Funding: The study was conducted as part of the state task of the Ministry of Science and Higher Education (agreement №075-00337-20-02. project № 0714- 2020-0006), using the equipment of the N. N. Semenov Federal Research Center for Chemical Physics of the Russian Academy of Sciences.

Author contribution: Bormotov DS — experiment, data analysis, manuscript editing; Shamraeva MA — data analysis, preparation of illustrations, manuscript writing; Kuzin AA — experiment; Shamarina EV — experiment, ion source development; Eliferov VA — ion source development; Silkin SV — experiments, data analysis; Zhdanova EV — data analysis; Pekov SI — study concept, manuscript writing; Popov IA — search for sources of funding, project management, manuscript editing.

Compliance with ethical standards: the study was approved by the Ethics Committee of N. N. Burdenko National Medical Research Center of Neurosurgery (protocols №40 of 12 April 2016 and №131 of 17 July 2018) and conducted in accordance with the Declaration of Helsinki (2000 and subsequent revisions). All patients signed a voluntary informed consent form to participate in the study with use of biomaterials for research purposes.