A Mussel-Inspired Facile Method to Prepare Multilayer-AgNP-Loaded

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Bio-interactions and Biocompatibility

A mussel-inspired facile method to prepare multilayer-AgNP-loaded contact lens for early treatment of bacterial and fungal keratitis Xiaoqi Liu, Jiang Chen, Chao Qu, Gong Bo, Lang Jiang, Hui Zhao, Jing Zhang, Yin Lin, Yu Hua, Ping Yang, Nan Huang, and Zhenglin Yang ACS Biomater. Sci. Eng., Just Accepted Manuscript • Publication Date (Web): 26 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018

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ACS Biomaterials Science & Engineering

Technology of Materials Huang, Nan; Southwest Jiaotong University, College of Materials Science and Engineering Yang, Zhenglin ; Sichuan Key Laboratory for Disease Gene Study, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, China.

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ACS Biomaterials Science & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

A mussel-inspired facile method to prepare multilayer-AgNP-loaded contact lens for early treatment of bacterial and fungal keratitis ‡

‡

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Xiaoqi Liu1,2,3 , Jiang Chen1 *, Chao Qu4 , Gong Bo2,3, Lang Jiang1, Hui Zhao5, Jing Zhang4, Yin Lin3, Yu Hua3, Ping Yang1*, Nan Huang1, Zhenglin Yang2* 1. Institute of Biomaterials and Surface Engineering, Key Lab. for Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, NO.111 of the North 1st Section of Second Ring Road, Chengdu, CN 610031, China 2. Sichuan Key Laboratory for Disease Gene Study, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, NO.32 of the West 2nd Section of First Ring Road, Chengdu, CN 610072, China. 3. Department of Laboratory Medicine, Sichuan Academy of Medical Sciences &Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, NO.32 of the West 2nd Section of First Ring Road, Chengdu, CN 610072, China. 4. Department of Ophthalmology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, NO.32 of the West 2nd Section of First Ring Road, Chengdu, CN 610072, China 5. School of Medicine, University of Electronic Science and Technology of China, No.2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China. ‡

These authors contributed equally to this work

*Corresponding author: [email protected] (Jiang Chen) *Corresponding author: [email protected] (Ping Yang) *Corresponding author: [email protected] (Zhenglin Yang)

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Abstract: The use of contact lenses for the early treatment of bacterial or fungal keratitis has become a new research focus. Two main requirements of the therapeutic contact lenses are anti-microbial ability and visible light transmittance. Silver nanoparticles (AgNPs), as a non-specific anti-microbial component, have been loaded onto contact lenses for the treatment of bacterial and fungal keratitis. Recently, it was reported that via a simple immersion method, AgNPs can be synthesized and fixed onto the surface of the poly-dopamine (PDA)-coated materials. However, in this study, we found that the above traditional method has the disadvantages of poor AgNP loading and low visible light transmittance, which could be induced by limited amount of phenolic hydroxyl groups on and second oxidation of the PDA coating respectively. To overcome these disadvantages, in this paper, we provided a facile and novel method to robustly bind multilayer-AgNPs on contact lens surfaces by using dopamine as reducing agent and bio-glue. In comparing with the monolayer-AgNP-loaded contact lenses fabricated by the traditional method, the multilayer-AgNP-loaded contact lenses had excellent anti-microbial ability and better visible light transmittance. Moreover, the multilayer-AgNP-loaded contact lens had low cytotoxicity to human corneal epithelial cells and anti-inflammation property. Furthermore, the shortcoming of decreasing visible light transmittance induced by excess adherence of AgNPs on the multilayer-AgNP-loaded contact lens was alleviated by decreasing the size of AgNPs through altering the concentration of dopamine and AgNO3. Contact lenses loaded with small AgNPs ([email protected], diameter≈25-50nm) had approximately the same Ag+ release and anti-microbial abilities, but significantly better visible light transmittance and anti-inflammatory properties than the contact lenses loaded with large AgNPs (Ag@PDA-5, diameter≈50-75nm). After that, in vivo testing indicated the promising therapeutic strategy of multilayer-AgNP-loaded contact lenses ([email protected]) for early bacterial keratitis and fungal keratitis. In addition, PDA coating could provide reactive sites to immobilize other biomolecules or drugs on this multilayer-AgNP-loaded contact lens for further combination therapies in treating bacterial or fungal keratitis. Finally, the stability of the visible light transmittance of multilayer-AgNP-loaded contact lens was detected. The visible light transmittance of [email protected] was weakened after cultured with the extremely high concentration of bacterial, while it was stable in the moderate work environment. Since PDA coating had been wildly used to modification implantation devices, however, few studies about PDA coating modified contact lens was reported so far. Therefore, this research also provides an important basis for using PDA coating to modify the therapeutic contact lens. Key word: Contact lens; Dopamine; Multilayer-AgNPs; Anti-microbial; Visible light transmittance;

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1. Introduction Bacterial and fungal keratitis often cause ocular morbidity and blindness. They are usually caused by drug-resistant bacteria (i.e. Pseudomonas aeruginosa (P. aeruginosa)) 1 or drug-resistant saprophytic fungal pathogens (i.e. Aspergillus Fumigatus (A. Fumigatus)) 2. Once the diagnosis of bacterial or fungal keratitis is confirmed, rapid and effective treatment is critical for controlling subsequent diffuse infection, inflammation, and chronic ulceration. Eye drops are the major method for the early treatment of bacterial or fungal infection. However, eye drops are very limited because of their poor bioavailability, which could be mainly induced by the short retention time of eye drops3-4. Therefore, an effective drug delivery system is desirable for the early treatment of bacterial or fungal infection. Recently, it was reported that contact lenses that carry and release drugs at sustained rates can achieve more efficient therapeutic effects with smaller side effects than eye drops 5-8. Therefore, the use of contact lenses for early treatment of bacterial or fungal keratitis has become a new research focus. Sliver nanoparticles (AgNPs) are well known for their excellent broad-spectrum anti-microbial benefits and low toxicity toward mammalian cells 9-11. AgNPs are also being tested either as alternatives to antibiotics or in combinatory therapies to kill multidrug-resistant P. aeruginosa and A. Fumigatus 12. Therefore, the potential application of the AgNP-loaded contact lenses in the early treatment of bacterial or fungal keratitis has attracted attention 2, 12. Both in situ and ex situ methods have been developed to incorporate AgNPs onto material surfaces 13. However, for the in situ methods, the binding force between the AgNPs and materials is usually weak 14-15. On the other hand, the ex situ methods generally require complex modification and functionalization of either AgNPs or material surfaces to promote their strong bonding 16-19. Therefore, to overcome the above shortcomings, the synthesis and fixation of AgNPs onto poly-dopamine (PDA) coatings has recently become a very popular method. Since reported by H. Lee et. al, the mussel-inspired poly-dopamine (PDA) coatings have become very popular for biomaterials surface modification because that PDA coatings not only can be easily covered on almost all materials and provides the second reaction active sites 20, but also are non-cytotoxic and non-inflammatory 21-23. Since PDA coating was widely used to modify the implantation devices such as vascular stent24 and bone tissue engineering scaffolds25, however, few studies about using PDA coating to modify the contact lens was reported so far. Recently, it was reported that via a simple immersion method, AgNPs can be synthesized and fixed onto the surface of PDA-coated materials by the reduction of AgNO3 solution and immobilization of AgNPs with phenolic hydroxyl groups on PDA coatings 26-30. Undoubtedly, the synthesis and fixation of AgNPs on PDA coatings provide a facile method for fixing AgNPs on contact lenses. However, two main disadvantages still remain in the use of this method for fixing AgNPs on contact lenses: (1) The insufficient amount of loaded AgNPs: Because of the limited amount of phenolic hydroxyl groups that remains on the PDA coating, usually, only a monolayer of sparse AgNPs is synthesized and loaded onto the surface 27-30, which might induce an insufficient ability to release Ag+, thus resulting in insufficient anti-microbial ability 31. (2) The deepened yellow color by the second oxidization of PDA coating: Good visible light transmittance to distinguish colors, e.g. yellow in traffic lights, is an important requirement of contact lenses besides anti-microbial ability 12. Aqueous solutions of dopamine are colorless. When dopamine is oxidized by metal ions or when dopamine is self-polymerized to form PDA 3


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coatings, the phenolic hydroxyl groups on dopamine are partially oxidized to quinone groups, inducing the yellow color of the dopamine solution or PDA coating 32-33. Therefore, we supposed that the use of PDA coatings to reduce the Ag+ to Ag0 to synthesize AgNPs could induce the second oxidization of phenolic hydroxyl groups to quinone groups, thereby resulting in the deepened yellow color of the contact lens. Since using layer-by-layer (LBL) deposition method by repeating the deposition PDA coating and reducing AgNO3 procedure was reported can fabricate multilayer AgNP film and solve the first disadvantages34. However, the LBL method might strongly weaken the visible light transmittance of contact lens because of the second oxidization of PDA coating. Therefore, to overcome the above disadvantages of the traditional method, a facile new method was desirable to fabricate contact lenses with tightly bonded multilayer AgNPs films with good visible light transmittance. To our best knowledge, this multilayer-loaded contact lens could be obtained with the aid of dopamine molecular in the solution, which can act as a reduction agent and a bio-glue. On one hand, dopamine in solution could be used as a reducing agent to synthesize PDA-coated AgNPs via the reduction of Ag+ to Ag0 and then self-polymerize on the AgNPs 35. On the other hand, during the self-polymerization of dopamine onto materials, the dopamine molecule was also reported to act as a bio-glue to bind metallic oxide nanoparticles robustly on material surfaces 36. Inspired by the above knowledge, in this study, we used an excessive dose of dopamine to reduce Ag+ to Ag0 to prepare AgNPs. Thereafter, the surplus dopamine could self-polymerize and cover the AgNPs. Then, the PDA-coated AgNPs were multilayer deposited onto the contact lens, and the surplus dopamine was expected to self-polymerize on the AgNPs and the contact lens to form a strong connection between the AgNPs, as well as between AgNPs and the contact lens. This method could provide excellent anti-microbial ability, avoid the second oxidation of PDA coating and provide the contact lens with good visible light transmittance. In addition, the PDA coating on the surface of the multilayer-AgNPs film could provide active sites (such as phenolic hydroxyl groups) to bind to other biomolecules or drugs (e.g. hyaluronic acid) 37-38 for the combined treatment of bacterial or fungal keratitis. The key point of multilayer-AgNP-loaded contact lens is to fix enough AgNPs on the contact lens to provide sufficient Ag+ to kill microbes. However, if too many AgNPs are loaded onto the contact lens, the visible light transmittance of AgNPs could also decrease. Therefore, releasing more Ag+ by loading relatively few AgNPs is desirable. It was reported that at the same concentration, smaller AgNPs released more Ag+ than larger ones did 39. Therefore, we altered the size of AgNPs by changing the concentration of dopamine and AgNO3 to balance Ag+ release and visible light transmittance. Contact lenses also require low cytotoxicity 40 and low inflammatory properties 41. To our best knowledge, the size of AgNPs and Ag+ release are important factors that affect cytotoxicity and inflammatory response 42-43. Overall, it is a big challenge to comprehensively adjust the above factors to obtain multilayer-AgNP-loaded contact lenses with excellent anti-microbial ability, good visible light transmittance, low cytotoxicity, and low inflammatory properties. In this study, we deposited multilayer AgNPs onto Etafilcon A contact lenses at different concentrations of AgNO3 and dopamine. Then, the visible light transmittance, Ag+ release, particle size, stability, chemical properties, and hydrophilicity of multilayer-AgNP-loaded contact lenses were evaluated. The anti-microbial ability, cytotoxicity, and inflammatory properties of the contact lenses were also evaluated in vitro. Finally, the curative effects of the contact lenses on 4



bacterial and fungal keratitis were evaluated in vivo to determine whether the multilayer-AgNP-loaded contact lenses have potential applications in the early treatment for bacterial and fungal keratitis.

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2. Materials and Methods 2.1. Materials Etafilcon A contact lenses (Acuvue®) were purchased from Johnson & Johnson Co. Ltd., (China). Dopamine hydrochloride was supplied by Sigma-Aldrich Co. Ltd. (China). Silver nitrate (AgNO3) was obtained from Shanghai Chemical Reagent Co. Ltd. (Shanghai, China). MicroBCA was obtained from Pierce Biotechnology Inc. (Rockford, USA). MH broth, glycerin, and wort broth were purchased from HopeBio Co. Ltd. (Qingdao, China). Blood agar plates, SGC fungi Medium, and DensiCHEK Plus® were obtained from bioMerieux Co. Ltd. (France). P. aeruginosa and A. Fumigatus were obtained from Sichuan Provincial People's Hospital. Human corneal epithelial cells (HCECs) and mice macrophages were obtained from Guge Co. Ltd. (Wuhan, China). Mouse interleukin-6 (IL-6) ELISA Kit was obtained from Sigma-Aldrich Co. Ltd. (China). New Zealand white rabbits (4 kg) were sourced from the Sichuan provincial experimental animal special committee farm in Chengdu. 2.2. Preparation of AgNP-loaded contact lens

Fig. 1. The strategy for the fabrication of monolayer- and multilayer-AgNP-loaded contact lens. Contact lenses were treated as illustrated in Fig. 1 and described in detail below. To prepare monolayer-AgNP-loaded contact lens, the contact lens was immersed into a dopamine solution (2 mg/mL, Tris buffer, pH = 8.5, 20°C) for 4 h to deposit the PDA coating. Then, the contact lens with PDA coating was immersed in an AgNO3 solution with a concentration of 60 mmol/L for 4 h at 20°C. After washing in distilled water, the monolayer-AgNP-loaded contact lens was denoted as MONO. 6



On the other hand, to obtain the multilayer-AgNP-loaded contact lens, 0.9 mol and 1.8 mol of Ag+ were mixed with 0.5 mol and 1.0 mol of dopamine (with 1.0 mol and 2.0 mol of phenolic hydroxyl groups), respectively. In detail, 0.225 mL and 0.45 mL of aqueous AgNO3 solution (4 mol/L) were added to 30 mL of dopamine solution (Tris buffer, pH = 8.5) at concentrations of 2.5 mg/mL and 5 mg/mL, respectively, and stirred at 20°C for 4 h to generate PDA-coated AgNPs. Then the AgNPs were centrifuged three times at 2000 rad/min for 5 min. After that, the AgNPs in the supernatant were collected. Then, the contact lens was immersed into the solution consisting of the collected AgNPs and surplus dopamine for 4 h at 20°C to obtain the multilayer-AgNP-loaded contact lens. After washing in distilled water, the multilayer-AgNP-loaded contact lenses were denoted by the concentrations of dopamine as [email protected] and Ag@PDA-5. 2.3. Characterization of AgNP-loaded contact lens The surface topography of AgNP-loaded contact lenses was examined by scanning electron microscopy (SEM Quanta 200, FEI, Holland). The element distribution on the surface was analyzed by energy dispersive spectroscopy (EDS, Quanta 200, FEI, Holland). The UV-vis absorption spectra of AgNP-loaded contact lenses was measured on a UV-vis spectrophotometer (UV-2550, Shimadzu, Japan). The hydrophilicity of AgNP-loaded contact lenses was examined using a drop shape analysis system (DSA 100, Krüss, Germany) by the sessile drop method (5-µL droplet). The surface compositions of the AgNP-loaded contact lenses were detected by X-ray photoelectron spectroscopy (XPS, XSAM800, Kratos Ltd., UK). The instrument was equipped with a monochromatic Al Kα (1486.6 eV) X-ray source operated at 12 kV × 15 mA at a pressure of 2 × 10-10 mB. The C1s peak at 284.8 eV was used as a reference for charge correction. The amount of phenolic hydroxyl group on the contact lenses was detected by microBCA test, which was described elsewhere44-45. Briefly, the linear absorbance at 562 nm could be read after the interaction between phenolic hydroxyl group and BCA test solution. The stability of AgNP attachment on the contact lenses was examined by SEM after 10 min and 20 min of ultrasonic cleaning in water at a frequency of 40 kHz and power of 150 W. 2.4. Ag+ release The monolayer- and multilayer-AgNP-loaded contact lenses were immersed in 1.0 mL of PBS (0.067 M, pH 7.3) using a thermostatic shaker concussion (37°C, 60 rpm) and the soaked solution was replace and collected every day. After 4 days, Ag+ ions in the soaked solutions were analyzed by inductively coupled plasma optical emission spectrometry (Agilent 725, USA). 2.5. In vitro testing of anti-bacterial activity P. aeruginosa gathered from the cornea of a P. aeruginosa keratitis patient was inoculated into a blood agar plate and cultivated in an incubator at 37°C. After the appearance of many colonies, they were eluted with saline and adjusted to 1 × 108 CFU/mL by DensiCHEK Plus, and 10 μL was added into 0.99 mL of MH broth in each well of a 24-well plate. The final concentration of P. aeruginosa in each well was 1 × 106 CFU/mL. The contact lens was added into the P. aeruginosa MH broth and immersed. After incubating at 37°C for 24 h, the bacteria were counted by a serial dilution plate counting method. Each assay was carried out in triplicate.

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2.6. In vitro testing of anti-fungal activity A. fumigatus gathered from the corner of an A. fumigatus keratitis patient was inoculated into an SGC fungi agar plate and cultivated in an incubator at 28°C, After the appearance of many colonies, they were eluted with saline and adjusted to 1 × 108 spores/mL using a microscope, and 10 μL was added into 0.99 mL of wort broth in each well of a 24-well plate. The final concentration of A. fumigatus spores in each well was 1 × 106 spores/mL. The contact lens was added into the A. fumigatus wort broth and immersed. After incubating at 28°C for 24 h, the spore count was determined by a serial dilution plate counting method. Each assay was carried out in triplicate. 2.7. Cytotoxicity assays Human corneal epithelial cells (HCECs) were used in in vitro experiments to confirm the safety of the multilayer-AgNP-loaded contact lenses. HCECs were cultured on a 24-well plate at 37°C for 24 h. After that, the multilayer-AgNP-loaded contact lenses were put into the 24-well plate and cultured for 24 h and 48 h to test the cytotoxicity of Ag+ released by AgNPs on HCECs. The cell culture medium was replaced every 24 h. The cell shape was observed by optical microscopy. The cell density was counted from ten random pictures. The cytotoxicity of the multilayer-AgNP-loaded contact lenses was detected by CCK-8 kit 46. 2.8. Inflammatory properties of multilayer-AgNP-loaded contact lens Peritoneal macrophages from Sprague Dawley rats were cultured on samples at a concentration of 5 × 104 cells/mL to test the inflammatory properties of multilayer-AgNP-loaded contact lenses. After incubation at 37°C for 24 h, the cells on the samples were observed by optical microscopy. The cell activity on samples was detected by CCK-8. IL-6 secreted by macrophages was determined by related kits after one day of culture. 2.9. In vivo testing 2, 47 All animal procedures were approved by the executive of the animal care and ethics committee at the University of Southwest Jiaotong University, and performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. New Zealand white rabbits (4 kg) were sourced from the Sichuan provincial experimental animal special committee farm in Chengdu. After acclimatization for one week, the nictitating membrane was removed surgically from both eyes under general anesthesia. Recovery was allowed for a minimum of one week. Then, to construct the animal model for bacterial keratitis, two 5-mm central corneal scratches on one eye were induced using a 23-gauge needle under general anesthesia, and 20 μL of a P. aeruginosa strain 6294 solution (approximately 2 × 106 CFU/mL) was placed on the eye. To construct the animal model for fungal keratitis, 20 μL of an A. fumigatus solution (approximately 2 × 106 spore/mL) was injected into the corneal stroma. After that, the eyes were held closed for 2 min. Pain control was achieved through subcutaneous injection of 0.02 mg/kg buprenorphine every 12 h. At 6 h after the scratch and bacterial introduction, AgNP contact lenses and normal contact lenses were placed in the left or right eyes of the rabbits randomly. Photo of both eyes were acquired 24 h and 48 h after P. aeruginosa injection and 0, 1, 2, 3, 4, 6, 8, and 16 days after A. fumigatus spore injection. The rabbit eyes infected by P. aeruginosa for 48 h and A. fumigatus for 16 days were stained by hematoxylin and eosin (H&E) and observed by optical microscopy. 8



2.10. Statistics All experiments were performed in triplicate (n = 3). The statistical significance between the sample groups was assessed by SPSS11.5 software using one-way ANOVA and LSD posthoc test. A value of p < 0.05 was considered statistically significant.

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3. Results and Discussion 3.1. Characterization of the monolayer- and multilayer-AgNP-loaded contact lenses

Fig. 2. (A1–A2) Photos and (B) SEM images of AgNP-loaded contact lenses. (C) EDS results of [email protected]. (D) Surface coverage of AgNPs in [email protected], Ag@PDA-5, and MONO. (E) Ag+ released from exposed surface versus time in 1 mL of water for AgNP-loaded contact lenses. (F-G) Particle diameter of AgNPs on [email protected] and Ag@PDA-5. (H) Phenolic hydroxyl group detected by microBCA test. Fig. 2(A1-A2) shows the representative images of AgNP-loaded contact lenses, where color differences can be clearly seen when comparing with the Control. The yellow (brown) color increased and the ability to distinguish colors decreased in the following order: Control > PDA-2 > [email protected] > Ag@PDA-5 > MONO (Fig. 2A1, A2). The colors of words below Control, PDA-2, and [email protected] can be easily distinguished, but distinguishing the colors of words below of Ag@PDA-5 became relatively difficult. However, it was hard to distinguish between the yellow 10



words and white words below MONO. Fig. 2B shows the SEM images showed that multilayer nanoparticles were compactly loaded on [email protected] and Ag@PDA-5, while only monolayer nanoparticles were loosely loaded on MONO. Furthermore, Fig. 2B also shows the nanoparticles on Ag@PDA-5 were larger than those on [email protected]. In attention, the improved surface roughness induced by the fixed AgNP could induced more adsorption of protein, which may resulting uncomfortable feeling when the patient wear the contact lens. As shown in Fig. 2C, the EDS results revealed that the nanoparticles were composed of Ag, indicating that the nanoparticles were AgNPs. Fig. 2D shows the surface coverage of AgNPs, which was approximately 100% on [email protected] and Ag@PDA-5, and decreased to 17.2% on MONO. As shown in Fig. 2E, the release of Ag+ from [email protected] and Ag@PDA-5 was nearly ten times higher than that from MONO. Fig. 2F and Fig. 2G shows that most AgNPs on the [email protected] had a diameter between 25–50 nm, while most AgNPs on the Ag@PDA-5 had a diameter between 50–75 nm. Fig. 2H shows the amount of phenolic hydroxyl group on the contact lenses. The optical density (OD) value of microBCA solution at 562nm on PDA-2, MONO, [email protected] and Ag@PDA-5 were 1.25, 0.12, 0.80, 0.97 respectively. It was interesting that when the contact lens was only deposited by PDA (PDA-2), it was nearly colorless. However, after immersion into the AgNO3 solution, the monolayer-AgNP-loaded contact lens (MONO) became a very deep yellow-brown. It is worth noting that MONO loaded fewer AgNPs but presented a deeper yellow-brown color than [email protected] and Ag@PDA-5. Meanwhile, Fig. 2H shows that the amount of phenolic hydroxyl group on PDA-2 was dramatically decreased to 1/10 after immersed into AgNO3 solution, indicating most of the phenolic hydroxyl group on MONO was oxidized by Ag+. Therefore, we suppose that the deep yellow-brown color of MONO could be related to the second oxidation of the PDA coating by Ag+. When Ag+ was reduced to Ag0, the phenolic hydroxyl groups on the PDA coating were oxidized to quinone groups with yellow color 32-33, which induced the deeper yellow-brown color of MONO. This result indicated that the second oxidation of the PDA coating by Ag+ could be the main factor for the deep brown color of the monolayer-AgNP-loaded contact lens. Therefore, in avoiding the second oxidation of the PDA coating, the multilayer-AgNP-loaded contact lens showed better optical properties than that of the monolayer-AgNP-loaded contact lens fabricated by the traditional method. On the other hand, the results of phenolic hydroxyl group amount indicated that the reactive phenolic hydroxyl group on PDA-2.5 and PDA-5 were abundant. Therefore, the multilayer AgNP films could be further modified with biomolecules or drugs on the active sites of the PDA coating 38 for further combination therapies for bacterial and fungal keratitis. For example, the PEG could be covalently immobilized on the PDA coating to suppress the improved protein adsorption on the multilayer-AgNP-loaded contact lens which might be induced by the increasing of the surface roughness. Furthermore, the amount of Ag+ released from [email protected] and Ag@PDA-5 was much higher than that released from MONO (Fig. 2E). Since the anti-microbial ability of AgNPs was reported to be directly related to Ag+ release 31, this result indicated that the multilayer-AgNP-loaded contact lens may have better anti-microbial ability compared with the monolayer-AgNP-loaded contact lens.

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3.2. In vitro anti-microbial ability of the monolayer- and multilayer-AgNP-loaded contact lenses

Fig. 3. (A) Photos of P. aeruginosa cultured with contact lenses for 24 h. (B) Photos of A. fumigatus cultured with contact lenses for 24 h. (C) Concentration of P. aeruginosa cultured with contact lenses for 24 h. (D) Concentration of A. fumigatus cultured with contact lenses for 24 h. As shown in Fig. 3A, the untreated contact lens and 24-well plate were used as Control and Blank, respectively. After P. aeruginosa was cultured for 24 h, the culture solutions of Blank, Control, and MONO were turbid, while the culture solutions of [email protected] and Ag@PDA-5 were transparent. On the other hand, Fig. 3B shows after A. fumigatus was cultured for 24 h, numerous fungal colonies were observed in the culture solutions of Blank, Control, and MONO, while the culture solutions of [email protected] and Ag@PDA-5 were transparent. The concentrations of P. aeruginosa and A. fumigatus in culture solution after culturing with [email protected] and Ag@PDA-5 were much lower than that in MONO and the initial concentrations (Fig. 3C, D), showing that as expected, the multilayer-AgNP-loaded contact lens had stronger anti-microbial ability than the monolayer-AgNP-loaded contact lens. In addition, there was no significant difference in the anti-microbial ability between [email protected] and Ag@PDA-5.

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3.3. Characterization of the multilayer-AgNP-loaded contact lenses

Fig. 4. (A) Close-up view of the C1s, (B) N1s, and (C) Ag3d peaks of multilayer-AgNP-loaded contact lenses detected by XPS. (D) UV-vis spectra of [email protected] and Ag@PDA-5. (E) Contact angle measurements. (F) Stability of AgNPs on the contact lenses versus ultrasonic cleaning time. The untreated contact lens was used as Control. We further investigated the chemical properties of the multilayer-AgNP-loaded contact lens. Changes in the surface composition of the contact lenses were analyzed by XPS. Close examination of the C1s peaks (Fig. 4A) revealed that peaks at 285.6 eV, which could be attributed to C-N, emerged from [email protected] and Ag@PDA-5, indicating the deposition of PDA coating 48-49. Since XPS mainly reveals the information of the surface at a depth of 0.1–10 nm 50, this result indicates that the PDA coatings were deposited onto the AgNPs. One suspicion is that PDA coating could decrease the oxygen permeability of contact lens and thus induced the corneal hypoxia. However, Petr Henke et al. had reported that the oxygen permeability of polystyrene (PS) nanofiber material was only slightly decreased after coated by PDA51. Moreover, PDA coating was also reported to be used for construction of mixed matrix membrane with high oxygen permeability 52. Therefore, we suppose the PDA coating has good oxygen permeability and further determined it in the animal model (See Fig. 8). Close examination of the N1s peaks and the atomic percentage of N (Fig. 4B) indicated that more PDA was deposited onto the surface of AgNPs on Ag@PDA-5 than on [email protected], which could be related to the higher concentration of dopamine used for the fabrication of Ag@PDA-5. On the other hand, Ag3d peaks and the atomic percentage of Ag (Fig. 4C) revealed that more AgNPs 13


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were exposed on Ag@PDA-5 than on [email protected]. The Ag3d5/2 and Ag3d3/2 peaks of [email protected] and Ag@PDA-5 were found at 367.5 eV to 367.8 eV and 373.5 eV to 373.8 eV, respectively, which could be attributed to Ag2O 53-55. These results indicate that the AgNPs on [email protected] and Ag@PDA-5 consist of Ag2O. It was interesting that significantly more AgNPs were exposed on Ag@PDA-5 than on [email protected], while the amount of Ag+ released from Ag@PDA-5 and [email protected] was approximate the same (Fig. 2E). We supposed that one of the most possible reasons could be related to the smaller size of the AgNPs on [email protected]. It was reported that smaller AgNPs have a stronger ability to release Ag+ than larger AgNPs 31, 39. The UV-vis spectra of [email protected] and Ag@PDA-5 are shown in Fig. 4D. The absorbance peaks at approximately 370 nm were attributed to the PDA coating. On the other hand, the absorbance peaks at approximately 440 nm were attributed to the AgNPs 56. Ag@PDA-5 showed slightly and significantly stronger absorbance at both 370 nm and 440 nm, respectively, than that of [email protected], indicating the slightly and significantly higher deposition of PDA and AgNPs, respectively, on Ag@PDA-5 than those on [email protected]. This result was consistent with the XPS result of N1s and Ag3d (Fig. 4B, C). The absorbance at 400–760 nm (wavelength of visible light) of [email protected] was lower than that of Ag@PDA-5, indicating the better visible light transmittance of [email protected]. Moreover, this result indicates that the deeper brown color (Fig. 2A) and the lower visible light transmittance of Ag@PDA-5 were mainly induced by the deposition status of AgNPs (i.e. amount and size), rather than PDA. [email protected] had approximately the same Ag+ release ability (Fig. 2E) and anti-microbial ability (Fig. 3) but significantly better visible light transmittance property (Fig. 2A, Fig. 4E) than Ag@PDA-5. This indicates that altering the size of AgNPs by changing the concentration of dopamine and AgNO3 could be an effective method to balance Ag+ release (anti-microbial ability) and visible light transmittance. Contact angle measurements are shown in Fig. 4E. The contact angle of Control was approximately 95.7°. On [email protected] and Ag@PDA-5, the contact angle decreased to approximately 48.5° and 42.1°, respectively. The improved hydrophilicity of the multilayer-AgNP-loaded contact lenses could be induced by the synthetic effect of PDA deposition 57, AgNP loading 58, and the nano-porous surface 59 composed of AgNPs. The stability of AgNPs on the contact lenses was detected by ultrasonic cleaning for 10 min and 20 min (Fig. 4F.). No significant difference was observed on the contact lenses before and after ultrasonic cleaning, indicating the good stability of AgNPs on the contact lenses 36. In summary, the multilayer AgNP@PDA coating mainly changed the surface property of contact lens in the following point: (1) Increasing of reactive groups, such as phenolic hydroxyl group and quinone group, by the deposition of PDA coating. (2) Fixed antimicrobial AgNP. (3) Yellow color, which could be induced by both the PDA coating and the AgNP. (4) Increased hydrophilicity, which could be induced by both the PDA coating and the AgNP. (5) Increased surface roughness, which was induced by the fixed AgNP.

3.4. Cytotoxicity of the multilayer-AgNP-loaded contact lenses 14



Fig. 5. (A) HCECs cultured with contact lenses for 24 h and 48 h. (B) Cell density. (C) Cell viability detected by CCK-8. The untreated contact lens was used as Control. The corneal epithelium is a self-renewing, stratified epithelial sheet that provides the first line of defense against invading micro-organisms 60. Generally, the epithelial sheet is separated from the contact lens by tear films 61. Therefore, the cytotoxicity of the multilayer-AgNP-loaded contact lens on HCECs could be mainly induced by the release of Ag+ rather than the direct contact of AgNPs. HCECs were cultured with [email protected] and Ag@PDA-5 to study the potential cytotoxicity of the multilayer-AgNP-loaded contact lenses. As shown in Fig. 5A, the number of HCECs and their morphology when cultured with contact lenses were examined by optical microscopy. After incubation for 24 h, HCECs cultured with all contact lenses exhibited an elliptic or rounded morphology, and after incubation for 48 h, HCECs cultured with all samples exhibited a polygonal morphology. The density of HCECs cultured with the untreated contact lens was higher than that of PDA2.5 and Ag@PDA-5. However, the difference was not statistically significant (Fig. 5B). The result of CCK-8 testing (Fig. 5C) was consistent with the statistical result of cell density. The results of cytotoxicity suggest that the multilayer-AgNP-loaded contact lenses may not be cytotoxic to HCECs. The cytotoxicity of AgNP suspensions was attributed to the AgNPs and Ag+ released from AgNPs 43. However, in this study, the AgNPs were tightly fixed on the surface of the contact lenses. Therefore, the Ag+ released from AgNPs could be the main factor inducing the cytotoxicity. It was reported that very low cytotoxicity was found when treating A549 human lung 15


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carcinoma epithelial-like cells with suspensions containing 0.6 μg/mL Ag+ and 1.9 μg/mL AgNPs for one day, while suspensions containing 1.0 μg/mL Ag+ and 0.5 μg/mL AgNPs presented high cytotoxicity 43. In this study, the rates of Ag+ release in PBS of both [email protected] and Ag@PDA-5 were approximately 0.45-0.65 μg/mL every day (Fig. 2E), which indicated that the concentration of Ag+ in the HCEC culture medium could be close to 0.6 μg/mL after being cultured for 24 h. Therefore, the low cytotoxicity of [email protected] and Ag@PDA-5 was reasonable, as the cell culture medium was replaced every 24 h. Furthermore, the multilayer-AgNP-loaded contact lenses may not present cytotoxicity in an in vivo setting where cells are organized in complex 3D tissue structures 62. 3.5. Inflammatory response of the multilayer-AgNP-loaded contact lenses

Fig. 6. (A) Macrophages cultured with contact lenses for 24 h and 48 h. (B) Cell viability. (C) Interleukin-6 (IL-6) release. The untreated contact lens was used as Control. Bacterial and fungal keratitis are usually induced by injury of the cornea, which is often accompanied by inflammation. Although the process of inflammation is essential for protecting the injured site from invading pathogens, inflammation could also slow the rate of healing and is one of the contributing factors associated with the formation of chronic wounds 63. Therefore, it is necessary to alleviate inflammation. The in vitro inflammatory response of multilayer-AgNP-loaded contact lenses was assessed by culturing macrophages on the contact lenses (Fig. 6). After 24 h of culture, on the untreated contact lens, the adhered macrophages were obviously spread with extended pseudopodia, while the macrophages on [email protected] and on Ag@PDA-5 presented a spherical shape (Fig. 6A). CCK-8 and IL-6 release decreased in the following order: Control > Ag@PDA-5 > [email protected] (Fig. 6B, C). These results indicate that the AgNPs on the contact lenses were cytotoxic to the adhered macrophages, thus presenting anti-inflammatory properties 64. Both the Ag+ ions reacted with thiolate groups to form the Ag–S bond in cellular65, and the generation of ROS from AgNP66 could be the reason of the cytotoxic to macrophages. Furthermore, it was reported that smaller AgNPs possessed higher cytotoxicity to macrophages42, 66. Therefore, the stronger anti-inflammatory 16



effect of [email protected] could be related to the smaller AgNPs that were loaded. 3.6. Early therapeutic effect of [email protected] on bacterial keratitis in vivo

Fig. 7. (A) Photos of rabbit eyes infected by P. aeruginosa. (B) Hematoxylin and eosin (H&E) staining of rabbit eyes infected by P. aeruginosa for 48 h. Rabbits wearing untreated contact lenses were used as the Control. Considering the results of anti-microbial ability, visible light transmittance, cytotoxicity, and inflammatory response, [email protected] was selected to undergo anti-microbial testing in vivo. Compared with the Control group, multilayer-AgNP-loaded contact lenses ([email protected]) exhibited significant therapeutic effect in rabbits with early bacterial keratitis induced by P. aeruginosa infection. As shown in Fig. 7A, after infection with P. aeruginosa for 24 h, the rabbit eye wearing the untreated contact lens became cloudy and partially opaque, while the rabbit eye wearing the [email protected] contact lens showed only slight cloudiness with a discernible pupil. After infection with P. aeruginosa for 48 h, the rabbit eye wearing the untreated contact lens became uniformly opaque with a white ulcer, while the rabbit eye wearing the [email protected] contact lens still only showed slight cloudiness with a discernible pupil. Fig. 7B shows the H&E staining of rabbit eyes infected by P. aeruginosa for 48 h. The thickness of the cornea was significantly decreased in the [email protected] group compared to that in the Control group after infection for 48 h. Meanwhile, the infiltrating inflammatory cells and inflammatory responses of [email protected] were reduced compared with those in the untreated contact lens. All of the above results indicate that the multilayer-AgNP-loaded contact lens might represent a promising therapeutic strategy for early bacterial keratitis treatment.

3.7. Early therapeutic effect of [email protected] on fungal keratitis in vivo 17


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Fig. 8. (A) Photos of rabbit eyes infected by A. fumigatus. (B) Hematoxylin and eosin (H&E) staining of rabbit eyes infected by A. fumigatus for 16 days. Rabbits wearing untreated contact lenses were used as the Control. Compared with the Control group, [email protected] contact lenses exhibited significant therapeutic effect in rabbits with fungal keratitis induced by A. fumigatus infection. As shown in Fig. 8A, after infection with P. aeruginosa for 3 days, the rabbit eye wearing the untreated contact lens became cloudy with a white dotted ulcer, while the rabbit eye wearing the [email protected] contact lens was still clear. After infection with P. aeruginosa for 6 days, the Control group became partially opaque with a massive white ulcer, while the [email protected] group only showed slight cloudiness with a discernible pupil. After being infected for 8 days, the Control group became uniformly opaque with a massive white ulcer and slight hyphema, while the [email protected] group was cloudy with a discernible pupil. Finally, after being infected for 16 days, the Control group was uniformly opaque and showed heavy hyphema, while the [email protected] group was still cloudy with a discernible pupil. On the other hand, after the rabbit wear the PDA coated contact lens ([email protected]) for 16 days, the significant corneal hypoxia was not observed. This result indicated that the PDA coated 18



multilayer-AgNPs-loaded contact lens have good oxygen permeability. Fig. 8B shows the H&E staining of rabbit eyes infected by A. fumigatus for 16 days. The cornea pathology was significantly ameliorated in the [email protected] group compared to the Control group. Meanwhile, the infiltrating inflammatory cells and inflammatory response of the [email protected] group were reduced compared with those in the Control group. All of above results indicate that the multilayer-AgNP-loaded contact lens might represent a promising therapeutic strategy for early fungal keratitis treatment. 3.8. Stability of the visible light transmittance of multilayer-AgNP-loaded contact lens

Fig. 9. The color change of [email protected] in different conditions The PDA coating on the multilayer-AgNP-loaded contact lens still had phenolic hydroxyl group. When the contact lens is stored in the care solution, or is used for the bacterial and fungal keratitis treatment, the oxygen in the care solution or the reactive oxygen species (ROS) generated by the microbial67 on the infected cornea could oxidized the remained phenolic hydroxyl group to the yellow quinone groups, and thus damage the nice visible light transmittance of the contact lens. Therefore, it was important to discover the stability of the visible light transmittance, namely, the stability of color of multilayer-AgNP-loaded contact lens in the store and work environments. As shown in Fig. 9, the color of [email protected] did not change significantly after stored in care solution for 1 month which could be related to the care solution prevent the contact lens from contact with air. This result indicating the visible light transmittance of the contact lens could be stable in the common stored and deliver environment. However, to further prevented oxidation of PDA coating, add some antioxidant, such as Vitamin C68 , in the contact lens care solution could be a promising method. On the other hand, after cultured with P. aeruginosa for 12h, the yellow color of the contact lens was only deepened in the extremely high concentration of bacterial, rather than in the moderate concentration of bacterial. In vivo test showed that the color of the contact lens worn by the P. aeruginosa infect rabbit for 48h was not changed, while it was slightly deepened after worn by the A. fumigatus infect rabbit for 16 days. However, the colors of words below the slightly deepened contact lens still can be easily distinguished. The AgNP loaded PDA coating was not oxidized and become dark yellow when contact with low concentration of bacterial in vitro, or contact with infected rabbit eyes for a short time (24 h), which could be related to the AgNP kill the bacteria quickly, and thus suppressing the generation 19


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of ROS by the bacteria. However, when the AgNP loaded PDA coating contact with extremely high concentration of bacterial, or contact with infected rabbit eyes for a long time (16 days), the PDA coating was oxidized and become dark yellow, which could be induced by the ROS generated by the survived microbial or the oxidative stress environment of the injured eyes. This result indicated the visible light transmittance of [email protected] was relatively stable in the moderate work environment. Therefore, if only in consideration of the visible light transmittance properties, the multilayer-AgNP-loaded contact lens can be used as week or half month disposable contact lenses for early keratitis treatment.

20



4. Conclusion In conclusion, we have provided a facile method to robustly bind multilayer-AgNPs on contact lens surfaces using dopamine as a bio-glue. In comparison with the monolayer-AgNP-loaded contact lens fabricated by traditional processes through PDA coating, the multilayer-AgNP-loaded contact lens had better anti-microbial ability in vitro, which could be related to the higher Ag+ release and better visible light transmittance, induced by avoiding the second oxidation of the PDA coating. Furthermore, the Ag+ released from the multilayer-AgNP-loaded contact lens exhibited low cytotoxicity to HCECs, while the AgNPs loaded on the contact lens showed high cytotoxicity to macrophages, thus inducing anti-inflammatory effects. On the other hand, the shortcoming of the decrease in visible light transmittance induced by the excess of adhered AgNPs on the multilayer-AgNP-loaded contact lens was alleviated by decreasing the size of the AgNPs through changing the concentration of dopamine and AgNO3. In comparison with the contact lens with larger AgNPs (Ag@PDA-5, diameter = 50–75 nm), the contact lens with smaller AgNPs ([email protected], diameter = 25–50 nm) had approximately the same Ag+ release and anti-microbial abilities, but significantly better visible light transmittance and anti-inflammatory properties. After that, the early curative effects of the multilayer-AgNP-loaded contact lens ([email protected]) on bacterial and fungal keratitis were tested in vivo. The pathological changes in rabbit eyes induced by P. aeruginosa and A. fumigatus were alleviated significantly in the [email protected] group, indicating the promising therapeutic strategy of multilayer-AgNP-loaded contact lenses for bacterial and fungal keratitis. Additionally, since the AgNPs were covered by PDA coating, other biomolecules or drugs can be immobilized on this multilayer-AgNP-loaded contact lens through combining with PDA coating for further combination therapies for bacterial and fungal keratitis. Finally, the stability of the visible light transmittance of multilayer-AgNP-loaded contact lens was detected. The visible light transmittance of [email protected] was weakened after cultured with the extremely high concentration of bacterial, while it was stable in the moderate work environment. Since PDA coating had been wildly used to modification the implantation devices, few study about PDA coating modified contact lens was reported so far. Especially, the color change of PDA coated contact lens under oxidation environment, such as AgNO3 solution and bacterial conditions. Therefore, this research also provides an important basis for using PDA coating to modify the contact lens. Acknowledgements This study was supported by the National Natural Science Foundation of China (31700821 (J.C), 81271047 (XQ.L), 81570848 (C.Q)); the Department of Science and Technology of Sichuan Province (2016JY0082 (XQ.L), 2015JZ0004 (C.Q.)); the Department of Sichuan Provincial Health (17PJ504 (XQ.L)). We thank all the participants in this study. Reference 1.

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Table of Contents (TOC) Graphic For Table of Contents Use Only A mussel-inspired facile method to prepare multilayer-AgNP-loaded contact lens for early treatment of bacterial and fungal keratitis ‡ 1,2,3‡ 1‡ Xiaoqi Liu , Jiang Chen *, Chao Qu4 , Gong Bo2,3, Lang Jiang1, Hui Zhao5, Jing Zhang4, Yin Lin3, 3 1 1 Yu Hua , Ping Yang *, Nan Huang , Zhenglin Yang2*

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A Mussel-Inspired Facile Method to Prepare Multilayer-AgNP-Loaded

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