrous mats Cellulose mats were cut into small pieces, and then dispersed in purified water. The supernatants of cellulose mats suspension, TA solution and CS solution were used to measure their ζ-Potential with a Nano25 zetasizer (Malven, England). Field emission scanning electron microscopy (FE-SEM) (Zeiss, Germany) was carried out by observing the surface morphology of the CA mats and LBL-structured mats. The 7

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surface characteristic elements of the resultant mats were measured by X-ray photoelectron spectroscopy (XPS) using an axis ultra DLD apparatus (Kratos, UK). The chemical groups in these materials were analyzed via Fourier transform infrared (FT-IR) spectroscopy, which was recorded by a Nicolet170-SX (Thermo Nicolet Ltd., USA). The measuring range was from 4000 to 400 cm-1. X-ray diffraction (XRD) was

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measured by a diffractometer type D/max-RA (Rigaku Co., Japan) with Cu target and

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Ka radiation (λ=0.154 nm), in which the scattering range (2θ) was 3-60° and the

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scanning rate was 5°/min. A stress-strain response was utilized to characterize the

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mechanical properties of these samples, which was carried out on a tensile tester

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(ETM502A, Shenzhen-wance Instrument Co., Ltd., China). A drop shape analysis system CAST® 3.0 (USA KINO Industry Co., Ltd., USA) was utilized to detect the

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the drop was 1.0 μL.

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water contact angle of these cellulose mats at ambient temperature, and the volume of

2.5 In vitro antibacterial activity assay The antibacterial activity of the mats was assessed via the shake flask method [36]. Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus were selected as the representative microorganisms in this assay. All samples were cut into 2×2 cm2 squares, sterilized under an ultraviolet lamp for 30 minutes and put into 4 mL bacteria suspensions (104 cfu/mL) in tubes. Then, these test tubes were placed into an orbital shaker for incubation at 37℃ for 16 hours. After proper dilution with physiological saline, 50 L of the diluted bacteria suspension was inoculated onto an aseptic 8

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nutrition agar plate. After the plates were incubated at 37℃ for 16 hours, the number of bacteria colonies in the plates was counted to estimate the antibacterial effects of these mats. This work was conducted in triplicate for each group. The antibacterial intensity was calculated by the following equation: （1）

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the number of bacteria colonies of the test groups.

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where N0 is the number of bacteria colonies of the blank control groups and Ni is

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3. Results and discussion

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3.1ζ-potential of solution or suspension of starting materials

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The ζ-potential value of TA solution (pH = 5.0) and cellulose mats was -5.3 and -24.9 mV, while the ζ-potential value of CS solution (pH = 3.4) was +25.2 mV, as

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shown in Table 1. CS can assemble on the surface of cellulose mats due to the

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electrostatic interaction between positively charged CS and the negatively charged cellulose mats. The amino groups of CS carry positive charges at pH = 3.4 [23], and the deprotonation of the phenolic hydroxyl groups at pH = 5.0 leads to a negatively charged TA [6]. Thus, the main force of the LBL assembly process was the electrostatic interaction between CS and TA [37, 38]. 3.2 Morphology characterization To determine the influence of the coated films on the mats, the prepared nanofibrous mats were observed by FE-SEM. Fig. 1a shows the morphology and structure of the cellulose nanofibrous mats, which served as a control among the 9

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modified samples that had different numbers of coated films presented in Fig. 1b-g. It was obvious that the prepared nanofibrous mats had a three-dimensional structure with micro and submicro interspaces. These are the typical characteristics of electrospun nanofibrous mats and have been reported in other research [39, 40]. Meanwhile, owing to the solvent drying after electrospinning, there were some

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junctions among the fibers, as determined by FE-SEM.

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In Fig. 1, compared with the LBL-modified mats, the cellulose mats exhibited

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smallest average fiber diameter of 317 ± 133 nm (Fig. 1a`). The fiber diameter

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increased as the number of bilayers increased, which was caused by the deposition of

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CA and CS. The growth mechanism of the fiber diameter has been discussed in our previous work. Some dense bundles, junctions and protuberances on the surface of the

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3.3 XPS analysis

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fibers in cellulose mats contributed to the increasing fiber diameter.

XPS scans were conducted to analyze the surface elemental composition of the LBL-structured mats. Fig. 2a reveals that oxygen (O) and carbon (C) are present on the surface of the prepared mats, which have binding energies approximately 531.4 and 285.0 eV, respectively. The LBL-structured mats had a peak approximately 400 eV for nitrogen (N) (Figs. 2b-e), which demonstrated that CS was successfully coated onto

the cellulose

mats.

Comparing

Cellulose-(CS/TA)0.5

(Fig.

2b) with

Cellulose-(CS/TA)1.0 (Fig. 2c), the peak approximately 399.3 eV was attributed to an amine, as shown in Fig. 2b [41]. After coating with TA, a new peak appeared at 401.4 10

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eV (Fig. 2c), which was attributed to protonated amine. When CS was the outermost layer, the amine groups of CS became deprotonated after the mats were washed in neutral NaCl solution and dried. Interestingly, some of the amine groups of CS were still protonated when TA was the outermost layer of the mats because the hydroxyl groups of TA could form hydrogen bonds with the protonated amine groups of CS,

same

phenomenon

can

be

observed

in

the

comparison

between

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The

of

which resulted in the protection towards those groups for keeping protonated [35, 42].

-p

Cellulose-(CS/TA)10.0 (Fig. 2e) and Cellulose-(CS/TA)10.5 (Fig. 2d). In Fig. 2e, the

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outermost layer was TA. The nitrogen peak had two peaks for the curve fit, which

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were at 399.4 eV (amine) and 401.4 eV (protonated amine). These peaks were related to the protonation of the amine groups of CS under the effect of TA. Nevertheless,

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there was only an N 1s peak at approximately 399.1 eV that was allocated to an amine

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group, as shown in Fig 2d, because the outermost layer was CS. Therefore, it can be concluded that TA and CS were successful coated on the surface of cellulose mats. 3.4 FT-IR spectroscopy

The FT-IR spectra of CS, TA, cellulose and LBL-modified mats are presented in Fig. 3. CS exhibited an absorption feature approximately 1159 cm-1, which was attributed to the antisymmetric stretch of C-N stretch of the saccharine structure [41]. Two weak peaks at approximately 1267 cm-1 and 1419 cm-1 were assigned to δO-H [43] and -CH2 bending [41], respectively. The amide group in CS had a characteristic peak at 1648 cm-1 [44]. The characteristic peaks of TA at 1710 cm-1 and 1203 cm-1 11

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were attributed to ester groups (νC=O and νC-OCH). The CH bending and phenolic νC-OH peaks were at 1322 cm-1 and 1029 cm-1, respectively. Three peaks at 1614 cm-1, 1535 cm-1 and 1448 cm-1 were assigned to the stretching C=C vibration from the aromatic ring of TA [45]. The characteristic peak of C-O-O for cellulose was found at 1649 cm-1 [46]. Compared to the spectra of cellulose, two new peaks at 1160 cm-1

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(C-N) and 1267 cm-1 (δO-H) were appeared in the spectra of Cellulose-(CS/TA)0.5.

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The presences of C-N and δO-H indicated the existence of CS. In addition, in the

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spectra of Cellulose-(CS/TA)1.0, the characteristic peaks were appeared at 1700 and

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1207 cm-1 (ester groups ), 1513 cm-1 and 1454 cm-1 (the stretching C=C vibration )

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and 1029 cm-1 (phenolic νC-OH). These bonds demonstrated the existence of TA in Cellulose-(CS/TA)1.0. In brief, CS and TA have been successfully coated onto the

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3.5 XRD patterns

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cellulose mats, which coincides with the results of XPS analysis.

The chemical structures and phases of CS, TA, the cellulose, Cellulose-(CS/TA)0.5 and Cellulose-(CS/TA)1.0 were detected by XRD, and the obtained patterns are shown in Fig. 4. The patterns of CS showed a strong peak at 20.2° and a weak peak at 29.5° in Fig. 4a [47]. Besides, a broad peak was observed ranged from 16.8° to 32.6° attributed to the amorphous region of TA [48]. The partial enlargement in Fig. 4b displayed some differences among the patterns of Cellulose, Cellulose-(CS/TA)0.5 and Cellulose-(CS/TA)1.0. After coating with CS, Cellulose-(CS/TA)0.5 exhibited three minor peaks around 18.1°, 22.6° and 11.4° [49]. It has been reported that the peaks 12

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were related to the hydrated “tendons” conformation of CS [50]. Meanwhile, two new peaks appeared at 15.0° and 21.2° in the patterns of Cellulose-(CS/TA)1.0 after the deposition of TA. This was associated with characteristics of anhydrous crystalline conformation [51]. Therefore, these results indicated the presences of CS and TA. 3.6 Mechanical properties

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Fig. 5 displays mechanical properties of the LBL-structured and pure cellulose mats,

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including tensile strength and elongation at break. In Fig. 5b, the control mats without

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LBL structured films had a low tensile strength of 4.42 ± 2.15 MPa. However, the

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tensile strength of Cellulose-(CS/TA)1.0 was 8.82 ± 2.09 MPa, which was 4.40 MPa

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higher than that of the control. Apparently, the tensile strength of the mats by LBL modification was significantly increased. As the coating bilayer numbers increased,

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the tensile strength was enhanced. The tensile strength of Cellulose-(CS/TA)5.0 was

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8.13 ± 1.65 MPa, while that of Cellulose-(CS/TA)10.0 was 9.95 ± 1.25 MPa. Compared with Cellulose-(CS/TA)1.0, both of them had stronger tensile strength. The reason for this strengthening might be the interaction between CS and TA. As was reported by the other authors [52-54], TA can obviously enhance the tensile strength of the mats as a crosslinker [55], and this increase can be accounted for the crosslinks caused by hydrogen bonds between TA and CS. As for the elongation at break, Fig. 5b reveals that the elongation of mats ranges from 6.70 ± 2.64% to 8.95 ± 5.28%, in which LBL-structured mats show slightly higher elongation at break than that of cellulose mats. TA as a kind of the phenolic 13

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compounds can contribute to the interaction between CS and TA on the surface of the mats. The coating of CS and TA can enhance the elongation at break. However, the elongation of Cellulose-(CS/TA)10.0 was lower than that of Cellulose-(CS/TA)5.0. This might be because the deposition of larger amounts of TA and CS greatly increased the physical cross-linking [56], which could lead to a decrease of elongation at break and

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an increase of tensile strength. Consequently, the mechanical properties of the mats

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were strengthened by TA and CS through LBL modification.

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3.7 Water contact angle

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Dynamic changes of water contact angle of these mats are represented in Fig. 6.

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The time interval is defined as the time between the moment the water droplet contacts the surface and the moment the water contact angle is 0°. It could be

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considered that all samples had prominent hydrophilicity and wettability, as the initial

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water contact angle was within 90° and the time interval was shorter than 2 s [57]. However, there were still some differences due to the number and composition of different bilayers. The water contact angle was enlarged from the initial 26.4° to the maximum (78.8°) in Fig. 6b, meaning the hydrophilicity of the mats was reduced after the deposition of CS and TA. It can be concluded that coating with CS enhanced the hydrophilicity of the mats when comparing Cellulose with Cellulose-(CS/TA)0.5. However, the water contact angle of Cellulose-(CS/TA)1.0 was 73.8° after coating with TA, so TA can cause the hydrophilicity of the mats to decrease. As shown in Fig. 6a, compared to the time interval of pure cellulose mats, the 14

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time interval of LBL structured mats was prolonged from 0.6 s to approximately 1.4 s. This increase indicated that the wettability of the mats was affected by the deposition of CS and TA. The time interval of Cellulose-(CS/TA)0.5 was shorter compared to the interval of Cellulose. Hence, the coating of CS can slightly increase the wettability of the mats. However, the time interval of Cellulose-(CS/TA)1.0 was longer than that of

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Cellulose-(CS/TA)0.5, which showed that the wettability of the mats was much weaker.

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Thus, the deposition of TA could reduce the wettability of the mats.

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It has been studied that the wettability and hydrophilicity were important factors

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for bacteria adhesion due to the interfacial properties of bacteria. In most cases, the

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material surfaces with moderate wettability and hydrophilicity are preferable for bacterial adherence versus surfaces with superwettability and superhydrophilicity [58].

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As the number of layers increased, the wettability and hydrophilicity of the

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LBL-structured mats was reduced. Proper wettability and hydrophilicity of the materials would improve bacteria adhesion on the surface of the material [59]. When bacteria adhered onto the surface of the mats, CS and TA came in contact with the bacteria. This contact was beneficial for the antibacterial activity of CS and TA. 3.8 Antibacterial activity To detect the antibacterial activity of the studied mats, E. coli and S. aureus were chosen as representative bacteria. As displayed in Fig. 7, the LBL mats all possessed antibacterial activity against the experimental bacteria, particularly S. aureus. In general, the antibacterial activity increased with an increasing number of coated 15

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bilayers. However, the LBL mats apparently had better antibacterial ability against S. aureus than E. coli. The antibacterial ability of Cellulose-(CS/TA)1.0 against S. aureus was more than 99%, while that against E. coli it was only 28.42%. The higher sensitivity of S. aureus might be attributed to the capability of TA for direct binding to the peptidoglycan layer of Gram-positive bacteria, which is a common antibacterial

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mechanism for polyphenols [12]. Positively charged CS could also be a biological

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adhesive due to the negatively charged lipopolysaccharide on the outer membrane

-p

[60]. However, the peptidoglycan of the Gram-negative bacteria layer was thinner and

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the components of cell wall could not bind to polyphenols, which led to the lower

lP

antibacterial activity against E.coli for the mats [12]. Moreover, when the outermost layer was TA, the LBL structured mats displayed a slightly better antibacterial activity

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against E. coli. However, Cellulose-(CS/TA)10.0 displayed a lower antibacterial

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activity against E. coli (78.36%) than that of Cellulose-(CS/TA)10.5 (86.80%). The reason might be that the composition of the outermost layer did not play a role as important as the previous case, in which the number of coatings was large enough. 4. Conclusion Cellulose-(CS/TA)n was successfully prepared by alternate LBL deposition of CS and TA onto electrospun nanofibrous mats. The raw materials were available from biomass resources. The LBL-structured mats exhibited improved mechanical properties, appropriate hydrophilicity and good antibacterial properties. In addition, as the number of bilayers increased, the mechanical strength and hydrophobicity of the 16

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LBL-modified mats improved. The antibacterial properties of these samples against E. coli and S. aureus improved, among which the Cellulose-(CS/TA)10.5 exhibited the best antimicrobial properties , presenting antibacterial activities of over 86% and 99%, respectively. Therefore, these conclusions illustrate that the LBL-modified cellulose mats are excellent antibacterial materials and have considerable development

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potential for food packaging or wound dressing.

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Acknowledgments

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This work was supported by the National Key Research and Development

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Program (No. 2016YFB0303303) of China and National High Technology Research

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and Development Program of China (863 program, No. 2015AA020313), partially supported by the Natural Science Foundation of Hubei Province of China (Team

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Project, No.2015CFA017) and the Fundamental Research Funds for the Central

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Universities of China (No. 2042017kf0175).

17

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Samples

TA

CS

Cellulose

ζ-Potential (mV)

-5.3 ± 3.6

+25.2 ± 1.5

-24.9 ± 1.4

Table.1. ζ-Potential (mV) of cellulose template, TA solution (pH=5.0) and CS solution

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(pH=3.4).

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Figure captions: Scheme 1. Schematic diagram illustrating the LBL modification on nanofibrous mats. Fig. 1. FE-SEM images and the fiber diameter distribution histograms of the nanofibers: (a, a`) cellulose mats, (b, b`) Cellulose-(CS/TA)0.5, (c, c`) Cellulose-(CS/TA)1.0, (d, `d) Cellulose-(CS/TA)5.0, (e, e`) Cellulose-(CS/TA)5.5

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(f, f`) Cellulose-(CS/TA)10.0, (g, g`) Cellulose-(CS/TA)10.5. (The average

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diameter of 100 fibers. Error bars represented the standard deviation (n=3).)

3.

FT-IR

spectra

Cellulose-(CS/TA)1.0.

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TA,

CS,

Cellulose,

Cellulose-(CS/TA)0.5

and

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scans with the curve fit of N1s.

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Fig. 2. (a) XPS spectra of composite of LBL-structured mats and (b-e) XPS narrow

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Fig. 4. XRD patterns of CS, TA, Cellulose mats and LBL-structured mats.

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Fig. 5. (a) Representative stress-strain behavior (b) strain and stress of Cellulose mats and LBL-structured mats. (Error bars represent the standard deviation (n=3).) Fig. 6. (a) water contact angle curves decaying with time for Cellulose and LBL-structured mats; (b) images of water contact angle of Cellulose and LBL-structured mats with different contact times. Fig. 7. Antibacterial activity against E.coli and S.aureus of (a) Cellulose-(CS/TA)0.5, (b) Cellulose-(CS/TA)1.0, (c) Cellulose-(CS/TA)5.0, (d) Cellulose-(CS/TA)5.5, (e) Cellulose-(CS/TA)10.0, (f) Cellulose-(CS/TA)10.5. (Error bars represented the standard deviation (n=3).) 28

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Fig. 6

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