PROCESS FOR GRAFTING BIOACTIVE POLYMERS ONTO METALLIC MATERIALS

Abstract

The present invention relates to a process for grafting polymers onto a metallic material, comprising the following steps: a) oxidation of the surface of the metallic material, resulting in an oxidized metallic material; b) grafting of a polymer at the surface of said oxidized metallic material by radical polymerization of a monomer, said radical polymerization comprising an initiation step and a propagation step, said initiation step being carried out by UV irradiation with a UV source diffusing a power at the surface of the material of greater than 72 mW.Math.cm.sup.2, said UV irradiation being carried out for a duration greater than 15 minutes and less than 180 minutes, said process resulting in a grafted metallic material. The present invention also relates to the materials capable of being obtained by this process, and applications of the latter, in particular as articular or dental implants.

Claims

1. Process for direct grafting of bioactive polymers onto a prosthetic metallic material in titanium or titanium alloy, comprising the following steps: a) oxidizing the surface of the metallic material, leading to an oxidized surface of metallic material; b) grafting a polymer on the oxidized surface of said metallic material, by radical polymerisation of a monomer placed in the presence of the oxidized surface of the metallic material, said radical polymerisation comprising an initiation step and a propagation step, said initiation step being performed by UV irradiation with a UV source applying power onto the surface of the material higher than 72 mW.Math.cm.sup.2, said UV irradiation being performed for a time of more than 30 minutes and less than 180 minutes, said process leading to a prosthetic metallic material in titanium or titanium alloy grafted with bioactive polymers.

2. The process according to claim 1, wherein said initiation step is performed by UV irradiation with a UV source applying power of between 72 mW.Math.cm.sup.2 and 20 W.Math.cm.sup.2.

3. The process according to claim 1, wherein said initiation step is performed by UV irradiation with a UV source for a time of 90 minutes or less.

4. The process according to claim 1, wherein said initiation step is performed by UV irradiation with a UV source applying power of between 72 mW.Math.cm.sup.2 and 260 mW.Math.cm.sup.2.

5. The process according to claim 1, wherein said initiation step is performed without heating in addition to UV irradiation.

6. The process according to claim 1, wherein the concentration of monomer(s) in the solution is between 0.2 and 1 mol.Math.L.sup.1.

7. The process according to claim 1, wherein the metallic material is an alloy of titanium with nickel, vanadium, aluminium, niobium, and/or molybdenum.

8. The process according to claim 1, wherein said monomer is an olefin.

9. The process according to claim 1, wherein the monomer is sodium styrene sulfonate (NaSS).

10. The process according to claim 1, wherein the monomer is selected from among sulfonates, phosphonates and/or carboxylates.

11. The process according to claim 1, wherein said radical polymerisation is conducted in the absence of oxygen.

12. The process according to claim 1, wherein the initiation step is performed prior to or concomitantly with the propagation step.

13. The process according to claim 1, wherein it comprises a cleaning step performed prior to the oxidation step, the time between the end of the cleaning step and the start of the oxidation step being less than 16 hours.

14. The process according to claim 1, wherein the oxidation step a) is performed by treating the material with an aqueous solution comprising an oxidant and an acid.

15. The process according to claim 1, wherein the oxidation step a) is performed by anodic treatment.

16. The process according to claim 1, wherein the grafted metallic material has a grafting rate of said polymer higher than 1.5 g.Math.cm.sup.2.

17. The process according to claim 1, characterized in that said initiation step is performed by UV irradiation with a UV source for a time equals or less than 120 minutes.

18. The process according to claim 7, characterized in that said metallic material is the alloy TiAl.sub.6V.sub.4.

19. The process according to claim 10, characterized in that the monomer is selected among acrylic acid, methacrylic acid, methyl methacrylate (MMA), N-(sodium phenylsulfonate) acrylamide (NaAS), N-(sodium phenylsulfonate) methacrylamide (NaMS), ethylene glycol methacrylate, methacrylate phosphate, methacryloyl-di-isopropylidene, vinylbenzylphosphonate (VBP), ethyl 2-[4-(dihydroxyphosphoryl)-2-oxa-butyl]acrylate (MA154), or mixture thereof.

20. The process according to claim 16, characterized in that the grafted metallic material has a grafting rate of said polymer higher than 3 g.Math.cm.sup.2.

Description

DESCRIPTION OF THE FIGURES

[0218] FIG. 1 schematically illustrates one embodiment of the process of the invention using the different intermediate species involved at each step of the process. Material (1) corresponds to a non-treated prosthetic metallic material having a native oxidation layer on the surface. Material (2) has undergone the oxidation step a) and has hydroperoxide functions on its surface of which the density is equal to or greater than the OH functions of the material in the native state. Material (3) has undergone an initiation step via UV irradiation: homolytic cleavage of the OO or OH bond has occurred giving rise to O radicals on the surface. This initiated material (3) is then placed in the presence of an olefin of formula CH.sub.2=CR.sub.1A (where for example R.sub.1 represents H, and A represents Ph-SO.sub.3Na), and is subjected to the polymerisation step to lead to the grafted material (4).

[0219] FIG. 2 is a bar chart illustrating the effect of oxidation step a) on the grafting rate of a prosthetic material in titanium (Example 3). The Y-axis represents the grafting rate in g.Math.cm.sup.2. The left-hand bar (A) represents the mean grafting rate obtained with 6 samples of titanium material after subjection to steps a) and b) of the process of the invention, and the right-hand bar (B) represents the mean grafting rate obtained with 2 samples of titanium material after subjection solely to step b) of the process of the invention (no controlled oxidation, only natural oxidation).

[0220] FIG. 3 gives three infrared spectra: spectrum of crude titanium (non-treated prosthetic material i.e. in the native state, top spectrum), spectrum of non-grafted polyNaSS (middle spectrum), and spectrum of a material in titanium grafted with polyNaSS according to the process of Example 1 (bottom spectrum). The Y-axis represents transmittance (in %). The X-axis represents the wave number (in cm.sup.1).

[0221] FIG. 4 is a bar chart illustrating the impact of waiting time between the cleaning step and oxidation step. The Y-axis represents the grafting rate in g.Math.cm.sup.2. The left-hand bar (A) represents the mean grafting rate obtained for a titanium material subjected to the oxidation step 16 hours after the cleaning step, and the right-hand bar (B) represents the mean grafting rate obtained with a titanium material subjected to the oxidation step 2 hours after the cleaning step.

[0222] FIG. 5 illustrates the grafting rate of a metallic material in titanium in Example 4 as a function of UV irradiation time of the oxidized material in 0.32 M monomer solution. The Y-axis represents the grafting rate in g.Math.cm.sup.2, and the X-axis represents UV irradiation time in minutes. The values given are mean values over three experiments.

[0223] FIG. 6 illustrates the grafting rate of a metallic material in titanium as a function of power per unit area of UV irradiation, for an exposure time of 45 min on a titanium alloy material (FIG. 6A) and on a titanium material (FIG. 6B), in 0.7 M monomer solution. The values given are mean values over three experiments.

EXAMPLES

[0224] The advantages of the present invention will become apparent in the light of the following examples concerning particular embodiments of the invention, but which cannot be construed as being limiting.

Example 1: Implementation of the Process of the Invention

[0225] 1.1. Implementation of the Process

[0226] The metallic material in this example is a material in titanium or titanium alloy.

[0227] 1.1.1 Polishing

[0228] The surfaces of the metallic material in titanium may first be polished.

[0229] Mechanical polishing of titanium discs is performed by means of an automatic arm mounted on a rotating polisher, using grinding paper of decreasing grit size (Struers). First polishing with grade 500 paper (hereafter P500) removes a thickness of about 1/10.sup.th millimetre. Polishing is then refined using grade 1200 paper of lesser grit size (hereafter P1200).

[0230] The protocol used was the following: the discs were polished 1 to 2 minutes with P500 paper and a rotating speed of 200 rpm, and then 1 to 2 minutes with P1200.

[0231] After polishing, the samples were washed by immersion in an acetone solution (overnight), then 215 min in acetone in an ultrasonic bath and finally 315 min in distilled water in an ultrasonic bath. They were then dried at 60 C. and used immediately or stored under argon.

[0232] 1.1.2 Cleaning

[0233] The polished metallic material was then subjected to a cleaning step in a mixture of H.sub.2O/HF/HNO.sub.3 (88:2:10). The solution used for this washing was a mixture of water, a 24 M aqueous solution of hydrofluoric acid and a 10 M aqueous solution of nitric acid in respective proportions of (88:2:10) (v/v/v), left under agitation for 1 minute. The samples were oven dried at 60 C.

[0234] 1.1.3 Oxidation

[0235] The cleaned metallic material was then subjected to an oxidation step via chemical treatment. The metallic material was immersed in a mixture of concentrated sulfuric acid H.sub.2SO.sub.4 and hydrogen peroxide H.sub.2O.sub.2.

[0236] The samples were immersed in a volume v of concentrated sulfuric acid H.sub.2SO.sub.4 (50% dilution in water for the alloy) under agitation for 1 minute. An equivalent volume v of hydrogen peroxide H.sub.2O.sub.2 (30% by volume in water) was added and the samples left in this mixture under agitation for 3 minutes. The oxidized surfaces were then rinsed in 3 baths of water for 3 minutes.

[0237] Alternatively, the cleaned metallic material can be subjected to an oxidation step via anodic treatment.

[0238] 1.1.4 Grafting

[0239] Thereafter, the oxidized metallic material is immersed in a degassed aqueous solution of sodium styrene sulfonate monomer (NaSS) at 0.7 mol/L or 0.32 mol/L. The solution in which the oxidized material was immersed was exposed for a time varying between 15 min and 240 min as a function of samples to UV irradiation from a UV source of wavelength 365 nm and 200 W power. As a function of the distance between the lamp and the metallic material (from 5 cm to 30 cm), the power per unit area varied between 72 mW.Math.cm.sup.2 and 226 mW.Math.cm.sup.2.

[0240] 1.2. Characterization:

[0241] The presence of the polymers grafted on the surface was measured using different methods.

[0242] 1.2.1. Toluidine Blue (TB) Colorimetric Method

[0243] The grafted metallic samples were placed in contact with a 5.10.sup.4 M TB solution (adjusted to pH 10 with sodium hydroxide) at a temperature of 30 C. for 6 hours. This step corresponds to TB complexing with the monomer units of the grafted polymer. The samples were then abundantly rinsed with 1.10.sup.3M sodium hydroxide solution to remove non-complexed TB. Rinses were halted when the solution became colourless. The complexed TB was decomplexed with 50% acetic acid solution that was left in contact with the titanium samples for 24 hours. The solution obtained was assayed by spectrophotometry using a Perkin Elmer Lambda 25 spectrophotometer (Biomacromolecules 2006, 7, 755-760).

[0244] 1.2.2. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR).

[0245] The samples were directly analysed (without preparation) by ATR-FTIR on Perkin Elmer Spectrum Two apparatus.

[0246] 1.2.3. Measurement of Contact Angle

[0247] Measurements of contact angles were made on a drop of water deposited on the surface of the oxidized or grafted samples, using KRUSS: DSA100 apparatus providing information on surface changes of hydrophilic or hydrophobic type.

[0248] 1.3. Results

[0249] 1.3.1 Validation of Grafting

[0250] For the samples obtained by implementing the process described under item 1.1., the characteristic bands of the sulfonate group at 1180 cm.sup.1 and 1128 cm.sup.1, and the vibrational doublet at 1010 1040 cm.sup.1, symmetric vibration at 1040 cm.sup.1 were observed in the Attenuated Total Reflectance Fourier Transform Infrared spectrum (ATR-FTIR, see FIG. 3).

[0251] 1.3.2 Importance of the Oxidation Step

[0252] Measurement of the amount of polyNaSS polymers grafted on the surface of the titanium was carried out by complexing the sulfonate groups of the polymers with Toluidine Blue both on those samples that had been subjected to the process described under item 1.1 (e.g. polishing, cleaning, oxidation), and on samples of metallic material that had not been subjected to an oxidation step (e.g. only polishing and cleaning).

[0253] Therefore, for the samples subjected to the entirety of the process described under item 1.1., a grafting rate in the order of 8 g/cm.sup.2 was observed (see FIG. 2) whereas the samples not subjected to the controlled oxidation step displayed a grafting rate of 0.62 g/cm.sup.2.

[0254] Oxidation of the metallic material via chemical oxidation as well as anodic oxidation gave satisfactory results.

[0255] It is to be noted that a sample of material in oxidized titanium immersed in a solution of polyNaSS (e.g. Acros, Mn=70000 g/mol, batch N.sup.o: A012503701, CAS: 24704-18-1) at a concentration of 0.7 mol/L then abundantly washed by rinsing in water, but not subjected to a grafting step properly so-called, gives values of 0.3 g/cm.sup.2 when measured by complexing with Toluidine Blue. This experiment allows the hypothesis to be set aside according to which the polymer is merely adsorbed on the surface of the oxidized metallic material (e.g. titanium).

[0256] To conclude, the oxidation step is essential to obtain a grafted metallic material according to the invention. It allows the grafting rate to be increased by a factor of 25 (7.7 vs. 0.3 g/cm) compared with grafting on a metallic surface having natural oxidation.

[0257] 1.3.3. Measured Properties

[0258] On pure titanium material (i.e. non-grafted starting titanium i.e. not having undergone the process of the invention) the contact angle is 595.

[0259] The samples of grafted material obtained with the process described under item 1.1. have a contact angle of 152, i.e. a decrease in the contact angle of 44 between the non-treated surface and the grafted surface.

[0260] To conclude, the grafted metallic materials obtained with the process of the invention have a much more hydrophilic surface than non-grafted metallic materials, and this is particularly made possible by the prior oxidation step.

Example 2: Importance of the Time Between Cleaning and Oxidation

[0261] 2.1. Protocol

[0262] The metallic material in this example is a material in titanium. 15 samples of said metallic material were used.

[0263] The surfaces of the 15 samples of titanium metallic material were first polished and then cleaned in a mixture of H.sub.2O/HF/HNO.sub.3 (88:2:10).

[0264] The cleaned 15 samples were then subjected to an oxidation step.

[0265] After a waiting time varying from 2 hours to 16 hours, the 15 oxidized samples were subjected to the grafting step in an aqueous solution of sodium styrene sulfonate monomer (NaSS).

[0266] The other conditions used were identical to those described in Example 1.

[0267] 2.2. Results

[0268] FIG. 4 shows that the time between the end of cleaning and the start of oxidation is of importance regarding the grafting rate of the method of the invention.

[0269] if a time of 16 hours or more separates the end of the cleaning step and the start of the oxidation step, the grafting rate is not optimal (e.g. 1.09 g/cm.sup.2).

[0270] It is therefore preferable to carry out the oxidation step fairly rapidly after the cleaning step.

Example 3: Influence of Irradiation Time on Grafting Rate

[0271] 3.1. Protocol

[0272] The metallic material in this example was a material in titanium.

[0273] 15 samples of said metallic material were used.

[0274] The surfaces of the 15 samples of titanium metallic material were first polished.

[0275] The 15 samples were then cleaned in a mixture of H.sub.2O/HF/HNO.sub.3 (88:2:10).

[0276] Thereafter, the 15 cleaned samples were subjected to an oxidation step via chemical treatment.

[0277] The 15 oxidized samples were subjected to the grafting step in an aqueous solution of sodium styrene sulfonate monomer (NaSS).

[0278] The other conditions used were identical to those described in Example 1.

[0279] 3.2. Results

[0280] The grafting rate of polyNaSS on the surface of the 15 samples of titanium was examined by complexing the sulfonate groups of the polymers with Toluidine Blue.

[0281] The results given in Table 1 and FIG. 5 show that the optimal results i.e. a grafting rate higher than 1.5 g/cm.sup.2, were obtained in this case with UV irradiation of between 30 and 120 minutes.

TABLE-US-00001 TABLE 1 Time (min) Mean (g .Math. cm.sup.2) 15 0.43 30 2.91 45 4.19 60 6.79 90 3.15 120 2.18 180 1.15 240 1.09

Example 4: Influence of Power Per Unit Area of UV Irradiation on Grafting Rate

[0282] 4.1. Protocol

[0283] The metallic material in this example was material in titanium or titanium alloy.

[0284] 15 samples of said metallic material were used.

[0285] The surfaces of the 15 samples of metallic material in titanium or titanium alloy were subjected to a cleaning step.

[0286] The 15 cleaned samples were subjected to an oxidation step.

[0287] The 15 oxidized samples were then immersed in an aqueous solution of sodium styrene sulfonate monomer (NaSS).

[0288] The solution in which the oxidized material was immersed was exposed for 45 min at distances varying between 5 centimetres and 30 centimetres to UV irradiation from a UV source of 200 W and wavelength 365 nm, the power per unit area therefore varying between 72 mW.Math.cm.sup.2 and 226 mW.Math.cm.sup.2.

[0289] The other conditions used were identical to those described in Example 1.

[0290] 4.1. Results

[0291] FIG. 6 shows that power per unit area higher than 72 mW.Math.cm.sup.2 is needed to allow satisfactory grafting on the metallic material.