Papers by Maria Nikolova, Мария Николова
Applied Sciences
The surface cold working (SCW) of austenitic stainless steel (SS) causes martensitic transformati... more The surface cold working (SCW) of austenitic stainless steel (SS) causes martensitic transformation in the surface layers, and the percentage fraction of the strain-induced martensite depends on the degree of SCW. Higher content of α′−martensite increases the surface micro-hardness and fatigue strength, but deterioration of the corrosion resistance is possible. Therefore, the desired operational behaviour of austenitic SS can be ensured by the corresponding degree of SCW and heat treatment. This article evaluates the effects of SCW performed by diamond burnishing (DB) and heat treatment on the surface integrity (SI), rotating fatigue strength, and corrosion resistance of AISI 304 austenitic SS for two initial states: as-received hot-rolled bar and initially heat-treated at 1100 °C for one hour followed by quenching in water. Then, DB was implemented as a smoothing and hardening process, both alone and in combination with heat treatment at 350 °C for three hours after DB. The electro...
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Materials
To fix the bone in orthopedics, it is almost always necessary to use implants. Metals provide the... more To fix the bone in orthopedics, it is almost always necessary to use implants. Metals provide the needed physical and mechanical properties for load-bearing applications. Although widely used as biomedical materials for the replacement of hard tissue, metallic implants still confront challenges, among which the foremost is their low biocompatibility. Some of them also suffer from excessive wear, low corrosion resistance, infections and shielding stress. To address these issues, various coatings have been applied to enhance their in vitro and in vivo performance. When merged with the beneficial properties of various bio-ceramic or polymer coatings remarkable bioactive, osteogenic, antibacterial, or biodegradable composite implants can be created. In this review, bioactive and high-performance coatings for metallic bone implants are systematically reviewed and their biocompatibility is discussed. Updates in coating materials and formulations for metallic implants, as well as their pro...
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Journal of Cluster Science, 2021
Magnesium oxide (MgO) nanoparticles were fabricated at the ambient temperature by a chemical prec... more Magnesium oxide (MgO) nanoparticles were fabricated at the ambient temperature by a chemical precipitation method. The as-synthesized nanoparticles were analyzed by using X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDS), particle size analyzer (PSA), Fourier transform infrared spectroscopy (FTIR), and UV–Vis absorption spectroscopy. The strain and crystallite size of the prepared nanopowders were studied by means of X-ray profile calculations. The size–strain plot (SSP) and Williamson–Hall (W–H) techniques were applied to investigate the effect of crystallite size and obtained strain in the lattice based on the peak broadening of MgO nanopowders. Various models such as size–strain plot (SSP), uniform deformation stress model (UDSM), uniform deformation model (UDM), and uniform deformation energy density model (UDEDM) method were applied to estimate certain physical parameters including strain, energy density, and stress values. Besides, the measured crystallite size by the above-mentioned models, FESEM, and TEM images and Scherrer's equation were compared to each other. The optical band gap energy of the nanoparticles estimated from the UV–Vis absorption spectrum was found to be equal to 4.6 and 4.9 eV.
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International Journal of Molecular Sciences, 2021
Vacuum cathodic arc TiN coatings with overlaying TiO2 film were deposited on polished and surface... more Vacuum cathodic arc TiN coatings with overlaying TiO2 film were deposited on polished and surface roughened by electron beam modification (EBM) Ti6Al4V alloy. The substrate microtopography consisted of long grooves formed by the liner scan of the electron beam with appropriate frequencies (500 (AR500) and 850 (AR850) Hz). EBM transformed the α + β Ti6Al4V mixed structure into a single α’-martensite phase. Тhe gradient TiN/TiO2 films deposited on mechanically polished (AR) and EBM (AR500 and AR850) alloys share the same surface chemistry and composition (almost stoichiometric TiN, anatase and rutile in different ratios) but exhibit different topographies (Sa equal to approximately 0.62, 1.73, and 1.08 μm, respectively) over areas of 50 × 50 μm. Although the nanohardness of the coatings on AR500 and AR850 alloy (approximately 10.45 and 9.02 GPa, respectively) was lower than that measured on the film deposited on AR alloy (about 13.05 GPa), the hybrid surface treatment offered improvem...
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Applied Physics A, 2021
In this study, we proposed a cost-effective and simple one-step sonochemical route to synthesize ... more In this study, we proposed a cost-effective and simple one-step sonochemical route to synthesize Mg(OH)2 and MgO nanostructures by using natural brine. The structure, morphology, and chemical composition of as-synthesized nanostructures were confirmed by XRD, FESEM, TEM, EDS, and FT-IR spectroscopy. The possible growth mechanism of Mg(OH)2 nanoplates and MgO nanoparticles (with an average crystallite size of 22.59 nm and 19.86 nm, respectively) was investigated, and the effect of ultrasound waves on the morphologies was described. The optical properties of nanoparticles were studied by utilizing UV–Vis spectroscopy. The optical energy band gap of the samples (Eg(Mg(OH)2) = 4.8 eV, Eg(MgO) = 4.9 eV) was estimated and used for calculating refractive index (n) and dielectric constant (e∞) parameters via three known models (Ravindra et al., Herve and Vandamme, and Ghosh et al.), in which Ravindra et al. model was selected as acceptable for enhancing their efficiency of dye-sensitized solar cells and other optical applications. The emission peaks for Mg(OH)2 (400 nm) and MgO (380 nm) nanopowders at photoluminescence (PL) measurements indicated that despite obtained from cheap and available impure precursor, the products have potential applications in opto-electronic devices.
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Biomimetics, 2020
The development of new nanomaterials with high biomedical performance and low toxicity is essenti... more The development of new nanomaterials with high biomedical performance and low toxicity is essential to obtain more efficient therapy and precise diagnostic tools and devices. Recently, scientists often face issues of balancing between positive therapeutic effects of metal oxide nanoparticles and their toxic side effects. In this review, considering metal oxide nanoparticles as important technological and biomedical materials, the authors provide a comprehensive review of researches on metal oxide nanoparticles, their nanoscale physicochemical properties, defining specific applications in the various fields of nanomedicine. Authors discuss the recent development of metal oxide nanoparticles that were employed as biomedical materials in tissue therapy, immunotherapy, diagnosis, dentistry, regenerative medicine, wound healing and biosensing platforms. Besides, their antimicrobial, antifungal, antiviral properties along with biotoxicology were debated in detail. The significant breakthr...
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Bioactive Materials, 2019
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SN Applied Sciences, 2019
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Hybrid Nanocomposites, 2019
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SN Applied Science, 2019
Considering metal oxide nanoparticles as important technological materials, authors provide a com... more Considering metal oxide nanoparticles as important technological materials, authors provide a comprehensive review of researches on metal oxide nanoparticles, their synthetic strategies, and techniques, nanoscale physicochemical properties, defining specific industrial applications in the various fields of applied nanotechnology. This work expansively reviews the recent developments of semiconducting metal oxide gas sensors for environmental gases including CO 2 , O 2 , O 3 , and NH 3 ; highly toxic gases including CO, H 2 S, and NO 2 ; combustible gases such as CH 4 , H 2 , and liquefied petroleum gas; and volatile organic compounds gases. The gas sensing properties of different metal oxides nanoparticles towards specific target gases have been individually discussed. Promising metal oxide nanoparticles for sensitive and selective detection of each gas have been identified. This review also categorizes metal oxides sensors by analyte gas and also summarizes the major techniques and synthesis strategies used in nanotechnology. Additionally, strategies, sensing mechanisms and related applications of semiconducting metal oxide materials are also discussed in detail. Related applications are innumerable trace to ultratrace-level gas sensors, batteries, magnetic storage media, various types of solar cells, metal oxide nanoparticles applications in catalysis, energy conversion, and antennas (including microstrip and patch-type optically transparent antennas), rectifiers, optoelectronic, and electronics.
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IJMS, 2021
Vacuum cathodic arc TiN coatings with overlaying TiO2 film were deposited on polished and surface... more Vacuum cathodic arc TiN coatings with overlaying TiO2 film were deposited on polished and surface roughened by electron beam modification (EBM) Ti6Al4V alloy. The substrate microtopography consisted of long grooves formed by the liner scan of the electron beam with appropriate frequencies (500 (AR500) and 850 (AR850) Hz). EBM transformed the + Ti6Al4V mixed structure into a single ’-martensite phase. Òhe gradient TiN/TiO2 films deposited on mechanically polished (AR) and EBM (AR500 and AR850) alloys share the same surface chemistry and composition (almost stoichiometric TiN, anatase and rutile in different ratios) but exhibit different topographies (Sa equal to approximately 0.62, 1.73, and 1.08 m, respectively) over areas of 50 50 m. Although the nanohardness of the coatings on AR500 and AR850 alloy (approximately 10.45 and 9.02 GPa,
respectively) was lower than that measured on the film deposited on AR alloy (about 13.05 GPa), the
hybrid surface treatment offered improvement in critical adhesive loads, coefficient of friction, and
wear-resistance of the surface. In phosphate buffer saline, all coated samples showed low corrosion potentials and passivation current densities, confirming their good corrosion protection. The coated EBM samples cultured with human osteoblast-like MG63 cells demonstrated increased cell attachment, viability, and bone mineralization activity especially for the AR500-coated alloy, compared to uncoated polished alloy. The results underline the synergetic effect between the sub-micron structure and composition of TiN/TiO2 coating and microarchitecture obtained by EBM.
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AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow ma... more AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using "phase diagram" module of FactSageto predict the steels' phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe 3 O 4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance.
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Biomimetics, 2020
The development of new nanomaterials with high biomedical performance and low toxicity is essenti... more The development of new nanomaterials with high biomedical performance and low toxicity is essential to obtain more efficient therapy and precise diagnostic tools and devices. Recently, scientists often face issues of balancing between positive therapeutic effects of metal oxide nanoparticles and their toxic side effects. In this review, considering metal oxide nanoparticles as important technological and biomedical materials, the authors provide a comprehensive review of researches on metal oxide nanoparticles, their nanoscale physicochemical properties, defining specific applications in the various fields of nanomedicine. Authors discuss the recent development of metal oxide nanoparticles that were employed as biomedical materials in tissue therapy, immunotherapy, diagnosis, dentistry, regenerative medicine, wound healing and biosensing platforms. Besides, their antimicrobial, antifungal, antiviral properties along with biotoxicology were debated in detail. The significant breakthroughs in the field of nanobiomedicine have emerged in areas and numbers predicting tremendous application potential and enormous market value for metal oxide nanoparticles.
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Bioactive materials, 2019
Considering the advantages and disadvantages of biomaterials used for the production of 3D scaffo... more Considering the advantages and disadvantages of biomaterials used for the production of 3D scaffolds for tissue engineering, new strategies for designing advanced functional biomimetic structures have been reviewed. We offer a comprehensive summary of recent trends in development of single-(metal, ceramics and polymers), composite-type and cell-laden scaffolds that in addition to mechanical support, promote simultaneous tissue growth, and deliver different molecules (growth factors, cytokines, bioactive ions, genes, drugs, antibiotics, etc.) or cells with therapeutic or facilitating regeneration effect. The paper briefly focuses on divers 3D bioprinting constructs and the challenges they face. Based on their application in hard and soft tissue engineering, in vitro and in vivo effects triggered by the structural and biological functionalized biomaterials are underlined. The authors discuss the future outlook for the development of bioactive scaffolds that could pave the way for their successful imposing in clinical therapy.
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Physical surface properties including surface roughness, topography, morphology, and wettability ... more Physical surface properties including surface roughness, topography, morphology, and wettability could influence the implant material behavior, bio-response, bacterial contamination and contact with other bio-active surfaces or fluids. This work investigates micro-and nanoscale roughness parameters and surface morphology of PVD deposited (Ti,Al,V)N/TiO 2 coating using optical microscopy, white light interferometry (WLI), contact profilometer and scanning electron (SEM) microscopy. Results indicated that vacuum oxidized surface possessed medium roughness values, anisotropy in surface texture and irregular morphology. The vacuum oxidation of the nitride maintained the oxide with nano-crystal size and showed pores at the interface between the layers. The effect of prolonged exposure to Ringer-Braun solution droplet on the modified crystalline structure of the oxide was also explained.
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The advanced methods for treatment of materials with concentrated energy fluxes provide major opp... more The advanced methods for treatment of materials with concentrated energy fluxes provide major opportunity for obtaining wear, fatigue, corrosion resistant and hard surfaces or persistently engraved ones with bitmaps in the form of texts or images. Today, we are aware of many methods of treatment but the laser technology is known to be highly accurate in positioning. In this respect, the laser treatment together with additionally applied combustible particulate substances (like magnesium paste, black powder, REX-C100-C900, etc.) on the treated surface enables obtaining of enhanced tribological properties while guaranteeing a certain depth of the treatment. The present study aims at determining a regime for obtaining lasting traces with fiber laser for decorative purposes on an austenitic AISI 301 sheet steel. The result of the applied treatment is evaluated by means of microstructure, XRD analysis and tribological examinations. They show that the use of the concentrated power-controlled light beam that transmits the energy to the active magnesium paste produces qualitative and process-controlled surface treatments.
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Although the biocompatibility of Ti has been confirmed, it is still difficult to meet all the req... more Although the biocompatibility of Ti has been confirmed, it is still difficult to meet all the requirements, such as antibacterial ability, osseointegration and mechanical properties. Titanium alloys have a high friction coefficient while interacting with bone or tissue, which can cause wear debris, pain and loosening of implants. This situation could be avoided by using alloy surface modification by a durable, mechanically stable, wear resistant TiN coating with a low friction coefficient as a base for an overlaying adjacent nanostructured TiOx. The complex coating will ensure the lowering of friction and elasticity modulus f the surface, while fatigue strength, mechanical, wear, cracking and corrosion resistances, biocompatibility and hydrophilicity will be enhanced. The influence of applied coating on the mechanical properties, adhesion strength and surface morphology of TiN and coatings vacuum oxidized in the chamber was studied. The surface morphology was analyzed by light microscopy after the film deposition. Surface roughness of the samples was evaluated and XRD analyzer was used to obtain diffraction patterns. The mechanical properties, i.e. hardness, modulus of elasticity and coating strength were characterized by nano-indentation technique. HV adhesion test was utilized to compare adhesion and brittleness of the coatings. Adhesion strength was evaluated by generally accepted scratch test technique. In addition, surface hydrophilicity was utilized to compare different surface contact angles.
Key words: biocompatibility; implant
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The bioactivity and biocompatibility of the implants are determined by nanostructured surface mod... more The bioactivity and biocompatibility of the implants are determined by nanostructured surface modification. Because of the enormous potential of biomaterials, the latter are in focus of the scientific researches all over the world. Surface films play a key role in corrosion and osseointegration processes of implants. Many research efforts have been directed towards improving the bone/implant interface, with the aim of accelerating bone healing and improving bone anchorage to the implant, typically following two different approaches. In the first strategy, the interface is improved chemically by incorporating inorganic phases, such as calcium phosphate, on or into the TiO2 layer. In the second strategy, the interface is improved physically by the architecture of the surface topography. The purpose is to achieve an active implant’s surface, which could eliminate the complication of fibrous encapsulation and enhance healing process on bone regeneration through the process of binding with peptides and other active molecules.
The paper deals with the general requirements for biomaterials, the influence of the surface characteristics on the competition between desirable cells and various bacteria, the characteristics of currently used implant materials and the latest developments in coatings on implants. The problems, the advantages and disadvantages of the different surface modification technologies are discussed. The goal of this paper is to make a review of biomaterial surface modifications, which, are designed for and are in the usage in study and practice.
Key words: biocompatibility, implant materials, nanostructured coatings
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This paper presents the results of combined surface treatment of the contact bodies of the electr... more This paper presents the results of combined surface treatment of the contact bodies of the electrical contacts of electromagnetic contactors of type K6E. Movable and fixed contact elements of metal composite Ag-CdO are oxy-nitricarburized in regime of durability treatment. On the oxy-nitricarburized surface TiN coatings are deposited with thickness in the nano scale in order to prolong the durability of the electrical contacts. The phase composition is examined by X-ray qualitative analysis. The topography is represented by digital images and 3D images. An abrasive wear test is also realized using the "Ball - wear" method. Using special laboratory stand discharge is simulated by spark and studied. The electrical wear of the contact bodies of electrical contacts are studied – the changes in their contact resistance after oxy-nitricarburizing treatment and subsequently applied TiN coating.
Keywords: electrical apparatus, contact bodies, oxy-nitricarburizing treatment, nanostructured coatings, wear resistance
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Издателство на Технически Университет - Варна
Abstract: The study considers the thermo-chemical treatment of iron alloys containing carbide- an... more Abstract: The study considers the thermo-chemical treatment of iron alloys containing carbide- and nitride forming elements (Cr, Mo, V, Ti, etc.) in order to increase the hardness and wear resistance of the substrate. It is ascertained that there is a strong surface strengthening effect after the oxy-nitrocarburizing process in some of the samples. The increased hardness corresponds to enhanced wear resistance. Furthermore the highly allowed substrate retains its properties after the process.
Кеy words: oxy-nitrocarburizing; vacuum, phase structure, alloyed steels
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Papers by Maria Nikolova, Мария Николова
respectively) was lower than that measured on the film deposited on AR alloy (about 13.05 GPa), the
hybrid surface treatment offered improvement in critical adhesive loads, coefficient of friction, and
wear-resistance of the surface. In phosphate buffer saline, all coated samples showed low corrosion potentials and passivation current densities, confirming their good corrosion protection. The coated EBM samples cultured with human osteoblast-like MG63 cells demonstrated increased cell attachment, viability, and bone mineralization activity especially for the AR500-coated alloy, compared to uncoated polished alloy. The results underline the synergetic effect between the sub-micron structure and composition of TiN/TiO2 coating and microarchitecture obtained by EBM.
Key words: biocompatibility; implant
The paper deals with the general requirements for biomaterials, the influence of the surface characteristics on the competition between desirable cells and various bacteria, the characteristics of currently used implant materials and the latest developments in coatings on implants. The problems, the advantages and disadvantages of the different surface modification technologies are discussed. The goal of this paper is to make a review of biomaterial surface modifications, which, are designed for and are in the usage in study and practice.
Key words: biocompatibility, implant materials, nanostructured coatings
Keywords: electrical apparatus, contact bodies, oxy-nitricarburizing treatment, nanostructured coatings, wear resistance
Кеy words: oxy-nitrocarburizing; vacuum, phase structure, alloyed steels
respectively) was lower than that measured on the film deposited on AR alloy (about 13.05 GPa), the
hybrid surface treatment offered improvement in critical adhesive loads, coefficient of friction, and
wear-resistance of the surface. In phosphate buffer saline, all coated samples showed low corrosion potentials and passivation current densities, confirming their good corrosion protection. The coated EBM samples cultured with human osteoblast-like MG63 cells demonstrated increased cell attachment, viability, and bone mineralization activity especially for the AR500-coated alloy, compared to uncoated polished alloy. The results underline the synergetic effect between the sub-micron structure and composition of TiN/TiO2 coating and microarchitecture obtained by EBM.
Key words: biocompatibility; implant
The paper deals with the general requirements for biomaterials, the influence of the surface characteristics on the competition between desirable cells and various bacteria, the characteristics of currently used implant materials and the latest developments in coatings on implants. The problems, the advantages and disadvantages of the different surface modification technologies are discussed. The goal of this paper is to make a review of biomaterial surface modifications, which, are designed for and are in the usage in study and practice.
Key words: biocompatibility, implant materials, nanostructured coatings
Keywords: electrical apparatus, contact bodies, oxy-nitricarburizing treatment, nanostructured coatings, wear resistance
Кеy words: oxy-nitrocarburizing; vacuum, phase structure, alloyed steels