RU2631889C1 - Insert of hip joint endoprosthesis acetabular component made of polymeric nanocomposite material - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: insert of the acetabular component is manufactured by thermo-pressing from a nanocomposite material, based on ultrahigh molecular weight polyethylene (UHMWPE) and multiwalled carbon nanotubes (MWNTs). MWNT introduction into UHMWPE is carried out by dry mixing using planetary-type mills. Multiwalled carbon nanotubes are introduced to increase product wear resistance in an amount of 0.1 to 2 wt %. The surface of the polymer liner well has grade 11 of roughness. The friction pair consisting of the acetabular component - endoprosthesis head made of the Co-Cr-Mo alloy, has the following characteristics: friction torque of 1.3 N⋅m; no visible traces of wear of the acetabular component friction surface, acetabular component lifetime is more than 10 years.

EFFECT: invention allows effective treatment or prevention.

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Description

The invention relates to medicine, namely to traumatology and orthopedics, and is used for hip joint replacement. The developed liner is used as an acetabular component in hip arthroplasty. The liner of the acetabular component is made by thermal pressing of a nanocomposite material based on ultra-high molecular weight polyethylene and multi-walled carbon nanotubes (MWCNTs). Thanks to the use of the thermal pressing method in the manufacture of the product, it is possible to achieve the 11th class of surface roughness of the well of the acetabular component. The technical result is achieved due to the introduction of MWCNTs in UHMWPE and the formation of a grade 11 surface roughness of the hole of the polymer liner, which increases the life of the liner, reduces the friction coefficient and reduces the run-in time of the product.

The service life of hip and knee endoprostheses largely depends on the performance of the friction unit (friction pair). The friction unit consists of a head and an acetabular component (liner). The acetabular component of the hip endoprosthesis can be made of metal, ceramic, and polymer. According to a number of properties, polymer liners made from UHMWPE are the most promising for use in arthroplasty.

A known endoprosthesis liner (RU No. 2295320 A61F 2/30) made of isotropic pyrolytic carbon. Isotropic pyrolytic carbon is obtained by pyrolysis of hydrocarbons at high temperature by deposition of a special graphite substrate on the inner surface.

The disadvantages of this invention include the technological complexity of obtaining pyrolytic carbon and the need for subsequent machining to obtain the final product.

The standard procedure for the manufacture of polymer liners for the acetabular component of endoprostheses from UHMWPE consists in the manufacture of rods by plunger extrusion or thermal pressing, followed by the extrusion of polymer liners from these rods (Steven M. Kurtz, UHMWPE biomaterials handbook, second edition, Elsevier Inc., US 20130046042).

The disadvantages of the acetabular components made in this way include the low utilization of the material and the high surface roughness of the insert pocket.

Most often, polymer liners are made from crosslinked UHMWPE. Crosslinking is carried out chemically or by radiation. A patent is known (EP 2384774 A2) in which the polymer liner was made of radiation-cross-linked UHMWPE.

The disadvantage of this liner is the decrease in ductility, fatigue strength and crack resistance of the material as a result of the use of radiation crosslinking.

Known liner from UHMWPE (BY (11) 6855 C08J 9/28 A61F 2/34) with a microporous structure in the supporting surface formed by processing in liquid paraffin.

The disadvantages of this insert include the risk of oxidative processes and recrystallization in the material, with a change in the complex of physicomechanical properties of the material when it is heated to a temperature close to the melting temperature of UHMWPE and kept in liquid paraffin.

Known acetabular component of the endoprosthesis (US 5645594 A) consisting of 2 and / or 3 different layers made of UHMWPE, a mixture of polymethyl methacrylate and UHMWPE, and / or polymethyl methacrylate. The idea of using the multilayer structure of the acetabular component is to reduce the creep of the product under the action of compressive loads.

The disadvantage of this liner is the danger of destruction of the product along the boundaries of the bonding of polymer layers of various chemical nature.

Known liner acetabular component (US 20140148911 A1) made of modified vitamin E crosslinked UHMWPE. The use of vitamin E is justified by an increase in oxidation stability and an increase in the fatigue strength of crosslinked UHMWPE.

The disadvantages of the inserts of the acetabular component obtained from cross-linked UHMWPE with vitamin E include the effect of the latter on the process of crosslinking of polymer macromolecules. If vitamin E is introduced into UHMWPE before the crosslinking process begins, it reduces the efficiency of crosslinking of macromolecules, as it is an acceptor for the free radicals formed (Parth M., Aust N., Lederer K. Studies on the effect of electron beam radiation on the molecular structure of ultra-high molecular weight polyethylene under the influence of alpha-tocopherol with respect to its application in medical implants J Mater. Sci. Mater. Med. 2002 13 (10): 917-21). With increasing concentrations of vitamin E in UHMWPE, this effect is enhanced. The decrease in the efficiency of cross-linking UHMWPE negatively affects its wear resistance. The introduction of vitamin E into UHMWPE after the process of radiation exposure allows maintaining a high degree of crosslinking of macromolecules, however, the diffusion of vitamin E into a bulk product is not uniform, which leads to the formation of an inhomogeneous structure in the acetabular component.

The closest in technical essence to the technical result achieved is the liner of the acetabular component (US 20050043815 A1) made of crosslinked UHMWPE with oriented structure. In this prototype, the manufacture of the product is carried out by thermal pressing of a pre-cross-linked UHMWPE blank in a mold. UHMWPE preform is formed by thermal pressing or plunger extrusion in the form of a rod. After which it is subjected to electron irradiation, to stitch the structure and cut into washers. The mold in which the thermopressing of the product takes place provides the acetabular component of a given configuration. Thermal pressing is carried out by applying pressure and temperature.

A disadvantage of the acetabular component obtained by this method is a possible decrease in fatigue strength and crack resistance of ultra-high molecular weight polyethylene, as a result of a decrease in its ductility caused by crosslinking of the structure after electron irradiation.

The technical result consists in the formation of the acetabular component of the hip joint prosthesis, which has high wear resistance, low coefficient of thorns and high quality of the surface of the hole. The developed acetabular component meets the requirements of GOST 31621-2012. Implants for surgery. Replacing a joint with a total endoprosthesis. Determination of the durability of the friction unit of the hip joint endoprosthesis by the method of torque assessment:

- the surface of the hole of the liner corresponds to the 11th class of roughness;

- the friction moment does not exceed 1.5 N⋅m:

- the coefficient of restoration of joint mobility is not less than 100;

- there are no visible signs of wear on the friction surface of the acetabular component.

The technical result is achieved due to the formation of a polymer liner of the acetabular component of the hip joint endoprosthesis by heat pressing from a nanocomposite material, including a matrix of ultrahigh molecular weight polyethylene and filler, which is used as multi-walled carbon nanotubes, in the following ratio of mass components. %:

Filling: 0.1-2

Ultra-high molecular weight polyethylene: the rest.

When the content of multi-walled carbon nanotubes is less than 0.1% of the mass, the friction moment exceeds 1.5 N⋅m. When adding multi-walled carbon nanotubes more than 2% of the mass. the likelihood of their chipping from the volume of the polymer matrix increases. The introduction of MWCNTs in UHMWPE is carried out by dry mixing in a planetary mill. The formation of the acetabular component is carried out by thermal pressing in the temperature range 180-190 ° C and a pressure of 20-50 MPa. The invention is illustrated in FIG. 1, where a diagram of the thermal pressing of the acetabular component is presented, where 1 is the lower matrix, 2 is the upper matrix, 3 punch, 4 is the molded product. The surface roughness of the insert pocket is formed upon contact with the punch 3. Thermal pressing is carried out at a temperature of 180-200 ° C and a pressure of 40 MPa.

Example 1

Ultra high molecular weight polyethylene made by Ticona, Celanese is used as a feedstock. As a reinforcing additive, multi-walled carbon nanotubes with a diameter of 4-15 nm and a length of more than 2 μm in an amount of 2% of the mass are used. The introduction of MWCNTs in UHMWPE is carried out by dry mixing using planetary mills. The formation of the acetabular component is carried out by the method of thermal pressing, using a punch 11 of the surface roughness class, to form the surface of the hole of the product. The appearance of the polymer inserts of the acetabular component made of a polymer nanocomposite material UHMWPE / 2% MWCNTs is shown in FIG. 2.

The acetabular component has the following characteristics:

- the surface of the well of the acetabular component corresponds to the roughness class 11;

- diameter of the well of the acetabular component 28 mm:

- wall thickness of the acetabular component 8.3 mm:

- non-sphericity less than 50 microns.

A friction pair — an acetabular component made of a nanocomposite material — an endoprosthesis head made of Co-Cr-Mo alloy, tested in accordance with GOST 31621-2012, has the following characteristics:

- friction moment 1.3 N⋅m;

- there are no visible signs of wear on the friction surface of the acetabular component;

- the life of the acetabular component is more than 10 years.

Example 2

Ultra high molecular weight polyethylene made by Ticona, Celanese is used as a feedstock. As a reinforcing additive, multi-walled carbon nanotubes with a diameter of 4-15 nm and a length of more than 2 μm in the amount of 0.1% of the mass are used. The introduction of MWCNTs in UHMWPE is carried out by dry mixing using planetary mills. The formation of the acetabular component is carried out by the method of thermal pressing, using a punch 11 of the surface roughness class, to form the surface of the hole of the product.

The acetabular component has the following characteristics:

- the surface of the well of the acetabular component corresponds to the roughness class 11;

- diameter of the well of the acetabular component 28 mm;

- wall thickness of the acetabular component 8.3 mm;

- non-sphericity less than 50 microns.

A friction pair - an acetabular component made of nanocomposite material - an endoprosthesis head made of Co-Cr-Mo alloy, tested in accordance with GOST 31621-2012, has the following characteristics:

- friction moment 1.4 N⋅m;

- there are no visible signs of wear on the friction surface of the acetabular component;

- the life of the acetabular component is more than 10 years.

Claims (2)

A polymer liner of the acetabular component of the hip joint endoprosthesis, having a grade 11 roughness of the surface of the hole, a coefficient of joint mobility recovery of at least 100 and a friction moment of not more than 1.5 N⋅m, including a matrix of ultra-high molecular weight polyethylene and a filler, which use multi-walled carbon nanotubes, in the following ratio of components wt.%: Filler 0.1-2 Ultra High Molecular Polyethylene Rest

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