From the beginning of the 21st century, there has been an increased interest in the development of various nanostructured technical materials, medical and pharmacological preparations, and substances with unique physicochemical and biomedical properties. In this regard, the attention of many researchers in the world was focused on the study of systemic, organ, cellular and subcellular effects of nanomaterials on living systems, on determining their safety for human health, both when used in medicine and at home, as well as in factory production conditions. Of important concern is the possible negative impact of nanoparticles (NPs) from insoluble materials, such as metals, on the health of workers in areas where workers come into direct contact with NPs. As far back as 15-20 years ago, there was no data at all about what possible occupational diseases might lie in wait for such workers, by what methods and means these diseases could be detected, and what additional actions were needed to reduce the risks of developing occupational diseases and disability of workers at such enterprises. There were no official norms for MPS and MPCs for NPs and nanostructured materials. There were not even any scientifically substantiated (not to mention standardized) specialized methods for studying the biological hazard of NPs. Accordingly, the organization of scientific research on the study of the biosafety of NPs, on the development of methods for assessing the toxicity of nanomaterials, was very relevant and promising at the time of the creation of our Laboratory. 

     Our Laboratory of medical and physical research from the moment of its creation in 2009 has started this study. A scientific review on the problem was prepared, objectives, ways and possible methods for their solutions were formulated (see our publications). It was decided to focus the main efforts of the laboratory on the study of the possible negative impact of metal NPs on the brain and behavior of humans and animals, also due to the fact that the topic of the brain and cognitive functions of the brain is closely related to the topic of intelligent robotics. Immediately in 2009-2010, the first pilot experimental studies were initiated and carried out to study the negative effect of silver NPs (a colloidal solution of pure, uncoated, Ag NPs) on small and young laboratory animals (white mice) at daily "per os" introduction of NPs with potable water. Contrary to a number of known literary data, we did not reveal any serious toxic action of silver NPs on white mice within a month of daily administration of NPs to mice in concentrations up to 100 mg/l. Two generations of posterity from the mice with NPs consumption without any visible defects of their birth and development are traced. It was not revealed also any both antimicrobial and bacteriostatic actions of a colloidal solution of silver NPs on cultures of golden staphylococcus (S.aureus 209 P), of intestinal stick (E.coli 26941) and other microorganisms. This research was spent together with the laboratory of microbiology at MONIKI, and it was shown that due to a low solubility of silver in water there are no chemical mechanisms of antibacterial action of silver NPs. Thus, antibacterial properties of pure silver and silver NPs is the myth. At the same time, for adult mice of comparable age with the average age of the industry workers (46-48 years), a certain toxic action of NPs of silver was recorded. It means that for the professional pathology medicine the study needs to be conducted on animals of a middle and advanced age for whom protective forces of their organism are already reduced. 

     In 2012-2020, studies on NPs safety continued with the use of NPs of titanium dioxide, cerium, Au, etc. We have observed the strong cardiotoxicity of gold NPs. For silver NPs together with the National Research Center "Kurchatov Institute" we found their penetration into the brain of laboratory animals and, apparently, for the first time in the world we have measured quantitative parameters of their penetration into the brain and accumulation there (see our paper here (PDF, 270K)). Therefore, all further investigations were focused on the study of cognitive dysfunctions in animals with chronic consumption of NPs and with controlled penetration of NPs into the brain through the blood-brain barrier. These cognitive experiments were conducted in the laboratory using the water Morris maze and the author's methods of animal's selection and training (see our paper on the method here (PDF, 270K)). The research was supported by RFBR grants No. 15-32-20429_mol_a_ved and No. 19-015-00145a. However, all our results indicated the absence of serious brain dysfunctions in laboratory animals and their offspring with chronic consumption of NPs, rather than a violation of cognitive functions. Violations were found, but they were not as pronounced as originally expected.

     In general, over 10 years of research, we made the following conclusions for ourselves (see our final article here (PDF, 402K)):
     - The more toxic the NP's material itself, the more toxic the NPs from it. Inert metals such as gold or silver are the least toxic.
     - Cognitive disorders in animals can only be detected in a group of "capable" individuals. It requires methods for selecting animals into groups according to their level of the "intelligence".
     - In the amounts of oral consumption of NPs that can be realistically imagined in everyday life and (or) at work, casual consumption or even one-time intentional consumption, the effect of NPs on the brain and cognitive abilities of a healthy adult is minimal, if not absent at all.
     - The effect of NPs on newly born offspring and on elderly animals is more pronounced.
     - What affects the body and cognitive abilities of animals more strongly - the NPs themselves or the material of the NP's protective coating - remains not completely clear yet.

     In spite of our results still indicated the absence of serious brain dysfunctions in animals with chronic consumption of NPs, the study also gave the unexpected fundamental new results:
     1) It is possible that the relative mass of the animals' brain relative to the body weight is more higher when the more higher animal's cognitive abilities are shown in the Morris test. This can serve as an additional objective criterion for the correct selection of animals in groups according to their level of cognitive abilities based on the performance of the cognitive Morris test (see the article with preliminary results here (PDF, 434K)).
     2) The memory of the passage of the water maze in animals is preserved for a long time, probably for the whole life.
     3) NPs with a diameter of less than 50 nm, even when consumed orally, easily enter the blood, are carried throughout the body, can overcome the blood-brain barrier and accumulate in the neuronal tissues of the brain. At the same time, their removal from the brain back is difficult.
     4) Silver nanoparticles accumulated in the body of females and/or males may possibly contribute to the birth of identical twins (see the article with preliminary results here (PDF, 454K)). NPs less than 50 nm in diameter apparently easily overcome the placental barrier and enter the offspring. In the offspring, silver NPs are also found in the neuronal tissues of the brain, although their path of getting into the offspring with mother's milk is also possible.

    Nevertheless, over 10 years of research, in all cases, no peculiarities of the influence of metal NPs on the brain and behavior of animals in comparison with other toxic agents, especially with special potent substances (opiates, etc.), were noticed. Apparently, it also makes no sense for healthy individuals to expect it from other NPs. Thus, from a scientific point of view, the problem loses its intrigue. We have not studied the effect of NPs on animals with various diseases. This problem is of even less interest to us, because it is more medical than physical. Therefore, we close the direction of studying the toxicity of NPs in our Laboratory. Our latest large review (in Russian, sorry) in 3 parts as of statement at the end of 2020 can be found here (PDF, 689K), here (PDF, 668K) and here (PDF, 700K). It details the state of research in the world, our own results, materials and methods, and provides guidance on unexplored issues for the future for those who wish to continue the research. For example, the distribution of accumulating NPs in different parts of the brain has not yet been studied. It is possible that some regularities can be revealed here, for example, the obvious connection between the accumulation of NPs in different parts of the brain versus "intellectual" abilities of animals. Good luck to those who follow us and beyond us!