Tese_TÃ¢nia Vieira.pdf - Ubi Thesis

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Chapter III – Results and Discussion The combination of the two types of nanoparticles (AgNPs and chitosan/dextran nanoparticles) herein produced provided results for MIC as lower as 1.5 µg/mL with AgNPs produced by NaBH 4 reduction, and 3.0 µg/mL with AgNPs produced by C 6 H 8 O 6 reduction. Still, AgNPs produced into chitosan/dextran nanoparticles with NaBH 4 or with C 6 H 8 O 6 presented a higher MIC value, 23.50 µg/mL and 11.75 µg/mL respectively, compared to those produced by the combination of both types of nanoparticles. The AgNPs produced into chitosan/dextran nanoparticles were too big, which can be a disadvantage in terms of the antibacterial activity, as already reported for AgNPs. The combination of both nanoparticles presented a better antibacterial activity than AgNPs alone. Therefore, such combination was an advantage to improve the antibacterial activity of AgNPs. MBC values also determined in this work were in all cases, except for the chitosan/dextran nanoparticles with AgNPs (C 6 H 8 O 6 ), above of those obtained for MIC. Thereby, a higher concentration of AgNO 3 was needed to kill the bacteria. In this study, chitosan was not able to eradicate the bacteria. However, it was able to inhibit bacteria growth as observed through MIC assay. Hereupon, the ability to completely kill bacteria is due to the bactericidal effect of AgNO 3 . As mentioned in chapter I, the mechanism by which the AgNPs are able to interact with the bacteria is not fully understood (Kim et al. 2007; Raffi et al. 2008; Guzmán et al. 2009; Potara et al. 2011). However, there are some reports that showed that the AgNPs may attach on the surface of the cell membrane and disturb its power function, such as permeability and electron transport chain (Kim et al. 2007; Guzmán et al. 2009). AgNPs can also penetrated inside the bacteria and caused damage by interacting with phosphate and sulfur containing compounds, such as DNA (Raffi et al. 2008). Finally, the production of ROS by the AgNPs is also responsible for their antimicrobial mechanism (Kim et al. 2007; Potara et al. 2011). Even though the antibacterial mechanism of AgNPs is not totally understood, the antimicrobial effect of Ag + has been quite well known and it is routinely used in the pharmaceutical industry for wound healing and similar anti-infection-related applications (Parashar et al. 2011). These new AgNPs with chitosan/dextran nanoparticles showed to have biocidal effect and potential to reduce bacterial growth for practical applications. 3.5. Evaluation of the cytotoxic profile of the produced nanoparticles Nowadays orthopedic surgery is extremely important and several biomaterials are used for bone regeneration (Campoccia et al. 2010). The coating of orthopaedic implants with AgNPs is an interesting strategy to decrease the postoperative infection rates (Albers et al. 2011). However, silver induced cytotoxicity to bone cells has not been investigated in detail (Albers et al. 2011). Therefore, in this study the cytotoxic profile of the different types of nanoparticles, herein 42
Chapter III – Results and Discussion produced, was characterized using human osteoblast cells, through optical microscopy images and MTS assay. There are several studies reporting different results about citotoxicity of AgNPs in different eukaryotic cells. The toxicity of these particles is described as being dependent of their size, shape, agglomeration and concentration (Samberg et al. 2010). For instance, the toxic effects of AgNPs have been reported in mammalian cells, including alteration of the normal function of mitochondria, the increase of membrane permeability, and the generation of ROS (Martinez-Gutierrez et al. 2010). In previous studies AgNPs have been coated and others hybridized with other materials to form nanocomposites (Chen et al. 2008). Moreover, nanoparticulate colloids may need different stabilizers to avoid aggregation and prevent toxicity (Chen et al. 2008). All these features combined may probably modify the intrinsic physicochemical properties of silver and, therefore, give rise to modifications in cellular uptake, interaction with biological macromolecules and translocation within the human body (Chen et al. 2008). Additionally, there are different results for toxicity of coated AgNPs. For example, Samberg and coworkers reported that uncoated particles caused significant toxicity to human cells, while the carbon-coated particles had no adverse effects (Samberg et al. 2010). In this case, the toxicity of AgNPs was reduced due to the carbon coating that prevented the direct contact of the particle surface with cellular components, avoiding toxicity (Samberg et al. 2010). Cao and co-workers verified that the addition of chitosan to silver/chitosan composites avoid the toxicity of AgNPs (Cao et al. 2010). On the other hand, Li and coworkers reported that PVP-coated AgNPs are more toxic than the uncoated AgNPs (Li et al. 2011). In this study, human osteoblast cells were seeded at the same initial density in 96 well plates, with nanoparticles, herein produced, at different concentrations (high, low and the MIC concentration and with the supernatant) and without nanoparticles in order to access their cytotoxicity. The different nanoparticles and their concentrations used are presented in table 5. 43
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UNIVERSIDADE DA BEIRA INTERIOR Ciê
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Acknowledgments First of all, I wou
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Page 11 and 12: Table of Contents 1. Introduction .
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Page 16 and 17: List of Tables Chapter I - Introduc
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