# Silver Nanowires: Synthesis, Antibacterialativity and Biomedical Applications
## 4 Toxicity of Silver Nanowires  
In contrast to the literature dedicated to the toxicity of silver nanoparticles to eukaryotic cells, animals and humans, scarce work is available for silver nanowires. [PERSON] et al. [71] noted disagreement in literature about the mechanism of toxicity of silver nanospecies to eukaryotic cells in _in vitro_ culture; data collected by different groups disagreed on whether these nanomaterials act by the sole effect of released Ag\({}^{+}\) or by a combined effect of released ions and direct action of the nanoparticles. Therefore, they hypothesized that these differences might be due to a change in chemical properties of the elemental silver in contact with the cell culture media used for the _in vitro_ investigations. They found that AgNPs, when incubated with protein-rich cell culture medium, underwent sulfidation, with formation of Ag\({}_{2}\)S crystals on their surface (Figure 3a,b). However, they were unable to demonstrate that the process was due to the presence of the proteins and suggested that, even though Ag\({}^{+}\) have a high affinity for sulfur-rich proteins, the sulfidation reaction required the presence of other oxidizing agents in order to occur. This study highlighted the need to further study the chemistry of AgNPs _in vitro_ and _in vivo_ to better understand their antibacterial activity and eukaryotic toxicity mechanisms. Figure 3: (**a,b**) Evidence of chemical modification of the AgNW surface in contact with cell culture medium; formation of Ag\({}_{2}\)S crystals [Reproduced from [71] with permission. Copyright (2013) ACS]. SEM images of (**c**) untreated erythrocytes with biconcave discocyte shape and (**d**) erythrocytes treated with AgNWs, presenting a echinocyte shape with evident spicules [Reproduced from [72] with permission. Copyright (2014) Elsevier]. A limited number of investigations have reported _in vitro_ cell toxicity studies, such as [PERSON] et al. [42], who tested a AgNW-treated polymeric surface (polyethylene naphthalene) on mouse embryonic fibroblasts. They found significantly reduced cell bioavailability after 24 h; however, they did not investigate AgNWs on their own and did not study this further, presenting little or no insight into the reason for the observed toxicity. Human dermal fibroblasts grown on another AgNW-loaded polymeric surface (polydimethylsiloxane) showed a concentration-dependent toxicity; however, it was possible to identify a AgNW concentration that had good compatibility and high antibacterial efficacy [41]. Additionally, in this case, no further study was conducted to elucidate the mechanism of toxicity. [PERSON] et al. studied the toxicity of AgNWs on erythrocyte rheology and compared it to the effects of AgNPs [72]. They found that the hemolytic effect observed was not due to the release of Ag\({}^{+}\) ions, but was dependent on size and surface area of the nanosheets, with AgNWs showing the least toxicity overall. Interestingly AgNWs caused the most evident deformation of red blood cells from biconcave discocytes to echinocytes associated with decreased cell deformability (Figure 2c,d); this would require further studies to better understand what process is involved in this morphological modification. [PERSON] et al. [7] tested AgNPsNWs (\(>\)10 um in length) with fibroblasts and adenocarcinoma cells and were able to visualize internalized wires, but this was not associated with evident decrease in cell viability. They further observed that AgNPs had a different effect on the cell cycle of normal and cancer cells, further studies could investigate if these differences have potential to be exploited in specific tumor targeting for diagnostic and therapeutic purposes. _In vivo_ studies are even more limited that _in vitro_ ones; an _in vivo_ toxicity study carried out by [PERSON] et al. evaluated the effect of AgNPs length on rats after intrated instillation of a bolus dose [73].