WO1987000059A1

WO1987000059A1 - Surgical resorbable devices with layered composite structure

Info

Publication number: WO1987000059A1
Application number: PCT/FI1986/000071
Authority: WO
Inventors: Pertti Törmälä; Jyrki Kilpikari; Juha Laiho; Markku Tamminmäki; Arto Ritakorpi; Taito Mikkonen
Original assignee: Materials Consultants Oy
Priority date: 1985-07-09
Filing date: 1986-07-02
Publication date: 1987-01-15
Also published as: FI78238B; FI852706A0; EP0239577A1; AU6135686A; FI852706L; FI78238C; CA1277602C

Abstract

Surgical, resorbable osteosynthesis device or its component like plate, balk, nail, rod, bar or screw. The device or the like comprises a three-dimensional solid composite body which is manufactured of at least one resorbable polymer, copolymer or polymer alloy which device or component has layered composite structure. The device or component is constructed at least of tough and flexible at least partially resorbable polymeric surface layer (1) and of at least partially resorbable inner layer (2) which is substantially stiffer and harder than the surface layer. The device or the like may comprise an inner core (3) which is flexible and at least partially resorbable of its character.

Description

"Surgical resorbable devices with layered composite structure".

This invention describes new resorbable surgical osteosynthesis devices for operative treatment (internal fixation) of bone fractures, osteotomies and arthrodesis.

In detail, this invention describes osteosynthesis devices or their parts, such as plates, screws, balks, nails or rods, which are manufactured of body resorbable (soluble) material combination in such a way that the osteosynthesis devices or their components have layered composite structure.

Body absorbable materials and osteosynthesis devices have been described in several patents as in U.S. Pat. 3 463 158, U.S. Pat. 3 620 218 and U.S. Pat. 3 739 773, which comprise medullary nails, osteosynthesis plates, screws and hollow cylinders which are manufactured of polyglycolic acid. G.B. Pat. 1 034 123 shows osteosynthesis devices which are manufactured of poly-β-hydroxybutyric acid and poly-β-hydroxypropionic acid. U.S. Pat. 4 052 988 shows surgical devices manufactured of poly-p- dioxanone. U.S. Pat. 4 279 249 shows osteosynthesis parts which comprise composite parts constituted by a matrix of polylactic acid or a copolymer thereof; said copolymer comprising at least 90% of units derived from lactic acid, said matrix containing a reinforcement element in the shape of fibers, threads, films, fabrics, or strands embedded therein and present in an amount of 5 to 50% by weight based on the total weight of the osteosynthesis part, said element . being made of polyglycolic acid or a copolymer thereof.

Different resorbable materials have hardness and stiffness values which differ considerably from each other. Polyglycolides, polylactides and poly-β- hydroxybutyric acid are fairly stiff materials and therefore also notch sensitive and they break under bending or shearing easily (bending strength and shear strength of bulk samples is typically 40-60 MPa).

Poly-p-dioxanone and many of its derivatives are soft, flexible (elastic) and tough materials, which often do not break at all during normal bending experiments.

Surgical osteosynthesis devices must be both stiff and tough. This invention describes surgical osteosynthesis devices, which are three-dimensional samples, such as plates, screws, balks, nails or rods and which have layered composite structure. This structure is constructed of at least partially resorbable material layers in such a way that the surface layer of the composite sample is constructed of a tough and flexible, resorbable polymeric material (polymer, copolymer or polymer alloy) and the layer below it is constructed of a at least partially resorbable material which is clearly stiffer and harder than the surface layer. Additionally the core of the layered resorbable composite material can be flexible of its character. The composite structures of this invention give possibilities to combine advantageously the desirable properties of the flexible resorbable polymers and stiff resorbable polymers and to eliminate the un- favourable mechanical properties of single materials when one manufactures macroscopical surgical samples, which are applied in the internal fixation of the bone fractures, osteotomies, arthrodesis, luxations or other tissue damages.

When one manufactures a macroscopical surgical device with the structure described in this invention, the tough and flexible resorbable surface layer decreases the notch sensitivity of the sample and improves therefore the toughness (impact resistance) and the shear strength of the composite sample. Additionally the flexible and tough resorbable polymers are as a rule more hydrophobic of their nature than the stiff ones. Therefore the tough and flexible surface layer acts also as a hydrolysis barrier which favourably decreases the loss rate of the mechanical bending strength of the composite sample in hydrolytic conditions (like in tissue conditions). On the other hand, the stiff resorbable layer below the surface layer gives for the macroscopic sample the stiffness which is necessary in bone surgical internal fixation applications.

A favourable embodiment of this invention from the point of view of bending stiffness and tensile strength is such a composite sample, where also the core of the stiff layer is flexible and elastic. In this case the resorbable stiff material composes a tubular structure, which is favourable from the point of view of bending stiffness and on the other hand the flexible and elastic core increases the tensile strength of the sample.

The different layers of the composite samples of the invention can be reinforced with resorbable fibers, threads, cords or corresponding structures. The different resorbable layers can be also self- reinforced as is described in EPO-appl. 86105465.8.

The invention is described more closely with reference to the enclosed figures la-b.

Figure la shows typical embodiments of this invention. Figure la shows the cross-sections of a cylindrical and a rectangular resorbable osteosynthesis device or its component like plate, medullary nail or osteosynthesis balk (BE Pat. 900 513), which is composed of the surface layer 1, which is constructed of flexible, (elastic) and tough resorbable polymer, copolymer or polymer alloy and of the inner part 2 which is constructed of stiffer and harder resorbable polymeric material. The surface layer 1 and/or the inner part 2 can additionally contain resorbable reinforcing elements (such as fibers, threads, cords etc.) or the surface layer 1 and/or the inner part can be self-reinforced (e.g. manufactured by sintering or by partial melting of pressurized resorbable fibrous material). Figure lb shows the cross-sections of a cylindrical and of a rectangular osteosynthesis device or its component, which is composed of flexible and tough resorbable surface layer 1, of stiff resorbable inner part 2 and of flexible and elastic core 3. Also in this case at least one of the layers can be reinforced with resorbable reinforcing elements.

Flexible, tough resorbable polymers, which are suitable for surgical applications and which can be applied as surface layers 1 or cores 3 of the osteosynthesis devices of the invention, are e.g. poly-p-dioxanone and its derivatives and as a rule polymers, which are synthetized of the following monomer:

R-CH C=0

R-C-R H-C-R'

where R and R' can be hydrogen-, methyl- or ethyl group.

The surface layer 1 or core 3 can be manufactured also of polyesteramides, which contain long hydrocarbon chains in their structure. E.g. the following polyesteramides, which are copolymers of diamine, hydroxy acid and diacid (U.S. Pat. 4 343 931) can be applied in surface layer 1 or core 3 of the osteosynthesis devices of the invention:

(Structural formula I)

where x is e.g. 11-14, giving flexible polymers with melting points between 80 - 100°C.

The stiff inner part 2 of the osteosynthesis devices of the invention can be manufactured of e.g. polyglycolides, polylactides, glycolide/lactide copolymers and of poly-β-hydroxybutyric acid.

The invention is illustrated by means of the following examples.

EXAMPLE 1

The melt of polyglycolic acid (internal viscosity |_η | = 1.2 in 0.5% hexafluoroisopropanol solution at 25°C, melting point T = 224°C) was injection moulded to cylindrical bars (length 70 mm, diameter 0 4 mm). The bars were coated with 0.25 mm thick layer of poly-p-dioxanone (PDS) ( | η| = 0.80 in 0.1% tetra- chlorethane solution at 25°C, Tm = 110°C) by** injection moulding which gave cylindrical layered composite rods with 0 4.5 mm. EXAMPLE 2

Surgical polyglycolic acid sutures (trade name Dexon, size 2 USP) were sintered at 220°C temperature and 2000 bar pressure to cylindrical self-reinforced bars (length 70 mm, 0 4 mm). The bars were coated by injection moulding with 0.25 mm thick layer of poly-p-dioxanone (|η| = 0.8, T = 110°C), which gave cylindrical layered composite bars with 0 = 4.5 mm. The shear load carrying capacity of layered (PDS coated) bars was 2100 N. The shear load carrying capacity of the corresponding non-coated self-reinforced polyglycolide bars was 1800 N.

The bending strength of layered (PDS coated) composite bars after three weeks immersion at 37°C in destilled water was 230 N/mm². The bending strength of corresponding non-coated self-reinforced poly¬ glycolide bars after three weeks immersion at 37°C in destilled water was 80 N/mm².

EXAMPLE 3

Polyglycolic acid melt (|η| = 1.2, T = 224°C) was injection moulded to tubular samples (length 70 mm, outer diameter 4 mm, inner diameter 1.5 mm). The inner cores of tubes were filled and outer surfaces were coated with PDS by means of injection moulding giving layered composite rods with 0 4.5 mm (chf. fig. lb). EXAMPLE 4

Glycolide/lactide copolymer sutures, polyglactin 910 (trade name Vicryl) were sintered at 180°C temperature and 2000 bar pressure to tubular, - self-reinforced samples (length 70 mm, outer diameter 4 mm, inner diameter 1.5 mm). The inner cores of tubes were filled and outer surfaces were coated with PDS by means of injection moulding giving layered composite rods with 0 4.5 mm( chf. fig. lb).

EXAMPLE 5

Glycolide/lactide copolymer sutures, polyglactin 910 (trade name Vicryl) were sintered at 180°C temperature and 2000 bar pressure to tubular, self-reinforced samples (length 70 mm, outer diameter 4 mm, inner diameter 1.5 mm). The inner cores of tubes were filled and outer surfaces were coated with polyesteramide (structural formula I, where x = 12, M = 40 000) by means of injection moulding giving layered composite rods with 0 4.5 mm (chf. fig. lb).

Claims

1. Surgical, resorbable osteosynthesis device or its component like plate, balk, nail, rod, bar or screw, which comprises a three-dimensional solid composite body which is manufactured of at least one resorbable polymer, copolymer or polymer alloy which device or component has layered composite structure, c h a r a c t e r i z e d in that the device or component is constructed at least of tough and flexible at least partially resorbable polymeric surface layer (1) and of at least partially resorbable inner layer (2) which is substantially stiffer and harder than the surface layer.

2. Surgical, resorbable osteosynthesis device or its component as claimed in Claim 1, c h a r a c- t e r i z e d in that the device or component is constructed of tough and flexible at least partially resorbable polymeric surface layer (1), of at least partially resorbable inner layer (2) which is substantially stiffer and harder than the surface layer and of inner core (3) which is flexible of its character.

3. Surgical, resorbable osteosynthesis device or its component as claimed in Claims 1 and 2, c h a¬ r a c t e r i z e d in that at least one layer of the structure of osteosynthesis device or its component is reinforced with resorbable reinforcing elements.

4. Surgical, resorbable osteosynthesis device or its component as claimed in Claim 3, c h a r a c¬ t e r i z e d in that the reinforcing elements are fibers, threads, cords, bands or like.

5. Surgical, resorbable osteosynthesis device or its component as claimed in Claims 1-4, c h a r a c¬ t e r i z e d in that the surface layer (1) and/or the inner core (3) has been manufactured of a polymer of a monomer having the formula:

where R and R' can be hydrogen-, methyl- or ethyl group, the said polymer generally comprising following units:

where R' and R can be hydrogen-, methyl- or ethyl groups and n - the degree of polymerization.

6. Surgical, resorbable osteosynthesis device or its component as claimed in Claims 1-5, c h a r a c¬ t e r i z e d in that the surface layer (1) and/or the inner core (3) has been manufactured of poly-p- dioxanone.

7. Surgical, resorbable osteosynthesis device or its component as claimed in Claims 1-5, c h a r a c¬ t e r i z e d in that the surface layer (1) and/or the inner core (3) has been manufactured of polyesteramide (structural formula I).

8. Surgical, resorbable osteosynthesis device or its component as claimed in Claims 1-7, c h a r a c¬ t e r i z e d in that the stiff inner layer (2) has been manufactured of at least one of the following resorbable polymers: polyglycolide, polylactide, glycolide/lactide copolymer or poly-β-hydroxy- butyrate.