Patent Application
20110125277
The present invention relates generally to an implant device, and more specifically the invention relates to an implant device for an articular surface in a joint such as a knee, elbow or shoulder. The present invention also relates to a method for manufacturing such an implant.
Pain and overuse disorders of the joints of the body is a common problem. For instance, one of the most important joints which is liable to wearing and disease is the knee. The knee provides support and mobility and is the largest and strongest joint in the body. Pain in the knee can be caused by for example injury, arthritis or infection. The weight-bearing and articulating surfaces of the knees, and of other joints, are covered with a layer of soft tissue that typically comprises a significant amount of hyaline cartilage. The friction between the cartilage and the surrounding parts of the joint is very low, which facilitates movement of the joints under high pressure. The cartilage is however prone to damage due to disease, injury or chronic wear. Moreover it does not readily heal after damages, as opposed to other connective tissue, and if healed the durable hyaline cartilage is often replaced by less durable fibrocartilage. This means that damages of the cartilage gradually become worse. Along with injury/disease comes a problem with pain which results in handicap and loss of function. It is therefore important to have efficient means and methods for repairing damaged cartilage in knee joints.
Today's knee prostheses are successful in relieving pain but there is a limit in the lifetime of the prostheses of 10-15 years. The surgical operation is demanding and the convalescence time is often around 6-12 months. In many cases today, surgery is avoided if training and painkillers can reduce the pain. Prostheses are therefore foremost for elderly patients in great pain, at the end of the disease process; a totally destroyed joint. There are different kinds of prostheses, such as half prosthesis, total prosthesis and revision knee, the latter used after a prosthesis failure. The materials used in today's knee prostheses are often a combination of a metal and a polymeric material, but other materials such as ceramics have also been used. The size of knee prostheses makes it necessary to insert them through open surgery.
Smaller implants for replacement of damaged cartilage have also been developed (see e.g. US2003060887, WO2004075777 and US20020022889 recited below in the prior art section). These are however, still rather large and/or require big and robust attachment means to firmly attach the implant to the underlying bone.
Other attempts practiced at various clinics around the world with the main objective to repair or rebuild cartilage include biological approaches such as micro fractures, cartilage cell transplantation (ACI), periost flap, and mosaic plasty surgery. All treatments have shown only limited results, with implications such as high cost, risk of infection, risk of loosening, limited suitability for patients of different ages and the extent and location of damage.
The advantages of implants have stimulated a further development of smaller implants that can be implanted with less invasive surgery. In this development there has also been an effort to achieve small joint implants that have a minimal influence on the surrounding parts of the joint. In addition, better fitting and ideally tailor made implants are desired.
The patent documents US2003060887, US20030171820, US20070255412, US20060116774 and US20020062154 show examples of various implants comprising a bioactive material combined with different types of more inert material.
Examples of prior art concerned with fixation of implant to bone tissue are found in the publications: WO2004075777, WO2005084216, WO2006004885, WO2006091686, US2007179608 and US20020022889.
Examples of prior art appearing on the market can currently be found under the following http links:
http://www.arthrosurface.com
http://www.conformis.com/
http://www.advbiosurf.com/
The patent document US20070021838 describes joint implants having a bone-contacting side and an articular side, with at least one post extending from the bone contacting side for the purpose of fastening the implant to the bone. The articular side is made of a biocompatible material such as a medical alloy, medical plastics, ceramics or natural substrates. The bone-contacting side is treated to impart improved osteoinductive/osteoconductive properties. In one example, the bone-contacting side is provided with a nano-scale textured surface promoting bone in- and on-growth. In another example, osteoinductive and osteoconductive materials may also be incorporated into or on the surface of the bone-contacting portion. As shown in this piece of prior art, the implant is shaped as a fairly thin plate with a slight convexity or concavity to follow the contour of an articulate surface in a joint.
Patent document U.S. Pat. No. 6,306,925B1 also shows an implant with a composite material comprising layers of bioactive glass reinforced with ductile layers of metal.
Patent document WO2006/083603 describes the production of a functionally graded material (FGM) net shaped body with FAST/SPS where the different materials included are a metal or a metal alloy in combination with a ceramic such as an oxide, nitride or carbide, or another metal or metal alloy.
The overall object of the present invention is to provide a solution to the problem of providing a small joint implant for the replacement of damaged cartilage, which can be inserted through arthroscopy, a small open surgery operation or a combination thereof. A specific object of the present invention is to provide an implant that is devised for, on one hand, an efficient long term fixation to the bone and, on the other hand, for providing a wear resistant surface to substitute for damaged cartilage.
The overall problem to be solved by the present invention is to provide an implant with improved mechanical properties, the implant being a thin plate-shaped implant of the kind having a wear resistant articulate surface and a bioactive surface and being devised for repair of damaged cartilage.
The present invention further addresses the following problem aspects:
The present innovation relates to a new medical implant structure suitable for articular surface implants such as knee implants, where said implant can be inserted through a small surgical operation such as arthroscopy, a small open surgery or a combination thereof. The implant is provided with dual functionalities by having a first surface which is wear resistant and devised for facing the articulating part of the joint, and a second surface which is bioactive and devised for facing the bone structure underlying the cartilage. The wear resistant surface comprises a biocompatible wear resistant first metal, metal alloy or ceramic and provides a load bearing surface which is strong and hard enough to resist the wearing forces acting upon it through the movement of the joint. The bioactive surface comprises a sintered material having a homogenous microstructure comprising a mixture of a second metal, metal alloy or ceramic and a bioactive ceramic material or bioactive glass. The sintered material provides firm long-term attachment of the implant to the bone, by stimulating bone growth and bone integration, thus forming a bioactive surface, and at the same time provides a durable bone-contacting surface to the implant. The bioactive ceramic or bioactive glass promotes firm attachment to the bone while the integrated metal, metal alloy or ceramic gives the desired mechanical properties. Preferably the bioactive surface comprises a sintered material having a homogenous microstructure of stainless steel and hydroxyapatite (HA).
A consequence of the invention is that a minimal surgical operation and minimal modifications on the underlying bone and surrounding tissue are required when preparing for the implant surgery and with minimal effects on the tissue after implantation. The bioactive implant in accordance with the invention enables implantation without a rigorous initial (primary) fixation, yet yielding a durable tong-lasting (secondary) fixation. This, on one hand gives a long life length of the implant in situ and on the other hand has a positive effect on the possibility for performing further surgery, in cases when such is needed, for example total joint replacement.
In a first aspect, the inventive concept comprises medical implant (1) for application in an articulating surface of a joint, comprising a plate-shaped structure having a first surface (5) and a second surface (7) facing mutually opposite directions,
In a further aspect, the inventive concept comprises such a medical implant of claim, wherein the second surface is a sintered mixture having a homogenous microstructure comprising the bioactive ceramic or bioactive glass and the second metal, metal alloy or ceramic.
Further varieties of the inventive concept comprise such an implant comprising any of the following optional individual or combinable aspects:
Other aspects and features of the inventive concept are described in the detailed description below.
The invention will be explained in more detail in the following description, referring to the enclosed figures, where:
The present innovation relates to a new medical implant structure and material and use of such a material in a medical implant for an articular surface implant, as well as a method for manufacturing such a medical implant and medical implant structure. The implant is suitable for replacement of cartilage in the knee joint, to stop or retard further cartilage break-down. The invention may however have other useful applications, such as in a medical implant for an articulating surface of any other joint in the body, e.g. elbow, ankle, finger, hip, toe and shoulder.
The body 2 of the medical implant 1 comprises a first surface 5, which is configured to face the articulating part of the joint and is wear resistant, and a second surface 7, which is configured to face the bone and is bioactive. The first surface 5 should preferably have a profile which on the whole matches the curvature of the original anatomical surface at the site of incision, as e.g. illustrated in
The first, wear resistant, surface 5, which is also the articulate surface of the medical implant, comprises a biocompatible metal, metal alloy or ceramic, preferably stainless steel. The metal, metal alloy or ceramic is chosen to provide a wear resistant surface which is durable and resistant to the abrasive forces acting upon it as it articulates and moves in relation to the surrounding parts of the joint. The wear-resistant biocompatible material may consist of a metal, a metal alloy or a ceramic material. More specifically it can consist of any metal or metal alloy used for structural applications in the body, such as stainless steel, cobalt-based alloys, chrome-based alloys, titanium-based alloys, pure titanium, zirconium-based alloys, tantalum, niobium and precious metals and their alloys. If a ceramic is used as the biocompatible material, it can be a biocompatible ceramic such as aluminium oxide, silicon nitride or yttria-stabilized zirconia.
Stainless steel is a material which is well documented for the application in implants and prostheses. It also provides a material which is hard and strong enough to withstand and tolerate the large mechanical forces and heavy and changing work loads subjected to it in the joint. Different grades exist where the properties have been optimised for applications in the human body. An example of a stainless steel for use in an embodiment of the present invention is an alloy mainly comprising iron, carbon, chromium (12-20%), molybdenum (0.2-3%), and nickel (8-15%).
It should also be understood that the first, wear resistant, surface 5 may also be further surface treated in order to e.g. achieve an even more durable surface or a surface with a lower friction coefficient. Such treatments may include, for example, polishing, heat treatment, precipitation hardening or depositing a suitable surface coating.
The second, bioactive, surface 7 of the medical implant 1, which is also the bone-contacting surface, comprises a sintered material having a homogenous microstructure of metal, metal alloy or ceramic and a bioactive ceramic material or bioactive glass. The purpose of the bioactive surface 7 is to provide long-term firm adherence of the medical implant 1 to the underlying bone, by stimulating the bone to grow into or onto the implant surface. Several bioactive materials that have a stimulating effect on bone growth are known and have been used to promote adherence between implants and bone. Examples of such prior art bioactive materials include bioactive glass, bioactive ceramics and biomolecules such as collagens, fibronectin, osteonectin and various growth factors. A commonly used bioactive material in the field of implant technology is the bioactive ceramic hydroxyapatite (HA). HA is the major mineral constituent of bone and is able to slowly bond with bone in vivo. Thus, HA coatings have been developed for medical implants to promote bone attachment. Unfortunately HA is a brittle material and the bonding between HA and prior art metallic implants is weak and subject to fracture. Another bioactive material commonly used in prior art is bioactive glass. Bioactive glasses, generally comprising SiO2, CaSiO3, P2O5, Na2O and/or CaO and possibly other metal oxides or fluorides, are able to stimulate bone growth faster than HA, but are also weak and in themselves tack the necessary mechanical properties required by articulate joint implants.
Previous attempted solutions for providing a bioactive surface on a medical implant have been e.g. to deposit or spray bioactive material onto the surface of an implant, to adsorb bioactive material to the surface or to design a layered composite material of e.g. metal and bioactive glass. As indicated above, these solutions suffer from the disadvantage that bioactive material which is deposited, sprayed or adsorbed onto the surface of the implant is prone to wear or peel off. For example, both HA and bioactive glass are brittle and have not this far been enabled to adhere firmly to the body of the implant. Also, the layered solution, where bioactive glass is reinforced by metallic layers or thin metal foils, is prone to cracking and peel.
In the present invention, a bioactive surface 7 is provided by incorporating by sintering a bioactive ceramic or bioactive glass into a metal, metal alloy or ceramic. Thereby, a sintered mixture material having a more or less homogenous microstructure comprising the bioactive ceramic or bioactive glass and the metal, metal alloy or ceramic is formed. In this way the bioactive ceramic or glass is fully integrated with and supported by the metal, metal alloy or ceramic structure. The bioactive ceramic or bioactive glass promotes firm attachment to the bone while the metal, metal alloy or ceramic gives the desired mechanical properties. Thus the second surface 7 is a bioactive surface which is strong enough to be integrated with the bone without breaking, which is resistant to wearing and peel and at the same time adheres firmly to the body 2 of the medical implant 1.
In the homogenous microstructure the constituent material components are evenly distributed in the structure. It should be understood that a complete homogeneity is desired but in practise not readily achievable, thus the microstructure may consequently comprise less homogeneous portions.
Generally, the content of the bioactive ceramic or bioactive glass in the second surface is more than 20% and preferably more than 30%. This high ratio of the bioactive material combined with satisfying mechanical properties is enabled by the sintering of the bioactive material with a metal, metal alloy or ceramic according to the invention.
The bioactive ceramic of the sintered mixture material of the second surface 7 is preferably hydroxyapatite (also called hydroxylapatite, HA). Hydroxyapatite has the chemical composition Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two molecules. The bioactive material may also be any of the ceramics calcium sulphate, calcium phosphate, calcium aluminates, calcium silicates, calcium carbonates or bioactive glass, or combinations thereof.
The metal, metal alloy or ceramic content of the bioactive, second surface 7 is selected from any metal, metal alloy or ceramic used for structural applications in the body, such as stainless steel, cobalt-based alloys, chrome-based alloys, titanium-based alloys, pure titanium, zirconium-based alloys, tantalum, niobium, precious metals and their alloys, as well as aluminium oxide, silicon nitride or yttria-stabilized zirconia.
The metal, metal alloy or ceramic of the sintered mixture material of the second surface 7 is preferably a cobalt chromium alloy CoCr or stainless steel, or another suitable metal, metal alloy or ceramic. In a preferred embodiment the second surface comprises a cobalt chromium alloy CoCr or stainless steel and HA in a ratio in the range of 20:80 to about 80:20, for example 70:30, 50:50 or 30:70.
Further, small amounts, up to 10 wt %, of sintering additives such as oxides of phosphorous, sodium, magnesium, potassium, silver, aluminium, titanium and/or silicon can be added to the hydroxyapatite powder to facilitate the sintering process.
The second surface, i.e. the surface of the bioactive material can be rough or porous in order to facilitate the attachment of the implant to the bone.
The first, wear resistant, surface 5 and the second, bioactive, surface 7 are fixed or adhered to one another by means of a sintered material structure that in different embodiments is realized in different manners. In one variety a first surface layer comprising the first wear resistant surface 5 is sintered to a second surface layer comprising the second bioactive surface 7. In another variety there is provided an intermediate layer sintered between the first surface layer and the second surface layer.
An example of an FGM 9 in an embodiment of the present invention, shown in
In another embodiment of the present invention, schematically illustrated in
In the embodiments illustrated in
The long-term integration, herein called secondary fixation, of the implant with the bone, stimulated by the bioactive ceramic or bioactive glass, evolves over time. In order to promote more immediate attachment of the implant to the bone as it is implanted into the body, the implant may also be designed with a small device 4 for immediate, mechanical attachment, herein called primary fixation. The primary fixation means 4 may e.g. be devised as a physical structure, glue, bone cement or the like. By physical structure is meant a protrusion, such as one or more of a small screw, peg, keel, barb or the like, as exemplified in e.g.
The primary fixation means 4 may, if configured as a physical structure, comprise e.g. the metal, metal alloy or ceramic, as in the first surface, or a sintered mixture material of a metal, metal alloy or ceramic and a bioactive ceramic or bioactive glass, as in the second surface.
These primary fixation means, e.g. protrusions in the shape of pegs, comprise in one embodiment the bioactive material and have a length of 1 to 10 mm, typically 2-5 mm, and a diameter of 1 to 5 mm, typically 2 to 4 mm. In another embodiment, the length is between 1 and 20, and typically 3-10 mm, and the diameter is typically 1-4 mm. When in place in the joint, the protrusions should penetrate the sub-chondral bone plate and engage the cancellous bone. The protrusion will give stability and promote the attachment of the bioactive material to the bone.
The implant and FGMs comprised in the implant can be prepared through different techniques such as conventional powder metallurgy processing, vapour deposition and sintering techniques. The preferred technique for producing said implant is consolidation through sintering. The sintering technique is preferably electric pulse assisted consolidation (EPAC), also referred to as spark plasma sintering (SPS), pulsed electric current sintering (PECS), field assisted sintering technique (FAST), plasma-assisted sintering (PAS) and plasma pressure compaction (P2C). Electric pulse assisted consolidation includes processes based on heating a material to be compacted with a pulsed DC current. The process allows very rapid heating under high pressures. This process, hereafter referred to as SPS, has proved to be very well suited for the production of functionally graded materials. SPS gives advantages such as no need of binders in the powders and a controlled shrinkage of the material during the compaction. Further, the possibility to rapidly change the temperature and pressure makes it easier to tailor the microstructure of the material and to optimize the sintering conditions compared to conventional compaction techniques.
The general way to form a FGM through spark plasma sintering today is to build it up layer by layer with different compositions. Further, prior to sintering, the powders can be pressed together and thereby form a so called green body, which is an un-sintered item to become a ceramic upon sintering, which is later on inserted into the SPS unit to be sintered.
The spark plasma sintering technique is used for manufacturing the gradient components, i.e. the surfaces and the layers, in an exemplifying embodiment of this invention. However, gradient materials produced through alternative methods can also be used for the same purpose, for example sintering methods such as hot pressing, hot isostatic pressing or pressureless sintering. SPS combines rapid heating, a short holding time at the desired sintering temperature and a high pressure for sintering of the components.
The pressure used during the process of the present invention is between 10 and 150 MPa, preferably between 30 and 100 MPa. The heating rate applied is between 5 and 600° C. min−1, preferably 50-150° C. min−1. The sintering temperature and time are chosen so that a total or near total densification, implying a density of at least 95%, or at least 97% of the theoretical density, will be obtained for the layer comprising essentially 100 wt % biocompatible wear resistant metal, metal alloy or ceramic. This temperature is between 800° C. and 1300° C., typically 900° C.-1100° C. The holding time during the sintering process is between about 1 minute and about 30 minutes, typically between about 2 minutes and about 10 minutes.
The SPS technique uses a combination of a high current and a low voltage. A pulsed DC current with typical pulse durations of a few ms and currents of 0.5-30 kA flows through the punches, die and, depending on the electrical properties of the specimen, also through the specimen. The electrical pulses are generated in the form of pulse packages where the on: off relation is in the region of 1:99 to 99:1, typically 12:2 (12 pulses on, 2 off). The pressure is applied on the two electrically conducting punches of the powder chamber, in a uniaxial direction.
The sintering procedure preferably also includes a high heating rate (a steep heating ramp) and a short holding time at the desired sintering temperature. The cooling down of the sample can either be programmed or the sample will cool down automatically as the current is switched off.
In a general overview of an embodiment of a single sintering step production method in accordance with the invention, the method comprises the following steps.
In this general embodiment, the component is produced through sintering in a single step, said production process comprising the steps:
The fully sintered component may after the sintering process be treated with different methods to obtain a finished product, said methods may comprise surface machining, blasting, etching, grinding and polishing.
A more detailed example of a single step embodiment of an individual fitting production method adapted for tailor made production of an embodiment of the implant comprises the following steps:
In a general overview of an embodiment of a multistep production method in accordance with the invention, the method comprises the following steps.
In this general embodiment, the component is produced through sintering in multiple steps, said production process comprising the steps:
In the multi step embodiment mentioned above, step i) comprises the materials for the wear resistant side and the protrusion, while step iv) comprises the material for the bioactive surface.
In another embodiment, step i) above comprises at least two different kinds of materials, resulting in different materials on the wear resistant surface and in the protrusion forming primary fixation means.
The fully sintered component may after the sintering process be treated with different methods to obtain a finished product, said methods may comprise surface machining, blasting, etching, grinding and polishing.
A functionally graded material (FGM) is characterised by a gradual change of material properties with position. An FGM 9 may in some embodiments, as the one schematically shown in
In a preferred embodiment the FGM has a first surface layer 10 comprising the first surface 5, comprising relatively dense stainless steel, having a relative density of at least 95-97%, sintered using steel powder having a small particle size (<25 μm). The second surface layer 11 comprising the second surface 7, comprises a sintered mixture material with a cobalt chromium alloy CoCr or stainless steel and a bioactive ceramic or bioactive glass, sintered e.g. using a cobalt chromium alloy CoCr or stainless steel powder having a particle size of <50 μm, or preferably about <22 μm. The intermediate layer 12 comprises a layer of relatively porous stainless steel, with a relative density between 50 and 98%, preferably between 60 and 95%, sintered using steel powder having a large particle size (>75 μm). The porous intermediate layer 12 picks up and distributes the tension and forces that build up between the first 5 and the second 7 surfaces and thus prevents the surfaces from cracking. In various forms of this embodiment the metal, metal alloy or ceramic of the different layers may be of varying composition, e.g. having a composition of <0.3% carbon, 2-3% molybdenum, <0.045% phosphorous, <1% silicon, 10-14% nickel, 16-18% chromium, <2% manganese, <0.03% sulphur and iron to balance for the first wear resistant surface, and a cobalt-chromium alloy without nickel in the surfaces facing the bone. Such an alloy can for example have the composition 0.2-0.3% carbon, 5-7% molybdenum, 0.15-0.2% nitrogen, 26-30% chromium and cobalt The ratios (%) are herein indicated in percentage per weight. An advantage of the FGM of the described embodiment is that it may be manufactured so as to give a medical implant having an implant body 2 which is very thin.
The embodiment described above may comprise primary fixation means 4, as for example illustrated in
In one embodiment, the invention provides a method for producing an implant with a biocompatible wear resistant material having a transition to a bioactive part, said biocompatible wear resistant material being a metal or metal alloy, comprising the steps:
An FGM may in other embodiments be achieved by a gradual change of material composition with position. In one embodiment of the invention, the medical implant comprises an FGM 9 designed with two or more layers comprising a gradual change in the ratio of wear resistant metal, metal alloy or ceramic to bioactive ceramic or glass. The implant body 2 in the embodiment exemplified in
The gradient material of this embodiment of the invention consists of a number of layers, typically between 4 and 25, or more typically between 7 and 20, with different compositions in each layer. Preferred embodiments comprise between 3 and 25, or more typically between 3 and 10 layers. The outermost layers of the component consist of the biocompatible material, forming a load-bearing surface, and the bioactive material, with or without addition of the wear-resistant material for improved stability, forming a bone-contacting surface, respectively. A more detailed description of the structure of this embodiment is given below in the section describing a method for producing the embodied structure.
The present embodiment of the invention also provides a functionally graded material, where one of the layers essentially comprises stainless steel and one of the layers essentially comprises the bioactive material, and other layers, if present, essentially comprise a mixture of stainless steel and the bio active material.
In another preferred embodiment the invention also provides a functionally graded material, where the first surface 5 essentially comprises dense stainless steel and the second surface 7 comprises a sintered mixture material of a cobalt chromium alloy CoCr or stainless steel and a bioactive ceramic/glass material, and other layers, if present, comprise a mixture of stainless steel and the bioactive ceramic or glass material, ranging in ratio of stainless steel:bioactive ceramic material between 0:100 and 70:30. Preferably the bioactive ceramic material is hydroxyapatite.
In one embodiment, the invention provides a method for producing a multi-layer design FGM with a biocompatible wear resistant material having a gradual transition to a bioactive part, said biocompatible wear resistant material being a metal or metal alloy, comprising the steps:
In varieties of this embodiment, the number of layers in the functionally graded material is between 4 and 25, or preferably between 5 and 15, wherein said bioactive material, or the layers comprising said bioactive material, further comprises a maximum of about 50 wt % stainless steel, or a maximum of about 30% stainless steel.
The present invention comprises a functionally graded material obtained by the above method, where one of the layers essentially comprises stainless steel and one of the layers essentially comprises the bioactive material, and other layers, if present, essentially comprise a mixture of stainless steel and the bioactive material.
A gradient material of hydroxylapatite (HAP) and stainless steel (SS) was prepared. 11 different powder mixtures were prepared with the following compositions:
The 11 different powders were produced through mixing stainless steel 316 L (D90<22 μm) and/or hydroxylapatite (D50<5 μm) in a liquid medium in a ball mill for 2 h followed by drying in a conventional oven. The powders were inserted layer by layer in a graphite die chamber and the chamber was closed by two punches. The sample was sintered in a SPS unit and the temperature was initially automatically raised to 600° C. Subsequently, a heating rate of 100° C. min−1 was applied. The sample was densified at 1000° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 100 MPa. The component was shaped as a cylinder with a diameter of 20 mm and a height of 5 mm. The layers were free of cracks.
A gradient material of hydroxylapatite (HAP) and stainless steel (SS) was prepared. 8 different powder mixtures were prepared with the following compositions:
The eight different powders were produced through mixing stainless steel 316 L (D90<22 μm) and/or hydroxylapatite (D50<5 μm) in a liquid medium in a ball mill for 2 h followed by drying in a conventional oven. The powders were inserted layer by layer in a graphite die chamber and the chamber was closed by two punches. The sample was sintered in a SPS unit and the temperature was initially automatically raised to 600° C. Subsequently, a heating rate of 100° C. min−1 was applied. The sample was densified at 1000° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 75 MPa. The component was shaped as a cylinder with a diameter of 20 mm and a height of 4 mm. The layers were free of cracks.
A gradient material of hydroxylapatite (HAP) and stainless steel (SS) was prepared. 6 different powder mixtures were prepared with the following compositions:
The six different powders were produced through mixing stainless steel 316 L (D90<22 μm) and/or hydroxylapatite (D50<5 μm) in a liquid medium in a ball mill for 2 h followed by drying in a conventional oven. The powders were inserted layer by layer in a graphite die and the die was closed by two punches. The sample was sintered in a SPS unit and the temperature was initially automatically raised to 600° C. Subsequently, a heating rate of 100° C. min−1 was applied. The sample was densified at 950° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 100 MPa. The component was shaped as a cylinder with a diameter of 20 mm and a height of 3 mm. The layers were free of cracks.
A knee with damaged cartilage was scanned with CT and the result thereof was converted to a CAD-drawing. Graphite tools for the SPS chamber were formed according to the requirements from the CAD-drawing in order to sinter a tailor made component in the graphite tool. The lower punch had two holes for formation of the bioactive protrusions. A stainless steel/hydroxylapatite gradient material was formed through spark plasma sintering according to Example 1, with 11 different layers. The sample was densified at 1000° C. for 5 minutes. The sintering took place under vacuum and the pressure was 75 MPa.
A gradient material of hydroxylapatite (HAP) and stainless steel (SS) was prepared. 6 different powder mixtures were prepared with the following compositions:
The six different powders were produced through mixing stainless steel 316 L (D90<22 μm) and/or hydroxylapatite (D50<5 μm) in a liquid medium in a ball mill for 1 h followed by drying in a conventional oven. The powders were inserted layer by layer in a graphite die and the die was closed by two punches. The sample was sintered in a SPS unit and the temperature was initially automatically raised to 600° C. Subsequently, a heating rate of 100° C. min−1 was applied. The sample was densified at 1000° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 75 MPa. The component was shaped as a cylinder with a diameter of 20 mm and a height of 3 mm. The pure hydroxylapatite layer at one side of the cylinder cracked and the experiment was therefore not successful. Compared to the material according to this example, the functionally graded material according to the invention is more mechanically stable.
An implant component consisting of two different compositions of medical stainless steel and hydroxyapatite was prepared. Further, different grain sizes of one of the stainless steel grades were applied. The component was sintered in two steps. One layer of stainless steel powder Micro-Melt 316 L (d50<22 μm, Carpenter Technology) was first placed into a graphite die of a diameter 15 mm. On top of that layer, Micro-melt CCM+ stainless steel powder (44-105 μM, Carpenter Technology) was placed on top of the 316 L powder. The graphite die was closed by two graphite punches and the materials were sintered in a SPS unit. The temperature was initially automatically raised to 600° C. and subsequently a heating rate of 100° C. min−1 was applied. The sample was densified at 950° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 75 MPa. The component was shaped as a cylinder with a diameter of 15 mm and a height of 10 mm.
The sintered cylinder was put in a turning machine and was turned so the Micro-melt CCM+ part was shaped into a protrusion.
The shaped stainless steel component was thereafter put back into a graphite die. A layer of Micro-melt CCM+ stainless steel (177-420 μm, Carpenter Technology) was put on top of the 316 L material, on the same surface as the protrusion. A powder was prepared through mixing 50/50 (wt %) of Micro-Melt CCM+ stainless steel (d50<22 μm, Carpenter Technology) and hydroxyapatite (d50<5 μm). A layer of this powder mixture was placed on top of the coarse grained CCM+ powder. The sample was again densified, according to the set-up above with a sintering temperature of 950° C., a pressure of 75 MPa and a sintering holding time of 5 min. Following the sintering, the wear resistant surface was shaped to obtained desired curvature. The implant component was thereafter blasted (shot peening) to remove graphite from the surface as well as to create a roughness on the bioactive surface. The wear resistant surface was polished.
An implant component consisting of two different compositions of medical metal alloys and hydroxyapatite was prepared. Further, different grain sizes of one of the metal alloy grades were applied. The component was sintered in two steps. One layer of stainless steel powder Micro-Melt 316 L (d50<22 μm, Carpenter Technology) was first placed into a graphite die of a diameter 15 mm. Micro-Melt CCM+ cobalt-chrome powder (44-105 μm, Carpenter Technology) was placed on top of the 316 L powder. The graphite die was closed by two graphite punches and the materials were sintered in an SPS unit. The temperature was initially automatically raised to 600° C. and subsequently a heating rate of 100° C. min−1 was applied. The sample was densified at 950° C. for 5 minutes. The temperature was measured with an optical pyrometer focused on the surfaces of the sintering die. The sintering took place under vacuum. The pressure was kept at 75 MPa. The component was shaped as a cylinder with a diameter of 15 mm and a height of 10 mm.
The sintered cylinder was put in a milling cutter and was machined so the Micro-Melt CM+ part was shaped into a two protrusions.
The shaped metal alloy component was thereafter put back into a graphite die. A powder was prepared through mixing 50/50 (wt %) of Micro-Melt CCM+ cobalt chrome powder (d50<22 μm, Carpenter Technology) and hydroxyapatite (d50<5 μm). A layer of this powder mixture was placed on top of the coarse grained CCM+ powder. The sample was again densified, according to the method above with a sintering temperature of 950° C., a pressure of 75 MPa and a sintering holding time of 5 min. Following the sintering, the wear resistant surface was shaped to obtain desired curvature. The implant component was thereafter blasted (shot peening) to remove graphite from the surface as well as to create a roughness on the bioactive surface. The wear resistant surface was carefully polished.
The implant is introduced into the joint by surgical treatment, such as by means of a closed procedure, i.e. by arthroscopy as opposed to open surgery, or a small open surgical operation which is much smaller than operations for today's knee prostheses. This provides for minimal postoperative morbidity. The implant is not conceived of as a joint prosthesis but rather as an artificial biomaterial for installation into a portion of an articular surface, i.e. for cartilage replacement. Prosthetic replacement may become necessary at a later stage and the present procedure should preferably not interfere with subsequent joint arthroplasty. It is therefore important with an implant, according to the present innovation, that is not interfering with a possible future prosthesis. The use of bio materials in this procedure implies, as has been explained above, a wear-resistant component as well as a bioactive component, as opposed to biological solutions using cell or tissue transplants.
The implant according to the present invention is, as mentioned above, suitable for the knee joint, but the implant is also useful for other joints such as elbow, ankle or finger joints. The knee joint is however the joint most often suffering from the conditions approachable by this implant.
For the surgical treatment, either of two situations may be at hand: 1) a chondral fracture, where the sub-chondral bone plate typically is completely denuded of cartilage over a confined area with sharp edges to the surrounding intact cartilage or 2) a focal area of degenerated cartilage.
Two surgical methods of the present invention may comprise the following steps:
For some joints, it is anticipated that the two stages in point 2 above can be made at one operative procedure where a cartilage defect is “created” through excision of worn edges of degenerated cartilage until stable and healthy cartilage is reached and the defect is created to fit an implant that is prefabricated to fit the underlying bone. In this case the operation will be performed as a small open, as opposed to scopic, procedure.
The implant of the present invention may be implanted or used on one side, tibial or femoral, of the knee or on both sides in the knee. In the latter case as two separate components, one on the tibial side and one on the femoral side.
Production of the implant in accordance with invention are in different production methods made for individual fitting or in standard dimensions. In an embodiment of the individual fitting production method, the implant will be custom made for a particular joint of a particular patient in order for the curvature of the implant component to be identical to that of the sub-chondral bone plate at the site of insertion. In the alternative standard dimension variety, it is for example provided a kit of implant components of different sizes and shapes available, implying no need for individual tailoring.
In an individual fitting production method, the implant may be produced after drawings obtained after a CT scan or MRI of the specific part of the body intended for the implant. The tailored shape is obtained through production in a tailor made mould, or through post sintering treatment, including cutting, grinding and polishing or a mixture thereof.
The production method would in this embodiment comprise the steps of:
In a standard dimensions production method the implant is formed according to a standard size and shape, typically a cylindrical or slightly elongated component, and that the individual design is obtained through post compaction grinding of the gradient material according to drawings created for the specific patient.
Another embodiment of the present invention comprises a kit which contains a selection of implants according to the invention, wherein the selection of implants comprises implants of different sizes and shapes. This means that an implant according to the invention, which is of suitable size and shape for the patient to be treated, is available for the surgeon who adjusts the excision of the cartilage to the available components.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08155701.9 | May 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/055506 | 5/6/2009 | WO | 00 | 1/24/2011 |
