In situ synthesis of silver nanoparticles uniformly distributed on polydopamine-coated silk fibers for antibacterial application

https://doi.org/10.1016/j.jcis.2015.04.015Get rights and content

Abstract

Fabrication of silver nanoparticles (AgNPs)-modified silk for antibacterial application is one of the hottest topics in the textile material research. However, the utilization of a polymer as both 3-dimensional matrix and reductant for the in-situ synthesis of AgNPs on silk fibers has not been realized. In this work, a facile, efficient and green approach was developed to in-situ grow AgNPs on the polydopamine (PDA)-functionalized silk. AgNPs with the size of 30–90 nm were uniformly deposited on the silk fiber surface with the PDA coating layer as a reduction reagent. The AgNPs exhibit excellent face-centered cubic crystalline structures. The bacterial growth curve and inhibition zone assays clearly demonstrate the antibacterial properties of the functionalized silk. Both high Ag+ release level and long-time release profile were observed for the as-prepared AgNPs–PDA-coated silk, indicating the high-density loading of AgNPs and the possible long-term antibacterial effects. This work may provide a new method for the preparation of AgNPs-functionalized silk with antibacterial activity for the clothing and textile industry.

Introduction

Silk from Bombyx mori cocoons is a natural fiber consisting of two main proteins: fibroin and sericin. Because of its luxury sheen and excellent skin affinity, silk has been regarded as “the queen of textiles” and used in textile productions for thousands of years. Over the past decade the application of silk has been extended to the biomedical field as degradable surgical sutures [1] and scaffolds for tissue engineering [2], [3] due to its remarkably mechanical property, biocompatibility and controllable degradability [4]. Although silk could provide a lot of unique properties, the protein nature makes it a matrix for bacterial adhesion and thriving, further resulting in its deformation and even degradation [5]. Further applications of silk textiles and silk-based materials are greatly hindered by the easy adherence and growth of bacteria. In recent years tremendous efforts have been dedicated to the development of unique silk fabrics with antibacterial activity. Surface modification with antimicrobial substances is one of the most acceptable methods. Antimicrobial peptides [6], metal ions [7], polymers [8] and nanomaterials [9], [10], [11] have been employed to functionalize silk surface. Among them, silver nanoparticle (AgNP) is the most attractive one because it has a broad spectrum of antibacterial effects on both Gram-negative and Gram-positive bacteria [12], [13].

In the early stage of research, AgNPs are pre-synthesized firstly and then immobilized on silk surface via physical or chemical adsorption. Since the procedures are quite complicated and tedious, the strategy has been gradually abandoned. The in situ growth of AgNPs on silk surface has been developed as an effective alternative strategy, during which silver ions (Ag+) adsorbed on the silk surface are reduced to form AgNPs. The simple process and the strong binding of AgNPs on silk render the in situ synthesis a better approach for the preparation of AgNPs-coated silk.

Reduction of Ag+ is an essential step for the in situ growth of AgNPs on silk. Chemical reagents such as hydrazine, glucose, sodium borohydride and citrate as well as ultrasound microwave [14] and γ-radiation [15] have been utilized to induce the Ag+ reduction reaction. However, either environment-unfriendly chemicals or expensive instruments are needed in those works. In our previous study, we developed a method to directly immobilize AgNPs on silk via UV-assisted reduction of Ag+ [9]. The approach is green and facile, but UV-caused aging of silk may occur after a long-term exposure. Aggregation of AgNPs on silk is also a main defect for the UV-assisted approach and most of the existing methods. Besides the reductants, high capacity loading of AgNPs is another critical issue that needs to be considered during the preparation of AgNPs-functionalized silk. Various polymers such as polyamide network polymer, poly(vinyl pyrrolidone) and polyacrylic acid have been employed as a 3-dimensional matrix for the high-density growth of AgNPs recently [16], [17], [18]. However, the utilization of a polymer as both 3-dimensional matrix and reductant for the in-situ synthesis of AgNPs on silk fibers has not been realized.

Polydopamine (PDA) is a biocompatible synthetic mimic of mussel adhesive proteins, which forms via polymerization of dopamine, a hormone and neurotransmitter in human body. Since it possesses metal ion chelating capability and redox activities [19], PDA could induce the reduction of Ag+ into AgNPs. More importantly, it has been reported that PDA can adhere on almost all material surfaces [20]. Therefore, PDA could serve as a very promising material to coat the silk surface for in situ growth of AgNPs. The use of PDA for silk surface coating may provide three benefits: firstly, PDA may serve as a 3-dimensional matrix for high-density loading of AgNPs; secondly, PDA could adsorb silver ions and further reduce them into AgNPs without the introduction of other reductants; thirdly, the presence of PDA could avoid direct exposure of AgNPs to oxygen and slow down the release of silver ions. So far, there is no report on PDA-coated silk and its application for the preparation of AgNPs-functionalized silk.

In the present study, PDA was coated on silk and further used to adsorb and reduce silver ions for the fabrication of AgNPs-functionalized silk. The as-prepared silk fibers were characterized with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), Fourier transfer infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) to verify the PDA coating and the growth of AgNPs on the silk surface. Antimicrobial tests including zone of inhibition and growth curve assays were conducted to investigate the antibacterial properties of the AgNPs–PDA-coated silk with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as model microbes. The release of Ag+ from silk surface-immobilized AgNPs was also explored.

Section snippets

Chemicals

Silver nitrate (AgNO3) (AR, ⩾99.8%) and dopamine hydrochloride were bought from Aladdin (Shanghai, China). Tris (hydroxymethyl) aminomethane (Tris) and hydrochloric acid (HCl) were purchased from Sigma–aldrich (St. Louis, MO, USA). Deionized water (resistance over 18  cm) was generated by a Millipore Q water purification system.

Preparation of AgNPs–PDA-coated silk fibers

Raw silk fibers obtained from B. mori silkworm cocoons were degummed in a sodium carbonate (0.05% (w/v)) solution at the boiling temperature for 0.5 h, followed by a

Results and discussion

In order to find the best dopamine concentration for uniform PDA coating, SEM was conducted to investigate the surface morphologies of pristine and PDA-coated silk fibers that were prepared at different dopamine concentrations (Fig. 1). The degummed silk fiber has a very smooth surface, suggesting the successful removal of sericin from raw silk (Fig. 1A). Rough surfaces with a lot of tiny dots can be observed for silk fibers treated with 0.2 and 0.5 mg/mL dopamine solutions. The phenomenon

Conclusions

In the present study, we developed a facile, efficient and green PDA-mediated approach for the preparation of AgNPs-functionalized silk without the introduction of additional reduction reagents. 1.0 mg/mL dopamine solution is recommended to be applied for PDA coating on silk surface. Then AgNPs with the size range of 30–90 nm were synthesized and uniformly distributed on silk fiber, showing excellent face-centered cubic crystalline structures. The PDA coating and AgNPs growth process do not

Acknowledgments

This work is financially supported by Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energies under cstc2011pt-sy90001, Start-up grant under SWU111071 from Southwest University and Chongqing Science and Technology Commission under cstc2012gjhz90002. Z.S. Lu would like to thank the supports by the Specialized Research Fund for the Doctoral Program of Higher Education (RFDP) (Grant No. 20130182120025), Chongqing Natural Science Foundation (cstc2012jjA1137) and Young

References (34)

  • G.H. Altman et al.

    Biomaterials

    (2002)
  • X. Chen et al.

    Biomaterials

    (2008)
  • G. Li et al.

    Mater. Sci. Eng., C

    (2012)
  • L. Bai et al.

    Appl. Surf. Sci.

    (2008)
  • S. Davarpanah et al.

    Appl. Surf. Sci.

    (2009)
  • Z.S. Lu et al.

    Eng. Aspects

    (2014)
  • G. Li et al.

    J. Colloid Interface Sci.

    (2011)
  • Z.S. Lu et al.

    J. Colloid Interface Sci.

    (2014)
  • L. Guo et al.

    Eng. Aspects

    (2013)
  • A.R. Abbasi et al.

    Ultrason. Sonochem.

    (2011)
  • X. Wang et al.

    Chem. Eng. J.

    (2012)
  • V. Ball et al.

    J. Colloid Interface Sci.

    (2012)
  • Q. Lu et al.

    Acta Biomater.

    (2010)
  • X.X. Feng et al.

    Int. J. Biol. Macromol.

    (2007)
  • S.A. Khan et al.

    Dyes Pigm.

    (2012)
  • R.L. Moy et al.

    Am. Fam. Phys.

    (1991)
  • H.J. Jin et al.

    Biomacromolecules

    (2004)
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