Antimicrobial Nanotubes: From Synthesis and Promising Antimicrobial Upshots to Unanticipated Toxicities, Strategies to Limit Them, and Regulatory Issues

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, single-walled carbon nanotubes (SWNTs) have, in particular, 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 generated interest in medicinal applications, such as target delivery, improved imaging, tissue regeneration, medication, and gene delivery, which provide 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, contradictory opinions exist regarding these findings. Moreover, the problem of controlling CNT-based products has become particularly evident, especially in relation to their large-scale production and the nanosized forms of the carbon that constitute 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. Against this background, and after an overview of CNMs and CNTs, the antimicrobial properties of pristine and modified SWNTs and MWCNTs as well as the most relevant in vitro and in vivo studies on their possible toxicity, have been reported. Strategies and preventive behaviour to limit CNT risks have been provided. Finally, a debate on regulatory issues has also been included.