Assessment of Anisotropic Acoustic Properties in Additively Manufactured Materials: Experimental, Computational, and Deep Learning Approaches.

The influence of acoustic anisotropy on ultrasonic testing reliability poses a challenge in evaluating products from additive technologies (AT). This study investigates how elasticity constants of anisotropic materials affect defect signal amplitudes in AT products. Experimental measurements on AT samples were conducted to determine elasticity constants. Using Computational Modeling and Simulation Software (CIVA), simulations explored echo signal changes across ultrasound propagation directions. The parameters A13 (the ratio between the velocities of ultrasonic transverse waves with vertical and horizontal polarizations at a 45-degree angle to the growth direction), A3 (the ratio for waves at a 90-degree angle), and Ag (the modulus of the difference between A13 and A3) were derived from wave velocity relationships and used to characterize acoustic anisotropy. Comparative analysis revealed a strong correlation (0.97) between the proposed anisotropy coefficient Ag and the amplitude changes. Threshold values of Ag were introduced to classify anisotropic materials based on observed amplitude changes in defect echo signals. In addition, a method leveraging deep learning to predict Ag based on data from other anisotropy constants through genetic algorithm (GA)-optimized neural network (NN) architectures is proposed, offering an approach that can reduce the computational costs associated with calculating such constants.

3D printing in pediatric neurosurgery: experimental study of a novel approach using biodegradable materials.

PURPOSE: 3D printing technologies have become an integral part of modern life, and the most routinely used materials in reconstructive surgery in children are biodegradable materials. The combination of these two technologies opens up new possibilities for the application of innovative methods in neurosurgery and a patient-centered approach in medical care. The aim of the study was to determine whether a physician without specialized programming and printing skills could independently create materials in a clinical setting for the treatment of patients. METHODS: We conducted a preclinical study on 15 male Balb-C mice. Cylindrical materials made of polylactic acid (PLA) plastic were 3D printed. Sterilization of the obtained material was performed using a cold plasma sterilizer with hydrogen peroxide vapor and its plasma. The sterile material was implanted subcutaneously into the mice for 30 days, followed by histological examination. Using open-source software for modeling and printing, plates and screws made of PLA plastic were manufactured. The produced components were tested in the biomedical laboratory of the institute. RESULTS: The histological material showed that no inflammatory changes were observed at the implantation site during the entire observation period. The cellular composition is mainly represented by macrophages and fibroblasts. There was a gradual resolution of the material and its replacement by native tissues. Research conducted to assess the effectiveness of material sterilization in a cold plasma sterilizer demonstrated its high bactericidal efficiency. CONCLUSION: The method we developed for obtaining biodegradable plates and fixation elements on a 3D printer is easy to use and has demonstrated safety in a preclinical study on an animal model.

Production of Workpieces from Martensitic Stainless Steel Using Electron-Beam Surfacing and Investigation of Cutting Forces When Milling Workpieces.

The aim of this study was to investigate cutting force when milling 40 × 13 stainless steel samples obtained via electron-beam surfacing. The samples were obtained by surfacing the wire made from the martensitic 40 × 13 stainless steel. The microstructure of the samples and the hardness are discussed in the present study. Emphasis is placed on the study of cutting forces when handling the samples. The structure of the samples obtained by electron-beam surfacing consisted of tempered martensite. The average hardness of the samples was similar to the hardness obtained after quenching and tempering the samples-576 HV for horizontally printed workpieces and 525 HV for vertically printed workpieces. High-speed milling, high-efficiency milling, and conventional milling have been proven to be suitable for handling such workpieces. This study shows that an increase in milling width leads to a gradual decrease in specific cutting force. As the milling depth increases, the specific cutting force decreases intensively at first but then more slowly with time. Machining the workpieces made of the martensitic stainless steel and produced by electron-beam surfacing requires the use of purely carbide mills with a diameter of at least 12 mm. Using a high-speed steel as a tool material results in the rapid failure of the tool. The cutting conditions during the investigation allowed for a decrease in the temperature of the cutting edge, cutting force, and the low-rigid end mill bending. Therefore, this study has made it possible to select modes that allow for a reduction in the vibration of the lathe-fixture-tool-part system.

Experimental Study on Mechanical Properties of Different Resins Used in Oral Environments.

Background and Objectives: Acrylic resins remain the materials of choice for removable prosthesis due to their indisputable qualities. The continuous evolution in the field of dental materials offers practitioners today a multitude of therapeutic options. With the development of digital technologies, including both subtractive and additive methods, workflow has been considerably reduced and the precision of prosthetic devices has increased. The superiority of prostheses made by digital methods compared to conventional prostheses is much debated in the literature. Our study's objective was to compare the mechanical and surface properties of three types of resins used in conventional, subtractive, and additive technologies and to determine the optimal material and the most appropriate technology to obtain removable dentures with the highest mechanical longevity over time. Materials and Methods: For the mechanical tests, 90 samples were fabricated using the conventional method (heat curing), CAD/CAM milling, and 3D printing technology. The samples were analyzed for hardness, roughness, and tensile tests, and the data were statistically compared using Stata 16.1 software (StataCorp, College Station, TX, USA). A finite element method was used to show the behavior of the experimental samples in terms of the crack shape and its direction of propagation. For this assessment the materials had to be designed inside simulation software that has similar mechanical properties to those used for obtaining specimens for tensile tests. Results: The results of this study suggested that CAD/CAM milled samples showed superior surface characteristics and mechanical properties, comparable with conventional heat-cured resin samples. The propagation direction predicted by the finite element analysis (FEA) software was similar to that observed in a real-life specimen subjected to a tensile test. Conclusions: Removable dentures made from heat-cured resins remain a clinically acceptable option due to their surface quality, mechanical properties, and affordability. Three-dimensional printing technology can be successfully used as a provisional or emergency therapeutic solution. CAD/CAM milled resins exhibit the best mechanical properties with great surface finishes compared to the other two processing methods.

Investigation of the Resistance to High-Speed Impact Loads of a Heterogeneous Materials Reinforced with Silicon Carbide Fibers and Powder.

Pioneering studies on the additive manufacturing of a cermet heterogeneous material using SiC ceramic fiber were carried out. Unique studies of the damage staging (cratering) and the transition to the destruction of the formed material during high-speed impact created with the help of an electrodynamic mass accelerator have been carried out. It has been shown that the use of ceramic fiber in a metal matrix reduces the impact crater depth by 22% compared to material with ceramic particles. For the first time, the phase composition of the resulting composite was studied using synchrotron radiation. It was shown that, as a result of laser exposure, silicon carbide SiC is dissolved in the titanium matrix with the formation of secondary compounds of the TiC and Ti5Si3C types. It has been established that the use of SiC ceramic fibers leads to their better dissolution, in contrast to the use of SiC ceramic particles, with the formation of secondary phase compounds, and to an increase in mechanical characteristics.

Development and Processing of New Composite Materials Based on High-Performance Semicrystalline Polyimide for Fused Filament Fabrication (FFF) and Their Biocompatibility.

Samples of composite materials based on high-performance semicrystalline polyimide R-BAPB (based on the dianhydride R: 1,3-bis-(3',4,-dicarboxyphenoxy)benzene and diamine BAPB: 4,4'-bis-(4″-aminophenoxy)diphenyl)) filled with carbon nanofibers and micron-sized discrete carbon fibers were obtained by FFF printing for the first time. The viscosity of melts of the composites based on R-BAPB, thermal, mechanical characteristics of the obtained composite samples, their internal structure, and biocompatibility were studied. Simultaneously with FFF printing, samples were obtained by injection molding. The optimal concentrations of carbon fillers in polyimide R-BAPB for their further use in FFF printing were determined. The effect of the incorporation of carbon fillers on the porosity of the printed samples was investigated. It was shown that the incorporation of carbon nanofibers reduces the porosity of the printed samples, which leads to an increase in deformation at break. Modification of polyimide with discrete carbon fibers increases the strength and Young's modulus sufficiently but decreases the deformation at break. The cytotoxicity analysis showed that the obtained composite materials are bioinert.

Use of Additive Technologies in Surgical Treatment of Chronic Posterior Dislocations of the Shoulder.

The aim of the study was to evaluate the efficiency of additive technologies in surgical treatment of patients with osteochondral defects of the humeral head articular surface against the background of chronic posterior dislocation of the shoulder by means of comparing clinical and radiological results with the McLaughlin procedure. Materials and Methods: A prospective randomized comparative group clinical study was conducted, which included 20 patients who in 2019-2021 underwent surgical treatment of chronic posterior dislocation of the shoulder in the Traumatological and Orthopedic Department of the Institute of Traumatology and Orthopedics of the Privolzhsky Research Medical University (Nizhny Novgorod, Russia). Depending on the type of surgery, all patients were divided into 2 groups: group 1 (n=10) was subject to McLaughlin procedure, whereas group 2 (n=10) - to reconstruction of the humeral head using a customized implant based on additive technologies (3D printing). To assess postoperative results, 6 months after the surgery all patients underwent the following procedures: X-ray imaging of the shoulder joint in two projections, CT scanning, and angulometry as well as provided their responses in line with the following questionnaires: Visual Analog Scale (VAS), Disabilities of the Arm, Shoulder and Hand (DASH), American Shoulder and Elbow Surgeons Shoulder Score (ASES), Constant Shoulder Score (CSS), Shoulder Rating Questionnaire (SRQ), and the Hospital for Special Surgery Shoulder Surgery Expectations Survey (Survey of patient, SP). Results: Both the McLaughlin procedure and the reconstruction of the humeral head using a customized implant made using additive 3D printing technologies increased the range of motion in the shoulder joint, mitigated the pain syndrome and improved the patients' quality of life. During the postoperative period, there were no infectious complications in both groups. The total bed-day in group 1 was 7 [5; 9] days; in group 2, it was 8 [6; 9] days. There was no recurrence of dislocation or progression of osteoarthritis of the shoulder joint in patients in both groups during 6 months after the surgery. The ASES, SP, SRQ, CSS, DASH, and VAS questionnaires assessment for both groups showed a statistically significant improvement for all indicators in the postoperative period. There were no statistically significant differences found between the groups as to the results of angulometry and answering the questionnaires. Conclusion: Customized implants made using additive technologies can shorten the surgery duration by 1.3 times, whereas the volume of intraoperative blood loss - by at least 1.5 times compared to the McLaughlin procedure.

Synthesis of Metal Matrix Composites Based on CrxNiy-TiN for Additive Technology.

The novelty of this work consists of obtaining original fundamental data on the laws of synthesis of new metal matrix composite materials for additive technologies. CrN + TiNi composites were obtained using the method of self-propagating high-temperature synthesis. In this work, analysis of the parameters of the synthesis of composite materials as well as their structure and phase composition were carried out. A scheme for the formation of a composite structure is established; it is shown that the phase composition is represented by 54.6 wt.% CrN and 45.4 wt.% TiNi. It was shown that composites based on the system are suitable for machines that make use of direct laser deposition to grow layers of materials. Sample structure and phase parameters were studied. It is shown that titanium nitride particles are uniformly distributed in the CrNi intermetallic matrix, the TiN particle size ranges from 0.3 to 9 µm and the average particle size is 2.8 µm. The results obtained indicate the possibility of synthesizing promising metal matrix composite materials for additive technologies. Such materials may have increased hardness, operating temperature and strength.

Determination of Fire Parameters of Polyamide 12 Powder for Additive Technologies.

The use of additive technologies keeps growing. Increasingly, flammable powder materials are also used in additive technologies, and there is a risk of explosion or fire when using them. The current article deals with the determination of fire parameters of a powder sample of polyamide Sinterit PA12 Smoth in accordance with the EN 14034 and EN ISO/IEC 80079-20-2 standards. For that purpose, a sample at a median size of 27.5 µm and a humidity of 0% wt. was used. The measurements showed that the maximum explosion pressure of the PA12 polyamide sample was 6.78 bar and the value of the explosion constant Kst was 112.2 bar·m·s-1. It was not possible to determine the MIT value of the settled dust, since the melting point of polyamide sample is low. The MIT of the dispersed dust was 450 °C. Based on the measured results, it can be stated that the powdered polyamide PA12 poses a risk in terms of explosions and fires. Therefore, when using polyamide PA12 in additive technologies, it is necessary to ensure an effective explosion prevention.

Biocompatibility and Osseointegration of Calcium Phosphate-Coated and Non-Coated Titanium Implants with Various Porosities.

The aim of the investigation was to study the influence of pore size and the presence of a biologically active calcium phosphate coating in porous 3D printed titanium implants on the process of integration with the bone tissue. Materials and Methods: Samples of cylindrical implants with three different pore diameters (100, 200, and 400 µm) were fabricated from titanium powder on the Arcam 3D printer (Sweden) using electron beam melting technology. A calcium phosphate coating with a thickness of 20±4 µm was applied to some of the products by microarc oxidation. Cytotoxicity of the implants was determined in vitro on human dermal fibroblast cultures. The samples were implanted in the femoral bones of 36 rabbits in vivo. The animals were divided into 6 groups according to the bone implant samples. The prepared samples and peri-implant tissues were studied on days 90 and 180 after implantation using scanning electron microscopy and histological methods. Results: All samples under study were found to be non-toxic and well biocompatible with the bone tissue. There were revealed no differences between coated and non-coated implants of 100 and 200 µm pore diameters in terms of their histological structure, intensity of vascularization in the early stages, and bone formation in the later stages. Samples with pore diameters of 100 and 200 µm were easily removed from the bone tissue, the depth of bone growth into the pores of the implant was lower than in the samples with pore diameter of 400 µm (p<0.001). There were differences between coated and non-coated samples of 400 µm pore diameter, which was expressed in a more intensive osseointegration of samples with calcium phosphate coating (p<0.05). Conclusion: The optimal surface characteristics of the material for repairing bone defects are a pore diameter of 400 µm and the presence of a calcium phosphate coating.

[Skull defect repair in children using a 3D-printing technology]. / Kranioplastika defektov cherepa u detei s ispol'zovaniem tekhnologii 3D-pechati.

Currently, 3D-printing technologies are increasingly used in neurosurgery. Active development of this approach is valuable to improve preoperative planning, intraoperative navigation, and manufacturing of realistic training models. In this manuscript, the authors report an experience of the pediatric neurosurgical department of the Almazov National Medical Research Center regarding 3D-printing technologies in manufacturing of individual implants for skull defect closure. The main aspects of this technology, advantages and disadvantages are considered. Moreover, the authors describe several cases of creating individual implants for children with skull defects of various origins, dimensions and complexity.

A Study of Characteristics of Aluminum Bronze Coatings Applied to Steel Using Additive Technologies.

The influence of laser power on the microstructural, strength, and tribological characteristics of aluminum bronze coatings applied to steel by laser cladding was studied. It was found that with an increase in laser power, the morphology of the coating surface becomes more uniform without extreme height differences. This study revealed that the coating microstructure corresponds to that of a composite material and consists of a bronze matrix and iron dendrites of different sizes (depending on the laser power). Such a microstructure affects the microhardness indices, which have a scatter of values over the coating thickness. There is a diffusion zone at the steel-bronze interface, which promotes adhesion of the matrix and coating materials. According to the results of tribological tests, the dry friction coefficient for the studied samples is in the range of 0.389-0.574.

Structure and Properties of ZrO2⁻20%Al2O3 Ceramic Composites Obtained Using Additive Technologies.

This investigation focused on obtaining samples from ceramic composite materials, based on the ZrO2⁻20%Al2O3 system, using the additive layer-by-layer fusion technology for thermoplastic systems. The structure and phase composition of the initial powders were studied, experimental samples were produced, and the structure and properties of the experimental samples that were obtained using additive technologies were analysed. The measured static bending strength of the samples was 450 ± 70 MPa, microhardness was 14 GPa, and the elasticity modulus was 280 ± 25 GPa. The strength of these samples are slightly inferior to that of similar materials, obtained using Ceramic Injection Molding technology because our samples were characterised by the residual porosity of about 15%.

[Additive technologies in neurosurgery]. / Additivnye tekhnologii v neirokhirurgii.

Modern achievements of technical progress, in particular additive technologies (ATs) and three-dimensional printing, have been increasingly introduced in neurosurgical practice. The increasing complexity of surgical interventions requires thorough planning of surgery and a high level of training of young neurosurgeons. Creation of full-scale three-dimensional models for planning of surgery enables visualization of the anatomical region of interest. Additive technologies are especially extensively used in reconstructive surgery of skull defects. ATs enable fast and efficient solving of the following tasks: - generation of accurate models of the skull and an implant; - development and fabrication of individual molds for intraoperative formation of implants from polymeric two-component materials (e.g., PMMA); - fabrication of individual implants from titanium alloys or polyetheretherketone (PEEK) for further use in surgery.