Patent Application
20220154322
The present application pertains to the field of materials for use in medical implants, and relates in particular to a preparation method and application of an oxidized ceramic layer on the surface of zirconium and zirconium alloy.
As have been confirmed by scientists many years ago, zirconium and zirconium alloys have excellent mechanical properties, corrosion resistance and biocompatibility. Therefore, they have been recognized as very good materials for use in medical implants. For the materials used for medical implants, service life of the medical implant is most important. Especially, when the medical implant is used in the young patient, the desirable implant is able to be used throughout the lifetime of the patient.
However, zirconium and zirconium alloys are not sufficiently resistant to wear, which limits their application to bearing implants such as hip and knee joint replacements. The service lifespan of such bearing implants are affected by the factors including not only mechanical properties, corrosion resistance and biocompatibility of the used zirconium or zirconium alloy but also the generated wear of zirconium or zirconium alloy surface as it moves relative to another contacting surface made of, such as ultra-high molecular weight polyethylene. Such wear not only create numerous wear particles to enhance friction coefficients of articular surfaces and thus further intensify wear, but also release metal ions that may cause long-lasting harm to human health. Therefore, it is necessary to strengthen wear resistance property when zirconium or a zirconium alloy is used manufacture such bearing types of implant devices.
U.S. Pat. No. 2,987,352 A discloses to oxidize a zirconium/zirconium alloy in air to form a blue-black oxide layer on their surfaces. The formed blue-black oxidation ceramic surface layer is very hard and compact, imparting significantly improved wear resistance to the zirconium/zirconium alloy. Following this thought, U.S. Pat. No. 5,037,438 A discloses a zirconium alloy prosthesis with a zirconium oxide surface. However, the oxidation ceramic surface layer generally has a non-uniform thickness. In order to decrease friction coefficients of relative movement surfaces to alleviate wear, it is necessary to reduce the roughness of the surface oxidation ceramic layer as much as possible. Therefore, the oxide surface layer must be finely polished. However, the polishing process results in various thickness losses of the oxide surface layer at different locations. Besides, the blue-black oxidation ceramic surface layer tends to have a very thin and uneven thickness. This causes the complete removal of the oxidation ceramic surface layer at locations with thinner thicknesses, and thus results in the loss of integrity of the oxidation ceramic surface layer, which seriously impairs wear resistance of the prosthesis. The uneven oxidation ceramic surface layer results in an uneven contact with the metal substrate at the interface, which weakens bonding strength between the oxidation ceramic surface layer and the metal substrate. This causes an easy peel-off of the oxidation ceramic surface layer from the metal substrate during use, and thus brings great risks.
Further studies have shown that the growth of a zirconium oxide coating proceeds at a rate that is not constant and will experience a turning point. Before this point, increase of thickness for the coating follows the parabolic profile and the formed oxidation ceramic surface layer has an excellent compactness, a high bonding strength and a good wear resistance. After this point, increase of thickness for the coating follows the linear profile, and the formed coating has numerous micro-cracks therein, a poor bonding strength and a bad wear resistance (Tatsumi Arima et al., Oxidation properties of Zr—Nb alloys at 973-1273 K in air. Progress in Nuclear Energy, 51(2009):307-312.). For an oxidation ceramic surface layer, an optimal thickness is in the range of 3-7 μm. With the thickness in this range, the coating possesses an optimal internal compactness, a high bonding strength and an excellent wear resistance. However, in practical operations, after a formed oxidation ceramic surface layer is polished to a target surface roughness Ra of 0.02 μm or less required for a medical implant, the oxidation ceramic surface layer lose a thickness of 2-5 μm. Obviously, if the oxidation ceramic surface layer having a thickness within the optimal thickness range has been polished, the remaining oxidation ceramic surface layer would have an ultimate thickness that cannot meet application requirements. Whereas, in order to obtain a sufficient remaining thickness of the oxidation ceramic surface layer after the polishing process, it is required to form an initial oxidation ceramic surface layer with an increased thickness. However, the increased thickness impairs properties of the oxidation ceramic surface layer.
Additionally, polishing is indispensible in traditional surface oxidation process. If the cooling process after the completion of high-temperature oxidation is a slow cooling process, the oxidation ceramic surface layer has its thickness further increased in this cooling process as the zirconium or a zirconium alloy is still exposed in the oxidizing atmosphere. However, the oxide layer formed at improper temperatures has a poor quality and has to be polished and removed. If the cooling process is a quick cooling process, due to the significant temperature difference between the inside and outside of the workpiece, thermal stress causes micro-cracks to develop in an outermost surface area of the oxide layer easily. This also results in the necessity of polishing and removal of such area.
In view of the above cases, it is desirable to develop a new method for controlling the roughness of the oxidation ceramic surface layer to avoid the adverse effects of the polishing process on the oxidation ceramic surface layer.
In order to overcome the above problems, present application proposes a method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy, which is able to directly obtain the oxidation ceramic surface layer having a satisfied roughness and a controlled uniform thickness without the need of a polishing process after the surface oxidization treatment on the zirconium or zirconium alloy, and thus enables to solve the problems of the surfaces of the zirconium or zirconium alloys caused by polishing of the oxidation ceramic surface layer. Here, the term of “zirconium/zirconium alloy” refers to that the method for preparing an oxidation ceramic surface layer is applicable to pure zirconium metal and zirconium alloys.
In order to solve the above problems, present application provides a method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy, comprising steps of:
1) lowering a roughness of a targeted area of the zirconium or zirconium alloy on which a surface oxidization treatment is to be performed, the roughness being controlled to 0.01 μm or less;
2) performing the surface oxidation treatment in an atmosphere containing an oxidizing gas to form an oxidation ceramic surface layer; and
3) introducing an inactive gas to replace the oxidizing gas used in step 2) and initiating a cooling process to complete preparation of the oxidation ceramic surface layer without performing a subsequent treatment of lowering a roughness of the oxidation ceramic surface layer.
Optionally, the roughness is lowered to a value in the range of 0.002 μm to 0.010 μm in step 1).
Optionally, after the oxidation treatment in step 2), a thickness of the oxidation ceramic surface layer on the targeted area is controlled within a range of 1 μm to 20 μm.
Optionally, the surface oxidation treatment in step 2) comprises heating to a temperature in the range of 500° C. to 700° C. and maintaining the temperature for 0.5-10 h.
Optionally, the roughness of the targeted area is lowered in step 1) by means of grinding, mechanical polishing, fine machining, vibratory polishing or any combination thereof.
Optionally, the inactive gas in step 3) is one or more selected from the group consisting of nitrogen and rare gases.
Optionally, the targeted area for the surface oxidization treatment is an area to be brought into direct contact with another bearing surface.
Optionally, the atmosphere containing the oxidizing gas in step 2) is an atmosphere containing oxygen and/or ozone.
The present application also provides a method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy, comprising steps of:
1) lowering a roughness of a targeted area of the zirconium or zirconium alloy on which a surface oxidization treatment is to be performed, the roughness being controlled to 0.01 μm or less;
2) performing the surface oxidization treatment on the surface of the zirconium or zirconium alloy to form an oxidation ceramic surface layer; and
3) lowering a roughness of the formed oxidation ceramic surface layer.
The present application also provides a material for use in medical implants, comprising a metal substrate, an oxygen-rich diffusion layer and an oxidation ceramic surface layer, the metal substrate being made of zirconium or a zirconium alloy, wherein the oxygen-rich diffusion layer and the oxidation ceramic surface layer are formed by the method as defined above.
Optionally, the medical implants are bearing implants used in hip joint or knee joint.
According to present application, roughness of a surface has been controlled before the surface oxidization treatment, thereby enabling the surface roughness after oxidization treatment to meet application requirements directly. Moreover, the replacement of oxidizing gas with the inactive gas after the surface oxidization treatment avoids the formation of poor-quality layer that has to be removed during the cooling process. The above two advantages enables to completely avoid the necessity of subsequent polishing process, and to remain integrity and uniformity of the oxidation ceramic surface layer as well as ensuring the protective property of the oxidation ceramic surface layer.
In the figures,
10, oxidation ceramic surface layer; 20, oxygen-rich diffusion layer; 30, metal substrate.
The method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy comprises the following specific steps:
(1) Lowering roughness Ra of the zirconium/zirconium alloy surface on which the surface oxidization treatment is to be performed, at least the portion thereof to be brought into direct contact with another bearing surface to a value below 0.01 μm (i.e., Ra<0.01 μm), preferably in the range of 0.002-0.010 μm (i.e., Ra=0.002-0.010 μm), more preferably in the range of 0.003-0.008 μm (i.e., Ra=0.003-0.008 μm). For example, Ra may be lowered into the range of 0.004-0.007 μm (i.e., Ra=0.004-0.007 μm) or of 0.005-0.006 μm (i.e., Ra=0.005-0.006 μm). Here, the word “bearing” means the relationship that the surface of the implant is to be squeezed against and moves relative to another object (another implant or human bone, etc.), such as the relationship between the tibial joint surface of knee joint and the femoral joint surface. The term of “another bearing surface” refers to the surface of another implant or human bone to be brought into contact with the implant surface that has been performed a surface oxidization treatment.
The common zirconium or zirconium alloy medical implants that have been performed surface oxidization treatments, in particular hip or knee joint prostheses fabricated from zirconium-niobium alloys, are generally required to have a surface roughness of 0.02 μm or less. Such surface roughness has to be realized by polishing the oxidation ceramic surface layer after oxidation treatment in prior art. On the contrary, according to present application, the metal surface is pre-treated to control the roughness within a predetermined range in advance. Inventors have confirmed through repeat experiments that the metal having the roughness within the predetermined range is able to be oxidized and thus form an oxidation ceramic surface layer having a surface roughness that meets application requirements directly, enabling to omit the polishing step after the oxidization treatment. In this surface roughness control step, if the roughness Ra is lowered to a value above 0.010 μm, the oxidation ceramic layer resulting from the surface oxidation treatment may have a surface roughness Ra greater than 0.02 μm that fails to satisfy requirements; and if the roughness Ra is lowered to 0.002 μm or less, the cost is too high and the roughness exceed actual needs, which is thus not recommended in consideration of cost effectiveness
The surface roughness modification can be accomplished by grinding, mechanical polishing, fine machining, vibratory polishing or any combination thereof.
(2) Performing a surface oxidation treatment to the zirconium or zirconium alloy that has the surface roughness thereof changed in step (1). Specifically, the zirconium or zirconium alloy from step (1) is placed in an atmosphere containing an oxidizing gas, heated to a temperature in the range of 500-700° C. (Preferably, 550-600° C.) and maintained the zirconium or zirconium alloy at the high temperature for 0.5-10 h (Preferably, 2-6 h). The oxidation ceramic surface layer formed on the zirconium or zirconium alloy has a thickness of 1-20 μm, preferably 3-10 μm, more preferably 3-7 μm, e.g., 4 μm, 5 μm or 6 μm. The oxidizing gas refers to the gas having an oxidizability, such as oxygen or ozone, and the atmosphere containing the oxidizing gas refers to the atmosphere that contains said oxidizing gas and is preferred to be air in consideration of economy and easy availability.
If the oxidation ceramic surface layer grows to have an excessively large thickness, the occurrence of numerous micro-cracks in the layerc as well as the poor bonding strength and bad wear resistance are resulted. If the layer is too thin, it may suffer from insufficient wear resistance. If the oxidation ceramic surface layer has a thickness in the above range, the layer is able to have an optimal internal compactness, a high bonding strength and an excellent wear resistance. The surface oxidation ceramic layer does not need to be too thick as there is no need to polish the layer in subsequent. Therefore, the thickness of surface oxidation ceramic layer can be controlled within the above range directly and the elimination of subsequent polishing enables to prove integrity and uniformity of the oxidation ceramic surface layer, resulting in additional improvements in its overall performance.
Preferably, during a cooling process, the oxidizing gas may be replaced by introducing nitrogen or an inert gas such as helium, neon or argon, or any combination thereof. In this way, surface oxidation treatment of the zirconium/zirconium alloy is terminated and the temperature slowly declines to room temperature.
The subsequent replacement with the inactive gas avoids the formation during the cooling process of a membrane layercoating with inferior quality that has to be removed in subsequent, thus resulting in a further increase in the quality of the oxidation ceramic surface layer. Through the upstream roughness control and the downstream gas replacement, the polishing after oxidization treatment is successfully omitted and thus the problems arising from the polishing are solved.
The above method can be used to fabricate a material for use in medical implants, which includes a metal substrate 30, a oxygen-rich diffusion layer 20 and a oxidation ceramic surface layer 10 that are arranged from inside to outside, as shown in
It is to be noted that in each of the metallurgical microscope photographs shown in
For ease of understanding, the method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy will be further described below with reference to several embodiments. These embodiments are presented for the mere purpose of illustrating the present application and do not limit protection scope thereof in any sense.
Unless particularly noted, each material or reagent used in the following embodiments is commercially available, and each process or parameter adopted in the method can be realized by conventional techniques.
Zr-2.5 Nb alloy (a zirconium alloy containing 2.5 wt % of Nb) samples were ground and polished so that Sample 1 had a lowered surface roughness Ra of 0.3792 μm and Sample 2 had a lowered surface roughness Ra of 0.0038 μm. The samples 1 and 2 were together placed into a tube furnace, heated to 550° C. in air and maintained at the temperature for 6 h. Subsequently, air was evacuated and argon was introduced to the furnace. After the slow cooling at a rate of 5° C./min to 100° C. or below, the samples 1 and 2 were taken out and measured with a roughness gauge. The results showed, after the oxidation treatment, the roughness Ra of Sample 1 increased to 0.6852 μm and that of Sample 2 increased to 0.0158 μm.
As can be seen from
By contrast, Sample 2 of
Industrial pure zirconium were ground and polished so that Sample 3 had a lowered surface roughness Ra of 0.3886 μm and Sample 4 had a lowered surface roughness Ra of 0.0042 μm. Samples 3 and 4 were together placed into a tube furnace, heated to 600° C. in air and maintained at the temperature for 4 h. Subsequently, air was evacuated and argon was introduced to the furnace. After the slow cooling at a rate of 5° C./min to 100° C. or below, the samples 3 and 4 were taken out and measured with a roughness gauge. The results showed, after the oxidation treatment, the roughness Ra of Sample 3 increased to 0.7705 μm and that of Sample 4 increased to 0.0158 μm.
As shown in
As shown in
Zr-2.5 Nb alloy samples were ground and polished so that Sample 5 had a lowered surface roughness Ra of 0.0056 μm and Sample No. 6 had a lowered surface roughness Ra of 0.0055 μm. Samples 5 and 6 were placed into separate tube furnaces, and were both heated to 600° C. in air and maintained at the temperature for 4 h. Subsequently, for the furnace with Sample 5 placed therein, air was evacuated from and argon was introduced to the furnace following by the slow cooling at a rate of 5° C./min to 100° C. or below. Then, Sample 5 was taken out from the furnace. By contrast, Sample 6 was slowly cooled still in the oxidizing atmosphere at a rate of 5° C./min to 100° C. or below and then taken out. As measured with a roughness gauge, after the oxidation treatment, the roughness Ra of Sample 5 increased to 0.0162 μm and that of Sample 6 increased to 0.0426 μm.
In summary, according to present application, roughness Ra of a zirconium/zirconium alloy surface has been lowered to Ra<0.01 μm before the surface oxidization treatment, allowing the oxidation ceramic surface layer to grows to the optimal thickness as well as enabling to control the roughness just within the required range (Ra<0.02 μm) of finished product. The cooling process in an inert atmosphere enables to avoid performance degradation of the oxidation ceramic surface layer during the cooling process, thereby enabling the grounding and polishing treatment after the oxidation treatment to be omitted to obtain an integral oxidation ceramic surface layer. In addition, as it is unnecessary to reserve a certain thickness for the loss arising from the grinding and polishing treatment, the oxidation ceramic surface layer is allowed to grow exactly to the optical thickness. This enables the oxide layer to have an optimal internal compactness, a high bonding strength and an excellent wear resistance.
It is to be noted that, the medical implants as mentioned herein refer to implantable medical instruments that can be placed into surgically created or naturally occurring cavities in human bodies. Examples of the medical implants may include, but are not limited to, surgical implants such as artificial joints, (orthopedic, spinal, cardiovascular and neurosurgical) implants, structural prostheses, dentures and other artificial organs; implants made of metal materials (including stainless steel, cobalt-based alloys, titanium and alloys thereof and shape memory alloys), polymers, high molecular materials, inorganic non-metallic materials, ceramic materials, etc.; implantable instruments such as implantable orthopedic instruments, implantable aesthetic and plastic surgical instrument and materials; implantable appliances such as bones (plates, screws, pins, rods), intra-spinal fixation devices, staplers, patellar concentrators, bone wax, bone repair materials, plastic surgical materials, heart or tissue repair materials, intraocular filling materials, nerve patch, etc.; interventional instruments such as interventional catheters, stents, embolization and other devices; and orthopedic (orthopedic) surgical instruments such as scalpels, drills, scissors, forceps, saws, chisels, files, hooks, needle slickers, active instruments, extremity extension braces, multi-purpose unilateral external fixation devices and other instruments for orthopedic (orthopedic) surgical use.
Finally, it is to be noted that the above embodiments are provided merely to illustrate the technical solution of present application and are not intended to limit it in any way. Although the present application has been described in detail with reference to the above embodiments, modifications to those embodiments are still possible, or equivalent substituents of all or some of the technical features thereof can be made by those of ordinary skill in the art. Such modifications substituents do not cause the essence of corresponding technical solution to depart from the protection scope of the various embodiments of the present application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201910173412.8 | Mar 2019 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/118460 | 11/14/2019 | WO | 00 |
