Advanced Biomaterials and Biodevices (Tiwari/Advanced) || Assembly of Polymers/Metal Nanoparticles and their Applications as Medical Devices

Ashutosh Tiwari and Anis N. Nordin (eds.) Advanced Biomaterials and Biodevices, (343–366)

2014 © Scrivener Publishing LLC

343

10

Assembly of Polymers/Metal Nanoparticles and their Applications as Medical Devices

Magdalena Stevanović

Institute of Technical Sciences of the Serbian Academy of Sciences

and Arts, Belgrade, Serbia

AbstractMetallic nanoparticles have attracted much attention and have found applications

in diff erent fi elds such as medicine, pharmacy, controlled drug delivery, optics,

electronics, and other areas. Among the most promising nanomaterials with anti-

bacterial and antiviral properties are metallic nanoparticles (silver, gold, platinum,

etc), which exhibit increased chemical activity due to their large surface to volume

ratios, crystallographic surface structure and unique size-dependent optical, elec-

trical and magnetic properties. However, it has been reported that bare metallic

nanoparticles can be toxic. Th is supports the concept that this toxicity is associated

to the presence of the bare metallic nanoparticle surface, while particles protected

by an organic layer, i.e. polymer, are much more biocompatible, and thereby less

toxic. Unrelated to the bare metallic surface, several recent studies indicate that,

at a cellular level, metal nanoparticles interact with biological molecules within

mammalian cells and can interfere with the antioxidant defense mechanism lead-

ing to the generation of reactive oxygen species (ROS). Increase of ROS levels may

result in signifi cant damage to cell structures known as oxidative stress.

Th is review article reports on obtaining metallic nanoparticles with special

emphasis on obtaining silver nanoparticles, their incorporation within various

polymer materials, physiochemical and biological properties of such obtained sys-

tems as well as about their application as medical devices.

Keywords: Metal nanoparticles, polymers, silver nanoparticles, medical devices

*Corresponding author: [email protected]; magdalena.stevanovic@gmail

.com

344 Advanced Biomaterials and Biodevices

10.1 Introduction

Nanomaterials are at the leading edge of the rapidly developing fi eld of nanotechnology [1, 2]. Typically, though not exclusively, nanoparticles are defi ned as submicroscopic particles between 1 and 100 nm [3]. In recent years noble metal nanoparticles have been the subjects of focused researches due to their unique electronic, optical, mechanical, magnetic and chemical properties that are signifi cantly diff erent from those of bulk materials [1–5]. Th eir unique size-dependent properties make these materials superior and indispensable in many areas of human activity [5–10]. For example, intense research has led to a more comprehensive understanding of cancer at the genetic, molecular, and cellular levels pro-viding an avenue for methods of increasing antitumor effi cacy of drugs while reducing systemic side eff ects. Nanoparticulate technology is of particular use in developing a new generation of more eff ective cancer therapies capable of overcoming the many biological, biophysical, and biomedical barriers that the body stages against a standard intervention. Nanoparticles show much promise in cancer therapy by selectively gain-ing access to tumor due to their small size and modifi ability [8]. Th ey are formulated out of a variety of substances and engineered to carry an array of substances in a controlled and targeted manner [8]. Discoveries in the past decade have demonstrated that unique properties of gold, silver and platinum nanoparticles, are strongly infl uenced by shape and size. Th is has motivated an increase in research on the synthesis routes that allow better control of shape and size for various nano-biotechnological applications. Currently metal nanoparticles (Figure 10.1) are used in various biomedical applications such as probes for electron microscopy to visualize cellular components, drug delivery (vehicle for delivering drugs, proteins, pep-tides, plasmids, DNAs, etc), detection, diagnosis and therapy (targeted and non-targeted), as antibacterial and antiviral agents, etc. (Table 10.1).

However, it has been reported that bare metallic nanoparticles can be toxic. Th is supports the concept that this toxicity is associated to the pres-ence of the bare metallic nanoparticle surface. Also, at a cellular level, metal nanoparticles may interact with biological molecules and can inter-fere with the antioxidant defense mechanism leading to the generation of ROS. Particles protected by an organic layer, i.e. polymer, are much more biocompatible, and thereby less toxic.

Th e main focus of this article is to provide an overview of design and properties of platinum, gold, and silver nanoparticles with special emphasis on obtaining silver nanoparticles, their incorporation within

Assembly of Polymers/Metal Nanoparticles 345

Selenium

GoldPalladium

Copper

Metal nanoparticles

Iron

Zink oxide

Silver

Platinum

Figure 10.1 Types of metal nanoparticles which are used in biomedical fi eld.

Table 10.1 Types of metal nanoparticles and their applications.

Metal nanoparticles Applications

Gold

DNA labeling

Biosensors

Antiviral

Antibacterial

Drug delivery

Cancer therapy

Molecular imaging

Diagnosis and therapy

Palladium Biocatalysis

CopperAntiviral

Antibacterial

IronMolecular imaging

Cancer therapy

Zinc oxide

Antiviral

Antibacterial

Cosmetics

(Continued)


various polymer materials, physiochemical and biological properties of such obtained systems as well as about their application as medical devices.

10.2 Platinum Nanoparticles

Platinum-based therapeutic agents are widely used in medicine [11–20]. Platinum nanoparticles (nano-Pt) have been reported to possess anti-oxidant and anti-tumor activities. Platinum complexes, such as cisplatin, have been used for a decades to treat a number of maladies (any disorder or disease of the body, especially one that is chronic or deepseated) [11]. However, the use of platinum nanoparticles (PtNPs) in medicine is still in its nascent state [21]. Various approaches for making nanoparticles have been proposed in the literature (Figure 10.2). Th e most common method for the synthesis of platinum nanoparticles is by chemical reduction of metal salts, chief among these reduction agents are ethylene glycol and sodium borohydride [22, 23]. For example, Guo et al. synthesised PtNPs using borohydride as the reducing agent and citric acid as a stabilizer [24]. By varying the ratio of citric acid to the metal salt, they were able to form PtNPs ranging in size [24]. Th e morphology of PtNPs can be controlled by the precursor reduction conditions while employing supercritical fl uid reactive deposition [25]. Herricks et al have described a scheme to gener-ate PtNPs with various size and shape [22]. In this method, polyethylene glycol serves as the reduction agent and solvent. Further modifi cation of structure was obtained by changing the NaNO

3/Pt ratio [22]. Additionally,

platinum nanoparticles exhibit morphology (size and shape) dependent catalytic properties [26]. Other agents such as poly(N-vinyl-2-pyrrolidone) have been used in conjunction with NaBH4 reduction of H

2PtCl

6 6H

2O

Metal nanoparticles Applications

Silver

Medical devices

Antiviral

Antibacterial

Platinum Cancer therapy

Selenium

Cancer therapy

Antiviral

Antibacterial

Table 10.1 (Cont.)


[27, 28]. Th e size of Pt nanoparticles can be produced using chemical rip-ening [29].Th e initial step of this multistep, multi-seed process starts with small individual platinum seeds in an water solution containing sodium citrate and L-ascorbic acid. Th e fi nal diameter of the nanoparticles relies on the concentration of chloroplatinic acid and the initial seed size [29].

10.3 Gold Nanoparticles

Gold have fascinated scientists for ages and are now heavily utilized in chemistry, biology, engineering, and medicine [30–32]. Th ese materials can be synthesized reproducibly, modifi ed with apparently limitless chem-ical functional groups, and, in certain cases, characterized with atomic-level precision. Many examples of highly sensitive and selective assays based upon gold nanoconjugates have been described in the literature. Recently, focus has turned to therapeutic possibilities for such materials. Structures which behave as gene-regulating agents, drug carriers, imaging agents, and therapeutics have been designed and studied in the context of cells and many diseases [30–32]. Th ese structures are not simply chosen as

Nanoparticle synthesis

Top down methods

(size reduction)

Mechanical

milling

Chemical

etchingSputtering

Ablation

Explosion

processes

Botom up methods

(build up from smaller entities)Physicochemical

solvent/nonsolventAerosol

processes

Sol/gel synthesisCondensation

Re

du

ction

Precipitation

Metal salts Metal nanoparticles

Vapor

deposition

Figure 10.2 Various approaches for making nanoparticles.


alternatives to molecule-based systems, but rather for their new physico-chemical properties, which confer substantive advantages in cellular and medical applications.

Depending on their morphology, degree of aglomeration, and local environment, gold nanoparticles can appear red, blue, or other colors (Figure 10.3). Th ese visible colors refl ect the underlying coherent oscilla-tions of conduction-band electrons, plasmons, upon irradiation with light

Increasing particle size

Increasing aspect ratio

Figure 10.3 Photographs of aqueous solutions of gold nanospheres (upper panels) and

gold nanorods (lower panels) as a function of increasing dimensions. Corresponding

transmission electron microscopy images of the nanoparticles are shown (all scale bars

100 nm). [1, Th e reference 1 is an open-access article distributed under the terms of the

Creative Commons Attribution License, which permits unrestricted use, distribution, and

reproduction in any medium, provided the original work is properly cited.]


of appropriate wavelengths. Th ese plasmons underlie the intense absorp-tion and elastic scattering of light, which in turn forms the basis for many biological sensing and imaging applications of gold nanoparticles [33–46]. Th e elastic light-scattering properties of gold nanoparticles are suffi cient to detect individual nanoparticles in a visible light microscope with approxi-mately 10(2) nm spatial resolution.

Jain et al have used Mie theory and discrete dipole approximation method to calculate absorption and scattering effi ciencies and optical reso-nance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods [47]. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed show an absorption cross-section 5 orders higher than conventional absorbing dyes, while the magnitude of light scattering by 80-nm gold nanospheres is 5 orders higher than the light emission from strongly fl uorescing dyes. Jain et al have stated that the variation in the plasmon wavelength maximum of nanospheres, i.e., from approximately 520 to 550 nm, is too limited to be useful for in vivo applications. Th ey have found that gold nanoshells have optical cross-sections comparable to and even higher with that of the nanospheres. Also gold nanorods show optical cross-sections comparable to nanospheres and nanoshells, however, at much smaller eff ective size.

Th e growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail by Kimling et al [48]. Th ey have exam-ined growth of gold nanopaticles to explore the parameter space of reac-tion conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defi ned size distribution, following the earlier work of Turkevich and Frens [43, 49–50]. Th e reaction is initi-ated thermally or in comparison by UV irradiation, which results in simi-lar fi nal products. Th e kinetics of the extinction spectra show the multiple steps of primary and secondary clustering leading to polycrystallites.

Subrata et al have produced cubic gold nanoparticles under UV pho-toactivation by using a chiral reagent, 2-naphthol, under alkaline solution as a reductant for HAuCl(4) in CTAB micelle [51]. Prolonged irradia-tion helped the digestion of the primarily evolved spherical particles into smaller gold nanocubes, which then act as tiny cubic seeds, leading to the formation of larger nanocubes [51].

Alivisatos et al have described a strategy for the synthesis of ‘nanocrys-tal molecules’, in which discrete numbers of gold nanocrystals are orga-nized into spatially defi ned structures based on Watson-Crick base-pairing interactions [52]. Th ey attached single-stranded DNA oligonucleotides of


defi ned length and sequence to individual nanocrystals, and these assemble into dimers and trimers on addition of a complementary single-stranded DNA template. Th ey have anticipated that this approach should allow the construction of more complex two- and three-dimensional assemblies.

Recently, Kang et al have conjugated gold nanoparticles with specifi c peptides and they were successful in selectively transporting them to the nuclei of cancer cells [53]. Confocal microscopy images of DNA double-strand breaks showed that localization of gold nanoparticles at the nucleus of a cancer cell damages the DNA. Gold nanoparticle dark-fi eld imaging of live cells in real time revealed that the nuclear targeting of gold nanopar-ticles specifi cally induces cytokinesis arrest in cancer cells, where binucle-ate cell formation occurs aft er mitosis takes place. Flow cytometry results indicated that the failure to complete cell division led to programmed cell death (apoptosis) in cancer cells. Th ese results show that gold nanopar-ticles localized at the nuclei of cancer cells have important implications in understanding the interaction between nanomaterials and living systems.

Despite the great excitement about the potential uses of gold nanopar-ticles for medical diagnostics, as tracers, and for other biological applica-tions, researchers are increasingly aware that potential nanoparticle toxicity must be investigated before any in vivo applications of gold nanoparticles can move forward [33, 54, 55].

10.4 Silver Nanoparticles

Silver nanoparticles have characteristic optical, electrical, and thermal properties and are being integrated into products that range from photo-voltaics to biological and chemical sensors. Examples include conductive inks, pastes and fi llers which utilize silver nanoparticles for their high elec-trical conductivity, stability, and low sintering temperatures. Additional applications include molecular diagnostics and photonic devices, which take advantage of the novel optical properties of these nanomaterials. An increasingly common application is the use of silver nanoparticles for anti-microbial coatings, and many textiles, keyboards, wound dressings, and biomedical devices now contain silver nanoparticles that continuously release a low level of silver ions to provide protection against bacteria.

Th e literature describes diff erent methods for obtaining silver nanopar-ticles, including chemical reduction, solid-state synthesis, sonochemical synthesis, in-situ radical polymerization, and spray pyrolysis [56]. Th rough the optimization of experimental conditions, it is possible to synthesize nanoparticles of diff erent sizes and morphologies. Such optimization


relates to concentrations of reactants, temperature, pH, reducing agents, diff erent surfactants and reaction media, and these can signifi cantly aff ect the stability of the resulting particles [57].

Th e application of silver nanoparticles in medicine can be broadly divided into diagnostic and therapeutic uses. Early diagnosis to any dis-ease condition is vital to ensure that early treatment is started and perhaps resulting in a better chance of cure. Lin et al reported silver nanoparticle based surface-enhanced raman spectroscopy (SERS) in non-invasive can-cer detection [58]. Th is approach is highly promising and may prove to be an indispensable tool for the future.

Th e enhancement in the optical and photothermal properties of noble metal nanoparticles arises from resonant oscillation of their free electrons in the presence of light, also known as localized surface plasmon resonance (LSPR) [59, 60]. Th e plasmon resonance can either radiate light (Mie scat-tering), a process that fi nds great utility in optical and imaging fi elds, or be rapidly converted to heat (absorption); the latter mechanism of dissipation has opened up applications in several new areas. Th e ability to integrate metal nanoparticles into biological systems has had greatest impact in biol-ogy and biomedicine.

In terms of therapeutics, one of the most commonly used application of silver nanoparticles is in wound healing. Compared with other silver compounds, many studies have demonstrated the superior effi cacy of sil-ver nanoparticles in healing time, as well as achieving better cosmetic aft er healing. In the study of Kwan et al, it was shown that in wounds treated with silver nanoparticles, there was better collagen alignment aft er healing when compared to controls, which resulted in better mechanical strength [61].

10.5 Assembly of Polymers/Silver Nanoparticles

In nanoparticle-polymer composites, polymer can serve diff erent pur-poses: as assembling the nanoparticles into clusters, serving as a matrix that includes ordering and anisotropic orientation of the nanoparticles, acting as a functional element, as organic protective layer, etc. Polymers can be tailored to serve either one of these functions or all.

Th e most important requirement for the creation of polymer-nanopar-ticle composites is that the polymer and the protective organic layer on the surface of the nanoparticle are chemically compatible. Th is compa-tability enables inhomogeneous dispersion of the nanoparticles in the solid polymer matrix, which in certain systems may be viewed as a form of assembly [62].


Th e literature has described the synthesis of composites of sil-ver nanoparticles with polymers such as cellulose [63], polyurethane [64], poly(acrylamide) [65], chitosan [66], poly(e-caprolactone) [67], poly(styrene) [68], poly(methylmethacrylate) [69], montmorillonite [70], polyvinyl alcohol [71], etc. Th ese have provided materials in the forms of fi lms, scaff olds, fi bers or graft s. Th e literature has also describes the obtaining of poly(l-lactide) and poly(lactide-co-glycolide) nanofi bers containing AgNps using an electrospinning method [72], as well as the obtaining of poly(lactide-co-glycolide) /silver composite graft s by extrac-tion methods [73].

In the study of Stevanovic et al, polyglutamic acid (PGA) (Figure 10.4) was used as the organic layer (a capping agent) for silver nanoparticles obtained using saccharose as a reducing agent. PGA was chosen as the cap-ping agent to make the AgNps more biocompatibile and to protect them from agglomerating in the medium [74].

In general, stabilization of nanoparticles is achieved by adding cap-ping agents, which bind to the nanoparticle surface via covalent bonds or by chemical interaction. Th ese capping agents are essential to prevent nanoparticle aggregation and increase the solubility of the nanosystem, and also can be used as a site for bioconjugation of the nanoparticle with important molecules. Diff erent capping agents include biodegradable polymers, oligosaccharides and polysaccharides.

PGA-capped AgNps (AgNpPGAs) were additionally encapsulated within poly(lactide-co-glycolide) spheres to ensure their release over an extended period of time, and therefore their extended antimicrobial eff ects.

Sureshkumar et al have successfully developed a facile method to pre-pare a magnetic silver nanocomposite [63]. Th e 3-D nanofi brous structure of bacterial cellulose was homogenized with a ferric and ferrous mixture by a high speed blender. Magnetite nanoparticles were precipitated and

Figure 10.4 PGA as capping agent of silver nanoparticles.


incorporated into cellulose nanostructure by adjusting the homogenate to alkaline pH. Th e magnetic bacterial cellulose nanofi ber soaked in dopa-mine solution will be coated with an adherent self-polymerized polydopa-mine layer. Since the polydopamine surface is very eff ective for reducing silver ion, silver nanoparticles were incorporated into the dopamine treated magnetic bacterial cellulose by soaking in silver nitrate solution. Th e mag-netic silver nanocomposite possesses a high antimicrobial activity against the model microbes Escherichia coli and Bacillus subtilis. It also has poten-tial as a mild fermentation medium sterilizing agent that a freshly prepared LB medium shows no appreciable contamination aft er incubating with Ag nanocomposite for 4 h and removed by an external magnet.

As it was already mentioned above, silver nanoparticles could be strong bactericidal agents but they also can be cytotoxic. Embedding them in a polymer matrix may reduce their cytotoxic eff ect. In the study of Liu et al, silver nanoparticles in three average sizes were tested for their antibacterial activities and cytotoxicity. Nanocomposites from a new waterborne poly-etherurethane ionomer and silver nanoparticles were prepared without the use of any crosslinker. It was observed that the antibacterial activity of silver nanoparticles against Escherichia coli started at the eff ective con-centration of 0.1–1 ppm, while that against Staphylococcus aureus started at higher concentrations of 1–10 ppm. Cytotoxicity of silver nanoparticles was observed at the concentration of 10 ppm. Silver nanoparticles with smaller average size showed greater antibacterial activity as well as cyto-toxicity. Th e PEU synthesized in this study showed high tensile strength, and the addition of AgNPs at all sizes further increased its thermal stability. Th e delicate surface features of nanophases, however, were only observed in nanocomposites with either small- or medium-sized AgNPs. PEU-Ag nanocomposites had a strong bacteriostatic eff ect on the growth of E. coli and S. aureus. Th e proliferation of endothelial cells on PEU-Ag nanocom-posites was enhanced, whereas the platelet adhesion was reduced. Th e expression of endothelial nitric oxide synthase gene was upregulated on PEU-Ag containing small-sized AgNPs (30 ppm) or medium-sized AgNPs (60 ppm). Th is eff ect was not as remarkable in nanocomposites from large-sized AgNPs. Overall, nanocomposites from the PEU and 60 ppm of the medium-sized (5 nm) AgNPs showed the best biocompatibility and anti-bacterial activity. Addition of smaller or larger AgNPs did not produce as substantial an eff ect in PEU, especially for the larger AgNPs.

Vimala et al have reported the preparation of semi interpenetrating hydrogel networks (SIHNs) based on cross-linked poly (acrylamide) pre-pared through an optimized rapid redox-solution polymerization with N,N -methylenebisacrylamide in presence of three diff erent carbohydrate


polymers, namely gum acacia, carboxymethylcellulose and starch. Th ey have obtained highly stable and uniformly distributed silver nanoparticles with hydrogel networks as nanoreactors via in situ reduction of silver nitrate using sodium borohydride as reducing agent. Th e formation of silver nanoparti-cles has been confi rmed with ultraviolet visible spectroscopy, fourier trans-form infrared spectroscopy, X-ray diff raction analyses. Th ermogravimetric analysis provides the amounts of silver nanoparticles exist in the hydrogel networks. Transmission electron microscopy results demonstrate that aca-cia employed hydrogels have regulated the silver nanoparticles size to 2–5 nm where as carboxymethylcellulose and starch composed hydrogel net-works result in a heterogeneous size from 2 to 20 nm.

Potara et al have reported the formation of chitosan-coated silver nanoparticles of triangular shape in solution by synergistic action of chito-san and trisodium citrate in the presence of silver seeds and ascorbic acid [66]. It has been revealed that these anisotropic AgNps entrapped in bio-polymeric shells are particularly stable and can be successfully used as ver-satile plasmonic substrates for molecular sensing in solution. In particular, the binding of the probe molecule monolayer (para-aminothiophenol) at the surface of individual chitosan-coated silver nanoparticles was demon-strated both by LSPR shift s and SERS spectra. While the LSPR-shift assay is operational for signaling molecular binding events, the SERS allows iden-tifying the probe molecules and elucidating its orientation on the metal surface. Th e proof of concept for biosensing applications and dual func-tionality of plasmonic platform are evaluated through the combined LSPR-SERS detection of signifi cant biological molecules, adenine. Potara et al have stated that the potential of chitosan-silver nanostructures to extend the standard approach of LSPR sensing by integrating SERS measurements and operate as dual plasmonic sensors would be very attractive for investi-gation of analytes in biological fl uids.

Nanofi bers of poly(e-caprolactone) (PCL) which poses antimicrobial activity were prepared by electrospinning of a PCL solution with small amounts of silver-loaded zirconium phosphate nanoparticles for potential use in wound dressing applications [67]. Th ese fi bers have maintained the strong killing abilities of Ag + existed in the nanoAgZ against the tested bacteria strains and discoloration has not been observed for the nanofi -bers. Th e authors have tested the biocompatibility of nanofi bers as poten-tial wound dressings, i.e. primary human dermal fi broblasts were cultured on the nanofi brous mats. Th e cultured cells were evaluated in terms of cell proliferation and morphology. Th e results indicated that the cells attached and proliferated as continuous layers on the nanoAgZ-containing nanofi -bers and maintained the healthy morphology of human dermal fi broblasts.


A comparative study on the self-assembled nanostructured morphology and the rheological and mechanical properties of four diff erent triblock copolymers, based on poly(styrene-block-butadiene-block-styrene) and poly(styrene-blockisoprene-block-styrene) matrices, and of their respec-tive nanocomposites with 1 wt% silver nanoparticles, is reported by Peponi and coworkers [68]. In order to obtain well-dispersed nanoparticles in the block copolymer matrix, dodecanethiol was used as surfactant. Th e block copolymer with the highest PS content shows the highest tensile modulus and tensile strength, but also the smallest elongation at break. When silver nanoparticles treated with surfactant were added to the block copolymer matrices, each system studied shows higher mechanical properties due to the good dispersion and the good interface of Ag nanoparticles in the matrices. Furthermore, it has been shown that semiempirical models such as Guth and Gold equation and Halpin-Tsai model can be used to predict the tensile modulus of the analyzed nanocomposites.

Travan and coworkers have developed an antimicrobial non-cytotoxic coating for methacrylic thermosets (biomaterials for dental and orthopedic applications) by means of a nanocomposite material based on a lactose-mod-ifi ed chitosan and antibacterial silver nanoparticles [69]. Th e authors have performed the in vitro tests for a biological characterization of the material which showed that the nanocomposite coating is eff ective in killing both bac-terial strains (gram+ and gram- strains) and that this material does not exert any signifi cant cytotoxic eff ect towards tested cells (osteoblast-like cell-lines, primary human fi broblasts and adipose-derived stem cells), which are able to fi rmly attach and proliferate on the surface of the coating. It was stated that such biocompatible antimicrobial polymeric fi lms containing silver nanoparticles may have good potential for surface modifi cation of medical devices, especially for prosthetic applications in orthopedics and dentistry.

Silver nanoparticles were synthesized into the interlamellar space of montmorillonite (MMT) by using the γ-irradiation technique in the absence of any reducing agent or heat treatment by Shameli and coworkers [70]. Th ey have used silver nitrate and γ-irradiation as the silver precursor and physical reducing agent in MMT as a solid support. Th e MMT was suspended in the aqueous AgNO

3 solution, and aft er the absorption of sil-

ver ions, Ag+ was reduced using the γ-irradiation technique. Th e proper-ties of Ag/MMT nanocomposites and the diameters of silver nanoparticles were studied as a function of γ-irradiation doses. Th e interlamellar space limited particle growth and face-centered cubic silver nanoparticles with a mean diameter of about 20–30nm were produced. SEM images indicated that there were structure changes between the initial MMT and Ag/MMT nanocomposites under the increased doses of γ-irradiation. Furthermore,


energy dispersive X-ray fl uorescence spectra for the MMT and Ag/MMT nanocomposites confi rmed the presence of elemental compounds in MMT and silver nanoparticles. Th e results indicated that increasing the γ-irradiation dose enhanced the concentration of Ag-NPs. Also, the par-ticle size of the silver nanoparticles slowly increased when γ-irradiation dose of 1 to 20 kGy was applied. When the γ-irradiation dose increased from 20 to 40 kGy, the particle diameters decreased suddenly as a result of the induced fragmentation of Ag-NPs. Th e interactions between silver nanoparticles with the surface of MMT were weak due to the presence of van der Waals interactions. Th e synthesized Ag/MMT suspension was found to be stable more than three months without any sign of precipitation.

Pragatheeswaran et al have used polyol process for the synthesis of silver nanoparticles embedded in polyvinyl alcohol [71]. Silver nanoparticles were deposited on glass plates by dip coating method and exposed to DC glow discharge plasma for 10 minutes and 60 minutes. Position of surface plasmon resonance peak changed aft er the samples were exposed to DC glow discharge plasma, which reveals that the DC glow discharge plasma can be used as a size controlling agent for the silver nanoparticles embedded in polyvinyl alcohol.

Xing et al have used electrospining method for the preparation of sil-ver-containing poly(L-lactide-co-glycolide) nanofi brous scaff olds [72]. Nanofi brous scaff olds were prepared by electrospining a bend solution of poly(L-lactide-co-glycolide) and silver nanoparticles in 1,1,1,3,3,3,-hexa-fl uoro-2-propanol. Th e resulting fi bers ranged from 420 to 590 nm in diameter. To evaluate the possibility of using silver-containing PLGA as a tissue engineering scaff old, experiments on cell viability and antibacte-rial activity were carried out. As a result, PLGA nanofi brous scaff olds hav-ing silver nanoparticles of more than 0.5 wt% showed antibacterial eff ect against Staphylococcus aureus and Klebsiella pneumonia. Furthermore, silver-containing PLGA nanofi brous scaff olds showed viability, indicating their possible application in the fi eld of tissue engineering.

By incorporating silver ions into alginate fi bres, highly absorbent algi-nate wound dressings with antimicrobial properties have been made by Qin et al [75]. Th ey have shown that by incorporating fi ne particles of sil-ver sodium hydrogen zirconium phosphate, the silver-containing alginate fi bres can maintain the white physical appearances while providing a sus-tained release of silver ions when in contact with wound exudates. Test results have proven that these fi bres are highly eff ective against bacteria.

Nanoparticles synthesized by the various methods have been used in diverse in vitro diagnostic applications [76–94]. Most of all metallic nanopar-ticles, gold and silver nanoparticles have been found to have broad spec-trum antimicrobial activity against human and animal pathogens [95–114].


However there is still a lot of room for research. Particularly, recent fi ndings indicate that the compound delays the wound-healing process and that sil-ver may have serious cytotoxic activity on various host cells. It is necessary to examine all available evidence about eff ects, oft en contradictory, of sil-ver on wound infection control and on wound healing trying to determine the practical therapeutic balance between antimicrobial activity and cellular toxicity [115–133]. Th e ultimate goal remains the choice of a product with a superior profi le of infection control over host cell cytotoxicity.

10.6 Conclusion

Owing to their unique properties, metallic nanoparticles fi nd wide-range applications, from medicine and pharmaceutics to electronic industry, optics, etc. Presently there is great interest for the polymer-metallic nanoparticles systems in the fi eld of biomedical applications based on the need for a system with a high antibacterial and antiviral activity against bacteria and viruses on contact, without the release of toxic biocides. Th is chapter reports on obtain-ing metallic nanoparticles such as platinium, gold and silver. It focuses on obtaining silver nanoparticles, their incorporation within various polymer materials, a physiochemical and biological property of such obtained sys-tems as well as about their application as medical devices.

Acknowledgements

M.S. acknowledges the support from the Ministry of Education, Science and Technological Development of the Republic of Serbia, under Grant No. III45004: Molecular designing of nanoparticles with controlled mor-phological and physicochemical characteristics and functional materials based on them.

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