pH-responsive linkages-enabled layer-by-layer assembled antibacterial and antiadhesive multilayer films with polyelectrolyte nanocapsules as biocide delivery vehicles

Journal of Drug Delivery Science and Technology 54 (2019) 101251

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pH-responsive linkages-enabled layer-by-layer assembled antibacterial and antiadhesive multilayer films with polyelectrolyte nanocapsules as biocide delivery vehicles

T

Haoyuan Caia,b,c,d, Peng Wanga,c,d,∗, Dun Zhanga,c,d,∗∗ a

Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, 266071, China University of Chinese Academy of Sciences, 19 (Jia) Yuquan Road, Beijing, 100039, China c Open Studio for Marine Corrosion and Protection, Qingdao National Laboratory for Marine Science and Technology, 1 Wenhai Road, Qingdao, 266237, China d Center for Ocean Mega-Science, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, 266071, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Antibacterial pH-responsive Layer-by-layer Self-polishing Antiadhesive

Application of the polymer capsules as vehicles for antibacterial surface against bacterial infections is restricted by spontaneous leakage and specifically responsive release of antibacterial agents. Herein, we present the integration of pH-responsive nanocapsules as delivery tools for hydrophobic biocide within layer-by-layer (LbL) films utilizing alternating imine linkages as the driving force for assembly, thus enabling the introduction of drug and controlled release. The novel capsules are fabricated by means of electrostatic LbL assembly, namely, tannin acid/chitosan nanocapsules embedded with triclosan@cetyltrimethylammonium bromide micelles (TCS@CTAB/TA/CH). The nanocapsules achieve an excellent pH-responsive activity that the release efficiency of antibacterial agent triclosan (TCS) increases by nearly 61.8% from pH 8 to 4. Subsequently, the smart nanocapsules are alternatively incorporated via imine linkage into the dextran aldehyde (DA) polyelectrolyte multilayers in LbL deposition (denoted as (DA-TCS@CTAB/TA/CH)n films). The as-prepared samples are characterized by FTIR, FESEM, TEM, DLS and AFM. Noticeably, the (DA-TCS @CTAB/TA/CH)20.5 film exhibites optimal pH-responsive activity with release concentration of TCS up to 4.01 mg/L at pH 6. The bacteriostatic percentages of (DA-TCS@CTAB/TA/CH)20.5 against E. coli and P. aeruginosa are respectively 99.62% and 97.35% after 24-h incubation at pH 6. Besides, the multilayers are capable of supplying a long-term (30 days) antibacterial property. The self-polishing mechanism of (DA-TCS@CTAB/TA/CH)n films is proposed to illuminate the enhanced antibacterial and antiadhesive performances. It seems that the films present a promising way to incorporate biocide to resist bacterial infections and prolong the antimicrobial activity of antibacterial surface.

1. Introduction Bacterial adhesion and subsequent biofilm formation on biomedical devices posed a serious threat for human health, because it could cause infections and expose patients to life-threatening risks. To solve this problem, antibacterial coating has emerged as an effective strategy to resist bacterial and pathogenic infections [1,2]. In the last decade, a variety of techniques to design coatings with antibacterial property were reported [3–5]. Layer‐by‐Layer (LbL) assembly is a simple, effective, reproducible, flexible and highly versatile method for fabricating particular

composition and structure [6–10]. This method has been exploited to combat bacterial adhesion, fabricate polymeric coatings that kill on contact, or incorporate various molecules such as proteins, enzymes, drugs and nanoparticles into the surface coatings without loss of their functional activity [11–14]. In particular, recent advances in LbL-assembled antibacterial polyelectrolyte multilayers (PEMs) involving direct incorporation of cationic antibiotics and polymer-bound prodrugs into multilayer films, or encapsulation of the drugs within block copolymer micelle templates into multilayers [15–17]. Although drugreleasing coatings have shown to be successful in these works, continuous elution of antibacterial agents seemed to be problematic in the

∗ Corresponding author. Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, 266071, China. ∗∗ Corresponding author. Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, 266071, China. E-mail addresses: [email protected] (P. Wang), [email protected] (D. Zhang).

https://doi.org/10.1016/j.jddst.2019.101251 Received 13 June 2019; Received in revised form 22 August 2019; Accepted 2 September 2019 Available online 03 September 2019 1773-2247/ © 2019 Published by Elsevier B.V.

2

[50]

[49]

Agar disc diffusion test

18 h, 100% 24 h, 100% Obvious zone of inhibition Plating and colony counting

E. coli S. aureus E. coli, S. aureus

[48] Obvious zone of inhibition Agar disc diffusion test

Petrifilm assay

Metal ion coordination polymerzation TNTs–NH2–Ag@Zn-BIX 8

Zn2+

Amoxicillin, Ibuprofen Ag+ Gelation CP/OD hydrogel 7

TA CA60/TA/Zn hydrogel 6

Gelation

PMAA hydrogel-like coating 5

LbL assembly

LbL assembly (PDA/Alg-CAP @CS-8)20 film 4

Gentamicin

pH = 7.5, pH = 5.0, pH = 7.4, pH = 3.0, pH = 7.4, pH = 5.5, pH = 7.4, pH = 4.0, pH = 7.4, pH = 4.0,

2 h, 70%; 2 h, 100% 15 h, < 5%; 15 h, 20% 36 h, 55%; 36 h, 99% 22 d, 1250 μg/mL; 22 d, 2200 μg/mL 22 d, 200 μg/mL; 22 d, 930 μg/mL

E. coli

[47]

[24]

91% 96% 89% 100% 18 h, 18 h, 18 h, 48 h, Plating and colony counting

E. coli S. aureus P. aeruginosa S. aureus

LbL assembly TA/antibiotic film 3

Polymyxin B, Gentamicin, Tobramycin Capsaicin

LbL assembly (TCA/MPEG-PCL-CS)/PAA film 2

Triclosan

pH = 8.5, 60 d, 10.5 ppb; pH = 4.0, 60 d, 16.9 ppb

[29] 24 h, nearly 90% Quantification by UV–vis S. epidermidis, E. coli

4 h, 95% Plating and colony counting S. aureus

[45] Obvious zone of inhibition Kirby-Bauer assay S. aureus

pH = 7.4, 13 d, 100%; pH < 3.5, 13 d, no release pH = 7.4, 72 h, 67%; pH = 5.5, 72 h, 89% pH = 7.5, 30 d, no release; pH = 5.5, 30 d, 33–35% LbL assembly (PEO-b-PCL/PAA)30 film 1

Triclosan

Synthesis method Component No

Table 1 Summarization of antibacterial performance by different pH-responsive films.

Antibacterial agent

Release performance

Model bacteria

Assessment method

Antibacterial performance

References

case of clinically relevant antibiotics, because of the emergence of antibiotic resistant bacteria [18,19]. Another problem was spontaneous leakage of the bactericidal agents to environment influenced the lifespan of antibacterial films and resulted in enormous costs for maintenance [3,20]. Therefore, coatings that delivered drug molecules only when and where needed, was a promising means which also alleviated the toxicity problem and premature depletion. The controlled-release PEMs films have been developed that release functional molecules in response to various environmental stimuli such as pH, electric or magnetic field, ionic strength and temperature [14,21–23]. By incorporating drugs into the PEMs, the rate of erosion could be controlled, allowing prolonged drug delivery. However, it posed a great challenge to integrate directly small, uncharged, and hydrophobic drugs into PEMs due to the lack of common functional group. One approach that encapsulated the hydrophobic drugs into the polyelectrolyte capsules, which could act as vehicles for agents to be introduced in PEMs. The integration of nanocapsules into PEMs films has been previously reported, which relied on covalent bonding or electrostatic interaction between the polyelectrolyte and the capsular corona block [24–26]. Recently, microbes have been regarded as an outside stimulus for developing the intelligent antibacterial films [27,28]. Where formed biofilms caused local pH decrease, the antibacterial agents within the polyelectrolyte thin films were released responsively to kill bacteria [3]. A great deal of effort has been devoted to prepare various pHresponsive antibacterial PEMs as shown in Table 1. Among various pHresponsive packaging materials, natural tannic acid (TA) with antibacterial, antioxidant and antitumor properties, and chitosan (CH), which was biocompatible, biodegradable and nontoxic, have been applied in the fields of drug delivery and antibacteria [29,30]. Electrostatic LbL-assembly of TA with cationic polyelectrolytes to prepare microcapsules was first reported by Lvov and co-workers [31,32]. TA provided a favorable electrostatic combination with cationic polymer CH for efficient retention and controlled release of drugs [32]. LbLassembly of TA was considered as a promising approach to fabricate degradable capsules with sustained drug delivery ability [33,34]. The use of antibacterial agents to prevent infection still might be clinically unavoidable. Triclosan (TCS) as a broadspectrum antimicrobial agent with immediate and persistent antibacterial effectiveness [35]. Sun et al. first incorporated TCS into cetyltrimethylammonium bromide (CTAB) surfactant micelles [36]. These micelles with positive charge character could assemble with partner polyelectrolytes to construct multilayer nanocapsules [37]. To fabricate pH-responsive PEMs, the covalent LbL assembly can be applied [38]. The covalent bonds such as imine, oxime and hydrazide have been widely reported in drug delivery systems due to the drugs could be controlled release by regulating [39–41]. It was feasible to bring pH-cleavable covalent linkages in pH-responsive PEMs to relieve bacterial adhesion. Naturally occurring polysaccharides such as dextran and its derivatives have drawn great attention in biomolecular, biomedical and untifouling fields as their abundance, biocompatibility and biodegradability [42–44]. In this work, pH-responsive TCS@CTAB/TA/CH nanocapsules were synthesized by electrostatic LbL assembly (Fig. 1a). The release efficiency of TCS was detected. Subsequently, the nanocapsules were integrated to fabricate self-polishing antibacterial and antiadhesive (DATCS@CTAB/TA/CH)n films (n = 5.5, 10.5, 20.5) via LbL assembly in aldehyde-amine reactions (Fig. 1b). Various characterization methods were performed to test as-prepared nanocapsules and films. The pHresponsive property and release efficacy of TCS from (DA-TCS@CTAB/ TA/CH)n films were tested by concentration of TCS and Kirby-Bauer assay, respectively. The significant short/long-term antibacterial and antiadhesive properties of the LbL films for E. coli and P. aeruginosa were determined by plate colony counting and live/dead bacterial cell staining methods. Additionally, the (DA-TCS@CTAB/TA/CH)n films were proved with self-polishing ability in slightly acidic environments

[46]

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Fig. 1. (a) Procedure for the preparation of nanocapsules by the electrostatic LbL assembly. (b) Preparation of PEMs via imine-linked LbL assembly on the glass slide.

v/v acetic acid of the appropriate TA (1 mg/mL; TA as negative charged layer) and of the appropriate CH (1 mg/mL; CH as positive charged layer) were alternatively injected into 5 mL of previously prepared TCS@CTAB solution with continuous stirring at room temperature. After 20 min, the TCS@CTAB/TA/CH nanocapsules were obtained.

from bacterial adhesion, which could be helpful for enhanced antibacterial and antiadhesive activities. 2. Experimental section 2.1. Chemicals and materials

2.3. Fabrication of (DA-TCS@CTAB/TA/CH)n films Triclosan (97%, TCS) was supplied by Aladdin Chemistry Co. Ltd (China). Cetyltrimethyl ammonium bromide (99%, CTAB), tannic acid (TA), chitosan (CH), sodium periodate and dextran (Mw 40000) were obtained from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Dopamine hydrochloride (98%) was purchased from Shanghai Macklin Biochemical Co. Ltd (China). All reagents were analytically pure grade without further purification. Dextran aldehyde (DA) was prepared based on previous report and the details shown in Text S1, the sample was characterized by proton nuclear magnetic resonance spectroscopy (1H NMR, Fig. S1). The E. coli (ATCC25922) and P. aeruginosa (ATCC27853) were obtained from Rishui Biotech Co. Ltd (Qingdao, China). The Live/Dead™ BacLight™ Bacterial Viability Kit was purchased from life technologies (America).

Glass slides of 1 × 2.5 cm2 in area were ultrasonically rinsed with deionized water, acetone and ethanol, and then dried by N2. Polydopamine was used as anchor layer on the pristine glass surfaces under the guidance of previous report [51]. Briefly, the glass slides were immersed in the 2 g/L dopamine hydrochloride solution for 24 h. After the reaction, the slides were removed, washed with deionized water. The acquired glass substrates were first soaked in 4 g/L DA aqueous solution for 15 min and washed three times with deionized water. Subsequently, the substrates were introduced into TCS@CTAB/ TA/CH nanocapsule solution (1 g/L) for another 15 min and rinsed again three times. By repeating the DA deposition process once more, the 1.5 bilayers film of DA polymer and TCS@CTAB/TA/CH nanocapsule denoted (DA-TCS@CTAB/TA/CH)1.5 was obtained. Similarly, substrates functionalized with (DA-TCS@CTAB/TA/CH)5.5, (DATCS@CTAB/TA/CH)10.5, and (DA-TCS@CTAB/TA/CH)20.5 films were prepared by alternative deposition in DA and TCS@CTAB/TA/CH nanocapsule solution, which were then dried with N2.

2.2. Preparation of TCS@CTAB/TA/CH nanocapsules The nanocapsule was prepared by the LbL protocol, involving in the sequential addition of different polyelectrolytes to uncharged guests [37]. In a typical synthesis (Fig. 1a), 0.15 g CTAB was dissolved in 40 mL deionized water. 400 μL CH2Cl2 solution of TCS (80 mg/mL) was poured into the CTAB micelle solution and ultrasonicated for 1 h. After being left open overnight under continuous stirring to allow CH2Cl2 to volatilize, the solution was filtered to remove any precipitated TCS, obtaining TCS@CTAB micelle. Further, 5 mL aqueous solution with 1%

2.4. pH-responsive release of TCS from TCS@CTAB/TA/CH nanocapsules and (DA-TCS@CTAB/TA/CH)n films The dialysis bag contained 2.5 mL of TCS@CTAB/TA/CH solution was immersed in 150 mL of phosphate-buffered saline (PBS) solution 3

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Fig. 2. FTIR spectra of (a) TCS@CTAB/TA/CH, (b) CH, (c) TA and (d) TCS and enlarged FTIR spectra from (a, b, c, d).

with various pH values of 4, 5, 6, 7 and 8 for 21 h. The dialysate was analyzed by UV–vis spectrophotometry at 281 nm to determine the release concentration of TCS. To measure the pH response of (DATCS@CTAB/TA/CH)n films, the sample was immersed in 10 mL of PBS solution with different pH values of 4, 5, 6, 7 and 8, and kept shaking at 30 °C. The concentration of TCS was measured spectrophotometricly after shaking for a certain time. The amount of TCS released from the nanocapsule or film was determined using calibration curve for TCS in water (Fig. S2).

sterile tube containing 20 μL E. coli suspension in 10 mL LB medium. These tubes were shaken at 180 rpm and incubated at 30 °C for 12 and 24 h. The number of bacteria in the suspension was determined by plating and colony counting. The respective confocal images of attached bacteria were obtained. Furthermore, the film thickness before and after incubating in bacterial suspension was also confirmed by SEM.

2.5. Antibacterial and antiadhesive performances of (DA-TCS@CTAB/TA/ CH)n films

The as-prepared samples were characterized by FTIR, FESEM, TEM, DLS and AFM. More information and details are shown in Text S2.

2.7. Characterization

2.5.1. Short-term antibacterial and antiadhesive performances The antimicrobial performance of the prepared (DA-TCS@CTAB/ TA/CH)n films against E. coli and P. aeruginosa was determined by plating and colony counting. Briefly, The bacterial strains were inoculated and grown in Luria broth (LB) medium overnight at 30 °C prior to the antibacterial test. 20 μL of bacterial suspension was inoculated in a sterile tube containing 10 mL medium of pH 4, 6 or 8. The film-coated substrate was placed into the sterile tube and incubated at 30 °C for 24 h. The resulting bacterial suspension (20 μL) was under colony counting by agar plating and incubating overnight at 30 °C. The glass slides were also taken out for test at 24 h of incubation. They were then placed in a 24-well plate and stained with the Live/ Dead™ BacLight™ Bacterial Viability Kits. The bacterial adhesion of the prepared (DA-TCS@CTAB/TA/CH)n films was subsequently identified by the confocal laser scanning microscope.

3. Results and discussion 3.1. Characterization of prepared TCS@CTAB/TA/CH nanocapsules Fig. 2 exhibited the FTIR spectra of the samples. In the spectrum of CH, the peak at 2876 cm−1 is attributed to the C–H stretching vibration. The peaks at 1655 and 1597 cm−1 correspond to amine group [53]. In spectrum of TA, the peak at 1718 cm−1 is assigned to the stretching vibration of C]O moieties [54]. The peaks at 1612, 1536 and 1448 cm−1 are attributed to the C]C–C stretching vibration of aromatic ring [55]. The peak at 1196 cm−1 belongs to the C–O stretching vibrations of TA groups. In spectrum of TCS, the characteristic peaks at 1505, 1471 and 1418 cm−1 are consistent with skeletal vibrations relating C–C stretching in the benzene ring [56]. The peaks at 909, 856 and 795 cm−1 in the spectrum are the consequence of C–H bond out-ofplane bending in the aromatic ring, while the peak at 1102 cm−1 is related to C–Cl absorption [57,58]. In addition, the TCS@CTAB/TA/CH exhibited similar spectral line with CH. While the peaks at 2918 and 2850 cm−1 were observed, which were ascribed to the C–H stretching vibrations of –CH2 and –CH3 in the CTAB molecules [59]. Some characteristic peaks (1471, 909 and 856 cm−1) of TCS shifted to the higher wave number due to formed micelle between CTAB molecule and TCS. The peaks at 1722, 1604 and 1196 cm−1 are attributed to the TA groups. These results indicated that the TCS was incorporated into the nanocapsules. Morphological features of TCS@CTAB/TA/CH nanocapsules are observed by FESEM and TEM. As can be seen from Fig. 3a, b, c, the nanocapsules are closed to spherical in shape with diameters of 500–600 nm and rough surface morphology. A rough surface structure is very common for films and capsules made of CH due to its high flocculating ability [32]. Dynamic light scattering (DLS) also suggested that the hydrodynamic diameter of the nanocapsules was about 568 nm (Table 2). As show in TEM picture in Fig. 2d, the spherical TCS@CTAB micelles form large aggregate that is distinctly enwrapped with gauzelike TA/CH sheets. These results demonstrate that the TCS@CTAB/TA/ CH nanocapsules are prepared successfully.

2.5.2. Long-term antibacterial and antiadhesive performances The substrates with deposited (DA-TCS@CTAB/TA/CH)n films were taken out for antibacterial tests after 1, 3, 5, 10 and 30 days of immersion in PBS solution with various pH values. They were immersed in the sterile tube containing 20 μL bacterial suspension in 10 mL culture medium. The suspension was shaken at 180 rpm and incubated at 30 °C for 24 h. The bacterial suspension (20 μL) was then used for plating and colony counting. 2.6. Self-polishing performance of (DA-TCS@CTAB/TA/CH)n films The (DA-TCS@CTAB/TA/CH)n films were soaked in 10 mM NaBH4 solution for 0.5 h to reduce the imines to secondary amines, denoted as the (DA-TCS@CTAB/TA/CH)n (Reduced) films [52]. And then the substrates coated with (DA-TCS@CTAB/TA/CH)20.5 and (DATCS@CTAB/TA/CH)20.5 (Reduced) were soaked in the acidic solution (pH 6). The film thickness of these glass slides was continuously measured at specific time intervals for 24 h by the ellipsometry. In addition, the pristine glass substrate, (DA-TCS@CTAB/TA/CH)20.5 (Reduced) and (DA-TCS@CTAB/TA/CH)20.5 films were immersed separately in the 4

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Fig. 3. FESEM (a, b, c) and TEM (d) images of the TCS@CTAB/TA/CH nanocapsules.

In order to study the pH-responsive mechanism of TCS@CTAB/TA/ CH nanocapsules, DLS is employed to determine the size of nanocapsules in PBS solution with pH values of 4, 5, 6, 7 and 8. As can be seen from Fig. 4b, the maximum diameter of nanocapsules was obtained at pH 4 (801 ± 39 nm), which was around 254 nm larger than the minimum size observed at pH 8. The buffer solutions of pH 5, 6 and 7 gave the size of the nanocapsules was 700 ± 34, 625 ± 31 and 575 ± 28 nm, respectively. Consequently, the size of TCS@CTAB/TA/ CH nanocapsules increased with decrease of pH value. In acidic environment, the nanocapsules exhibited large hydrodynamic diameter, indicating the capsule walls enlarged and released TCS more easily. With the environment became neutral, the hydrodynamic diameter of the nanocapsules reduced dramatically, leading to less release of TCS in solution. The smallest diameter of the nanocapsule was observed in alkaline condition, where the minimum release concentration of TCS was achieved. Fig. 4c proposed the tentative pH-triggered mechanism of TCS@CTAB/TA/CH nanocapsules. Under neutral and alkaline environments, about 10% of the phenol groups are ionized base on the pKa of weak polyphenol acid TA ≈ 8.5 [29]. Therefore, phenol groups of TA interact electrostatically with partially protonated amino groups of CH, resulting in the polymer network of nanocapsules shrink and the TCS becomes difficult to release [60]. When the environment became acidic, the ionization of TA decreased and the protonation of the amino group of CH enhanced, leading to a rise in the number of positive charges and electrostatic repulsion within the polymer system [24,61]. Then the TCS@CTAB/TA/CH exhibited swell of the encapsulating materials, and the introduced biocide was released out. Sun et al. confirmed that the disintegration of the incorporated CTAB micelles in water resulted in the release of TCS from the polyelectrolyte films [36]. The E. coli was applied to assess the antibacterial performance of TCS@CTAB/TA/CH nanocapsules in conditions of pH 4, 5, 7 and 8. The control group (without nanocapsules) showed the bacterial colony number declined with continuous decrease of pH value. Previous study has demonstrated that E. coli species normally multiplied over the range of pH 4.5 to 9, and low pH levels inhibited the growth of the bacteria [62]. The antibacterial activity was achieved by introducing

Table 2 The mean size, polydispersity index (PDI) and zeta potential of samples. Sample

Size (nm)

PDI

Zeta potential (mV)

TCS@CTAB/TA/CH TCS@CTAB/TA TCS@CTAB CTAB TA CH

568.37 ± 5.09 491.20 ± 9.81 / / / /

0.353 ± 0.027 0.248 ± 0.011 / / / /

53.41 ± 0.74 −16.28 ± 1.12 41.71 ± 3.60 25.62 ± 2.48 −12.57 ± 2.03 41.06 ± 3.85

The mean diameter, polydispersity index (PDI) and zeta potential of TCS@CTAB/TA/CH nanocapsules are presented in Table 2. The mean diameter of nanocapsules was 568.37 ± 5.09 nm, corresponding to the morphological results. To determine whether the LbL self-assembly was successful, the zeta potential was measured. Since TCS@CTAB micelles with large positive charges, which made them more likely to be covered by alternating deposition of the oppositely charged TA polyelectrolyte. Furthermore, the zeta potential of TCS@CTAB/TA/CH was positive, suggesting that the negative charge surface of TCS@CTAB/TA was covered completely by cationic CH.

3.2. pH-responsive release of TCS from TCS@CTAB/TA/CH nanocapsules The pH-responsive performance of nanocapsules was confirmed by measuring the dialysate containing released TCS at different intervals within 21 h. As shown in Fig. 4a, the released concentration of TCS increased significantly with the decrease of pH value. Initially, the releasing concentration of TCS increased rapidly for pH 4 and 5, which was followed by that of pH 6, 7 and 8. The released TCS concentration at pH 4 reached the maximum at nearly 4.11 mg/L within 21 h, corresponding to the release efficiency of 93.33%. And those of pH 5, 6 and 7 remained at 2.93, 2.15 and 1.86 mg/L, respectively. By contrast, the TCS concentration at pH 8 barely changed after 4 h, the release efficiency only reached 31.11% within 21 h. These results indicated that the TCS@CTAB/TA/CH nanocapsules possessed pH-responsive property. 5

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Fig. 4. (a) The released concentration of TCS in different pH condition. (b) The hydrodynamic sizes of TCS@CTAB/TA/CH nanocapsules in different pH environment. (c) The pH-responsive schematic illustration of TCS@CTAB/TA/CH. The E. coli incubated in LB medium with different pH at 30 °C for 7 h, followed by diluted to 103 with 0.85% NaCl solution and finally took 20 μL suspensions spread on the solid medium.

nanocapsules compared with the control group. The TCS@CTAB/TA/ CH showed the antibacterial rates of 8.30% and 8.59% at pH 7 and 8, respectively. However, for antibacterial activitiy in acidic environment, the capsules showed obviously increased antibacterial rates of 90.91% and 78.57% for pH 4 and pH 5. These results suggested that acidic environments facilitated the release of TCS. 3.3. Characterization of as-prepared (DA-TCS@CTAB/TA/CH)n films The FTIR spectra of the films are shown in Fig. 5. In spectrum of polydopamine, the adsorption peak at 2941 cm−1 is ascribed to the stretching vibration of C–H [63]. The peak at 1630 cm−1 is assigned to the stretching vibration of aromatic ring and bending vibration of N–H [64]. The peaks at 1512 cm−1 and 1293 cm−1 can be attributed to N–H shearing vibration of the amide group and the phenolic C–O–H stretching vibration, respectively [65]. The peak at 1461 cm−1 is consistent with C]C stretching vibration in benzpyrole, which is observed

Fig. 5. FTIR spectra of (a) polydopamine, (b) TCS@CTAB/TA/CH, (c) DA and (d) (DA-TCS@CTAB/TA/CH)n

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Fig. 6. Surface morphology, cross section and AFM image of (a, d, g) (DA-TCS@CTAB/TA/CH)5.5, (b, e, h) (DA-TCS@CTAB/TA/CH)10.5 and (c, f, i) (DA-TCS@CTAB/ TA/CH)20.5 films.

the TCS@CTAB/TA/CH nanocapsules are integrated in multilayers. The spectrum of DA shows peaks at 1720 cm−1 and 1153 cm−1 are ascribed to stretching vibration of the carbonyl group and C–H stretching vibration, respectively [66,67]. After deposition of DA layers, a new characteristic peak at 1639 cm−1, attributed to C]N bond of the imine linkage, appearing in the spectrum d [68]. The appearance of C]N

in spectrum d, suggesting that polydopamine is deposited on glass surfaces [63]. The peaks at 2918 cm−1, 2850 cm−1, 1722 cm−1 and 1604 cm−1 in spectrum b are assigned to C–H stretching vibration of the CTAB molecules, C]O and C]C–C stretching vibrations of TA groups, respectively. Compared with spectrum d, the stretching vibrations of C–H are found at 2922 cm−1 and 2851 cm−1, indicating that 7

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species indicates the (DA-TCS@CTAB/TA/CH)n films are prepared successfully by aldehyde-amine condensation reaction. The surface topography of the multilayer films is observed by SEM (Fig. 6a–c). It is clear that the TCS@CTAB/TA/CH nanocapsules with sphere structure stacking orderly and tightly on the film surface, which is consistent with previous studies [69,70]. The thickness of (DATCS@CTAB/TA/CH)5.5, (DA-TCS@CTAB/TA/CH)10.5 and (DATCS@CTAB/TA/CH)20.5 was 3.77 μm, 3.91 μm and 4.17 μm, respectively (Fig. 6d–f). As shown in Fig. 6f, we were able to observe the incorporated capsule structures by taking a TEM image of a cross-section of the (DA-TCS@CTAB/TA/CH)20.5 film, finding that the capsule structures are indeed incorporated within the film without significant fusion and rupture. Additionally, capsules within the films are closely located, and they formed a network structure with the DA matrix within the LbL polymer film. The atomic force microscopy (AFM) image of the (DA-TCS@CTAB/ TA/CH)n films was also obtained to observe their surface morphologies (Fig. 6g–i). The root-mean-square roughness (Rq) over an area of 5 × 5 μm2 of the polydopamine surface is 1.14 nm (Fig. S3). It increases to 2.31 nm after deposition of the 5.5 bilayers (Fig. 6g). With more bilayers are deposited, the morphology of the multilayer surface become rougher. For instance, the Rq value of the (DA-TCS@CTAB/TA/ CH)10.5 and (DA-TCS@CTAB/TA/CH)20.5 films is 3.34 nm and 5.09 nm, respectively (Fig. 6h and i). As observed in previous study of vesicles integrated in polymer films, the number of the nanocapsules (small white spots) distributed on the multilayer surfaces was growing with depositing from 5.5 to 20.5 bilayers [69]. The exposed size of nanocapsules on the film surfaces determined in this way exhibited diameter of 100–300 nm and height of 20–100 nm, indicating some deformation and burial of the nanocapsules in underlying films [71,72]. AFM analysis of dry multilayers stored at 25 °C for 10 days showed similar punctate patterns without obvious change in dimension (Fig. S4), suggesting the potential for (DA-TCS@CTAB/TA/CH)n films to sustain the integrity of structure under dry-state storage.

The static water contact angle (SWCA) was measured to quantify the hydrophilicity of (DA-TCS@CTAB/TA/CH)n films. Fig. 7a showed the SWCA and the corresponding water droplet image. The SWCA of the pristine glass surface was 58.2°, and it reduced to 48.8° as the 5.5 bilayers were assembled. The minimum SWCA of 26.7° was observed for the (DA-TCS@CTAB/TA/CH)20.5 films, suggesting the hydrophilicity of the films improved continuously as more bilayers were deposited [52].

3.4. Short-term antibacterial activity of the (DA-TCS@CTAB/TA/CH)n films The pH is a particularly relevant stimulus for antibacterial films, since many bacteria metabolically acidify their local environment [46]. Below, we explored the response of (DA-TCS@CTAB/TA/CH)n films during short-term exposure to PBS solution with different pH. As can be seen from Fig. 7b, TCS concentration released from (DA-TCS@CTAB/ TA/CH)20.5 film reached the maximum value of 4.01 mg/L at pH 6 with an exposure time of 24 h, which was respectively 1.32 and 1.96 times higher than that of pH 5 (3.03 mg/L) and pH 4 (2.05 mg/L). When exposed to the neutral and alkaline environments, these films behaved as dormant state and released biocide concentration declined to 1.82 mg/L for pH 7 and 1.27 mg/L for pH 8. Such a release was caused by the cleavage of imine linkages between TCS@CTAB/TA/CH vehicles and DA layers at a specific pH range from 5.0 to 6.5, while they were stable relatively above the neutral pH [40,41,73]. To evaluate the antibacterial property of (DA-TCS@CTAB/TA/CH)n films, the modified Kirby-Bauer assay was performed [74]. E. coli was selected as model gram-negative bacteria. Glass substrate coated with LbL film was gently placed on culture of E. coli in a LB agar plate. After 24 h of incubation, all (DA-TCS@CTAB/TA/CH)n films caused a obvious zone of inhibition (ZOI) for E. coli (Fig. 7c–e), suggesting the released TCS retained its activity and was effective for inhibiting the growth of gram-negative bacteria. Moreover, it was clear that the ZOI gradually became larger with improve of film layers from 5.5 to 20.5,

Fig. 7. (a) Static water contact angle of the glass slide and (DA-TCS@CTAB/TA/CH)n films (n = 5.5, 10.5 and 20.5). (b) Release profile of TCS from (DA-TCS@CTAB/ TA/CH)20.5 film in different pH environment. The Kirby-Bauer disk diffusion assay from (c) 5.5, (d) 10.5 and (e) 20.5 bilayer films. 8

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Fig. 8. The colony number of (a) E. coli and (c) P. aeruginosa in LB medium after 24 h of contact with the different (DA-TCS@CTAB/TA/CH)n films. The bacteriostasis of (b) E. coli and (d) P. aeruginosa corresponding to the each counting result. The inset of b and d are SEM images of E. coli and P. aeruginosa before (left) and after (right) exposed to the films respectively. Note: scale bar = 1 μm.

24 h of contact with the multilayers, as shown in insets of Fig. 8b, d. The cell edges of bacteria were slightly unclear and their morphology changed irregularly, suggesting they were damaged irreversibly. The pH-responsive release of TCS promoted the application of the antibacterial (DA-TCS@CTAB/TA/CH)n films under an acidic micro-environment caused by microbial adhension. Antiadhesive activity of the multilayers was determined by live/ dead bacterial cell staining method. In the environment with same pH value, less and less live E. coli (green dots in Fig. 9a–l) or P. aeruginosa (green dots in Fig. 9a1-l1) cells were observed with the increase of bilayers, while a mass of live cells could be found on the pristine glass surface. It indicated that all polymer films had excellent antifouling activity, and the (DA-TCS@CTAB/TA/CH)20.5 films possessed the best antifouling property against the two bacteria. As revealed by the SWCA and AFM analyses, the surface hydrophilicity and roughness increased gradually with more bilayers were assembled. The synergistic effect of the two surface properties contributed to a better antiadhesive performance. At the same number of bilayers, the red dots at pH 6 accounted for the most proportion, which was followed by the counterpart at pH 4. For the sample incubated at pH 8, there were the most green dots and fewest red dots on the surfaces, suggesting the lowest antiadhesive performance. These findings showed that the antibacterial and antiadhesive properties against the E. coli and P. aeruginosa were improved with the use of (DA-TCS@CTAB/TA/CH)20.5 films at pH 6, which were consistent with those presented in Fig. 8.

suggesting increasing diffusion of biocide to the ambient medium. The release of TCS facilitated the application of the antibacterial (DATCS@CTAB/TA/CH)n films. We evaluate the antibacterial property of (DA-TCS@CTAB/TA/CH)n films at different pH environments. Correspondingly, the results of colony counting and bacteriostasis for each film against E. coli and P. aeruginosa were shown in Fig. 8. The bacteriostasis rate is calculated by: B= (M-N)/M × 100%

(1)

where B is the bacteriostasis rate, M and N are the amounts of viable bacteria in blank and experimental groups, respectively. It can be observed from Fig. 8a that the amount of E. coli bacteria decreased significantly with reduce of pH from 8 to 4 in the blank group (from approximately 1003 × 106 to 68 × 103), indicating low pH levels were able to inhibit the growth of the bacteria [62]. The P. aeruginosa exhibited identical trend that the bacterial amount decreased from 250 × 104 (pH 8) to 42 × 104 (pH 4) (Fig. 8c). While the (DATCS@CTAB/TA/CH)n films effectively eradicated E. coli and P. aeruginosa in LB medium compared with the blank group, revealing the polymer multilayers had excellent antibacterial performance. As shown in Fig. 8b, the bacteriostasis rate of (DA-TCS@CTAB/TA/CH)5.5 films against E. coli was 51.57%, 74.09% and 46.84% at pH 4, 6 and 8, respectively. It indicated that the (DA-TCS@CTAB/TA/CH)5.5 films achieved optimal antibacterial performance in the environment of pH 6. Similarly, the 10.5 and 20.5 bilayer films could kill most E. coli of 95.50% and 99.62% at pH 6. These results corresponded with the analyses given by pH-responsive release of TCS from multilayers. By comparing the three polymer films, it was seen that the (DATCS@CTAB/TA/CH)20.5 possessed the highest antibacterial activity. Furthermore, the bacteriostasis rate of (DA-TCS@CTAB/TA/CH)5.5, (DA-TCS@CTAB/TA/CH)10.5 and (DA-TCS@CTAB/TA/CH)20.5 films was nearly 57.73%, 83.95% and 97.35% against the P. aeruginosa at pH 6, respectively (Fig. 8d). With increase of deposited bilayers from 5.5 to 20.5, the bactericidal effect of the multilayers improved remarkably. These results suggested that efficient release of biocide was triggered by pH decrease nearby (DA-TCS@CTAB/TA/CH)n films, and that high antibacterial activity of the films could be ascribed to locally high concentrations of TCS released. Additionally, SEM images were provided to evaluate the bacterial morphology changes before and after

3.5. Long-term antibacterial performance of the (DA-TCS@CTAB/TA/ CH)n films Since the release efficiency of antifouling agents affected the longterm service of antibacterial coatings, the stability and long-term activitiy of the best (DA-TCS@CTAB/TA/CH)20.5 film were tested. The substrates deposited with (DA-TCS@ CTAB/TA/CH)20.5 film were immersed in PBS solution with diferent pH values for 1, 3, 5, 10 and 30 days. The TCS release profile and antibacterial results were shown in Fig. 10a, b. As shown in Fig. 10a, the released concentration of TCS increased rapidly at pH 4, 5 and 6 during 1–10 days, while the trend became slow from 10 to 30 days. Under pH 7 and 8, the release profiles rose up smoothly and the concentration of TCS was almost steady after 9

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Fig. 9. Confocal images of E. coli on the (a, e, i) pristine glass slides, (b, f, j) (DA-TCS@CTAB/TA/CH)5.5, (c, j, k) (DA-TCS@CTAB/TA/CH)10.5 and (d, h, l) (DATCS@CTAB/TA/CH)20.5 films after 24 h of incubation in LB medium with pH 4 (1st row), 6 (2nd row) and 8 (3rd row), respectively. Confocal images of P. aeruginosa on the (a1, e1, i1) pristine glass slides, (b1, f1, j1) (DA-TCS@CTAB/TA/CH)5.5, (c1, j1, k1) (DA-TCS@CTAB/TA/CH)10.5 and (d1, h1, l1) (DA-TCS@CTAB/TA/CH)20.5 films after 24 h of incubation in LB medium with pH 4 (4th row), 6 (5th row) and 8 (6th row), respectively.

10

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Fig. 10. (a) Long-term release of TCS from (DATCS@CTAB/TA/CH)20.5 film in different environment. (b) The colony number of P. aeruginosa in LB medium after 24 h of contact with the treated (DA-TCS@CTAB/TA/CH)20.5 film, which was immersed in different pH environment for a certain time before antibacterial assay. (c) The colony number of E. coli in PBS solution after being in contact with the pristine glass substrate and (DA-TCS@CTAB/TA/CH)20.5 film over different periods of time. A fresh bacterial suspension was added to the solution every day. (d) Confocal images of E. coli on the pristine glass surface and (DA-TCS@CTAB/TA/CH)20.5 film after 30 days.

3.6. Self-polishing performance of the (DA-TCS@CTAB/TA/CH)n multilayers

5 days. The TCS concentration reached to be 4.89, 6.22, 8.37, 3.52 and 2.57 mg/L at pH 4, 5, 6, 7 and 8 after 30 days of immersion, respectively. It indicated that the largest TCS release amount is achieved in the environment of pH 6, and this performance is important to control release of the antibacterial agent as well as extend life span of the coating. The antibacterial analysis against P. aeruginosa was further conducted for studying the pH-responsive property of (DA-TCS@CTAB/ TA/CH)20.5 films and the result was shown in Fig. 10b. The released TCS amount was relatively low at pH 7 and 8 within 30 days (Fig. 10a). As a result, the colony number of P. aeruginosa remained at a low level after 30 days, indicating that the films still possessed an excellent antibacterial activity. However, in acid environments, the concentration of TCS increased rapidly from 1 to 10 days, and then slowly after 10 days. It demonstrated that the amount of TCS in the (DA-TCS@CTAB/ TA/CH)20.5 film declined rapidly within 10 days, and only a few TCS could be released after that. Hence, the colony number of bacteria reached to a high level after 30 days (253 × 104, 219 × 104 and 171 × 104 for pH 6, 5 and 4, respectively) due to the inferior bactericidal activity. The pH-responsive property of (DA-TCS@CTAB/TA/ CH)20.5 film could be well applied to control release of the biocide. To simulate the human physiological environment, PBS buffer solution (pH 7.4) was selected to test the long-term antibacterial and antiadhesive properties of the (DA-TCS@CTAB/TA/CH)20.5 film over 30 days by adding a fresh E. coli bacterial suspension to the solution every 24 h. As the E. coli multiplied, the acetic acid secreted led to pH reduction in their local environment, resulting in triggering (DATCS@CTAB/TA/CH)20.5 film to release more TCS [75]. As shown in Fig. 10c, the (DA-TCS@CTAB/TA/CH)20.5 film was able to eradicate E. coli in the solution up to 30 days of incubation. Importantly, no living bacterial cells (green dots) were observed on the (DA-TCS@CTAB/TA/ CH)20.5 film surface (Fig. 10d). Thus, the (DA-TCS@CTAB/TA/CH)20.5 multilayers were capable of supplying a long-term antibacterial and antiadhesive properties in human body environment.

The LbL-assembled films can undergo self-polishing since the imine linkages are cleavable under acidic conditions [39,76]. As shown in Fig. 11a, the thickness of the (DA-TCS@CTAB/TA/CH)20.5 film decreased rapidly from 4.19 to 3.09 μm in the first 6 h of exposure, followed by a slight decrease until a final thickness of 2.70 μm was achieved after 24 h. On the contrary, the (DA-TCS@CTAB/TA/CH)20.5 (Reduced) film exhibited minimum reduction in thickness from 4.23 to 4.01 μm over a 24-h exposure, suggesting that cleavage of the reduced film was negligible. To determine the self-polishing effect of the (DA-TCS@CTAB/TA/ CH)n films in enhancing antibacterial and antiadhesive performances. The antibacterial propertity against E. coli of (DA-TCS@CTAB/TA/ CH)20.5 and (DA-TCS@CTAB/TA/CH)20.5 (Reduced) films were performed by counting method. The colonies of bacteria remained at a low level compared with blank group after 24 h of contact with (DATCS@CTAB/TA/CH)20.5 film (Fig. 11b). The bacteriostasis rate of such film keep at 95.40% against E. coli (Fig. 11c). Although the high concentration of bacteria accelerated the formation of an acidic environment, as bacteria degraded organics during their growth and metabolism [77,78]. However, the (DA-TCS@CTAB/TA/CH)20.5 (Reduced) film could not control the release of biocide because the imine linkages were reduced to secondary amines partly. Therefore, the antibacterial performance of the reduced film showed an obvious decline. Compared with the(DA-TCS@CTAB/TA/CH)20.5 film, the 24-h bacteriostasis rate of reduced multilayer decreased by nearly 64.08% (Fig. 11c). It indicated that the reduced films could not keep outstanding antibacterial activity. After incubation in bacteria suspension for 24 h, both the (DATCS@CTAB/TA/CH)20.5 (Reduced) and (DA-TCS@CTAB/TA/CH)20.5 films were superior to the pristine glass substrate in antiadhesive performance (Fig. 11d). Specifically, some clusters of dead bacteria were found on the (DA-TCS@CTAB/TA/CH)20.5 surface. However, a mass of adhension and aggregation of live bacteria on the (DA-TCS@CTAB/TA/ CH)20.5 (Reduced) surface due to the absence of self-polishing property, resulting in a lower antiadhesive ability compared to the (DATCS@CTAB/TA/CH)20.5 film. Furthermore, the thickness profile of the 11

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Fig. 11. (a) Ellipsometric thickness versus time of the (DA-TCS@CTAB/TA/CH)20.5 and (DA-TCS@CTAB/TA/CH)20.5 (Reduced) films incubated in acidic solution. (b) The colony number and (c) bacteriostasis of E. coli after exposuring to different films for 12 h and 24 h. (d) Confocal images of the pristine glass, (DA-TCS@CTAB/ TA/CH)20.5 and (DA-TCS@CTAB/TA/CH)20.5 (Reduced) surfaces after 24 h of contact with the E. coli. (e) SEM cross-section images of (DA-TCS@CTAB/TA/CH)20.5 film before (left) and after (right) 24-h incubation.

enhanced antibacterial and antiadhesive performances of (DATCS@CTAB/TA/CH)n films in present work. Bacterial attachment accelerated the formation of biofilms and led to an acidic microenvironment, inducing the cleavage of pH-responsive imine linkages. Thus the outer layer of DA that covered with biofilms detached and the interior layer of TCS@CTAB/TA/CH nanocapsules was exposed to the surroundings. With the heavily biofouling occurred, the nanocapsule layer was destroyed and released biocide TCS, which resulted in death and

(DA-TCS@CTAB/TA/CH)20.5 multilayer before and after 24-h incubation in bacterial suspension was measured by SEM. The film thickness decreased slightly from 4.19 to 3.13 μm after 24 h of incubation (Fig. 11e), indicating that a part of bilayers was detached from the film surface. The result was consistent with that observed in Fig. 11a, demonstrating the bacterial adhension-triggered self-polishing capacity of the (DA-TCS@CTAB/TA/CH)n films in the presence of biofouling. Fig. 12 summarized the tentative self-polishing mechanism for the 12

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Fig. 12. Proposed self-polishing mechanism for the enhanced antibacterial and antiadhesive performances of (DA-TCS@CTAB/TA/CH)n films.

detachment of microorganisms. Subsequently, the (DA-TCS@CTAB/ TA/CH)n films refreshed and then underwent self-polishing antibacterial and antiadhesive cycles. The self-polishing property of the films was realized by cleavage of pH-responsive imine linkage under acidic environment, which enhanced the efficacies of antibacteria and antiadhesive.

China (41576079, 41922040), Qingdao National Laboratory for Marine Science and Technology (QNLM2016ORP0413) and AoShan Talent Program Supported by Qingdao National Laboratory for Marine Science and Technology (No. 2017ASTCP-ES02).

4. Conclusion

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jddst.2019.101251.

Appendix A. Supplementary data

In summary, novel TCS@CTAB/TA/CH nanocapsules were firstly fabricated by electrostatic LbL assembly. The as-prepared nanocapsules exhibited outstanding pH-responsive release activity in acid environment, which was much faster than those in neutral/alkaline environments. It can be ascribed to that TA/CH served as valves triggered by pH/bacteria to control the release of TCS. After preparation of (DATCS@CTAB/TA/CH)n films, the pH response property still existed for the multilayers. Furthermore, the short-term antibacterial and antiadhesive performances were excellent against typical strain E. coli and bacteria P. aeruginosa particularly for (DA-TCS@CTAB/TA/CH)20.5 film. Additionally, the sustained release of TCS from the multilayers endowed the films with satisfactory antibacterial and antiadhesive properties within 30 days. The improved antibacterial and antiadhesive efficacies were attributed to self-polishing ability of the multilayer films in process of bacteria reproduction. Overall, we anticipate that these (DA-TCS@CTAB/TA/CH)n films will provide a universal means to extend service life in practical applications for biomedical antibacterial coatings with controllable release functionality.

References [1] E.L. Cyphert, H.A. von Recum, Emerging technologies for long-term antimicrobial device coatings: advantages and limitations, Exp. Biol. Med. 242 (2017) 788–798 http://doi.org/10.1177/1535370216688572. [2] D. Campoccia, L. Montanaro, C.R. Arciola, A review of the biomaterials technologies for infection-resistant surfaces, Biomaterials 34 (2013) 8533–8554 http://doi. org/10.1016/j.biomaterials.2013.07.089. [3] H.S. Lee, S.S. Dastgheyb, N.J. Hickok, D.M. Eckmann, R.J. Composto, Targeted release of tobramycin from a pH-responsive grafted bilayer challenged with S. aureus, Biomacromolecules 16 (2015) 650–659 http://doi.org/10.1021/ bm501751v. [4] S. Poyraz, I. Cerkez, T.S. Huang, Z. Liu, L.T. Kang, J.J. Luo, X.Y. Zhang, One-step synthesis and characterization of polyaniline nanofiber/silver nanoparticle composite networks as antibacterial agents, Acs Appl. Mater. Inter. 6 (2014) 20025–20034 http://doi.org/10.1021/am505571m. [5] R.B.K. Wakshlak, R. Pedahzur, B. Menagen, D. Avnir, An antibacterial copper composite more bioactive than metallic silver, J. Mater. Chem. B 4 (2016) 4322–4329 http://doi.org/10.1039/c6tb00719h. [6] G. Decher, Fuzzy nanoassemblies: toward layered polymeric multicomposites, Science 277 (1997) 1232–1237 http://doi.org/10.1126/science.277.5330.1232. [7] P.T. Hammond, Form and function in multilayer assembly: new applications at the nanoscale, Adv. Mater. 16 (2004) 1271–1293 http://doi.org/10.1002/adma. 200400760. [8] X. Yang, F. Qian, G. Zou, M. Li, J. Lu, Y. Li, M. Bao, Facile fabrication of acidified gC3N4/g-C3N4 hybrids with enhanced photocatalysis performance under visible light irradiation, Appl. Catal. B Environ. 193 (2016) 22–35 http://doi.org/10.1016/j. apcatb.2016.03.060. [9] W. Ding, H. Zhuo, M. Bao, Y. Li, J. Lu, Fabrication of organic-inorganic nanofiltration membrane using ordered stacking SiO2 thin film as rejection layer assisted with layer-by-layer method, Chem. Eng. J. 330 (2017) 337–344 http://doi.org/10. 1016/j.cej.2017.07.159.

Conflicts of interest There are no conflicts to declare. Acknowledgements This work was funded by National Natural Science Foundation of 13

Journal of Drug Delivery Science and Technology 54 (2019) 101251

H. Cai, et al.

[10] W. Ding, Y. Li, M. Bao, J. Zhang, C. Zhang, J. Lu, Highly permeable and stable forward osmosis (FO) membrane based on the incorporation of Al2O3 nanoparticles into both substrate and polyamide active layer, RSC Adv. 7 (2017) 40311–40320 http://doi.org/10.1039/c7ra04046f. [11] J.H. Fu, J. Ji, W.Y. Yuan, J.C. Shen, Construction of anti-adhesive and antibacterial multilayer films via layer-by-layer assembly of heparin and chitosan, Biomaterials 26 (2005) 6684–6692 http://doi.org/10.1016/j.biomaterials.2005.04.034. [12] J.A. Lichter, M.F. Rubner, Polyelectrolyte multilayers with intrinsic antimicrobial functionality: the importance of mobile polycations, Langmuir 25 (2009) 7686–7694 http://doi.org/10.1021/la900349c. [13] J.S. Rudra, K. Dave, D.T. Haynie, Antimicrobial polypeptide multilayer nanocoatings, J. Biomater. Sci. Polym. Ed. 17 (2006) 1301–1315 http://doi.org/10.1163/ 156856206778667433. [14] B.S. Kim, S.W. Park, P.T. Hammond, Hydrogen-bonding layer-by-layer assembled biodegradable polymeric micelles as drug delivery vehicles from surfaces, ACS Nano 2 (2008) 386–392 http://doi.org/10.1021/nn700408z. [15] K.C. Wood, H.F. Chuang, R.D. Batten, D.M. Lynn, P.T. Hammond, Controlling interlayer diffusion to achieve sustained, multiagent delivery from layer-by-layer thin films, P. Natl. Acad. Sci. USA 103 (2006) 10207–10212 http://doi.org/10.1073/ pnas.0602884103. [16] H. Chen, Z. Ye, L. Sun, X. Li, S. Shi, J.J. Hu, Y.Y. Jin, Q.W. Xu, B.L. Wang, Synthesis of chitosan-based micelles for pH responsive drug release and antibacterial application, Carbohyd. Polym. 189 (2018) 65–71 http://doi.org/10.1016/j.carbpol. 2018.02.022. [17] B. Thierry, P. Kujawa, C. Tkaczyk, F.M. Winnik, L. Bilodeau, M. Tabrizian, Delivery platform for hydrophobic drugs: prodrug approach combined with self-assembled multilayers, J. Am. Chem. Soc. 127 (2005) 1626–1627 http://doi.org/10.1021/ ja045077s. [18] G. Taubes, The bacteria fight back, Science 321 (2008) 356–361 http://doi.org/10. 1126/science.321.5887.356. [19] M. Li, C. Schlaich, M.W. Kulka, I.S. Donskyi, T. Schwerdtle, W.E. Unger, R. Haag, Mussel-inspired coatings with tunable wettability, for enhanced antibacterial efficiency and reduced bacterial adhesion, J. Mater. Chem. B 7 (2019) 3438–3445 http://doi.org/10.1039/c9tb00534j. [20] Z.L. Zheng, X. Huang, M. Schenderlein, D. Borisova, R. Cao, H. Mohwald, D. Shchukin, Self-healing and antifouling multifunctional coatings based on pH and sulfide ion sensitive nanocontainers, Adv. Funct. Mater. 23 (2013) 3307–3314 http://doi.org/10.1002/adfm.201203180. [21] D.J. Schmidt, J.S. Moskowitz, P.T. Hammond, Electrically triggered release of a small molecule drug from a polyelectrolyte multilayer coating, Chem. Mater. 22 (2010) 6416–6425 http://doi.org/10.1021/cm102578j. [22] S. Pavlukhina, S. Sukhishvili, Polymer assemblies for controlled delivery of bioactive molecules from surfaces, Adv. Drug Deliv. Rev. 63 (2011) 822–836 http://doi. org/10.1016/j.addr.2011.03.017. [23] Z. Zhu, N. Gao, H. Wang, S.A. Sukhishvili, Temperature-triggered on-demand drug release enabled by hydrogen-bonded multilayers of block copolymer micelles, J. Control. Release 171 (2013) 73–80 http://doi.org/10.1016/j.jconrel.2013.06.031. [24] X.P. Hao, W.H. Wang, Z.Q. Yang, L.F. Yue, H.Y. Sun, H.F. Wang, Z.H. Guo, F. Cheng, S.G. Chen, pH responsive antifouling and antibacterial multilayer films with Selfhealing performance, Chem. Eng. J. 356 (2019) 130–141 http://doi.org/10. 1016/j.cej.2018.08.181. [25] P.M. Nguyen, N.S. Zacharia, E. Verploegen, P.T. Hammond, Extended release antibacterial layer-by-layer films incorporating linear-dendritic block copolymer micelles, Chem. Mater. 19 (2007) 5524–5530 http://doi.org/10.1021/cm070981f. [26] K. Emoto, M. Iijima, Y. Nagasaki, K. Kataoka, Functionality of polymeric micelle hydrogels with organized three-dimensional architecture on surfaces, J. Am. Chem. Soc. 122 (2000) 2653–2654 http://doi.org/10.1021/Ja993821g. [27] S.J. Yan, H.C. Shi, L.J. Song, X.H. Wang, L. Liu, S.F. Luan, Y.M. Yang, J.H. Yin, Nonleaching bacteria-responsive antibacterial surface based on a unique hierarchical, Acs Appl. Mater. Inter. 8 (2016) 24471–24481 http://doi.org/10.1021/ acsami.6b08436. [28] P.C. Nalam, H.S. Lee, N. Bhatt, R.W. Carpick, D.M. Eckmann, R.J. Composto, Nanomechanics of pH-responsive, drug-loaded, bilayered polymer grafts, Acs Appl. Mater. Inter. 9 (2017) 12936–12948 http://doi.org/10.1021/acsami.6b14116. [29] I. Zhuk, F. Jariwala, A.B. Attygalle, Y. Wu, M.R. Libera, S.A. Sukhishvili, SelfDefensive layer-by-layer films with bacteria-triggered antibiotic release, ACS Nano 8 (2014) 7733–7745 http://doi.org/10.1021/nn500674g. [30] W.L. Chiang, Y.C. Hu, H.Y. Liu, C.W. Hsiao, R. Sureshbabu, C.M. Yang, M.F. Chung, W.T. Chia, H.W. Sung, Injectable microbeads with a thermo-responsive shell and a pH-responsive core as a dual-switch-controlled release system, Small 10 (2014) 4100–4105 http://doi.org/10.1002/smll.201400842. [31] T. Shutava, M. Prouty, D. Kommireddy, Y. Lvov, pH responsive decomposable layerby-layer nanofilms and capsules on the basis of tannic acid, Macromolecules 38 (2005) 2850–2858 http://doi.org/10.1021/ma047629x. [32] T.G. Shutava, Y.M. Lvov, Nano-engineered microcapsules of tannic acid and chitosan for protein encapsulation, J. Nanosci. Nanotechnol. 6 (2006) 1655–1661 http://doi.org/10.1166/jnn.2006.225. [33] G. Paramasivam, M. Vergaelen, M.R. Ganesh, R. Hoogenboom, A. Sundaramurthy, Hydrogen bonded capsules by layer-by-layer assembly of tannic acid and poly(2-npropyl-2-oxazoline) for encapsulation and release of macromolecules, J. Mater. Chem. B 5 (2017) 8967–8974 http://doi.org/10.1039/c7tb02284k. [34] M.V. Lomova, A.I. Brichkina, M.V. Kiryukhin, E.N. Vasina, A.M. Pavlov, D.A. Gorin, G.B. Sukhorukov, M.N. Antipina, Multilayer capsules of bovine serum albumin and tannic acid for controlled release by enzymatic degradation, Acs Appl. Mater. Inter. 7 (2015) 11732–11740 http://doi.org/10.1021/acsami.5b03263. [35] W. Zhang, P.K. Chu, J.H. Ji, Y.H. Zhang, X.Y. Liu, R.K.Y. Fu, P.C.T. Ha, Q. Yan,

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58]

14

Plasma surface modification of poly vinyl chloride for improvement of antibacterial properties, Biomaterials 27 (2006) 44–51 http://doi.org/10.1016/j.biomaterials. 2005.05.067. X. Wang, Y. Wang, S. Bi, Y.G. Wang, X.G. Chen, L.Y. Qiu, J.Q. Sun, Optically transparent antibacterial films capable of healing multiple scratches, Adv. Funct. Mater. 24 (2014) 403–411 http://doi.org/10.1002/adfm.201302109. L.Y. Zakharova, A.R. Ibragimova, E.A. Vasilieva, A.B. Mirgorodskaya, E.I. Yackevich, I.R. Nizameev, M.K. Kadirov, Y.F. Zuev, A.I. Konovalov, Polyelectrolyte capsules with tunable shell behavior fabricated by the simple layerby-layer technique for the control of the release and reactivity of small guests, J. Phys. Chem. C 116 (2012) 18865–18872 http://doi.org/10.1021/jp305660c. Y.M. Zayas-Gonzalez, D.M. Lynn, Degradable amine-reactive coatings fabricated by the covalent layer-by-layer assembly of poly(2-vinyl-4,4-dimethylazlactone) with degradable polyamine building blocks, Biomacromolecules 17 (2016) 3067–3075 http://doi.org/10.1021/acs.biomac.6b00975. Z.S. Ge, S.Y. Liu, Functional block copolymer assemblies responsive to tumor and intracellular microenvironments for site-specific drug delivery and enhanced imaging performance, Chem. Soc. Rev. 42 (2013) 7289–7325 http://doi.org/10.1039/ c3cs60048c. E. Fleige, M.A. Quadir, R. Haag, Stimuli-responsive polymeric nanocarriers for the controlled transport of active compounds: concepts and applications, Adv. Drug Deliv. Rev. 64 (2012) 866–884 http://doi.org/10.1016/j.addr.2012.01.020. R. Tong, L. Tang, L. Ma, C.L. Tu, R. Baumgartner, J.J. Cheng, Smart chemistry in polymeric nanomedicine, Chem. Soc. Rev. 43 (2014) 6982–7012 http://doi.org/10. 1039/c4cs00133h. E.M. Bachelder, T.T. Beaudette, K.E. Broaders, J. Dashe, J.M.J. Frechet, Acetalderivatized dextran: an acid-responsive biodegradable material for therapeutic applications, J. Am. Chem. Soc. 130 (2008) 10494–10495 http://doi.org/10.1021/ ja803947s. P.S. Pramod, K. Takamura, S. Chaphekar, N. Balasubramanian, M. Jayakannan, Dextran vesicular carriers for dual encapsulation of hydrophilic and hydrophobic molecules and delivery into cells, Biomacromolecules 13 (2012) 3627–3640 http:// doi.org/10.1021/bm301583s. H.X. Yu, Y.T. Zhang, X.B. Sun, J.D. Liu, H.Q. Zhang, Improving the antifouling property of polyethersulfone ultrafiltration membrane by incorporation of dextran grafted halloysite nanotubes, Chem. Eng. J. 237 (2014) 322–328 http://doi.org/10. 1016/j.cej.2013.09.094. B.-S. Kim, S.W. Park, P.T. Hammond, Hydrogen-bonding layer-by-layer-assembled biodegradable polymeric micelles as drug delivery vehicles from surfaces, ACS Nano 2 (2008) 386–392 http://doi.org/10.1021/nn700408z. B.L. Wang, H.H. Liu, Z.F. Wang, S. Shi, K.H. Nan, Q.W. Xu, Z. Ye, H. Chen, A selfdefensive antibacterial coating acting through the bacteria-triggered release of a hydrophobic antibiotic from layer-by-layer films, J. Mater. Chem. B 5 (2017) 1498–1506 http://doi.org/10.1039/c6tb02614a. V. Albright, I. Zhuk, Y.H. Wang, V. Selin, B. van de Belt-Gritter, H.J. Busscher, H.C. van der Mei, S.A. Sukhishvili, Self-defensive antibiotic-loaded layer-by-layer coatings: imaging of localized bacterial acidification and pH-triggering of antibiotic release, Acta Biomater. 61 (2017) 66–74 http://doi.org/10.1016/j.actbio.2017.08. 012. N. Ninan, A. Forget, V.P. Shastri, N.H. Voelcker, A. Blencowe, Antibacterial and anti-inflammatory pH-responsive tannic acid-carboxylated agarose composite hydrogels for wound healing, Acs Appl. Mater. Inter. 8 (2016) 28511–28521 http:// doi.org/10.1021/acsami.6b10491. J. Qu, X. Zhao, P.X. Ma, B. Guo, Injectable antibacterial conductive hydrogels with dual response to an electric field and pH for localized “smart” drug release, Acta Biomater. 72 (2018) 55–69. T.T. Wang, X.M. Liu, Y.Z. Zhu, Z.D. Cui, X.J. Yang, H.B. Pan, K.W.K. Yeung, S.L. Wu, Metal ion coordination polymer-capped pH-triggered drug release system on titania nanotubes for enhancing self-antibacterial capability of Ti implants, ACS Biomater. Sci. Eng. 3 (2017) 816–825 http://doi.org/10.1021/acsbiomaterials.7b00103. G. Xu, D. Pranantyo, L.Q. Xu, K.G. Neoh, E.T. Kang, S.L.M. Teo, Antifouling, antimicrobial, and antibiocorrosion multilayer coatings assembled by layer-by-layer deposition. Involving host-guest interaction, Ind. Eng. Chem. Res. 55 (2016) 10906–10915 http://doi.org/10.1021/acs.iecr.6b02190. G. Xu, P. Liu, D. Pranantyo, K.G. Neoh, E.T. Kang, Dextran- and chitosan-based antifouling, antimicrobial adhesion, and self-polishing multilayer coatings from pHresponsive linkages-enabled layer-by-layer assembly, Acs Sustain. Chem. Eng. 6 (2018) 3916–3926 http://doi.org/10.1021/acssuschemeng.7b04286. L. Qi, Z. Xu, X. Jiang, C. Hu, X. Zou, Preparation and antibacterial activity of chitosan nanoparticles, Carbohydr. Res. 339 (2004) 2693–2700 http://doi.org/10. 1016/j.carres.2004.09.007. C.W. Oo, M.J. Kassim, A. Pizzi, Characterization and performance of Rhizophora apiculata mangrove polyflavonoid tannins in the adsorption of copper (II) and lead (II), Ind. Crops Prod. 30 (2009) 152–161 http://doi.org/10.1016/j.indcrop.2009. 03.002. S. Çakar, N. Güy, M. Özacar, F. Fındık, Investigation of vegetable tannins and their iron complex dyes for dye sensitized solar cell applications, Electrochim. Acta 209 (2016) 407–422 http://doi.org/10.1016/j.electacta.2016.05.024. A. Celebioglu, O.C. Umu, T. Tekinay, T. Uyar, Antibacterial electrospun nanofibers from triclosan/cyclodextrin inclusion complexes, Colloids Surf., B 116 (2014) 612–619 http://doi.org/10.1016/j.colsurfb.2013.10.029. F. Kayaci, O.C. Umu, T. Tekinay, T. Uyar, Antibacterial electrospun poly (lactic acid) (PLA) nanofibrous webs incorporating triclosan/cyclodextrin inclusion complexes, J. Agric. Food Chem. 61 (2013) 3901–3908 http://doi.org/10.1021/ jf400440b. M. Jug, I. Kosalec, F. Maestrelli, P. Mura, Analysis of triclosan inclusion complexes

Journal of Drug Delivery Science and Technology 54 (2019) 101251

H. Cai, et al.

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

(2013) 11136–11142 http://doi.org/10.1039/c3sm52070f. [69] D.V. Volodkin, P. Schaaf, H. Mohwald, J.C. Voegel, V. Ball, Effective embedding of liposomes into polyelectrolyte multilayered films: the relative importance of lipidpolyelectrolyte and interpolyelectrolyte interactions, Soft Matter 5 (2009) 1394–1405 http://doi.org/10.1039/b815048f. [70] P.C. DeMuth, J.J. Moon, H. Suh, P.T. Hammond, D.J. Irvine, Releasable layer-bylayer assembly of stabilized lipid nanocapsules on microneedles for enhanced transcutaneous vaccine delivery, ACS Nano 6 (2012) 8041–8051 http://doi.org/10. 1021/nn302639r. [71] M. Michel, Y. Arntz, G. Fleith, J. Toquant, Y. Haikel, J.C. Voegel, P. Schaaf, V. Ball, Layer-by-layer self-assembled polyelectrolyte multilayers with embedded liposomes: immobilized submicronic reactors for mineralization, Langmuir 22 (2006) 2358–2364 http://doi.org/10.1021/la053006g. [72] D. Volodkin, Y. Arntz, P. Schaaf, H. Moehwald, J.C. Voegel, V. Ball, Composite multilayered biocompatible polyelectrolyte films with intact liposomes: stability and temperature triggered dye release, Soft Matter 4 (2008) 122–130 http://doi. org/10.1039/b713563g. [73] Z. Ge, S. Liu, Functional block copolymer assemblies responsive to tumor and intracellular microenvironments for site-specific drug delivery and enhanced imaging performance, Chem. Soc. Rev. 42 (2013) 7289–7325 http://doi.org/10.1039/ c3cs60048c. [74] S.Y. Yin, Y. Goldovsky, M. Herzberg, L. Liu, H. Sun, Y.Y. Zhang, F.B. Meng, X.B. Cao, D.D. Sun, H.Y. Chen, A. Kushmaro, X.D. Chen, Functional free-standing graphene honeycomb films, Adv. Funct. Mater. 23 (2013) 2972–2978 http://doi. org/10.1002/adfm.201203491. [75] K.B. Andersen, K. Vonmeyenburg, Are growth-rates of escherichia-coli in batch cultures limited by respiration, J. Bacteriol. 144 (1980) 114–123. [76] J.Z. Du, X.J. Du, C.Q. Mao, J. Wang, Tailor-made dual pH-sensitive polymer-doxorubicin nanoparticles for efficient anticancer drug delivery, J. Am. Chem. Soc. 133 (2011) 17560–17563 http://doi.org/10.1021/ja207150n. [77] Z. Yan, P. Shi, J. Ren, X. Qu, A "Sense-and-Treat" hydrogel used for treatment of bacterial infection on the solid matrix, Small 11 (2015) 5540–5544 http://doi.org/ 10.1002/smll.201501958. [78] K. Tram, P. Kanda, B.J. Salena, S.Y. Huan, Y.F. Li, Translating bacterial detection by DNAzymes into a litmus test, Angew. Chem. Int. Ed. 53 (2014) 12799–12802 http://doi.org/10.1002/anie.201407021.

with beta-cyclodextrin and its water-soluble polymeric derivative, J. Pharmaceut. Biomed. 54 (2011) 1030–1039 http://doi.org/10.1016/j.jpba.2010.12.009. T. Wang, W. Li, D. Xu, X. Wu, L. Cao, J. Meng, A novel and facile synthesis of black TiO 2 with improved visible-light photocatalytic H2 generation: impact of surface modification with CTAB on morphology, structure and property, Appl. Surf. Sci. 426 (2017) 325–332 http://doi.org/10.1016/j.apsusc.2017.07.153. J. Li, H. Ejima, N. Yoshie, Seawater-Assisted self-healing of catechol polymers via hydrogen bonding and coordination interactions, Acs Appl. Mater. Inter. 8 (2016) 19047–19053 http://doi.org/10.1021/acsami.6b04075. K.Y. Lee, D.J. Mooney, Alginate: properties and biomedical applications, Prog. Polym. Sci. 37 (2012) 106–126 http://doi.org/10.1016/j.progpolymsci.2011.06. 003. J.C. Wilks, J.L. Slonczewski, pH of the cytoplasm and periplasm of Escherichia coli: rapid measurement by green fluorescent protein fluorimetry, J. Bacteriol. 189 (2007) 5601–5607 http://doi.org/10.1128/Jb.00615-07. Y.Q. Lin, L.B. Li, L.L. Hu, K.Y. Liu, Y.A. Xu, Multifunctional poly(dopamine)-assisted synthesis of silver nano particles/carbon nanotubes nanocomposite: toward electrochemical sensing of hydrogen peroxide with enhanced sensitivity, Sens. Actuators B Chem. 202 (2014) 527–535 http://doi.org/10.1016/j.snb.2014.05.113. X.S. Liu, J.M. Cao, H. Li, J.Y. Li, Q. Jin, K.F. Ren, J. Ji, Mussel-Inspired polydopamine: a biocompatible and ultrastable coating for nanoparticles in vivo, ACS Nano 7 (2013) 9384–9395 http://doi.org/10.1021/nn404117j. J.W. Fu, Z.H. Chen, M.H. Wang, S.J. Liu, J.H. Zhang, J.N. Zhang, R.P. Han, Q. Xu, Adsorption of methylene blue by a high-efficiency adsorbent (polydopamine microspheres): kinetics, isotherm, thermodynamics and mechanism analysis, Chem. Eng. J. 259 (2015) 53–61 http://doi.org/10.1016/j.cej.2014.07.101. J.F. Pan, L. Yuan, C.A. Guo, X.H. Geng, T. Fei, W.S. Fan, S. Li, H.F. Yuan, Z.Q. Yan, X.M. Mo, Fabrication of modified dextran-gelatin in situ forming hydrogel and application in cartilage tissue engineering, J. Mater. Chem. B 2 (2014) 8346–8360 http://doi.org/10.1039/c4tb01221f. E. Jalalvandi, L.R. Hanton, S.C. Moratti, Preparation of a pH sensitive hydrogel based on dextran and polyhydrazide for release of 5-flurouracil, an anticancer drug, J. Drug Deliv. Sci. Technol. 44 (2018) 146–152 http://doi.org/10.1016/j.jddst. 2017.12.011. J.J. Wu, Q. Zhao, C.Z. Liang, T. Xie, Enzymatically degradable oxidized dextranchitosan hydrogels with an anisotropic aligned porous structure, Soft Matter 9

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