Tese_Tânia Vieira.pdf - Ubi Thesis

Chapter I - Introduction
materials (Yin et al. 2005; Guidelli et al. 2011). These special and unique properties could be
attributed to their small sizes and large specific surface area (Guzman et al. 2011). All of this
makes the inorganic nanoparticles adequate for applications in biomedicine, catalysis,
electronics, energy science, magnetic, mechanics, optics, and so on (Shahverdi et al. 2007;
Fayaz et al. 2010). A number of recent works in this field, describe the possibility of generating
new types of nanostructured inorganic materials with designed surface and structural properties
(Sondi et al. 2004). Thus, the preparation, characterization, surface modification, and
functionalization of nanosized inorganic particles open the possibility to formulate a new
generation of bactericidal materials to avoid microbial biofilm formation on biomaterials surface
(Sondi et al. 2004; Lipovsky et al. 2011). Nanoparticles with antibacterial properties offer many
distinctive advantages with respect to the therapy with antibiotics since they allow the reduction
of in vivo toxicity, overcoming the problem of resistance to the antibiotics, and lowering the
cost associated with their production (Huh et al. 2011).
Among the different types of nanoparticles, the metallic ones are the most promising
candidates for this purpose, since they show good antibacterial properties (Ruparelia et al. 2008;
Rai et al. 2009), due to their high specific surface area, high fraction of surface atoms (Hung et
al. 2007; Shahverdi et al. 2007; Martin et al. 2011), and small size. These properties allow
nanoparticles to interact closely with cellular membranes of the bacteria. In addition to these
characteristics, this kind of nanoparticles release metal ions in solution, which increases the
antibacterial properties (Ruparelia et al. 2008). Another properties of these nanoparticles are
the long life and the heat resistance (Potara et al. 2011). Well-known metallic nanoparticles
with these properties are the silver nanoparticles (AgNPs).
1.3. Silver Nanoparticles
The unique antimicrobial properties of silver in the treatment of infections have been
known for a long time (Gurunathan et al. 2009; Häntzschel et al. 2009; Mohammed Fayaz et al.
2009). Since 1000 BC, Egyptians, Greeks, Romans and other ancient civilizations used silver
vessels to store perishable foods, to produce silver cutlery, glassware and dishes (Vasilev et al.
2010). Silver was also used with medical purposes for rheumatism, tetanus, gonorrhea and wound
healing treatment (Vertelov et al. 2008). In the 18 th century, silver nitrate (AgNO 3 ) was used for
the treatment of venereal diseases, fistulae from salivary glands, bone abscesses (Rai et al.
2009), and ulcers (Neal 2008). Dilute solutions of AgNO 3 have been used since the 19 th century in
treatment of infections and burns (Ip et al. 2006). Due to the successful of the registered cases,
in 1920s silver was recognized by the United States Food and Drug Administration for its
antimicrobial activity and was regulated for wound management (Neal 2008). In 1940s, after
penicillin was introduced in the market, the use of silver for the treatment of bacterial
infections was reduced (Rai et al. 2009). Silver reappear again in the 1960s when Moyer
introduced the use of 0.5% AgNO 3 for the treatment of burns as previously done in the 19 th
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