Method for surface treatment of a biocompatible metal material and implant treated by said method

Abstract

The invention relates to a method for surface treatment of a biocompatible metal material, such as an implant, which comprises the following consecutive steps: i) abrasive mechanical treatment of the surface of said material using abrasive calcium phosphate grains, such as a mixture of hydroxyapatite and tricalcium phosphate; ii) acid treatment by hot dipping of said material in a bath comprising sulphuric acid and hydrochloric acid, followed by at least one rinse with demineralised water; iii) sodic treatment by hot dipping of said material in a soda bath followed by at least one rinse with demineralised water and drying in hot air. The implant thus treated has a surface with increased roughness with a triple level of porosity (macro-, micro- and nano-porosity) as well as improved hydrophilic properties. The method can be used for implants made of titanium alloys, such as the TA6V ELI alloy.

Claims

1. A process for the surface treatment of a biocompatible metal implant, comprising the steps of: i) abrasive mechanical treatment of the surface of said material by means of abrasive grains based on calcium phosphate; ii) acid treatment by soaking, at a temperature above 40 C., said material in a bath comprising sulfuric acid and hydrochloric acid, followed by at least one rinse with demineralized water; and iii) sodium treatment by soaking, at a temperature above 40 C., said material in a sodium hydroxide-based bath having only sodium hydroxide, followed by at least one rinse with demineralized water and by hot air drying.

2. The process as claimed in claim 1, wherein the biocompatible metal material is a titanium alloy.

3. The process as claimed in claim 1, wherein the biocompatible metal material is an alloy of titanium, aluminum and vanadium, preferably the alloy known as TA6V ELI.

4. The process as claimed in claim 1, wherein the mixture of hydroxyapatite and tricalcium phosphate grains comprises from 80% to 90% of hydroxyapatite and from 10% to 20% of tricalcium phosphate.

5. The process as claimed in claim 4, wherein the abrasive grains of hydroxyapatite and tricalcium phosphate have a particle size of between 160 and 400 micrometers, preferably between 200 and 360 micrometers.

6. The process as claimed in claim 1, wherein the acid bath comprises from 45% to 55% by volume of 95% sulfuric acid and from 45% to 55% by volume of 37% hydrochloric acid.

7. The process as claimed in claim 6, wherein the acid treatment is carried out by soaking said material in a bath at a temperature between 60 C. and 70 C. for a duration of from 18 to 30 minutes, preferably from 20 to 25 minutes.

8. The process as claimed in claim 1, wherein the sodium treatment is carried out by soaking said material in sodium hydroxide at a molar concentration of 4 to 6 M and at a bath temperature of between 60 C. and 70 C. for a duration of between 18 and 30 minutes, preferably between 20 and 25 minutes.

9. The process as claimed in claim 1, wherein the abrasive grains based on calcium phosphate are a mixture of hydroxyapatite and tricalcium phosphate.

10. The process as claimed in claim 1, wherein the step of acid treatment by soaking is followed by two rinses with demineralized water.

11. The process as claimed in claim 1, wherein the step of sodium treatment by soaking is followed by two rinses with demineralized water.

12. The process as claimed in claim 1, wherein the sodium hydroxide is at least at a concentration of 4 M (moles/L).

13. The process as claimed in claim 12, wherein the sodium hydroxide is at a concentration of 4 M-6 M (moles/L.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be clearly understood on reading the following description of an exemplary embodiment, with reference to the appended drawings, in which:

(2) FIG. 1 is a scanning electron microscopy image, with a magnification of 500, of the surface of an implant treated according to the process of the present invention;

(3) FIG. 2 is an image of the surface of the implant from FIG. 1 with a magnification of 2000;

(4) FIG. 3 is an image of the surface of the implant from FIG. 1 with a magnification of 5000;

(5) FIG. 4 is an image of the surface of the implant from FIG. 1 with a magnification of 10 000;

(6) FIG. 5 is an image of the surface of the implant from FIG. 1 with a magnification of 30 000;

(7) FIG. 6 is a chart comparing the contact angles of the implant surfaces from examples 1 and 2 measured with various wetting agents.

EXAMPLES

Example 1 According to the Invention

(8) The surface treatment of an implant made of TA6V ELI alloy (according to the standard ASTM F136, a titanium-based alloy containing 6% by weight of aluminum and 4% by weight of vanadium: see table 1) is carried out according to a treatment known as nano-etching in three consecutive steps, described in detail below.

(9) TABLE-US-00001 TABLE 1 Fe O N C H max. % max. % max. % max. % max. % Al % V % 0.25 0.13 0.05 0.08 0.012 5.50-6.50 3.50-4.50

Step 1: Mechanical Treatment

(10) The implants are sandblasted with an abrasive composed of hydroxyapatite (85%5%) and tricalcium phosphate (15%5%) having a Vickers hardness equal to 532 Hv, having a diameter of the powder grains of between 160 and 400 m, with a predominance of grains having a size of between 200 and 360 m in diameter.

(11) This step consists in creating porosities having a size ranging up to 250 m in diameter.

(12) The grains of abrasives are projected using a nozzle positioned at around 10 to 20 cm from the surface of the implant under a pressure of from 5 to 7 bar for 6010 seconds.

Step 2: Acid Treatment

(13) This step consists in creating porosities of several tens of microns in diameter and in depth homogeneously over the entire surface treated.

(14) The treatment is carried out in a mixture composed of two acids. The acid composition and the treatment parameters are described below: composition of the bath: 50%5% by volume of 95% sulfuric acid and 50%5% by volume of 37% hydrochloric acid, treatment temperature: 672.5 C., treatment time: 221 min, with stirring of the bath.

(15) A longer treatment time or a temperature above the range indicated results in an attack of the macro-roughness created in step 1.

Step 3: Sodium Treatment

(16) The objective of this treatment is to create a tissue of nanometer-size porosity at the surface of the implant.

(17) This step is carried out in a sodium hydroxide bath, as follows: composition of the bath: 50.5 M (50.5 mol/L) sodium hydroxide, bath temperature: 672.5 C., treatment time: 221 min, stirring of the bath.

(18) An insufficient sodium treatment (insufficient NaOH concentration, for instance of less than 4 mol/L, lower temperature or shorter treatment time) leads to surfaces that are less hydrophilic with contact angles in the presence of distilled water, ethylene glycol or diiodomethane of greater than 50, or even greater than 70, and also to an insufficient nanoporosity.

Results of SEM Observations

(19) The images obtained by observation with the scanning electron microscope, presented in FIGS. 1 to 5 at various magnifications (respectively 500, 2000, 5000, 10 000 and 30 000), reveal a very uneven and very rough surface.

(20) The surface has, specifically, an appearance with porosities of several tens of microns in diameter which themselves comprise porosities of several microns in diameter and in depth. These same microporosities also comprise porosities having a diameter and a depth of less than a micron, namely several hundred nanometers. The presence of this triple level of porosity at the surface of the material constitutes a significant advantage for the osseointegration of the implant.

(21) It is even possible to observe, on the SEM image with a magnification of 30 000, a tissue of very fine fibers that covers the entire treated surface.

(22) EDS analyses (Energy Dispersive Spectroscopy analyses, carried out under vacuum with a FEI QUANTA 200 machine) of this surface reveal a strong presence of titanium and of oxygen (therefore probably of titanium oxide), as presented in table 2 below which compares the chemical composition of the treated surface and that of the crude alloy before treatment.

(23) TABLE-US-00002 TABLE 2 Composition by weight (%) Elements Alloy with treated surface Crude alloy Titanium 66.15 86.95-89.20 Oxygen 26.11 0.5 Aluminum 3.50 5.5-6.75 Vanadium 1.92 3.5-4.5 Carbon 1.44 0.08 Sodium 0.11 Iron 0.4 Hydrogen 0.015

(24) The surface of the alloy treated according to the invention has lower contents of aluminum and of vanadium than those present at the surface of a crude grade 23 (TA6V ELI) titanium alloy. These analyses also demonstrate the strong presence of oxygen at the surface of the treated implant, which means that there is formation of a titanium oxide layer.

Comparative Example 2

(25) A surface treatment of an implant made of Straumann SLA titanium-based alloy is carried out according to the same three steps and under conditions identical to those of example 1 above.

Roughness Measurements

(26) The results of the Ra and Rz roughness measurements (carried out using a MITOTOYO SJ400 machine) comparing the surfaces of the implants treated according to example 1 and comparative example 2 are presented in table 3 below.

(27) The meanings of Ra and Rz are the following:

(28) Ra: mean deviation. It is the arithmetic mean of the absolute values of the deviations, between the peaks and the valleys. Ra measures the distance between this mean and the central line.

(29) Rz: regularity. It is the mean of the greatest difference in height between the highest point of a peak and the lowest bottom of a valley, observed over 5 lengths.

(30) TABLE-US-00003 TABLE 3 Surfaces tested Ra Rz Comments Example 1 1.90 m 10.46 m The surface of the Example 2 1.83 m 10.03 m implant from example (Comp.) 1 is rougher than that of the implant from example 2

Contact Angle Measurements

(31) Contact angle measurements were carried out with three different liquids (distilled water, ethylene glycol and diiodomethane) for the implants from examples 1 and 2. The results, presented in FIG. 6, show significant differences when the wetting agent is either distilled water or ethylene glycol, demonstrating a much greater hydrophilic nature for the surface treated according to the process of the present invention.