2D transition metal borides (MBenes) have emerged as promising post-MXene materials with potential application in various biotechnological fields. Although they possess prospective bioactive properties due to boron in their structure, the experience gained from MXenes shows that an in-depth understanding of their biological recognition and response as well as the exploration of their biological applications are highly challenging. This makes the identification of the most promising 2D MBenes for future biological research and final industrial applications rather complicated. Herein, MBenes are differentiated from MXenes and further untangled for their bioactivity-generating features. It is expected that MBenes' positive or negative biological impact on living organisms and different types of cells connect with their morphological, structural and physicochemical features in the context of relevant environments. Necessary toxicological data are also highlighted, which are key aspects to enable MBenes' safe application in biotechnology and nanomedicine. Furthermore, a perspective for the rational development and design of novel biotechnological solutions based on MBenes is provided, which will meet the legal safety requirements for nanomaterials. In this regard, this work is an unprecedented contribution toward strategies for regulatory development for MBene/MXene-type nanomaterials. It provides an inspiration for future biotechnological and nanotoxicological approaches using MBenes.

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BackgroundThe biological activity of MXenes has been studied for several years because of their potential biomedical applications; however, investigations have so far been limited to 2D titanium carbides. Although monolayered Ti2NTx MXene has been expected to have biological activity, experimental studies revealed significant difficulties due to obstacles to its synthesis, its low stability and its susceptibility to oxidation and decomposition.ResultsIn this paper, we report our theoretical calculations showing the higher likelihood of forming multilayered Ti2NTx structures during the preparation process in comparison to single-layered structures. As a result of our experimental work, we successfully synthesized multilayered Ti2NTx MXene that was suitable for biological studies by the etching of the Ti2AlN MAX phase and further delamination. The biocompatibility of Ti2NTx MXene was evaluated in vitro towards human skin malignant melanoma cells, human immortalized keratinocytes, human breast cancer cells, and normal human mammary epithelial cells. Additionally, the potential mode of action of 2D Ti2NTx was investigated using reactive oxygen tests as well as SEM observations. Our results indicated that multilayered 2D sheets of Ti2NTx showed higher toxicity towards cancerous cell lines in comparison to normal ones. The decrease in cell viabilities was dose-dependent. The generation of reactive oxygen species as well as the internalization of the 2D sheets play a decisive role in the mechanisms of toxicity.ConclusionsWe have shown that 2D Ti2NTx in the form of multilayered nanoflakes exhibits fair stability and can be used for in vitro studies. These results show promise for its future applications in biotechnology and nanomedicine.

Despite intensive research on the application of two-dimensional (2D) materials, including MXenes, in nanomedicine, the knowledge concerning the mechanisms responsible for their observed bio-effects is far from being understood. Here we present insight into the mechanism of toxicity in vitro of the 2D Ti3C2 MXene. The most important results of this work are that using simple, inexpensive, post-delamination treatments, such as ultrasonication or mild thermal oxidation it is possible to ‘tune’ the cytotoxicity of the Ti3C2T z flakes. Sonication of Ti3C2T z flakes, or sonication followed by mild oxidation in the water at 60 °C, renders them selectively toxic to cancer cells as compared to non-malignant ones. It relates to the appearance of superficial titanium (III) oxide (Ti2O3) layer corresponding to the type of post-treatment. The presence of surface-Ti2O3 results in a noticeably higher generation of oxidative stress compared to pristine 2D Ti3C2. Our findings give evidence that the sonication and thermal treatments were successful in changing the nature of the surface terminations on the Ti3C2T z surfaces. This study makes a significant contribution to the future rationalized surface-management of 2D Ti3C2 MXene as well as encourages new rationalized applications in biotechnology and nanomedicine. Bullet points: 1. First study on 2D Ti3C2 MXene superficially oxidized to titanium (III) oxide i.e. Ti2O3. 2. By sonication Ti3C2Tz MXene flakes followed by mild thermal oxidation in the water at 60 °C for 24 h, it is possible to ‘tune’ the toxicity of the flakes to cancerous cell lines. 3. Decreases in cell viabilities were dose-dependent. 4. Highest cytotoxic effect was observed for thermally oxidized samples. 5. The thermally oxidized samples were also selectively toxic towards all cancerous cell lines up to 375 mg l−1. 6. Reactive oxygen species generation was identified as a mechanism of toxicity.