Bone-treating devices and their manufacturing method

• US 5,431,652 A
• Filed: 12/22/1992
• Issued: 07/11/1995
• Est. Priority Date: 12/25/1991
• Status: Expired due to Term

• Current Assignee: BMG, Inc., Guze Limited
• Original Assignee: Agency of Industrial Science & Technology (Government of Japan), Gunze Limited
• Inventors: Shimamoto, Takeshi, Kaito, Akira, Oka, Takashige, Adachi, Minori, Hyon, Suon H., Nakayama, Kazuo
• Primary Examiner(s): Brown, Michael A.
• Application Number:
  US07/994,788
• Time in Patent Office: 931 Days
• Field of Search: 606/72-77, 623/13, 623/16, 623/11, 623/66, 525/410, 525/415, 528/354
• US Class Current: 606/76
• CPC Class Codes: A61B 17/58 for osteosynthesis, e.g. bone plates, screws , setting implements or the like A61B17/14, A61B17/16 take precedence
• CPC Class Codes: A61B 2017/00004 (bio)absorbable, (bio)resorbable or resorptive
• CPC Class Codes: A61L 31/06 obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds A61L31/041 takes precedence
• CPC Class Codes: A61L 31/148 Materials at least partially resorbable by the body
• CPC Class Codes: C08L 67/04 Polyesters derived from hydroxycarboxylic acids, e.g. lactones C08L67/06 takes precedence

Abstract

Bone-treating devices made of biodegradable polymers having a high-density and a high-orientation along the major axis, which have a density of 1.260 g/cm³ or more (when measured by the sink and float method) and which possess the bending strength and the bending strength-retaining characteristic defined by the following equations:

A≧B≧23 (kgf/mm.sup.2)                        (1)

B/A≧0.85                                            (2)

wherein A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37° C. and preparing the same.

Claims

1. Bone-treating devices made of biodegradable polymers having a high-density and a high-orientation along the major axis, which have a density of 1,260 g/cm³ or more (when measured by the sink and float method) and which possess the bending strength and the bending strength-retaining characteristic defined by the following equations:

space="preserve" listing-type="equation">A≧

B≧

23 (kgf/mm.sup.2) (1)

space="preserve" listing-type="equation">B/A≧

0.85 (2)

wherein A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37°

C.

2. Bone-treating devices as defined in claim 1, which have a density between 1.265 and 1,285 g/cm³.

3. Bone-treating devices as define in claim 1, which have the bending strength and the bending strength-retaining characteristic expressed by the following equations:

space="preserve" listing-type="equation">A≧

B≧

25 (kgf/mm.sup.2) (1'"'"')

space="preserve" listing-type="equation">B/A≧

0.90 (2'"'"')

wherein A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37°

C.

4. The devices as defined in claim 1, in which lactic acid polymers with a viscosity-average molecular weight of 50,000 or more as a raw material are used as biodegradable polymers.

5. The devices as defined in claims 4, in which L-lactic acid polymers are used as lactic acid polymers.

6. The devices as defined in claim 4, in which lactic acid polymers have a viscosity-average molecular weight of 250,000 to 500,000.

7. The method for manufacturing bone-treating devices comprising hydrostatically extruding biodegradable polymers by applying pressure to a pressure medium so as to indirectly extrude the biodegradable polymer at a temperature between the glass transition point and the melting point thereof to produce high-density products in which the molecules of the polymer are oriented along the major axis and which have a density of 1,260 g/cm³ or more when measured by the sink and float method, and the bending strength and the bending strength-retaining characteristic defined by the following equations:

space="preserve" listing-type="equation">A≧

B≧

23 (kgf/mm.sup.2) (1)

space="preserve" listing-type="equation">B/A≧

0.85 (2)

where A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37°

C.

8. The method as defined in claim 7, wherein the polymer is extruded at an extrusion rate of 4:

1 to 15;

1.

9. The method as defined in claim 8, wherein the polymer is extruded at least 2 times to yield a total extrusion ratio of 4:

1 to 15;

1.

10. The method as defined in claim 7, in which lactic acid polymers are used as biodegradable polymers.

11. The method as defined in claims 10, in which L-lactic acid polymers are used as lactic acid polymers.

12. The method as defined in claim 10, in which the temperature and ratio of extrusion for poly-L-lactic acid are 140°

±

10°

C. and 5;

1 to 10;

1, respectively.

13. The method as defined in claim 7 wherein the devices have the bending strength and the bending strength-retaining characteristic expressed by the following equations:

space="preserve" listing-type="equation">A≧

B≧

25 (kgf/mm.sup.2) (1'"'"')

space="preserve" listing-type="equation">B/A≧

0.90 (2'"'"')

wherein A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in the phosphate buffer at 37°

C.

14. The method as defined in claim 7, wherein the polymer is extruded at a temperature between the glass transition point and the melting point of the polymer.

15. The method as defined in claim 14, wherein the polymer is extruded at a temperature slightly lower than the melting point of the polymer.

16. A method for manufacturing bone-treating devices comprising differential pressure extrusion of biodegradable polymers by hydrostatically applying first pressure (P₁) in a direction of extrusion and second counter pressure (P₂), in which P₁ is larger than P₂,

at a temperature between the glass transition point and the melting point thereof to produce high-density products in which the molecules of the polymer are oriented along the major axis and which have a density of 1,260 g/cm³ or more when measured by the sink and float method, and the bending strength and the bending strength-retaining characteristic defined by the following equations:

space="preserve" listing-type="equation">A≧

B≧

23 (kgf/mm.sup.2) (1)

space="preserve" listing-type="equation">B/A≧

0.85 (2)

where A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37°

C.

17. A method for manufacturing bone-treating devices comprising extruding biodegradable polymers by applying hydrostatical pressure (P) and drawing pressure (F), in which P and F are applied in a direction of extrusion at a temperature between the glass transition point and the melting point thereof to produce high-density products in which the molecules of the polymer are oriented along the major axis and which have a density of 1,260 g/cm³ or more when measured by the sink and float method, and the bending strength and the bending strength-retaining characteristic defined by the following equations:

space="preserve" listing-type="equation">A≧

B≧

23 (kgf/mm.sup.2 (

     1)

space="preserve" listing-type="equation">B/A≧

0.85 (2)

where A is the initial bending strength and B is the bending strength after 90-days immersion of the devices in a phosphate buffer at 37°

C.