EP4775716A1

EP4775716A1 - Method for fabrication of a mechanically stable nanostructured metal surface and a device for manufacturing such a surface

Info

Publication number: EP4775716A1
Application number: EP25151881.7A
Authority: EP
Inventors: Ita Junkar; Metka Bencina; Will Richards
Original assignee: Jožef Stefan Institute
Current assignee: Jožef Stefan Institute
Priority date: 2025-01-14
Filing date: 2025-01-14
Publication date: 2026-07-15

Abstract

The present invention discloses an innovative and highly optimized process for synthesizing nanostructured metallic surfaces by introducing key modifications to traditional surface treatment techniques, specifically electrochemical anodization and non-thermal (low-pressure) plasma treatment. The disclosed procedure overcomes several limitations of conventional methods, such as inconsistent structural quality and limited material compatibility, by strategically enhancing the interaction between the metal substrate and the external treatment environment. By optimizing variables such as voltage, treatment duration, and plasma power, the process facilitates the creation of nanostructures that exhibit significantly improved mechanical properties, including enhanced strength, hardness, and wear resistance. These surface modifications result in materials with superior performance characteristics, making them particularly suitable for use in high-performance applications across a variety of fields, including medical devices, environmental monitoring systems, and industrial components subject to extreme wear and corrosion conditions. The described method offers an advanced, scalable approach to producing high-quality nanostructured metallic surfaces with precise control over morphology, porosity, and surface functionality, thereby opening new opportunities for innovation in the design and manufacturing of advanced materials for both specialized and broad-use applications.

Description

Field of the invention

The present invention concerns a method for manufacturing a mechanically stable nanostructured metal surface and a device for manufacturing such a surface.

Background of the invention

Nanotubular surfaces, especially TiO₂ have been intensively researched, and used in a wide range of applications, e.g., water splitting, sensors, photovoltaics, photocatalysts, and electronic devices (Kim M. et al., J Mater Chem 2021, 9:2239-2247, Kim S, J Phys Chem C 2015, 119:21497-21503). The field of nanostructured metallic surfaces, particularly those demonstrating mechanically stable characteristics such as nanoporous and nanotubular configurations, has become a cornerstone in modern material science and engineering. This is notably evident in the utilization of titanium-based materials, high entropy alloys (HEA) and various stainless-steel grades such as 304 and 316(L), which are at the forefront of these advancements. The superior properties associated with these nanostructured surfaces are increased mechanical stability, augmented surface area, enhanced biocompatibility, and corrosion resistance, which provide a substantial foundation for their application across diverse industrial sectors, including biomedicine, driving innovation and improving the efficacy of traditional materials.
In the field of (bio)medicine, the invention and application of nanostructured surfaces represent a significant advancement, especially in the development and enhancement of medical implants (Park J, Nano Lett 2007, 7:1686-1691). Nanostructured materials, engineered with precision to display distinct porous or tubular configurations, exhibit good biocompatibility as an essential characteristic for any substance intended for implantation within the human body. These kinds of materials also provide increased available surface area for cellular interaction, which is beneficial in enhancing the adhesion and proliferation of cells, such as endothelial cells or osteoblasts (the bone-forming cells). In this case, the elevated cellular activity not only accelerates the healing process but also fortifies the bond between the implant and the surrounding bone tissue, crucial for the implant's success and longevity. The structured nanopores and nanotubes mimic the natural architecture of bone, making them an ideal scaffold for bone regeneration and integration, thereby facilitating a more natural and efficient healing process. Moreover, nanostructured surfaces also allow for controlled drug release, a feature that can be harnessed to further reduce infection rates and promote healing. By embedding therapeutic agents directly into the nanoporous structure, localized delivery can be achieved directly at the implant site, offering another layer of post-operative protection and facilitating quicker recovery times.
Furthermore, the mechanical stability inherent in these nanoengineered surfaces is of paramount importance. The bodily environment is one of dynamic stresses and strains, particularly in the context of load-bearing implants such as hip replacements or dental roots. The robust nature of these nanostructured materials ensures they can withstand the continuous biomechanical stresses exerted by the human body without compromising their structural integrity. By enhancing the natural bonding process between the implant and the bone, the nanoengineered surfaces of this invention ensure that the implants are not only more likely to be successfully integrated into the biological system but also to sustain their functionality over an extended period, reducing the likelihood of implant rejection or failure. The interface created by nanostructured surfaces presented herein and the biological environment markedly decrease the risk of post-surgical complications, particularly infections, which are a significant concern, especially following orthopaedic and dental procedures. Consequently, this diminishes the patient's need for revision surgeries, which are not only costly but also present additional risks and discomforts to the patient.
In the energy sector, nanostructured metal surfaces are important features of the design and performance of components in fuel cells, batteries, and solar panels. The enhanced surface area of nanoporous or nanotubular materials increases the electrochemical activity, thereby improving the efficiency and energy density of these devices. This is particularly critical as the global demand for sustainable and clean energy sources continues to escalate. Furthermore, the mechanical stability of these nanostructures under extreme operational conditions, such as high temperatures and corrosive environments, ensures the longevity and reliability of energy systems, which is vital for economic and environmental sustainability.
Moreover, in environmental engineering, for example, these materials are being utilized in water treatment and filtration systems to remove pollutants and pathogens with unprecedented efficiency. The unique properties of nanoporous and nanotubular surfaces, including their large surface-to-volume ratios and tailored chemical functionalities, enable the selective adsorption and breakdown of contaminants, thereby contributing to the provision of clean and safe water resources.
Several patent applications focus on the development of nanostructured surfaces, including nanoporous and nanotubular morphologies. For example, EP3496776A1 ( WO2018029166A1 ) outlines a method for generating a specific morphology of a nanotubular matrix, particularly one containing titanium dioxide (TiO₂), aimed at reducing the adhesion and activation of platelets on medical devices. This is achieved through conventional electrochemical anodization. The method resulted in surfaces that are significantly beneficial for devices in contact with blood, such as stents and artificial heart valves, thereby aiming to mitigate thrombus formation on the surface of the implant material. The unique aspect of this technique is its reliance solely on electrochemical anodisation, using a platinum (Pt) electrode as the cathode and a titanium-based material as the anode, notably excluding any form of plasma treatment during nanotube formation The surfaces produced by this method are specifically designed to enhance the biocompatibility and safety of blood-contacting medical devices.
Similarly, US20180228937A1 discloses the formation of biocompatible nanostructures on the surface of metallic, ceramic, or polymer materials. Thus, US20180228937A1 discloses the creation of biocompatible nanostructured articles aimed at enhancing surface areas for tissue and cell growth, suitable for both in vitro testing and in vivo implantation. It involves a synthesis method that includes the application of a biocompatible layer with nanotubes onto substrates through lithographic pattering or by thin-film deposition followed by chemical etching or electrochemical anodization process to optimize the structures for enhanced cell compatibility and growth. This method is particularly relevant for medical applications such as dental, spinal, and orthopaedic implants. However, the method outlined in US20180228937A1 differs from the present invention among others as it does not incorporate atmospheric plasma treatment according to the present invention.
US20110159273A discloses a method for coating medical device surfaces, including implants, with micro- and nanoparticles (like silver and titanium dioxide nanoparticles, diamond, hydroxyapatite, and nanostructured aluminium oxide) using a non-thermal low-pressure plasma technique. This method, employing carrier gases like O₂ and Ar, fixes nanoparticles to medical device surfaces to reduce microorganism adhesion. The core process involves non-thermal low-pressure plasma treatment. The claims focus on the structure, composition, and application of biocompatible materials for medical devices and implants, but they do not explicitly address mechanical stability. Moreover, plasma method is in this case used for surface pre-treatment and subsequent fixation of micro and nanoparticles, which is not the same as in our approach, where nanostructure is formed from the substrate layer with the aid of plasma activated electrolyte.
In US6006763A , a surface treatment method for substrates is described, utilizing a gas discharge at or around atmospheric pressure to produce activated gas or active species for treatment. Depending on the gas used, this method can either form a metal oxide film on a substrate's metal circuit (using oxygen) or reduce a metal oxide film, such as on liquid crystal panel transparent electrodes (using hydrogen or organic substances). The technique also introduces a unique approach by treating surfaces with activated liquid, generated by exposing a liquid to the discharged active species, thus avoiding thermal or electrical substrate damage. This activated liquid can be applied through immersion or spraying, providing flexibility in surface treatment processes. The present invention differs at least in that the modified surface functions as a second electrode, meaning the modification is not merely achieved through active species created in the liquid. Instead, according to the present invention a combination of electrochemical anodization and active species created by the atmospheric pressure plasma is provided, which is at the same time used as a second electrode.

The object of the present invention

The object of the present invention is providing of a mechanically stable metal surface comprising a nanotubular morphology.

Summary of the present invention

This problem is solved by the appended independent claims. Preferred embodiments of the invention are defined by the dependent claims.
According to the present invention a method for manufacturing a mechanically stable nanostructured metal surface is provided. The method comprises immersing a metal surface in a liquid electrolyte and subsequently depositing a nanostructured oxide layer on the metal surface by using a combination of electrochemical anodization and atmospheric pressure plasma treatment is provided, wherein according to the invention the plasma electrode acts as a cathode and generates atmospheric pressure plasma to activate the electrolyte and facilitate the formation of the nanostructured oxide layer, characterized in that the generated atmospheric plasma simultaneously activates the electrolyte and ensures formation of the nanostructured oxide layer.
Therefore, an advantageous synthesizing procedure, highlighting the strategic modifications and optimizations introduced to traditional methodologies, which offers an advanced approach for the fabrication of nanostructured metallic surfaces with improved mechanical stability/strength and environment more friendly approach. Such nanostructured materials are suitable for a wide range of applications in medical, environmental, and industrial fields.
Furthermore, the present invention discloses a synthesizing procedure for creating mechanically stable nanostructured surfaces, including nanoporous and nanotubular geometries, on metallic substrates, including Ti-based materials, HEA and various grades of stainless steel.
Advantegeusly the procedure according to the invention embodies an advanced, comprehensive approach that significantly enhances nanostructured surface mechanical stability compared to traditional fabrication techniques, including anodic oxidation, chemical vapor deposition (CVD), and electrochemical deposition. Optimization and integration of the method in accordance with the present invention surpass the limitations commonly associated with standard practices, leading to the development of nanostructured metallic surfaces with unprecedented mechanical stability.
Therefore, a fabrication of mechanically stable nanotubular surfaces is ensured, which could not be achieved by a conventional electrochemical anodization process. Furthermore, the present invention reduces the burden of harsh chemicals used for fabrication of nanotubes by conventional electrochemical anodization process, as well as reduces the time for their fabrication.
Advantageously the present invention uses at least 10 times lower concentrations of harsh chemicals (like Fluorine based chemicals; NH₄F, NH₄Cl, NaF, NH₄HF₂ and HF), while the fabrication process is at least 10 times faster.
Hence, a novel fabrication procedure with mechanically stable nanostructure and rapid fabrication process can be used for a variety of applications ranging from biomedicine (implants, sensors etc.) to industrial applications (photovoltaics, catalysis, batteries etc.).
However, according to the present invention a method for the preparation of a nanostructured, mechanically stable metallic surface made from Ti based alloys, HEA or stainless steel, is disclosed. This can be realized through the integration of a novel setup of electrochemical anodization and atmospheric plasma technique. The process according to the present invention allows to use lower concentration of electrolyte with much shorter treatment time. Due to plasma activated electrolyte and electrochemical anodization at the same time fabrication of nanoscale morphology (nanoporous or nanotubular) on the surface of metallic materials with superior mechanical properties, is achieved.
The mechanical stability of nanostructures on surfaces is frequently a critical factor in determining their durability and functional lifespan. This stability is essential for maintaining the integrity of the nanostructures under various environmental conditions and mechanical stresses. Consequently, ensuring this stability is paramount for applications in fields such as biomedical devices, sensors, and advanced coatings, where consistent performance and reliability are required. Continuous advancements in materials science and engineering are directed towards enhancing this stability to meet the rigorous demands of modern applications.
The standard according to known prior art procedure for electrochemical anodization often involves the use of platinum as the cathode material due to its excellent conductivity and corrosion resistance. Additionally, hydrofluoric acid (HF) is frequently utilized in this method. Role of HF is critical as it helps in removing oxides from the metal surface, thereby facilitating the formation of a more uniform and controlled nanostructure. In the present invention, a plasma electrode was utilized as the cathode. Argon (Ar), helium (He) or even air serve as gases for plasma generation and activation of the electrolyte. Ammonium fluoride (NH₄F) and ethylene glycol are commonly used as an electrolyte. The unique approach of manipulating inter-tubular spacing in nanostructured materials, particularly those forming nanopores or nanotubes, significantly contributes to their mechanical stability. By adjusting the spacing between these nanostructures, it is possible to engineer materials with nano topographic features that possess internal diameters ranging from 5 to 200 nm, according to an embodiment.
This precision in structural control not only tailors the physical properties of the materials but also markedly enhances their mechanical stability, which is not achieved by conventional electrochemical anodization. Despite the lack of well-defined inter-tubular spacing, the closer proximity and plasma assisted growth of these nanostructures plays a crucial role in reinforcing the material against mechanical stress. This configuration according to embodiments of the present invention minimizes the risk of structural collapse and deformation, thereby preserving the integrity and functionality of the material under various conditions. The ability to sustain these nano topographic features with exceptional mechanical stability opens up new avenues in the development of advanced materials for applications requiring high durability and reliability, including but not limited to, biomedical implants, sensors, and filtration systems. The interplay between nanostructure arrangement and mechanical properties exemplifies the potential of nano-engineering in achieving materials with superior performance characteristics.
In addition, fabrication of nanotubular structures by conventional electrochemical anodization process is subjected to the use of fluoride-based electrolytes, such as hydrofluoric acid (HF), ammonium fluoride (NH₄F) or sodium fluoride (NaF) where its concentration ranges from 0.1 to 1 wt%. In the case of present invention or in a preferred embodiment, accordingly, the concentrations can be at least ten times lower (0.01 to 0.1 wt%). Moreover, the treatment time in standard electrochemical anodization is between 1 to 3 h, while in the case of the present invention, treatment time is about ten times lower (5 to 20 min) for achieving the same length of nanotubes.
Thus, according to the invention, the use of fluoride-based electrolytes in much lower concentration is enabled, and further faster process and high reusability of the electrolyte in ensured, which overall reduces environmental impact.

Brief description of the drawings

The invention is herein described, by way of example, concerning the accompanying table/drawings, wherein:

Fig. 1: illustrates the side view of nanotubular structured formed on Ti prepared by an approach (Example 2) in accordance with the present invention, analysed by SEM. The cross-sectional view SEM images reveal the formation of highly uniform U-shaped titanium oxide nanotubes with smooth walls and a consistent well-defined arrangement that is a direct result of the optimized synthesis process according to the invention.
Fig. 2: illustrates the surface morphology of titanium oxide nanotubes prepared by conventional electrochemical anodization process (cf. Example 1) after the bending test, explained with reference to Example 3. After the bending test the titanium oxide nanotubes prepared by conventional electrochemical anodization process the nanotubular structure is damaged as cracks between the areas of nanotubes are observed.
Fig. 3: illustrates the surface morphology of the Ti nanotubes/nanopores prepared by the application of the method according to the present invention after the bending test, explained in Example 3. The SEM analysis reveals that the fabricated nanotubular structures prepared by the invention method are completely stable on the surface after bending test. In the case of nanotubes/nanopores prepared by the method of the invention, the morphology was only slightly fractured, but no substrate was exposed.
Fig. 4: schematic representation of the electrochemical anodization and atmospheric pressure plasma treatment, wherein the plasma electrode 1 acts as a cathode and the sample acts as anode 2. The plasma source generates reactive species which simultaneously activate the electrolyte 3 and ensure formation of the nanostructured oxide layer on the sample 1. The atmospheric pressure plasma source is connected with gas inlet (4) to allow plasma generation.

Detailed description of the invention

Against state-of-the-art, the method of the invention enables the formation of a mechanically stable oxide layer consisting of nanoporous/nanotubular morphology on the surface of Ti-based or high entropy alloys or stainless-steel substrates/foils. The morphology of the surface after treatment with the method of the invention was examined by Scanning Electron Microscopy (SEM) and the side view is shown in the Figure 1 to observe the formation of nanotubes formed on the surface.
In EP4467167A1 , the method for treatment of Ti and Ti alloys used for implants/medical devices, especially vascular stents, is described. The first step is the surface treatment of Ti and Ti alloys with electrochemical anodization and atmospheric plasma electrode in environmentally friendly electrolytes, the second step is UV treatment of the surfaces to activate the surface and to ensure an enhanced biological response. The process is done within the liquid (solely deionized water and/or additional salts like NaCl, KCI, phosphate buffer saline (PBS) and/or ethylene glycol, NaOH, glucose and/or natural extracts and combinations thereof with a pH value preferably in a range between 7 to 13 and a temperature value preferably in a range between 0 and 50 C°, preferably between 15 and 25 C°). The methods described in the patent application ( EP4467167A1 ) differ from the method described herein in several key steps:

i.) The media/electrolyte solution in the present invention are completely different and are similar to electrolytes used for fabrication of nanotubes or nanopores by conventional electrochemical anodization, while their concentration is much lower. Such electrolyte composition enables appropriate activation of electrolyte by plasma that allows for the uniform formation of mechanically stable nanotubes or nanopores, which is not possible with the conventional electrochemical anodization nor with method described in EP23175524.0 .
ii.) The fabricated surface topography on the anode (substrate material) is completely different to the invention EP23175524.0 , where nano-structured titanium oxide layer consists of micro and/or nano-flowers. In the case of the present invention, nanotubes or nanopores are fabricated on the surface of metallic materials.
iii.) The present invention deals with the mechanical stability of a nanostructured (nanoporous/nanotubular) layer on the surface of metallic substrates/materials, due to a specific interaction with plasma activated electrolyte and substrate, which enables growth of mechanically stable nanotubes or nanopores. This is of high relevance for numerous industrial and medical applications and could not be achieved in the case of the method described in EP23175524.0 nor in case of conventional electrochemical anodization process.

From the SEM images, it can be seen that the morphology of the surface after treatment by the method of invention is nanoporous/nanotubular. The innovative technique involves the use of electrochemical anodization combined with atmospheric plasma. The disclosed technique enables the formation of a high-quality nano-structured oxide layer on the surface of the said metallic substrate, which significantly influences the mechanical stability. The fabricated nanostructure according to embodiments of the present invention decreases the likelihood of structural collapse under mechanical stress or during manipulative processes, ensuring greater durability and resilience of the material compared to conventional electrochemical anodization process. Such improved mechanical properties are especially beneficial in applications where materials are subjected to rigorous conditions, including various engineering and biomedical uses.
The enhanced mechanical stability of fabricated nanostructured features positions these materials as prime candidates for the development of robust, high-performance devices and implants, highlighting their importance in advancing material science and technology.
The electrochemical anodization cell can be constructed from inert materials such as Teflon, quartz glass, or similar substances to ensure chemical resistance. At the base of the cell, the anode, which is the substrate material 2, is positioned. The atmospheric pressure plasma apparatus is engineered with several key components: a radio frequency (RF) step-up transformer coupled with an RF power supply or any other discharge to enable atmospheric pressure plasma; alternating-current (AC), direct current (DC), microwave discharge (MW), dielectric barrier discharges (DBD) and a tube, usually in the form of metallic tube positioned within the glass tube, which functions as an electrode (cathode). Additionally, the system incorporates a gas supply mechanism designed to regulate the precise flow rate of gas, predominantly argon or another noble gas, or a mixture thereof with air, oxygen, or nitrogen, ensuring optimal performance and efficiency. The material targeted for treatment, whether titanium alloy or high entropy alloys or stainless steel, acts as the anode within the system. In the cell the material targeted for treatment is submerged in the electrolyte solution; Ethylene Glycol or similar (Propylene Glycol, Diethylene Glycol, or Glycerol) and/or fluorine-based electrolytes such as Ammonium Fluoride (NH₄F), NH4CI, NaF, NH₄HF₂, and HF, or acids, and other electrolytes (like Perchloric acid (HClO₄), Sulfuric Acid (H₂SO₄), Phosphoric Acid (H₃PO₄), Chromic Acid (H₂CrO4), Oxalic Acid (C₂H₂O₄), Hydrochloric acid (HCl), Acetic acid (CH₃COOH), and Boric Acid (H3BO3), and combinations thereof, which due to plasma activation (cathode) enables simultaneous formation of mechanically stable nanotubes during anodization.
Utilizing this technique results in the formation of an oxide layer on the surface, characterized by densely packed nanopores or nanotubes. This method effectively creates a structured layer where the nano features are closely arranged, enhancing the surface's physical and functional properties. The process may be performed at room temperature or any convenient temperature which prevents thermal damage to the substrate. The surface of the metal is exposed to activated species from plasma and is used as an anode, which allows the surface to be oxidized and nanostructured.

Example 1: Ti substrate/foil treated with conventional electrochemical anodisation

Preparation of nanotubular structure on metal substrates by the conventional electrochemical anodisation method: Titanium (Ti) foils (0.1 mm thick, 99.6% purity) were used to create various nanostructures. Initially, the foils were cleaned using ultrasonication in acetone, ethanol, and deionized water for 5 minutes each, then dried with nitrogen. Nanostructured surfaces were produced using a previously described method (Junkar, Ita, et al. "Titanium dioxide nanotube arrays for cardiovascular stent applications." ACS omega 5.13 (2020): 7280-7289). Briefly, electrolytes based on ethylene glycol (≥99.5%) with added water and hydrofluoric acid (≥40%) were utilized for nanostructure formation. Anodization was performed at room temperature using a platinum gauze counter electrode. Afterward, the nanostructures were immersed in ethanol for 2 hours to eliminate organic residues, rinsed with distilled water, and dried under nitrogen. The morphology of the nanotubular structure on metal substrates by the conventional electrochemical anodisation method can be find elsewhere (Lee K, Mazare A, Schmuki P, Chem Rev 2014, 114:9385-9454).

Example 2: The method of invention

Preparation of nanotubular/nanoporous structure on metal substrates by the method of invention: Ti substrate was put into the electrolyte cell filled with the electrolyte. In this example the electrolyte was a solution of 0.1 % NH₄F in Ethylene Glycol (with 1.7 % d.H₂O). Ti substrate was anodized at 20 V for 30 minutes with atmospheric pressure plasma being operated at 12 A and 16 V with a flow rate of 1.0 sccm for argon gas. After the treatment, samples were thoroughly washed with deionized water and ultrasonicated for 5 min and temperature at 25 degrees Celsius. The surface exhibited nanotubular topography as seen in Fig. 1 .

Example 3: Bending tests; Ti substrate/foil treated with conventional electrochemical anodisation and the method of invention - mechanical performance

The mechanical stability of the nanotubular structure was assessed via a bending test. The bending test evaluates the mechanical performance of as-prepared nanotubular structures on the titanium (Ti) substrate after treatment through conventional electrochemical anodization and a novel method. In this test, the foil is subjected to bending using forceps to assess its mechanical properties.
Nanotubular structure prepared by conventional method was not structurally stable after bending test. It is clearly seen from Fig. 2 that the Ti foil is exposed over a large area, and the nanotubular structure is damaged (cracks between the areas of nanotubes are observed). In the case of nanotubes/nanopores prepared by the method of the invention ( Fig. 4 ), the morphology was only slightly fractured, but no substrate was exposed ( Fig. 3 ).
It is to be noticed that the term "comprising", used in the claims and description, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, it is to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features.
Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

Claims

A method for manufacturing a mechanically stable nanostructured metal surface (2), comprising:
a. immersing a metal surface (2) in a liquid electrolyte (3);

b. depositing a nanostructured oxide layer on the metal surface (2) by using a combination of electrochemical anodization and atmospheric pressure plasma treatment, wherein the plasma electrode (1) acts as a cathode and generates atmospheric pressure plasma to activate the electrolyte (3) and facilitate the formation of the nanostructured oxide layer, characterized in that the generated atmospheric plasma simultaneously activates the electrolyte (3) and ensures formation of the nanostructured oxide layer.
The method of claim 1, wherein the liquid electrolyte comprises of water and Ethylene Glycol or similar; Propylene Glycol, Diethylene Glycol, or Glycerol and fluorine-based electrolytes such as Ammonium Fluoride (NH₄F), NH₄Cl, NaF, NH₄HF₂, and HF, or acids, and other electrolytes like Perchloric acid (HClO₄), Sulfuric Acid (H₂SO₄), Phosphoric Acid (H₃PO₄), otho-phosphoric acid, Chromic Acid (H₂CrO₄), Oxalic Acid (C₂H₂O₄), Hydrochloric acid (HCl), Acetic acid (CH₃COOH), and Boric Acid (H₃BO₃), and combinations thereof with a pH value in a range between 2 to 13 and a electrolyte temperature value preferably in a range between 0 and 50°C, preferably between 15 and 25°C.
The method of claims 1 or 2, wherein the metal surface is selected from the group consisting of titanium, titanium-based alloys, stainless steel (including types 304, 316 and 316L), and high entropy alloys (composed of multiple principal elements, including cobalt, chromium, iron, manganese, nickel, aluminum, titanium, zirconium, hafnium, niobium, tantalum, and tungsten.).
The method according to one of the preceding claims, wherein the cathode generating atmospheric pressure plasma is an atmospheric pressure plasma source device, which may operate at different discharge setups that allow for production of stable gas discharge, whereby an electrical connection between the grounded metal surface and the plasma cathode is provided.
The method according to one of the preceding claims, wherein the gas for generation of the atmospheric pressure plasma is Ar, He, other noble gas, air, oxygen (O2), nitrogen (N2) or a or different combinations thereof.
The method according to one of the preceding claims, wherein the immersing of the metal surface in the liquid provides a coating of the surface with the nanoporous/nanotubular structured oxide layer, where the size of the pores varies from 5 to 200 nm.
The method according to one of the preceding claims, wherein the nanostructured oxide layer comprises a nanoporous or nanotubular morphology with internal diameters ranging from 5 to 200 nm.
The method according to one of the preceding claims, wherein the nanostructured oxide layer is formed with nanopores and nanotubes to enhance the surface physical and functional properties.
The method according to one of the preceding claims, further comprising subjecting the fabricated nanostructured oxide layer to ultrasonication in deionized water to assess mechanical stability.
A device for fabricating a mechanically stable nanostructured metal surface (2), comprising:
a. a liquid electrolyte (3) container;

b. an electrochemical anodization setup for immersing a metal surface in the liquid electrolyte;

c. an atmospheric plasma treatment apparatus with a plasma electrode (1) acting as a cathode for generating atmospheric pressure plasma to simultaneously activate the electrolyte and facilitate the formation of a nanostructured oxide layer on the metal surface.
The device of claim 10, further comprising a gas supply mechanism (4) for regulating the flow rate of gas, wherein the gas is selected from the group consisting of Ar, He, other noble gas, air, oxygen (O2), and nitrogen (N2) or different combinations thereof for generation of the atmospheric pressure plasma.
The device according to any of the claims 10 or 11, wherein the electrochemical anodization setup includes an anode for positioning the metal surface and a platinum gauze counter electrode.
The device according to any of the claims 10 to 12, further comprising a plasma source device operating at radiofrequency (RF) or other discharges like but not limited to direct barrier discharge (DBD), alternating-current (AC), direct current (DC) or microwave (MW) discharge for generating the atmospheric pressure plasma, where the voltage between the grounded metal surface and the plasma cathode is between 10 and 60 V.
Nanostructured metal surface manufactured by the method according to claims 1 to 9.