Polymer Nanocomposite Coatings

Vikas Mittal

• Publisher: CRC Press
• Year: 2016
• Print ISBN: 9781466557307
• eBook ISBN: 9781000687217
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This work explores the use of composite nanotechnology for thin coatings on various substrates. It compiles recent advances in nanocomposite coatings for experienced researchers and provides background information for those new to the field. The book not only explains the synthesis of bulk nanocomposite materials, it describes their application in

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Silver-Polysaccharide Nanocomposite Antimicrobial Coatings

Andrea Travan, Eleonora Marsich, Ivan Donati, Massimiliano Borgogna and Sergio Paoletti

CONTENTS

1.1Introduction

1.2Antimicrobial Surfaces: Background Concepts

1.3Silver as Antimicrobial Agent

1.4Preparation and Characterization of Silver–Polysaccharide Nanocomposites

1.5Applications in the Biomedical and Food-Packaging Fields

1.6Silver Toxicity and Nano-Safety

1.7Future Trends

References

1.1 Introduction

Recently, research on nanoparticle synthesis and use has been gaining considerable attention in the area of medicine, biology, and materials engineering owing to their chemical, biological, and physical properties, which depends on particle chemistry, structure, and dimensions

Nanocomposites are by definition materials that contain domains or inclusions in the nanometer size scale. Nowadays, there is an increasing interest toward nanocomposite materials that exploit the antimicrobial properties of silver at the nanoscale for various aims, especially in the biomedical and food industry. For these fields, the regulation of harmful effects (toxicity) is of primary importance, and in this perspective, the preparation and stabilization of nanoparticles must be carried out using biocompatible polymers; to this end, natural polysaccharides are emerging as the most appropriate choice acting both as nontoxic reducing agents and as cell-friendly matrix

These bioactive systems are particularly important when the antimicrobial activity has to be exerted by direct contact with the material surface; in these cases, silver–polysaccharide nanocomposites can be constructed in the form of coatings, films, or sheets.

This chapter aims at providing an overview of the state of art in the field of silver–polysaccharide systems, with particular attention to biomedical and food-packaging fields. Following a brief introduction and background concepts of antimicrobial surfaces, the antimicrobial activity of silver nanoparticles (AgNPs) is discussed. Then, details on the main routes of preparation of silver–polysaccharide coatings and films are reported, and some relevant applications and significant results over the last few years are presented. Subsequently, a section is devoted to discuss the controversial issue of nano-safety and the potential risk of silver-related toxicity. Finally, the future of this promising class of materials is tentatively devised.

1.2 Antimicrobial Surfaces: Background Concepts

Bacterial adhesion to material surfaces and interfaces is the first step in bacterial colonization, which can lead to a mature biofilm. The insertion of a biomaterial into a body causes an immediate reaction that leads to the deposition of organic matter on its surface, indicated as “conditioning film,” composed essentially of proteins and platelets. This intermediate layer connects the substratum and the adhering microorganisms [1]. Bacterial adhesion is a complex interplay of different phenomena such as Brownian motion, gravitation, diffusion, convection, and the intrinsic motility of microorganisms. The overall process of bacterial adhesion can be described by means of the so-called model. This is composed of an initial reversible interaction between the bacterial membrane and the material surface, followed by a second stage that includes specific and nonspecific interactions between adhesion proteins expressed on the bacterial surface and binding molecules on the material surface. The second step is slowly reversible, although it is often referred to as irreversible [2].

There are several aspects to take into account when designing an antimicrobial surface. Roughness, stiffness, charge, degree of hydrophobicity, Lewis acid–base character, hydrogen bonding capacity [3], van der Waals forces, and specific receptor–adhesion interactions [4] play an important role on bacterial adhesion. Several authors have attempted to theoretically predict the adhesion of microbes on surfaces by means of a physical–chemical approach indicated as the DLVO (Derjaguin, Landau, Verwey, Overbeek) theory [5–7] (for an extended discussion, see [8]). The DLVO approach is based on a thermodynamic treatment of the bacterial adhesion, which includes in the description of the free energy of microbial adhesion (ΔG^adh), a balance between. Lifshitz–van der Waals forces (ΔG^LW, generally attractive) and electrostatic forces generated from the overlap of the electrical double layer of the microbial cell and the substratum (ΔG^EL, generally repulsive). By means of this thermodynamic approach, predictions on the physical–chemical properties of the surface to be sought for discouraging bacterial adhesion have been successfully attained. It was found that the increase in hydrophilicity of the surface led to a decrease in microbial adhesion, as predicted on the of the DLVO theory. Along this line, the modification of the surface with poly(ethyleneoxide) was reported to reduce the bacterial adhesion on polyurethane [4]. The increase in hydrophilicity of poly(vinyl chloride) by oxygen plasma was found to decrease the adhesion of Pseudomonas aeruginosa strains, although bacterial biofilm formation is not completely impeded [9].

Microbial adhesion is also influenced by the physical–chemical characteristics of bacteria. The hydrophobicity of the bacterial cell wall, determined basically by its chemical composition in terms of biomolecules synthesized, has a lower effect when compared to the hydrophobicity of the substratum. As a general consideration, it can be stated that for the same substratum, the higher the hydrophobicity of the bacteria the higher their adhesion, and the biofilm is formed. The more hydrophilic Staphylococcus aureus was found to adhere to a lower extent than the more hydrophobic Escherichia coli [10]. In addition, different strains of the same bacterium show marked differences in the hydrophobicity/hydrophilicity properties [11,12]. For reasons resumed earlier, predictions of the bacterial adhesion on a substratum based on the DLVO approach shows several limitations. Indeed, the colonization of bacteria at the implant interface strongly depends on many factors that often are microorganism dependent (temperature, flow conditions, and concentration of glucose and oxygen). Consequently, even for a single strain and material surface, environmental stimuli can affect the relative importance of both adhesion mechanisms and material surface characteristics. In addition, the use of medium containing proteins, due to the adsorption of the latter on the surface of materials, complicates the analysis. Moreover, bacterial cells show peculiar features that could affect their adhesion to surfaces. In fact, microbial cell surfaces are heterogeneous in composition and are with a high level of complexity, which is normally not taken into account when considering a physical–chemical modeling at the molecular level. Simple concepts like, for example, distance—partially lose their meaning considering that appendages on microbial cell surfaces can become as long as 1 μm [8]. The importance of surface roughness on the adhesion of bacteria was recently reviewed [13,14]. It is generally agreed that irregularities on the polymeric surface promote bacterial adhesion, while ultrasmooth ones prevent biofilm deposition [15–17]. It has been reported that roughening of the surface increased bacterial adhesion and biofilm formation [18], although a direct correlation has not been found [19]. This is because the initial bacterial adhesion probably locates where the cells are sheltered from the shear forces of the body fluids. In addition, the higher the roughness of the surface, the higher the total surface available for adhesion [10] Among the different topographic modifications, the presence of well-distributed etched pits on the material surface was reported to bring about an effect on bacterial adhesion, which depends on the dimension of the pits and of the bacterial species considered [20,21].

As to the influence of the stiffness of the surface of the material, it has been reported that this physical parameter modulates mechano-selective adhesion of Staphylococcus epidermidis and E. coli. In particular, the increase in Young’s modulus of the polyelectrolyte layers on the substrate correlates positively with the adhesion of the bacterial strains in the range of 1–100 MPa [22]. However, an extended analysis on this line is still partially lacking.

Prevention or limitation of bacterial colonization on the surface of biomaterials has been generally pursued by means of three strategies (Figure 1.1).

In the first strategy, the surface of the biomaterial is selected or modified to show hydrophilic or ultrahydrophobic properties [4,23–25]. This passive substrate aims at preventing the bacteria to achieve the two adhesion stages based on a physical–chemical incompatibility between the material surface and the bacterial cell wall. However, different bacterial species have different physical–chemical features, and the “passive surface” approach has a limited spectrum activity that hampers its efficacy. Polymeric materials engineered at the nano- and microstructures play a fund...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Editor
• Contributors
• 1 Silver-Polysaccharide Nanocomposite Antimicrobial Coatings
• 2 Polymer Nanocomposite Coatings: Effect of Crosslinkers and Fillers on the Microstructure and Gas Permeation
• 3 Carbon Nanotubes-Polytetrafluoroethylene Nanocomposite Coatings
• 4 Organic–Inorganic Hybrid Coatings with Enhanced Scratch Resistance Properties Obtained by the Sol–Gel Process
• 5 Chitosan–Magnesium Aluminum Silicate Nanocomposite Coatings
• 6 View from Inside to the Surface of Nanocomposite Coatings
• 7 Properties of Nanocomposite Hard Coatings on Polycarbonate
• 8 UV-Cured Polymer: Boehmite Nanocomposite Coatings
• 9 Protective Coatings Based on Silsesquioxane Nanocomposite Materials
• 10 POSS-Containing Nanocomposite Polymer Coatings
• 11 Nanocomposite PPy Coatings for Al Alloys Corrosion Protection
• 12 Ultrasound-Assisted Synthesis and Its Effect on the Properties of CaCO3–Polymer Nanocomposites
• Index