METHOD FOR ELECTROCHEMICAL SURFACE TREATMENT OF BIOMEDICAL PRODUCTS MADE OF TITANIUM OR TI-BASED ALLOYS

Abstract

 The invention relates to the method for electrochemical surface treatment of biomedical product made of titanium or Ti-based alloys characterized in that it comprises the steps: Immersion of the degreased and cleaned biomedical product into the electrolyte consisting of Reline or Glyceline; galvanostatic etching treatment of the biomedical product at the current density 1 to 20 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 5 V for 5 to 60 min. at a temperature 15 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 6 to 30 V for 5 to 60 min. at a temperature 15 to 40 °C; and subsequent cleaning of the biomedical product from electrolytes residuals.

Description

Technical field

[0001] The invention relates to the technical field of electrochemical surface treatment of biomedical products based on Ti and Ti-alloys.

Background art

[0002] Ti and Ti-alloys remain the most common materials for the manufacture of prostheses and implants. However, titanium and its alloys cannot meet all clinical requirements without a special pretreatment of their surfaces. Therefore, preliminary surface treatment (modification) of biomedical Ti-based alloys is often performed in order to improve the biological, chemical, and physical-mechanical properties. The common types of these surface modifications are associated with mechanical, laser, chemical and electrochemical surface treatments and also with combinations of these techniques. Electrochemical surface treatment method is generally considered as one of the most efficient, convenient and adaptable technique for improvement of the physical-mechanical surface properties of titanium and titanium-based alloys [1].

[0003] Usually, the process of electrochemical surface treatment of titanium alloys is carried out in electrolytes based on concentrated acids (e.g., H₂SO₄, HF, H₃PO₄, HNO₃, HClO₄, etc.) and alcohols mixtures. These electrolytes are environmentally hazardous, toxic and sometimes explosive. It is obvious that the use of highly concentrated acidic electrolytes is not only environmentally unsafe, but also dangerous for humans. In this regard, the search for environmentally friendly and safety alternatives to the classical acidic electrolytes for electrochemical surface treatment of Ti and Ti-alloys is important and relevant [2].

[0004] Recently, the environmentally friendly solvent Ethaline has been proposed as an alternative to the most-common acidic electrolytes for the electropolishing of titanium alloys [3]. Despite the numerous positive properties, use of Ethaline in electrochemical surface treatment of titanium alloys has several disadvantages, such as poor reproduction of the electropolishing results, which in some cases leads to the subpar quality of the processed surfaces, and insufficient effectivity of the process.

[0005] The aim of this invention is to provide electrolytes for electrochemical surface treatment of titanium alloys prostheses and implants that are environmentally friendly, highly efficient and gives a reliably repeatable results, that are also cheap, easy to prepare, easily biodegradable.

Summary of the invention

[0006] This invention relates to the surface modification of biomedical Ti and Ti-alloys in deep eutectic solvent Reline or Glyceline at room temperatures without additional heating or cooling.

[0007] Reline is a eutectic mixture of choline chloride (vitamin B 4) and urea in molar ratio of components 1:2, respectively.

[0008] Glyceline is a eutectic mixture of choline chloride (vitamin B 4) and glycerol in molar ratio of components 1:2, respectively.

[0009] All mentioned chemicals (vitamin B 4, urea and glycerol) in Reline and Glyceline individually and their mixture are environmentally friendly.

[0010] For highly efficient electrochemical surface treatment (electropolishing or electrochemical surface etching) the formation of viscous near-electrode surface layer plays key role due to the crucial place of diffusion control in etching and polishing processes. It has been found out that a thickness and density of the near-electrode viscous layer suitable for high processing efficiency can be achieved for deep eutectic solvents with higher viscosity (density). The more viscous the electrolyte, the faster the formation of a near-electrode layer of suitable thickness and density is achieved. Moreover, the higher the viscosity and density of the electrolyte the more stable surface layer is formed. In this connection the mixtures such as Reline or Glyceline, that have relatively high density and also high viscosity at the room temperature are eminently suitable to be used as electrolytes for the electrochemical surface treatment according to this invention. The density of Reline is 1.24 g cm^-3 and viscosity is 750 cP (at 25 °C), the density of Glyceline is 1.19 g cm^-3 and viscosity is 259 cP (at 25 °C) (for comparison, the same parameters for Ethaline is 1.12 g cm^-3 and 37 cP, respectively).

[0011] It was discovered that the second important factor, which can increase the efficiency of electropolishing or electrochemical etching, is a change in the mechanism of electrochemical processes (a decrease in the activation energy due to a change in the nature of intermediate particles, a decrease in the number of stages in the overall electrochemical reaction, etc.). The deep eutectic solvents Reline and Glyceline, which contains urea and glycerol, except ethylene glycol that component of Ethaline, will provide formation of the intermediate complexes with different nature (urea and glycerol Ti - containing complexes, except ethylene glycol Ti - containing complexes in Ethaline).

[0012] Furthermore, it has been found out that absorption of water from the air causes spontaneous changes in the composition of the electrolyte and its properties. Water can interact with both hydrogen bond donors and hydrogen bond acceptors of deep eutectic solvents and then break down the hydrogen bond interactions between organic salt and hydrogen bond donors by forming a multi-hydrogen bonds with the hydrogen bond donors. Thus, water adsorption can change physical and chemical properties of deep eutectic solvents. An uncontrolled change in the composition of the electrolyte can lead to poor reproduction of the electropolishing results and to a decrease in the quality of the processed surfaces. Thus, using a mixture with low hygroscopicity such as Reline, in the treatment according to the invention, leads to high-quality of the processed surfaces and also to a higher reproducibility of the results.

[0013] The method for electrochemical surface treatment of biomedical products made of titanium or Ti-based alloys according to the present invention comprises the steps:

• Immersion of cleaned and degreased biomedical product into the electrolyte consisting of Reline or Glyceline,
• Galvanostatic etching treatment of the biomedical product at the current density 1 to 20 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 5 V for 5 to 60 min. at a temperature 15 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 6 to 30 V for 5 to 60 min. at a temperature 15 to 40 °C,
• Subsequent cleaning the biomedical product from electrolyte residuals.

Preliminary cleaning and degreasing of prostheses and implants surface before proposed electrochemical treatment is must be done. Such cleaning can be performed in ultrasonic water bath with 1-5 weight % of caustic soda during 5-10 min. at 40-60 °C followed by frequent rinsing with water and drying in a stream of hot air until completely dry.

[0014] Subsequent cleaning from electrolyte residuals after proposed electrochemical treatment can be performed in water ultrasonic bath during 5 to 15 min. and air drying until the water has completely evaporated.

[0015] Proposed electrochemical method of surface treatment of biomedical Ti and Ti-alloys in Reline or Glyceline is a highly efficient and eco-friendly technic for the surface properties enhancement. This kind of treatment allows improving the surface chemistry, morphology, topography and such surface properties as wettability, corrosion resistance and bio-compatibility, which is very important for Ti and Ti-alloys for biomedical application.

[0016] Reline has melting point 12 °C, so at room temperatures it is a colorless transparent liquid with numerous attractive characteristics, such as cheapness, safety, non-toxicity, non-volatility, thermal stability, non-flammability, sustainability, and biodegradability. Melting point of Glyceline is -44 °C, thus, at all temperatures higher than -44°C this eutectic mixture is liquid.

[0017] Reline and Glyceline possess noticeable benefits in comparison with ordinary acidic electrolytes, such as high effectivity, eco-friendliness, low coast, resource-saving, low corrosivity towards steel equipment and human health safeness. Moreover, Reline and Glyceline have significant advantages as electrolytes for the electrochemical treatment in comparison with Ethaline, such as higher density and viscosity, higher biodegradability and lower price. Additionally, Reline is characterized by significantly lower hygroscopicity in comparison with Ethaline.

[0018] Higher density and viscosity are playing an important role in formation of suitable conditions for the mass transfer of particles involved in the electrochemical reactions. In this connection physicochemical properties of Reline or Glyceline are more preferred for electrochemical processing of Ti and its alloys in comparison with Ethaline.

[0019] The key factor for the biodegradability of deep eutectic solvents (DESs) is the neutrality of each hydrogen bond donor and acceptor, which produces a natural DESs mixture and can be easily metabolized by bacteria and fungi. Biodegradability of Glyceline reaches 100 % in 28 days, Reline reaches 97.1 % in 28 days. In comparison, biodegradability of Ethaline is 81.9 % in 28 days. Thus, from ecological point of view, the industrial use of Reline or Glyceline is preferable.

[0020] The comparative characteristic of physicochemical and bio properties of deep eutectic solvents Glyceline, Reline and Ethaline is presented in Table 1.

[0021] It must be also noted also that Glyceline and Reline are cheaper in comparison with Ethaline.

Table 1. Comparative characteristic of physicochemical and bio properties of deep eutectic solvents Glyceline, Reline and Ethaline.

Eutectic mixture	Density (ρ), g cm-3	Viscosity (η), cP	Biodegradability, % in 28 days
Glyceline	1.19	259	95.9-100
Reline	1.24	750	97.1
Ethaline	1.12	37	81.9

[0022] The important parameter of solvents such as a vapor pressure also for Glyceline electrolyte is better (lower) in comparison with other deep eutectic solvents (table 2), it is mean that Glyceline evaporates less compared to others DESs (Ethaline and Reline).

Table 2. Vapor pressure of Glyceline, Ethaline and Reline at 30 °C.

Eutectic mixture	Vapor pressure / P, mm Hg
Glyceline	27.9
Ethaline	29.9
Reline	30.6

[0023] The mechanism of electrochemical treatment of Ti and Ti-based alloys in Ethaline related with electrooxidation of Ti and formation one-dimensional Ti-glycolate complexes. The mechanism of electrochemical treatment of pure titanium and Ti-alloys in Glyceline and Reline is different from that, which observed for Ethaline.

[0024] Electrooxidation of Ti in glycerol enriched media (Glyceline) probably takes place with formation of Ti-glycerolate complexes like intermediate state for Ti²⁺, Ti³⁺ stabilization before complete oxidation to the Ti⁴⁺. The possibility of existence of Ti - glycerolate complexes in glycerol containing media is discussed previously in [4, 5].

[0025] The mechanism of titanium and Ti-alloy electrooxidation in Reline is as follows. Urea as one of the main Reline components involves in formation of urea coordinated Ti complexes. The principle possibility of formation urea coordinated titanium trichloride complexes is already known [6]. Thus, a possible intermediate stable product of titanium electrooxidation in Reline is the complex Ti(III)[OC(NH)₂]6Cl₃. In addition, urea can be coordinated in complex with titanium tetrachloride as TiCl₄·2Urea [7]. For urea and its derivatives, the coordination to titanium (IV) is always through the oxygen atom. According to the mentioned previously facts probably several types of complexes can be founded during Ti and Ti-alloy electrochemical surface treatment in Reline (titanium trichloride and titanium tetrachloride urea complexes).

[0026] The proposed electrochemical treatment of bio-medical Ti and Ti-alloys in Reline or Glyceline can be realized in two different modes: potentiostatic (constant potential) and galvanostatic (constant current). Galvanostatic treatment is recommended for biomedical protheses and implants with well-known surface area and potentiostatic one for biomedical products with very complex shape, for which accurate measurement of the surface area is difficult or impossible.

[0027] The procedure of galvanostatic surface treatment realizes in two electrode system, where working electrode is Ti or Ti-alloy prosthesis or implant and counter electrode is Pt-grid or graphite with surface area comparable to the workpiece. Reline or Glyceline is used as an electrolyte for surface treatment. The volume of Reline/Glyceline can be variated depending on size of titanium bio-medical product.

[0028] The optimal time of treatment (5-60 min.) can be variated depending on initial state of Ti or Ti-alloy product (initial roughness, contamination, etc.).

[0029] For the best processing results prosthesis or implant must be located in electrochemical cell (bath) coaxially relative to the counter electrode, in this case the distance between all points of the workpiece and the counter electrode is approximately the same and current distribution uniform.

[0030] Electrochemical surface treatment must be carried out at temperature interval 15-40 °C. At temperatures below 15 °C it is possible local crystallization processes, which will change the electrolyte composition; at temperatures higher than 40 °C the conditions of the dissolution process will be changed from mass transfer controlled, which will lead to a significant deterioration in the processing result.

[0031] The procedure of potentiostatic surface treatment (treatment under constant potential, voltage) realizes in three electrode system, where working electrode is Ti or Ti-alloy prosthesis or implant, counter electrode is Pt-grid or graphite with surface area comparable to the workpiece and reference electrode is Ag - wire, the electrode relative to which the potential in electrochemical cell is measured and controlled. For potentiostatic treatment can be used the same like for galvanostatic treatment volume of electrolyte, temperatures and time of treatment depending on desired result of surface morphology. The potential (E [V]) during the treatment procedure controls by potentiostat.

[0032] For electrochemical surface etching processing current densities is 1-20 mA cm^-2; for electropolishing is 25-100 mA cm^-2.

[0033] In potentiostatic mode of treatment etching potentials is 1-5 V; for electropolishing is 6-30 V.

[0034] Notice that for the best processing results in potentiostatic mode prosthesis or implant must be located in electrochemical cell (bath) coaxially relative to the counter electrode the same like for potentiostatic treatment.

[0035] Summarized parameters of electrochemical treatment of Ti and Ti-based alloys in Reline and Glyceline are presented in table 3.

[0036] The volume of electrolyte (Reline or Glyceline) is arbitrary depending on size and shape of the workpiece.

Table 3. Summarized parameters of electrochemical processing of Ti and Ti-based alloys in Reline and Glyceline.

t/°C	τ/min.	electrolyte	Current density (i) [mA cm-2] galvanostatic treatment	Voltage/potential (E) [V] potentiostatic treatment
15-40	5-60	Reline	1-20 (surface roughening/etching)	1-5 (surface roughening/etching)
			25-100 (surface polishing)	6-30 (surface polishing)
15-40	5-60	Glyceline	1-20 (surface roughening/etching)	1-5 (surface roughening/etching)
			25-100 (surface polishing)	6-30 (surface polishing)

Detailed description

Example 1

[0037] 3D printed implants made of Ti-6AI-4V alloy - electrochemical treatment in Reline.

[0038] Reline was prepared by mixing of choline chloride (ChCI) and urea at a molar ratio of components 1:2 (ChCl : urea). The mixing was carried out at 250 rpm and 70 °C for 2 hours until a homogenous transparent colorless liquid was formed. After cooling electrolyte was ready for electrochemical using.

[0039] 3D printed Ti-6AI-4V alloy implants were degreased and cleaned before electrochemical processing. Ti-alloy details were immersed in ultrasonic water bath with 1 weight % of caustic soda for 5 min. at 40 °C. Afterwards the residues of the cleaning composition were thoroughly rinsed off with water. After drying in hot air flow Ti-6AI-4V alloy implants were ready for electrochemical treatment.

Electrochemical treatment procedure - galvanostatic mode:

[0040] Galvanostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Reline was carried out in a two-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode. Electrochemical surface treatment was done in galvanostatic mode at two current densities (5 mA cm^-2 and 25 mA cm^-2). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². Thus, processing currents were 0.04 A and 0.12 A, respectively. The suitable volume of Reline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0041] After galvanostatic electrochemical surface treatment in Reline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0042] One of the main characteristics of the treated surface is its roughness. For this reason, measurements of the surface roughness parameter (RMS) before and after the proposed electrochemical treatment were made. RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. In the case of the first example RMS values for galvanostatic treatment were 1366 nm and 183 nm for current densities of treatment 5 mA cm^-2 and 25 mA cm^-2, respectively. For untreated sample RMS parameter is 497 nm. Thus, galvanostatic surface etching in Reline leads to the noticeable roughening of the implant surface, and galvanostatic surface polishing in Reline, on the contrary, markedly reduce surface roughness and leads to the surface leveling.

Electrochemical treatment procedure - potentiostatic mode:

[0043] Potentiostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Reline was carried out in a three-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode and Ag-wire was used as a pseudo-reference electrode. Electrochemical surface treatment was done in potentiostatic mode at two chosen potentials (4 V and 15 V). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². The suitable volume of Reline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0044] After potentiostatic electrochemical surface treatment in Reline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0045] After the potentiostatic treatment in Reline, as in the case of galvanostatic treatment, the roughness (RMS parameter) of the implant surfaces was measured. RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. The RMS values for potentiostatic treatment in Reline were 1410 nm and 175 nm for potentials of treatment 5 V and 30 V, respectively. For untreated sample RMS parameter is 497 nm. Thus, potentiostatic surface etching in Reline leads to the noticeable roughening of the implant surface, and potentiostatic surface polishing in Reline, on the contrary, markedly reduce surface roughness and leads to the surface leveling.

Example 2

[0046] 3D printed implant made of Ti-6AI-4V alloy - electrochemical treatment in Glyceline.

[0047] Glyceline was prepared by mixing of choline chloride (ChCI) and glycerol at a molar ratio of components 1:2 (ChCI : glycerol). The mixing was carried out at 400 rpm and 70 °C for 1 hour until a homogenous transparent colorless liquid was formed. After cooling electrolyte was ready for electrochemical treatment of Ti-alloy implants.

[0048] 3D printed Ti-6AI-4V alloy implants were degreased and cleaned before electrochemical processing. Ti-alloy details were immersed in ultrasonic water bath with 1 weight % of caustic soda for 5 min. at 40 °C. Afterwards the residues of the cleaning composition were thoroughly rinsed off with water. After drying in hot air flow Ti-6AI-4V alloy implants were ready for electrochemical treatment.

Electrochemical treatment procedure - galvanostatic mode:

[0049] Galvanostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Glyceline was carried out in a two-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode. Electrochemical surface treatment was done in galvanostatic mode at two current densities (5 mA cm^-2 and 25 mA cm^-2). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². Thus, processing currents were 0.04 A and 0.12 A, respectively. The suitable volume of Glyceline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0050] After galvanostatic electrochemical surface treatment in Glyceline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0051] The result of electrochemical treatment in Glyceline under galvanostatic conditions was evaluated by measuring the surface roughness (RMS parameter). RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. The RMS values for galvanostatic surface treatment in Glyceline were 1245 nm and 226 nm for current densities of treatment 5 mA cm^-2 and 25 mA cm^-2, respectively. For untreated sample RMS parameter is 497 nm. Thus, galvanostatic surface etching in Glyceline leads to the noticeable roughening of the implant surface, and galvanostatic surface polishing in Glyceline, on the contrary, markedly reduce surface roughness and leads to the surface leveling.

Electrochemical treatment procedure - potentiostatic mode:

[0052] Potentiostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Glyceline was carried out in a three-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode and Ag-wire was used as a pseudo-reference electrode. Electrochemical surface treatment was done in potentiostatic mode at two chosen potentials (4 V and 15 V). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². The suitable volume of Glyceline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0053] After potentiostatic electrochemical surface treatment in Glyceline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0054] The result of electrochemical treatment in Glyceline under potentiostatic conditions was evaluated by measuring the surface roughness (RMS parameter). RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. The RMS values for potentiostatic surface treatment in Glyceline were 1280 nm and 220 nm for potentials of treatment 5 V and 30 V, respectively. For untreated sample RMS parameter is 497 nm. Thus, potentiostatic surface etching in Glyceline leads to the noticeable roughening of the implant surface, and potentiostatic surface polishing in Glyceline, on the contrary, markedly reduce surface roughness and leads to the surface leveling.

Comparative Example 3

[0055] 3D printed implant made of Ti-6AI-4V alloy - electrochemical treatment in Ethaline.

[0056] Ethaline was prepared by mixing of choline chloride (ChCI) and ethylene glycol at a molar ratio of components 1:2 (ChCI : Ethgl). The mixing was carried out at 300 rpm and 70 °C for 1 hour until a homogenous transparent colorless liquid was formed. After cooling electrolyte was ready for electrochemical treatment of Ti-alloy implants.

[0057] 3D printed Ti-6AI-4V alloy implants were degreased and cleaned before electrochemical processing. Ti-alloy details were immersed in ultrasonic water bath with 1 weight % of caustic soda for 5 min. at 40 °C. Afterwards the residues of the cleaning composition were thoroughly rinsed off with water. After drying in hot air flow Ti-6AI-4V alloy implants were ready for electrochemical treatment.

Electrochemical treatment procedure - galvanostatic mode:

[0058] Galvanostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Ethaline was carried out in a two-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode. Electrochemical surface treatment was done in galvanostatic mode at two current densities (5 mA cm^-2 and 25 mA cm^-2). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². Thus, processing currents were 0.04 A and 0.12 A, respectively. The suitable volume of Ethaline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0059] After galvanostatic electrochemical surface treatment in Ethaline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0060] The result of electrochemical treatment in Ethaline under galvanostatic conditions was also evaluated by comparison of the roughness of the samples before and after electrochemical treatment. The measured parameters RMS (the Root Mean Square of a surfaces measured microscopic peaks and valleys) for samples, which were treated at 5 mA cm^-2 and 25 mA cm^-2, are 1123 nm and 286 nm, respectively. The sample of untreated Ti-6AI-4V alloy is characterized by RMS = 497 nm. Thus, surface processing in Ethaline deep eutectic solvents under galvanostatic mode at low current density (5 mA cm^-2) leads to the surface etching with increasing of surface roughness and at high current density (25 mA cm^-2) leads to the surface smoothing.

Electrochemical treatment procedure - potentiostatic mode:

[0061] Potentiostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Ethaline was carried out in a three-electrode thermostated cell using potentiostat Metrohm Autolab PGSTAT302N (Switzerland). Ti-6AI-4V alloy implants served as working electrodes, Pt-grid with surface area comparable to the workpiece was an auxiliary electrode and Ag-wire was used as a pseudo-reference electrode. Electrochemical surface treatment was done in potentiostatic mode at two chosen potentials (4 V and 15 V). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². The suitable volume of Ethaline for treatment of implants with mentioned surface area is 120 ml. The temperature during treatment was kept at a constant value of 25 °C using a thermostat Julabo model ME v.2 (Germany). The duration of electrochemical treatment was 20 min. for each implant.

[0062] After potentiostatic electrochemical surface treatment in Ethaline, 3D printed implants of Ti-6AI-4V alloy were thoroughly rinsed with bidistilled water in ultrasonic chamber, afterwards dried in air without any additional procedures.

[0063] The potentiostatic electrochemical surface treatment in Ethaline at different potentials affects the surface roughness of titanium alloy implants. The measured parameters RMS (the Root Mean Square of a surfaces measured microscopic peaks and valleys) for samples, which were treated at 5 V and 30 V, are 1173 nm and 280 nm, respectively. The sample of untreated Ti-6AI-4V alloy is characterized by RMS = 497 nm. Thus, surface processing in Ethaline under potentiostatic conditions leads to the surface etching at low potential of treatment (5 V) and to the surface smoothing, when used high potential of treatment (30 V).

[0064] Surface treatment results for different electrolytes and conditions of treatment can be easily evaluated using Table 4.

Table 4. Comparative characteristic of the surface finishing results for different examples of the surface treatment.

Example	Mode of treatment	Processing current density or potential (i/E, mA cm-2, V)	Surface roughness (RMS, nm)
Untreated Ti-6AI-4V	-	-	497
Example 1	Galvanostatic	5 mA cm-2	1366
		25 mA cm-2	183
	Potentiostatic	5 V	1410
		30 V	175
Example 2	Galvanostatic	5 mA cm-2	1245
		25 mA cm-2	226
	Potentiostatic	5 V	1280
		30 V	220
Example 3	Galvanostatic	5 mA cm-2	1123
		25 mA cm-2	286
	Potentiostatic	5 V	1173
		30 V	280

[0065] As clearly visible form the presented in table 4 data, surface etching and electropolishing effectiveness for different electrolytes are different. Probably, the different intensity of etching and electropolishing in these electrolytes is due to differences in the rate of electrooxidation of alloy components, which may depend on the physicochemical properties of electrolytes and nature of formed complexes. The presented result confirms that electrochemical surface treatment in Glyceline and Reline more effective in comparison with Ethaline: with the same conditions of treatment (current, potential, time of processing) it is possible to obtain rougher and smoother surfaces of Ti-6AI-4V alloy implants according to the special needs.

Literature

[0066] 

1. K.-H. Kim, N. Ramaswamy. Electrochemical surface modification of titanium in dentistry, Dent. Mater. 28, 1 (2009) 20-36.

2. B. Walivaara, B.O. Aronsson, M. Rodahl, J. Lausmaa, P. Tengvall. Titanium with different oxides: in vitro studies of protein adsorption and contact activation. Biomaterials 15, 10 (1994) 827-834.

3. Kityk A., Protsenko V., Danilov F., Pavlik V., Hnatko M., Soltys J. Enhancement of the surface characteristics of Ti-based biomedical alloy by electropolishing in environmentally friendly deep eutectic solvent (Ethaline). Colloids and Surfaces A: Physicochemical and Engineering Aspects 613 (2021) 126125.

4. Das J., Freitas F., Evans I., Nogueira A., Khushalani D. A facile nonaqueous route for fabricating titania nanorods and their viability in quasi-solid-state dye-sensitized solar cells. J. Mater. Chem. 20 (2010) 4425-4431.

5. Cristino A.F., Matias I.A.S., Bastos D.E.N., Galhano dos Santos R., Ribeiro A.P.C., Martins L.M.D.R.S. Glycerol Role in Nano Oxides Synthesis and Catalysis. Catalysts 10 (2020) 1406.

6. Li J.G., Yang X., Ishigaki T. Urea coordinated titanium trichloride Ti(III)[OC(NH)2]6Cl3: a single molecular precursor yielding highly visible light responsive TiO2 nanocrystallites. J Phys Chem B. 110 (2006): 14611-8.

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Claims

1. A method for electrochemical surface treatment of biomedical product made of titanium or Ti-based alloys wherein it comprises steps:

- Immersion of the degreased and cleaned biomedical product into the electrolyte consisting of Reline or Glyceline;

- Galvanostatic etching treatment of the biomedical product at the current density 1 to 20 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 5 V for 5 to 60 min. at a temperature 15 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 5 to 60 min. at a temperature 15 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 6 to 30 V for 5 to 60 min. at a temperature 15 to 40 °C;

- Subsequent cleaning of the biomedical product from electrolytes residuals.

2. The method according to the claim1, characterized in that, degreasing and cleaning of the biomedical product before immersion to the electrolyte is performed in ultrasonic water bath with 1-5 weight % of caustic soda during 5-10 min. at 40-60 °C followed by multiple rinsing with water and drying in a stream of hot air until completely dry.

3. The method according to the claim 1 or 2, characterized in that, the subsequent cleaning of the biomedical product from electrolytes residuals is performed in water ultrasonic bath during 5 to 15 min. and air drying until the water has completely evaporated.

4. The method according to the claim 1 or 2, characterized in that, the biomedical product is prostheses or implant.