WO2006089920A2

WO2006089920A2 - Biodegradable osteosynthesis system for use in the entire locomotor system and corresponding production method

Info

Publication number: WO2006089920A2
Application number: PCT/EP2006/060197
Authority: WO
Inventors: Gabriel Caduff; Andreas Rothenbuehler
Original assignee: Gabriel Caduff; Andreas Rothenbuehler
Priority date: 2005-02-23
Filing date: 2006-02-23
Publication date: 2006-08-31
Also published as: WO2006089920A3; CH698152B1

Abstract

The invention relates to an implantable, biodegradable osteosynthesis system for operational connections on the level of the locomotor system. Said system is capable of absorbing major forces and can therefore be used in the entire locomotor system, in particular in the load-bearing skeleton. The inventive system comprises at least one motion-stable or load-stable element which has a strength that is equal to or greater than 300 N/mm2 and which is produced from a biodegradable composite material with a matrix and fibers integrated into the matrix. The chemical composition and structure of the fibers integrated into the matrix differs from those of the matrix. As a result of the suitable biomechanical properties, the locomotor system is able to bear weight already at an early stage after surgery. The times for hospitalisation, rehabilitation and absences from work can be substantially reduced. The osteosynthesis system makes it possible to largely replace traditional metal implants. A method for producing the inventive biodegradable osteosynthesis system is also disclosed.

Description

Biodegradable osteosynthesis system for use in the entire musculoskeletal system and manufacturing process

Technical area

The Binding refers to a biodegradables

An osteosynthesis system for use throughout the musculoskeletal system and a method of making the same according to the independent claims.

State of the art

Biodegradable implants in the non-structural skeletal or dental field have long been known and used. The materials used are very well researched and documented in their bi o mechanical and biochemical properties.

The metallic implants commonly used in the supporting skeleton are metal loosening, fractures,

Incompatibilities etc. possible. The disadvantage is that these implants, although motion, but are not stable in load at an early stage. In addition, they are often removed, especially in the supporting skeletal area, and therefore require further surgical intervention. The lack of load stability makes longer periods of relief necessary, which is why with previous osteosynthetic materials no significant reduction of the rehabilitation time could be achieved.

Previous applications of biodegradable and fiber reinforced plastics as the osteosynthesis material can be characterized as follows, according to CA-A1-2,205,231

i) dispersion-reinforced composites ii) particle-reinforced composites iii) fiber-reinforced composites

CA-A2-2,205,231 at the same time discloses a dispersion- and particle-reinforced composite having material properties which do not reach the required strengths for skeletal osteosynthesis systems.

Other systems that use biodegradable materials already use fiber-reinforced composites. However, these also have insufficient strength. An example of such a fiber reinforced composite having a polymer matrix with insufficient material properties is known from EP-A2-0,146,398. Also, other approaches to laminates of osteosynthesis plates with directional fibers (CA-A1 -2,301, 900), directed short fibers (US-B1 - 6,511 1, 51 1) or combinations thereof (CA-A1 -2,301, 900), the also do not meet the requirements.

So far, it has not been possible to develop a biodegradable osteosynthesis system, which would meet the stability requirements to be used in the entire musculoskeletal system. In addition, the prior art does not provide systems consisting of a biodegradable implant and associated fasteners such as screws, nails, wires, etc., all of the elements involved being made of a biodegradable material. Conventional biodegradable, non-fiber reinforced fasteners of sufficient strength must be made in the manufacturing process with such high pressure that the degradation time is massively increased and the benefits of degradability can not be exploited.

Presentation of the invention

The invention seeks to avoid the disadvantages of the implants known from the prior art and has for its object to provide a biodegradable osteosynthesis system, which is suitable for use in the entire musculoskeletal system, and with which at the same time Hospitalization times, rehabilitation and lost time after surgery are shortened.

It is a further object of the invention to provide a biodegradable osteosynthesis system in which not only the implant itself meets the strength requirements, but also the required fasteners, which are also made of a biodegradable, fiber-reinforced composite material, so that similar properties of involved parts can be achieved.

It is a further object of the present invention to provide a biodegradable osteosynthesis system of a fiber-reinforced composite, which is particularly suitable for the abovementioned, inventive tasks by selection of the fibers used, the matrix materials and the fiber orientation.

The objects according to the invention are achieved by a biodegradable osteosynthesis system for use in the entire musculoskeletal system, comprising at least one implant that is resistant to movement and / or stress and consists of a biodegradable composite material with a matrix and fibers integrated into the matrix Structure of the integrated into the matrix fibers can distinguish from the matrix, with a strength of the composite of at least 300 N / mm ² . Bn load-stable osteosynthesis implant must be in the bearing

Skeleton area can take at least one force (F ₁ ), which corresponds to the load that must take the intact bone under load (F _K ), and have a stiffness that corresponds substantially to the rigidity of the intact bone.

The objects according to the invention are also achieved by a production method of a biodegradable osteosynthesis system for use in the entire musculoskeletal system with the features of the independent method claim. By the present invention, a cost and risk reduction can be achieved, since a further Engriff for removal, as in metallic implants, is no longer necessary. The achieved so far technical and surgical standards, which were achieved with metallic implants, but at the same time advantageously preserved. The osteosynthesis system according to the invention can be processed with the same well-known apparatus and tools known from metallic implants. Since the postoperative rehabilitation time is shortened by the load-stable implants, a cost reduction can be additionally achieved by the invention.

A particular advantage arises when the system of motion and / or load-stable Eementen, such as rats, screws, wires, nails, intramedullary nails, etc., is assembled, and all elements are made of biodegradable materials. The inventive system with the features described above can also consist only of individual elements, such as screws or other connecting means with the inventive features that connect parts of the musculoskeletal system together. The screws used should advantageously have a load of 3000 N and a

Tangential force of 3700 N can take up in order to be used on supporting parts of the skeleton can (M üller, M. E et al: manual of osteosynthesis, 3rd edition, Springer-Verlag 1992). The system should be designed so that all elements have substantially similar degradation time.

The stability of implants for use in the entire musculoskeletal system can be achieved by a matrix material with embedded fiber material, wherein the chemical composition and structure of the fibers integrated into the matrix can differ from the matrix. For example, undirected short fibers or oriented long fibers, for example of carbon or polyglycolide PGA, are suitable as the fiber material. The typical fiber length of long fibers is in the cm range and corresponds to the length used, for example, in pressing. The typical fiber length of short fibers corresponds fiber-reinforced injection molding compounds and is in the mm range. With reinforcement by fibers, the composite gains strength and rigidity. Compared to the already known biodegradable Ost eosyntheseim plants short fiber reinforced implants can be produced in a very simple and cost-effective manner by injection molding. There is a sufficient number of combinations of matrix and fiber material with a sufficiently large difference between the melting temperatures, so that a simultaneous processing of fiber and matrix in the injection molding process is advantageously possible. In addition to short or long fibers, according to the invention, it is also possible to use textile surface structures, such as nonwovens, woven fabrics, scrims, braids, knitted fabrics, knitted fabrics.

Suitable matrix materials according to the invention are known lactide / glycolide, copolymers, polylactides, etc., which have the appropriate degradation rates and thermal stabilities. The molecular weight of the polymer should, in order to positively influence the degradation time, be between 10'0OO and 10 million u and preferably between 150'000 and 600'000 u.

The matrix material can be supplemented by additives or coatings, such as X-ray contrast agents, antibiotics, as well as bioceramic particles (bioglass) for increasing the strength or hydroxyapatite for improving bone healing. However, this is not necessary to achieve the required strength.

The implant and / or the connecting means can be produced in addition to the mentioned injection molding process in the fiber spraying, spin coating, pultrusion, injection winding or legal process or in a combination thereof.

The generally low melting temperatures of the matrix materials also allow plastic shape changes to be made under the action of temperature during surgery to conform the implant to the shape of the bone. The inventive osteosynthesis system advantageously replaces conventional metallic osteosynthesis implants.

Brief description of the figure

The invention will be explained in more detail with reference to the single FIGURE, which shows an example of an inventive osteosynthesis system consisting of a plate and two screws. Only the elements important to the understanding of the invention are shown.

Ways of carrying out the invention

The invention relates to an implantable, biodegradable osteosynthesis system for operative attachments in the musculoskeletal system. The 9ystem is capable of accepting larger forces and can thus be used in the entire musculoskeletal system, especially in the area of bumpy skeletons. Surgery to remove the implants is usually not needed. The system is particularly suitable for use in the skeleton of the human body, but it can also be used in the animal body.

According to the invention, the biodegradable

An osteosynthesis system consisting of a movement- or load-stable implant made from a bio-atoxically degradable composite material with a matrix and fibers integrated into the matrix, whereby the chemical composition and structure of the fibers integrated into the matrix may differ from the matrix.

Both the strength σ and the elastic modulus E of implants can be adapted by selecting suitable matrix materials and varying the proportion of fibers in the matrix material. In addition, the fiber size and the ratio are also between fiber length and fiber diameter as well as the fiber orientation for the material parameters are decisive.

For an osteosynthesis implant in the supporting skeletal area, the required strength can be described by the forces and forces acting on the bone. The force acting on a material causes a state of tension and deformation. If the applied force exceeds the fracture limit or the deformation exceeds the elongation at break, the failure of the system occurs. The fracture strain of the cancellous bone and cortical bone is about 2% each. The tensile strength of the human cortical bone is about 100 N / mm ² , the shear strength 80 N / mm and the modulus of elasticity reaches values up to 20O00 N / mm ² .

For the implants in the skeletal region of the present invention eosynthesesystems the following conditions must be met:

a) The movement-stable implant must have all forces (F ₁ ) and moments

(M ₁ ) occurring on an operated part of the body without load (F _K b _ew , Mκb _ew ):

Flbew ≥ 1 ^" Kbew M fcew ≥ M Kbew

b) The load-stable implant of the eosynthesis system must be able to absorb all forces (F ₁ ) and moments (M ₁ ) of the intact body part (F _Kbe i, Mκ _be i):

Primer ≥ Fκbel M ftel ≥ M Kbel

c) The rigidity of the load-stable implant des

Ost eosynthesesystems E ₁ in the area of the connection between bone and implant must correspond approximately to the stiffness of the bone E _κ . Ei ~ EK

d) The osteo εynthesis system should have an interfemetary compression of F _κ ~ 600 N for the attachment in the supporting skeletal region

Allow promotion of bone healing.

Various approaches exist for the calculation of short fiber reinforced plastics (e.g., Nielsen, LE; Chen RE: Young's modulus of composites filled with randomly oriented fibers.) Compos. Mater. 3

(1968) 352-358 or Halpin. J. C; Kardos, J.L: The Halpin-Tsai equations: A review. Polym. Closely. 16 (1976) 344-352). For the time being, the general calculation procedure for fiber composites is based on a micro- and macro-mechanical analysis and finally on a failure analysis. For the micromechanical analysis, the equation of Halpin-Tsai can be used, which in the general form reads as follows:

With

ξ = k * l l d

P _F

M _R = - PM

p \ Elastic characteristic of the composite p _M : Corresponding characteristic of the matrix p _F \ Corresponding characteristic of the fiber ξ \ Form factor c _F \ Fiber volume fraction l, d: Length and thickness of the fibers k: Constant The macro mechanical consideration of short fiber reinforced plastics can be done with the mixing rule:

Pi c = Pi 1 FOR ₁ + P ₂₂ FOR ₂ (2)

^~ p _2C = P ₂₂ FOR ₁ + P _{1 λ} FOR ₂ (3)

with composite characteristic values of the respective direction

FOR _n : percentage of fibers in each direction

Already with a composite of PLLA (poly-L-lactide) as matrix material and 60% non-oriented PGA polymer fibers (polyglycolides), equations (2) and (3) can be determined to be about 200 N / mm ² , which already exceeds previous approaches cited in the "state of the art." When carbon short fibers are used, E moduli from equations (1), (2), and (3) can be between 10 and 20 kN / mm ² and strengths σ above 25'00 O N / mm ^2. The typical fiber length of short fibers corresponds to fiber-reinforced injection molding compounds and is in the mm range.

Table 1

In addition to the use of short fibers and long fibers can be used. The typical fiber length of long fibers is in the cm range and corresponds to the length, which is used for example during pressing. With the use of directed long fibers, in particular for screws, the strengths σ can be further increased. In addition to short or long fibers according to the invention also textile Rächengebilde such as nonwovens, fabrics, scrims, Gef sechte, knitted fabrics, knits are used.

The system according to the invention consists of one or more implants which are either stable in movement and / or load-stable and have a strength σ of the composite material of at least 300 N / mm ² . The higher strengths achieved with the selected material combinations, the smaller implants can be used. In this embodiment, advantageous embodiments of the invention are implants having a strength of at least 400 to 500 N / mm ² , of at least 750 N / mm ² or of more than 1000 N / mm ² .

The movement-stable implant of the osteosynthesis system can absorb the forces and moments resulting from the bending weight of the operated part of the body.

The load- _stable implant of the osteosynthesis system can have at least forces F, _bθ and moments M | _bθ ι on which the intact musculoskeletal system under load F _K at, M _K must take. The stiffness of the load-stable osteosynthesis system 5 in the area between the musculoskeletal system and the implant corresponds approximately to the rigidity of the intact musculoskeletal system E "and will thus be approximately between 10 and 20 kN / mm ² .

The basticity moduli of human bone are known to those skilled in the art and have been determined in several experimental studies.

With the described inventive

Osteosynthesis systems are created biodegradable implants, which can also be used on supporting parts of the skeleton. Conventional biodegradable implants do not have sufficient strength for use in the area of bumpy skeletons. Metallic implants in the region of the supporting skeleton are stable to movement, ie the body parts to be fixed are in the fixed position during their healing, but can only be moved with the brow weight of the operated body part, without additional burden. Higher loads, such as those caused by walking, are not possible until the bone is largely cured.

The in the previously used metallic

Osteosynthetic Implants Different stiffness between bone and implant leads under load to various strains and thus loosening or fatigue fractures of the implant. The

Load capacity of the patient skeleton is thus possible only after extensive bone healing. Implants which, in addition to the stability of movement, also have load-stable properties, allow the patient to mobilize the patient quickly and thus shorten the rehabilitation time due to the isoelasticity between the implant and the affected parts of the musculoskeletal system. The higher strengths achieved with the selected material combinations, the smaller implants can be used.

The inventive system with the above-described

Features may consist only of screws or other fasteners that connect parts of the musculoskeletal system together. It may also consist of the already mentioned plates (pull hole, sliding hole and special applications), intramedullary nails and connecting means such as wires (cerclage wires, Kirschner wires, etc.), nails, or screws (Corticaliε / cancellous bone), wherein the connecting means also from a biodegradable composite with a matrix and fibers integrated into the matrix. The single FIGURE shows a possible form of such inventive biodegradable east heosynthesesystems, which consists for example of a Ostheosyntheseplatte and two screws shown. However, the materials for implants and connectors need not be the same for all elements of the eosynthesis system. The involved elements of the system according to the invention advantageously have substantially the same rate of degradation. Various factors influence this rate of degradation:

Molecular mass of the polymer: The molecular mass of the polymer should be between 10'0OO and 10 million u and is preferably between 150'000 - 600'00O u. The fiber content is for reinforcement only and has no significant influence on the rate of degradation. The rate of degradation is determined almost exclusively by the matrix material.

• Chemical structure of the matrix material

The chemical structure of the matrix material is essentially decisive for the degradation time. Of the biodegradable materials used today, the degradation rates are known. Suitable matrix materials according to the invention are known lactide / glycolide, copolymers, polylactides, etc., which are suitable

Degradation rate and thermal stability.

Porosity:

The larger the pores in the matrix material, the faster the degradation takes place. The pore size is definable by the manufacturing process and the additives. As a possible additive sodium chloride can be used.

• Additives: Various additives can be added to the matrix and influence the rate of degradation as appropriate. As can be seen from many patents, these processes are well known.

• Pressure conditions during the manufacturing process:

Too high pressures and concomitantly higher strength of the material delay the rate of degradation. For implants, therefore, material combinations must be specified that are sufficient Strengths and stiffness can be achieved without excessively increasing the rate of degradation.

The fiber composite implant may be characterized by anisotropic and / or within the implant different material properties. Due to different material properties within the implant this can be adapted to different requirements, such as a higher stiffness in the fracture zone or to the maintenance of isoelasticity over wide areas of the bone.

The matrix material can also be supplemented with additives or coatings such as X-ray contrast agents, antibiotics, bioceramic particles (bioglass) or hydroxyapatite to improve bone healing or to increase the strength. However, this is not necessary to reach the required strength.

Compared to the already known biodegradable implants short-fiber reinforced implants can be produced in a simple and cost-effective manner by an injection molding process. There is a sufficient number of combinations of matrix and fiber material with a sufficiently large difference between the melting temperatures, so that a simultaneous processing of fiber and matrix by injection molding is possible (see Table 1). Other methods, such as fiber spraying, spin coating, pultrusion, injection, wrapping or raking methods, or combinations thereof, are applicable within the scope of the invention.

The generally low melting temperatures of the matrix materials also make it possible to perform plastic shape changes of the implants before or during the operation under the influence of temperature.

For biodegradable materials already known and well-established sterilization procedures exist. By means of the present invention, the novel fiber composite implants according to the invention can be produced inexpensively. At the same time, the invention is associated with a cost and risk reduction, since further interventions to remove the implants are no longer necessary. However, the technical and surgical standards achieved so far, as well as the processing techniques that have been achieved with metallic implants, remain advantageously preserved. Due to suitable biomechanical properties, a very early load carrying skeletons is possible after surgery. Hospitalization times, rehabilitation and lost time can be shortened. Since the postoperative rehabilitation time is shortened by the load-stable implants, a cost reduction can additionally be achieved by the invention. Thus, it has been possible by the inventive osteosynthesis system conventional metallic implants largely replaced.

Claims

claims

1. Biodegradable Osteosyntheseεystem for deployment as an implant in the entire musculoskeletal system, consisting of at least one movement or load-stable implant and / or connecting means as elements of the system of a biodegradable composite material with a matrix and integrated into the matrix fibers, wherein the chemical composition and Distinguish the structure of the fibers integrated into the matrix from the matrix, with a strength (σ) of the composite of at least 300 N / mm ² .

2. Biodegradable osteosynthesis system according to claim 1, characterized in that the elements can take at least the forces (F | _bθW ) and moments (M | _bθW ) that occur on an operated part of the body without load (F _K b _ew , M _K bew) ,

3. Biodegradable osteosynthesis system according to claim 1 or 2, characterized in that the elements can take at least forces (F | _bθ ι) and moments (M ibei) of the intact body part (F _K at "M" bei), wherein the stiffness E ₁ in the region of the connection between the body part and the implant essentially corresponds to the rigidity of the intact body part E _K.

4. Biodegradable osteosynthesis system according to one of claims 1 to 3, characterized in that the elements of the system consist of biodegradable composite materials which have substantially the same degradation time.

5. Biodegradable osteosynthesis system according to one of claims 1 to 4, characterized in that at least one element of the system contains aligned short fibers embedded in the matrix.

6. Biodegradable Osteoεynthesesystem according to one of

Claims 1 to 4, characterized in that at least one element of the system contains directed long fibers embedded in the matrix.

7. Biodegradable osteosynthesis system according to one of

Claims 1 to 4, characterized in that at least one element of the system textiles contains avenues.

8. Biodegradable osteosynthesis system according to one of claims 1 to 7, characterized in that a polymer, polylactide, a bioceramic or carbon fiber is used as the fiber material.

9. Biodegradable osteosynthesis system according to one of claims 1 to 8, characterized in that a polymer, copolymer or polylactide is used as the matrix material.

10. Biodegradable osteosynthesis system according to one of claims 1 to 9, characterized in that the elements are characterized by anisotropic M aterialeigenschaften.

1 1. Biodegradable osteosynthesis system according to one of claims 1 to 10, characterized in that the elements are characterized by different strengths and stiffnesses within the implants.

12. Biodegradable osteosynthesis system according to one of claims 1 to 1 1, characterized in that the composite materials in addition to the matrix and fiber material are supplemented by bioceramic materials, contrast agents, antibiotics or hydroxyapatite.

13. Biodegradable osteo-synthesis system according to one of claims 1 to 12, characterized in that the elements can be produced with one or a combination of the following processes: lamination, injection molding, fiber spraying, spin coating, pultrusion or injection winding or legal processes.

14. Biodegradable osteosynthesis system according to one of claims 1 to 13, characterized in that at least one element of the system is plastically deformable under the action of temperature.

15. Biodegradable osteosynthesis system according to one of claims 1 to 14, characterized in that the system is suitable for use at supporting points of the skeleton.

16. A method for producing a biodegradable osteosynthesis system for use as an implant in the entire musculoskeletal system, comprising the following steps: at least one implant and / or connecting means as elements of the system are made of a biodegradable composite material with a matrix and fibers integrated into the matrix, wherein the chemical The composition and structure of the fibers integrated into the matrix differ from the matrix, with a strength (σ) of the composite of at least 300 N / mm ² .

17. A method for producing a biodegradable osteosynthesis system according to claim 16, characterized in that elements of the system are manufactured so that they can take up at least the forces (Fibew) and moments (M | _bθW ), which on an operated body part without load (F _K bew, M _K bew) occur.

18. A method for producing a biodegradable osteosynthesis system according to claim 16 or 17, characterized in that elements are produced which at least the forces (Fibei) and moments (M ι _bθ ι) of the intact body part (F _K at; M _K bei) on Take the stiffness egg in the area of the connection between the body part and implant corresponds approximately to the rigidity of the intact body part E _K.

19. A method for producing a biodegradable osteosynthesis system according to any one of claims 16 to 18, characterized in that elements of the system are produced, which consist of biodegradable composite materials having substantially the same degradation time.

20. A method for producing a biodegradable osteosynthesis system according to any one of claims 16 to 19, characterized in that at least one element of the system is produced with undirected short fibers which are embedded in the matrix.

21. A method for producing a biodegradable osteosynthesis system according to any one of claims 16 to 19, characterized in that at least one element of the system is prepared with long fibers directed, which are embedded in the matrix.

22. A method for producing a biodegradable osteosynthesis system according to any one of claims 16 to 19, characterized in that at least one element of the system is produced with textile fabrics.

23. A method for producing a biodegradable osteosynthesis according to any one of claims 16 to22, characterized in that a polymer, polylactide, a bioceramic or carbon fiber is used as the fiber material.

24. A method for producing a biodegradable osteosynthesis system according to any one of claims 16 to23, characterized in that a polymer, copolymer, or polylactide is used as the matrix material.

25. A process for producing a biodegradable osteosynthesis system according to any one of claims 16 to 24, characterized in that the elements are prepared with anisotropic material properties.

26. Method for producing a biodegradable

Osteosynthesis system according to one of Claims 16 to 25, characterized in that the cones are produced with different strengths and stiffnesses within the implants or connecting means.

27. Method for producing a biodegradable

Osteosynthesis system according to one of claims 16 to 26, characterized in that the composite materials in addition to the matrix and fiber material are supplemented by bioceramic materials, contrast agents, antibiotics or hydroxyapatite.

28. Method for producing a biodegradable

Osteosynthesis system according to one of claims 16 to 27, characterized in that at least one FJement is laminated or produced by injection molding, fiber spraying, spin coating, pultrusion, injection, winding, or right method or a combination thereof.