WO2003049780A1

WO2003049780A1 - Biocompatible composite material with an osteotropic action

Info

Publication number: WO2003049780A1
Application number: PCT/EP2002/013891
Authority: WO
Inventors: Massimo Monti
Original assignee: Tech-Medical S.R.L.
Priority date: 2001-12-10
Filing date: 2002-12-06
Publication date: 2003-06-19
Also published as: AU2002358639A1

Abstract

The present invention relates to a biocompatible composite material with an osteotropic activity, suitable for integrating and reconstructing portions of bone tissue in the human body and effecting bone implantations. The composite material of the invention comprises a dispersion of hydroxyapatite, or biological glass, in the form of particles or blocks, inside a biocompatible adhesive matrix consisting of a hydrolyzed product of a fish origin.

Description

BIOCOMPATIBLE COMPOSITE MATERIAL WITH AN OSTEOTROPIC ACTION

The present invention relates to a biocompatible composite material with an osteotropic action.

More specifically, the present invention relates to a biocompatible composite material with an osteotropic activity suitable for integrating and reconstructing portions of bone tissue and bone implantations and an adhe- sive material incorporated in said composite.

The present invention concerns the bio-medical field and in particular that relating to materials for surgical or dental bone reconstruction and for use in orthopedic or dental bone implantations . It is known that in surgical practice and in particular orthopedics and dental treatment, it is often necessary to fill bone cavities and structures, eliminate defects and level-differences in bone structures and reconstruct portions of bone tissue, in such a way as to restore the morphology of the injured bone section or subject to modifications.

Particularly in surgical reconstruction techniques, it is necessary to fill bone cavities and restore portions of bone structures operating with precise tech- niques which allow the full recovery of the original morphology of the bone segment which has been injured or which is subject to structural modifications.

Current surgical reconstruction techniques resort to the use of highly biocompatible osteotropic materials which are implanted or deposited in the injured bone structure so as to stimulate the bone cells and/or reconstruct the portion of bone tissue of interest.

The scarcity of bone tissue represents a problem for bone reconstruction therapy to such an extent as to in- duce operators in the field to identify and produce biocompatible materials capable of promoting the osteogene- sis process.

The most recent bone reconstruction techniques resort to the use of osteotropic biocompatible materials which are implanted or deposited close to the structure to be treated so as to stimulate the reconstruction of the bone tissue and restore the original situation.

When the bone structure is restored, the biocompatible material is consequently englobed in the neo-formed bone tissue. From a surgical point of view, the operation involves depositing or grafting a pre-established quantity of osteotropic material close to the injured bone structure, avoiding its dispersion in the surrounding tissues. Surgical operations on anatomical structures which are difficult to reach, such as maxillo-facial surgery, not only require a considerable surgical expertise and manual ability, but also the use of high precision guides and surgical instruments. For example, in dental or max- illo-facial surgery, the bone tissue must be integrated in anatomical areas which are extremely narrow and difficult to reach with common surgical instruments.

The deposition operations of these biocompatible materials are not however easy to manage due to the high manual ability and experience required on the part of the doctor to obtain an appropriate implantation.

It is, in fact, a question of correctly dosing the quantity of biocompatible material with an osteotropic action strictly necessary for reconstructing the injured bone portion and depositing it or grafting it as close as possible to the injury, to prevent the material being dispersed in the surrounding tissues during the healing process.

Should, in fact, the biocompatible osteotropic ate- rial not be adequately dosed and be deposited in a smaller quantity than the optimal amount, the bone recovery will not be satisfactory. Viceversa, when the biocompatible material is dosed in greater quantities than necessary, there is the risk of dispersion in the surround- ing tissues thus jeopardizing recovery of the bone injury and causing a waste of costly material.

Substitutes of bone tissues are also known, which combine an inorganic phase with an organic phase similar to that of bone tissue and suitable cross-linking agents. The use of these substitutive materials of bone tissues has proved to be not fully satisfactory due to various incompatibilities observed between the inorganic component and the organic component during the bone reconstruction phase. Suspensions based on cross-linked collagen and bio- materials are also known in scientific literature.

These fluid suspensions, however, are only used for implantations by injection in soft tissues and as such are consequently unsuitable for use in bone reconstruc- tion surgery where a high operating and bone remodeling precision is required.

Furthermore, these materials are not satisfactory due to various incompatibilities between their inorganic and organic components which do not always allow a bone reconstruction to be obtained with a homogeneous density and also as a result of the difficulties encountered in making the materials adhere to the injured bone structures .

One of the general objectives of the present inven- tion consists in eliminating or significantly reducing the occurrence of the drawbacks observed in the known art.

A further objective of the present invention consists in providing a composite material for repairing, substituting or increasing various portions of the bone or cartilage tissue of human beings or animals, which is highly biocompatible.

Another objective of the invention consists in providing a biocompatible composite material with high os- teogenicity properties, which consequently rapidly promotes the formation of new bone tissue close to the implantation point.

Yet another objective of the invention consists in providing a biocompatible composite material with an os- teotropic action, which can be easily dosed and allows simple deposition on the part of the surgeon in the areas to be treated.

A further objective consists in providing a biocompatible composite material with an osteotropic action which can be easily and rapidly used in dental surgery for the restructuring and remodeling of bone structures of the masticatory apparatus .

Yet another objective of the present invention consists in providing an adhesive material of a natural ori- gin, particularly suitable in bone reconstruction, which can be used during surgical reconstruction operations for the adhesion of materials for bone reconstruction.

In view of the above objectives and others which will be evident from the following description, a first aspect of the present invention relates to a bio-active composite material with an osteotropic and/or osteogenic action, comprising a biocompatible material and a biocompatible matrix, in which said biocompatible material is a biological glass and/or hydroxyapatite and said bioco - patible matrix is an adhesive material of a natural origin. Said adhesive material is conveniently a polypeptide derivative in the form of gelatin, preferably of a fish origin.

The present invention derives from the affirmation that the combination of a biocompatible matrix with biological glass or bioglass has an osteotropic and restructuring effect on bone tissues, of the synergic type.

In particular, the incorporation of a biological glass in a compact form with a varying porosity or in the form of particles dispersed in a semi-solid phase with a polypeptide base, allows a composite material to be obtained, which can be easily applied to tissues in need of treatment, without requiring a preventive dosage of the osteogenic bioglass component. Furthermore, the composite material of the invention has physico-chemical characteristics which enable it to be easily applied without having to resort to the use of particular surgical instruments and to be anchored when required without the risk of dispersions or displacements during the clinical heal- ing process .

The composite material of the invention can conveniently comprise a biocompatible material made of biological glass in the form of powder or granules or blocks incorporated inside a gelatin polypeptide matrix. A gelatin suitable for use in the invention comprises a gelified aqueous solution of animal proteins for example of a bovine or equine or swine origin and preferably of fish origin.

The gelatin used in the composite material of the invention is advantageously supplied in a highly purified form, of the type suitable for pharmacological use, conveniently in gel form.

The presence of gelatin creates both characteristics of ductility and malleability of the composite material of the invention and also characteristics of cohesion with soft tissues, such as connective tissues, which surround the bone structures .

According to another aspect of the present invention, said biocompatible matrix is an adhesive material of a natural origin based on a protein derivative of a fish origin. In particular, said biocompatible material is based on a protein derivative comprising a protein or polypeptide mixture of a fish origin.

More specifically, the biocompatible material of the present invention is a hydrolyzed product of a fish origin with an adhesive action. This biocompatible adhesive material is typically in the form of a gluey protein hydrolyzed product, conveniently obtained by means of a thermal extraction process. According to any embodiment of the invention, said adhesive material derives from fresh fish skins and is in the form of a protein-based gelatin.

For example, in order to obtain the adhesive material, fresh fish is desquamated by removing the skin and subjecting it to a series of washings with water or antimicrobial solutions.

The adhesive material is subsequently subjected to a protein extraction technique which conveniently uses solutions suitable for the extraction of amino-acids. The adhesive material extracted is then filtered, optionally washed to remove the typical fish odour and concentrated in a pale yellow powder or in a stabilized solution or possibly frozen for preservation.

The adhesive of the invention typically contains from 5 to 15% by weight of dry protein material, preferably about 10% by weight.

It has been observed that the adhesive material of the invention preferably comprises at least 18 a ino acids among which proline and hydroxyproline can be men- tioned, which are the most important for reaching a satisfactory gelifying capacity of collagen.

Suitable biocompatible materials within the scope of the invention include hydroxyapatite and biological glass or bioglass and their mixtures. These materials are es- sentially cooled liquids, with an amorphous or ceramic- glass structure which are obtained by means of the high temperature thermal treatment of mixtures of oxides until melting.

During the subsequent cooling phase, the molten ma- terial passes directly to the solid state without crystallizing, maintaining the non-crystalline amorphous structure of the liquid.

In particular, the biological glass or bioglass which can be used within the scope of the invention is a transparent bio-active material based on silicon, and en- globing other elements capable of forming bonds with bone tissues, cartilages, soft and connective tissues.

According to another embodiment, said bioglass comprises a composition based on Si0₂ combined with at least another oxide selected from calcium, sodium, potassium oxides and their mixtures .

According to another embodiment, said biological glass also comprises phosphorous, magnesium oxides and their mixtures. In accordance with another embodiment, said biological glass comprises Si0₂, P₂O5, CaO and at least one other compound selected from Na₂0, K₂0, MgO, CaF₂, Fe₂θ3 and their mixtures .

According to another embodiment, said oxides also comprise tantalum oxides such as Ta₂Os, lanthanum oxides such as La₂0₃, and their mixtures.

In accordance with yet another embodiment of the invention, said biological glass also comprises F ions, conveniently in quantities close to 2.1% by weight. The term bio-active material refers to a biocompatible material which exerts a response to the material-bone tissue interface which promotes the formation of a bond between the tissue and material itself.

The biological glass used within the scope of the invention is conveniently supplied in granular form or as a fine powder with a varying particle-size or as blocks with a varying porosity depending on the specific uses.

For example, the biological glass granules can have dimensions ranging from 0.5 to 1.8 mm or reach dimensions of a few microns.

It has been observed that following the deposit of an effective quantity of composite material of the invention on the tissue to be treated, there is an exchange of ions with said tissue treated, as a result of the contact of the biological glass with a body fluid. The ion exchange mainly causes the release of ions, for example sodium and calcium ions from the composite material, creating a first layer of silica gel a few minutes after application. In this way, a physio-chemical bond is created between the biological glass, the soft tissue and bone structure. At the same time, the adhesive material, with the contribution of simple animal proteins, exerts an adhesion and regeneration action of the tissues treated. The ion exchange thus creates an environment which conveniently promotes the formation of a layer of hy- droxy-carbonate apatite (HCA) , which is substantially the same as the mineral phase of natural bone. This phenomenon causes a more rapid regeneration and restructuring of the bone than that obtained with other conventional mate- rials.

Another advantage deriving from the use of the material of the invention lies in the fact that the layer of hydroxy-carbonate apatite initiated by the biological glass component is biologically equivalent to the mineral phase of human bone tissue and is therefore recognized by the tissues as a natural body, and not synthetic or foreign.

The formation of this layer intervenes together with the biological process with respect to the depositing of collagen and cellular differentiation, producing a chemical bond and an increased cicatrization of the bone injury.

The contemporaneous presence in the composite ate- rial of the invention of biological glass or hydroxyapa- tite which provides structural and mechanical support near the bon reparation or restructuring site and the biocompatible adhesive material which provides a protein contribution, produces a synergic regeneration activity of the bone tissue treated.

In addition, the consistency and mechanical resistance of the biological glass, combined with the ductility of the gelatin, make the composite material malleable and moldable thus allowing its reduction into laminas, bars, threads or other forms which facilitate its medi- cal-surgical use.

The material of the invention can be applied in numerous pathological conditions in which an osteotropic or osteo-inducing action is required. In particular, the composite material of the invention containing biological glass in the form of compact blocks can be applied in orthopedic surgical therapy for use in vertebral surgery and revision arthroplasty. Furthermore, the composite material can be applied as a filler or reconstruction material in maxillo-facial or cranium-facial surgery as a graft or self-grafting extender.

The composite material of the invention can also be applied in reconstruction surgery as a bone reconstruc- tion component, for example following resections of benign tumours and after bone removal as a result of traumas and in endoprosthesis substitutions.

In surgical use, the composite material of the invention can be supplied in a laminar form with a high density of bioglass.

When used for dental purposes, the composite material of the invention is particularly suitable in the reconstruction of bone defects in various dental diseases. This material in particles with an osteotropic or osteogenic action advantageously comprises hydroxyapa- tite, biological glass or bioglass and their mixtures.

According to an embodiment, the material of the invention is sterilized before use, for example by means of gamma rays to allow it to be free of contaminations and suitable for medical-surgical applications.

According to another embodiment, the composite material of the invention also comprises a polyhydroxyl compound, preferably consisting of glycerol and glycerol esters in order to increase the plasticity properties. It has been observed that by increasing the percentage of glycerol the flexibility and elasticity characteristics also increase, whereas by reducing the quantity of glycerol, a more rigid composite structure is obtained.

In particular, it has been found that suitable quan- tities of glycerol generally vary from 2-6% by weight with respect to the weight of gelatin.

The term osteogenic used within the scope of the present invention refers to the capacity of the material or biocompatible composite to increase or accelerate the growth of new bone tissue by means of one or more bone restructuring mechanisms such as osteogenesis, osteocon- duction, and osteo-induction.

The term incorporation or deposit refers to the biological mechanism with which the guest composite material is incorporated close to the bone or cartilage structures or formations in order to stimulate one or more of the bone restructuring activities mentioned above.

According to an embodiment of the invention, the composition of the composite material of the invention in hydrate phase comprises:

Biocompatible material with an osteogenic/osteotropic action in particles 90-60% Adhesive material of a fish origin 2-15% Glycerol 2-15% Water 0.1-15%

The composite material having the above composition is conveniently subjected to drying by evaporation under vacuum, heating it to a temperature not higher than about 40°C to avoid modifications in the adhesive component. The composite material obtained at the end of the evaporation is in anhydrous phase and has the following contents :

Biocompatible material with an osteogenic/osteotropic action in particles 95.9-70% Adhesive material of a fish origin 2-15% Glycerol 2-15%

Water 0.1-2%

The composite material in anhydrous phase is malleable and is typically modelled to reduce it to laminas, bars, threads or other forms which facilitate its rapid use after sterilization, for example by exposure to gamma rays.

The elasticity and flexibility characteristics of the composite material are mainly influenced by the pres- ence of glycerol, so that, on increasing its presence, the elasticity increases, on reducing it, the composite has a more rigid appearance.

The characteristics and advantages of a composite material with an osteotropic action will be more evident from the following illustrative but non-limiting description, referring to the enclosed schematic figure showing an embodiment of the composite material with an osteotropic and/or osteogenic action of the invention.

With reference to the enclosed figure 1, it can be observed that the composite material is in the form of a spongy laminar structure with a high density of hydroxy- apatite or biological glass.

The composite material illustrated in figure 1 is particularly suitable for application in the reconstruc- tion of bone defects and in various dental diseases.

When, on the contrary, the composite material has a higher density of hydroxyapatite or bioglass it is specifically suitable for application in bone reconstruction after the surgical resection of benign tumours or after bone removal as a result of traumas or in the substitu- tion of parts of bones.

For medical-surgical uses, the composite material of the invention is advantageously used in anhydrous form, cut into suitably-sized blocks for application or using appropriately-dimensioned preformed pieces. The composite material of the invention is advantageously used for producing osteotropic aids for medical use.

The following examples are solely provided for illustrating the present invention and should in no way be considered as limiting its protection scope, which is defined by the enclosed claims. EXAMPLE 1

In a first phase of the embodiment of a composite material according to the invention, the following co po- nents were mixed and dispersed in aqueous phase: Biological glass 61.35%

Gelatin of a fish origin 13.56%

Glycerol 12.65%

Water 12.44% The dispersion thus obtained was then subjected to drying by evaporation in a rarified atmosphere, by heating the mixture to a temperature not higher than 40°C in order to avoid the denaturation of the gelatin.

At the end of the evaporation phase, the mixture had a reduced water content and a semi-solid consistency suitable for applications in the surgical and dental field. The composition was as follows:

Biological glass 70.00% by weight

Gelatin 15.05% by weight

Glycerol 14.04% by weight

Water 0.91% by weight

EXAMPLE 2

'A polypeptide derivative in the form of a gelatin of a fish origin, obtained by the alkaline treatment of skin cleavages (raw material) , conveniently effected in a lime solution for a time exceeding 50 days and subjected to thermal treatment at a temperature higher than 138°C for at least 4 seconds, was subjected to physico-chemical analysis before being used as a biocompatible matrix within the scope of the invention: Gelatinizing capacity 162 gr. Bloom Humidity 10.6% Sulfur dioxide 28.1 ppm Peroxides absent Total ashes 0.93%

Arsenic less than 1 ppm

Heavy metals less than 50 ppm

Anti-microbial preserve substances absent pH 5.5

A bacteriological analysis of the gelatin provided a total count of less than 100 cfu/g. EXAMPLE 3

Four compositions of biological glass systems are provided, particularly suitable for the uses according to the invention.

The biological glass was conveniently produced by mixing metal oxides in a powder mixer or homogenizer and subsequently transferring it to a crucible, made of refractory material, such as platinum. On progressively heating the mixture of oxides, it was melted at a temperature of over 1 00°C, conveniently at about 1500°C. The cooled glass system mass has the following physico- mechanical parameters:

Bioglass system 3 above had the following additional physico-mechanical data:

Ultimate compression strength (MPa 800+300

Ultimate tensile strength (MPa) 110+50

Flexural strength (MPa) 173 (±12)

KIC (MPa^ml/2) 2.52 (±0.5) Thermal esp. coeff. (°C^_1) 10.40x10^"° (+0.02)

Young modulus (GPa) 85 (±5)

Vickers hardness (MPa, 1 kg) 7.70(±0.80)

Density (g/cm³) 2.76(+0.05)

Specific surface (<40μm) m²/g 0.46 Thermal exp. coefficient (°C^_1) 1.25xl0^"5 (±0.5)

EXAMPLE 4

A biocompatible adhesive material based on a protein hydrolyzed product according to an embodiment of the invention, was analyzed. The adhesive material was in the form of a gelatinous extract deriving from fresh cod skin. The hydrolyzed product had the following amino-acid percentage distribution with respect to the total weight of amino-acids: Aspartic acid 6.10% Treonine 2.60%

Xerine 5.62%

Glutamic acid 10.13%

Proline 13.09%

Glycine 21.99%

Alanine 9.62%

Valine 1.93%

Methionine 1.88-s

Isoleucine 1.15%

Leucine 2.48%

Tyrosine 0.32%

Phenyl alanine 2.02%

Hydroxy lysine 0.95%

Lysine 3.41%

Histidine 0.85%

Arginine 8.25%

Hydroxy proline 8.30%

EXAMPLE 5

An aqueous solution of an adhesive material deriving from frozen fish skin containing 10% by weight of dry matter, was analyzed, obtaining the following results: Appearance viscous liquid

Colour pale yellow pH (sol.) 3.8-4.8

Proteins (sol.) (Biuret) > 9.5% Ashes < 1%

Total count < 1000 g/g

Coliforms < 10 g/g

Sulfite reducing anaerobes 10 g/g

Salmonella absent in 25 g EXAMPLE 6

A protein-based adhesive material in powdery form according to an embodiment of the invention, containing

10% by weight of dry matter, was analyzed, obtaining the following results: Appearance fine powder

Colour pale yellow pH (sol.) 6.5 ± 1

Proteins (sol) (Biuret) > 90%

Ashes < 5% Total count < 1000 g/g

Coliforms < 10 g/g

Sulfite reducing anaerobes 10 g/g

Salmonella absent in 25 g

Gel strength 80-100 bloom

Claims

1. A bio-active composite material with an osteotropic or osteogenic action comprising a biocompatible material and a biocompatible matrix, characterized in that said biocompatible material is selected from the group comprising biological glass, hydroxyapatite and their mixtures and said matrix is an adhesive material of a natural origin.

2. The material according to claim 1, characterized in that said biological glass comprises silicon, phosphorous and calcium oxides.

3. The material according to claim 1 or 2, characterized in that said biological glass comprises Si0₂, P2O5, CaO and at least one other compound selected from Na₂0, K₂0, MgO, CaF, Fe₂03 and their mixtures.

4. The material according to any of the claims 1-3, characterized in that it comprises a further oxide selected from tantalum oxide, lanthanum oxide and their mixtures.

5. The material according to claim 1 or 2, characterized in that said biological glass essentially consists of Si0₂, P2O5, CaO, Na₂0, ₂0, MgO, CaF₂.

6. The material according to claim 1 or 2, characterized in that said biological glass essentially consists of Si0, P2O5, CaO, Na₂0, K₂0, MgO, CaF₂, Ta₂0₅ and La₂0₃.

7. The material according to any of the previous claims 1-6, characterized in that said adhesive material of a natural origin is a polypeptide derivative of a bovine or swine or fish origin.

8. The material according to claim 7, characterized in that said adhesive material is a polypeptide derivative of a fish origin in the form of a gelatin suitable for medical use.

9. The material according to claim 7, characterized in that said adhesive material comprises a protein or polypeptide mixture deriving from fish skin.

10. The material according to any of the previous claims 1-9, characterized in that it also comprises a polyhy- droxyl compound for increasing its plasticity.

11. The material according to claim 10, characterized in that said polyhydroxyl compound is glycerol or a glycerol ester.

12. The material according to any of the previous claims 1-11, characterized in that it is in sterile form.

13. Use of a material according to any of the claims 1- 12 for the production of an aid with an osteotropic or osteogenic action.

14. Use of the material according to any of the claims 1-13 for the production of a surgical or dental aid for the reconstruction of bone or cartilage tissue.

15. A biocompatible adhesive material of a natural origin, particularly suitable for bone reconstruction, characterized in that it comprises a protein derivative of a fish origin.

16. The adhesive material according to claim 15, characterized in that said protein derivative is based on a protein hydrolyzed product of fish skin.

17. The adhesive material according to any of the previous claims 14-16, characterized in that it comprises from 5 to 15% by weight of dry protein matter.

18. The adhesive material according to any of the previous claims 15-17, characterized in that it comprises pro- line and hydroxy proline.

19. The adhesive material according to any of the previ- ous claims 15-18, characterized in that it can be obtained by the extraction of the amino-acids contained in fish skin with amino-acid solvents.