Annotation of the results obtained in 2022
During the reporting period (2022), the following work was performed: A new type of inhibitor- and polymer-containing coatings were formed on the surface of a biresorbable magnesium alloy in order to reduce the intensity of its corrosion degradation for subsequent use in the field of implant surgery. A comparative study of the anticorrosion properties of various composite bioactive coatings on the surface of a magnesium alloy (formed using the plasma electrolytic oxidation method and including cerium nitrate and/or a polymer-containing component, polycaprolactone), was carried out using a combination of physicochemical methods of analysis. The rate of corrosion degradation of the formed coatings and the assessment of the intensity of electrochemical processes occurring on the surface under in vitro conditions were determined. The effect of the composition, morphology, and structure of composite coatings on the level of their protective properties, determined by means of a complex of electrochemical analysis methods in combination with optical and electron microscopy was studied. The mechanism of the process of self-healing of the formed composite coatings on the surface of a bioresorbable magnesium alloy in biological media in vitro was established. The systematization and evaluation of the results obtained during 3 years of the project implementation was carried out, according to the methods of formation and properties of various types of composite inhibitor-containing coatings formed on a magnesium alloy. The optimal method for obtaining an inhibitor-containing bioactive composite coating on magnesium alloys, which is most suitable for implant surgery, was determined. The following scientific results have been obtained: During the implementation of the plan of the third year of this project, studies were carried out aimed at developing a method for modifying the surface of bioresorbable magnesium alloys of the Mg-Mn-Ce (MA8) and Mg-Ca (Mg-0.8Ca) system by forming hybrid inhibitor- and polymer-containing coatings for reducing the intensity and increasing the uniformity of their corrosion degradation, as well as the possibility of subsequent practical use in the field of implant surgery. As a result of the work, the following results were obtained: - electrolyte composition and oxidation mode of magnesium alloys of Mg-Mn-Ce and Mg-Ca systems were selected and optimized. Using the PEO method, a porous ceramic-like coating containing hydroxyapatite was obtained on the surface of the material; - using cerium nitrate as an example, a method for impregnating a PEO-layer with a corrosion inhibitor was selected and optimized. A significant increase in the level of corrosion resistance of the materials under study was established; - the method was developed to increase the level of corrosion resistance of the material and prevent premature release of the inhibitor from the pores of the PEO-layer, not associated with the corrosion process, by modifying the obtained composite coatings with a bioresorbable polymer material - polycaprolactone (PCL). As a result of treatment with a polymer component, hybrid inhibitor-containing layers were obtained, the pores of which were sealed with a polymer (GP-NC005, GP-NC01); - using SEM/EDS analysis, XRD and XPS methods the composition of composite coatings was established and the presence of a corrosion inhibitor was confirmed. The presence of the inhibitor in the pores of the PEO-layer, as well as its distribution on the surface and over the thickness of the coating, was established by confocal Raman microspectroscopy; - electrochemical tests were carried out in physiological saline solution (0.9% NaCl solution), isotonic human blood plasma. Based on the analysis of the results obtained, it was found that samples with a hybrid coating (GP-NC01) are characterized by the best resistance to corrosion processes. Using the EIS and PDP methods, it was found that samples with this coating are characterized by the lowest value of the corrosion current density (after 1 h exposure to 0.9% NaCl Ic = 4.1∙10–7 A/cm2, after 24 h exposure Ic = 1, 7∙10–7 A/cm2) and the highest value of polarization resistance (after 1 h exposure Rp = 6.8∙10^4 Ohm‧cm2, after 24 hours exposure Rp = 2.3∙10^5 Ohm‧cm2), as well as the highest value impedance module; - the electrochemical behavior of samples in the minimum essential medium (MEM) at the microlevel was established using local scanning methods SVET / SIET. The intensity of electrochemical processes occurring on the surface was determined under in vitro conditions. A new technique for fixing a local change in the current density (I) and the values of pH (by static point monitoring in a previously formed surface defect of the protective layer) was developed and modified. As a result of the analysis of the obtained dependences of I and pH on the exposure time of samples for inhibitor-containing coating systems, the manifestation of self-healing properties was established; - the rate of corrosion degradation of samples with the studied surface layers was established by gravimetry and volumemetry methods. After 7 days of keeping the samples in a 0.9% sodium chloride solution, it was found that the samples GP-NC01 (4.6∙10-5 mm/year) are characterized by the lowest corrosion rate. When analyzing optical images obtained after long-term exposure of samples in an electrolyte solution, for GP-NC01, the absence of visible corrosion damage was revealed; - the level of electrochemical resistance of samples of magnesium alloy of the Mg-Ca system was determined. It was shown that inhibitor-containing surface layers provide a significant increase in the level of anticorrosion protection for samples of all the alloys under study; - the prospects of using hybrid coatings containing a bioresorbable polymer material and a biocompatible corrosion inhibitor were established to provide controlled resorption and increase the bioactivity of magnesium-based implant materials for their subsequent use in medical practice. Based on the results of the final comparative evaluation of the effectiveness of the studied corrosion inhibitors (8-hydroxyquinoline, stearic acid, cerium nitrate), which are part of the PEO-layer, the following was obtained: - based on a comprehensive analysis of the results of electrochemical tests, it was found that the best corrosion resistance is exhibited by coatings obtained by two-stage sequential treatment with stearic acid (GP-2SP) and cerium nitrate (GP-NC01) with subsequent processing of the obtained composite layers with a polymer material. It was found that materials with these types of coatings are characterized by low electrochemical activity, the best resistance to aggressive environments, the stability of providing active anticorrosion protection, and also most effectively exhibit self-healing properties; - the mechanism of corrosion degradation in a chloride-containing medium (for example, a physiological solution of 0.9% NaCl) of magnesium alloy samples (for example: Mg-Mn-Ce, Mg-Ca systems) with coatings impregnated with the studied corrosion inhibitors was established. The mechanism of self-healing of inhibitor-containing coatings formed and studied during 3 years of work on a grant from the Russian Science Foundation was described in detail. During the reporting period of the project (2022), the results of this research were published in scientific journals, such as the Journal of Magnesium and Alloys (Q1, two articles), Non-Ferrous Metals (Q2), St. Petersburg Polytechnic University J. Physics and Mathematics (two articles), indexed in the WoS, Scopus and RSCI databases, as well as the Monograph (TECHNOSPHERA JSC, Moscow) (RSCI) for familiarization of the Russian and international public. The results of research obtained in the course of a grant from the Russian Science Foundation were covered in seven reports at six international and all-Russian conferences and symposiums.

 

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Annotation of the results obtained in 2020
During the accounting period (2020), the following works were performed: By the end of the first year of the project implementation, studies aimed at developing a method for modifying the surface of a bioresorbable magnesium alloy in order to reduce the intensity of its corrosion degradation, were carried out. The optimization of modes and proportioning of electrolytic systems for plasma electrolytic oxidation (PEO) was carried out in order to form anticorrosive bioactive coatings on magnesium alloys with a surface morphology suitable for impregnating a corrosion inhibitor. The selection of inhibiting substances harmless to humans, suitable for the protection of promising in biomedicine magnesium alloys (for example, the Mg-Mn-Ce system), was carried out. A method for impregnating of inhibitors (for example, 8-hydroxyquinoline) into the porous structure of a PEO-coating was optimized. Methods for enhancing the anticorrosive properties of coatings and retaining inhibitors in the pores of the coating by sealing the pores of the surface layer with composite polymer materials (using a biodegradable polymer polycaprolactone), providing the necessary period of corrosion protection, were developed. Participation in the work of three international and all-Russian conferences and symposia. The research results obtained during the implementation of the Russian Science Foundation grant were published in 5 articles, one of which belongs to the first quartile (Q1) edition. The following scientific results were obtained: During the implementation of the project, the carried out studies were aimed at developing a method for modifying the surface of the MA8 bioresorbable alloy of the Mg – Mn – Ce system in order to reduce its corrosion degradation rate. The following conclusions were made: 1. Based on the results of theoretical and experimental studies, composition of the electrolyte and mode parameters for plasma electrolytic oxidation of the MA8 magnesium alloy were selected. Optimization of the composition of electrolytic systems and PEO modes has been carried out. The bioactive hydroxyapatite-containing PEO-coating was formed on the samples` surface. It was established that the morphology of the obtained PEO layer, expressed by the presence of pores and microdefects, is suitable for further impregnation of the coating with a corrosion inhibitor. 2. Using the 8-hydroxyquinoline (8-HQ) as an example, a method of porous PEO-coating impregnation with inhibitor was selected in order to increase the corrosion resistance of the processed material. Based on the results of evaluating the electrochemical properties of composite inhibitor-containing coatings, it was established that impregnation of PEO-coating with 8-hydroxyquinoline decreases the corrosion current density Ic of the samples, and also increases the polarization resistance Rp by more than 3 times, in comparison with PEO-coating without 8-HQ. The effect of self-healing of the inhibitor-containing coating was established by the method of potentiodynamic polarization after a long exposure (for 22 h) of the samples in a 3 % NaCl solution. This is confirmed by a fourfold decrease in the Ic value, in comparison with the data obtained for base PEO-coating before immersion tests. 3. A method was developed for enhancing the anticorrosive properties of coatings and retaining the inhibitor in the pores of the PEO-layer (reducing the spontaneous release of the inhibitor unrelated to the corrosion process) by modifying the formed coating with a biodegradable polymer material – polycaprolactone (PCL). Methods of coating formation using a system of PCL solutions in dichloromethane and acetone are presented. The optimal concentration of PCL in solutions (6 wt. % ) was determined, and modes for the formation of hybrid coatings obtained by combined treatment of PEO-layers with polycaprolactone and 8-hydroxyquinoline were developed. Based on the results of the study, it was revealed that among all the studied layers, hybrid coatings obtained by processing in a dichloromethane solution containing 6 wt.% of polycaprolactone and 15 g/l of 8-hydroxyquinoline are characterized with the best corrosion resistance. The effectiveness of the inhibitor in the composition of hybrid coatings has been established, reaching 80.1 % and slightly changing during long-term exposure of the material in a chloride-containing medium to 83.9 %. 4. The prospects of using hybrid coatings containing a biodegradable polymer material and a self-healing corrosion inhibitor harmless to humans for controlled bioresorption and increasing the bioactivity of magnesium-based implantation material for its subsequent use in medical practice have been established. During the reporting period of the project (2020), the research results were published in scientific journals such as Applied Surface Science (Q1), Materials (Q2), Basic & Clinical Pharmacology & Toxicology (Q2), Solid State Phenomena (Q3), indexed in the databases “Web of science”, Scopus and RSCI, for the Russian and international public. The results of the research obtained during the implementation of the grant of the Russian Science Foundation were highlighted in the work of three international and all-Russian conferences and symposiums. During the period from July 30 to August 03, 2020, the team of project performers took part in the V Asian school-conference on physics and technology of nanostructured materials ASCO-NANOMAT 2020, Vladivostok, Russia with two oral presentations. The results obtained in the framework of the research conducted under the project of the RSF No. 20-13-00130 "Inhibitor-containing bioactive composite coatings on magnesium alloys for implant surgery" were presented. The project performers also participated in the international Symposium on Materials Science and Engineering (Seoul, South Korea) from August 21 to August 23, 2020. The oral report "Composite coatings formed on PEO pretreated MA8 magnesium alloy in aqueous suspension of PTFE" presented the results obtained in the framework of the research conducted under the RSF project No. 20-13-00130. Participation in the International Conference on Biomedicine, Bioinformation and Intelligent Computing, BBIC2020, China, Hangzhou, 07/19/2020 - 07/29/2020. The report presented the results obtained in the project of the Russian Science Foundation No. 20-13-00130.

 

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Annotation of the results obtained in 2021
During the accounting period (2021), the following works were performed: By the end of the second year of the project implementation, studies were performed with the aim of developing the method of formation of inhibitor- and polymer-containing coatings of a new type on the surface of a bioresorbable magnesium alloy in order to reduce the intensity of its corrosive degradation for subsequent use in the field of implant surgery. Using local scanning techniques (scanning vibrating electrode technique- SVET, scanning ion selective electrode technique - SIET) and traditional electrochemical methods (EIS, PDP), the mechanism of the corrosion process of magnesium alloys (for example, the Mg-Mn-Ce system) with composite coatings formed using the plasma electrolytic oxidation (PEO) and treatment with inhibitor (for example, stearic acid) and / or polymer-containing components (for example, polycaprolactone - a bidegradable polymer compatible with the human body) was studied. The corrosion resistance of PEO-coatings formed on the surface of the Mg-Ca alloy was determined. Electrochemical tests were carried out in vitro in physiological solution in terms of ionic composition closest to human blood plasma (using the cell culture medium - Minimal Essential Medium, MEM). The effect of protective coatings and corrosion products formed on the surface of a biodegradable magnesium alloy on the rate of bioresorption of the implantation material was established. Corrections were made and the optimization of method of composite layer formation was carried out on the basis of the data analysis obtained on the basis of local methods for studying heterogeneous corrosion, as well as a comprehensive analysis of the corrosion behavior of a bioresorbable magnesium alloy. Participation (with 7 reports) in the work of five international and all-Russian conferences and symposia. The research results obtained during the implementation of the second year of the Russian Science Foundation project were published in 4 articles, three of which belong to the first quartile (Q1) editions. The following scientific results were obtained: During the implementation of the plan of the second year of this project, studies were performed aimed at developing the method of modifying the surface of bioresorbable magnesium alloys of the Mg-Mn-Ce, Mg-Ca systems by forming inhibitor- and polymer-containing coatings of a new type in order to reduce the intensity, increase the uniformity of its corrosion degradation and the possibility of its prolonged subsequent practical use in the field of implant surgery. The following conclusions were obtained: 1) Based on the available literature data on the research topic, the electrolyte composition and the oxidation mode of the magnesium alloy of the Mg-Mn-Ce system were selected and optimized. Using the PEO method, a bioactive calcium-phosphate coating with a convoluted surface was formed on the surface of the substrate material. It was found that the resulting morphology of the protective layer is a suitable matrix for further impregnation with a biocompatible magnesium corrosion inhibitor and a polymer material. 2) Using stearic acid (SA) as an example, the method of impregnating the pores of the PEO-layer with an inhibitor was selected and optimized in order to ensure a decrease in the electrochemical activity of the processed material. The correct type of solvent has been identified (1: 1 mixture of ethyl alcohol and deionized water). Based on the results of evaluating the electrochemical properties of composite inhibitor-containing coatings, it was found that impregnation of the PEO-coating with stearic acid reduces the corrosion current density of samples Ic by 18 folds, in comparison with a PEO-coating without SA. 3) The method was developed to improve the anticorrosive properties and reduce the probabylity of spontaneous release of the inhibitor from the pores of the coating (not associated with the corrosion process) by treating the formed inhibitor-containing composite layer with a biodegradable polymer - polycaprolactone (PCL). Methods for creating hybrid coatings by sequential impregnation of the base PEO-layer with stearic acid and PCL (GP-2SP), as well as one-stage application of PCL and SA from a solution based on dichloromethane (GP-1SP) are presented. 4) The composition of the formed protective layers was determined by the X-Ray diffraction method and X-Ray photoelectron spectroscopy. The presence of stearic acid (as well as calcium stearate) and polycaprolactone in the composition of the protective layers was confirmed. Using confocal Raman microspectroscopy in the scanning mode, the presence and distribution of a corrosion inhibitor and polymer material on the surface of the composite coating was established. 5) Electrochemical tests were carried out in vitro in physiological solution with the ionic composition similar to human blood plasma (for example, 0.9 % sodium chloride solution and cell culture medium - Minimal Essential Medium). Based on the results of the experiments, it was found that among the samples under study, hybrid coatings obtained by two-stage deposition of an inhibitor and a polymer (GP-2SP) have the best protective properties. Using traditional electrochemical methods (EIS, PDP), it was found that this type of coatings is characterized by the lowest value of the corrosion current density (before exposure to 0.9 % NaCl Ic = 1.70ˑ10-8 A/cm2, after 24 h exposure Ic = 1, 25ˑ10–7 A/cm2) and the highest value of the polarization resistance (before exposure Rp = 2.60ˑ106 Ohm‧cm2, after exposure Rp = 1.59ˑ105 Ohm‧cm2), as well as the highest value of the impedance modulus (before exposure |Z|f = 0.1 Hz = 104620 Ohm‧cm2, after exposure |Z|f = 0.1 Hz = 23860 Ohm‧cm2). 6) Magnesium alloys with a base PEO-layer and with polymer-containing coating (KP-P) were studied by local scanning electrochemical methods (scanning vibrating electrode technique- SVET, scanning ion-selective electrode technique - SIET) in the surface mapping mode. The level of anticorrosive protection of the samples, achieved by treating the porous part of the coating with a polycaprolactone solution, was determined. The advantage of the protective properties of the composite coating was shown (no intense electrochemical processes were established on the surface during 48 h of exposure to MEM environment), in comparison with the base PEO-layer (activation of corrosion damage was observed after 1 h of the experiment). 7) The mechanism of local corrosion behavior of samples with various types of coatings using SVET / SIET methods was established at the microscale level. The new methodic was developed and proposed for recording local values of current density and pH in the area of the artificially formed defect, at a point scan mode directly above the surface of an uncoated sample for accurate and detailed determination of the inhibitor's effect on the process of suppressing the corrosion. For coating systems containing a corrosion inhibitor, trends in changes in local parameters were established that related to the function of active corrosion protection. The contribution of stearic acid to the process of self-healing of the formed coating was established. 8) The influence of protective coatings and corrosion products formed on the surface of a biodegradable magnesium alloy on the rate of bioresorption of the implantation material was established. Using SEM / EDS analysis of cross-sections and gravimetric measurements of samples with various types of coatings obtained after 7 days of exposure to MEM, a lower intensity of corrosion degradation was found, as well as a minimum degradation rate of the alloy with hybrid coatings containing a corrosion inhibitor and a polymer material. A 5 times decrease in the rate of corrosion degradation for a sample with GP-2SP was established as compared to the sample with a base PEO-layer on the surface. 9) Corrosion resistance of coatings formed by the PEO method on the surface of Mg-Ca alloy was determined. It is concluded that an equal level of anti-corrosion protection is formed by a PEO-layer on the surface of alloys belonging to two different systems (Mg-Mn-Ce, Mg-Ca). 10) Based on a comprehensive analysis of electrochemical properties (including local methods) of bioresorbable magnesium alloy samples with protective coatings, the adjustments were made and the method of composite layer formation was optimized. The obtained experimental results indicate the necessity of hybrid coating formation in two stages, taking into account the higher protective properties of a sample with GP-2SP in comparison with a magnesium alloy treated with an inhibitor and a polymer in one stage - GP-1SP. The effectiveness of the inhibitor in the composition of such a coating was 99.3%. 11) It was established that hybrid coatings containing a biodegradable polymer material and a corrosion inhibitor harmless to humans are promising for controlled bioresorption and increasing the bioactivity of magnesium-based implants for its subsequent use in medical practice. During the second year of the project (2021), the research results were published in scientific journals such as Corrosion Science (Q1), Journal of Magnesium and Alloys (Q1), Journal of Molecular Liquids (Q1), MATEC Web of Conferences, indexed in databases " Web of science", Scopus and RSCI, for the Russian and international public. The research results obtained in the period of the implementation of a grant of the Russian Science Foundation were highlighted in the work of five international and all-Russian conferences and symposia. During the period from 17 to 19 May 2021, the team of project performers took part in the work of the 1st Corrosion and Materials Degradation Web Conference (CMDWC 2021). The report "Formation of hybrid bioactive coatings on magnesium alloy for biomedical applications" presented the results obtained in the project of the Russian Science Foundation No. 20-13-00130. The results of the research dealt with the formation of inhibitor-containing coatings on the surface of biodegradable alloys, which protect the magnesium-based material from corrosion, were presented. During the period from June 14 to June 16, 2021, the team of project performers took part with an invited report at the 26ᵗʰ International Conference on Port and Ocean Engineering under Arctic Conditions (POAC 2021, Moscow, Russia). The results obtained during the implementation of the project of the Russian Science Foundation No. 20-13-00130 were presented. During the period from 15 to 18 June 2021, the team of project performers took part in the work of the organizing committee and made an invited report at the 7th Congress of Federation of Asian Polymer Societies (FAPS2021, Moscow, Vladivostok, Russia). The theses of the report indicate that the work was financially supported by the grant of the Russian Science Foundation No. 20-13-00130. During the period from September 6 to 10, 2021, the team of project performers took part with three reports (oral presentation, poster presentation, as well as absentee presentation) in the international scientific and technical conference "International Conference on Modern Trends in Manufacturing Technologies and Equipment 2021 "(ICMTMTE 2021, Russia, Sevastopol). The results obtained in the framework of the project of the Russian Science Foundation No. 20-13-00130 "Inhibitor-containing bioactive composite coatings on magnesium alloys for implant surgery" were presented. The project performers also participated in the international conference "Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems" (Sol-Gel 2020, Uzbekistan, Samarkand, 11.11.2021 - 15.11.2021, poster presentation). The report presented the results obtained in the framework of the project of the Russian Science Foundation No. 20-13-00130.

 

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