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Project titleMultifunctional biodegradable coatings of new generation for controlling the resorption of magnesium-based materials: self-healing mechanism, personalized medicine

AffiliationInstitute of Chemistry, Far Eastern Branch, Russian Academy of Sciences,

Research area 03 - CHEMISTRY AND MATERIAL SCIENCES, 03-402 - Electrochemistry and corrosion of metals

KeywordsHybrid coatings, plasma electrolytic oxidation, bioactivity, corrosion mechanism, protective properties, corrosion inhibitor, scanning vibrating electrode technique, scanning ion selective electrode technique, bioresorbable magnesium alloys, heterogeneous corrosion process, functional material, magnesium, additive technologies, biodegradable implants, self-healing

Annotation
In the recent years, in the field of medicine and health care, great attention is being paid to increase the quality and average lifetime of the population, to improve the quality of medical care, and to create the favorable conditions for restoring health. Injury is one of the most frequent reasons of temporary disability and mortality of people. In addition, the damage from injuries in the world results in sufficient economic costs. For the treatment and restoration of bone tissue integrity in the case of complex fractures, the metal implants (osteofixers) in the form of plates, pins and screws necessary for fixing bone fragments in a certain position are used. Particular attention has recently been paid to the development of temporary bioresorbable implants. Such products perform their function during the rehabilitation period, and then continuously dissolve in the body. The use of such material in implant surgery removes the need for repeated surgical intervention to remove the implant after recovering the patient. In the world, many scientific groups are working to develop new bioactive and bioresorbable metal-based implants. Due to the unique mechanical characteristics of magnesium and its alloys, which are close to the parameters of bone tissue, Mg-containing products are considered as an ideal candidates for the role of temporary bioresorbable implants. Given the high corrosiveness of magnesium and its alloys in various environments, the use of such materials in the environment of the human body can be limited by premature dissolution of the temporary implant until the total rehabilitation of patient. The presence in the composition of magnesium alloys of various phases, intermetallic inclusions with different corrosion activity, leads to the appearance of galvanic couples, which increase the corrosion process. To reduce the rate of biodegradation of Mg-containing materials, it is necessary to create a protective layer on their surface. This is possible only if a correlation is established between the formation conditions of the protective layer and its electrochemical, morphological characteristics. The modified bioactive layer on the surface of the bioresorbable material must protect the temporary implant for a certain fixed period, intended for the treatment of injury due to bone tissue increasing. The service life of such a product will depend on the severity of the fracture and will be governed by the technological modes of the protective coating. Considering that one of the tasks of world science is to provide the required properties of products used in various fields (including the field of implant surgery, personalized medicine), this project aims to develop physicochemical bases and methods of multifunctional anticorrosive coatings formation on the surface of Mg-containing materials using plasma electrolytic oxidation (PEO) and subsequent treatment with corrosion inhibitors and bioinert polymeric material. The method of plasma electrolytic oxidation is one of the most promising and called-for methods of applying oxide layers with a wide range of functional properties. Application of PEO method enables one to form calcium phosphate layers (including those containing hydroxyapatite), which allows to achieve the necessary biocompatibility of the implant and to increase the osteogenesis. However, these coatings do not adequately protect the Mg alloy agains corrosion. One of the main causes of corrosiveness in this case is the presence of macro- and mesopores in the protective coating, through which corrosive components diffuse to the substrate. However, this disadvantage of the PEO layer can be turned into an advantage. The presence of a porous outer layer allows it to be used as a container for materials or substances that have an inhibitory effect on the corrosion process of a magnesium alloy. Moreover, to create a reliable protective layer that preserves the bioactive properties of the Mg-containing material, it is necessary to control the process of pore narrowing and their sealing in the surface part of the PEO-coating. One of the ways to solve this problem is to modify the PEO-layer, which ensures the formation of a composite corrosion-resistant bioactive coating, which limits the access of the corrosive environment to the material, on the one hand, and accelerates the growth of bone tissue, on the other. The presence of a bioactive component such as hydroxyapatite in the PEO layer will contribute to the growth of bone tissue and improve the biocompatibility of the implantable material in the human body. The presence of a corrosion inhibitor in the composition of the protective layer will give active protection to the material in case of damage to the coating, and will also provide the surface of the temporary implant with antibacterial properties. The urgency of this project is related to the necessity to develop methods for forming hybrid anticorrosion bioactive coatings on the surface of magnesium and its alloys, which allow to maintain the mechanical strength and integrity of the implant during the time required for bone healing and restoration of its functions, and contributing to osteogenesis processes during the rehabilitation period. At present, magnesium alloys doped with elements non-toxic to the body, for example, calcium, manganese are of particular interest. Due to the presence of these elements in the human body (calcium is the main element of bone tissue; manganese is essential for maintaining a healthy bone structure, affects the function of the immune system, blood clotting, regulation of cellular energy and the synthesis of neurotransmitters; magnesium is an integral part of absolutely all tissues and cells of the human body), magnesium alloys, doped with elements non-toxic to the body, are highly biocompatible and promising for use in implant surgery as a bioresorbable material. In recent years, the development of personalized medicine has been observed. The development of methods for the rapid manufacture of the implant is underway. These implants are individually suitable for a particular patient, given its anatomical and physiological features, as well as the level of bone damage due to injury. Progress in the field of additive technologies directly contributes to the development of opportunities for creating individual implants of various geometries. In this paper, the objects of study will be biocompatible magnesium alloys and pure magnesium, obtained using additive technology – direct laser deposition. The development of new materials representing hybrid coatings consisting of an anticorrosion bioactive layer obtained by the PEO method, impregnated with inhibitor, as well as bioinert polymer will significantly expand the field of practical application of materials based on magnesium and make them real and promising candidates for application in implant surgery. Thus, during the project implementation, multifunctional composite polymer-containing protective coatings on the surface of bioresorbable magnesium alloys and pure magnesium, obtained using additive technologies, will be developed. It should be noted that the directed formation of bioactive anticorrosion coatings on the surface of bioresorbable magnesium-containing material for implant surgery is possible only with careful study of their properties using new local (Scanning Vibrating Electrode Technique (SVET), Scanning Ion-Selective Electrode Technique (SIET)) and traditional electrochemical methods: 1) the nature and features of electrochemical processes on the surface of magnesium based materials; 2) the mechanism of bioresorption of materials in vitro; 3) the effect of corrosion products formed on the surface on the rate of bioresorption of the implant material; 4) the influence of the formed surface layers on the intensity and mechanism of the corrosion process. Thus, the proposed approaches will allow to develop methods for direct formation of hybrid bioactive coatings with antibacterial and self-healing properties on Mg-containing materials, providing the necessary bioresorption rate of the implant material in the body medium, as well as accelerating osteogenesis. The proposed approaches in the field of formation and study of the electrochemical properties of oxide structures correspond to the world level. At the same time, application of these methods to the study of heterostructures formed on bioresorbable magnesium-containing materials by plasma electrolytic oxidation method is innovative. The scientific novelty of the proposed approaches is to establish and scientifically substantiate the correlation between the formation conditions, composition and electrochemical properties of surface layers on magnesium alloys and pure magnesium, obtained using additive technologies that are promising for use in implant surgery. The heterogeneity of the hybrid layers of magnesium-containing materials (including those treated using PEO method), as well as the staging and bioresorption mechanism in vitro will be studied for the first time using localized scanning electrochemical methods (SVET, SIET) combined with traditional methods for assessing the corrosion rate. Solving the tasks of this project of developing new strategies for actively controlling the kinetics of bioresorption of magnesium-containing implants will increase the efficiency of using products in the field of biomedicine, which in turn will contribute to the development of the domestic market of Russian Federations products.

Expected results
During this project implementation, methods will be developed to reduce the corrosion rate (bioresorption) of magnesium-containing materials that are promising for implant surgery. The fundamentals of the regulation of material resorption will be revealed by studying the nature of the surface state evolution due to the occurrence of electrochemical reactions and adsorption-desorption processes. By constant current and alternating current methods (electrochemical impedance spectroscopy, potential-dynamic polarization), unique data will be obtained on the level of corrosion currents both under open circuit potential condition and during polarization in solutions simulating the environment of the human body. Using complementary modern local scanning probe electrochemical methods for surface investigation: Scanning Vibrating Electrode Technique (SVET) and Scanning Ion-Selective Electrode Technique (SIET) the electrochemical (corrosive) behavior of the original material will be determined, as well as its heterogeneity including coatings formed by plasma electrolytic oxidation (PEO), and hybrid layers on the surface of Ca-and-Mn-containing magnesium alloys, and pure magnesium, obtained by three-dimensional printing. Analysis of corrosion resistance will allow to choose the formation conditions, composition, and structure of protective surface layers, to detect and study areas of heterogeneity, and also to establish the features of the morphology of the surface PEO-layer and hybrid polymer-containing coating, impregnated with inhibitor. The scientific basis for the formation of protective coatings on the surface of bioresorbable magnesium-based materials using the PEO method will be developed. A comparative assessment will be made of the specific features of the corrosion process at the micro level on samples of alloys with different types of surface treatment. Determination of the physicochemical characteristics of heterolayers on the surface of magnesium alloys will help to correct and optimize electrolyte compositions and PEO modes. The features of the corrosion process of magnesium-based materials with a hybrid PEO-coating in a physiological solution close in composition to the environment of the human body will be established and studied. Such an integrated approach, based on the knowledge of the mechanism of corrosion destruction caused by the heterogeneity of the material, will provide the possibility of direct coating formation with desired properties. The obtained results will find application in the industrial implementation of the technology of surface treatment of materials for the needs of implant surgery and personalized medicine. Based on the analysis and generalization of experimental results obtained during the project, the prospects of using new generation coatings in implant surgery will be established by studying the relationship between the formation conditions, composition and electrochemical properties of heterogeneous surface structures of implant materials. The influence of biologically harmless corrosion inhibitors and polymer, which are in the composition of the surface layer, on the electrochemical properties of composite coatings on magnesium alloys will be established. Features of the bioresorption process of Mg-based materials with a hybrid coating in a physiological solution that is close in composition to the environment of the human body will be identified and studied. Principles will be established for the formation of protective polymer-containing coatings, impregnated with inhibitors, on the surface of magnesium-based materials, promising for use in implant surgery (magnesium alloys with calcium, magnesium alloys with manganese, pure magnesium, formed by additive technology). New scientific approaches will be created to improve the corrosion resistance of materials used in implant surgery. The established correlation between the conditions of formation, the heterogeneity of the composition, the electrochemical properties of multifunctional hybrid coatings will make it possible to predict and regulate the level of protective properties of the surface layers in biological corrosive environments. In the course of this project, the study of the physicochemical features of the magnesium implants corrosion, a summary of the obtained results, and preparation of materials of the results of this investigation for publication will be made. In particular, a study of the materials, which are promising for use in implant surgery will be carried out. In this work calcium-containing magnesium alloy – bioresorbable alloy Mg0.8Ca, manganese-containing alloy MA8 and pure magnesium (˃ 99 wt.%) obtained using additive technology — direct laser deposition will be studied. Methods for the formation of protective coatings based on the PEO method will be proposed. Electrochemical and anticorrosion properties of the formed surface layers will be carefully studied. The influence of the composition and nature of the heterogeneity of magnesium-containing materials on their corrosion activity will be established. The novelty of this project is based on the study of the kinetics and mechanism of corrosion processes in vitro of bioresorbable magnesium-based materials using modern local scanning methods for studying the surface: SVET and SIET. The SVET method allows one to study the local changes of current density due to the potential difference on the surface as a result of ion fluxes between the cathode and anode areas. This method has become one of the most effective and widely used to study the corrosion processes on the surface of materials. The SIET method allows to perform micropotentiometric measurements using ion-selective microelectrodes. Using the SIET method, one can obtain information on the local concentration of certain ions (H+, Cl–, Mg2+, Na+, etc.) in the solution at a quasi-constant distance between the microelectrode and the active surface of the material under study. In this project a local change in the concentration of hydrogen ions (pH of the medium), due to the occurrence of corrosion processes on the surface of magnesium and its alloys will be established. The use of these methods to determine the electrochemical activity of the surface layers on the biocompatible magnesium alloys and pure Mg, obtained by additive technology, is appropriate, given the high probability of intense localized corrosion processes on the surface of the material under study. The formation of hybrid coatings will be implemented by introducing into the porous part of the coating a corrosion inhibitor compatible with the human body (for example, sodium oleate, benzotriazole, 1,2,3-triazole), which has antibacterial properties and reduces the possibility of intense electrochemical processes on the implant surface. To regulate the rate of biodegradation of the material, the PEO layer will be modified using a bioinert material (for example, polycaprolactone, polyvinylidene fluoride, superdispersed polytetrafluoroethylene) – the component of the composite coating. As a result of PEO-coating treatment with a polymer it becomes possible to control the filling of the pores of the PEO-layer, which not only improves the anticorrosion properties of the material, but also provides biological activity and controlled bioresorption of the magnesium implant. The creation of new scientific approaches to improve the corrosion resistance of biocompatible materials used in implant surgery corresponds to the current trends in the organization of basic and applied research, and in the degree of originality and novelty of the methods and used materials is at the forefront of modern materials science. Thus, the results of the project will have both fundamental and applied significance. According to the results of the project, papers will be published in leading peer-reviewed scientific journals in this area, indexed in the Web of Science, Scopus, RISC citation systems (for example, Corrosion Science, Materials, Surface & Coatings Technology, etc.). Successful implementation of the project will provide an opportunity to develop evaluation criteria, recommendations, technological solutions and technical requirements for the implementation of new methods of multifunctional hybrid coating formation on the surface of implant materials for the adaptation of technology into the real economy area.

Annotation of the results obtained in 2021
During the report period (2021-2022), the following work was performed: Research aimed at the formation of anticorrosive bioactive hybrid coatings on the surface of bioabsorbable magnesium alloy of the Mg-Mn system and magnesium samples made by direct laser deposition to increase the corrosion resistance of the processed implant material, were carried out. Electrolytic systems for carrying out the PEO process in order to form coatings on magnesium alloys with a surface morphology suitable for corrosion inhibitor impregnation were developed. Harmless to humans inhibitory agents with antibacterial properties (sodium oleate and benzotriazole) suitable for corrosion protection of magnesium alloys promising in biomedicine were selected. A method for impregnating inhibitors into the porous structure of a PEO-coating was worked out. Methods were developed to enhance the anticorrosive properties of coatings and retain inhibitors in the pores of the coating by sealing the pores of the surface layer with nanosized polymeric materials (for example, biocompatible biodegradable polymeric material polycaprolactone), to provide the required level and duration of the period of corrosion protection. Corrections and optimization of the hybrid coating formation method based on a comprehensive analysis of the corrosion behavior of a bioabsorbable magnesium alloy were carried out. Participation (with 7 reports) in five international and all-Russian conferences and symposiums. The results of research obtained during the first year of the Russian Science Foundation project were published in 5 articles, two of which belong to publications included in the first quartile (Q1). The following scientific results were obtained: During the performing the work, according to the plan of the first year of this RSF project, studies were carried out aimed at a creation of a method for modifying the surface of bioresorbable magnesium alloy (for example, MA8 - the Mg-Mn system, as well as magnesium obtained by additive technology - AT-Mg) by forming hybrid coatings, containing organic biocompatible corrosion inhibitors and bioabsorbable polymeric material in order to reduce its degradation rate by the function of active corrosion protection of prolonged action. As a result of the study, the following was obtained: 1. the composition of electrolyte and parameters of oxidation mode of the studied materials were selected. As a result of the procedure of plasma electrolytic oxidation on the surface of MA8 and AT-Mg, a durable biocompatible ceramic-like coating with a developed surface was obtained. It was shown that surface heterogeneity (including the presence of open pores) is suitable for filling with modifying agents - biocompatible corrosion inhibitors and polymeric material. Magnesium, periclase, and forsterite were detected in the coatings by X-ray phase analysis; 2. inhibitory agents harmless to humans (in particular including antibacterial properties) were chosen, suitable for corrosion protection of magnesium alloys promising in biomedicine. Using benzotriazole (Btr, B) and sodium oleate (NaOl, ON) as an example, we selected and optimized the method for the most efficient impregnation of PEO-layer pores with corrosion inhibitors, as well as reducing the rate of its release from the heterooxide matrix by processing the obtained composite coatings with bioresorbable polymeric material - polycaprolactone. Methods for creating hybrid coatings by sequential impregnation of the base PEO-layer with NaOl/Btr at various concentrations and PCL (GP-ON 0.05-2, GP-ON 0.1-2, GP-B 0.05-2, GP- B 0.1-2), as well as one-stage application of NaOl / Btr and PCL from a solution based on dichloromethane (GP-ON 0.05-1, GP-ON 0.1-1, GP-B 0.05-1 , GP-B 0.1-1); 3. Using X-ray photoelectron spectroscopy, as well as confocal Raman microspectroscopy, the composition of the formed surface composite inhibitor-containing layers was established and the presence of sodium oleate and benzotriazole, as well as their distribution over the surface of the coatings was confirmed at the microlevel; 4. The level of corrosion protection of the MA8 magnesium alloy and AT-Mg was established by electrochemical tests using potentiodynamic polarization and electrochemical impedance spectroscopy methods. It is shown that among the oleate-containing coatings formed on the MA8 magnesium alloy, the best corrosion resistance is possessed by GP-ON 0.1-2 ones (the highest recorded value of the impedance modulus |Z|f=0.1 Hz was 1140200 Ω∙cm2, the corrosion current density and the value of polarization resistance after holding in an aggressive environment for 24 h were, respectively, IC = 2.98ˑ10-9 A‧cm-2, Rp = 2.99ˑ107 Ω∙cm2). A comparative analysis of the results of electrochemical tests of benzotriazole-containing coatings made it possible to establish the best barrier properties for GP-B 0.1-1 coatings (|Z|f=0.1Hz = 699190 Ω cm2, IC=3.02ˑ10– 8 A‧cm-2, Rp = 1.84ˑ106 Ω‧cm2). For coatings obtained on AT-Mg, the best protective properties are characterized by oleate-containing hybrid coatings AT-Mg + GP OH (|Z|f=0.1 Hz = 55630 Ω cm2, IC = 3.71 10–8 A cm–2); 5. The electrochemical behavior of the hybrid coatings GP-ON 0.1-2 and GP-B 0.1-1 was evaluated during exposure to a solution imitating human blood plasma (Hanks` solution). Oleate- and benzotriazole-containing surface layers are characterized by the stability of corrosion behavior during 7 days of exposure in the studied medium. This may indicate that the formed coatings can provide the level of corrosion protection necessary and sufficient to ensure the mechanical integrity of the surgical implant during the initial period of bone tissue formation - the bone formation phase (7-10 days from the moment of fracture); 6. volumetric and gravimetric tests were carried out, the analysis of the results of which made it possible to confirm the results obtained by traditional electrochemical methods. Samples with GP-OH 0.1-2 are characterized by the smallest volume of released hydrogen (VH2 = 85 µl/cm2) and the smallest weight loss (0.0132±0.0026 mg cm–2 day–1) among all the studied layers; 7. Using high performance liquid chromatography (HPLC), it was found that sealing the pores of the PEO-coating with a polymeric material contributes to a significant reduction in the amount of inhibitor diffusing into the corrosive solution. This confirms the effectiveness of the studied method for modifying the surface of bioresorbable magnesium alloys; 8. Based on the results of a comprehensive analysis given in the framework of this study, the relationship between the composition, structure and properties of hybrid coatings on magnesium alloys and magnesium obtained using additive technology, with the composition of electrolytes and modes of plasma electrolytic oxidation was established. The effectiveness of using hybrid anticorrosive biologically active PEO-coatings containing a bioresorbable polymeric material - polycaprolactone in the porous part and a biocompatible corrosion inhibitor (sodium oleate and benzotriazole) is shown to provide the required level and duration of the period of corrosion protection and controlled biodegradation of biomedical products from magnesium and its alloys. During the reporting period (2021-2022), the results of presented research were published in scientific journals, such as the Journal of Magnesium and Alloys (Q1), Journal of Molecular Liquids (Q1), Nonferrous Metals (Q2), indexed in databases “ WoS”, Scopus and RSCI, as well as the Bulletin of the Far East Branch of the Russian Academy of Sciences (RSCI) to familiarize the Russian and international public. The results of research obtained during the implementation of the Russian Science Foundation grant No 21-73-10148 were covered at five international and all-Russian conferences and symposiums.

Publications

1. Gnedenkov A.S., Filonina V.S., Sinebryukhov S.L., Sergienko V.I., Gnedenkov S.V. Гибридные полимерсодержащие покрытия, импрегнированные ингибитором коррозии, для защиты биорезорбируемых магниевых имплантатов Вестник Дальневосточного отделения Российской академии наук, номер 5(219), стр. 56-64 (year - 2021) https://doi.org/10.37102/0869-7698_2021_219_05_05

2. Gnedenkov A.S., Lamaka S.V.,Sinebryukhov S.L., Filonina V.S., Zheludkevich M.L., Gnedenkov S.V. Фундаментальные аспекты локальной коррозии магниевых сплавов, перспективных для имплантационной хирургии Цветные металлы, Выпуск 12, Страницы 47 - 522021 (year - 2021) https://doi.org/10.17580/tsm.2021.12.07

3. Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Egorkin V.S., Ustinov A.Yu., Sergienko V.I., Gnedenkov S.V. The detailed corrosion performance of bioresorbable Mg-0.8Ca alloy in physiological solutions Journal of Magnesium and Alloys, Available online 29 December 2021 (year - 2021) https://doi.org/10.1016/j.jma.2021.11.027

4. Mashtalyar D.V., Nadaraia K.V., Belov E.A., Imshinetskiy I.M., Kiryukhin D.P., Sinebryukhov S.L., Buznik V.M., Gnedenkov S.V. Synthesis of polymeric system based on polyethylene oxide and tetrafluoroethylene telomers to obtain films with switchable wettability Journal of Molecular Liquids, Volume 350, 15 March 2022, 118225 (year - 2021) https://doi.org/10.1016/j.molliq.2021.118225

5. Podgorbunsky A.B., Imshinetskiy I.M., Mashtalyar D.V., Gnedenkov A.S., Sinebrukhov S.L., Gnedenkov S.V. Использование синтетического наноразмерного гидроксиапатита для формирования биоактивных антикоррозионных покрытий на магнии Вестник Дальневосточного отделения Российской академии наук, номер 5(219), стр. 43-55 (year - 2021) https://doi.org/10.37102/0869-7698_2021_219_05_04

6. - В России создали модель деградации материалов имплантатов в организме ТАСС НАУКА, - (year - )

7. - ХИМИКИ СОЗДАЛИ МОДЕЛЬ ДЕГРАДАЦИИ МАТЕРИАЛОВ ИМПЛАНТАТОВ В ЖИДКОСТЯХ ОРГАНИЗМА Информация взята с портала «Научная Россия» (https://scientificrussia.ru/) Научная Россия, - (year - )

8. - Химики создали модель деградации материалов имплантатов в жидкостях организма Поиск, - (year - )

9. - Химики создали модель деградации материалов имплантатов в жидкостях организма Nano news net, - (year - )

10. - Химики создали модель деградации материалов имплантатов в жидкостях организма Об этом сообщает "Рамблер". Далее: https://news.rambler.ru/tech/48104142/?utm_content=news_media&utm_medium=read_more&utm_source=copylink Рамблер, - (year - )

11. - Химики создали модель деградации материалов имплантатов в жидкостях организма Indicator, - (year - )

12. - Исследователи выяснили, как деградирует материал имплантатов в жидкостях организма Научно-популярный журнал Машины и механизмы ММ, - (year - )

13. - Ученые продолжают работу над созданием материалов для имплантатов RU24pro, - (year - )

14. - Российские ученые создали модель деградации материалов имплантатов в организме РНФ, - (year - )

Annotation of the results obtained in 2022
During the second year of the implementation of the Russian Science Foundation project No. 21-73-10148 (2022-2023), the following research work was carried out aimed at developing the reliable anticorrosive protection for biodegradable materials based on magnesium: Methods for introducing biocompatible corrosion inhibitors (using benzotriazole as an example) into the composition of a hybrid coating were developed. The hybrid coating was formed using the plasma electrolytic oxidation method and contained the microcapsules – halloysite nanotubes as containers for the controlled release of the inhibitor from the coating at the moment of the corrosion degradation initiation of the magnesium alloy (using the Mg-Mn alloy system as an example) and magnesium (using a sample of magnesium produced by additive technology using direct laser deposition). The corrosion mechanism of the magnesium alloy with hybrid inhibitor- and/or polymer-containing components (using polycaprolactone as an example) was determined using localized scanning electrochemical methods (Scanning Vibrating Electrode Technique - SVET and Scanning Ion-selective Electrode Technique - SIET). A complex of electrochemical tests was carried out under in vitro conditions, specifically in solution mimicking the ionic composition closest to human blood plasma (in Hank's Balanced Salt Solution (HBSS) and 0.9% sodium chloride solution). The influence of protective anticorrosive hybrid coatings and corrosion products formed on the surface of the biodegradable magnesium alloy on the degradation rate of the material was determined. Adjustments and optimization of the hybrid layer formation method on the surface of the biodegradable magnesium alloy and additive magnesium were carried out based on the analysis of results obtained using electrochemical methods (SVET/SIET/EIS/PDP). Participation was taken (with 9 presentations) in seven international and all-Russian conferences and symposiums. The research results obtained during the second year of the Russian Science Foundation project implementation were published in 11 articles, two of which belong to journals in the first quartile (Q1). The following scientific results have been obtained: During the second-year implementation of the project funded by the Russian Science Foundation (RSF), the methods of anticorrosion protection for biodegradable magnesium alloys (using the MA8 alloy as an example) and direct laser deposition-manufactured magnesium samples (DLD-Mg) were developed. This was achieved through the application of multifunctional hybrid protective coatings, containing halloysite nanotubes loaded with the corrosion inhibitor benzotriazole, embedded in a biodegradable polymeric matrix of polycaprolactone. The aim was to improve the barrier properties of the investigated materials for their future practical application as implants. The following results were obtained: 1. The electrolyte composition and processing conditions for the MA8 magnesium alloy were selected using the plasma electrolytic oxidation (PEO) method. PEO treatment resulted in the formation of a porous ceramic-like coating on the material surface, containing periclase (MgO) and forsterite (Mg2SiO4). It was demonstrated that all the elements comprising the surface layer compounds are microelements of the human body, indicating the biocompatibility of the obtained coatings. The morphology of the PEO-coating surface allowed for further functionalization through directed impregnation with modifying agents. 2. Halloysite nanotubes (HNT) were chosen as nanocarriers for the corrosion inhibitor in the surface layer. The optimal impregnation method of HNT with the corrosion inhibitor benzotriazole (BTA) and their incorporation into the matrix of the biodegradable polymer material, polycaprolactone (PCL), was determined. Hybrid coatings were formed on the surface of the MA8 magnesium alloy based on the PEO-layer, containing etched (to increase the volume of internal cavities - the internal diameter varies from 10 to 17 nm) and non-etched HNT loaded with BTA within the polymeric matrix of PCL (designated as GC-HNT-T-BTA and GC-HNT-BTA, respectively). Additionally, a composite coating was prepared, consisting of polycaprolactone and HNT without an inhibitor, to assess the effectiveness of the inhibitor. 3. The elemental and chemical composition of the formed protective layers was determined, as well as the uniform distribution of nanocarriers with inhibitors throughout the thickness of the hybrid coatings. 4. The level of corrosion protection for samples made of the MA8 magnesium alloy and DLD-Mg with different types of coatings was established through electrochemical testing using potentiodynamic polarization and electrochemical impedance spectroscopy. It was revealed that the MA8 alloy samples with hybrid coatings (GC-HNT-T-BTA: |Z|f=0.1 Hz = 1020000 Ω·cm2, IC= 9.8·10–9 A·cm2, Rp = 2.4·106 Ω·cm2 after 24 hours of exposure) demonstrated the best corrosion resistance during long-term exposure in Hank's Balanced Salt Solution (HBSS). Significant improvement in the barrier properties of the magnesium sample obtained by additive technology was also observed, with a 19-fold increase in resistance (|Z|f=0.1Гц increase from 1833 Ω·cm2 for the sample with the PEO-layer to 34922 Ω·cm2 for GC-HNT-T-BTA). 5. The corrosion rate was evaluated using volumetry and gravimetry methods based on the determination of the hydrogen evolution level and the mass loss of samples after 7 days of exposure to a 0.9% sodium chloride solution. Among all tested samples, the GP-GNT-T-BTA samples exhibited the lowest volume of hydrogen evolution (VH2 = 0.13 ml/cm2), the lowest mass loss (0.07 mg·cm–2·day–1), and the lowest corrosion rate (0.14 mm/year). 6. The local electrochemical activity of samples with the investigated coatings in vitro in Hank's solution was assessed using Scanning Ion-selective Electrode (SIET) and Scanning Vibrating Electrode Techniques (SVET). It was found that during a 24-hour exposure, the GC-HNT-T-BTA sample with a pre-created surface defect showed suppression of corrosion at the microscale, confirming the manifestation of self-healing effects. The hybrid-coated samples exhibited low values of local current density and pH throughout the experiment. 7. The degradation mechanism of samples with hybrid protective layers was identified, and the involvement of corrosion inhibitor in the self-healing process was determined. Activation of the corrosion process and controlled release of the inhibitor from the nanotubes led to a reduction in the material's corrosion activity through the adsorption of BTA on the surface of magnesium and its alloys in the defect area with formation of the complex of Mg(BTA)2. This passive layer prevented the penetration of aggressive chloride ions and facilitated the formation of crystalline corrosion products, protecting the material against degradation. The effect of corrosion products formed on the surface on the biodegradation rate of magnesium and its alloy material was demonstrated. Adjustments were made and the formation process of the hybrid layer was optimized based on the analysis of results obtained using electrochemical methods. 8. The effectiveness and prospects of using hybrid coatings (GC-HNT-T-BTA and GC-HNT-BTA samples) containing halloysite-based nanotubes loaded with the biocompatible corrosion inhibitor benzotriazole and the biodegradable polymer material polycaprolactone for controlling the resorption process of magnesium and its alloy biomedical products were established. In the reporting year of the project implementation (2022-2023), the research results were published in scientific journals such as the Journal of Magnesium and Alloys (Q1), Polymers (Q1), St. Petersburg Polytechnic University Journal: Physics and Mathematics (indexed in the "WoS," Scopus, and RSCI), Genes and Cells (RSCI), Vestnik DVO RAN (RSCI), as well as Monographs (Technosphere Publishing, Moscow) (RSCI). The research findings obtained during the implementation of the Russian Science Foundation project No. 21-73-10148 were presented in nine presentations at seven international and all-Russian conferences and symposiums.

Publications

1. Filonina V.S., Gnedenkov A.S., Sinebryukhov S.L., Minaev A.N., Gnedenkov S.V. In vitro corrosion behavior of bioresorbable Mg-Ca alloy with hydroxyapatite-containing protective coating St. Petersburg Polytechnic University Journal. Physics and Mathematics, 2022, Vol. 15, No. 3.1, P. 227-231 (year - 2022) https://doi.org/10.18721/JPM.153.138

2. Gnedenkov A.S., Filonina V.S., Sinebryukhov S.L., Gnedenkov S.V. Композиционные стеаратсодержащие покрытия для контроля скорости резорбции биомедицинских изделий из магниевого сплава МА8 Вестник Дальневосточного отделения Российской академии наук, номер 6(226), стр. 46-56 (year - 2022) https://doi.org/10.37102/0869-7698_2022_226_06_4

3. Gnedenkov A.S., Kononenko Ya.I., Sinebryukhov S.L., Filonina V.S., Vyaliy I.E., Gnedenkov S.V. Влияние ингибиторов группы азолов на антикоррозионную эффективность покрытий, сформированных на алюминиевом сплаве Вестник Дальневосточного отделения Российской академии наук, номер 6(226), стр. 57-65 (year - 2022) https://doi.org/10.37102/0869-7698_2022_226_06_5

4. Gnedenkov A.S., Nomerovskii A.D., Tsvetnikov A.K., Sinebryukhov S.L., Gnedenkov S.V. Формирование композиционных полимерсодержащих покрытий на стали Ст3 с применением технологии холодного газодинамического напыления Вестник Дальневосточного отделения Российской академии наук, номер 6(226), стр. 35-45 (year - 2022) https://doi.org/10.37102/0869-7698_2022_226_06_3

5. Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Gnedenkov S.V. Особенности коррозии биорезорбируемых магниевых сплавов: in vitro исследования, формирование защитных покрытий ГЕНЫ И КЛЕТКИ, 2022. Том: 17, № 3. С. 55. (year - 2022)

6. Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Plekhova N.G., Gnedenkov S.V. Smart composite antibacterial coatings with active corrosion protection of magnesium alloys Journal of Magnesium and Alloys, Volume 10, Issue 12, December 2022, Pages 3589-3611 (year - 2022) https://doi.org/10.1016/j.jma.2022.05.002

7. Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Ustinov A.Y., Sukhoverkhov S.V., Gnedenkov S.V. New polycaprolactone-containing self-healing coating design for enhance corrosion resistance of the magnesium and its alloys Polymers, Polymers 2023, 15(1), 202 (year - 2023) https://doi.org/10.3390/polym15010202

8. Kononenko Ya.I., Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Vyaliy I.E., Gnedenkov S.V. Composite triazole-containing PEO-coatings for effective corrosion protection of AlMg3 aluminum alloy St. Petersburg Polytechnic University Journal. Physics and Mathematics, 2022, Vol. 15, No. 3.1, P. 173-178 (year - 2022) https://doi.org/10.18721/JPM.153.129

9. Nomerovskii A.D., Gnedenkov A.S., Sinebryukhov S.L., Gnedenkov S.V. Preparation of layered double hydroxide on PEO-coated MA8 magnesium alloy: electrochemical and corrosion properties St. Petersburg Polytechnic University Journal. Physics and Mathematics, 2022, Vol. 15, No. 3.1, P. 197-203 (year - 2022) https://doi.org/10.18721/JPM.153.133

10. Suchkov S.N., Nadaraia K.V., Imshinetskiy I.M., Mashtalyar D.V., Sinebrukhov S.L., Gnedenkov S. V. Evaluation of surface free energy of bioactive coatings in titanium and magnesium alloy St. Petersburg Polytechnic University Journal. Physics and Mathematics, 2022, Vol. 15, No. 3.1, P. 191-196 (year - 2022) https://doi.org/10.18721/JPM.153.132

11. Gnedenkov A.S., Sinebryukhov S.L., Filonina V.S., Sergienko V. I., Gnedenkov S.V. Физико-химические основы локальной гетерогенной коррозии магниевых и алюминиевых сплавов ТЕХНОСФЕРА, Москва, Москва, ТЕХНОСФЕРА, 2022. 424 с.: илл. 287, библиогр. 877 назв. (year - 2022) https://doi.org/10.22184/978-5-94836-661-6

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