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    • 专利摘要:
    The invention relates to an implant comprising a substrate and a coating on a surface of the substrate, the coating containing silicon nitride and having a thickness of 1 to 15 μm. The coating is formed by physical vapor deposition at a deposition temperature of more than 100 ° C, has a hardness of 5 to 45 GPa and, as deposited, has a surface roughness Ra of less than 50 nm.
    公开号:CH707707B1
    申请号:CH00279/14
    申请日:2012-08-30
    公开日:2021-10-29
    发明作者:Pettersson Maria；Engqvist Hakan；Olofsson Johanna；Hultman Lars
    申请人:Ihi Ionbond Ag；
    IPC主号:
    专利说明:

    Field of invention
    This invention relates to implants that contain an abrasion resistant coating.
    Background of the invention
    Joint replacement is one of the most commonly performed orthopedic surgeries. A complete joint replacement has an average lifespan of around 15 years. The reason for the shortage in the implants can be one or more factors, but is often caused by debris from the wearing surface of the implant. Abrasion particles from implants are associated with inflammation, which leads to bone loss and possibly loosening of the implant, Sargeant et al., "Hip Implants: Paper V. Physiological Effects", Materials & Design, 27 (2006) 287-307. It has been found that the chemistry and particle size of such particles are very important to the inflammatory response, Sargeant et al. (2006) and Sargeant et al., "Hip Implants - Paper VI - Ion Concentrations", Materials & Design 28 (2007) 155-171.
    Metals based on cobalt chromium (CoCr) are commonly used as biomaterials for implants and have been shown to be relatively good biocompatible materials for joint applications. Their mechanical properties are adequate for use as joint implants that bear a load. However, experiments have shown that CoCr particles, which are released through abrasion and corrosion, can impair bone growth, Aspenberg et al., "Benign response to particles of diamond and SiC: bone chamber studies of new joint replacement coating materials in rabbits" , Biomaterials, 17 (1996) 807-812. Titanium alloys and stainless steels have also been widely used in joint implants, Sargeant et al. (2006). The main risks with metal alloy implants are the release of metal ions from corrosion and abrasion, and these metal ions can be carcinogenic. The debris can also lead to bone resorption, Sargeant et al. (2007).
    The use of an insulation made of ultra high molecular weight polyethylene (UHMWPE) in a metal or ceramic head with a relatively low measured coefficient of friction has been proposed, but the UHMWPE liner often wears and generates a relatively large amount of debris, which aseptic loosening Xiong et al., "Friction and wear properties of UHMWPE / Al2O3ceramic under different lubricating conditions", Wear, 250 (2001) 242-245.
    [0005] Alumina (Al2O3) and zirconia (ZrO2) ceramics have been used in joint replacement to provide high abrasion resistance and chemical inertness. However, ceramic materials have poor tensile strength, and alumina components in joint replacements have been shown to release debris due to their poor toughness. The particles released from alumina and zirconia are also inert and are not reabsorbed by the body. There are other ceramic materials that are showing promising results. For example, silicon nitride (Si3N4) has a higher fracture toughness and is more resistant to microcrack propagation than aluminum oxide, Bal et al., "Fabrication and Testing of Silicon Nitride Bearings in Total Hip Arthroplasty: Winner of the 2007 'HAP' PAUL Award", The Journal of Arthroplasty , 24 (2009) 110-116. No. 4,608,051 A describes a prosthesis for completely or partially replacing a posterior wall of the auditory canal, on the surface of which an insoluble bioinert material, for example silicon nitride, can be applied. A prosthesis can include a partial coating that includes at least one additive layer with a thickness of 0.25 µm to 5 µm.
    A solution to the problems with joint implants made of bulk metal or ceramic joint implants is the coating of a metal joint with an abrasion-resistant ceramic coating with low corrosion, for example a titanium nitride coating. The problems of inert debris, which cause long-term problems such as inflammation and aseptic loosening, have not been resolved.
    Accordingly, there is a need for abrasion and corrosion resistant biomedical implants, particularly for use as artificial joints to overcome the problems of debris and associated high inflammation.
    Summary of the invention
    Accordingly, it is an object of this invention to provide implants that overcome the various disadvantages of the prior art.
    This invention relates to an implant comprising a substrate and a coating on a surface of the substrate, the coating containing silicon nitride and having a thickness of 1 µm to 15 µm, characterized in that the coating: by physical vapor deposition at a Precipitation temperature of more than 100 ° C is formed; has a hardness of 5 to 45 GPa; and, as deposited, has a surface roughness Ra of less than 50 nm.
    In addition, a method for obtaining an implant is described which comprises the coating of a surface of an implant substrate with a coating that contains silicon nitride and has a thickness of about 1 μm to about 15 μm by means of physical vapor deposition.
    The implants of this invention are advantageous for obtaining implants having a combination of properties suitable for use in vivo while also providing improved abrasion resistance and, in particular, a reduced tendency to release debris causing inflammation and implant loosening, to be unfolded. In particular, particles released by these implants are resorbable and reduce the possibility of inflammation and implant loosening that result from debris.
    These and additional advantages, objects, and embodiments of this invention will become more apparent from the detailed description that follows.
    Brief description of the drawings
    The detailed description will be more fully understood with reference to the drawings, in which: FIG. 1 shows X-ray diffraction (XRD) patterns of SixNy coatings on CoCr substrates and of CoCr substrates as described in Example 1. FIG. Figures 2A and 2B show transmission electron microscope (TEM) images of the coating 8 described in Example 1: Figure 2A shows the selected area electron diffraction (SAED) corresponding to Si3N4; Figure 2B shows a high resolution TEM (HRTEM) image of a Si3N4 lattice within the coating. Figures 3A and 3B show the appearance of the surface of coatings at two magnifications using scanning electron microscopy (SEM), 67 ° sample diffraction, as described in Example 1: Figure 3A is coating 5 on Si substrate; Figure 3B is coating 2 on CoCr substrate. FIGS. 4A-4D show SEM images of cross-sections of coatings on silicon wafers showing the resulting coating microstructure as described in Example 1: FIG. 4A shows coating 3 with a fine columnar structure, FIG. 4B shows coating 5 with a columnar structure, FIG Fig. 4C shows coating 8 with a columnar structure, Fig. 4D shows coating 10 without a distinguishable columnar structure. 5 shows the coefficient of friction versus the number of revolutions for SixNy coatings, bulk CoCr and bulk Si3N4 as described in Example 1. The gray area means the area in which almost all coating curves lie with the exception of coatings 2 and 5 (not shown in the diagram). 6 is an SEM image of the surface appearance of the wear marks on coating 8 after 10,000 revolutions at two different magnifications, 67 ° sample inclination, as described in Example 1. The coating is smoothed in the abrasion track. 7 shows optical profile images of abraded surfaces and the calculated cross-sectional areas of the traces of abrasion. The z-scale is enlarged 23 times more than the x, y-scale. FIGS. 8A-8C show different structures of (a) dense, (b) laminar and (c) columnar materials as described in Example 2. Figure 9 shows scratches on coatings deposited on silicon wafers for: Panel (a) SixNy coating 16, (b) SixNy coating 12, (c) SixNyCz coating 20 deposited with a Si target power of 4 kW , and (d) SixNyCz coating 22 deposited at 1 kW as described in Example 2. The arrow indicates the direction of scratching. 10 shows the coefficient of friction versus number of revolutions from the ball-on-disk test for test runs for 10,000 cycles as described in Example 2. FIG. 11 shows the cross section of the traces of wear after 10,000 revolutions in the ball-on-disk test, as described in Example 2. FIGS. 12A and 12B show XRD spectra of (a) SixNy and (b) SixNyCz coatings as described in Example 2. FIGS. 13A-13D show SEM images of the coating 12 with additional treatment steps as described in Example 2: an increased adhesion from FIG. 13A, in which the standard process is retained, to FIG. 13B, which introduces an etching process before deposition, FIG. 13C with intermittent biasing steps and FIG. 13D with a nitrogen gradient and high frequency during precipitation. 14 shows coating 12 with a thickness of 8 μm, as described in Example 2. 15 shows the concentration of free Si in PBS solutions with different pH after 35 and 75 days, as described in Example 2. 16 shows the concentration of silicon in PBS, measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), as described in Example 2.
    The drawings do not limit the invention, which is defined in the claims.
    Detailed description
    This invention relates to implants that include a substrate and a coating. The coating is abrasion-resistant with high mechanical strength and forms absorbable abrasion particles. Methods for obtaining abrasion-resistant biomedical implants are also described.
    The implant substrate can be any desired implant material. In specific embodiments, the substrate can be ceramic or metallic. Suitable metals can be found in the group of cobalt-chromium alloys, stainless steel alloys, titanium and titanium alloys. In another embodiment, the substrate can be formed from ultra high molecular weight polyethylene (UHMWPE). Combinations of two or more of these materials can also be used. In a more specific embodiment, the substrate is a cobalt-chromium alloy. The substrate can be cleaned and / or polished to a very fine final surface prior to coating. According to one embodiment, the substrate is polished to give an end surface with a surface roughness (Ra) of less than 10 nm prior to obtaining the abrasion resistant coating of this invention because a coarse substrate typically increases the generation of debris compared to a smooth surface, and conversely, a smooth surface reduces the tendency to generate debris. Within this disclosure, the surface roughness is measured with an optical profiler in PSI mode (phase shift interferometry) over an area of ∼400 × 500 µm using a x10 lens and FOV 1 in a Wyko, NT-110 Veeco, described by Kim, "Surface Roughness of Ceramic Femoral Heads after In-Vivo Transfer of Metal Correlation in Polyethylene Wear", Bioceramics and Alterantive Bearings in Join Arthroplasty, J.-D. Chang, K. Billau (ed.) Steinkopff (publisher), 2007, pp. 49-57, measured.
    The coating material is based on silicon nitride and the coating has a thickness of 1 μm to 15 μm. In a specific embodiment, the coating has a thickness of about 1 µm to about 10 µm. Above about 15 µm the coating adhesion is too weak, while below about 1 µm the coating life is too short. As discussed in detail below, the coating is formed by a physical vapor deposition (PVD) process. The hardness of the coating is in the range between 5 and 45 GPa and more specifically from about 15 to 45 GPa, measured with a commercial nanoindenter (CSM Instruments UNHT) with a Berkovich tip using the Oliver-Pharr method (Oliver et al. , An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, Journal of Materials Research, 7 (1992) 1564-1583). The elastic modulus is also measured using the Oliver-Pharr method.
    The coating, as deposited, has a surface roughness Ra of less than 50 nm, more specifically less than about 20 nm. In further specific embodiments, the coating can be polished to a fine surface roughness of less than about 10 nm roughness, with im Prior art methods can be used. In additional specific embodiments, the coatings have a coefficient of friction less than about 0.5, more specifically less than about 0.3, or more specifically less than about 0.25. In further exemplary embodiments, the coating has an abrasion resistance after 10,000 revolutions in bovine serum solution of less than about 10 × 10 7 mm 3 / Nm, measured according to the technique described in Example 1.
    The coating can have a single layer, multiple layers and / or a gradient structure in terms of composition and can optionally be provided with an adhesive layer, if desired. The coating can be crystalline, nanocrystalline or amorphous or a combination of crystalline, nanocrystalline and amorphous. The coating can also contain crystals which are embedded in an amorphous phase. In specific exemplary embodiments, the coating contains Si3N4 or has the formula SixNy, where 2 <x <4 and 3 <y <5, and can be an α-phase, β-phase, gamma phase or an amorphous phase or a combination thereof. A typical average grain size of the coating is less than 1 µm or more specifically less than 500 nm, giving a coating with high strength. In more specific embodiments, the average grain size is greater than about 1 nm.
    The coating can also contain additions of C, H, O or combinations thereof. In specific embodiments, the substitutions are individually below 20 atom% and in a more specific embodiment they are combined less than 20 atom%. Thus, in specific exemplary embodiments, the silicon nitride coating has a composition SixNyWz, where WC, H and / or O and 2 <x <4 and 3 <y <5 and z is such that the material is less than 20 atomic% C, H or O contains. For very high degrees of substitution, the lattice structure is not stable, and other less abrasion-resistant or non-resorbable phases form.
    When abrasion particles are released from the coating, the abrasion particles are small, in some embodiments below 1 micron and in further embodiments below 100 nm. Such particles therefore have a large surface area compared to their volume, which is the rate of dissolution for the particles increased in body fluid.
    The coating described is preferably formed by PVD and in a specific embodiment it is deposited using the reactive sputtering process, wherein nitrogen gas (N2) is admitted into the chamber and with the sputtered molecules (here mainly Si) from a target (a silicon-containing Material) reacts. Suitable flow rates of N2 and argon (Ar) are shown in Table 1. Other gases can also be supplied to the chamber for reaction with the sputtered atoms. For example, ethylene, C2H4, which results in a coating of carbon and hydrogen, can be fed to the chamber. A preferred flow rate of C2H4, if used, is shown in Table 1. The target is suitably silicon. Any exemplary targets include, but are not limited to, silicon carbide, silicon nitride. The power of the target is suitable of 150 W and more. In specific exemplary embodiments, the sputtering process is carried out by radio frequency sputtering, for example with a frequency of more than 10 kHz, more specifically 13.56 kHz.
    In a more specific embodiment, the coatings of this invention are deposited by high power pulse magnetron sputtering (HiPIMS). The coatings can then be deposited using a silicon target in an Ar / N2 atmosphere. Extra carbon can optionally be obtained in the coatings using a carbon target or from a carbon-containing gas / liquid, for example C2H4. The samples can be rotated in the chamber to obtain precipitates of silicon and the carbon target. Precipitation parameters such as target performance and temperature in the chamber can be varied, with the formation of different microstructures and compositions, as indicated in the examples; see Table 3. Suitable parameters for additional exemplary embodiments of the deposition of the coatings are also given in Table 4.
    The substrate temperature during the coating process can be varied as desired. In specific embodiments, the temperature is from about 100 ° C to 600 ° C, more specifically about 200 ° C to 400 ° C. The chamber pressure during the coating process can be varied as desired. In specific embodiments, the chamber pressure is normally from about 0.5 · 10 6 to 2 · 10 5 bar. In specific embodiments, the working gas is typically argon gas.
    The above-mentioned additives (C, H, O) and / or the precipitation process can be used to increase the hardness, the elastic modulus, the abrasion resistance, solubility, surface energy and / or chemical affinity, for example the retention of synovial fluid on the Control coating surface of the coating in vivo. The additives and / or the deposition process can thus influence the functionality of the coating. Higher solubility of the coating results in faster absorption of debris when formed in vivo. In one embodiment, the solubility is controlled via solid substitutions in the silicon nitride lattice. For SixNiy coatings, a higher hardness and a higher elastic modulus are generally obtained if the coating is applied with a lower Si target power, for example in the range from 1 kW to 4 kW. For SixNiyCz coatings, a lower surface roughness is generally obtained if the coating is applied with a lower Si target power, for example in the range from 1 to 4 kW. In addition, the composition can be varied to obtain a desired crystalline structure. For example, dense microstructures with a higher abrasion resistance can be obtained with SixNiy coatings, while columnar and laminar structures can be obtained with SixNiyCz coatings.
    The implants can be of any desired physical shape for use in various locations on the body, and a portion or all of the substrate can be coated with the coating of this invention. For joint implants, the head or the socket can be coated, but it is preferred that both components are coated with the silicon nitride based coating. Both components can have the same type of substrate, e.g. cobalt-chromium-cobalt-chromium, or can be made of different materials. In the case of modular hip joints, both the male and the female part can be coated in order to reduce wear. For knee joint implants, either only the femoral or the tibial component or both components are coated with the silicon nitride-based coating as described herein. For elbow joint implants, either only the bearing parts of the ulnar component, the humeral component, the bearing and the hinge pin are coated, or all of these parts can be coated. Likewise, components for other joints including, not limited to, the shoulder, wrist, knee, fingers and toes, orthopedic and dental screws, needles and plates can be provided with the silicon nitride based coating as described herein.
    Examples
    The following examples demonstrate various embodiments of this invention, the silicon nitride coatings provided on CoCr substrates, and test various properties of the implants.
    example 1
    SixNy coatings were deposited on CoCr substrates of the ASTM F1537 type and also on silicon wafer substrates. First, the substrates were polished to a surface roughness (Ra) of about 8 nm. Before precipitation, the substrates were cleaned by ultrasound in acetone and ethanol for 5 minutes each. The coatings were deposited using reactive RF sputtering (13.56 kHz) using a silicon target with an Ar / N2 plasma atmosphere. Several process parameters were varied to optimize the coating composition and microstructure; See Table 1. For two of the coatings, ethylene gas (C2H4) was introduced into the chamber as a reactive agent to dope the coatings with C. All substrates were heated during the deposition with the exception of coating 2. In order to avoid overheating of the target, the coating process alternated between 10 min sputtering and a 3-minute break for a total sputtering time of 2 hours with the exception of coating 3, which is a coating time of 3 hours. The parameters for coating 1 were the starting parameters and the parameters for the other coatings were varied by this combination.
    Table 1: Parameters during the coating process
    1 - CoCr 10 30 1.0 280 0 300 2 Si CoCr 10 30 1.0 25 0 300 3 Si CoCr 10 30 1.0 280 0 150 4 Si CoCr 10 30 0.5 280 0 300 5 Si CoCr 10 30 1.5 280 0 300 6 - CoCr 30 15 1.0 280 0 300 7 - CoCr 20 20 1.0 280 0 300 8 Si CoCr 20 20 1.5 280 0 300 9 Si - 20 20 0.5 280 0 300 10 Si CoCr 10 30 1.3 280 9 · 10 <-4> 300 11 Si CoCr 10 30 1.3 280 1.5 · 10 <-4> 300
    The coatings were evaluated using nano hardness measurements. The coating hardness was found to be about 22 GPa, which is about the same as that for bulk Si3N4.
    Coating analysis
    EDS (Energy Dispersive Spectroscopy) analysis showed that the coatings contained about 3-5% C, 54-60% N and 36-41% Si, based on atomic percent, and the individual composition for each coating can be seen from table 2. It should be noted that there is a general error in determining the compositions using EDS of about ± 2 atom%, this should be added to the above limits.
    No crystalline structure in the coatings was found in X-ray diffraction (XRD); see Fig. 1. The only crystalline reflections observed could be attributed to Co, Cr and Co3Mo using the International Center for Diffraction Data, References: Cobalt PDF No. 15-0806, Chromium PDF No. 88-2323, and Cobalt-Molybdenum PDF No. 29-0488. But a noticeable amorphous peak in diffraction from the coating (particularly No. 8) at 20-35 ° C was observed; see Fig. 1.
    The selected area electron diffraction (SAED) of the coating 8 using transmission electron microscopy (TEM) produced ring-like patterns with sharp dark speckles, which represent a nanocrystalline structure; Figure 2A. By indexing the electron diffraction pattern, it was evident that all rings were Si3N4. Furthermore, high resolution TEM (HRTEM) images reveal grid edges consistent with a polycrystalline material, Figure 2B. This means that the coatings are nanocrystalline and amorphous.
    Nearly all of the SixNy coatings exhibited a fine surface nanostructure, as illustrated in Figure 3A. The only exception was Coating 2 (deposited at a lower substrate temperature) which showed thin coating spots; Figure 3B. The surface roughness (Ra) of the coating 2 is too great, about 250 nm, while it is about 5 nm on Si substrates and 10 nm on CoCr substrates for the other coatings. This corresponds to an Ra of about 3 to 8 nm for the Si and CoCr substrates before coating deposition.
    The pictures of the cross-sections of the coatings show that the character of the coating structure differs, as shown in FIGS. 4A-4D. Coatings 5 and 8 (Figures 4B and 4C) have a columnar structure and a thickness of approximately 1.4 µm. Coating 3, Fig. 4A (lower energy applied to target) has a similar structure to coatings 5 and 8, but with finer pillars, and the coating thickness is approximately 600 nm. Coating 10, Fig. 4D (deposited with C2H4) is approximately 1 , 2 µm thick, has a much coarser microstructure than coatings 3, 5 and 8, but not as a pronounced columnar structure. Each coating with the exception of coating 3 had a thickness of 1.2-1.8 µm, however this variation within a sample could also be due to the decreasing rate of deposition from the center below the target.
    Friction and abrasion test
    The coatings were tested tribologically using a ball-on-disk system, the coated disks against a stationary polished ball made of Si3N4 (6 mm diameter, Spekuma, Sweden, represents a coated counter surface) were pushed during the Coefficient of friction was measured continuously. The process was performed in a similar manner to ASTM F 732-00 (Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses, ASTM International, 2006). Under the ball, the tested material was rotated to form an abrasion track with a diameter of 5 mm at a speed of 0.04 m / s and a normal load of 1 N at room temperature. The abrasion test was carried out in a serum solution of 25% fetal bovine serum (Gibco) with sodium azide and ethylenediaminetetraacetic acid (EDTA) according to ASTM F 732-00. The abrasion rate is quantified with a specific abrasion rate according to the equation:
    The abrasion rate, with the exception of the ball, was calculated from the abraded cross-sectional area, measured with vertical scanning interferometry (VSI, Wyko NT-110). The friction measurements showed no significant difference in the coefficient of friction between the different types of coating and bulk CoCr, Figure 5. The majority of the coatings had a coefficient of friction between 0.12 and 0.22, represented by the gray area in Figures 4A-4D . Almost all tests began with a relatively quick and brief reduction in friction and then a longer increase in the coefficient of friction, which then stabilized after about 2000 revolutions. Coating 2 (deposited at a lower substrate temperature) had a coefficient of friction at 0.3 which is much higher than the rest of the coatings.
    The low rate of wear of the coating demonstrates the potential of these coatings for use on bearing surfaces of joints. The coating topography was gradually smoothed out while sliding against the Si3N4 ball in bovine serum solution as in coating 8, FIG. 6.
    The specific abrasion rate of the coatings after 10,000 revolutions was about 3 × 10 7 mm 3 / Nm, FIG. 7. In this picture, in which the z-scale has a higher magnification, there were grooves along the Abrasion trace also visible in the coating abrasion trace. The amount of abrasion of the coatings was similar to that of bulk Si3N4, which had a specific abrasion rate of about 1 × 10 7 mm 3 / Nm. For CoCr, the specific wear rate was much higher at around 60 × 10 7 mm 3 / Nm.
    hardness
    The hardness of the coatings was obtained with a commercial nanoindenter (CSM Instruments UNHT) with a Berkovich tip. A total of 30 notches per sample were completed with a maximum depth of 50 nm. The hardness and the elastic modulus were determined using the Oliver-Pharr method.
    Summary of the coating properties
    Despite the variation of several precipitation parameters, there were not so many differences in terms of chemical composition, phase composition, nanostructure, tribological properties or hardness; see table 2.
    Table 2: Coating properties as well as atomic composition for some investigated coatings
    1 0.15 5 40 54 3.0 · 10 <-7> 21.5 ± 2.7 2 * * 0.3 4 36 60 * 24.2 ± 3.0 3 0.2 4 41 55 2.7 · 10 <-7> 21.2 ± 2.0 4 0.15 4 40 56 3.2-10 <-7> 22.3 ± 2.5 8 0.15 3 39 58 3.2 10 <-7> 18.0 ± 2.2 10 0.15 5 39 56 3.0 · 10 <-7> 21.6 ± 3.7* The coating roughness was higher than the abrasion notches** The coating was deposited at a lower temperature
    Example 2
    SixNy and SixNyCz coatings were deposited on silicon wafers (001) with a high-performance pulse magnetron sputtering system (HiPIMS, CemeCon CC800 / 9, Germany). The vacuum chamber (85 × 85 × 100 cm) of the precipitation system on an industrial scale is equipped with four rectangular magnetron sputtering cathodes (50 × 8.8 cm), which face a table holder in the middle. Unipolar pulses were imposed on the magnetrons using a pulse unit (SINEX 3, Chemfilt Ionsputtering AB, Sweden) charged by a direct current (DC) power supply (Pinnacle, Advanced Energy). The precipitation was carried out with a silicon target with an Ar / N2 atmosphere. A Si target (purity 99.999%) was used for all precipitates. Extra carbon is obtained in a number of coatings (Nos. 18 to 28) with a carbon target (purity 99.5%). The samples are then rotated in the chamber to obtain precipitates of both silicon and the carbon target at a distance of 7.5 cm from the targets. For the SiN coatings, the substrate was statically perpendicular to the Si target, and for the SiCN coatings, the substrates were rotated. Precipitation parameters such as target performance and temperature in the chamber were varied, with the formation of different microstructures and compositions, see Table 3. Table 4 shows the constant parameters during the precipitation. Substrates were ultrasonically cleaned in acetone and ethanol in 5 min sequences and dried in dry N2 gas before introduction into the chamber.
    Table 3: Precipitation parameters for SixNy and SixNyCz coatings on silicon wafers, (*) are also reflected for CoCr substrate (ASTM F75)
    12 1000 0 250 1.2 13 2000 0 250 2.8 14 3000 0 250 4.3 15 4000 0 250 4.4 16 2000 0 520 2.5 17 3000 0 520 3.8 18 * 4000 500 250 0.50 19 * 4000 700 250 0.50 20 4000 1400 250 0.55 21 1000 700 250 0.40 22 1000 1000 250 0.85 23 1000 1400 250 0.80 24 * 4000 500 520 1.10 25 4000 700 520 0.70 26 4000 1400 520 0.70 27 1000 700 520 0.70 28 1000 1000 520 0.70
    Table 4: Parameters kept constant for all precipitation
    Pressure [Pa] 0.4 Ar flow [sccm] 360 N2 flow [sccm] 60 bias voltage [V] -100 pulse frequency [hz] 300 pulse width [μs] 200 substrate Si wafer
    The surface roughness (Ra) of the coatings on Si wafer substrates are approximately 10 nm, for samples deposited on CoCr substrates the Ra values are approximately 20 nm when measured over an area of approximately 0.3 mm 2 . When measured at more than 1 μm 2, the surface roughness of the coating on Si wafers was from 0.3 nm to 4 nm.
    The coatings exhibited three different types of structures seen in cross section, dense (coatings 12-17), laminar (coatings 18-20 and 24-26) and columnar (coatings 21-23 and 27-28), see Figures 8A-8C.
    Hardness measurements were carried out as in Example 1, but at a maximum depth of 40 nm. The elastic modulus is based on these measurements with Poisson ratios of 0.25 for coatings and the reference material Si3N4 (Walmsley et al, Poisson's Ratio of Low -Temperature PECVD Silicon Nitride Think Films, Journal of Microelectromechanical Systems, 16 (2007) 622-627) and 0.3 for CoCr.
    The hardness for SixNyCz coatings is in the range from 9 to 19 GPa and for SixNy coatings from 17 to 21 GPa. The elastic modulus of the SixNyCz coatings was from 167 to 212 GPa and that of SixNy coatings is from 148 to 218 GPa, see Table 6.
    The adhesion and cohesion were examined by micro-scratching; See Fig. 9. It is believed that the types of cohesive defects for SixNyCz coatings, cracks and chips are related to different microstructures for coatings deposited at different Si target powers. When deposited on CoCr, the defect load was only about half that of the Si wafers. This was expected due to the softer substrate material and poor adhesion to CoCr.
    Friction and abrasion test
    Abrasion and friction tests were carried out in the same manner as in Example 1 with a ball-on-disk test. The SixNy coatings tested for 10,000 revolutions had a coefficient of friction of approximately 0.20-0.28 (with the exception of coating 15), see Figure 10. SixNyCz coatings did not show the same abrasion resistance and abrasion through the coating before 10000 revolutions.
    The wear cross-sections are shown in FIG. The calculated specific wear rate is given in Table 6.
    composition
    XRD shows no crystalline structure in the coating, only a few small amorphous peaks can be seen, FIG. 12.
    EDS analysis showed the compositions in the coatings, see Table 5. The C content is in the range from 0 to 2 at.% Without using the carbon target and from 6 to 35 at.% With the carbon target. Si was from 37 to 77 at% and N was from 19 to 29. As above, the general error in determining compositions using EDS is about ± 2 at%. The XPS analysis confirms that the silicon atoms bind to nitrogen atoms.
    Summary of the coating properties
    The coating properties and the composition of Example 2 are summarized in Tables 5 and 6. The SixNy coatings showed a similar abrasion resistance as in Example 1 as well as a somewhat lower hardness.
    Table 5: Atomic composition for some coatings. Values with (*) are tested on CoCr substrate.
    12 1 69 29 13 2 74 24 14 1 75 23 15 0 76 22 16 1 74 23 17 1 77 21 18 6 68 25 18 * 8 68 23 19 9 65 25 19 * 9 66 23 20 14 62 22 21 23 46 26 22 30 40 26 23 35 37 24 24 6 70 24 24 * 8 70 22 25 9 71 19 26 15 66 18 27 22 49 26 28 29 44 25
    Table 6: Mechanical properties of some coatings. Values marked with (*) are tested on CoCr substrate.
    12 0.21 1.3 · 10 <-7> 21.2 ± 3.1 212 ± 18-214 ± 12 13 0.24 2.2 · 10 <-7> 18.4 ± 2.1 212 ± 14 - 260 ± 15 14 0.28 2.3 · 10 <-7> 17.2 ± 3.1 199 ± 22 - no tearing 15> 0.33 240 · 10 <-7> 17.2 ± 3 , 0 199 ± 30 - no cracking 16 0.20 2.1 10 <-7> 18.8 ± 2.6 201 ± 12 - 265 ± 8 17 0.27 4.8 10 <-7> 18, 8 ± 1.1 167 ± 8 - no tearing 18 - - 16.0 ± 1.6 199 ± 15 68 ± 6 85 ± 5 18 * - n / a 16.3 ± 2.8 216 ± 25 26 ± 2 36 ± 5 19 - - 15.2 ± 1.7 196 ± 12 55 ± 2 81 ± 7 19 * - n / a 16.1 ± 2.3 202 ± 16 20 ± 3 33 ± 4 20 - - 14.8 ± 3.5 178 ± 27 65 ± 7 83 ± 8 21 - - 10.7 ± 1.4 148 ± 12 39 ± 6 46 ± 3 22 - - 11.1 ± 1.6 149 ± 12 42 ± 2 52 ± 8 23 - - 9, 9 ± 1.6 137 ± 13 36 ± 2 42 ± 1 24 - - 18.5 ± 1.6 210 ± 10 68 ± 6 80 ± 4 24 * - n / a 17.0 ± 3, 9 218 ± 33 35 ± 3 67 ± 5 25 - - 18.2 ± 1.6 216 ± 11 77 ± 3 95 ± 5 26 - - 18.6 ± 2.6 202 ± 17 68 ± 5 86 ± 2 27 - - 17.5 ± 2.1 218 ± 16 86 ± 9 105 ± 15 28 - - 15.4 ± 2.6 195 ± 18 62 ± 4 76 ± 2 Si3N4 1.0 · 10 <-7> 7.4 ± 0.7 210 ± 14 n / an / a CoCr 60 · 10 <-7> 24.5 ± 4.5 314 ± 26 n / an / a
    Increased adhesion
    The coatings of Example 2 were further developed to increase the adhesion with an etching process before the deposition as well as with intermittent biasing steps or with a nitrogen gradient and high frequency during the deposition. The procedures are described in Tables 7 and 8. The difference in adhesion is shown in FIG. 13 in a Rockwell test with a load of 100 kg.
    Other alternatives for improving the adhesion can be provided by adhesive layers such as Si or Cr or a pulsed board as well as targets. Intermittent biasing steps and gradients are used to reduce residual stresses and improve the adhesion of the coating.
    Table 7: Etching process to increase adhesion
    Performance of the Ti target [W] 1500 Ar flux [sccm] 353 Kr flux [sccm] 267 Etching bias [V] -200 Temperature [° C.] -325 Duration [s] 180
    Table 8: Coating methods to increase adhesion
    Si target power [kW] 1 1 1 pressure [Pa] 0.4 0.4 0.4 Ar flow [sccm] 360 360 360 N2 flow [sccm] 60 60 0 to 100, in steps of 1 sccm / 60 s, then 60 bias voltage [V] -100 5x (-100 for 1400 s, -500 for 200 s) -100 pulse frequency [hz] 300 300 500 pulse width [µs] 200 200 200 temperature [° C] ~ 325 -325 -325
    High thickness
    Coatings with a high thickness of about 10 μm to 15 μm can be obtained. An example of a thick version of the coating 12 is shown in FIG.
    Solubility test
    Because of the very small amount of debris formation in the tests, it is very difficult to measure the rate of disintegration of the actual debris using the methods known to the inventors. Instead, a commercial silicon nitride powder (P95H, Akzo Nobel) was mixed with PBS using three different pH values: 4.8, 6.5 and 7.4. PBS has a natural pH of 7.4 and hydrochloric acid has been added to reduce the value. The mixture was stored in plastic tubes with plastic lids. The tubes were placed on a tilting platform shaker and stored at 37 ° C. for 35 and 75 days, respectively (Table 9). The average grain size of the powder was approximately 1 µm (measured by SEM and optical microscopy). 100 mg silicon nitride powder was mixed with 15 ml PBS. After the storage time, the mixture was filtered through a 0.2 µm PTFE membrane using a syringe. After filtration, ICP-MS (inductively coupled plasma mass spectrometry) was used to determine the silicon ion content of the solutions.
    Table 9: Solubility test: number of samples per pH and time
    Time (days) 35 4 4 4 1 1 1 75 4 4 4 1 1 1
    The concentration of free Si in the filtered solutions indicates that some powder was dissolved. The concentration of Si in the filtered PBS solutions was about 75 ml / 1 for all pH variations and about the same for the different incubation periods, see FIG. 15. All samples of the PBS solutions without any addition of powder showed Si concentrations of less than 0.5 ml / 1.
    Amorphous silicon nitride particles (approximately 30-50 nm) were also examined for dissolution in phosphate-buffered saline (PBS, pH 7.3, 37 ° C), Fig. 16. The particles are separated from PBS by centrifugation.
    The tests showed that wear-resistant, low-friction silicon nitride coatings can be produced at deposition temperatures of more than about 100 ° C. The abrasion resistance was considerably higher than with CoCr alone and similar to bulk silicon nitride ceramics. In addition, silicon nitride particles were shown to dissolve in simulated body fluids.
    The results show that it is possible to deposit silicon nitride films using sputtering techniques and that the films are more abrasion resistant than the substrate material. In addition, silicon nitride is slowly dissolved in simulated body fluids.
    The specific examples and embodiments described herein are illustrative only and are not intended to limit this invention, which is defined by the claims. Furthermore, embodiments and examples as well as advantages thereof are apparent to those skilled in the art in view of this description and fall within the scope of the claimed invention.
    credentials
    [1] A. Sargeant and T. Goswami, Hip Impants: Paper V. Physiological effects, Materials & Design 27 (2006) 287-307. [2] A. Sargeant and T. Goswami, Hip implants - Paper VI - Ion concentrations, Materials & Design 28 (2007) 155-171. [3] P. Aspenberg, A. Anttila, Y.T. Konttinen, R. Lappalainen, S.B. Goodman, L. Nordsletten and S. Santavirta, Benign response to particles of diamond and SiC: bone chamber studies of new joint replacement coating materials in rabbits, Biomaterials 17 (1996) 807-812. [4] D. Xiong and S. Ge, Friction and wear properties of UHMWPE / Al203 ceramic under different lubricating conditions, Wear 250 (2001) 242-245. [5] B.S. Bal, A. Khandkar, R. Lakshminarayanan, I. Clarke, A.A. Hoffman, and M.N. Rahaman, Fabrication and Testing of Silicon Nitride Bearings in Total Hip Arthroplasty: Winner of the 2007 "HAP" PAUL Award, The Journal of Arthroplasty 24 (2009) 110-116. [6] R.R. Wang, G.E. Welsch and O. Monteiro, Silicon nitride coating on titanium to enable titanium-ceramic bonding, Journal of Biomedical Materials Research 46 (1999) 262-270. [7] M. Matsuoka, S. Isotani, W. Sucasaire, L.S. Zambom and K. Ogata, Chemical bonding and composition of silicon nitride films prepared by inductively coupled plasma chemical vapor deposition, Surface and Coatings Technology 204 (2010) 2923-2927. [8] S.-L. Ku and C.-C. Lee, Surface characterization and properties of silicon nitride films prepared by ion-assisted deposition, Surface and Coatings Technology 204 (2010) 3234-3237. [9] H.P. Löbl and M. Huppertz, Thermal stability of nonstoichiometric silicon nitride films made by reactive dc magnetron sputter deposition, Thin Solid Films 317 (1998) 153-156. [10] K. Kazuo and N. Shinji, Ceramic-coated prosthetic implants, in Japan Kokai Tokyo Koho, N.S.P. Co, editor. 1989: Japan. [11] L. Huang, K.W. Hipps, J.T. Dickinson, U. Mazur and X.D. Wang, Structure and composition studies for silicon nitride thin films deposited by single ion bean sputter deposition, Thin Solid Films 299 (1997) 104-109. [12] International Center for Diffraction Data, References: Cobalt PDF No. 15-0806. [13] International Center for Diffraction Data, References: Chromium PDF No. 88-2323. [14] International Center for Diffraction Data, References: Cobalt-Molybdenum PDF No. 29-0488.
    权利要求:
    Claims (8)
    [1]
    1. An implant comprising a substrate and a coating on a surface of the substrate, the coating containing silicon nitride and having a thickness of 1 to 15 μm,characterized in that the coating:is formed by physical vapor precipitation at a precipitation temperature of more than 100 ° C; has a hardness of 5 to 45 GPa; and, as deposited, has a surface roughness Ra of less than 50 nm.
    [2]
    2. The implant of claim 1, wherein the coating contains up to 20 atomic percent of C, H or O individually.
    [3]
    3. The implant of claim 2, wherein the coating contains up to 20 atomic percent C; or up to 20 atomic percent of a combination of two or more of C, H and O contains.
    [4]
    4. The implant of any preceding claim, wherein the coating, as deposited, has a surface roughness Ra of less than 20 nm.
    [5]
    5. Implant according to one of the preceding claims, wherein the coating contains a nanocrystalline structure, an amorphous structure or a combination thereof.
    [6]
    6. Implant according to one of the preceding claims, wherein the coating has a multilayer structure.
    [7]
    7. Implant according to one of the preceding claims, wherein the substrate is formed from cobalt-chromium alloy, titanium, titanium alloy, stainless steel, ultra-high molecular weight polyethylene or ceramic.
    [8]
    8. The implant of claim 1, wherein the coating is formed by high power pulse magnetron sputtering.
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    US201161528899P| true| 2011-08-30|2011-08-30|
    SE1200277|2012-05-08|
    PCT/IB2012/054471|WO2013030787A1|2011-08-30|2012-08-30|Implants with wear resistant coatings and methods|
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