Osteointegration process for surgical prosthesis

Abstract

Coatings for osteointegration of surgical prosthesis are made in an Ion Plating Plasma Assisted plant, with a “reactive Magnetron sputtering” source, having a vacuum chamber, sputtering source, for instance a Magnetron, a vacuum connection to the pumping group, plasma, for instance DC, process gases input, a substrate holder biased, bias generator, for instance DC, RF generator, a matching network, and a RF plasma.

Description

The invention relates a vacuum thin films deposition process on surgical prosthesis, metallic or not, to enhance their osteointegration and to protect them from alteration induced by biological environment in which are inserted. The invention especially relates dental implants and orthopaedic prosthesis in titanium. The superficial treatment obtainable with the process in question gives the advantage to reduce, also more then fifty percent, the necessary time for a full osteointegration of the prosthesis in side the bone in which the prosthesis was implanted. A previous technique, subject of a previous patent, presents difficulties relating its industrial use, in fact it is based on a deposition process using pulsed laser ablation, “PLAD”, for very small surfaces coating, but it is not able to guarantee the necessary uniformity of thickness and characteristics in complicated samples like dental implants screws: all that results from accurate testing.

This and other drawbacks have been overcome by the present invention, that, in addition, allows the simultaneous coating of many samples (pieces) improving osteointegration characteristics and minimizing the rejection risk. The used thin film vacuum deposition technique, belongs to the reactive deposition field, in which the vaporized material, in this case titanium, reacts during the deposition with an organic gas inserted in the process chamber. As known, the improvement of the prosthesis osteointegration characteristics, depends, beside the deposited film type, also from the surgical prosthesis surface roughness. With the proposed process, subject of the present patent requested, the surface roughness is realized by a sandblasting process, using micro spheres of zirconium dioxide, ZrO₂, of optimal diameter around 120 microns, by obtaining in this way a satisfactory osteointegration. The deposited thin film composition is, in a rough outline, a mixture of the following compounds: titanium carbide, titanium dioxide, TiO₂, titanium sub-oxides, TiO_x, and, in addition, argon both bonded with other argon atoms and with oxygen atoms. With regard to the elemental composition, that is of the main elements constituting the treatments, argon, titanium, oxygen, the typical percentages are:

argon between 25% and 36%,

titanium between 25% and 30%,

oxygen from 33% to 40%.

With reference to the chemical bounds of the main elements which constitute the treatment, typical percentages of the titanium compounds are: TiC between 35% and 38%, TiO₂ between 30% and 37%, TiO_x between 26% and 34%. The argon compounds have a majority of the bond C—C about 50% with values about 35% of the bonds with titanium and the remaining percentage of the oxygen bonds.

The invention will be in the following described for an indicative and not limitative scope, with reference to the single FIGURE which will improve the understanding of the invention, taking present that the invention is essentially represented by a process performed on substrates in a “ion plating plasma assisted” plant, as specified in the following.

FIG. 1—schematic representation of a ion plating plasma assisted plant, with a “magnetron sputtering” source. The deposition process, which is the most innovative aspect of the invention, for which a patent defense is requested, is made in a vacuum plant like an ion plating plasma assisted, with a reactive magnetron sputtering source.

In the figures are visible:

• • 1 Vacuum plant
  • 2 magnetron sputtering source
  • 3 Pumping group connections
  • 4 Process gases inlet
  • 5 Biased substrate holder
  • 6 DC generator
  • 7 DC plasma
  • 8 RF generator
  • 9 Matching network
  • 10 RF plasma
  • 11 Substrates.

The magnetron sputtering 2 source is generally supplied in direct voltage, while the substrate holder 5 is generally biased through a RF power supply, 13.56 MHz. The substrate holder 5 can be rotating or fixed in front of the source 2, preferably at a distance from 5 to 15 centimeters. The material on the magnetron sputtering source is titanium. The process atmosphere is constituted, in some phases, by argon, while in the reactive phase it is an argon and ethylene mixture. In the following the process and relative parameters are described. The substrates 5, generally titanium, are at first, cleaned by a soap washing, when necessary and then by a solvent like hexane. The substrates are then mounted on the substrates holder 5, with direct contact with the RF biased element 10 which generates the plasma, taking care to not pollute the surface. Then the vacuum chamber 1 is closed and the vacuum is effected until a pressure of about 10 ton. Of course the pumping system is made in a way to not introduce pollution inside the chamber. A flux of argon is introduced until the pressure reaches a value between 2 and 3×10⁻³ ton. Then, an ionic cleaning process of the substrates is performed activating an RF discharge with a power density of about 0.5 watt/cm², with a voltage of about 500 volts for a five minutes duration typically. Then the RF discharge is interrupted and after the substrates have been shielded, in respect of the magnetron sputtering source, this is supplied by a DC tension of about 400 volts, with a power density of about 10 watt/cm², activating a plasma discharge for the cleaning and the decontamination of the titanium surface, for a duration of about five minutes. Then the DC voltage is interrupted and the shutter in front of the substrates is removed. Successively an adherence layer of titanium is deposited in “ion plating” mode, with an RF substrates bias of about 500 volts and a power density of about 0.25 watt/cm², while the magnetron sputtering source is supplied in DC, with a power density of about 5 watt/cm², for a duration of about two minutes. During this deposition phase of the adherence coating, the titanium deposition rate is accurately measured, by a thickness monitor, for instance using an oscillating quartz. Maintaining both the DC and RF supply, is introduced a flux of ethylene which produces, at the same powers, a reduction of the deposition rate which mast be reduced until a value of about 90% of the deposition rate in pure argon atmosphere. This flux of ethylene is equivalent to a partial pressure of about 6×10⁻⁵ Torr. The deposition is so performed maintaining these parameters constant until to a thickness of about 1.5 microns. At this point the DC and RF supply and the flux of the process gases are interrupted, and after the vent of the plant, the substrates, so ready, are dismounted from the substrates holder.

Claims

1. A process for coatings for osteointegration of surgical prosthesis, to perform using an ion plating plasma assisted plant, with a “reactive magnetron sputtering” source, being constituted, the plant, generally, by a vacuum chamber (1), sputtering source (2), for instance magnetron, vacuum connection (3) to the pumping group, plasma, for instance DC (7), process gases input (4), substrate holder biased (5), bias generator, for instance DC (6), RF generator (8), matching network (9), RF plasma (10), characterized, the process to be realized by the following steps: the substrates (11), usually titanium, are previously cleaned by a soap washing, if necessary, and then by a solvent like hexane;substrates (11) are mounted on the biased substrate holder (5) in direct contact with the RF biased element (10), taking care do not pollute the surface;the vacuum chamber (1) is closed and pumped until a pressure lower then 10−5 ton;a flux of argon is introduced until to reach a pressure value between 2 and 3×104 Torr;a cleaning of substrates (11) is performed starting an RF discharge with a power density of about 0.5 watt/cm2 with a voltage of about 500 volts, for a duration of about five minutes;the RF discharge is interrupted and after shielding the substrates (11), in respect of the magnetron sputtering source (2), this, (the magnetron sputtering source) is supplied by a DC voltage of 400 volts tension about, with a power density of about 10 watt/cm2, activating a plasma discharge for the cleaning and the decontamination of the titanium surface, for a duration for about five minutes;the supply DC is interrupted and the shutter in front of the substrates (11) is removed;successively, an adherence layer of titanium is deposited, in Ion Plating mode, with an RF bias of the substrates (11) of about 500 volts and with a power density of 0.25 watt/cm2, while the magnetron sputtering source is supplied in DC with a power density of about 5 watt/cm2, for a duration of about two minutes; during this deposition phase of the adherence layer, the titanium deposition rate is accurately measured by, for instance, an oscillating quartz thickness monitor;maintaining both the DC and RF supply, a flux of ethylene is introduced into the chamber, able to reduces with the same power density the deposition rate until to a value of about 90% of the deposition rate in pure argon atmosphere; this flux of ethylene is equivalent to a partial pressure of about 6×10−5 ton;then the deposition is performed maintaining these parameters constant until a thickness of about 1.5 micron;then, both the DC and RF supply and the flux of the process gases are interrupted; and after, the vent of the chamber the substrates are dismounted from the substrates holder and are so completed.

2. The process for coatings for osteointegration of surgical prosthesis, to perform into a ion plating plasma assisted plant, from a source “reactive magnetron sputtering” as defined in claim 1 wherein the composition of the deposited film is a mixture of titanium carbide and titanium dioxide, TiO2, titanium sub-oxides, TiOx, and in addition argon bonded with other argon atoms and/or oxygen atoms.

3. The process for coatings for osteointegration of surgical prosthesis as defined in claim 1 wherein in the chemical bonds of the main elements which constitute the treatment, the typical percentages of the titanium compounds are: TiC between 35% and 38%, TiO2 between 30% and 37%, TiOx between 26% and 34%, and relatively to the argon compounds there is a prevalence of the bond C—C around 50%, with values around 35% of bonds with titanium and the remaining percentage with oxygen.

4. The process for coatings for osteointegration of surgical prosthesis as defined in claim 1 wherein the magnetron sputtering source (2) is supplied in direct voltage, while the biased substrate holder (5) is biased through a RF supplier, typically at 13.56 MHz.

5. The process for coatings for osteointegration of surgical prosthesis as defined in claim 1 wherein the biased substrate holder (5) can be fixed or rotating in front of the source (2), preferably at a distance between five and fifteen centimeters.

6. The process for coatings for osteointegration of surgical prosthesis as defined in claim 1 wherein the material on the magnetron sputtering source (2) is typically titanium; the process atmosphere is constituted, in some phases, by argon and ethylene and the prosthesis to treat, typically in titanium, are roughened through a sandblasting process using micro-spheres, typically in zirconium dioxide, ZrO2, with a optimal diameter of about 120 microns.

7. The process for coatings for osteointegration of surgical prosthesis as defined in claim 4 wherein both the magnetron source and the biased substrate holder (5) are powered by a DC voltage or by any kind of alternate or pulsed frequency.

8. The process for coatings for osteointegration of surgical prosthesis as defined in claim 1 wherein the sputtering source can be also different from a magnetron.