Rapid Fabrication of Composite Hydrogel Microfibers for Weavable

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Rapid Fabrication of Composite Hydrogel Microfibers for Weavable and Sustainable Antibacterial Applications Chuntao Chen, Ting Zhang, Beibei Dai, Heng Zhang, Xiao Chen, Jiazhi Yang, Jian Liu, and Dongping Sun ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01351 • Publication Date (Web): 23 Sep 2016 Downloaded from http://pubs.acs.org on September 29, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

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

ACS Sustainable Chemistry & Engineering

Rapid Fabrication of Composite Hydrogel Microfibers for Weavable and Sustainable Antibacterial Applications Chuntao Chen,a Ting Zhang,b Beibei Dai,a Heng Zhang,a Xiao Chen,a Jiazhi Yang,a Jian Liu†b and Dongping Sun†a a

Institute of Chemicobiology and Functional Materials, School of Chemical Engineering,

Nanjing University of Science and Technology, 200 Xiao Ling Wei Street, Nanjing, Jiangsu Province, China. b

Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, 199 Ren Ai

Road, Suzhou Industrial Park, Suzhou, Jiangsu Province, China. †

Corresponding Author

E-mail: [email protected] (Dongping Sun)

ACS Paragon Plus Environment

1


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

Page 2 of 26

ABSTRACT: Microbial infections continue to pose a serious threat to human health, thus calling attention to the development of new materials with better antibacterial applications. Here we report a microfluidic approach to fabricate core-shell GO-AgNPs/BC (Graphene Oxide-Silver Nanoparticles/Bacterial Cellulose) hydrogel microfibers with controlled-releasing and longlasting antibacterial performance. Meters of the composite microfibers can be produced in one minute by using a homemade microfluidic wet-spinning device. The as-prepared microfibers exhibit well-controlled morphological features at the nanoscale and excellent mechanical properties. We have demonstrated that the composite microfibers can effectively sterilize both Gram positive and negative bacterial strains, while remain friendly to normal mammalian cells. This flexible approach of synthesizing core-shell composite microfibers promises important biomedical applications including materials science, tissue engineering, and regenerative medicine.

KEYWORDS: Micro-fabrication; Bacterial Cellulose; Hydrogel Microfibers; Sustainable; Antibacterial.

1 INTRODUCTION Microbial infections remain one of the major fatal reasons in clinical practice, for instance, about half million deaths in neonates every year result from infections including pneumonia, sepsis, meningitis, and so on.1 The healthcare costs associated with the treatment of resistant pathogens have reached $5 billion each year.2 Therefore, there is an increasing need to develop new materials and technologies for antibacterial applications with high effectiveness.3, 4 Up to date, various types of antibacterial reagents have been discovered, including antibiotics, metal ions, enzymes, and quaternary ammonium compounds.5-7 Researchers have been working


2

Page 3 of 26

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


intensively to integrate these antibacterial reagents into new materials or apply them in new formats.3 Among them, the noble metal silver is particularly interesting not only because of its long history as antibacterial household utensils in human civilization, but also on account of several unique advantages such as a broad spectrum of antimicrobial activities, and minimal side effects.2, 8 Silver nanoparticles (AgNPs) and its derivative composites are typically effective in antibacterial applications due to the tremendously enlarged surface area at the nanoscale.9,

10

Recently new development in antibacterial composites emerges by incorporating AgNPs with other 0, 1, 2 dimensional nanomaterials, such as AgNPs@SiO2 hybrid particles11, Ag-embedded TiO2 nanotubes12, or AgNPs-decorated graphene oxide (GO) nanosheets13. Studies on GOAgNPs suggest that a synergistic effect between the two components allows for more effective and swift disinfection than either Ag or GO alone.13-16 AgNPs have also been incorporated onto polymeric fiber,17 glass fiber,18 and electrospinning nanofibers19 with successful demonstration of antibacterial activities.20 However, AgNPs tend to fall off from the fiber surface because of their low resistance to attrition. There remain critical challenges which need to be addressed for practical antibacterial applications. Firstly, the antibacterial efficiency of many composite nanomaterials decays quickly, short of the sustainable bacterial-killing effect. Secondly, the nanomaterials in the colloidal solutions are usually difficult to separate from the residues after the treatment of killing bacteria, which limits their recycling use and increases the risk of chemical pollution to the environment. Thirdly, many antibacterial materials exhibit relatively high cytotoxicity to mammalian cells, which is a serious concern in clinical utilization. Therefore, it is an active research field to develop novel antibacterial materials with better solutions to these problems. Nowadays, the fabrication of microfiber have become a significant techniques in building multifunctional biomaterial. Yoo and co-workers21,

22

have down


3


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

Page 4 of 26

significant work on size-controlled fabrication of microfibers on a microfluidic chip using a 3D hydrodynamic focusing technique. Other studies23-25 also gave us many new guidance in microfabrication and an increasing application have been developed, including drug release and cell culture. Bacterial cellulose (BC) is a natural polysaccharide synthesized by a group of special microorganisms. BC nanofibers have been listed among the top candidate biomaterials because of their excellent biocompatibility and good mechanical strength.26-31 In the present work, we have developed a facile approach to synthesize GO-AgNPs/BC hydrogel microfibers with the microfluidic technology for effective antibacterial applications. The composite hydrogel microfibers exhibit a well-defined coaxial cable-like structure, with GO-AgNPs in the inner core layer and BC hydrogel in the outer shell layer. Meters of the composite hydrogel microfibers can be fabricated in one minute by using a homemade microfluidic wet-spinning device. The morphology and mechanical properties of the composite hydrogel microfibers have been investigated with the detailed characterization. Fabric of warp and weft can be made using GOAgNPs/BC hydrogel microfibers due to their excellent mechanical properties. The unique coreshell geometry of the composite microfibers can minimize the decay rate of bactericidal effect. We have demonstrated an efficient utilization of GO-AgNPs/BC microfibers to sterilize both Gram positive and negative bacterial strains in a recyclable manner. The cytotoxicity test of GOAgNPs/BC microfibers suggests a low side effect to mammalian cells as a potential living tissuefriendly material. Therefore, the GO-AgNPs/BC hydrogel microfibers promise important antibacterial applications in the biomedical field. 2 MATERIALS AND METHODS 2.1 Materials


4

Page 5 of 26

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


The graphite powders were obtained from Sigma-Aldrich. Silver nitrate in the grade of analytical purity was obtained from Sinopharm Chemical Reagent Co., Ltd. (China), and used without further purification. BC samples were cultivated using an Acetobacter xylinum NUST4.2 through a static fermentation process at 30 °C.32 After the treatment with 0.1 M of sodium hydroxide solution at 80 °C for 2 hours to rinse off the bacteria, BC samples were brought back to a neutral pH value by the repeated washing steps with distilled water. Cell culture medium RPMI-1640 and fetal bovine serum (FBS) were purchased from GIBCO. 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyl tetrazolium bromide was purchased from Sigma for the MTT assays. Deionized water was used in the experiments if no further specification was given. 2.2 Preparation of GO-AgNPs/BC hydrogel microfibers

Graphite oxide (GO) was prepared from natural graphite powders through a modified Hummers method.33 The GO-AgNPs were prepared in the following process as reported13: 20 mg GO was dispersed in 50 mL deionized water. Then 15 mg AgNO3 and 20 mg sodium citrate were added into the GO suspension. After violent stirring for 15 min, the temperature of the mixture was raised to boiling point and kept for 60 min. The solid product of the reaction was obtained by a repeated procedure of filtrating, washing and centrifugation. It was dried at 40 °C for 12 h. 1.5% (w/w) bacterial cellulose LiCl/DMAc solution was obtained through previous report.34 The resultant solution was stored at -20 °C overnight. It was thawed and stirred extensively at room temperature to obtain a dilute cellulose solution. The blank BC microfibers were continuously generated in a homemade coaxial microfluidic device using pipette tips and plastic T-shaped connecters (tip inner diameter 270 µm approximately). The typical flow rates of inner BC solution and ethanol layer were set at 20 and 50 mL h-1 respectively. Concentrated GOAgNPs suspension (10 mg mL-1) was prepared by gradually evaporating the water of dilute GO-


5


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

AgNPs solution.35,

36

Page 6 of 26

The GO-AgNPs/BC core-shell hydrogel microfibers were continuously

generated in a homemade double-coaxial microfluidic device (Figure 1 and Figure S1) with the help of micro-pump. For instance, the microfibers with the core/shell diameters of about 50 µm and 100 µm were produced by regulating the flow rates of the GO-AgNPs core, BC shell and ethanol sheath streamed to 10 mL h-1, 25 mL h-1 and 50 mL h-1, respectively. The coagulating bath was a mixture solution of ethanol/water (5:1, v/v). After injecting into the mixture and coagulating for about 30 min, the microfibers were shaped and then rinsed repeatedly by ethanol and deionized water until the pH reached 7. They were dried in air, and stored at 4°C before any subsequent test. 2.3 Characterization

Powder X-ray diffractometry in reflection mode was carried out over a range of 5-82° using a Bruker D8 Advance diffractometer with Cu Kα radiation (40 kV and 35 mA). Raman spectra were recorded from 250 to 2000 cm-1 on a Renishaw Invia Raman Microprobe using a 532 nm argon ion laser. UV-Visible (UV-Vis) spectra of GO and GO-AgNPs were obtained using a SP752-PC UV-Vis spectrophotometer (wavelength from 300 nm to 800 nm). Microscopic images were acquired with an optical microscope (Eclipse TE 200, Nikon, Melville, NY). Scanning electron microscopy (SEM) micrographs including EDS were obtained with an electron microscope (JSM-6300, JEOL, Peabody, MA). Transmission electron microscope (TEM) image acquisition was performed on a JEM-2100 (Japan) and operated at 200 kV. For the TEM measurements, samples were deposited onto the gold grids covered with holey carbon support films. XPS experiment was carried out on a RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with Mg K radiation (h = 1253.6 eV). The hydrodynamic diameter and zeta potentials of GO and GO-AgNPs were measured by DLS with a Zetasizer Nano90 Instrument (Malvern Instruments, Worcestershire, U.K.). The surface morphology and average height of GO


6

Page 7 of 26

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


nanosheets were determined by Multimode Nanoscope Scanning Probe Microscopy System (Bruker Dimension 3100 SPM, USA) using tapping mode operated at the room temperature. 2.4 Mechanical properties of GO-AgNPs/BC hydrogel microfibers

The tensile stress-strain tests were performed on a Microcomputer Control Electronic Universal Testing Machine (SHIMAZU AGS-100NS, Shimadzu Corporation). The strain rate was 5 mm min−1. Tensile test specimens were prepared by cutting the microfibers to 20 mm long yarn. 2.5 Antibacterial evaluation of GO-AgNPs/BC hydrogel microfibers

The antimicrobial activities of the GO, GO-AgNPs, and GO-AgNPs/BC microfibers were compared using the agar diffusion method. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used as the representative Gram positive or negative strains in our experiments. The Luria-Bertani (LB) medium was used for the growth of the bacteria. 20 µL aliquots of the GO and GO-AgNPs samples were dripped over the cell layer. GO-AgNPs/BC microfibers approximately 5-6 cm in length with a “NUST” typeface were incubated in 15 mL of either E. coli or S. aureus cultures under agar for 24 h at 30 °C. The diameters of the inhibition zones of bacteria were measured and compared by disc diffusion method. In addition, 100 cfu mL-1 E. coli and S. aureus bacteria cells were grown in 50 mL liquid LB medium supplemented with 10 µg mL-1 GO, GO-AgNPs, and GO-AgNPs/BC microfibers which contained the identical amount of GO-AgNPs. The antibacterial activities of GO, GO-AgNPs and GO-AgNPs/BC microfibers were determined by the shaking flask method. 50 mL liquid LB medium with bacteria concentration of 100 cfu mL-1 was mixed with 10 µg mL-1 AgNPs or GOAgNPs/BC microfibers (10 µg mL-1) and incubated at 30 °C for 12 h. The collected microfibers were washed with sterilized deionized water and employed for the next cycle of antibacterial


7


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

Page 8 of 26

tests. Growth rates and bacterial concentrations were determined by measuring optical density (OD) of LB in broth medium at 600 nm each hour. 2.6 Cytotoxicity of GO-AgNPs/BC hydrogel microfibers

Mammalian Cells human liver cells (L02) were cultured in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS) at 37 °C. Cells were grown on GO-AgNPs/BC microfibers at 37 °C for 24 h, and the cell viabilities were analyzed using MTT method.37 Immunostaining of the cytoskeleton of L02 cells with FITC-labeled anti-Actin antibody was performed using a well-documented method.38,

39

The fluorescent images were

acquired by a fluorescence microscope (Olympus) configured with a Nuance CCD camera (CRi, USA). As for the SEM images of cells on the microfibers, the cell samples were fixed with 3% glutaraldehyde for 2 h. They were dehydrated by incremental concentrations of ethanol solution (25%, 50%, 70%, 80%, 90%, 95% and absolute ethanol for 0.5h each, v/v), and subsequently freeze dried in a vacuum chamber for 24 h. 3 RESULTS AND DISCUSSION 3.1 Preparation of GO-AgNPs/BC hydrogel microfibers We fabricated a homemade microfluidic device to prepare composite microfibers in a continuous manner with the method of coaxial wet-spinning assembly (Figure 1a and Figure S1).40 The spinneret was featured with a cascade of plastic tips grafting the branched inlets. In our experiments, up to three different suspension/solutions could be pumped through the spinneret in a sheath flow manner, while in the literatrue41, 42 the spinneret was fabricated by inserting a stainless steel needle. We demonstrated that GO-AgNPs/BC composite microfibers could be produced with our device rapidly, with a production rate of 2 cm s-1. Further enhancement in the production throughput was optional by accelerating the flow rates. The freshly-prepared microfibers (Figure 1b) were washed with ethanol, and then dried at the


8

Page 9 of 26

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


ambient temperature. The dried microfibers (Figure 1c) shrank a little in diameter without any structural collapse. Their diameter can be recovered when they were immersed in an aqueous solution. The core/shell diameters (Figure 1d) of the composite microfibers were adjustable, depending on the flow rates during the preparation procedure. We performed a series of experiments using the homemade microfluidic devices to investigate the relationship between the microfiber diameters and the flow rates. As shown in Figure S2, microfibers can be produced with a wide range in diameter, from 50 µm up to 800 µm, by combinatorially adjusting the flow rates for the core/shell layers. We proposed that a diffusion-controlled process of the solvent exchange was predominant for the reconstruction of the hydrogel networking in the GO-AgNPs/BC microfibers. Based on the previous reports,43,

44

the regeneration of cellulose depended on coagulation during solvent

exchange, including solvent (DMAc) diffusing out of and non-solvent (ethanol) diffusing into the layer of cellulose molecules (Figure S7-S8). At the interface between the coagulating bath water/ethanol solution and sheath BC/DMAc fluid, there was a rapid exchange of ethanol and DMAc by short-range diffusion. It assisted the formation of a dense skin layer of BC hydrogel crosslinking with hydrogen bonds. During the drying process after BC precipitation, the shrinkage speed of the outer BC layer was faster than that of the inner GO-AgNPs core, forming a force to wrap the GO-AgNPs nanosheets more tightly.35 This ordered microstructure of GOAgNPs/BC might favor improved mechanical performance of the composite microfibers. 3.2 Structure and morphology The morphology and the cross-sectional composition of the as-prepared microfibers were examined by scanning electronic microscopy (SEM). There was clearly a two-layered coaxial cable-like structure in GO-AgNPs/BC microfibers, including the inner GO-AgNPs core and the


9


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

Page 10 of 26

outer BC shell layer (Figure 2a). Detailed characterization of GO and GO-AgNPs was presented in the electronic supplementary information (Figure S3-S6). Electron dispersive spectroscopy (EDX) further verified the existence of Ag element and it major located in the core of composite nanofibers (Figure 2b). The SEM images also revealed that GO nanosheets were densely stacked in the center of the microfibers (Figure 2c). GO nanosheets with an ordered alignment along the axis mainly resulted from the flowing process, which was a benefit for the improved mechanical strength of the microfibers.41 Figure 2d showed the details of the porous shell layer of BC hydrogel in the composite microfibers. XPS was employed to verify the chemical composition of the GO-AgNPs/BC microfibers (Figure 2e). In high-resolution XPS spectrum (Figure 2f), there were two characteristic peaks centered at 367.4 and 373.4 eV, corresponding to Ag 3d5/2 and Ag 3d3/2, respectively.45 The splitting of the 3d doublet of Ag was 6.0 eV, indicating the formation of metallic silver.46 Both the GO-AgNPs/BC microfibers and pure BC microfibers without the core of GO-AgNPs exhibited excellent mechanical robustness and flexibility. We demonstrated that tight knots could be made using these microfibers without breakdown (Figure 3a-b). The mechanical properties of the microfibers were further investigated using the standard methods described in the experimental section. The GO-AgNPs/BC microfibers or pure BC microfibers in identical diameters (~100 µm) were tested for side-by-side comparison. The deformation mechanism of these BC and GO-AgNPs/BC microfibers can be described by the tension-shear model, a prevalent theory for nanocomposites.47 As shown in Figure 3c, the Young's modulus and the tensile strength of BC microfibers were 6.30 ± 0.30 GPa and 148 ± 5.4 MPa, respectively. The Young's modulus of GO-AgNPs/BC microfibers was nearly comparable (6.24 ± 0.24 GPa), but the tensile strength of GO-AgNPs/BC microfibers was 225 ± 5.8 MPa, significantly higher than


10

Page 11 of 26

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


the control of BC microfibers. Accordingly, the breakage elongation of the composite microfibers (7.5%) was also better than bare BC microfibers (4.3%). There were two important molecular interactions including hydrogen bonds and Van der Waals interactions, which contributed to the incorporation of GO-AgNPs/BC microfibers at the interface of GO nanosheets and BC.45, 48, 49 Graphene and its derivatives were featured with a high in-plane Young’s modulus (nearly five times stronger than steel in the identical conditions) and the flexibility of being bent to large angles50, 51. Therefore, it allowed for a combination of excellent mechanical strength and flexibility by incorporating GO-AgNPs into the hydrogel microfibers. In addition, we attempted to make a fabric by knitting two thin threads of GO-AgNPs/BC microfiber (black color) and pure BC microfiber (white color) back and forth (Figure 3d) manually. It provided a proof-of-concept demonstration of weavable applications in the biomedical field using the composite hydrogel microfibers.36 3.3 Antibacterial performance of the GO-AgNPs/BC hydrogel microfibers The antibacterial performance of the GO-AgNPs/BC hydrogel microfibers was investigated by both Gram negative bacterial strains, E. coli and Gram positive bacterial strains, S. aureus.16 After incubated for 24 h at 30 °C, the areas surrounding the composite microfibers were obviously sterilized, indicating an effective antibacterial performance towards both E. coli and S. aureus (Figure 4a-b). In the control experiments, GO-AgNPs also exhibited very good antibacterial effects by the evidence of the sterilized zones, while the pure GO samples and BC microfibers displayed only a minimal effect in killing bacteria in the specified doses (Figure 4cd, column GO, Figure S9, BC microfibers). In the literature,2,

52

the mechanisms of AgNPs

antibacterial action are yet to be fully clarified, including the exact roles played by the nanoparticles and/or Ag+ ions released from the nanoparticle surface. However, there are some


11


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

Page 12 of 26

well-substantiated explanations for AgNPs or Ag+ ions to interfere with the microbes by inducing irreversible damage on membrane permeability, ROS generation, block of respiration, or inhibition of bacterial DNA replication. In our experiments, the hydrogel microfibers served as an important carrier for the sustained releasing of the biocidal component. Therefore, we further quantified the antibacterial efficiency of the composite microfibers in different incubation time, compared with the positive and negative controls (Figure 4e-f). In short incubation time such as 6 hours, the results of OD600 measurements verified that GO-AgNPs showed the highest antibacterial efficiency, while AgNPs or GO-AgNPs/BC hydrogel microfibers exhibited a moderate effect on bacteria sterilization. Interestingly, when the incubation time was prolonged from 6 hours to 12 hours, the relative increase of OD600 (percentagewise) treated with the composite microfibers was nearly comparable to the sample of GO-AgNPs. Both of them were significantly lower than the other controls. It indicated that the GO-AgNPs/BC microfibers might offer a sustainable antibacterial effect. Next we designed a series of experiments to focus on the antibacterial efficiency between the GO-AgNPs/BC microfibers and the sample of GO-AgNPs, since the latter gave the best performance among the control samples. As shown in Figure 5a-b, the bacterial OD600 values of GO-AgNPs were lower than GO-AgNPs/BC in the experiments of relatively short incubation time (6, 12, 24 h). However, the inhibitory power of GO-AgNPs was actually overtaken by GOAgNPs/BC microfibers in the longer incubation time. It suggested a slower decay rate for GOAgNPs/BC microfibers. In addition, after 6 cycles of reuse, GO-AgNPs/BC microfibers maintained a steady antibacterial efficiency (nearly 70~80% for either E. coli or S. aureus, while GO-AgNPs dropped quickly from 90% to only 20% leftover in the identical conditions. (Figure 5c-d). In the literature, the concerns of recyclability were raised in developing antibacterial


12

Page 13 of 26

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


reagents.53 For example, a method was reported to combine magnetic nanoparticles with silver nanoparticles (PMBC-Ag) on the nanostructured BC (PMBC-Ag). Unfortunately its antimicrobial efﬁciency was decreased by nearly a half in the experiment of reuse against B. subtilis by nearly 4~5 folds against E.coli. Therefore, the antibacterial performance of GOAgNPs/BC microfibers was outstanding in comparing the recyclability. It was attributed to the unique core-shell geometry of the composite microfibers, in which the BC shell layer assisted regulating the fall-off rate of AgNPs or Ag ions by enabling a sustainable releasing mode, instead. 3.4 Low cytotoxicity of GO-AgNPs/BC hydrogel microfibers on mammalian cells The biocompatibility of GO-AgNPs/BC composite microfibers was investigated using mammalian cells. The L02 cells were examined using the standard methyl thiazolyl tetrazolium (MTT) assay after incubation for 24 h. The concentrations of GO-AgNPs and GO-AgNPs/BC in the culture medium were titrated after normalization for a fair comparison. As shown in Figure 6a, more than 90% L02 cells were still alive after 24 h, with a concentration of the composite microfibers equal to 80 µg/mL GO-AgNPs. The same concentration of colloidal GO-AgNPs would only leave 40% of the cells alive. Even to 72 h, the cell viability was also keep at about 80%, at a concentration of 10 µg/mL GO-AgNPs (Figure S11). It demonstrated a tremendouslylower toxicity of GO-AgNPs/BC microfibers than GO-AgNPs, possibly due to a well-controlled releasing effect as a result of the BC hydrogel networking structure. Our experiments supported that the BC hydrogel microfibers could promote cell growth as a cell-friendly scaffold. After L02 cells were cultured on GO-AgNPs/BC hydrogel microfibers for 24 h, they were treated with a standard immunostaining method for the cellular skeleton structure, and imaged with a fluorescent microscope. As shown in Figure 6b, L02 cells were growing well on the microfibers.


13


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

Page 14 of 26

The fluorescent images also suggested that the cells maintained good cytoskeleton structure in their morphology (Figure S11-S12). In addition, the morphological features of L02 cells on GOAgNPs/BC microfibers were characterized with SEM (Figure 6b). The previous studies54 suggested that the cytotoxicity of Ag ion was derived from induced reactive oxygen species (ROS) generation and suppression of reduced glutathione (GSH). The chemical transformation from elemental silver (Ag0)n to Ag+ ions and other Ag-containing reactive species was also playing an important role in the cytotoxicity tests, showing a typical dose-dependent cytotoxicity relationship.55 In our composite hydrogel microfibers, the releasing behaviors of Ag ion or AgNPs were controlled and much slower than the colloidal GO-AgNPs samples. It provided a good explanation for the observed effect of low cytotoxicity of the GO-AgNPs/BC microfibers on the mammalian cells.56 Taken together, the composite hydrogel microfibers may find important biomedical applications such as surgical suture. 4 CONCLUSIONS In summary, we have developed a microfluidic approach for rapid fabrication of GO-AgNPs/BC hydrogel microfibers. In the composite microfibers, GO-AgNPs and BC hydrogel are assembled in a core-shell geometry with a well-defined morphology. The mechanical properties of the composite microfibers are overall improved, thus allowing for complicated folding or knitting operations in fabrics. The BC hydrogel shell layer enables a well-controlled and sustainable releasing of the antibacterial agents from the core layer. Therefore, the composite microfibers can be recycled for multiple rounds of antibacterial experiments with a minimum decay in efficiency. The composite microfibers show very low cytotoxicity to mammalian cells. As a flexible and robust method with the high-throughput performance, our approach can further be


14

Page 15 of 26

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


extended to synthesize varieties of composite microfibers for a broad range of biomedical applications. ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Optical micrographs of the double-coaxial laminar flow microfluidic device, and the composite microfibers; AFM image of GO sheets; SEM images of GO and GO-AgNPs; TEM images of GO-AgNPs; Raman spectra of GO and GO-AgNPs; UV-Vis absorption spectra of GO and GO-AgNPs; XRD analysis of GO and GO-AgNPs with different ratios of Ag and grapheme; Zeta potential of GO and GO/AgNPs in deionized water and ethanol solution. AUTHOR INFORMATION Corresponding Author * Tel: 025 8431 5079. Fax: 025 8443 1939. E-mail: [email protected] (Dongping Sun); [email protected] (Jian Liu). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by Advanced Catalysis and Green Manufacturing Collaborative Innovation Center (Changzhou University, 213164), Synergetic Research Center for Advanced Micro-Nano Materials and Technology of Jiangsu Province, Collaborative Innovation Center of Suzhou Nano Science and Technology, National Natural Science Foundation of China (Grants 51272106, 51303083 and 21275106), the Major State Basic Research Development Program


15


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

Page 16 of 26

(973 program, Grant 2013CB932702), the Fundamental Research Funds for the Central Universities (Grant 30920130121001), Research Fund for the Doctoral Program of Higher Education of China (RFDP) (Grant 20123219110015), the Nature Science Foundation of Jiangsu Province (BK20130759), the Science and Technology Innovation Fund of QiXia District (201528), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD, China). REFERENCES 1. Tshefu, A.; Lokangaka, A.; Ngaima, S.; Engmann, C.; Esamai, F.; Gisore, P.; Ayede, A. I.; Falade, A. G.; Adejuyigbe, E. A.; Anyabolu, C. H. Simplified antibiotic regimens compared with injectable procaine benzylpenicillin plus gentamicin for treatment of neonates and young infants with clinical signs of possible serious bacterial infection when referral is not possible: a randomised, open-label, equivalence trial. The Lancet 2015, 385, (9979), 1767-1776. 2. Rizzello, L.; Pompa, P. P. Nanosilver-based antibacterial drugs and devices: mechanisms, methodological drawbacks, and guidelines. Chem. Soc. Rev. 2014, 43, (5), 1501-1518. 3. Krishnamoorthy, M.; Hakobyan, S.; Ramstedt, M.; Gautrot, J. E. Surface-Initiated Polymer Brushes in the Biomedical Field: Applications in Membrane Science, Biosensing, Cell Culture, Regenerative Medicine and Antibacterial Coatings. Chem. Rev. 2014, 114, (21), 1097611026. 4. Tong, R.; Tang, L.; Ma, L.; Tu, C.; Baumgartner, R.; Cheng, J. Smart chemistry in polymeric nanomedicine. Chem. Soc. Rev. 2014, 43, (20), 6982-7012. 5. Kholmanov, I. N.; Stoller, M. D.; Edgeworth, J.; Lee, W. H.; Li, H.; Lee, J.; Barnhart, C.; Potts, J. R.; Piner, R.; Akinwande, D.; Barrick, J. E.; Ruoff, R. S. Nanostructured Hybrid Transparent Conductive Films with Antibacterial Properties. ACS nano 2012, 6, (6), 5157-5163. 6. Zhao, Y.; Ye, C.; Liu, W.; Chen, R.; Jiang, X. Tuning the composition of AuPt bimetallic nanoparticles for antibacterial application. Angew. Chem., Int. Ed. 2014, 53, (31), 8127-8131. 7. Saif, M. J.; Anwar, J.; Munawar, M. A. A novel application of quaternary ammonium compounds as antibacterial hybrid coating on glass surfaces. Langmuir 2008, 25, (1), 377-379. 8. Rai, M.; Yadav, A.; Gade, A. Silver nanoparticles as a new generation of antimicrobials. Biotechnol. Adv. 2009, 27, (1), 76-83. 9. Cui, J.; Hu, C.; Yang, Y.; Wu, Y.; Yang, L.; Wang, Y.; Liu, Y.; Jiang, Z. Facile fabrication of carbonaceous nanospheres loaded with silver nanoparticles as antibacterial materials. J. Mater. Chem. 2012, 22, (16), 8121-8126. 10. Kumar, R.; Munstedt, H. Silver ion release from antimicrobial polyamide/silver composites. Biomaterials 2005, 26, (14), 2081-2088. 11. Ko, Y.-S.; Joe, Y. H.; Seo, M.; Lim, K.; Hwang, J.; Woo, K. Prompt and synergistic antibacterial activity of silver nanoparticle-decorated silica hybrid particles on air filtration. J. Mater. Chem. B 2014, 2, (39), 6714-6722. 12. Mei, S.; Wang, H.; Wang, W.; Tong, L.; Pan, H.; Ruan, C.; Ma, Q.; Liu, M.; Yang, H.; Zhang, L.; Cheng, Y.; Zhang, Y.; Zhao, L.; Chu, P. K. Antibacterial effects and biocompatibility


16

Page 17 of 26

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


of titanium surfaces with graded silver incorporation in titania nanotubes. Biomaterials 2014, 35, (14), 4255-4265. 13. Tang, J.; Chen, Q.; Xu, L.; Zhang, S.; Feng, L.; Cheng, L.; Xu, H.; Liu, Z.; Peng, R. Graphene oxide-silver nanocomposite as a highly effective antibacterial agent with speciesspecific mechanisms. ACS Appl. Mater. Interfaces 2013, 5, (9), 3867-3874. 14. Luo, Z.; Yuwen, L.; Han, Y.; Tian, J.; Zhu, X.; Weng, L.; Wang, L. Reduced graphene oxide/PAMAM-silver nanoparticles nanocomposite modified electrode for direct electrochemistry of glucose oxidase and glucose sensing. Biosens. Bioelectron. 2012, 36, (1), 179-185. 15. Li, C.; Wang, X.; Chen, F.; Zhang, C.; Zhi, X.; Wang, K.; Cui, D. The antifungal activity of graphene oxide-silver nanocomposites. Biomaterials 2013, 34, (15), 3882-3890. 16. Yu, L.; Zhang, Y.; Zhang, B.; Liu, J. Enhanced antibacterial activity of silver nanoparticles/halloysite nanotubes/graphene nanocomposites with sandwich-like structure. Sci. Rep. 2014, 4, 4551. 17. Song, K.; Wu, Q.; Zhang, Z.; Ren, S.; Lei, T.; Negulescu, I. I.; Zhang, Q. Porous carbon nanofibers from electrospun biomass tar/polyacrylonitrile/silver hybrids as antimicrobial materials. ACS Appl. Mater. Interfaces 2015, 7, (27), 15108-15116. 18. Cabal, B.; Quintero, F.; Díaz, L. A.; Rojo, F.; Dieste, O.; Pou, J.; Torrecillas, R.; Moya, J. S. Nanocomposites of silver nanoparticles embedded in glass nanofibres obtained by laser spinning. Nanoscale 2013, 5, (9), 3948-3953. 19. Almajhdi, F. N.; Fouad, H.; Khalil, K. A.; Awad, H. M.; Mohamed, S. H.; Elsarnagawy, T.; Albarrag, A. M.; Al-Jassir, F. F.; Abdo, H. S. In-vitro anticancer and antimicrobial activities of PLGA/silver nanofiber composites prepared by electrospinning. J. Mater. Chem. Sci. 2014, 25, (4), 1045-1053. 20. Song, J.; Birbach, N. L.; Hinestroza, J. P. Deposition of silver nanoparticles on cellulosic fibers via stabilization of carboxymethyl groups. Cellulose 2012, 19, (2), 411-424. 21. Yoo, I.; Song, S.; Yoon, B.; Kim, J. M. Size-controlled fabrication of polydiacetyleneembedded microfibers on a microfluidic chip. Macromol. Rapid Commun. 2012, 33, (15), 125661. 22. Yoo, I.; Song, S.; Uh, K.; Lee, C. W.; Kim, J. M. Size-Controlled Fabrication of Polyaniline Microfibers Based on 3D Hydrodynamic Focusing Approach. Macromol. Rapid Commun. 2015, 36, 1272-1276. 23. Cheng, Y.; Zheng, F.; Lu, J.; Shang, L.; Xie, Z.; Zhao, Y.; Chen, Y.; Gu, Z. Bioinspired multicompartmental microfibers from microfluidics. Adv. Mater. 2014, 26, (30), 5184-90. 24. Xiao, Y.; Zhang, B.; Liu, H.; Miklas, J. W.; Gagliardi, M.; Pahnke, A.; Thavandiran, N.; Sun, Y.; Simmons, C.; Keller, G. Microfabricated perfusable cardiac biowire: a platform that mimics native cardiac bundle. Lab Chip 2013, 14, (5), 869-82. 25. Yetisen, A. K.; Hang, Q.; Manbachi, A.; Butt, H.; Dokmeci, M. R.; Hinestroza, J. P.; Skorobogatiy, M.; Khademhosseini, A.; Yun, S. H. Nanotechnology in Textiles. ACS Nano 2016, 87. 26. Huang, Y.; Zheng, M.; Lin, Z.; Zhao, B.; Zhang, S.; Yang, J.; Zhu, C.; Zhang, H.; Sun, D.; Shi, Y. Flexible cathodes and multifunctional interlayers based on carbonized bacterial cellulose for high-performance lithium–sulfur batteries. J. Mater. Chem. A 2015, 3, (20), 10910-10918. 27. Huang, Y.; Zhu, C.; Yang, J.; Nie, Y.; Chen, C.; Sun, D. Recent Advances in Bacterial Cellulose. Cellulose 2013, 21, (1), 1-30. 28. Klemm, D.; Heublein, B.; Fink, H.-P.; Bohn, A. Cellulose: Fascinating Biopolymer and


17


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

Page 18 of 26

Sustainable Raw Material. Angew. Chem., Int. Ed. 2005, 44, (22), 3358-3393. 29. Park, S.; Park, J.; Jo, I.; Cho, S. P.; Sung, D.; Ryu, S.; Park, M.; Min, K. A.; Kim, J.; Hong, S.; Hong, B. H.; Kim, B. S. In situ hybridization of carbon nanotubes with bacterial cellulose for three-dimensional hybrid bioscaffolds. Biomaterials 2015, 58, 93-102. 30. Märtson, M.; Viljanto, J.; Hurme, T.; Laippala, P.; Saukko, P. Is cellulose sponge degradable or stable as implantation material? An in vivo subcutaneous study in the rat. Biomaterials 1999, 20, (21), 1989-1995. 31. Chang, C.; Duan, B.; Cai, J.; Zhang, L. Superabsorbent hydrogels based on cellulose for smart swelling and controllable delivery. European Polymer Journal 2010, 46, (1), 92-100. 32. Sun, D.; Zhou, L.; Wu, Q.; Yang, S. Preliminary research on structure and properties of nano-cellulose. J. Wuhan Univ. Technol., Mater. Sci. Ed. 2007, 22, (4), 677-680. 33. William, S.; Hummers, J.; Offeman, R. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, (6), 1339–1339. 34. Soykeabkaew, N.; Sian, C.; Gea, S.; Nishino, T.; Peijs, T. All-cellulose nanocomposites by surface selective dissolution of bacterial cellulose. Cellulose 2009, 16, (3), 435-444. 35. Kou, L.; Huang, T.; Zheng, B.; Han, Y.; Zhao, X.; Gopalsamy, K.; Sun, H.; Gao, C. Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics. Nat. Commun. 2014, 5, 4754. 36. Onoe, H.; Okitsu, T.; Itou, A.; Kato-Negishi, M.; Gojo, R.; Kiriya, D.; Sato, K.; Miura, S.; Iwanaga, S.; Kuribayashi-Shigetomi, K.; Matsunaga, Y. T.; Shimoyama, Y.; Takeuchi, S. Metre-long cell-laden microfibres exhibit tissue morphologies and functions. Nat. Mater. 2013, 12, (6), 584-590. 37. Hanelt, M.; Gareis, M.; Kollarczik, B. Cytotoxicity of mycotoxins evaluated by the MTTcell culture assay. Mycopathologia 1994, 128, (3), 167-174. 38. Svensson, A.; Nicklasson, E.; Harrah, T.; Panilaitis, B.; Kaplan, D.; Brittberg, M.; Gatenholm, P. Bacterial cellulose as a potential scaffold for tissue engineering of cartilage. Biomaterials 2005, 26, (4), 419-431. 39. Dugan, J. M.; Gough, J. E.; Eichhorn, S. J. Directing the morphology and differentiation of skeletal muscle cells using oriented cellulose nanowhiskers. Biomacromolecules 2010, 11, (9), 2498-2504. 40. Shi, X.; Ostrovidov, S.; Zhao, Y.; Liang, X.; Kasuya, M.; Kurihara, K.; Nakajima, K.; Bae, H.; Wu, H.; Khademhosseini, A. Microfluidic Spinning of Cell-Responsive Grooved Microfibers. Adv. Funct. Mater. 2015, 25, (15), 2250-2259. 41. Zhao, Y.; Jiang, C.; Hu, C.; Dong, Z.; Xue, J.; Meng, Y.; Zheng, N.; Chen, P.; Qu, L. Large-Scale Spinning Assembly of Neat, Morphology-Defined, Graphene-Based Hollow Fibers. ACS nano 2013, 7, (3), 2406–2412. 42. Yu, Y.; Wen, H.; Ma, J.; Lykkemark, S.; Qin, H. X. A. Flexible Fabrication of Biomimetic Bamboo‐Like Hybrid Microfibers (pages 2494–2499). Advanced materials 2015, 26, (16), 2494-9. 43. Li, R.; Zhang, L.; Xu, M. Novel regenerated cellulose films prepared by coagulating with water: Structure and properties. Carbohydr. Polym. 2012, 87, (1), 95-100. 44. Lee, C. M. H. A. K. Y. P. K. S. a. S.-H. Microfluidic Chip-Based Fabrication of PLGA Microfiber Scaffolds for Tissue Engineering. Langmuir 2008, 24, (13), 6845-6851. 45. Jiang, B.; Tian, C.; Song, G.; Chang, W.; Wang, G.; Wu, Q.; Fu, H. A novel Ag/graphene composite: facile fabrication and enhanced antibacterial properties. J. Mater. Chem. Sci. 2012, 48, (5), 1980-1985.


18

Page 19 of 26

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


46. Pasricha, R.; Gupta, S.; Srivastava, A. K. A facile and novel synthesis of Ag-graphenebased nanocomposites. Small 2009, 5, (20), 2253-2259. 47. Xu, Z.; Sun, H.; Zhao, X.; Gao, C. Ultrastrong fibers assembled from giant graphene oxide sheets. Adv. Mater. 2013, 25, (2), 188-193. 48. Lu, H. F.; Narayanan, K.; Lim, S. X.; Gao, S.; Leong, M. F.; Wan, A. C. A 3D microfibrous scaffold for long-term human pluripotent stem cell self-renewal under chemically defined conditions. Biomaterials 2012, 33, (8), 2419-2430. 49. Si, H.; Luo, H.; Xiong, G.; Yang, Z.; Raman, S. R.; Guo, R.; Wan, Y. One‐Step In Situ Biosynthesis of Graphene Oxide–Bacterial Cellulose Nanocomposite Hydrogels. Macromol. Rapid Commun. 2014, 35, (19), 1706-1711. 50. Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.-H.; Kim, P.; Choi, J.-Y.; Hong, B. H. Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 2009, 457, (7230), 706-710. 51. Stankovich, S.; Dikin, D. A.; Dommett, G. H.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S. Graphene-based composite materials. Nature 2006, 442, (7100), 282-286. 52. Franci, G.; Falanga, A.; Galdiero, S.; Palomba, L.; Rai, M.; Morelli, G.; Galdiero, M. Silver nanoparticles as potential antibacterial agents. Molecules 2015, 20, (5), 8856-8874. 53. Sureshkumar, M.; Siswanto, D. Y.; Lee, C.-K. Magnetic antimicrobial nanocomposite based on bacterial cellulose and silver nanoparticles. Journal of Materials Chemistry 2010, 20, (33), 6948-6955. 54. Wang, L.; Zhang, T.; Li, P.; Huang, W.; Tang, J.; Wang, P.; Liu, J.; Yuan, Q.; Bai, R.; Li, B. Use of Synchrotron Radiation Analytical Techniques to Reveal Chemical Origin of Silver Nanoparticle Cytotoxicity. ACS nano 2015, 9, 6532-6547. 55. Piao, M. J.; Kang, K. A.; Lee, I. K.; Kim, H. S.; Kim, S.; Choi, J. Y.; Choi, J.; Hyun, J. W. Silver nanoparticles induce oxidative cell damage in human liver cells through inhibition of reduced glutathione and induction of mitochondria-involved apoptosis. Toxicol. Lett. 2011, 201, (1), 92-100. 56. Shah, S.; Yin, P. T.; Uehara, T. M.; Chueng, S. T.; Yang, L.; Lee, K. B. Guiding stem cell differentiation into oligodendrocytes using graphene-nanofiber hybrid scaffolds. Adv. Mater. 2014, 26, (22), 3673-3680.


19


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

Page 20 of 26

Figure 1. (a) Schematic illustration of the coaxial spinning process to produce the core-shell GOAgNPs/BC hydrogel microfibers; Hydrogen bonds assist the regeneration of the BC hydrogel microfibers in a coagulating bath of ethanol. (b) Optical photographs of the freshly-prepared GOAgNPs/BC microfibers. (c) Optical photographs of the dried GO-AgNPs/BC microfibers. (d) Optical micrographs of GO-AgNPs/BC microfibers with different diameters of the GO-AgNPs core.


20

Page 21 of 26

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


Figure 2. (a) SEM cross-sectional image of the core-shell GO-AgNPs/BC microfiber; (b) EDX mapping of Ag element in the central zone of (a); The morphological details of the GO nanosheets (c); and porous shell layer of BC hydrogel (d) in the composite microfiber; (e) XPS spectra of BC and GO-AgNPs/BC nanocomposite; (f) The spectral analysis of deconvolution in Ag3d.


21


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

Page 22 of 26

Figure 3. (a) SEM images of BC microfibers in different orientation or knitted structure; (b) SEM images of GO-AgNPs/BC microfibers in different orientation or knitted structure; (c) Stress-strain curves and tensile test results on BC and GO-AgNPs/BC microfibers, the strain rate: 5 mm min−1, Error bar: standard deviation (n = 3); (d) Optical photograph of a fabric demonstration interweaved using two thin threads of BC microfiber and GO-AgNPs/BC microfiber.


22

Page 23 of 26

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


Figure 4. The antibacterial performance of GO-AgNPs and the GO-AgNPs/BC hydrogel microfibers against Gram negative bacterial strains, E. coli (a, c and e) and Gram positive bacterial strains, S. aureus (b, d and f). Error bar: standard deviation (n = 3).


23


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

Page 24 of 26

Figure 5. Growth of E. coli (a) and S. aureus (b) in LB liquid medium in the presence of GOAgNPs or GO-AgNPs/BC microfibers (10 µg mL-1); The recyclability performance of GOAgNPs or GO-AgNPs/BC microfibers (10 µg mL-1) against E. coli (c) and S. aureus (d) with an incubation of 12 h in each cycle. The control samples without the antibacterial reagents were included

for

normalization.

Error

bar:

standard

deviation

(n

=

3).


24

Page 25 of 26

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


Figure 6. (a) Relative viabilities of L02 cells cultured in the media containing different concentrations of the GO-AgNPs and GO-AgNPs/BC microfibers for 24 h, Error bars: standard deviations (n = 3); (b) Fluorescence images (left) of L02 cellular skeleton structure and SEM images (right) of L02 cells cultured on the GO-AgNPs/BC microfibers.


25


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

Page 26 of 26

For Table of Contents Use Only

Rapid Fabrication of Composite Hydrogel Microfibers for Weavable and Sustainable Antibacterial Applications Chuntao Chen, Ting Zhang, Beibei Dai, Heng Zhang, Xiao Chen, Jiazhi Yang, Jian Liu† and Dongping Sun†

This manuscript reports a microfluidic approach to fabricate core-shell GO-AgNPs/BC hydrogel microfibers for antibacterial applications with a controlled-releasing and long-lasting effect.


26

Rapid Fabrication of Composite Hydrogel Microfibers for Weavable

Recommend Documents