INTRODUCTION:

Nanotechnology and the respective nanomaterials are employed in the research sector and also contained in many commercially available products. This raises the question whether such materials enter the human body and whether they can trigger health effects. The potential health risks are poorly investigated a number of studies have reported that free nanoparticles, due to their small size, can penetrate into the finest lung structures by breathing, cancause inflammatory reactions, and subsequently can enter the blood stream. Depending on these parameters, new properties are observable for these materials such as melting temperature¹, photoluminescence² and nonlinear optical properties³.

The circulatory system distributes such particles throughout the body, where they can enter other organs. Nanoparticles can also be actively or passively incorporated incells, and harmful effects cannot be excluded. The biological effects are not based on chemical composition alone: size, shape, surface texture, aggregation state and surface charge also play an important role. Among all the methods proposed, one of the simplest is the chemical reduction of a metal salt in an aqueous solution by citrate⁴. The present dossier examines the potential entry sites of nanoparticles into the human body and describes several biological effects which can be triggered.

Nanoparticles are not solely a product of modern technology, but are also created by natural processes such as volcano eruptions or forest fires. Naturally occurring a noparticles also include ultrafine sand grains of mineral origin (e.g. oxides, carbonates). In addition to commercially produced nanoparticles, many are unintentionally created by the combustion of diesel fuel (ultrafine particles) or during barbecuing. Synthetic nanoparticles find use in many applications. (e.g. as aerosols), as ultrafine powder, for films, distributed in fluids (dispersed, for example ferrofluids) or embedded in a solid body (nanocomposites). The present dossier focuses on those nanoparticles present in a solid state. Liposomes, micelles and vesicles, which are soluble nano-scale organic compounds and also fall into the category of nanoparticles, are omitted here.

Definition:

The term “nanoparticle” is a mixture of the words “nanos” (Greek: the dwarf) and “particulum” (Latin: particle). In the scientific context, “nano” primarily refers to a specific order of magnitude, namely 10-9. This can refer to a volume, a weight or a unit of time, whereby a nanometer (nm = 10-9 meters) corresponds to one millionth of a millimeter. To illustrate this more graphically, a nanometer has the same relation to a meter as the diameter of a hazelnut to the diameter of the Earth. In the framework of nanotechnology, the term “nano” refers almost exclusively to particle length. This means that those objects that extend in two dimensions from1 to several 100 nm are designated as nanoparticles. However, also includes filamentous objects such as nanotubes. This dossier therefore uses the definition of theEU-CommissionSCENHIR2, which is restricted to those objects whose extension in all three dimensions lies between 1 and100 nm. Those that extend in only two dimensions on the nm-scale are termednanotubes and particulate objects; those with only a single dimension under 100 nm are termed nanopellets.

Characteristics of Nanoparticles:

A decisive feature that makes nanoparticles technically interesting is their surface-to-volume ratio. This ratio increases with decreasing particle diameter. A nanoparticle is composed of a few to several thousand atoms. This means that a significant portion of the atoms are located on the particle surface. At a particle diameter of 10 nm, 20 % of the approximately 30 000 atoms 4 of the entire particle are positioned on its surface; at a particle diameter of 5 nm, the value increases to 40 % of the approximately 4000 atoms, and at 1 nm diameter, almost all of the about 30 atoms are on the surface. The surface atoms, as opposed to those inside the material, have fewer direct neighbors and therefore contain so-called unsaturated bonds. These are responsible for the higher reactivity of the particle surface. Increased reactivity is the basis for numerous applications.

One idea, for example, is that precisely controlling particle diameter will yield a new generation of catalysts with high selectivity; such catalysts will accelerate only those chemical processes that produce the target product from the raw materials. This high reactivity would also reduce the melting point, so that using nanoparticular raw materials would reduce the “firing” temperature in the case of ceramics. More importantly, the composites (solids composed of various materials) would shrink less during the hardening process, a particularly important feature in dental prosthetics for example. Even though the surface of an individual particle naturally decreases along with its diameter, the specific surface area of a powder increases as the size of its component particles drops – under the precondition that the same amount by weight is being considered. This explains why nano structured materials are interesting for filtration and catalysis. Nanoporous materials exhibit a large specific surface area on which the filtered substances can be deposited. They also have a high reactivity, which promotes adsorption or their catalytic effect.

Varying nanoparticle size not only modifier activity but can also alter the optical characteristics such as transparency, absorption, luminescence and scattering. Although particles measuring only a few nanometers in diameter lie far below the wavelength range of visible light (380 to 780 nm), they can absorb light of specific wavelengths (Figure 1).

Figure 1. Nanoparticle size

These effects can only be understood on a quantum mechanics level. In the case of quantum dots, which are composed of semiconductor materials, particle size can be used to adjust the wavelength of the fluorescence, for example. These optical features make nanoparticles especially interesting for applications in optoelectronics, cosmetics and medical diagnostics. An important feature for the magnetic behaviour of particles with a diameter in the nanometer range is that they magnetized permanent magnets in one direction. Nanoparticles therefore provide an opportunity to increase the storage capacity of magnetic data storage devices, which is determined by the number of magnetizable elements. Finally, the magnetic characteristics of nanoparticles are relatively insensitive to temperature fluctuations.

Production of nanoparticles and Nanomaterials:

Nanomaterials or nanoparticles are used in a broad spectrum of applications. Today they are contained in many products and used in various technologies. Most nanoproducts produced on an industrial scale are nanoparticles, although they also arise as byproducts in the manufacture of other materials. Most applications require a precisely defined, narrow range of particle sizes (monodispersity). Specific synthesis processes are employed to produce the various nanoparticles, coatings, dispersions or composites Defined production and reaction conditions are crucial in obtaining such size dependent particle features. Particle size, chemical composition, crystallinity and shape can be controlled by temperature, pH-value, concentration, chemical composition, surface modifications and process control. Two basic strategies are used to produce nanoparticles: “top-down” and “bottom up”. The term “top-down” refers here to the mechanical crushing of source material using a milling process. In the “bottom-up” strategy, structures are built up by chemical processes (Figure 1). The selection of the respective process depends on the chemical composition and the desired features specified for the nanoparticle Figure. 2 Methods of nanoparticle production: top-down and bottom.

Figure 2. Methods of nanoparticle production

Top-Down/mechanical-physical production processes:

“Top-down” refers to mechanical-physical particle production processes based on principles of micro system technology. The traditional mechanical-physical crushing methods for producing nanoparticles involve various milling techniques.

Milling processes:

The mechanical production approach uses milling to crush microparticles. This approach is applied in producing metallic and ceramic nanomaterials. For metallic nanoparticles, for example, traditional source materials (such as metal oxides) are pulverized using high-energy ball mills. Such mills are equipped with grinding media composed o wolfram carbide or steel. Milling involves thermal stress and is energy intensive. Lengthier processing can potentially abrade the grinding media, contaminating the particles. Purely mechanical milling can be accompanied by reactive milling: here, a chemical or chemo-physical reaction accompanies the milling process. Compared to the chemo-physical production processes (see below), using mills to crush particles yields product powders with a relatively broad particle-size ranges. This method does not allow full control of particle shape.

Bottom-up/Chemo-physical production processes:

Bottom-up methods are based on physicochemical principles of molecular or atomic self-organization. This approach produces selected, more complex structures from atoms or molecules, better controlling sizes, shapes and size ranges. It includes aerosol processes, precipitation reactions processes (Figure 3).

Figure 3. Nanopartical production

Gas phase processes (Aerosol processes):

Gas phase processes are among the most common industrial-scale technologies for producing nanomaterials in powder or film form. Nanoparticles are created from the gas phase by producing a vapour of the product material using chemical or physical means. The production of the initial nanoparticles, which can be in a liquid or solid state, takes place via homogeneous nucleation. Depending on the process, further particle growth involves condensation (transition from gaseous into liquid aggregate state), chemical reaction(s) on the particle surface and/or coagulation processes (adhesion of two or more particles), as well as coalescence processes (particle fusion).

Examples include:

· processes in flame-, plasma-, laser- and hot

· wall reactors, yielding products such as

· fullerees and carbon nanotubes:

Application of Nanoparticles:

The fields of application for nanoparticles are wide ranging. They play a major role in materials development. The great expectations we place on today’s modern nanoparticle containing materials is based on the hope that the different material properties such as conductivity, weight, stability, flexibility, heat resistance etc. can be specified independently from one another. Numerous nanotechnology products have been on the market for some time now. In the chemical sector this includes Carbon Black (soot particles), for example in printing black; in the automobile sector this includes scratch-resistant paints, filler in tires and anti-reflective layers. In the Life Sciences, nanoparticles are used for biochips as well as for so-called markers. They are also used in sunscreens and cosmetic products. In medical diagnostics, nanoparticles are increasingly being used as contrast media; they are also a tool in cancer therapy. Recently, nanoparticle applications have been introduced on the market in paints, polymer nanocompsoites and nanopigments. Concepts and prototypes exist for regenerative medicine (for example in tissue cultures), highly efficient hydrogen storage systems, self-healing materials, and coatings that switch their colour using sensor technology. Moreover, current efforts are being devoted to developing products to treat diseases and to affect a controlled release of medications.

Nanosilver:

Nanosilver and nanoparicles are considered two of the most useful commercial products belonging to the group of nanomaterials. Recently their use has reached one of the highest levels of cost-effectiveness

Silver is perhaps second only to gold in its use since antiquity as a metal and material for jewelry. Silver has, due to its antibiotic potential, a long history of medical and hygienic uses. During the previous century, the photochemical properties of silver compounds led to an increase of the use of silver and a peak of silver emission into the environment that has since declined considerably, due to the advent of digital photography and the implementation of stricter environmental legislation. In recent years, the use of silver as a biocide in the form of micro-crystals or nanoparticles has grown substantially, as these preparations are effective against many resistant populations and ‘biofilms’–aggregates of microorganisms in aqueous solution–that grow on the surfaces of bodies of water and inside water pipes. Consumer products utilizing nanosilver to fight bacterial growth constitute the fastest-growing category of nanoproducts. According to an inventory that relies on data supplied by producers (the ‘Project on Emerging Nanotechnologies’), nanosilver is being used in over two hundred consumer products2–including clothing, bedding material, cosmetics and beauty soaps. It is being incorporated into plastic storage containers for food, used in kitchen utensils, in paints and in fabric softeners. “Colloidal solutions”–solutions of elementary nanoparticulate silver or silver compounds – are being offered as dietary supplements. Independent scientific data concerning the numerous advertised health claims are lacking. This dossier presents an overview of the advantages and drawbacks of nanosilver use, possible consequences for human health and the environment, and describes the ongoing debate concerning the regulation of new products containing nanosilver.

Biocidal effects of silver:

Silver compounds and particles of elementary silver can release silver ions (Ag+)–through oxidation or other processes–that are responsible for the toxicity towards bacteria, fungi and algae. Few studies have investigated the interaction of silver nanoparticles with viruses. Silver ions can attach to the surface of cell membranes and disturb their proper functions. They can penetrate cells and cause damage by interacting with sulphur- or phosphorus-containing compounds (proteins). A study has shown that the bactericidal effect on gram negative bacteria is size-dependent and most pronounced for particles of 1–10 nm in diameter. Silver nanoparticles that have penetrated a cell can continue to release silver ions that exhibit their own antibacterial effect.

The smaller particles have a higher antimicrobial activity per equivalent mass unit than their larger particle counterparts as a result of their higher surface to volume ratio. Recent studies have reported a dose-dependent effect against even bacteria that had acquired resistance to antibiotics. Silver particles and silver ions have been demonstrated to be useful and effective in bactericidal applications in medical settings. However, the bactericidal mechanism is not completely understood.

Clinical studies have reported the existence of silver-resistant variants of bacteria. Experts have recommended abstaining from regular and widespread use of bactericidal agents in low doses, as this could encourage the emergence of resistant strains. Silver ions should be used only in high doses for well defined medical purposes.

Synthesis of silver nanoparticles:

a. Chemical and physical synthesis methods of AgNPs:

For biological use, the main aim of making AgNPs will be for them to be stable in solution, so that each silver nanoparticle can thoroughly be exposed to the cells in tissue and exert their maximal bio-effects. Since Turkevich et al. first reported their preparation of AgNPs based on the reduction of silver nitrate with citrate, similar updated methods have also been reported. Nowadays, AgNPs of different sizes and shapes can be made. In addition to chemical synthesis of AgNPs, Yen et al. reported the production of AgNPs by physical manufacturing. First, silver bulk material was ground into the silver target materials. This paper investigates n-Ag release from commercial clothing (speciﬁcally, socks) into water, as well as the form of this silver and the adsorption characteristics that determine its fate in WWTPs⁵.

Then they we’re vaporized to the atomic level by an electrically gasified method under vacuum then further condensed in the presence of inert gas, and piled up to form AgNPs. The sizes of AgNPs could be effectively managed depending on the evaporation time and electric current used. The AgNPs were collected in a cold trap and centrifuged to obtain the final product.

b. Biosynthesis of AgNPs from staphylococcus aureus and fungi:

Apart from chemical and physical methods, AgNPs can also be synthesized using a reduction of aqueous Ag ions with the culture supernatants of Staphylococcus aureus. The supernatant was added separately to the reaction vessel containing silver nitrate. The bioreduction of the silver ions in solution was monitored and the spectra measured in a UV-vis spectrophotometer at a resolution of 1 nm. Furthermore, Gajbhiye even reported the use of fungus Alternaria alternata to produce AgNPs.

Biological properties of silver nanoparticles:

1. Anti-bacterial properties of silver nanoparticles:

The utilization of silver as a disinfecting agent is not new, and silver compounds were shown to be effective against both aerobic and anaerobic bacteria by precipitating bacterial cellular proteins and by blocking the microbial respiratory chain system. Before the advent of silver nanoparticles, silver nitrate was an effective antibacterial agent used clinically. Afterwards, the use of silver agents decreased as antibiotics came into prominence during the last century. Nonetheless, the combination of silver and sulfonamide to form silver sulfadiazine, has remained useful in the treatment of burns, even to this day. Silver returned to prominence recently due to the emergence of antibiotic-resistant bacteria as a result of the overuse of antibiotics. With the advancement of nanotechnology, the interest in the use of the anti-bacterial efficiency of silver nanoparticles has been rekindled. Studies have demonstrated the toxicity of nanoparticle silver to bacteria^6,7,8,9,10 suggesting that the antimicrobial effects of silver may be detrimental to aquatic ecosystems. Therefore, it is important to characterize (as colloidal or ionic) and quantify the silver released from commercial products. Compared with silver compounds, the mechanism for the antimicrobial action of AgNPs may be similar, although neither is properly understood. However, because of the larger surface area to volume ratio, AgNPs may have much better efficiency. The possible mechanisms of action are:

1. Better contact with the microorganism—nanometer scale silver provides an extremely large surface area for contact with bacteria. The nanoparticles get attached to the cell membrane and also penetrate inside the bacteria;

2. Bacterial membranes contain sulfur-containing proteins and AgNPs, like Ag+, can interact with them as well as with phosphorus-containing compounds like DNA, perhaps to inhibit the function;

3. Silver (nanoparticles or Ag+) can attack the respiratory chain in bacterial mitochondria and lead to cell death;

2. General characteristics of silver nanoparticles and their entry portals into human body:

Silver nanoparticles have been synthesized through an array of methods, e.g. spark discharging, electrochemical reduction, solution irradiating and cryochemical synthesis, to name a few (Sun and Xia, 2002; Zhanget al., 2002; Bogle et al., 2006; Sergeev et al., 1999; Pyatenko et al., 2004). Particle morphologies include spheres, rods, cubes, wires and multifacets, normally within a size range of <100nm. As is the case with all nanomaterials, the principle characteristic of silver nanoparticles is their ultrasmall size. Ultrasmall particle size leads to ultralarge surface area per mass where a large proportion of atoms are in immediate contact with ambiance and readily available for reaction. Unique interactions with bacteria and virus have been demonstrated of silver nanoparticles of certain size ranges and shapes.

Small size also confers greater particle mobility both in the environment and in the body. Further, nanoparticles produced through different processes and for different purposes may vary in surface charge and agglomeration state. Some silver nanoparticles have coatings and others are hybridized with other materials to form nanocomposites (Kobayashi et al., 2005; Lesniak et al., 2005). In addition, nanoparticle colloids may need different stabilizers. Stabilization was achieved by coating the nanoparticle core with polyvinylpyrrolidone. A 0.14wt% silver coated nanoparticles solution in ethanol absolute 99% was used¹¹. All these combined may probably modify the intrinsic physiochemical properties of silver and may therefore give rise to modify cellular uptake, interaction with biological macromolecules and translocation within the human body. Adverse reactions can occur that would not otherwise be seen with silver in bulk form.

3. Nanosilver’s interactions with tissues and Routes of Exposure Respiratory system:

Being different than micron and above level particles that are largely trapped and cleared by upper airway mucocilliary escalator system, particles less than 2.5 nm can get down to the alveoli. The deposition of inhaled ultrafine particles (aerodynamic diameter <100 nm) mainly takes place in the alveolar region. Healthcare and hygiene spray products containing silver nanoparticles have entered daily use.

Most commercialized silver nanoparticles are usually less than 100 nm, way far under the 2.5 _m size. Of great concern are silver nanoparticle aerosol directly applied into the nasal or oral cavity, as concentrated nanoparticles can be channelled into the lungs. At the alveolar region, partic les will first encounter and be submersed into the surfactant lining of the alveoli before having contact with any cell. The submersion process seems to take place regardless of particle type and nature of the surface (Geiser et al., 2003; Gehr et al., 2000). Results of studies using different types of particles suggests that surfactant dipalmitoylphosphatidylcholine (DPPC) and surfactant protein (SP-D) are absorbed to the particle surface, which may be a mediation mechanism for toxicity of particulate matters (Liu et al., 1998; Kendall et al., 2004; Gerber et al., 2006). The surface structures of silica particles are found to interact with the lining fluid layer and produce surface radicals and ROS which are associated with silica particle’s specific toxicity and particle.

Skin:

Human abdominal full thickness skin was obtained as surgical waste. Prior to freezing, subcutaneous fat was removed and hair shaved. All the pieces of full thickness skin were stored in freezer at −25◦C for a period up to, but not exceeding, 4 months. It has been shown that this method of storage does not damage the skin since no difference in permeability was observed between fresh and frozen segments of the same skin in a separate series of experiments ¹². Through various techniques, textile fibers can be coated or impregnated with silver nanoparticles. These textiles are called “smart textiles” which are claimed to have advantages over normal textiles having the ability to inhibit growth of bacteria and mold. These anti-microbially active textiles have been employed for manufacturing of underwear, lingerie, socks as well as hospital and laboratory gowns and clothes. Nanosilver is gaining in textiles and there is an increase in interest due to its close contact with human skin. One of skin’s major roles is to provide protection to the underlying organs. It consists of an outer epidermis and dermis.

The stratum corneum layer of the epidermis is a strict barrier allowing limited penetration of particulate materials. This aspect has potential to serve as novel route for drug delivery and has attracted enormous pharmaceutical research interests (Shim et al., 2004; Lopez et al., 2005; Kohli and Alpar, 2004). Transdermal penetration of fine particles has been documented. For example, TiO2 particles (micron-sized), 1999).

Yet, data on nanosilver are few to none. For each kind of nanosilver-based textile, the release of nanoparticles from the textile fibers under various conditions, e.g. sweating, repetitive attrition and laundering needs to be investigated. Appropriate models should be employed to assess the possibility of transdermal penetration of silver nanoparticles since several recent studies have reported transdermal penetration of nanoparticles. Ryman-Rasmussen et al. (2006) demonstrated that quantum dots with diverse physicochemical properties could penetrate the intact stratum corneum barrier and localize within the epidermal and dermal layers. Fullerene-based peptides were also shown to be capable of penetrating intact skin and mechanical stressors could facilitate their traversion into the dermis (Rouse et al., 2007). Intradermal nanoparticles could enter subcutaneous lymphatics (Gopee et al., 2007).

Gastrointestinal tract:

All materials given orally are in close contact with the gastrointestinal tract (GIT) which has an overall surface area for nutrient exchange. Gastrointestinal ingestion is probably the most common voluntary route of exposure for nanosilver since numerous colloidal silver nanoparticle products are publicly peddled as so called “health maintainers” or “immuno-boosters”; most of them are used orally. Silver nanoparticles are also employed in products for water disinfection and food stabilization. Besides, particles discharged by respiratory mucocilliary escalation can end up in GIT. But despite extensive GIT exposure, apart from occasional cases of systemic argyria due to prolonged ingestion and disturbance of intestinal function, reports on local or systemic adverse effects of orally ingested nanosilver are remarkably few.

Never the less, the occurrence of systemic argyria after ingestion of colloidal nanosilver in itself is an evidence that translocation of silver nanoparticles from the intestinal tract takes place. The kinetic mechanism of nanosilver translocation is unclear, but it has been demonstrated that the intestinal lymphatic tissue (Peyer’s patches) can take up intestinal particles. Uptake can also take place trans-cellularly via normal enterocytes and through paracellular pathways. Particle characteristics like size, surface charge, and coatings can modify the translocation process. Particles once in the submucosal region are able to enter both lymphatics and capillaries. Lymphatic absorption may give rise to immune response, for instance the mucosal secretory immune function may probably be affected. At the same time those particles entering capillaries become circulatory and will soon encounter their first pass, i.e. liver. Based on the extent to which colloidal nanosilver is orally used, it is a logical assumption that ingested silver nanoparticles might have impact on the liver since the liver serves as the first checkpoint for everything absorbed through GIT before becoming systemic. As has been shown in the study by liver seems to be a major depository of circulatory ultrafine silver particles. Further, toxic effects of silver nanoparticles to liver cells have been reported from an in vitro experiment. In addition, at least one clinical report has associated impaired liver function to silver nanoparticles released from a wound dressing. As stated earlier, however, systemic toxicity of ingested nanosilver is scarcely seen. This situation may probably be accounted for by the presence in the GIT of a complex mixture of compounds including ingested food, digestive enzymes, electrolytes, and intestinal microbial flora, etc. Ingested nanoparticles can have interactions with these compounds, which might change reactivity and toxicity of the particles. This is of particular relevance to silver, as it is well known for its high affinity for the thiol groups of proteins. It has been described that medium high protein concentration could lessen the in vitro cytotoxicity of nanoparticles and nanosilver’s antibacterial activity could be blocked by thiol containing agents. Apart from that, GIT ingested particles will undergo sequential pH stress from gastric acid and intestinal fluids. Particle surface characteristics may be modified by the shift in ambient pH, which leads to altered solubility and ion state of the particles. The renewal of the epithelium also hinders nanoparticles penetration through the intestinal wall.

Anti-inflammatory properties of silver nanoparticles.

Apart from being an excellent anti-bacterial agent, we were also able to show, in the burn wound model, as well as in a peritoneal adhesion model in mice, that AgNPs had anti-inflammatory properties. In the burn model, significantly lower levels of the pro-inflammatory cytokine IL-6 were found in animals treated with AgNPs using quantitative real-time RT-PCR. Conversely, mRNA levels of IL-10, an anti-inflammatory cytokine, stayed higher in the AgNPs group in comparison with other silver compounds at all time points monitored during healing.

Polymorphonuclear cells (PMNs) and fibroblasts produced IL-6, which has been recognized as an initiator of events in the physiological alterations of inflammation; decreased expression of IL-6 may result in fewer neutrophils and macrophages recruited to the wound and less cytokines being released in the wound with subsequently lower paracrine stimulation of cellular proliferation, fibroblast and keratinocyte migration, and extracellular matrix production. IL-10 could inhibit the synthesis of pro-inflammatory cytokines, and also inhibits leukocyte migration toward the site of inflammation, in part by inhibiting the synthesis of several chemokines, including monocyte chemo attractant protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1).The differences found in mRNA levels of various cytokines further confirmed that AgNPs can effectively modulate cytokine expression during suppressing inflammation. Apart from our group, others have also demonstrated the anti-inflammatory effects of silver nanoparticles. Nadworny et al. explored the effect of AgNPs using a porcine model of contact dermatitis, while Bhol and Schechter utilized AgNPs in a rat model of ulcerative colitis.In both models, although the set of pro-inflammatory cytokines measured were different from ours (IL-1; TNF-), the findings did confirm that AgNPs had direct anti-inflammatory effects and improved the healing process significantly when compared with controls.

Applications of silver nanoparticles in medicine:

In the past, silver was used for a variety of clinical conditions including epilepsy, venereal infections, acnes and leg ulcers. Silver foil was applied to surgical wounds for improved healing and reduced post-operative infections, while silver and lunar caustic (pencil containing silver nitrate mitigated with potassium nitrate) was used for wart removal and ulcer debridement. Although some centers still use these solutions, they have been shown to be very impractical to use on large wounds or for extended time periods due to instability. With nanotechnology, the availability of silver nanoparticles has enabled the use of pure silver to achieve a rapid growth in medical practice. Since the size, shape and composition of silver nanoparticles can have a significant effect on their efficacy, extensive research has gone into synthesizing and characterizing silver nanoparticles. The application of nanosilver can be broadly divided into diagnostic and therapeutic uses.

a. Nanosilver in diagnosis and imaging-

Early diagnosis of any disease condition is vital to ensure that early treatment is started and perhaps resulting in a better chance of cure. For example, in patients undergoing general anesthesia for surgery, the risk of developing pulmonary complications will be lowered if any sub-clinical upper respiratory tract viral infections can be detected prior to surgery.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a powerful analytical tool that extends the possibilities of vibrational spectroscopy. SERS differs from standard Raman scattering in that the incoming laser beam interacts with the oscillations of plasmonic electrons in metallic nanostructures to enhance the vibrational spectra of molecules adsorbed to the surface. In a recent study, SERS was used to obtain the Raman spectra of the respiratory syncytial virus (RSV), using substrates composed of silver nanorods. It was shown in this study that the four virus strains tested were readily detected at very low detection limits.

In terms of detecting cancer, Au–Ag nanorods were used in a recent study as a nanoplatform for multivalent binding by multiple aptamers, so as to increase both the signal and binding strengths of the aptamers in cancer cell recognition. The molecular assembly of aptamers on the nanorods was shown to lead to a fold higher affinity than the original aptamer probes. Thus, these nanorod–aptamer conjugates are highly promising for use in specific cell targeting, as well as having the detection and targeting ability needed for cell studies, disease diagnosis, and therapy.

b. Nanosilver in therapeutics.

Wound healing is regarded as a complex and multiple-step process involving integration of activities of different tissues and cell lineages. Perhaps the most well documented and commonly used application of silver nanoparticles for this is in the use of wound dressings. In this regard, Acticoat®, which is the first commercial dressing made up of two layers of polyamide ester membranes covered with nanocrystalline silver ions, has been studied extensively. Acticoat® has been shown to have the lowest MIC and MBC values, and the fastest Kill kinetics against the five bacteria tested in vitro studies. FA number of different genera of fungi have been investigated in this effort and it has been shown that fungi are extremely good candidates in the synthesis of gold^{12, 13}, silver^{14, 15} and also quantum dots of the technologically important CdS by a purely enzymatic process¹⁶. Further, the sustained release of silver particles should minimize the likelihood of bacteria developing resistance to silver. In a randomized prospective clinical study involving 30 patients with each group of patients having comparable burn wound size, depth and location. Gold and silver nanoparticles have been produced by direct laser ablation of metal plates in a solution containing a suitable surfactant with pulsed nanosecond lasers delivering high energy pulses. This approach allows the formation of nanoparticles of a controlled size but with a significant polydispersity.¹⁸

Nano silver uses:

· Medical Products—wound dressings,

Surgical gauze, bandages

· Textiles and Clothing

· Sporting Goods

· Aerospace and Electronics

Nano Silver in Environment:

· Lake Ecosystem Nano Silver (LENS) Project*

· Effect of nano silver on aquatic environment

· Will monitor changes in lake’s ecosystem

· Track effects through entire food web

· Determine how resulting changes alter ecosystem

Function

Trent University- Natural Sciences and Engineering

Research Council of Canada, Environmental Canada Support- Fisheries and Oceans Canada

Medical use:

Silver–in the form of silver nitrate (AgNO3) – has been used since the 18th century for the disinfection of wounds. Until recently, a weak solution of silver nitrate was applied to the eyes to prevent or cure infections. The discovery of penicillin and sulphonamide drugs have, after the end of the Second World War, replaced silver as an antibiotic in most areas. An antibacterial combination product containing silver (Silver sulfadiazine) is still being used as a topical burn cream on second- and third-degree burns and for wound dressings after skin transplants. The efficacy of silver in the management of chronic wounds has not been confirmed.

Due to its antimicrobial activity, silver may have a positive effect on the wound bed, but it seems to be less useful in the treatment of infected wounds. Some adverse effects of silver products, such as damage to human cells and delayed wound healing, have also been described. For a number of years, coatings of silver oxide or silver alloy have been used on medical devices–such as catheters, implants and heart valves. Reports of postoperative complications following the use of silver coated prosthetic heart valves led to a recall in the year 2000. Contradictory findings concerning the risks of these types of heart valves have been reported.

Other uses of nanosilver:

The “Project on Emerging Nanotechnologies” at the Woodrow Wilson Center (USA) collects data of nanotechnology-based consumer products that are currently on the market. This inventory is using information supplied by the producer (‘manufactured-identified’). Among the more than 800 entries are over 200 products containing nanosilver. The information given by the producers about the character and the amount of silver particles is incomplete and not always trustworthy; in some cases ‘nano’ may have been used solely as an advertising claim.

Dietary supplements water-based solutions of silver nano particles:

Under the name of “colloidal silver” are claimed to have effects against germs, pathogens and diseases if used internally (a ‘colloid’ consists of the dispersion medium and the small dispersed particles with a diameter between approximately a few nm and 10 nm). Some of these preparations of “colloidal silver” contain silver salts in the place of elementary silver. According to the manufacturers, only products containing metallic silver particles bring beneficial health effects. Substantial scientific evidence supporting the use of these products for disease treatment does not exist, and their safety is not generally recognized.

Cosmetics and personal care products:

According to the claims of the producers, some brands of cosmetics contain bactericidal nano- or micro- particles of silver in order to protect the skin of people suffering from neurodermitic skin and itching. The German firm ‘Bio-Gate AG’ has developed a patented process that allows the use of antimicrobial silver in cosmetics. Advertisements for creams, body lotions, toothpaste, toothbrushes and combs mention the advantages of using silver nanoparticles in those products.

Water treatment:

Silver is – similarly to copper–a substance that can control microorganisms in water treatment works. Silver has been used for a number of years as biocidal agent in filter systems and as algicide to control algae in swimming pools. The US Environmental Protection Agency (EPA) approved the use of silver for this purpose in 1993. However, due to the toxicity of silver to fish and the maquatic environment, the discharge of effluents containing silver is subject to restrictions. Products containing silver have been applied in water pipes to eliminate the dangerous biofilms of bacteria that can cause Legionnaires’ disease In Japan, silver zeolite has been used as a bactericidal agent since 1983. Products containing silver salts are available to campers and hikers wishing to treat potable water and to remove bacteria. Ceramic or charcoal water filters are being offered with nanosilver incorporated in their outer layers, thus inhibiting bacterial growth on the filter.

Textiles:

The bactericidal properties of silver particles can be used to fight bacterial growth that causes unpleasant smells – and therefore many textiles incorporating nanosilver ingredients are available for purchase. Until recently, the production of textiles containing silver required considerable amounts of this metal, but the availability of nanosilver allows for a significant reduction. Products include Nano-Silver®-socks, undergarments, sportswear, bedding material and shoe liners. A study presented in 2008 on different brands of socks containing nanosilver found different levels of silver, ranging from 0.02 mg up to 30 mg silver per sock.

Some of these socks released almost 100 % of the silver particles after only four consecutive washings. Both silver particles and silver ions could be detected in the wash water.

Kitchen utensils and household appliances:

The biocidal effect of nanosilver is already being used in numerous appliances (according to the claims of the manufacturers), such as on the inner surfaces of refrigerators, in air purifiers, vacuum cleaners, hair cutters and trimmers. Silver nanoparticles have been incorporated into the plastic of food containers. Since 2005, a washing machine equipped with a ‘Silver Nano Health System’ has been available, containing a mechanism that produces bactericidal silver ions that are added during the wash. After objections concerning the increased burden of silver into the environment were raised by the Swedish environmental agency and the association of water treatment works, this product was removed temporarily from the Swedish market.

Paints, lacquers and sprays for surfaces:

Hospital acquired (nosocomial) infections caused by multi-resistant organisms have increased significantly. In the United States alone, more than 1.7 Million patients are affected each year, leading to about 100,000 deaths. Antimicrobial paint containing nanosilver particles could replace currently used organic biocides. In hospitals as well as in schools, offices, and in public transportation these new antimicrobial paints are already being used.

Other uses:

According to the manufacturers, nanosilver is a component of a multitude of products, such as fabric softener, drinking bottles, baby pacifiers, comforters, computer keyboards, condoms, female hygiene products, and fortifying agents for plants.

Health effects:

The World Health Organization (WHO) considers silver to be a toxic substance, although it only exhibits toxicity in humans and other mammals at very high doses. The US Environmental Protection Agency (EPA) declared silver to be a pesticide in 1954 and recommends the observation of limits for silver exposure. A ‘reference dose’ of not more than 0.005 mg silver per kilogram of body weight per day was recommended. The US Agency for Toxic Substances and Disease Registry (ATSDR) presented a general toxic profile for silver in 1990, where results of silver exposure on brain activity and lung function gained from animal studies are described. While these limits are valid for silver, they do not, however, consider the specific properties of silver nanoparticles. An observed detrimental effect of considerable doses of silver in humans is the permanent bluish-grey discoloration of skin and nails (argyria) and of the eyes, mucous membranes and internal organs (argyrosis). Silver is thereby deposited in tissues of the basal membranes of the skin, is no longer bioavailable, and does not damage the cells. It is not known whether silver nanoparticles are taken up by human tissue in the same manner. Argyria and argyrosis are cosmetic changes, and no resulting long-term health effects are known. It has been reported that workers who were exposed to silver and silver compounds in their workplaces for long periods of time showed changes of their blood cells and degenerative processes in the liver and kidneys. An in vitro study of rat liver cell cultures found changes in form and size of cells as well as the induction of oxidative stress resulting from concentrations between 5 and 50 mg/ml of silver nanoparticles 24, Another study reported that silver nanoparticles are capable of penetrating–in vitro–human cells. This experiment was performed using a diffusion cell in which a membrane consisting of intact human skin separated two chambers. The silver nanoparticles in one chamber could permeate this membrane. The location of silver nanoparticles was verified by TEM (transmission electron microscopy). Some particles could be detected in deeper skin layers. The effects of continuous exposure to nanosilver through nanosilver-treated fabrics (underwear, socks, bedding, etc.) on the beneficial layer of skin bacteria on healthy human skin have not been investigated. An ongoing clinical study compares the effects of a type of silver nanoparticle hand gel versus a common antibacterial hand gel.

ACKNOWLEDGEMENT:

Authors are highly Acknowledge the help of teaching staff of Rajarambapu College of Pharmacy, Kasegaon. For providing necessary information required for research work. Also we are highly Acknowledge the help and guidance of Dr M. M. Nitalikar.

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Received on 19.01.2019 Accepted on 28.02.2019

Asian J. Pharm. Tech. 2019; 9(2):115-124.

DOI: 10.5958/2231-5713.2019.00020.5