Abstract
Alginate is considered an exceptional biomaterial due to its hydrophilicity, biocompatibility, biodegradability, nontoxicity and low-cost in comparison with other biopolymers. We have recently demonstrated that the incorporation of 1% graphene oxide (GO) into alginate films crosslinked with Ca2+ cations provides antibacterial activity against Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis, and no cytotoxicity for human keratinocyte HaCaT cells. However, many other reports in literature have shown controversial results about the toxicity of GO demanding further investigation. Furthermore, the synergic effect of GO with other divalent cations with intrinsic antibacterial and cytotoxic activity such as Zn2+ has not been explored yet. Thus, here, two commercially available sodium alginates were characterised and utilized in the synthesis of zinc alginate films with GO following the same chemical route reported for the calcium alginate/GO composites. The results of this study showed that zinc release, water sorption/diffusion and wettability depended significantly on the type of alginate utilized. Furthermore, Zn2+ and GO produced alginate films with increased water diffusion, wettability and opacity. However, neither the combination of GO with Zn2+ nor the use of different types of sodium alginates modified the antibacterial activity and cytotoxicity of the zinc alginates against these Gram-positive pathogens and human cells respectively.
Highlights
Alginate is considered a very promising material with exceptional hydrophilicity, biocompatibility, biodegradability, nontoxicity and low-cost in comparison with other biopolymers [1]
Since graphene oxide (GO) nanosheets seems to be more effective against Gram-positive bacteria than Gramnegative bacteria [32,33], and we have shown that the inclusion of 1% w/w of GO into calcium alginate produced high growth inhibition on two clinically relevant Gram-positive bacteria (Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis (MRSE))[5], these two pathogens were tested on zinc alginates with and without the same amount of GO
Since we have recently reported that the incorporation of 1% w/w of GO in calcium alginate produced reinforced films with no cytotoxicity for human keratinocyte HaCaT cells [5] and alginate is a biomaterial approved by the US Food and Drug Administration (FDA) for human wound healing [36], our third hypothesis stated that neither the addition of GO nor the use of different types of sodium alginates would modified the cytotoxicity of the zinc alginates
Summary
Alginate is considered a very promising material with exceptional hydrophilicity, biocompatibility, biodegradability, nontoxicity and low-cost in comparison with other biopolymers [1]. Zinc alginates have shown strong antibacterial activity against a wide range of microorganisms [6,7,8,9] due to its inhibition of conserved metabolic pathways involved in synthesis of essential biomolecules or antioxidant depletion[10], and it is well-known that Zn2+ may produce toxic effects in human cells [11] Alternative materials such as graphene oxide (GO), which from the graphene family shows the easiest processing, larger scale production and less expensive cost [12], has recently exhibited antibacterial capacity and negligible mammalian cytotoxicity in calcium alginate [5]. Since we have recently reported that the incorporation of 1% w/w of GO in calcium alginate produced reinforced films with no cytotoxicity for human keratinocyte HaCaT cells [5] and alginate is a biomaterial approved by the US Food and Drug Administration (FDA) for human wound healing [36], our third hypothesis stated that neither the addition of GO nor the use of different types of sodium alginates would modified the cytotoxicity of the zinc alginates
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