JPH08322925A - In vivo degradable and absorptive rib fixing pin - Google Patents

Abstract

PURPOSE: To provide a fixing pin which can secure fixing force to a rib, which is adapted to join injured or broken rib parts to each other and fix the same in the case of an injury, a breakage and solution of continuity of the ribs. CONSTITUTION: A rib fixing pin uses moldings obtained by melt-molding and drawing polylactic acid, and the moldings are secondary-molded or cut to form a bow-like rod. The compressive flexural strength is 16.0×10<2> -25.0×10<2> kg/cm<2> , and the compressive flexural elastic modulus is 5.5×10<2> -24.0×10<2> kg/mm<2> . The fixing pin has such high strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rib fixing pin that fixes a rib until it is formed when the rib is damaged, fractured or separated.

[0002]

2. Description of the Related Art In orthopedics and the like, high strength bone joint plates and screws are used for reducing fractures.
Such an artificial material for osteosynthesis functions only until the fracture is healed, and it is necessary to remove it as soon as possible in order to prevent weakening of the bone after healing.

Most of clinically widely used bone joint plates and the like are made of metal at present, and ceramics have recently appeared. However, these materials have such problems that the elastic modulus of the material itself is too high and the strength of the surrounding bone is rather reduced, the elastic modulus is high and brittle, and the living body is damaged by elution of metal ions. Therefore, if a material that has elasticity equal to or slightly higher than that of living bone and that is biodegradable and absorbable is used for bone joining, not only reoperation for removal becomes unnecessary, but also foreign material. It should be possible to exclude various adverse effects caused by long-term presence in the living body.

Under such circumstances, development of bone cements using polylactic acid or lactic acid-glycolic acid copolymer, which are biodegradable and absorbable materials, has been actively promoted.

For example, M. Vert, F.F. Chabot et al. Have synthesized polylactic acid and lactic acid-glycolic acid copolymers for bone-bonding plates, and have 100% polylactic acid and a compressive bending elastic modulus of 3.4 GPa (340 kg / mm ² ). (Makromol Chem. Suppl., 5, 30-).
41, 1981). In addition, D. C. Tunc reports a plate for polylactic acid osteosynthesis with a compressive bending elastic modulus of 520 kg / mm ² (9th USA Biomaterials Society Abstracts,
6, 47, 1983).

Further, Japanese Patent Application Laid-Open No. 59-97654 discloses a method for synthesizing polylactic acid as a material for an absorbable bone fixing device. The tensile strength of this polylactic acid is about 580 kg / cm. ^The value is as low as ^2, and the method of molding polylactic acid is not described at all.

In addition, J. W. Leenslag, A. J. Pennings
Synthesized polylactic acid having a viscosity average molecular weight of about 1,000,000,
It has been reported that the compression bending elastic modulus of the osteosynthesis plate using the high molecular weight polylactic acid was 5 GPa (500 kg / mm ² ) (Biomaterials, 8, 70, 1987).
However, there is a problem in molding processability due to too high a molecular weight.

As described above, many studies have been reported for improving the mechanical properties of polylactic acid-based bone cements, and various methods have been tried, but they are still satisfactory in clinical use. Strength materials have not been developed. The inventors of the present invention proposed in Japanese Patent Application No. 62-333333 a biodegradable and absorbable surgical material having a strength that is about the same as or slightly higher than that of living bone, and obtained a material that can be used clinically. This material is used after being cut into various sizes and shapes of osteosynthesis plates, pins, screws, screws and the like.

[0009]

As described above, various polylactic acid-based bone-bonding materials have been developed. However, since their shapes were only straight plates, pins, etc. However, it was difficult to insert it into the costal bone marrow cavity. In addition, there was concern about the fixation in the medullary cavity.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a rod-shaped pin having an optimum shape as a rib fixing pin.

[0011]

The polylactic acid used in the present invention is as follows. That is, high molecular weight polylactic acid,
It is melt-formed, for example, extruded or press-formed under the temperature conditions of its melting point or 220 ° C.
Stretching was carried out in a nitrogen atmosphere or in oil in order to suppress the molecular weight reduction due to the temperature condition of 0 to 160 ° C. or oxidative decomposition. This has a compressive bending strength of 16.0 × 10 ^2.
It is a molded product of tough polylactic acid of ˜25.0 × 10 ² kg / cm ² , and a compression bending elastic modulus of 5.5 × 10 ^{2 to} 24.0 × 10 ² kg / mm ² . The present invention is a molded product of polylactic acid having the above-mentioned physical properties, which is molded into an arched rod in conformity with the shape of the ribs.

That is, the biodegradable and absorbable rib-fixing pin according to claim 1 of the present invention is a rod-shaped rib joint for which a melt-molded / stretched polylactic acid molded product has an arc shape. 2 has a compressive bending strength of the above polylactic acid molded product of 1
6.0 × 10 ^{2 to} 25.0 × 10 ² kg / cm ² , and the compression bending elastic modulus is 5.5 × 10 ^{2 to} 24.0 × 10 ² kg / cm ² .
It has a strength of mm ² .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid used in the present invention will be described in detail. The polylactic acid is prepared from an optically active L-form or D-form lactic acid by a conventional method (CE Love, US Pat.
68,182), synthesizing lactide, which is a cyclic dimer of lactic acid, and then subjecting the lactide to ring-opening polymerization. Since this polylactic acid is inferior in thermal stability, it is preferable that at least the viscosity average molecular weight is 300,000 or more in consideration of the decrease in the molecular weight at the time of melt molding. The higher the molecular weight, the higher the strength of the rib fixing pin can be obtained. Suitable for However, if the molecular weight is too high, high temperature and high pressure are required during the melt molding, resulting in a large decrease in the molecular weight, and as a result, the molecular weight after the melt molding becomes less than 200,000, resulting in high strength. It becomes difficult to obtain the rib fixation pin. Therefore, it is suitable to use one having a viscosity average molecular weight of about 300,000 to 600,000,
Those having a molecular weight of preferably 350,000 to 550,000, and particularly about 400,000 to 500,000 are particularly preferably used.

As described above, the polylactic acid molded product is made from polylactic acid as a raw material, and is melt-molded into a rod shape or a flat plate shape, for example, extrusion molding or press molding, and then uniaxially stretched in the longitudinal direction. Obtained by

Regarding the temperature condition of the melt extrusion molding, it is necessary to set the temperature range above the melting point of the above-mentioned polylactic acid and below 220 ° C. If the temperature is lower than the melting point, melt extrusion becomes difficult, and conversely, if the temperature is higher than 220 ° C., the molecular weight is markedly decreased due to the thermal instability of polylactic acid, and the viscosity average molecular weight after melt extrusion is less than 200,000. Because.

The molecular weight of the molded product after melt extrusion molding is preferably 200,000 or more, particularly preferably in the range of 250,000 to 400,000, and if it is less than 200,000, improvement in mechanical properties cannot be expected even by stretching. In order to minimize the decrease in the molecular weight, it is important to carry out melt extrusion molding at a temperature slightly higher than the melting point of the raw material polymer. Therefore, the raw material polymer having a molecular weight of about 400,000 to 500,000 as described above. When using, it is desirable to perform melt extrusion molding at a temperature condition of 200 ° C. or lower. From the viewpoint of mechanical strength, the molecular weight after molding is preferably higher.

Similarly, regarding the pressure condition of the melt extrusion molding, in order to suppress the decrease of the molecular weight as much as possible, it is desirable that the extrusion pressure is the minimum extrudable pressure in accordance with the viscosity (molecular weight) of the molten raw material polymer. Therefore, when the molecular weight of the raw material polymer is up to 600,000, 260 kg / cm ² or less, and when the molecular weight is between 400,000 and 500,000, 170 to 210 kg / cm.
An extrusion pressure of about ² is suitable.

Prior to melt extrusion molding, it is desirable that the raw material polymer pellets be dried by heating under reduced pressure to sufficiently remove water.

The extruded product obtained by melt extrusion molding has a viscosity average molecular weight of 200,000 or more.
It has considerable strength, but it is still below the desired strength. Therefore, as described above, the extruded product is further uniaxially stretched in the long axis direction (extrusion direction) in liquid paraffin, silicone oil, or a heated nitrogen stream to orient the polymer molecules and improve the strength.

The crystallinity of the material can be increased by heating during stretching. However, if the crystallinity of the material is increased by heat treatment, the initial strength is improved, but the molecular weight decreases, so the hydrolysis rate becomes faster, and the strength retention period becomes shorter than that of the amorphous material. is necessary. Therefore, the temperature condition during stretching is preferably in the range of 60 to 160 ° C., and when it is lower than 60 ° C., it is not preferable because it is too close to the glass transition temperature. Conversely, above 160 ° C, especially 18
When the temperature exceeds 0 ° C., the molecular weight decreases, and the sliding deformation of the molecules takes precedence, so that the molecular orientation does not occur and the improvement of the strength cannot be expected. Further, the heating time is preferably within 10 minutes.

Next, the draw ratio is preferably 2 to 6 times. If the stretching ratio is less than 2 times, the molecular orientation becomes insufficient and it is difficult to satisfactorily improve the strength. On the other hand, if the stretching ratio is 6 times or more, fibrillation occurs and the hydrolysis resistance decreases. Is.

The polylactic acid molded product obtained by the above-mentioned manufacturing method has biodegradability and absorbability, and there is almost no risk of adversely affecting it in vivo, unlike conventional metal materials. Moreover, the decrease in molecular weight during melt molding is minimized to maintain the viscosity average molecular weight after melt molding at 200,000 or more, and further molecular orientation and crystallization are imparted by stretching.
This polylactic acid molded product has a compressive bending strength of 16.0 × 10 ^2.
˜25.0 × 10 ² kg / cm ² , the compressive bending elastic modulus is 5.5 × 10 ^{2 to} 24.0 × 10 ² kg / mm ² , the crystallinity is 10 to 60%, and has high strength. It will be what you did.

The polylactic acid molded product thus obtained is formed into a curved bow-shaped molded product by secondary molding, cutting or the like to form a fixing pin for rib joint. The arcuate fixing pin facilitates insertion into the curved medullary cavity of the ribs, and because of the arcuate shape, the elastic pin can be press-fitted to increase the fixing force.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The rib fixing pin of the present invention will be described below with reference to examples.

Pellets of polylactic acid having a viscosity average molecular weight of 420,000 are dried under reduced pressure at 80 to 120 ° C. for 24 hours, and the dried pellets are placed in an extruder and left under reduced pressure for about 40 minutes. The temperature of the cylinder part is 19
8 ℃, adapter part 200 ℃, die part 200
The temperature was set to 0 ° C., and the mixture was melt-extruded into a square bar or a round bar. When the viscosity average molecular weight of the obtained molded product was measured, it was found to be 22
It was good. In addition, the following [Formula 1] was used for the viscosity formula in this case.

[Equation 1]

Next, this molded product was uniaxially stretched in the major axis direction twice in liquid paraffin at 105 ° C. to obtain a polylactic acid molded product.

Next, the stretched polylactic acid molded product was cut to obtain pins of the polylactic acid molded product shown in FIGS. 1 and 2. 1 shows a front view and FIG. 2 shows a plan view. The size of the pin is such that the length L is 37.5 mm and the length of one side is 3 mm to 4 m.
m has a substantially square cross section, and as is clear from FIG.
It is an arched rod having 50 curved surfaces. This is used as a rib fixing pin.

Physical properties and in vitro of the rib fixing pin
In order to investigate the strength deterioration at o, a test piece (dimension: φ5.0 mm x length 80 m from a uniaxially stretched polylactic acid molded product
m) was prepared. The compressive bending strength of the obtained test piece is 17
20 kg / cm ² , compressive bending elastic modulus is 610 kg / mm
² and the crystallinity was 28%.

Further, the test piece was dipped in a physiological saline solution at 37 ° C. for 3 months, and the compressive bending strength of the test piece was measured to be 1700 kg / cm ² , and the compressive bending elastic modulus was 600 kg / mm. ^2, it was found that does not occur the most strength deterioration.

The above-mentioned compressive bending strength and compressive bending elastic modulus are measured based on JIS K-7203, and the crystallinity is calculated from the density measured by the following method.

It was measured at 30 ° C. using a density gradient tube of n-hexane-carbon tetrachloride system. Prior to measurement, the sample was placed in n-hexane to remove air bubbles and degassed for 30 minutes.

The crystallinity was calculated from the measured density according to the following equation [Equation 2].

[Equation 2]

[0033]

As can be understood from the above description, since the biodegradable and absorbable rib fixing pin for rib joint of the present invention has an arcuate rod shape, the rib is inserted into the medullary cavity. It is easy to peel off, and the bow shape gives elasticity, making it easier to press fit and increasing the fixing force. Further, the fixing pin of the present invention does not break during joining because it has a certain strength.

[Brief description of drawings]

FIG. 1 is a front view of a rib fixing pin according to an embodiment of the present invention.

FIG. 2 is a plan view of the rib fixing pin of the present invention.

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[Procedure amendment]

[Submission date] June 18, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

Pellets of polylactic acid having a viscosity average molecular weight of 420,000 are dried under reduced pressure at 80 to 120 ° C. for 24 hours, and the dried pellets are placed in an extruder and left under reduced pressure for about 40 minutes. The temperature of the cylinder part is 19
8 ℃, adapter part 200 ℃, die part 200
The temperature was set to 0 ° C., and the mixture was melt-extruded into a square bar or a round bar. When the viscosity average molecular weight of the obtained molded product was measured, it was found to be 22
It was good. In addition, the following [Formula 1] was used for the viscosity formula in this case.

[Equation 1]

Claims (2)

[Claims] 1. A biodegradable and absorbable rib-fixing pin for joining ribs, which is rod-shaped and has a polylactic acid molded product obtained by melt-forming and stretching and having an arc shape. 2. A polylactic acid molded product having a compressive bending strength of 16.0.
^{× 10 2 ~25.0 × 10 2 kg} / cm 2, compression flexural modulus of ^{5.5 × 10 2 ~24.0 × 10 2} kg / mm 2
The biodegradable and absorbable rib fixing pin according to claim 1.