Antimicrobial Nanotubes Between Promising Outcomes, Un-anticipated Toxicities, Strategies to Limit Them and Regulatory Issues: A Review

Nanotubes (NTs) are nanosized tube-like structured materials made from various substances such as carbon, boron, or silicon. Carbon nanomaterials (CNMs), including carbon nanotubes (CNTs), graphene/graphene oxide (G/GO), and fullerenes have good interatomic interactions and possess special characteristics, exploitable in several applications, because of the presence of sp2 and sp3 bonds. Among NTs, CNTs are the most studied compounds, due to their nonpareil electrical, mechanical, optical and biomedical properties. Moreover, particularly single-walled carbon nanotubes (SWNTs) have demonstrated high ability as drug delivery systems and in transporting a wide range of chemicals across membranes and into living cells. Therefore, SWNTs more than other NT-structures, have piqued interest in medicinal applications, such as target delivery, improved imaging, tissue regeneration, medication and gene delivery, providing nanosized devices with higher efficacy and fewer side effects. SWNTs and multi walled CNTs (MWCNTs) have recently gained a great deal of attention for their antibacterial effects. Unfortunately, numerous recent studies have revealed unanticipated toxicities caused by CNTs. However, on these findings, contradictory opinions exist. Moreover, the problem of controlling CNTs-based products has become particularly evident, especially in relation to their high-scale production and the nanosized forms of the carbon constituting them. Important directive rules have been approved over the years, but further research and regulatory measures should be introduced for a safer production and utilization of CNTs. Upon this background, after an overview on CNMs and CNTs, the antimicrobial properties of SWNTs, as well as the most recent in vitro and in vivo studies on their possible toxicity with strategies to limit it have been provided and discussed in this review. Finally, a debate on the regulatory issues has been also included.