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This post was last edited by Shaobin Fluid on 2026-4-28 09:43. Stainless steel (such as 316L stainless steel), platinum-iridium alloy, tantalum, nitinol, cobalt-chromium alloy, titanium and its alloys, as well as pure iron and magnesium alloys, are the basic materials used for manufacturing stents. Stainless steel is the most common material used for manufacturing coated and uncoated stents. The brackets made of stainless steel exhibit suitable mechanical properties and excellent corrosion resistance. However, the clinical application of steel is limited by the ferromagnetism and low density of its alloys. Due to these properties, it is difficult to image steel using X-rays and magnetic resonance. Stainless steel implants can cause allergies to nickel, chromium, and molybdenum, leading to local immune responses and inflammation. Different materials are used as coatings on stainless steel brackets to improve X-ray visibility and biocompatibility. The use of stents representing stainless steel substrate systems with titanium or tantalum coatings allows for the combination of appropriate mechanical properties and biological inertness. Tantalum is characterized by good plasticity, high strength, wear resistance, weldability, corrosion resistance, insolubility, and biocompatibility; it is also clearly visible in X-rays and magnetic resonance imaging. Furthermore, due to these properties, tantalum is widely used not only in the electronics industry for protective coatings, anti-corrosion coatings, and optical coatings, as well as in the chemical industry, but also in biomedical applications such as orthopedics and dentistry, intravascular stents, and neurosurgical implants. However, its high density, complex manufacturing process, and relatively high cost make the use of tantalum challenging. For these reasons, various methods are currently being proposed to modify the surface properties of metal substrates in order to improve biological response by applying tantalum-based coatings. Modern processing methods enable the production of tantalum coatings for scaffolds that possess a fine-grained structure and optimal properties (tensile strength of up to 600 MPa and an elongation of around 30%). Along with its increased strength, tantalum offers high protection against active corrosion processes as well as electrochemical degradation of the metal surface structure in various environments. The development of techniques for creating functional tantalum nanoscale structural coatings has currently attracted great interest in the fields of medicine and materials science. The tantalum vapor deposition method used to form nanostructured coatings enables the creation of nanocoatings to modify surface properties and obtain biocompatible materials with desired characteristics. The optimal approach for modifying metal substrates with tantalum-based nanoscale coatings is to develop new, improved devices for medical applications (cardiovascular surgery, endoscopy, and orthopedics). It is worth noting that nanosstructured materials have a higher surface energy than typical materials, which enhances the adhesion of osteocytes and leads to greater bone integration. Surface properties of biomaterials (relief, hydrophobic-hydrophilic characteristics, chemical composition, etc.). ) It plays an important role in regulating the cellular response of biological organisms to biomaterials. Since the methods for depositing tantalum coatings involve altering the structure and properties of the material at the micron and nanoscale, it is recommended to evaluate the changes in structure and properties at these scales. Instrumental research methods such as atomic force microscopy (AFM) and nanoindentation (NI) allow for the study of the surface properties of tantalum and its compound thin films at the nanoscale, as well as for evaluating these properties and assessing the possibility of using such nanocoatings as biocompatible materials. Materials and Methods Ta, Ta2O5, TaN, and TaON coatings were deposited on polished stainless steel (316 L stainless steel) substrates by tantalum vapor deposition. The morphology of the coating was evaluated using atomic force microscopy with rapid dimension scanning on the QNM picofluidic system equipped with a CSG10_SS cantilever. The study of the microstructure and elemental composition of the samples was carried out using a JSM7001F scanning electron microscope (SEM), equipped with an X-ray energy-dispersive microanalysis probe system INCA ENERGY 350, at a magnification of 100,000 times. The operating voltage and probe current are 20 KV and 5 nA, respectively. The working distance is 10 millimeters. The microstructure was analyzed in the secondary electron mode (SEI mode). In contact mode, the wear of CoF and coatings in the \"plowing\" mode was investigated using a size-fast scanning atomic force microscope that employed a diamond probe on a D300 silicon console, with an initial tip radius of 33 nanometers. The stiffness of the cantilever is 13.84 N·m. During the testing, a normal load of 1.164 newtons (calculated value = 0.6 volts) was applied to each probe. The unchanged process parameters are as follows: scanning area of 20±4 m, 100 cycles, 256±256 points, and friction speed of 2.0 meters per second. The movement of the probe over the surface is back and forth. Therefore, silicon and diamond probes with different loads can be used to detect tantalum coatings with various friction mechanisms (Figure 1). In the “sliding” mode, the effect of friction influences the coefficient of friction, whereas the “tilling” mode characterizes the strength properties of the material during friction. Figure 1. Principle schemes of friction mechanisms: “sliding” and “plowing”. The friction force was recorded separately during forward and reverse scanning. In the processing procedure, the reverse scan image is subtracted from the obtained forward scan image to determine the average value of friction. The mechanical stress (contact pressure) in the area where the AFM probe comes into contact with the coated surface is determined using the AMES (Advanced Mechanical Engineering Solutions) contact pressure calculator. The wear amount V is estimated based on the cross-sectional area and perimeter of the wear track. The thickness of the coating was determined by scanning the cross-section of the coating with an atomic force microscope; the coating was obtained on a substrate after cooling the sample to liquid nitrogen within 10 minutes and breaking the cooled sample. Results and Discussion The elemental analysis of the coating by EDX spectroscopy (Figure 2) confirmed the presence of fundamental characteristic elements in the film, such as tantalum, oxygen, and nitrogen. The amount of tantalum is close to its atomic content in the compounds Ta2O5, TaN, and TaON. Apart from the main line of tantalum, the 2.2 keV peak corresponds to the secondary lines of tantalum (Figures 2b–d). Figure 2. EDX spectra of nanoscale coated layers: tantalum (a), tantalum oxide (b), tantalum nitride (c), and tantalum nitride oxide (d). Figure A1. XPS spectra of Ta-based coatings deposited on a steel substrate: Ta2O5(a) is Ta+5, Ta+5, Ta0 is Ta/Ta2O5(b), and Ta2O5(c) is O1s. The XRD spectra of the as-deposited and annealed Ta2O5 and TaON coatings were analyzed (Figure A2). Based on the XRD data, the amorphous nature of the deposited Ta2O5 coating was confirmed. After treatment at 700°C for 15 minutes, changes in the Ta205 coating were detected, as confirmed by the XRD pattern peaks, which became sharper and more intense (Figure A2). Figure A2. Diffraction X-ray patterns of Ta2O5 (a) and TaON (b) coatings after annealing at 973 K for 15 min and 1 h. Coating thickness and fracture microstructure Figure 3 shows the atomic force microscopy images of the fracture of the tantalum compound coating on the surface of the steel under study, along with its surface profile. Based on these curves, the thickness values of the coatings are as follows: Ta2O5 and TaON at 1500 nm, TaN at 800 nm, and Ta at 500 nm, which is confirmed by the scanning electron microscope data (Figure A3). Additionally, the fracture location of the coatings allows for a qualitative assessment of their brittleness. Figure 3. Atomic force microscopy images of the fracture of nanoscale coated layers: tantalum oxide (a), tantalum nitride oxide (b), tantalum nitride (c), and tantalum (d). Figure A3. Scanning electron microscope images of the cross-sections of nanoscale coated layers: tantalum oxide (a), tantalum nitride oxide (b), tantalum nitride (c), tantalum (d). During tantalum vapor phase deposition, the surface microstructure of the coating and its growth mechanism are determined by the balance between the substrate surface energy, the deposition material, the energy at the material-substrate interface, and the elastic stress energy in the growing film. A high-resolution atomic force microscope is required to reveal the surface morphology and roughness of smooth amorphous coatings on polished substrates. Based on the atomic force microscopy images, the microstructure of the polished stainless steel surface features irregular and protruding alloy phase particles with a diameter of 20–200 nanometers (arrow in Figure 4a). Figure 4. Images obtained by atomic force microscopy of stainless steel (a) and coatings: tantalum (b), tantalum oxide (c), tantalum nitride oxide (d), and tantalum nitride (e). Mechanical properties of the coating: Figure 5 shows the relationship between the indentation depth and the indentation load for both the coating and the steel. The shape of the curves and their position relative to the Y-axis indicate the distribution of the coating: the closer the curve is to the Y-axis, the harder the material. The region defined by the approach-retraction curve is characteristic of plastic deformation. Based on the curves, significant differences in the mechanical properties of the coating and the substrate are visible. Figure 5. The dependence curve of the load on the indentation depth h. The dependence of the mechanical properties of the studied coating on the tantalum atom content is shown in Figure 6. The higher the oxygen and nitrogen contents in the tantalum-based coating, the greater the surface microhardness. Figure 6. Relationship between the OH ratio, OH ratio, OH ratio, and η and the tantalum atom content in the tantalum-based coating. Tribological properties: The friction and wear test results in the “plowing” condition are shown in Figure 7. Wear marks on the TaON and Ta coatings are only visible under friction conditions. These trajectories demonstrate the effectiveness of the wear-resistant coating on tantalum-based steel. The wear traces on TaN (Figure 7d) and the Ta (Figure 7e) coatings are visible only in the PeakForce Error data type. Figure 7. AFM images of wear test results under a load of 1.164 Newtons, a speed of 2 meters per second, and 100 cycles on steel substrates and tantalum coatings: steel (a), Ta2O5 (b), TaON (c), TaN (d), Ta (e). Figure 8 shows the relationship between CoF and F of the coating during wear in the \"plowing\" mode and the number of friction cycles. Figure 8. Relationship between the obtained friction coefficient and the number of friction cycles for the coatings studied on the steel substrate. “The “sliding” mode better characterizes the effect of adhesion force. The CoF of stainless steel measured in the \"sliding\" mode was 0.072 (Figure 9). After depositing a nanostructured tantalum coating, the CoF decreased to 0.014 for Ta, and 0.019 for TaN and TaON. The CoF of the Ta2O5 coating in the “sliding” mode is 0.041. “The dependence of CoF on the tantalum atom content in the coating exhibits similar behavior in the “sliding” and “plowing” modes (Figure 9). Figure 9. Dependence of h, CoF (sliding), CoF (plowing), kv, and F on the tantalum atom content in the tantalum-based coating. Conclusion Nanoscale tantalum compound films were deposited on a stainless steel substrate using tantalum vapor phase deposition. It has been determined that the microstructure of the coating depends on the elemental composition. All tantalum-based coatings feature a granular structure. Depending on the composition of the coating, the particle size ranges from 5 to 20 nanometers. In some cases (Ta and TaN), the particles combine to form cells. All the obtained coatings had low roughness values. The optimal performance combinations for the coatings studied are TaN (with H at 10.0 GPa, E at 158.0 GPa, and H/E at 0.06) and TaON (with H at 13.3 GPa, E at 157.0 GPa, and H/E at 0.08). The tribological properties of the resulting coating are as follows: 0.019 for the “sliding” mode and 0.308 for the “plowing” mode; the specific volume wear is 4.2×10−13 m3/N·m. For the “sliding” mode, TaON-CoF has a value of 0.019, while in the “plowing” mode it is 0.444; the specific volume wear in this case is 6.1×10−13 m3/N·m. Therefore, the deposition of TaN reduced the specific volume wear of steel by more than 6 times, and that of TaON by more than 4 times. These tribological properties allow for a reduction in platelets on the surface of the stent, thereby preventing the formation of blood clots. Therefore, TaN and TaON coatings with special complex mechanical and tribological properties can be used as the upper layer of stainless steel stents.