Artificial joint

FIELD OF THE INVENTION

The present invention relates to the field of medicine and in particular to the field of orthopedics. Even more particularly the present invention concerns prosthetic devices, which are used for partial or total replacement of mammal's joints or for treatment of chronic conditions, like arthritis etc. Preferably the present invention refers to a new and improved artificial joint implants for replacement of the human knee or hip joints. It should be born in mind, however that the present invention is not limited strictly to knee and hip joints and that it can be implemented for replacement of any other artificial joints, where it is required to improve lubrication between articulated components, like ankles, elbows, wrists, finger joints, toe joints, intervertebral discs etc. The present invention refers also to a new method for lubricating of joint components.

BACKGROUND OF THE INVENTION From 1970's and 1980's and up today the hip and knee joint replacement surgery became a standard technique for treating chronic joint pain and injury. Figures 1-3 below show the peculiarities associated with the known in the art artificial joints. With reference to Fig.l it is shown a healthy human knee joint and the same joint damaged e.g. by osteoarthritis, rheumatoid arthritis or trauma. In the healthy joint a layer of synovial fluid lubricates the two opposite bones of the joint and a flat layer of cartilage tissue ensures that this lubricating layer is distributed homogeneously across the articulated surfaces of the joint components. In the joint with the damaged cartilage tissue the synovial fluid is displaced such that the joint is not lubricated homogeneously. This might be associated with the knee pain and disability and in this situation the knee replacement surgery is generally recommended. Such surgery is highly successful in relieving pain and restoring joint function.

Referring now to Fig.2 it is shown an example of artificial knee joint used in the replacement surgery. This surgery allows replacement of up to three bone components by respective metallic components. The metallic components replace correspondingly the femoral component of the joint, the tibial component and the patella component. It is seen that the replacement metallic femoral component embraces the end of the thighbone and it is configured with interior groove so the kneecap can move up and down smoothly against the bone as the knee bends and straightens. Usually, one large piece is used to overlap with the end of the bone. The replacement tibial component is configured as a flat metal platform covered by a polyethylene cushion. The cushion may be an integral part of the platform or be separate there from and it can be configured either with a flat surface or a raised, sloping surface. The replacement patellar component is configured as a dome shaped piece of polyethylene that duplicates the shape of the kneecap anchored to a flat metal plate. During functioning of the knee joint the articulated femoral component and the tibial component are relatively displaced and the metallic femoral component abrades the polyethylene cushion of the tibial component.

This is known that polyethylene (usually ultra-high molecular weight polyethylene) wears annually in the extent of up to 0.1 mm due to the friction against metallic surfaces of the joint implant (usually cobalt-chrome, titanium alloys or zirconium oxide ceramics). This wear might result in formation of microscopic particulate debris, which might cause inflammation. Furthermore since this wear changes the implant contact dimensions an additional joint implant surgical replacement might be required. The probability for such revised knee implant operation is 95% after 10-15 years, since the first operation has been made. Referring now to Fig.3 it will be explained how the similar problem arises in the hip joints. In Fig.3 is shown an artificial hip joint comprising a femoral and an acetabulum implant components. The femoral head (ball) fits into concaved depression in the acetabulum component (socket). In a natural joint the femoral component can smoothly move with respect to the acetabulum component by virtue of synovial fluid deployed between the femoral head as a thin layer, which efficiently lubricates the joint during motion. In a healthy natural hip joint, the surfaces of the bones where the ball and socket

rub together are very smooth and covered by a tough cartilage tissue, which preserves the homogeneity of the layer of the synovial fluid. In a damaged joint, e.g. due to arthritis, the cartilage tissue is displaced and homogeneity of the lubrication layer is deteriorated. Eventually functioning of the joint may become painful as the surfaces become worn due to friction.

One way for arthritis treatment is the total hip replacement. In total hip replacement surgery, the natural ball and socket that have been damaged by arthritis are removed and replaced with artificial joint implants, made of metal (cobalt-chrome alloy) and a durable plastic with high shock absorbance. An example of such plastic is polyethylene with ultra-high molecular weight. Unfortunately, due to lack of synovial fluid and due to insufficient lubrication this plastic material wears during relative displacement of the implant components and therefore the same problems arise, which have been mentioned above in connection with the artificial knee joint.

Furthermore, lack of synovial fluid and insufficient lubrication results in limitation of the patients activity, for example:

-patient must avoid repetitive heavy lifting;

-patient must avoid excessive stair climbing;

-patient must maintain appropriate weight;

-patient must avoid "impact loading" sports such as jogging, downhill skiing etc.; -patient must consult with his surgeon before beginning any new sport or activity;

-patient must avoid any physical activities involving quick stop-start motion, twisting or impacting;

-patient must avoid kneeling;

-patient must avoid low seating surfaces and chairs. One can conclude from the above that one of the main problems associated with the existing artificial joints is the unavoidable friction between the joint components and therefore reducing of this friction would be very desirable.

There are known various attempts to reduce friction between implant components of the artificial joints. In WO9619163 is described prosthetic knee joint in which the friction is reduced by mechanical means, i.e. by utilizing replaceable roller bearings. The roller bearing knee

replacement joint is provided with a femoral component positioned for articulation on a tibial component. The articulated surface of the tibial component has replaceable roller bearing units, which reduce friction between the components.

Another approach is disclosed in US 5641323 describing bone prostheses provided with incorporated therein fluid communicating passageways for conveying synovial fluid from a joint space to articulated surface of an artificial joint. The presence of this fluid provides lubricity to the joint and enables to utilize metal/metal, metal/ceramic and ceramic/ceramic articulation couples without the need for a low friction polymeric lining material. In EPO 128220 is disclosed another example of artificial joint based on the same approach. According to this solution the artificial joint is provided with a liquid storage unit with ultra fine recesses formed by ultra fine holes or grooves for holding a lubricating liquid. US2004068322 describes artificial joints with reduced friction which employ one or mores seals to trap the lubricating liquid inside the joint. The seal may surround the periphery of the joint components. Various lubricating fluids are applicable, including water or aqueous solutions, triglyceride oil, soybean oil, inorganic oil, glycerin, ethylene glycol or other animal, vegetable, synthetic oil or their combination. Still similar approach, based on retaining of the lubricating liquid between the joint components is disclosed in US6692529, which describes a hip replacement system having fat lubricant. The system includes a socket and a ball member affixed within the socket. The boll member is affixed to a stem and the stem is formed with a channel extending there along. The exterior of the ball member has at least one opening communicating with the channel. A fat lubricant fills a space between the exterior of the ball member and the cavity.

Thus many attempts exist for reducing friction in artificial joints.

On the other hand there are known in the art so-called ferrofluids, which are used in certain engineering applications for reducing friction between components of a friction couple. A ferrofluid is a stable colloidal suspension of sub-domain magnetic particles distributed within a liquid carrier. The particles, which have an average size of about lOOAngstrom

(IOnm), are coated with a stabilizing dispersing agent (surfactant) to prevent particles agglomeration even when a magnetic field with a strong gradient is applied to the ferrofluid. The surfactant should be matched to the carrier type and be capable to overcome the van der Vaals attraction and magnetic forces between the particles. The colloidal and thermal stability of a ferrofluid, which might be crucial to many applications, are greatly influenced by the choice of the surfactant. A typical ferrofluid may contain by volume 5% magnetic solid particles (usually Fe ₃ O ₄ ), 10% surfactant (usually dextran) and 85% of a base fluid, i.e. liquid carrier. The structure of a typical ferrofluid is schematically presented in Fig.4. In the absence of magnetic field, the magnetic moments of the particles are randomly distributed and the fluid has no magnetization. When a magnetic field is applied to a ferrofluid, the magnetic moments of the particles orient along the lines of the magnetic field almost instantly. In the magnetic field having a gradient the ferrofluid responds as a homogeneous magnetic liquid, which moves to the region of the highest flux. This means that ferrofluid has the fluid properties of a liquid and the magnetic properties of a sol id and it can be precisely positioned and controlled by the external magnetic field. The forces holding the magnetic fluid in the same position are proportional to the gradient of the external field and magnetization value of the fluid. By virtue of the above properties ferrofluids are used in such engineering applications like rotating shaft seals, in rotating anode X-ray tubes, in vacuum chambers for the semiconductor industry, in high speed computer disk drives, in journal bearings, in loudspeakers for dampening unwanted resonance, etc.

An example of using ferrofluid in a low friction bearing arrangement is described in US 4717266. The low friction bearing arrangement includes first and second poles of magnetically permeable material defining first and second pole surfaces, which are spaced apart. The pole surfaces define also the first and second side surfaces, which are aligned and a shaft is provided, which is located out of contact with the side surfaces. A ferrrofluid is positioned between the shaft and the side surfaces and is held adjacent the first and the second side surfaces by means of a fringing magnetic flux established between the side surfaces.

An example of using ferrofluids for sealing a shaft and a hub for a disk hard drive is described in WO 00/43698.

It can be readily appreciated, however, that the above engineering applications are distant from medicine in general and do not address to the artificial joint implants in particular. It should be pointed out that although the ferrofluids are known for a long time, nevertheless their use as a lubricant was limited so far to engineering applications Nevertheless, the ferrofluids recently became known also in some medical applications, like drug delivery, magnetic resonance imaging etc. In these applications magnetic properties of the nanoparticles are utilized for attaching them to antibodies, proteins, medical drugs etc., since the magnetic nanoparticles offer the possibility of being directed towards a specific target in the human body and remaining eventually localized, by means of an applied magnetic field. An example of using magnetic nanoparticles in medical application can be found in US20050107870. It can be appreciated however that these medical applications are irrelevant to the problem of reducing friction in artifjical joint implants.

In conclusion it can be stated that one skilled in the art would be motivated by none of the known in the art engineering and medical application to employ ferrofluids for reducing friction in the artificial joints. It can be also stated that despite there exist many attempts to reduce friction between articulating surfaces of artificial joint implants there still exist a need in a new and improved solution.

SUMMARY AND OBJECTS OF THE INVENTION

The idea of the present invention is to reduce friction between components of an artificial joint by providing continuous layer of lubricating fluid between articulated surfaces of the joint implant components.

In accordance with the invention the lubricating fluid comprises a stable ferrofluid suspension, which is kept between the articulated surfaces by virtue of magnetic field.

The main object of the invention, which is achievable by virtue of the above solution, is to decrease drastically abrasion and wear in artificial joint implants, and thus to increase joint durability and to improve its shock-absorbing property.

Still further object of the invention is to provide artificial joint in which the lubricating fluid can be easily and conveniently replenished by injecting a portion of the fresh ferrofluid between the articulated surfaces without necessity in a surgical operation.

Another object of the invention is to provide artificial joint, which has reduced wear without modifying the joint design and/or the process of its manufacturing.

The above objects are achieved by the present invention, which can be implemented as artificial joint and as method for lubricating articulated surfaces of an artificial joint.

In accordance with an embodiment referring to the artificial joint it comprises at least two articulated joint components implantable within a body of a patient, said components are relatively displaceable with respect to each other and a layer of a lubricating fluid is deployed between the components, wherein said layer is constantly retained between the joint components to prevent dry friction between the components irrespective of their mutual disposition.

In accordance with a further embodiment, said lubricating fluid is a ferrofluid and the joint is provided with a source of magnetic field, which retains the ferrofluid between the articulated surfaces of the joint components.

According to still further embodiment said magnetic field has intensity directed perpendicular to the articulated surfaces of the components.

In a yet further embodiment said source of magnetic field is at least one permanent magnet.

In the other embodiment said permanent magnet is configured as a solid plate locatable within at least one joint component.

In yet another embodiment said source of magnetic field is capable to produce magnetic field with intensity 28-52MGoe. In still another embodiment said ferrofluid is suspension of magnetizable particles within a biologically compatible carrier fluid.

In yet further embodiment the magnetizable particles are iron oxide particles having an average particle size of about 10 nm.

In the other embodiment a magnetic saturation in the range of 400-900 Gauss defines the magnetizable particles.

In still further embodiment said carrier fluid is selected from the group consisting of medical grade silicone or hyaluronate solution or carboxymethyl cellulose solution.

In another embodiment a surface-active material coats the magnetizable particles.

In the further embodiment the carrier fluid is defined by a viscosity of 50-600 centistokes and a vapor pressure of 10 ^'5 - 10 ^"10 Torr at 37 degrees C.

The idea and the objects of the invention have been summarized only briefly. For better understanding of the present invention as well of its advantages, reference will now be made to the following description of its various embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of examples only, with reference to the accompanying drawings, wherein:

Fig.l is a schematic illustration of distribution of synovial fluid in an ostheoarthritic knee joint and in a normal knee joint;

Fig.2 shows schematically an artificial knee joint;

Fig.3 shows a ball and socket artificial hip joint;

Fig.4 depicts schematically structure of a ferrofluid;

Fig.5 shows schematically structure of a friction pair provided with lubricating layer in accordance with the invention:

Fig.6 shows schematically an embodiment of the present invention implemented as an artificial knee joint;

Fig.7 shows schematically an embodiment of the present invention implemented as an artificial hip joint;

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to Figs.5a-5d it is schematically shown the idea of the present invention. In Fig.5a is seen a first component 10 of a pair of friction, e.g. configured as socket implant component of a hip artificial joint. Within the component 10 an insert 12 is located, which is made of material capable to produce constant magnetic field shown as

plurality of arrows 14. Since the implant component has bowed configuration, but the insert has rectilinear configuration the magnetic field is not homogeneous and has maximum magnetic strength in the middle part of the component, where the arrow has its maximum length. In Fig.5b is shown that in accordance with the invention a layer of ferrofluid 16 is deployed on the inwardly facing surface of the implant component and lubricates it. The lubricating layer changes its thickness and configuration according to the diagram of magnetic strength and it is seen that it has its maximum thickness where the magnetic strength is maximal. In Fig.5c and 5d is shown the first component and a second component 18 of the pair of friction, e.g. configured as socket and ball implant of an artificial hip joint. The magnetic insert 12 is located within the first component and produces magnetic field, which retains ferrofluid 16 between opposite articulated surfaces of the first and the second component. It is seen that although the second component is somewhat displaced from the middle of the first component either at right as in Fig. 5c or at left as in Fig. 5d, nevertheless thin layer of the ferrofluid is always retained by the magnetic insert and lubricates the articulated surfaces of both components. By virtue of this provision dry friction between the components is prevented since the ferrofluid always presents in the zone of friction irrespective of the disposition of the components. It has been unexpectedly revealed that this effect can be employed in artificial implant joints, in which the components of the joint are made of biocompatible material. Non- limiting examples of suitable biocompatible materials comprise cobalt-chrome alloys, titanium alloys, stainless 316L steel, zirconium oxide, zirconium, high-molecular weight polyethylene etc. Articulated components of the joint, which constitute pair of friction, could be made of similar or dissimilar compatible materials, like metal-metal, metal- ceramics, metal-plastic, plastic-plastic, ceramics-plastic etc. . Below are requirements, which should be met in order to implement the invention in artificial implant joints. As to the magnetic insert it should be made from the strongest permanent magnets, such as SmCo with (BH)max=30+/- 2MGoe or from MdFeB with (BH)max=45+/-2MGoe.

Furthermore, the insert should be located within at least one of the components in such a manner that direction of magnetic field produced by the insert is substantially perpendicular to the articulated implant surface, which is adjacent to the ferrofluid. The magnetic insert can be rigid or flexible. The rigid magnetic insert can be manufactured by consolidating shaped magnetic particles by methods of powder metallurgy. Mixing of magnetic particles with suitable filler like rubber or plastic powder and consequent shaping, e.g. pressing can make the flexible insert. The shape of the insert can be different, e.g. curved or rectilinear depending on the configuration of articulated surface of the joint implant component. IfNdFeB is used for making the magnetic insert it is recommended to coat the insert by an anti-corrosion coating, e.g. gold coating, since NdFeB magnets have low corrosion resistance.

The magnetic insert must be located inside the joint implant component within a dedicated recess provided in the implant. Upon placing the insert within the recess it has to be closed by a cover. The cover should not change the shape of the implant. After closing the cover should be reliably secured on the implant, for example, by welding. It is necessary to take into consideration that during welding the implant and the insert should not be heated over the Curie point, namely 800-850 degrees C for SmCo magnet and 160 degrees C for NdFeB magnet. The welding seam must be located remote from the friction area and it has to be polished.

Now requirements to the ferrofluid suitable for use in artificial joint implants will be defined.

The ferrofluid should be deployed between the articulated surfaces of the joint implant components and it should have the following properties: 1) complete biocompatibility; 2)high lubrication properties;

3) saturation magnetization within a range 400-900 Gauss;

4) viscosity within a range 50-600 centistokes at 37 degrees C;

5) vapor pressure within a range 10 ^"5 -10 ^'10 Torr at 37 degrees C; The ferrofluid vapor pressure must be as low as possible, to prevent its evaporation during prolonged service life.

6) the ferrofluid layer should have an optimal thickness to ensure minimal coefficient of friction between the articulated surfaces. In practice it should have thickness 0.005-0.24 mm depending on the type of the ferrofluid.

7) the ferrofluid must be located as close as possible to the magnetic insert; The reason for the last requirement lies in the fact that force of attraction between two permanent magnets is inverse proportional to the third power of the distance between them. In the present invention the distance, which should be taken into consideration for assessment of the attraction force is the distance between the insert surface and the ferrofluid surface. Having generally explained the gist of the invention and requirements for its implementation in artificial joint implants some not limiting specific embodiments will be described with the aim of the following non-limiting examples.

Example 1, use of ferrofluid lubricant in artificial knee joint implants.

With reference to Fig. 6 it is shown typical artificial knee joint, having femoral implant component 20 associated with femur 22 and having stemmed tibial plate implant component 24 associated with tibia 26. The tibial plate component is provided with a plastic cushion 28 made of polyethylene and facing towards low extremity of the femoral component. The upwardly facing surface of the plastic cushion and the downwardly facing surface of the femoral component constitute articulated surfaces ASl and AS2. It can be readily appreciated that if no lubricant is placed between the articulated surfaces ASl and AS2 dry friction followed by wear will take place when both joint implant components are relatively displaced. Furthermore, patella 30 is seen that is provided with lateral surface facing towards lateral wall 32 of the femoral component. Accordingly these lateral surfaces constitute additional articulated surfaces AS3, AS4. It can be realized that dry friction may take place if no lubricant is placed between the articulated surfaces AS3,AS4.

In accordance with the invention a layer of ferrofluid 34 is deployed at least between the surfaces AS1,AS2 and at least one magnetic insert 36 is placed within the tibial plate component. To efficiently prevent dry friction, the layer of the ferrofluid between the articulated components should have thickness not less than 5 micron.

The magnetic insert is located. within a dedicated depression 35 made within the tibial plate component and a cover 37 closes this depression as explained above. It is advantageous if similar arrangement is available between the articulated surfaces AS3, AS4 as well. This arrangement is shown in Fig. 6 and it is seen that it comprises a layer of ferrofluid 38 and magnetic insert 40 located within appropriate depression 39 made in patella. It should be borne in mind, however, that two such arrangements are not compulsory.

Magnetic inserts employed in the knee joint implant can be configured as thin flat discs and they can be made from SmCo, YX30 defined by (BH)max=28-32MGoe, Br=I 100- 120OmT. The other suitable material is NdFeB, 9N-45 defined by (BH)max=42-46MGoe, Br=1330-1370mT. Such magnetic inserts manufactures, for example, company YuXiang Magnetic Materials (China). The inserts should produce magnetic field directed perpendicular to their flat butt sides. Polyethylene or metal covers, adapted for hermetically sealing the depressions, should cover the magnetic inserts. The hermetical seam must be polished, in order not to deteriorate the implant shape.

As suitable ferrofluid one can use suspension of Fe ₃ O ₄ paramagnetic particles, having 10 nm average size and about 600 Gauss saturation magnetization. The particles should be covered by a surfactant, e.g. dextran or carbon biocompatible surfactants. As suitable carrier fluid one can use hyaloronate solution. This ferrofluid lubricant can be deployed between the articulated surfaces of the joint knee implant during surgical knee replacement operation, which is the same as a typical knee replacement operation. Example 2 use of ferrofluid lubricant in artificial hip joint implants. With reference to Fig. 7 it is shown typical artificial hip joint, having metallic femoral component 42, terminating by a ball-like femoral head extremity 44. The hip joint is provided also with a cup-like acetabulum implant component 46, which can be made of high molecular weight plastic material, e.g. polyethylene. The acetabulum component and the femoral head extremity constitute mutually a pair of friction and they are provided with respective articulated surfaces AS5, AS6. It can be readily appreciated that if no lubricant is placed between the articulated surfaces AS5 and AS6 dry friction

followed by wear will take place when femur implant component and acetabulum component is relatively displaced.

In accordance with the invention a layer of ferrofluid 48 is deployed between the articulated surfaces S5, S6 and a magnetic insert 50 is located within the acetabulum component. This magnetic insert produces magnetic field, which retains the ferrofluid between the articulated surfaces irrespective of the mutual disposition of the respective joint components. To prevent dry friction between articulated surfaces the thickness of the ferrofluid layer should be not less than 5 micron thickness.

It is shown in Fig. 7 that an additional magnetic insert 52 can be located within the lower extremity of the femur component. This insert is intended for retaining additional layer

54 of ferrfluid for lubricating between the lower extremity of femur and adjacent tissues.

One should bear in mind, however that the second insert and the second layer of ferrofluid is not compulsory.

The magnetic insert can be configured as flat disc having diameter 20 mm and height 8 mm. The magnetic inserts can be made of SmCo, YX30 defined by (BH)max=28-

32MGoe, Br=I 100-120OmT. Such magnetic inserts are manufactured e.g. by YuXiang

Magnetic Materials (China).

The magnetic field produced by the insert should be directed substantially perpendicularly to the flat butt sides of the magnetic insert. These magnetic insert is located within a suitable depression made in the acetabulum implant component. The depression is hermetically sealable by a cover preferably made from the same material as the acetabulum component.

The ferrofluid placed between the articulated surfaces can be biocompatible ferrofluid lubricant having the following properties: Carrying fluid: medical grade silicone.

Density: 1.384g/cm3 Viscosity: 350 centistokes Saturation magnetization: 750 Gauss.

It has been empirically revealed that using of ferrofliiid lubricant retained between articulated surfaces of an artificial joint implant is a very efficient means for reducing dry friction between the joint implant components.

With reference to Fig.8 are shown results of testing carried out on Biaxial Rocking Motion hip simulator at room temperature. The testing was conducted on artificial hip joint implant similar to that shown in Fig.7 and described in Example 1. The testing was carried out at the following conditions:

- Static Load 1 kN;

-Frequency of cycling 1 movement per second. -Time of continuous test: one hour.

-Number of cycles 3600.

Frictional torque was monitored during the testing. For comparison the same testing was conducted on hip joint implant with lubricating layer of silicone based ferrofluid, with lubricating layer of silicone lubricant deposited by spraying and without lubricating layer at all.

The thickness of the ferrofluid lubricating layer was 50micron and the thickness of the sprayed lubricating layer was 80 micron.

The corresponding mean values of the frictional torque were 0.075 Nxm (silicone based ferrofluid lubricating layer), 0.2 Nxm (silicone based sprayed lubricating layer) and 2.1 Nxm (no lubricating layer)

According to the test results one can readily appreciate that providing of lubricating layer of silicone based ferrofluid is very efficient means for reducing dry friction between articulated implant components;

Furthermore it has been observed that the temperature around the tested implant components (at 1 cm distance) increases at about 3 degrees C only during one hour of testing.

The present invention has been described using non-limiting detailed description of various embodiments thereof. It should be appreciated that the present invention is not limited by the above-described embodiments and examples and that one ordinarily

skilled in the art can make changes and modifications without deviation from the scope of the invention as will be defined below in the appended claims.

Below are listed only some of the modifications, which are within the scope of invention.

But this invention can be implemented for replacement of any other artificial joints, where it is required to improve lubrication between articulated components, like ankles, elbows, wrists, finger joints, toe joints etc.

It should also be appreciated that features disclosed in the foregoing description, and/or in the foregoing drawings and/or following claims both separately and in any combination thereof, be material for realizing the present invention in diverse forms thereof. When used in the following claims, the terms "comprise", "include'", "have" and their conjugates mean "including but not limited to".

As used herein, the terms "permanent magnet", "magnetic" etc. refer to any materials, which are source of magnetic field without external permanent magnet or without other sources of external magnetic field. Non-limiting examples of such materials are NdFeB ₅ SmCo magnets, ferrite ceramics, AlNiCo magnets, semi-hard magnets etc.

As used herein, the term "ferrofluid" refers to any suspension comprising magnetic particles coated by surfactant for prevention their agglomeration and distributed in liquid carrier medium.

As used herein, the term "joint implant" refers to any device, that is placeable in a patient' s body and which has a primary function such as treatment of disease or disorder.

Non-limiting examples of such functional implants are joint knee implants and joint hip implants.

As used herein the term "articulated" means refers to any pair of components or surfaces constituting a joint. As used herein, the term "wear" means mechanical removal of material from the surface of an object caused by friction with other relatively movable object.

As used herein, the term "shock absorbed" material is any material, which can operate as a damper.

As used herein, the term "durability of the implant" refers to its functional service life. As used herein, the term "biocompatible" refers to such material, which do not provoke biological organism's reaction after introducing of such material into organism. In the

present invention the term biocompatible is pertinent to joint implant components, to magnetic insert and to ferrofluid. Some non-limiting examples of '"biocompatible" materials comprise 316L stainless steel, cobalt-chrome alloy, biocompatible organic coating on the ferrofluid nanoparticles, such as metacrylated dextran, carbon or fibrin.

The scope of the invention is defined by the appended claims.