Andrey L. Nikolaev

Metal-coated polymer electrodes fabricated by additive manufacturing are promising tools for electrical discharge machining (EDM) of complex shapes; however, coating non-uniformity and thermomechanical degradation limit their performance. This study presents experimental and theoretical results for a hybrid tool electrode fabricated by stereolithography (SLA), followed by electroless and electrochemical copper plating, and used to machine St3 structural steel. Optical and scanning electron microscopy, energy-dispersive spectroscopy (EDS), atomic force microscopy, X-ray microtomography, Raman spectroscopy, simultaneous thermal analysis and nanoindentation were used to characterize the coating before and after EDM. The electroplated copper layer exhibited pronounced thickness non-uniformity (264–1225 µm), an edge effect and dendritic morphology associated with the primary current distribution and the absence of leveling additives. Surface modification during EDM was accompanied by changes in the elemental composition measured by EDS. After EDM, the Fe and C signals reached 23.32 wt.% and 35.56 wt.%, respectively, under the acquisition and quantification conditions used. These values characterize local surface composition and do not establish bulk incorporation of iron or carbon into the copper layer. No pronounced bulk thermal degradation was detected in the examined photopolymer specimens; exposure of the polymer base nevertheless promotes local damage. A coupled numerical model combines a boundary element calculation of copper deposition, normal coating recession and cavity formation; a single-discharge thermal solver provides diagnostic calculations. The model describes the principal copper-wear and cavity development trends for the investigated electrode, including the end face and chamfer and reproduction of coating and printing defects. Because only one electrode was fabricated, plated and tested, the work is presented as a detailed case study. The observed variability reflects within-specimen measurement scatter and spatial heterogeneity rather than reproducibility between independently manufactured electrodes. The results demonstrate the feasibility of SLA-printed copper-plated electrodes for EDM and identify coating uniformity, adhesion and thermal damage as factors affecting dimensional stability and service life. A solid copper control was not tested under identical conditions, so no direct experimental comparison of machining performance or wear resistance is presented. Seven residual thicknesses determine the deposition parameters, and three working-surface thicknesses determine two effective EDM parameters; all ten locations are calibration data. The mean absolute relative discrepancy is 1.47% for the working locations and 4.42% for all locations. These are fitting metrics. The calculated cavity depth of approximately 8.4 mm and steel removal rate of approximately 35 mm³/min have not been independently measured. Numerical verification and sensitivity analysis are distinguished from independent experimental validation.

The long-term success of orthopedic implants is fundamentally dependent on the synergy between mechanical performance and biological integration. Thus, a comprehensive investigation of both mechanical characteristics and microstructural parameters is essential for the development of reliable implant systems in hip arthroplasty, both in human medicine and veterinary practice. The present study provides a detailed analysis of the mechanical properties, microstructure, and chemical composition of a Ti-6Al-4V-based femoral implant using nanoindentation, scanning electron and optical microscopy, and energy-dispersive X-ray spectroscopy. Then, using finite element analysis, the influence of Young’s modulus on the stress–strain state of the endoprosthesis was evaluated. Dynamic loading conditions were considered by analyzing an impact on a cantilever beam, simulating an animal’s jump onto a supporting limb. For reliable numerical simulation, the model geometry was constructed utilizing computed X-ray microtomography. The numerical simulations were performed for three material cases: reference Ti-6Al-4V, experimentally characterized Ti-6Al-4V (with properties determined by nanoindentation), and CoCrMo alloy, which is also widely used in endoprosthetic applications. The influence of the founded mechanical characteristics on the stress–strain state of the prostheses was assessed. In particular, the results indicate that under dynamic loading conditions, the load-bearing capacity of CoCrMo is lower by approximately 30% and 21% compared to the reference and experimentally characterized Ti-6Al-4V, respectively.

A plane contact problem involving the indentation and sliding of a punch on the surface of an elastic half-plane with a functionally graded coating is considered. Adhesive friction acts at the contact. Young’s modulus and Poisson’s ratio of the coating vary with depth according to arbitrary, independent laws. The normal force is applied with some eccentricity to maintain parallelism of the punch motion. The problem is reduced to solving a system of dual integral equations in Fourier transforms for two unknown functions—even and odd. A unique approximate analytical method is used to solve these equations. After inverting the Fourier transform, approximate analytical expressions for the contact stresses and eccentricity are obtained.

Collagen is a major extracellular-matrix protein widely used in regenerative medicine, yet conventional terrestrial sources raise biosafety and acceptability concerns, motivating the search for marine alternatives. This study evaluates the jellyfish Rhizostoma pulmo (R. pulmo) from the Azov Sea as a sustainable collagen source and assesses its suitability for biomedical materials. Acid-soluble collagen was extracted using 0.5 M acetic acid and purified by salt precipitation and dialysis, followed by physicochemical/structural characterization (sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), Limulus amebocyte lysate (LAL) endotoxin testing, transmission electron microscopy (TEM), and immunofluorescence with type I collagen antibodies) and biological evaluation in vitro (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity on MRC5 fibroblasts; adhesion and proliferation assays on HeLa cells). The extracted collagen showed a high yield (~26.2%), a type I-like electrophoretic profile with α-, β-, and γ-components, fibrillar ultrastructure by TEM, and positive type I collagen immunoreactivity; endotoxin levels were low (0.461 EU/µL), and no cytotoxicity was detected under the tested conditions. Porous collagen sponges/scaffolds were fabricated by lyophilization, displaying interconnected pores with an average size of ~80 µm and pH-dependent swelling, and they supported 3D cell growth and tumor-cell dissemination in an in vitro breast carcinoma scaffold model. Overall, Azov Sea R. pulmo collagen demonstrates promising structural quality, low endotoxin burden, and cytocompatibility, supporting its potential as a marine biomaterial for sponge/scaffold-based tissue engineering and wound-related applications.

The effect of palladium addition to a hybrid Co/SiO₂ + HZSM-5 + Al₂O₃ catalyst on the combined Fischer–Tropsch (FT) synthesis and hydrocarbon hydroconversion process was studied. Catalysts with a Pd content of 0.075–0.3 wt.% were characterized by a complex of physicochemical methods, including synchrotron radiation X-ray diffraction (SR-XRD), temperature-programmed reduction with hydrogen (H₂-TPR), temperature-programmed desorption of hydrogen with oxygen titration (H₂-TPD/O₂ titration), IR spectroscopy of adsorbed pyridine, and STEM-EDX analysis. It was found that the addition of palladium decreases the cobalt oxide reduction temperature due to interphase hydrogen transfer. Tests in hydrocarbon synthesis at 240–250 °C, a pressure of 2 MPa, and an H₂/CO ratio of 2 showed that the sample with 0.15% Pd exhibits the highest selectivity for C₅+ hydrocarbons (66.8% at 240 °C) and stability for 150 h. Analysis of the synthesis products revealed a fivefold decrease in the proportion of alkenes and an increase in isoalkanes with increasing Pd concentration. This effect enables the in situ hydroprocessing of primary FT products in a single reactor. The results demonstrate that the targeted introduction of palladium into the hybrid system is an effective strategy for regulating its functionality, allowing for the one-stage production of high-quality fuels with a controlled hydrocarbon composition from syngas.

Nanoindentation usage for measurement of the dental materials and dental tissues properties, including pathologically altered ones is widespread in modern bioengineering practice when designing new experimental compositions for the regeneration and restoration of damaged enamel and dentine. Application of a sphero-conical indenter in such studies allows for the most delicate measurements of not only mechanical but also tribological characteristics. In the present paper, using a sphero-conical indenter, we conducted the ex vivo research of the mechanical (nanoindentation method) and tribological (nanoscratching with continuous recording of the friction coefficient) characteristics of a composite filling, enamel in its vicinity, glass ionomer cement filling, and infiltrant-modified enamel in the case of early caries. For each sample the measurements of the sound enamel area on the medial opposite part of the tooth were performed. At the same time, for a more detailed analysis of the results, scanning electron and atomic-force microscope images of the studied areas were presented. The advantages of using a polymer infiltrant over filling materials in the case of white spot lesion caries stage were demonstrated. Based on the collected data, it is possible to conclude that the use of composite material by a practicing dental clinician is more preferable in cases where minimally invasive methods of treating early caries are insufficient for effective treatment. If it is possible to use polymer infiltration, the clinician can achieve greater preservation of the patient's enamel by "completing" partially dissolved hydroxyapatite crystals with a polymer material, which allows achieving significant proximity of the mechanical and tribological characteristics of the modified enamel to sound tissue. The limitations of the methods used and ways to overcome them in the future studies are considered in the work as well.