JP2009240413A - Bone connecting material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bone connecting material having high affinity for bones and having such a mechanical property that high torque can be applied further to a fracture point even after an yield point. <P>SOLUTION: For the bone connecting material, bioceramic particulates are dispersed in a matrix made of a biodegradable absorptive polymer, and the water content of the bioceramic particulates is not more than 1.0%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an osteosynthesis material having a high affinity for bone and a mechanical property capable of applying a higher torque to the breaking point even after the yield point.

When a fracture is caused by a large external force applied to the living body, the bone damage is small, and it may heal spontaneously only by external fixation, but if the fractured bone stump is far apart or it breaks complicatedly When it dies, it can no longer be healed naturally by external fixation alone. In such a case, it is common to use a treatment method in which the fracture site is fixed for a certain period using osteosynthesis materials such as pins, plates, screws, etc., and these materials are removed after the bone has healed and healed. It is.

As these osteosynthesis materials, metal materials have been used from the viewpoint of strength. However, there is a concern that the material is corroded by burying the metal material in the living body for a long period of time and adversely affects the living body. Therefore, after the fracture is healed, it is necessary to perform a reoperation for removing the osteosynthesis material, and there is a great physical and mental burden on the patient.

Patent Document 1 describes a biodegradable and resorbable osteosynthesis material made of aliphatic polyester, particularly poly-L-lactic acid. Since the biodegradable and resorbable osteosynthesis material is gradually decomposed and absorbed after healing of the fracture, there is no need to remove it by re-operation.
However, these biodegradable and resorbable osteosynthesis materials may have insufficient bone fixation due to low interfacial adhesion between the bone tissue and the material. For this reason, it has been pointed out that bone holes may remain after the material is absorbed.

On the other hand, osteosynthesis materials in which bioceramics particles such as hydroxyapatite having high affinity with bone are dispersed in a matrix composed of a biodegradable and absorbable polymer have been studied (Patent Documents 2 to 4). By containing such bioceramics fine particles, the fusion of the osteosynthesis material and the surrounding bone is promoted, and the cells forming the bone enter the site where the material was present when the osteosynthesis material is decomposed. In the end, it is expected to replace bone tissue.

However, it is known that the biodegradable absorbable polymer and the bioceramic fine particles have low affinity. The mechanical properties of the material in which the biodegradable absorbable polymer and the bioceramic fine particles are combined are completely different from those of the material composed of the biodegradable absorbable polymer alone.

For example, FIG. 1 shows an osteosynthesis material (round bar shape) composed only of poly-L-lactic acid and an osteosynthesis material (round bar shape) in which hydroxyapatite fine particles are dispersed in a matrix composed of poly-L-lactic acid. A graph in the case of performing a torque test is schematically shown.
From FIG. 1, the osteosynthesis material composed only of poly-L-lactic acid once yields with a relatively low torque (yield point) when one end is fixed and the other end is twisted with torque. ), Even after the yield point, higher torque can be applied to the breaking point (hereinafter, such a property is also referred to as “sticky”). On the other hand, an osteosynthesis material in which hydroxyapatite fine particles are dispersed in a matrix made of poly-L-lactic acid has a high yield point, but once it yields, it cannot apply a higher torque ( Hereinafter, such a property is also referred to as “non-sticky”).

The mechanical properties have a great influence especially when an osteosynthesis material is used as a screw. That is, when an osteosynthesis material composed only of poly-L-lactic acid is used as a screw, even when the screw is damaged when it is screwed into the bone, there is "stickiness", so even higher torque Can be applied. Therefore, the damaged screw can be easily removed and a new screw can be screwed in again. However, when a screw which is an osteosynthesis material in which hydroxyapatite fine particles are dispersed in a matrix made of poly-L-lactic acid is used, once the screw breaks, it can be easily removed without "stickiness". Can not. Such a difference in mechanical properties was decisive at the surgical site.
JP-A-5-168647 JP 2003-159321 A JP 2004-351137 A JP 2002-325832 A

In view of the above-mentioned present situation, the present invention provides an osteosynthesis material having a high affinity for bone and having mechanical properties capable of applying a higher torque to the breaking point even after the yield point. Objective.

The present invention relates to an osteosynthesis material in which bioceramic fine particles are dispersed in a matrix composed of a biodegradable absorbable polymer, wherein the bioceramic fine particles are an osteosynthesis material having a water content of 1.0% or less. is there.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have determined that when bioceramic fine particles having a water content of 1.0% or less are used, the same “stickiness” as that comprising only a biodegradable absorbent polymer. It has been found that an osteosynthesis material having mechanical properties can be obtained, and the present invention has been completed.
The reason for this is not clear at this time. It has also been pointed out in paragraph number [0030] of Patent Document 4, for example, that water contained in the bioceramic fine particles to be blended may promote hydrolysis of the biodegradable absorbent polymer and lower its molecular weight. . However, osteosynthesis materials with “sticky” mechanical properties cannot be obtained using high molecular weight biodegradable polymers. This suggests that simple hydrolysis is not the only cause. Although the cause is unknown, a “sticky” osteosynthesis material can be obtained only when bioceramics particles having a water content of 1.0% or less are used.

In the osteosynthesis material of the present invention, bioceramic fine particles are dispersed in a matrix composed of a biodegradable polymer.
The biodegradable absorbable polymer is not particularly limited as long as it is hydrolyzed in vivo and absorbed by the living body. For example, poly-L-lactic acid, poly-D-lactic acid, poly-D, L -Lactic acid, a copolymer of L-lactic acid and D-lactic acid, a stereocomplex formed by blending poly-L-lactic acid and poly-D-lactic acid, a polyglycolic acid, a copolymer of glycolic acid and L-lactic acid, An aliphatic polyester such as a copolymer of glycolic acid and D-lactic acid is preferred. Especially, since it is excellent in strength and strength retention, poly-L-lactic acid, a copolymer of L-lactic acid and D-lactic acid mainly composed of L-lactic acid, and poly-D mainly composed of L-lactic acid. , L-lactic acid is more preferable. These biodegradable absorbable polymers may be used alone or in combination of two or more.

The bioceramic fine particles are not particularly limited, and examples thereof include hydroxyapatite, tricalcium phosphate, tetracassium phosphate and the like. Of these, hydroxyapatite is preferred because it is excellent in osteoconductivity and osteogenic ability. These bioceramics fine particles may be used alone or in combination of two or more.

The shape of the bioceramic fine particles is not particularly limited, and may be any of a spherical shape, a plate shape, a fiber shape, a tube shape, and the like. Of these, spherical materials are preferred because there is little physical irritation to the living body when the material is decomposed after implantation.

Although it does not specifically limit as a particle diameter of the said bioceramics microparticles | fine-particles, A preferable upper limit is 30 micrometers. When it exceeds 30 μm, when dispersed in a matrix composed of the biodegradable absorbable polymer, the contact area with the biodegradable absorbable polymer may become small and high mechanical properties may not be exhibited. A more preferable upper limit is 10 μm or less. The lower limit of the particle diameter is not particularly limited, but generally about 0.5 μm will be the limit.

The bioceramic fine particles have a water content of 1.0% or less. If it exceeds 1.0%, it is not possible to obtain a “sticky” osteosynthesis material. More preferably, it is 0.8% or less, More preferably, it is 0.7% or less.
The water content of the bioceramics fine particles is a thermal analyzer (TG / DTA; TG is a TG curve obtained by recording the change in weight of the sample with the rise (fall) of the ambient temperature with respect to time (temperature). DTA is to detect the temperature difference between the reference and the sample by the electromotive force of the thermocouple provided in the sample holder, and to make a DTA curve), using a nitrogen stream, at a rate of 10 ° C / min Can be measured by increasing the temperature.

Such bioceramic fine particles having a low water content can be obtained by firing the bioceramic fine particles. The firing conditions are not particularly limited as long as the water content can be achieved. For example, when the bioceramic fine particles are hydroxyapatite, firing is preferably performed at 500 ° C. or higher, more preferably 800 ° C. or higher. It is preferable. However, in the case of hydroxyapatite, if the firing temperature exceeds 1200 ° C., the osteoconductivity may be inferior.
In addition, although the bioceramic fine particles after firing can maintain a low water content for a certain period of time, depending on storage conditions, water may be absorbed in several months after firing. In such a case, it is preferable to perform firing again to reduce the water content.

The blending amount of the biodegradable absorbable polymer and the bioceramic particles in the osteosynthesis material of the present invention is not particularly limited, but the preferred lower limit of the blending amount of the bioceramics particles relative to the entire osteosynthesis material is 10% by weight, and the preferred upper limit. Is 50% by weight. If it is less than 10% by weight, excellent effects due to bioceramics such as bone conduction and osteogenesis may not be obtained, and if it exceeds 50% by weight, the strength of the resulting bone cement material may be inferior. . A more preferred lower limit is 20% by weight, and a more preferred upper limit is 40% by weight. In particular, when the blending amount of the bioceramic fine particles is 30% by weight or more, the obtained osteosynthesis material is excellent in X-ray contrast properties.

The method for producing the osteosynthesis material of the present invention is not particularly limited, and the biodegradable absorbable polymer and the bioceramic particles having a water content of 1.0% or less are equal to or higher than the melting point of the biodegradable absorbable polymer. After kneading at the above temperature, a method of molding by a conventionally known molding method such as an extrusion molding method may be used.
Such a method for producing the osteosynthesis material of the present invention is also one aspect of the present invention.

It does not specifically limit as a use of the bone cement of this invention, For example, a pin, a plate, a screw etc. are mentioned.
Since the bone joining material of the present invention has the above-described configuration, when one end of a round bar-shaped one is fixed and the other end is twisted by applying torque, it is further increased to the breaking point after the yield point. An excellent mechanical property that a high torque can be applied can be exhibited. Therefore, high performance is exhibited especially when a screw is used.

ADVANTAGE OF THE INVENTION According to this invention, it has the high affinity with respect to a bone, and can provide the osteosynthesis material which has the mechanical property which can apply still higher torque to a fracture | rupture point after a yield point.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
Hydroxyapatite fine particles having an average particle size of 30 μm were calcined at 800 ° C. for 2 hours to obtain calcined hydroxyapatite. The water content of the obtained calcined hydroxyapatite fine particles was measured by raising the temperature from room temperature to 1000 ° C. at a rate of 10 ° C./min using a TG / DTA measuring device DTG-60 manufactured by Shimadzu Corporation. %Met.

The calcined hydroxyapatite fine particles and poly-L-lactic acid (weight average molecular weight 200,000) are put into a biaxial stretching extruder so that the blending ratio of the calcined hydroxyapatite fine particles is 30% by weight, and kneaded at a temperature of 180 ° C. And then extruded to obtain pellets. The obtained pellets were extruded using a melt extruder to obtain a round bar having an average diameter of 7 mm. This round bar was stretched 3 times at 65 ° C. to prepare a stretched bar. The drawn rod was cut to obtain a rod-shaped molded body having a diameter of 3.0 mm and a length of 5.0 mm.

(Example 2)
A rod-shaped molded body was obtained in the same manner as in Example 1 except that hydroxyapatite fine particles having a water content of 0.70% were used.

(Comparative Example 1)
A rod-shaped molded body was obtained in the same manner as in Example 1 except that unfired hydroxyapatite fine particles that were not fired were used.
The unburned hydroxyapatite fine particles had a water content of 4.36%.

(Comparative Example 2)
A rod-shaped molded body was obtained in the same manner as in Example 1 except that hydroxyapatite fine particles having a water content of 5.86% were used.

(Evaluation)
One end of the obtained rod-shaped molded body was fixed, and the torque at the yield point and the breaking point when the other end was rotated at a speed of 1 rpm and twisted with torque was measured. The experiment was performed three times for each. FIGS. 2, 3, 4, and 5 show torque test charts with the rotation angle on the horizontal axis and the torque on the vertical axis.
In addition, the yield point and the breaking point were judged from the following viewpoints. That is, the maximum value that appears first after applying torque in the chart is taken as the yield point, and then the torque is continuously applied, and the maximum value that appears when the material breaks (a point where the value suddenly decreases) is taken as the break point. did.
The results are shown in Table 1.

ADVANTAGE OF THE INVENTION According to this invention, it has the high affinity with respect to a bone, and can provide the osteosynthesis material which has the mechanical property which can apply still higher torque to a fracture | rupture point after a yield point.

It is a graph at the time of performing a torque test about the bone joining material which consists only of poly-L-lactic acid, and the bone joining material which disperse | distributed the hydroxyapatite microparticles | fine-particles in the matrix which consists of poly-L-lactic acid. 2 is a chart of a torque test of a rod-shaped molded body manufactured in Example 1. FIG. 6 is a torque test chart of a rod-shaped molded body produced in Example 2. FIG. 6 is a torque test chart of a rod-shaped molded body manufactured in Comparative Example 1. FIG. 6 is a torque test chart of a rod-shaped molded body produced in Comparative Example 2. FIG.

Claims (4)

An osteosynthesis material in which bioceramics fine particles are dispersed in a matrix composed of a biodegradable absorbable polymer, wherein the bioceramics fine particles have a water content of 1.0% or less. . The bone cement material according to claim 1, wherein the bioceramic fine particles are hydroxyapatite fired at a temperature of 500 ° C or higher. The osteosynthesis material according to claim 1 or 2, wherein the biodegradable polymer is an aliphatic polyester. An osteosynthesis comprising a step of kneading a biodegradable absorbable polymer and bioceramic fine particles having a water content of 1.0% or less at a temperature not lower than the melting point of the biodegradable absorbable polymer. Material manufacturing method.

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