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

Abstract

 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 from mixture of 95 to 60 vol. % of Ethaline and 5 to 40 vol. % of ethyl alcohol, respectively; galvanostatic etching treatment of the biomedical product at the current density 2 to 20 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 4 V for 2 to 60 min. at a temperature 5 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 5 to 30 V for 2 to 60 min. at a temperature 5 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 safe alternatives to the classical acidic electrolytes for electrochemical surface treatment of Ti and Ti-alloys is important and relevant [2].

[0004] The above-mentioned disadvantages are partially solved by using Ethaline (deep eutectic mixture of choline chloride with ethylene glycol) as an electrolyte in the process of electrochemical surface treatment. Ethaline is environmentally friendly and non-toxic to humans [3]. Eco-friendly, biodegradable, resource-saving and affordable electrolyte Ethaline allows modeling the surface properties of titanium and its alloys in a wide range at room temperatures. However, Ethaline is characterized by an insufficient distribution of electric current and can be improved in terms of electrical conductivity. Moreover, it is desirable to reduce the price of the electrolyte without losing its attractive properties.

[0005] The aim of this invention is to provide an improved method of electrochemical surface treatment of titanium alloys, which is quick, efficient and cost-effective.

Summary of the Invention

[0006] It has been found out that combination of Ethaline and ethyl alcohol can be considered as a very perspective electrolyte for electrochemical surface treatment of titanium alloys. Addition of Ethyl alcohol into the Ethaline allows improvement of electrochemical treatment results, increase in efficiency of treatment and thus shortening processing time. Furthermore, replacement of a part of the electrolyte volume with a cheaper component will lead to an overall reduction in the cost of electrochemical processing.

[0007] The proposed invention demonstrates a novel electrochemical surface treatment technique for biomedical Ti and Ti-based alloys in eco-friendly solvent of new generation (deep eutectic mixture Ethaline) modified by addition of ethyl alcohol. The presented invention allows modeling surface properties of Ti biomedical products in wide range according to the individual needs of special uses. This invention has a great potential for industrial application: available reagents, simple equipment, highly effective result, environmental safety, safety for people and equipment, lack of competitive analogues.

[0008] The method for electrochemical surface treatment of biomedical product made of titanium or Ti-based alloys according to the present invention comprises steps:

• Immersion of the degreased and cleaned biomedical product into the electrolyte consisting from mixture of 95 to 60 vol. % of Ethaline and 5 to 40 vol. % of ethyl alcohol, respectively;
• Galvanostatic etching treatment of the biomedical product at the current density 2 to 20 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 4 V for 2 to 60 min. at a temperature 5 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 5 to 30 V for 2 to 60 min. at a temperature 5 to 40 °C;
• Subsequent cleaning of the biomedical product from electrolytes residuals.

[0009] According to the preferred embodiment, galvanostatic etching treatment or potentiostatic etching treatment is carried out for 8 to 20 min., preferably for 15 min.

[0010] According to the further preferred embodiment, galvanostatic etching treatment or potentiostatic etching treatment is carried out at the temperature 15 to 30°C, preferably at a temperature 25 °C or room temperature.

[0011] Degreasing and cleaning of the biomedical product before immersion to the electrolyte can be 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.

[0012] Subsequent cleaning of the biomedical product from electrolytes residuals can be performed in water ultrasonic bath during 5 to 15 min. and air drying until the water has completely evaporated.

[0013] The biomedical product can be a prostheses or an implant.

[0014] It is possible to obtain nanostructured surfaces for drug delivery. Biodegradation of electrolytes simplifies the utilization procedure.

[0015] The electrolyte according to the present invention is prepared in two steps:

The first step includes mixing of choline chloride (vitamin B 4) with ethylene glycol in molar ratio of components 1:2, respectively, and stirring them at a temperature of 70 °C for an hour until complete homogenization, after cooling to room temperature, the electrolyte is ready for second step.

In the second step, ethyl alcohol is added by portions under stirring to the prepared electrolyte at room temperature. After thorough mixing, the electrolyte is ready for use. The amount of added ethyl alcohol can be varied from 5 up to 40 volume percent, preferably 10 to 30 vol. %, more preferably 20 to 30 vol. %, the most preferably 30 vol. %.

[0016] Each 100 ml of electrolyte for use in the method according to present invention (modified electrolyte) may contain from 5 to 40 ml of ethyl alcohol and a balance of 95 to 60 ml of Ethaline, respectively. In the case when the addition of ethanol is less than 5 vol. %, the result of electrochemical treatment does not differ from the results of the pure Ethaline electrolyte, when more than 40 vol. % is added, the electrolyte starting to lose the properties of a deep eutectic mixture and the treatment results become worse.

[0017] Titanium or Ti-alloy workpieces (implants or prostheses) before electrochemical processing in modified electrolyte must be thoroughly degreased and cleaned. For degreasing and cleaning can be used any most-common composition for solid metal and alloy surfaces cleaning (aqueous alkaline and acidic composition). Residues of the cleaning composition must be thoroughly rinsed off with water. Titanium or Ti-alloy workpieces after drying is ready for electrochemical treatment.

[0018] Electrochemical surface treatment of Ti and Ti-alloys in Ethaline - Ethyl alcohol mixture can be carried out in a wide range of temperatures (any temperatures up to 40°C). Ethaline as a new type of room-temperature ionic liquids shows numerous attractive properties: it is easy to prepare, easily biodegradable and not harmful for the environment as compared with many other types of electrolytes. The melting point of Ethaline is -66 °C.

[0019] The freezing point of ethyl alcohol is -114 °C. Admit only that at temperatures higher than 40 °C the conditions of the electrochemical dissolution of Ti in Ethaline-containing media will be changed from mass transfer controlled, which will lead to a significant deterioration in the processing result. The best results of electrochemical treatment are achieved when the electrochemical reactions in the system proceed under diffusion control conditions, in this case diffusion is the rate-limiting stage. In Ethaline and in modified electrolyte electrochemical surface treatment at temperatures up to 40 °C proceeds under diffusion control, which ensures a high-quality result of processing. When the temperature of the electrolyte starts to be higher than 40 °C the rate-limiting stage changes from diffusion to charge transfer, in this case, the electropolishing result deteriorates. Therefore, an increase in temperature above 40 °C is undesirable for the Ethaline and the modified electrolyte.

[0020] For the best processing result prosthesis or implant must be located in electrochemical cell 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.

[0021] The proposed electrochemical treatment of bio-medical Ti and Ti-alloys in Ethaline - Ethyl alcohol mixture can be realized in two different modes: potentiostatic (constant voltage) and galvanostatic (constant current). Galvanostatic treatment is recommended for biomedical prostheses 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.

[0022] 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. Ethaline - Ethyl alcohol mixture is used as an electrolyte for surface treatment. The current density (i=I/s [A cm^-2], I - current, s - surface area of workpiece) during the treatment procedure controls by current source.

[0023] 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 and temperatures. The potential (E [V]) during the treatment procedure is controlled by potentiostat.

[0024] Electrolysis time (2-60 min.) can be variated depending on initial state of Ti or Ti-alloy product (initial roughness, contamination, etc.).

[0025] The volume of Ethaline - Ethyl alcohol mixture can be variated depending on size of treated bio-medical product.

Table 1: Summarized parameters of electrochemical surface treatment in Ethaline - Ethyl alcohol mixture

Electrolyte	Temperature [°C]	Current density (i) [mA cm-2] galvanostatic treatment	Voltage/potential (E) [V] potentiostatic treatment	Time [min.]
95-60 vol. % Ethaline + 5-40 vol. % Ethyl alcohol	up to 40	2 - 20 (surface roughening/etching)	1 - 4 (surface roughening/etching)	2 - 60∗
		25 - 100 (surface polishing)	5 - 30 (surface polishing)

∗ Depending on initial state, roughness and surface contamination, of workpiece and desired surface treatment result.

[0026] An improved method proposed in this invention involves the use of a modified electrolyte (Ethaline with the addition of ethyl alcohol). The improved composition of the electrolyte (Ethaline + ethyl alcohol) is characterized by higher electrical conductivity and better distribution of electric current in the system in comparison with the pure Ethaline, which provides a better result of electrochemical processing of Ti and Ti-based alloys. To achieve a similar surface profile results in a modified electrolyte, the required processing time is reduced by a factor of four. The modified electrolyte does not lose its attractive characteristics, but at the same time its cost noticeable decreases.

[0027] The method according to the present invention is suitable for Ti and also for Ti alloys, as its processing mechanism is primarily related to the electrochemical dissolution of titanium, so the technology works for pure titanium as well as for Ti alloys.

Brief description of the drawings

[0028] 

Fig. 1a - Optical microscope photos (magnification x4000) of untreated samples of Ti Grade 5.

Fig. 1b - Optical microscope photos (magnification x4000) of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline.

Fig. 1c - Optical microscope photos (magnification x4000) of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (10 vol. % Ethyl alcohol).

Fig. 1d - Optical microscope photos (magnification x4000) of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (15 vol. % Ethyl alcohol).

Fig. 1e - Optical microscope photos (magnification x4000) of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (20 vol. % Ethyl alcohol).

Fig. 1f - Optical microscope photos (magnification x4000) of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (30vol. % Ethyl alcohol).

Fig. 2a - The 3D and 2D surface profiles of untreated sample of Ti Grade 5.

Fig. 2b - The 3D and 2D surface profiles of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline.

Fig. 2c - The 3D and 2D surface profiles of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (10 vol. % Ethyl alcohol).

Fig. 2d - The 3D and 2D surface profiles of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (15 vol. % Ethyl alcohol).

Fig. 2e - The 3D and 2D surface profiles of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (20 vol. % Ethyl alcohol).

Fig. 2f - The 3D and 2D surface profiles of electrochemically polished samples of Ti Grade 5 (t = 25 °C, τ = 10 min., i= 30 mA cm^-2) in Ethaline - Ethyl alcohol mixture (30 vol. % Ethyl alcohol).

Detailed description

Example 1

[0029] The electrolyte for use in the method according to the present invention was prepared in two steps.

[0030] In the first step choline chloride (vitamin B 4) was mixed with ethylene glycol in molar ratio 1:2, respectively, and stirred at a temperature of 70 °C for an hour until complete homogenization. After cooling to room temperature, the electrolyte was ready for second step.

[0031] In the second step, 108 ml of Ethaline was mixed with 12 ml of Ethyl alcohol. Ethyl alcohol was added by portions under stirring at room temperature. After thorough mixing, the electrolyte is ready for use.

Preparation of workpiece:

[0032] 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.

[0033] Electrochemical surface treatment of Ti-6AI-4V alloy in Ethaline - Ethyl alcohol mixture was carried out at 25 °C.

Electrochemical treatment procedure - galvanostatic mode:

[0034] Galvanostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Ethaline - Ethyl alcohol mixture 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 (10 mA cm^-2 and 30 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 - Ethyl alcohol mixture 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 10 min. for each implant.

[0035] After galvanostatic electrochemical surface treatment in Ethaline - Ethyl alcohol mixture, 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. 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 920 nm and 312 nm for current densities of treatment 10 mA cm^-2 and 30 mA cm^-2, respectively. For untreated sample RMS parameter is 497 nm. Thus, galvanostatic surface etching in Ethaline - Ethyl alcohol mixture leads to the roughening of the implant surface, and galvanostatic surface polishing in Ethaline - Ethyl alcohol mixture, on the contrary, reduce surface roughness and leads to the surface leveling.

Electrochemical treatment procedure - potentiostatic mode:

[0036] Potentiostatic electrochemical surface treatment of 3D printed Ti-6AI-4V alloy implants in Ethaline - Ethyl alcohol mixture 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 20 V). The surface area of 3D printed Ti-6AI-4V alloy implants was 4 cm². The suitable volume of Ethalin-Ethyl alcohol mixture 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 10 min. for each implant. After potentiostatic electrochemical surface treatment in Ethaline - Ethyl alcohol mixture, 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.

[0037] After the potentiostatic treatment in Ethaline - Ethyl alcohol mixture, 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 Ethalin-Ethyl alcohol mixture were 923 nm and 309 nm for potentials of treatment 4 V and 20 V, respectively. For untreated sample RMS parameter is 497 nm. Thus, potentiostatic surface etching in Ethaline - Ethyl alcohol mixture leads to the roughening of the implant surface, and potentiostatic surface polishing in Ethaline - Ethyl alcohol mixture, on the contrary, reduce surface roughness and leads to the surface leveling.

Examples 2 to 4

[0038] The following electrolytes were prepared by the method disclosed in the Example 1. Prepared electrolyte solutions are listed in Table 2.

Table 2:

	Ethaline (ml)	Ethyl alcohol (ml)	Workpiece
Example 2	102	18	3D printed implants of Ti-6AI-4V alloy
Example 3	96	24	3D printed implants of Ti-6AI-4V alloy
Example 4	84	36	3D printed implants of Ti-6AI-4V alloy

[0039] Electrochemical surface treatment procedure was the same like in the Example 1. Galvanostatic treatment was done at current densities of 10 mA cm^-2 and 30 mA cm^-2, potentiostatic treatment at electrode potentials of 4 V and 20 V. Duration of treatment is 10 min. Volume of electrolyte is 120 ml. The auxiliary and reference electrode are the same as in example 1. The temperature during treatment was kept at a constant value of 25 °C.

[0040] The posttreatment cleaning of workpieces was the same like in the Example 1.

Comparative Examples 5 to 7

[0041] The following electrolyte solutions were prepared by the method disclosed in the Example 1. Prepared electrolyte solutions are listed in Table 3.

Table 3:

	Ethaline (ml)	Ethyl alcohol (ml)	Workpiece
Comp. example 5	120	0	3D printed implants of Ti-6AI-4V alloy
Comp. example 6	60	60	3D printed implants of Ti-6AI-4V alloy
Comp. example 7	117,6	2,4	3D printed implants of Ti-6AI-4V alloy

[0042] Electrochemical surface treatment procedure for comparative examples was the same like in Example 1. Galvanostatic treatment was done at current densities of 10 mA cm^-2 and 30 mA cm^-2, potentiostatic treatment at electrode potentials of 4 V and 20 V. Duration of treatment is 10 min. Volume of electrolyte is 120 ml. The auxiliary and reference electrode are the same as in example 1. The temperature during treatment was kept at a constant value of 25 °C.

[0043] The posttreatment cleaning of workpieces was the same like in example 1.

[0044] 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 Grade 5 (Ti-6AI-4V alloy)	-	-	497
Example 1	Galvanostatic	10 mA cm-2	920
		30 mA cm-2	312
	Potentiostatic	4 V	923
		20 V	309
Example 2	Galvanostatic	10 mA cm-2	1167
		30 mA cm-2	257
	Potentiostatic	4 V	1172
		20 V	253
Example 3	Galvanostatic	10 mA cm-2	1280
		30 mA cm-2	124
	Potentiostatic	4 V	1282
		20 V	122
Example 4	Galvanostatic	10 mA cm-2	1472
		30 mA cm-2	93
	Potentiostatic	4 V	1549
		20 V	91
Comp. example 5	Galvanostatic	10 mA cm-2	875
		30 mA cm-2	378
	Potentiostatic	4 V	874
		20 V	380
Comp. example 6	Galvanostatic	10 mA cm-2	876
		30 mA cm-2	377
	Potentiostatic	4 V	878
		20 V	376
Comp. example 7	Galvanostatic	10 mA cm-2	612
		30 mA cm-2	467
	Potentiostatic	4 V	615
		20 V	465

[0045] From table 4 can be seen that electrochemical surface etching in pure Ethaline (comp. example 5, conditions of treatment 10 mA cm^-2 or 4 V) leads to the surface roughening of 3D printed Ti-6AI-4V alloy implants, which confirmed by increasing of RMS from 497 nm (untreated sample) up to 875 nm (for galvanostatic conditions) and up to 874 nm (for potentiostatic conditions). In the same time surface electropolishing in pure Ethaline (comp. example 5, conditions of treatment 30 mA cm^-2 or 20 V) leads to the surface smoothing of 3D printed Ti-6AI-4V alloy implants, which confirmed by decreasing of RMS from 497 nm (untreated sample) up to 378 nm (for galvanostatic conditions) and up to 380 nm (for potentiostatic conditions). Admit that after adding of Ethyl alcohol to the Ethaline, an increase in roughness (RMS) during etching and a decrease in RMS during polishing are observed (examples 1-4, comp. example 6), which indicates the intensification of electrochemical processes. This effect is especially pronounced for an electrolyte containing 30 vol. % Ethyl alcohol (example 4), in this case RMS for etched sample reach the mark of 1472 nm (for galvanostatic conditions) and 1549 nm (for potentiostatic conditions); RMS for polished sample is 93 nm (for galvanostatic conditions) and 91 nm (for potentiostatic conditions). Such a noticeable increase in RMS during etching and a decrease in RMS during polishing indicate a high efficiency of electrochemical treatment in an electrolyte containing 30 vol. % Ethyl alcohol.

[0046] From the results presented in table 4 also can be concluded that small amount of Ethyl alcohol (2 vol. %, comp. example 6) is not enough for the pronounced effect of addition in Ethaline. A big amount of Ethyl alcohol (50 vol. %) in Ethaline (comp. example 7) leads to the destruction of existing hydrogen bonds and the formation of new ones, which leads to the transformation of the electrolyte from a deep eutectic solvent into an alcohol solution; such a transformation negatively affects the result of electrochemical processing.

[0047] Thus, the content of Ethyl alcohol in modified electrolyte for efficient electrochemical treatment of Ti and Ti-based alloys can vary from 5 to 40 vol. %; 10 - 30 vol. % will be considered as preferable and 30 vol. % as optimal content (see detail in table 4). Additionally, visually evaluate the results of electropolishing in pure Ethaline and in modified with Ethyl alcohol electrolytes are possible from Fig. 1a - If. The addition of Ethyl alcohol into the Ethaline electrolyte is positively affect the surface finishing result (Figure 1a to If). As clearly visible from optical microscope pictures, the surface of Ti Grade 5 samples after short time electropolishing in Ethaline - Ethyl alcohol mixtures start to be more homogeneous, amount of the surface defects is rapidly decreased. Moreover, obtained results confirm that Ethyl alcohol addition to the Ethaline leads to the surface homogenization after electropolishing at all other equal conditions. With increasing of Ethyl alcohol content in Ethaline - Ethyl alcohol mixture surface homogeneity is increased. It must be noted that electropolishing result in 30 vol. % Ethyl alcohol - Ethaline mixture (10 min.) is similar to that, which was observed for electropolishing in pure Ethaline during 40 min. Thus, the addition of Ethyl alcohol to the Ethaline can reduce the time of electrochemical treatment by approximately 4 times while achieving the same leveling results.

[0048] The surface profile pictures for discussed above samples are presented in Figure 2a-2f. The 3D and 2D surface profiles of untreated Ti-alloy sample and electrochemically polished in Ethaline and Ethaline - Ethyl alcohol mixtures are demonstrated in fig. 2a-2f. The 3D surface topographies for samples, which were treated in Ethaline - Ethyl alcohol mixtures (fig. 2b-2f), contain less amount of surface depressions, pits and defects in comparison with untreated sample (fig. 2a). The 2D surface profiles, which also presented on fig. 2a-2f, are confirmed that addition of Ethyl alcohol to the Ethaline leads to the noticeable smoothing of the Ti-6AI-4V surfaces after electropolishing procedure. From fig. 2a to fig. 2f you can see that surface profile line smoothing.

[0049] Fig. 1a-1f and fig. 2a-2f show that the best electropolishing results were observed for Ethaline electrolyte containing 30 vol. % Ethyl alcohol.

[0050] Obtained results confirms that even an initially very rough surface of 3D printed Ti-6AI-4V alloy can be electrochemically smoothed in a very short time by adding of ethyl alcohol to the Ethaline deep eutectic solvent.

Industrial applicability

[0051] The invention can be used for surface modification of biomedical Ti and Ti-alloy based products (mainly implants and prostheses). Also proposed surface treatment method can be used for Ti-based materials for galvanochemistry, aviation, rocket technology and marine shipbuilding, where surface purity, physical-mechanical properties and corrosion resistance play an important role. The Ti-based materials for photocatalytic application also can be improved with surface modification proposed in presented invention.

Literature

[0052] 

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., Šoltys 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.

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 from mixture of 95 to 60 vol. % of Ethaline and 5 to 40 vol. % of ethyl alcohol, respectively;

- Galvanostatic etching treatment of the biomedical product at the current density 2 to 20 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic etching treatment of the biomedical product at the potential 1 to 4 V for 2 to 60 min. at a temperature 5 to 40 °C; or galvanostatic electropolishing of the biomedical product at the current density 25 to 100 mA cm^-2 for 2 to 60 min. at a temperature 5 to 40 °C or potentiostatic electropolishing of the biomedical product at the potential 5 to 30 V for 2 to 60 min. at a temperature 5 to 40 °C;

- Subsequent cleaning of the biomedical product from electrolytes residuals.

2. The method according to the claim 1 or 2, characterized in that, galvanostatic etching treatment or potentiostatic etching treatment is carried out at the temperature 5 to 40°C, preferably at a temperature 25 °C.

3. The method according to any of the preceding claims, 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.

4. The method according to any of the preceding claims, 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.

5. The method according to any of the preceding claims, characterized in that, the biomedical product is prostheses or implant.

Drawing