Elsevier

Applied Surface Science

Volume 374, 30 June 2016, Pages 290-296
Applied Surface Science

Antimicrobial activity of biopolymeric thin films containing flavonoid natural compounds and silver nanoparticles fabricated by MAPLE: A comparative study

https://doi.org/10.1016/j.apsusc.2015.11.252Get rights and content

Highlights

  • We successfully deposited composite quercetin dehydrate-, resveratrol- and silver nanoparticle-polyvinylpyrrolidone thin coatings with chemical structure close to that of the starting materials by MAPLE.

  • Thin film morphology studies revealed a uniform surface without aggregates or grains on the top of the surface.

  • MAPLE-deposited thin films exhibited antibacterial activity against Gram-positive and Gram-negative bacterial strains.

  • We demonstrated the potential use of these hybrid systems and MAPLE deposition method for the development of new harmless, ecological antimicrobial strategies.

Abstract

The purpose of this study was to investigate the interactions between microorganisms, including the planktonic and adherent organisms, and biopolymer (polyvinylpyrrolidone), flavonoid (quercetin dihydrate and resveratrol)-biopolymer, and silver nanoparticles-biopolymer composite thin films that were deposited using matrix assisted pulsed laser evaporation (MAPLE). A pulsed KrF* excimer laser source was used to deposit the aforementioned composite thin films, which were characterized using Fourier transform infrared spectroscopy (FT-IR), infrared microscopy (IRM), scanning electron microscopy (SEM), Grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). The antimicrobial activity of thin films was quantified using an adapted disk diffusion assay against Gram-positive and Gram-negative bacteria strains. FT-IR, AFM and SEM studies confirmed that MAPLE may be used to fabricate thin films with chemical properties corresponding to the input materials as well as surface properties that are appropriate for medical use. The silver nanoparticles and flavonoid-containing films exhibited an antimicrobial activity both against Gram-positive and Gram-negative bacterial strains demonstrating the potential use of these hybrid systems for the development of novel antimicrobial strategies.

Introduction

Antimicrobial resistance has become a key issue affecting public health throughout the world [1], [2], reaching a crisis point in both hospitals [3] and community-acquired infections. Due to this important issue, the search for new classes of antibiofilm agents and therapeutic strategies has become a research priority [4]. One major cause rendering traditional antimicrobial treatments ineffective is the formation of bacterial biofilms [5]. Prevention of biofilm-associated infections frequently requires high concentrations of antimicrobial agents (often synthetic drugs) for biofilm penetration and microbial eradication. However, the use of high concentrations of antimicrobial agents is commonly associated with a higher incidence of undesired side effects ranging from relatively harmless (nausea, vomiting, diarrhea, skin rashes and itching) to serious and life-threatening (anemia, serious damage to organs such as kidneys, liver, ears, and to the nervous system, choking and difficulty in breathing, and allergic reactions (anaphylaxis) that can result in death) [6]. Many different approaches have been developed to decrease the incidence of medical device-related infection. One way to prevent infection is by modifying the surface of the devices in such a way that no bacterial adhesion could occur. Incorporation of antimicrobial agents in the bulk material or as a biopolymeric surface coating has been considered a viable alternative for incorporation of antibiotics [7]. New challenges and directions in antimicrobial coating research include sintering and developing novel material composites that meet specific requirements: proven biocompatibility and reduced toxicity, long lasting antimicrobial efficacy, material and application versatility [8]. Substantial attention has been focused on exploration and utilization of secondary metabolites of plants (phytochemicals) as an alternative to and/or in combination with traditional antibiotics for treating infections. Among the phytochemicals, flavonoids seem to be the most potentially useful candidates because they are widely distributed in edible plants and possess broad pharmacologic activity [9]. They are a group of heterocyclic organic compounds commonly found in fruit, vegetables, nuts, seeds, stems, flowers, tea, wine, propolis and honey [10]. The many pharmacological effects of flavonoids are linked to their ability to act as strong antioxidants and free radical scavengers, to chelate metals, and to interact with enzymes, adenosine receptors, and biomembranes [11]. They are used to treat disorders of the peripheral circulation, to lower blood pressure, and to improve aquaresis. Also, they are anti-inflammatory, antispasmodic, anti-allergic agents and possess antimicrobial activity [12].

Biopolymer coatings can be deposited by a wide variety of techniques that range in their complexity and applicability. The choice of an appropriate deposition technique depends upon the physicochemical properties of the biopolymer, the requirements for film quality and the substrate that is being coated. The simplest methods involve the application of a liquid solution of a biopolymer in a volatile solvent, including aerosols, dip coating, and spin coating. Some of these techniques are applicable to bulk polymer materials, including vacuum evaporation and laser processing. These techniques imply in situ polymerization using plasma, electrochemical, catalytic, or photo-activated processes to convert the starting material or monomer to a polymer on a substrate surface. In order to obtain thin, uniform and adherent coatings over an extended substrate surface area, or in localized areas, laser processing offers an attractive alternative because of its advantages: accurate and precise thickness control, preservation of chemical integrity, desirable physicochemical properties, compatibility with non-contact masking techniques and low levels of degradation. Among the various laser processing techniques, the most suitable approaches to fabricate high quality assays appropriate for antimicrobial investigations is matrix assisted pulsed laser evaporation (MAPLE) [13]. It provides a gentle mechanism for transferring many different types of compounds that include small and large molecular weight species (e.g., organic, polymeric and biologic molecules, conjugated molecules, nanoparticles and complex materials) from the condensed phase into the vapor phase without any significant degradation [14]. This transfer is achieved by careful optimization of the MAPLE deposition conditions (laser wavelength, laser fluence, repetition rate, target-substrate distance, solvent type, material concentration, substrate temperature, background gas, vacuum chamber pressure) [15]. The MAPLE system includes a pulsed laser beam, vacuum chamber, pump system, MAPLE target mounted on a refrigerated target holder, and a substrate. This technique is available in multiple variants. For example, resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) technique that uses an infrared laser wavelength tuned to vibrational modes in the target material provides a controllable and universal thin-film deposition for antimicrobial organic coatings [16], [17]. Ultraviolet (UV) laser based MAPLE (UV-MAPLE) was used for the deposition of polymer matrices that contained gentamicin antibiotic [18], [19] or silver nanoparticles [20] for antimicrobial applications. In our previous work, we have obtained functionalized biopolymer-antibiotic, biopolymer-flavonoid, and biopolymer-flavonoid-antibiotic coatings by UV-MAPLE that have demonstrated significant antimicrobial properties [21]. In the present study, we have used UV-MAPLE to obtain quercetin dehydrate-, resveratrol- and silver nanoparticle-polyvinylpyrrolidone biopolymer thin films, characterized their chemical structure and morphology by Fourier transform infrared spectroscopy (FT-IR), infrared microscopy (IRM), scanning electron microscopy (SEM), Grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM), and evaluated their antimicrobial activity against both Gram-positive and Gram-negative bacteria in view of the potential use of these hybrid systems for the development of novel antimicrobial strategies.

Section snippets

Materials

The coatings components considered in this study include quercetin dihydrate (Q) and resveratrol (R) flavonoids, polyvinylpyrrolidone (PVP) biopolymer (B), the silver nanoparticle (AgNP) dispersions in H2O or ethylene glycol (EG). The solvent used for MAPLE target preparation was dimethyl sulfoxide (DMSO). All of the chemicals were purchased from commercial sources: quercetin dihydrate from Sigma–Aldrich, St. Louis, MO, USA, resveratrol from Sigma–Aldrich Chemie GmbH, Steinheim, Germany and

FTIR investigations

The IR mapping studies of the drop-cast films and the related MAPLE-deposited thin films are shown in Fig. 1. The mapping intensity was built based on the intensity of IR absorbance of the monitored peaks (1643 cm−1, 2924 cm−1); they are directly proportional to the color changes starting from blue (the lowest intensity), green, yellow to finally red (the highest intensity) [22], [23]. According to Fig. 1, it can be seen that a uniform surface is obtained in the case of MAPLE-deposited films (

Conclusions

We have demonstrated in the case of quercetin dehydrate-, resveratrol- and silver nanoparticle-polyvinylpyrrolidone biopolymer that MAPLE is an efficient technique for obtaining thin films that preserve the chemical structure of the input materials. At a laser fluence of ∼80 mJ/cm2, the MAPLE-deposited thin film spectra showed a very close resemblance to the corresponding drop-cast FT-IR spectra in the characteristic fingerprint region. The surface morphology of the thin films as evidenced by

Acknowledgments

This work was supported by a grant of the Romanian National Authority for Scientific Research, CNCS-UEFISCDI: PN-II-ID-PCE-2011-3-0888 (209/5.10.2011). A.V. Surdu recognizes the financial support of Sectoral Operational Programme Human Resources Development, financed from the European Social Fund and by the Romanian Government under the contract number POSDRU/156/1.2/G/135764 “Improvement and Implementation of University Master Programs in the Field of Applied Chemistry and Materials Science -

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