JP2012179072A - Screw and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw for fixing a bone, which uses bioabsorbable resin as material and which does not often cause wrenching-off troubles when fastened and has high torsional strength.SOLUTION: The screw has a screw part where a screw thread is formed, and is for passing through one mass and the other mass and fastening them. The screw is formed by machining a stretched rod in such a way that the axial direction of the screw part matches with the axial direction of the stretched rod, the stretched rod being formed by subjecting a columnar rod of polylactic acid resin to torsional stretching in which the rod is twisted while being hot-stretched, wherein the torsion direction of the columnar rod is the same as the winding direction of the spiral of the screw thread.

Description

  The present invention relates to a screw made of a bioabsorbable resin used for a bone treatment tool used for fixing a bone part such as joining, fixation of a fracture part, fixation of a transplanted bone, fixation of a fracture around a joint, and the like.

  As bone treatment tools used to fix bone parts such as joints, fixation of bone fractures, fixation of transplanted bones, fixation of bone fractures around joints, etc., wires, plates, screws, pins, screws, staples, clips made of stainless steel, ceramics, etc. A rod or the like is used. These tools are not absorbed by the human body, and thus have the disadvantage of requiring re-operation for removal after healing, and because they are more rigid than human bones, the bones in the application area are shaved or the bones in the local area due to continuous acupuncture Disadvantages such as melting, reduced strength of new bone, and delayed growth of regenerated bone.

  On the other hand, a bone treatment tool using a bioabsorbable resin that is decomposed and absorbed in vivo as a constituent material has also been proposed. Since such a bone treatment tool is inferior in strength compared to a tool formed of stainless steel, ceramic, or the like, the strength has been improved by stretching (see, for example, Patent Documents 1 to 5).

  As this bioabsorbable resin, a bioabsorbable resin such as a polylactic acid resin is preferably used as a material (see, for example, Patent Document 6).

  Since such a bioabsorbable resin generally has a lower strength than general-purpose engineering plastics, it is disclosed that the strength is improved by stretching. (For example, see Patent Document 7)

  The stretched molded body made of bioabsorbable resin has a high tensile strength but a low torsional strength. When it is molded into a screw body and used as a screw, torque exceeding the specified value was given due to unforeseen circumstances during screwing. At times, there was a risk of destruction by twisting force. In addition, a bioabsorbable resin having a high degree of orientation has a lower biodegradability than a bioabsorbable resin having a low degree of orientation, and an excessively stretched molded product has a problem that the biodegradability is too low depending on the purpose of use.

Japanese Patent Publication No. 3-63901 Japanese Patent No. 2619760 Japanese Patent Publication No. 7-96024 Japanese Patent No. 3136120 Special table 2004-517758 gazette JP 2010-057443 A JP 2006-325862 A

  An object of the present invention is to provide a screw for fixing a bone, which uses a bioabsorbable resin as a raw material, has less trouble of being broken during fastening, has high torsional strength, and the like.

The gist of the present invention is that
A screw having a thread portion formed with a screw thread, for fastening one block and another block,
A columnar rod of polylactic acid resin is twisted while being thermally stretched in the axial direction, and a stretched rod is cut so that the axial direction of the threaded portion coincides with the axial direction of the stretched rod. Therefore, the twisting direction of the columnar rod is a screw having the same winding direction as the spiral of the thread.

In addition, the gist of the present invention is that
A screw having a thread part formed with a screw thread, for fastening through one mass and another mass;
Stretching rods that are twisted by twisting while stretching a columnar rod of polylactic acid resin in the axial direction, in the constant-length state or in an unconstrained state or in a constant load state in the longitudinal direction. The heat treatment is carried out at a temperature higher than the torsional stretching temperature in FIG. 5 so that the axial direction of the threaded portion coincides with the axial direction of the extending rod, and the torsional direction of the columnar rod is a helical thread. The screw is the same as the winding direction.

  The number of twists per screw of the screw may be 0.4 to 1.6 times.

Furthermore, the gist of the present invention is that
One gripping part that grips one end of a columnar rod of polylactic acid resin for stretching, and another gripping part that grips the other end,
Driving means for relatively moving the one gripping part and the other gripping part apart from each other;
A rotation driving means for rotating the one gripping portion around the separation direction of the one gripping portion and the other gripping portion;
The present invention resides in a twisting and stretching device for a polylactic acid resin columnar rod, comprising heating means for heating the columnar rod of polylactic acid resin gripped by the one gripping portion and the other gripping portion.

  The torsional stretching apparatus may further include other rotation driving means for rotating the other gripping portion around the separation direction between the one gripping portion and the other gripping portion.

  ADVANTAGE OF THE INVENTION According to this invention, the screw for fixing the bone which uses a bioabsorbable resin as a raw material, has few troubles to which a thread breaks at the time of fastening, and has high torsion strength is provided.

It is explanatory drawing which shows an example of the shape of the screw of this invention. It is explanatory drawing explaining the twist direction of the columnar rod in this invention. It is explanatory drawing which shows an example of the aspect of the twist extending | stretching apparatus of this invention. It is explanatory drawing explaining the measuring method of the torque strength of a screw.

  The screw according to the present invention is formed by cutting a drawn rod formed by twisting and stretching a columnar rod made of a polylactic acid-based resin in the axial direction into a screw shape.

  This columnar rod can be obtained by melting and extruding a polylactic acid resin according to a conventional method and molding it into a desired shape by any other method to obtain a preform.

  The screw of the present invention has a threaded portion in which a thread is formed, such as a joint between bones, a joint between a bone and a bone substitute made of an artificial material, or a joint between a bone and a living tissue such as a tendon. Used to join parts. That is, the screw of the present invention is a screw for screwing or penetrating one block and another block to fasten both.

  As a typical example of such a screw, as shown in FIG. 1, it engages with a screw part 4 in which a thread 3 is formed and a fastening driver for screwing the screw into a lump and fastening it. The screw 2 provided with the head 6 to be made is mentioned. Or the bolt-shaped screw | thread of the aspect which penetrates one lump and another lump and fastens both with a bolt nut type is mentioned.

  In the screw 2 of the aspect shown in FIG. 1, an engagement groove for engaging with a fastening driver may be formed at the tip of the side opposite to the head 6 of the screw 2. When the head 6 is threaded with unexpected excessive torque, the engaging groove is screwed into the lump on the opposite side of the head 6 by engaging a fastening driver with the engaging groove. This is useful when the screw portion 4 is taken out in a reverse direction.

  The direction of the spiral of the screw thread 3 is generally right-handed (right-handed) as shown in FIG. 1, but left-handed (reverse or left-handed) may be used depending on the application.

  In the case of right-handed winding, the winding direction of the screw thread 3 is clockwise. That is, in the present specification, the winding direction of the spiral is such that a moving point that moves along the spiral from one point on the spiral to another point is a plane that is orthogonal to the axis of the spiral and includes the other point. , The turning direction of the movement by the movement of the moving point of the point projected from the plane side perpendicular to the axis of the spiral and including the one point.

  The unstretched columnar rod made of polylactic acid resin is improved in strength by stretching, but the torsional strength is further improved by twisting while stretching the columnar rod in the axial direction. It was found to be. In this case, the screw is obtained by cutting the axial direction of the threaded portion so as to coincide with the axial direction of the elongated columnar rod.

  Moreover, the thread is formed so that the twisting direction of the unstretched columnar rod is the same as the spiral winding direction of the thread 3 of the thread portion 4 of the screw 2 obtained by this cutting process. That is, the thread 3 is a virtual straight line 33-1 (FIG. 2 (before stretching) twisted parallel to the axial direction of the circumferential surface of the columnar rod 32-1 on the circumferential surface of the columnar rod 32-1 before stretching. The winding direction of the virtual spiral 33-2 (FIG. 2 (after stretching)) formed by deformation by stretching is the same as the winding direction of the spiral of the thread 3. Note that FIG. It is for explaining the twisting direction of the columnar rod and the virtual spiral, and is not necessarily drawn according to the correct scale.

  If the torsion direction of the unstretched columnar rod is opposite to the spiral direction of the thread of the thread portion of the screw obtained by this cutting process, the torsional strength of the screw cannot be improved. .

  Assuming that the number of twists per screw is T and the torsional strength of the screw is t (T), t (T) is the number of twists from the time T is 0 (the number of twists per screw). As the number of twists increases, T is 0.015 L (times), and t (T) is significantly larger than t (0). From there, t (T) increases as T increases. When T is 0.8 to 1.2 times, t (T) is the maximum or close to the maximum value, and is most preferable. When T is 0.4 to 1.6 times, t (T) is significantly larger than t (0).

  When the total length of the screw is L, the total number of twists TR in torsional stretching, and the length of the rod after torsional stretching is LR, the value of TR × L / LR corresponding to T is 0.4. -1.6 (times) is preferred.

  In order to obtain a columnar rod having a high stretching strength and a high twisting strength, the stretching ratio in the torsional stretching is preferably 2 to 4 times.

  The columnar rod is preferably twisted and stretched in a heated state. The temperature in this twist stretching is preferably 50 to 90 ° C.

  In the present invention, an unstretched columnar rod may be twisted while being stretched after being stretched at a low stretch ratio (for example, 1.1 to 1.5 times). Such an aspect is also referred to as torsional stretching.

  The columnar rod that is twisted and stretched is preferably heat treated (annealed) in a constant length state, an unconstrained state, or a constant load state in the longitudinal direction in order to obtain high strength. The temperature of this heat treatment (annealing) is preferably higher than the stretching temperature. This heat treatment (annealing) may be performed in several stages under different conditions.

  Examples of the polylactic acid resin that is a material for the columnar rod used in the present invention include poly-L-lactic acid, poly-D-lactic acid, poly-D, L-lactic acid, and a copolymer of L-lactic acid and D-lactic acid. , L-lactic acid and D, L-lactic acid copolymer, D-lactic acid and D, L-lactic acid copolymer, poly-L-lactic acid and poly-D-lactic acid stereocomplex, polyglycol And an acid, a copolymer of L-lactic acid and glycolic acid, a copolymer of D-lactic acid and glycolic acid, and a copolymer of D, L-lactic acid and glycolic acid. These may be used alone or in combination of two or more. Among the above polymers, a polymer mainly composed of lactic acid (lactic acid polymer), that is, lactic acid homopolymer or copolymer is preferable. In particular, L-lactic acid polymers, ie, polymers mainly composed of L-lactic acid such as poly-L-lactic acid, copolymers mainly composed of L-lactic acid (for example, L-lactic acid and D-lactic acid or D, L-lactic acid). Copolymer), and a stereocomplex formed by blending poly-L-lactic acid and poly-D-lactic acid are excellent in strength and strength retention, and can be exemplified as preferable examples.

  The molecular weight of the polylactic acid resin used in the present invention can be in a wide range, but the polymer itself tends to decompose due to heat and cause a decrease in the molecular weight. In consideration of the decrease in the molecular weight during production, the viscosity average of the raw material polymer before molding It is preferable to use a polymer having a molecular weight of 50,000 or more. In particular, in the method of the present invention, those having a viscosity average molecular weight of about 250,000 to 500,000 are preferable from the viewpoints of degradability, strength retention, workability, cost and the like.

  FIG. 3 shows an example of an embodiment of a twist stretching apparatus that twists and stretches an unstretched columnar rod. The torsional stretching device 31 includes one gripping arm 34, another gripping arm 36, and driving means 38 that stretches the columnar rod 32 by relatively moving both in a direction away from each other.

  One grip 49 for gripping one end of the columnar rod 32 is provided at the tip of one grip arm 34. Another gripping part 50 for gripping the other end of the columnar rod 32 is provided at the tip of the other gripping arm 36.

  The other gripping arm 36 is moved in the direction of arrow Y by the linear motion mechanism of the moving mechanism unit 40, and the columnar rod 32 is twisted and extended.

  The moving mechanism unit 40 includes a feed screw mechanism. The moving mechanism unit 40 includes a ball screw 41 and a moving nut 43 that is screwed into the ball screw 41 and is linearly moved by being guided by a linear guide (not shown) in the longitudinal direction of the ball screw 41 as the ball screw 41 rotates. The gripping arm 36 is fixed to the moving nut 43 and moves together with the moving nut 43. Reference numeral 45 denotes a bearing of a bearing portion 47 that pivotally supports both ends of the ball screw 41. One gripping arm 34 is fixed to a bearing portion 47. The columnar rod 32 is placed in a heating tank 44 in which a heating liquid is stored while being held by one gripping portion 49 and another gripping portion 50, and the columnar rod 32 includes one gripping arm 34 and other It is immersed in the heating liquid 38 while being gripped by the gripping arm 36. By keeping the heating liquid 38 at a predetermined heating temperature by a heating means (not shown), torsional stretching in a heated state is performed.

  The ball screw 31 is driven by a motor 32 via a coupling 39.

  Further, the one gripping portion 49 has a structure that can rotate about a direction parallel to the extending direction (arrow Y), and is rotated by a rotation driving means (not shown), whereby the columnar rod 32 is twisted. . The other gripping arm 36 and one gripping portion 49 are simultaneously driven to twist and stretch.

  The other gripping part 50 may be provided at the tip of one gripping arm 34 and the one gripping part 49 may be provided at the tip of the other gripping arm 36. Alternatively, a gripping portion that rotates at the tip of each of the one gripping arm 34 and the other gripping arm 36 may be provided, and the columnar rod 32 may be twisted by rotating in reverse.

  The stretching apparatus shown in FIG. 3 stably twists to create a high-strength screw, holds the rod securely at both ends, and uniformly and reliably twists the entire length of the rod. Stretching is preferred.

Example An unstretched columnar rod (10.3 mmφ) made of a polylactic acid resin was twisted and stretched using a twisting stretching device 31 shown in FIG. The moving speed of the other gripping arm 36 was 37.5 mm / mim. The initial grip span was 100 mm. 62 ° C. glycerin was used as the heating liquid. The draw ratio was set to 2.5 times, and one gripping portion 49 was rotated at a constant speed in the direction of arrow T so that the columnar rod was twisted in the clockwise direction from the start to the end of the drawing. The total number of rotations was set at three levels: 4 rotations (about 180 degrees per screw), 8 rotations (about 360 degrees per screw), and 12 rotations (about 540 degrees per screw). (Examples 1, 2, and 3)

  The diameter of the columnar rod after twisted drawing was 6.4 mmφ, and the length between spans was 250 mm.

  The obtained columnar rod after torsion stretching was heat-treated at 120 ° C. for 15 minutes with a load of 1 kgf in the longitudinal direction, and then heat-treated at 80 ° C. for 15 minutes with a load of 1 kgf.

  The columnar rod after torsional drawing / heat treatment thus obtained was cut to produce a screw 2a (right screw) having the shape shown in FIG. The total length of the screw 2 is 30 mm, and the diameter of the throat 5 is 2.2 mmφ. The longitudinal direction of the columnar rod and the longitudinal direction of the screw 2 are the same.

The torsional strength (torque strength) of this screw was measured by a torque measuring device 60 of the mechanism shown in FIG. The torque measuring device 60 includes a grip portion 64 that grips the screw 2 and a detection portion 66 that incorporates a torque sensor and detects torque. After the screw part 4 of the screw 2 was screwed into the screw hole formed in the grip part 64, the grip part 64 and the screw part 4 were fixed so as not to move with each other, and then engaged with the head 6. The head 62 of the fastening driver is rotated at a rotational speed of 1 rpm in the screwing and fastening direction of the screw 2 (so that the screw 2 is twisted clockwise), and the torque of the screw 2 detected by the sensor is torque torque The maximum torque until breakage was displayed on the display unit (not shown) of the measuring device 60, and the torsional strength was used.
In each example and comparative example, three samples were measured, and the average value of the three measured values was taken as the breaking strength. The fracture at the time of measurement occurred at the throat 5.

Comparative Examples 1, 2, 3
A screw was prepared and the torsional strength was measured in the same manner as in Example 1 except that the rotation direction of one gripping portion 49 was reversed from that in Example 1 so that the columnar rod was twisted in the counterclockwise direction. . The total number of revolutions was set at 3 levels of 4 revolutions, 8 revolutions, and 12 revolutions.

Comparative Example 4
A screw was prepared and the torsional strength was measured in the same manner as in Example 1 except that one grip portion 49 was stopped.

Comparative Example 5
Except that the total number of rotations was set to 18 rotations, the torsional stretching was performed in the same manner as in Example 1, but kinks were generated in the columnar rod during the stretching, and the columnar rod bent and became linear. However, the length of the screw obtained by cutting was limited, and a screw having a total length of about 30 mm could not be obtained.

  Table 1 shows the measurement results of the torsional strength (torque strength) of the screws obtained in the examples and comparative examples.

  As shown in Table 1, the screw obtained from the columnar rod subjected to torsional stretching has a twisting direction (torque strength) when twisted in the thread winding direction (screwing direction of the screw). In the case where the twist direction in the twist stretching is the same as the winding direction of the screw thread, the result is higher than the screw obtained from the columnar rod subjected to the stretching only. When the twisting direction in twisting is opposite to the winding direction of the screw thread, the winding direction of the thread (when the twisting direction in twisting is the same as the winding direction of the thread) ( The result shows that the torsional strength (torque strength) is low when twisted in the screwing direction of the screw. In the opposite case, the thread is better than the thread obtained from a columnar rod that has been subjected only to stretching. Winding direction torsional strength (torque strength) when twisted in (screwing direction of the screw) to be low say results.

  Further, in comparison with Examples 1 to 3, in which the winding direction of the screw thread is the same direction as the twisting direction of torsional stretching, the torsional strength is obtained when the number of twists per screw is one revolution. (Torque strength) was the largest. That is, the torsional strength (torque strength) of the sample increased with an increase in the number of torsional rotations in the torsional drawing, and decreased as a result of the maximum value.

Although the embodiments of the present invention have been described above, the present invention can be implemented with various improvements, modifications, and variations based on the knowledge of those skilled in the art without departing from the spirit thereof. All belong to the scope of the present invention.

  The screw of the present invention is suitably used as a screw for fixing a mass composed of a living body such as bone.

2: Screw 3: Screw thread 4: Screw part 6: Head 31: Torsion stretching device 32: Columnar rod 34: One gripping arm 36: Other gripping arm 38: Driving means 49: One gripping part 50: Other gripping part 44: Heating tank

Claims (5)

A screw having a thread portion formed with a screw thread, for fastening one block and another block,
A columnar rod of polylactic acid resin is twisted while being thermally stretched in the axial direction, and a stretched rod is cut so that the axial direction of the threaded portion coincides with the axial direction of the stretched rod. Become
A screw in which the twisting direction of the columnar rod is the same as the winding direction of the spiral of the thread. A screw having a thread part formed with a screw thread, for fastening through one mass and another mass;
Stretching rods that are twisted by twisting while stretching a columnar rod of polylactic acid resin in the axial direction, in the constant-length state or in an unconstrained state or in a constant load state in the longitudinal direction. What is heat-treated at a temperature higher than the torsional stretching temperature in is made by cutting the axial direction of the threaded portion to coincide with the axial direction of the stretching rod,
A screw in which the twisting direction of the columnar rod is the same as the winding direction of the spiral of the thread.   The screw according to claim 1 or 2, wherein the number of twists per screw is 0.4 to 1.6. It is an apparatus used for extending | stretching the columnar rod of the said polylactic acid-type resin for producing the screw in any one of Claim 1 to 3,
One gripping part that grips one end of a columnar rod of polylactic acid resin for stretching, and another gripping part that grips the other end,
Driving means for relatively moving the one gripping part and the other gripping part apart from each other;
A rotation driving means for rotating the one gripping portion around the separation direction of the one gripping portion and the other gripping portion;
A twisting and stretching device for a polylactic acid resin columnar rod, comprising heating means for heating the columnar rod of polylactic acid resin gripped by the one gripping portion and the other gripping portion. The columnar rod of polylactic acid resin according to claim 4, further comprising other rotation driving means for rotating the other gripping portion around the separation direction of the one gripping portion and the other gripping portion. Torsion stretching device.

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