COMPOSITE BIOMATERIALS WITH IMPROVED BIOACTIVITY AND THEIR USE FOR BONE SUBSTITUTE

Abstract

The present invention concerns composite biomaterials comprising ceramic and a biodegradable polymer gel, with improved bioactivity, their process of preparation and their use for orthopedics, dentistry or reconstructive surgery, in particular for use as a bone filler.

Claims

1. A composite biomaterial with a nanosized porosity and comprising: a. a mineral component comprising a calcium phosphate ceramic, where said ceramic comprises: hydroxyapatite (HA); or tricalcium phosphate (TCP); or a mixture thereof in the form of biphasic calcium phosphate (BCP); and b. an organic component comprising a biodegradable polymer gel, characterized in that said composite biomaterial comprises deposited, or precipitated nanocrystals of apatite and one or more optional bioactive components.

2. The composite biomaterial according to claim 1, where said bioactive components are chosen from bioactive ionic species and active ingredients.

3. The composite biomaterial according to claim 1, where said ceramic further comprises fluoroapatite (FHA) and/or chloro-apatite (CLHA).

4. The composite biomaterial according to claim 1 wherein said phosphate is present in anyone of the following forms : Monocalcium phosphate monohydrate (MCPM) (Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O), Monocalcium phosphate anhydrous (MCPA) (Ca(H.sub.2PO.sub.4).sub.2), Dicalcium phosphate anhydrous (DCPA) (CaHPO.sub.4), Dicalcium phosphate dihydrate (DCPD) (CaHPO.sub.4.2H.sub.2O), Octacalcium phosphate (OCP) (Ca.sub.8H.sub.2(PO.sub.4).sub.6.5H.sub.2O), -Tricalcium phosphate (-TCP) (-Ca.sub.3(PO.sub.4).sub.2), -Tricalcium phosphate (-TCP) (-Ca.sub.3(PO.sub.4).sub.2), Amorphous calcium phosphate (ACP) (Ca.sub.3(PO.sub.4).sub.2), Hydroxyapatite (HA) (Ca.sub.10(PO.sub.4).sub.6(OH).sub.2), Tetracalcium phosphate (TTCP) (Ca.sub.4(PO.sub.4).sub.2O), as well as the deficient or ion-substituted calcium orthophosphates.

5. The composite biomaterial according to claim 1 where the biodegradable polymer gel is chosen from proteins, polysaccharides, aliphatic polyesters, and mixtures thereof.

6. The composite biomaterial according to claim 1 wherein said polymer gel is chosen from collagen, gelatin, fibronectin, chitosan, hyaluronic acid, alginate, cellulose and its derivate (HPMC, MC, HPC, CMC), PVA, PVP dextran, pullulan, poly (-hydroxy acid) PLA, poly (glycolic acid) PGA, their PLGA copolymers, poly (-caprolactone) PCL, poly(3-hydroxybutyrate) PHB, poly(3-hydroxyalcanoate) PHA, their derivatives and mixtures thereof.

7. The composite biomaterial according to claim 1 wherein the polymer gel is structured.

8. A bone substitute material comprising the composite biomaterial according to claim 1.

9. A porous metal implant coated with a composite biomaterial according to claim 1 and/or a macroporous calcium phosphate coating.

10. The composite biomaterial according to claim 1 for use for orthopedics, dentistry or reconstructive surgery.

11. A process for preparing the composite biomaterial according to claim 1 comprising: i. mixing said calcium phosphate ceramic with said biodegradable polymer gel optionally loaded with said bioactive component; and ii. reacting said mixture with supercritical CO.sub.2.

12. The process according to claim 11, wherein the reacting step ii is carried out at a pressure comprised between 2 and 10000 bar and a temperature comprised between 20 and 400 C.

13. The process according to claim 11, wherein the reacting step ii is carried out at a pressure comprised between 60 and 150 bar and a temperature comprised between 30 and 50 C.

14. The process according to claim 11, wherein said mixing step I comprises vacuum impregnation.

15. The process according to claim 11, wherein said mixing step i is carried out in the presence of an aqueous solution and/or one or more organic solvent.

16. The process according to claim 15 wherein said organic solvent is miscible in CO.sub.2.

17. The process according to claim 13 wherein, where an organic solvent is used, the process further comprises the step of removing said organic solvent before conducting step ii.

18. The process according to claim 11, wherein step ii is conducted in the presence of an aqueous solution.

19. The process according to claim 18 wherein the aqueous solution present in step ii comes from the polymer gel of step i or is added in the form of an extra aqueous solution (treatment solution).

20. The process of claim 18 wherein the amount of the aqueous solution present in step ii. is such that the weight (aqueous solution/ceramic) ratio (L/S ratio) is comprised between 0.2 and 50.

21. The process according to claim 18 wherein the aqueous solution is water optionally comprising bioactive components selected from the group consisting of bioactive ionic species and active ingredients.

22. The process according to claim 18, wherein said aqueous solution is SBF.

23. A ceramic obtainable by the process according to claim 11.

Description

FIGURES

[0136] FIG. 1 illustrates the interconnected polymer and ceramic networks and the formation of the nanocrystals in the course of the process of preparation of the modified ceramics of the invention. Top of FIG. 1 shows the ceramic without gel before treatment.

[0137] FIG. 1 (second line) was obtained with composites dried directly in CO.sub.2 supercritical dryer after CO.sub.2 supercritical treatment. FIG. 1 (third line) was obtained with the same composite than previous one but before drying in CO.sub.2 supercritical dryer, it was immersed into ethanol (organic solvent miscible in CO.sub.2) in order to eliminate water of the composite to exchange with ethanol and facilitate drying in supercritical conditions.

[0138] The following examples are given as a non-limiting illustration of the various objects of the invention.

EXAMPLE 1

Composite BCP/PVP-CMC+Acetate Sr/No Treatment Solution/Washing with Ethanol Before CO.SUB.2 .Drying

[0139] Ceramic cubes with dimension 3 mm*3 mm*3 mm (0.408 g) consist in 65% hydroxyapatite (HA) and 35% tricalcium phosphate (TCP). Their total porosity is between 60 and 85% and the pore size is between 150 and 400 m. A solution A is prepared from 2 g of strontium acetate dissolved in 100 ml of water.

[0140] The gel is formed using 0.05 g polyvinylpyrrolidone (PVP) and 0.2 g carboxymethylcellulose (CMC) in 20 ml of solution A.

[0141] Ceramics are introduced into the gel obtained. The gel is introduced into the porous ceramic network by subjecting the assembly (ceramics+gel) under vacuum and rapidly breaking the vacuum. The operation is performed 3 times. The composites obtained are removed from the gel.

[0142] Due to the fact that composites contain a large amount of water, they are directly placed in a chamber of a supercritical CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The temperature of the chamber is gradually increased to 50 C. and the pressure adjusted to 100 bar.

[0143] After 30 hours of treatment, the pressure is reduced very slowly (more than 60 minutes) to atmospheric pressure and the assembly is removed from the enclosure. In order to eliminate the water contained into the composites, they are introduced into absolute ethanol during 20 minutes. This operation is realized 2 times. The composites are then placed into the reactor enclosure of the CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The enclosure chamber is filled and partially emptied 2 times. Then, the chamber is filled in full with liquid CO.sub.2 and the temperature is gradually increased to 35 C. and the pressure adjusted to 75bar. After drying, the pressure is decreased very slowly (60 minutes to return to the atmospheric pressure).

EXAMPLE 2

Composite BCP/HPMC/SBF0.9+Alcohol/No Treatment Solution/No Washing with Ethanol Before CO.SUB.2 .Drying

[0144] Ceramic cubes with dimension 3 mm*3 mm*3 mm (0.284 g) consist in 65% hydroxyapatite (HA) and 35% tricalcium phosphate (TCP). Their total porosity is between 60 and 85% and the pore size is between 150 and 400m. A solution A of SBF (0.9) (simulated body fluid with 0.9*the amount of traditionally used for SBF). A solution B is prepared by mixing 21 g of ethanol and 5 g of solution A.

[0145] A polymer gel is formed from 2 g of metolose 90SH-4000SR (HPMC from Shinetsu) and 25 g of solution B.

[0146] Ceramics are introduced into the gel obtained. The gel is introduced into the porous ceramic network by subjecting the assembly (ceramics+gel) under vacuum and rapidly breaking the vacuum. The operation is performed 3 times. The composites obtained are removed from the gel.

[0147] They are placed directly (in the absence of treatment solution) in a chamber of a supercritical CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The temperature of the chamber is gradually increased to 50 C. and the pressure adjusted to 100bar. After 24 h of treatment, the pressure is decreased very slowly (more than 60 minutes) to return to the atmospheric pressure and the temperature is also decrease to return to the room temperature. In order to dry the composites, the chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The enclosure chamber is filled and partially emptied 2 times. Then, the chamber is filled in full with liquid CO.sub.2 and the temperature of the chamber is gradually increased to 35 C. and the pressure adjusted to 75 bar. After drying, the pressure is decreased very slowly (60 minutes to return to the atmospheric pressure). Results are illustrated in FIG. 1 (first and second line).

[0148] The morphology of the composite is assessed by scanning electron microscopy (FIG. 1, second line) and compared to the ceramic (FIG. 1, first line).

[0149] The two first pictures illustrate firstly the modifications of porous network of the initial ceramic due to addition of polymer and secondly the organic porous network of interconnected pores of varying sizes.

[0150] The third picture highlights carbonated nanocrystals formed by precipitation during supercritical CO.sub.2 treatment. These crystals formed after chemical reaction between carbonates and ionic species contained in SBF solution used to form the gel are located on the surface of polymer network as well as inside the polymer matrix forming a porous network.

EXAMPLE 3

Composite BCP/Metolose/SBF0.9+Alcohol/No Treatment Solution/Washing with Ethanol Before CO.SUB.2 .Drying

[0151] Ceramics and gel are the same than those used in example 2.

[0152] The protocol used for performing the treatment is the same as used in Example 2.

[0153] After 24 h of treatment, the pressure is decreased very slowly (more than 60 minutes) to return to the atmospheric pressure and the temperature is also decrease to return to the room temperature.

[0154] The composites are removed from the enclosure chamber and immersed into absolute ethanol during 20 minutes. This operation is realized 2 times with fresh ethanol solution. The composites are then placed into the reactor enclosure of the CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The enclosure chamber is filled and partially emptied 2 times. Then, the chamber is filled in full with liquid CO.sub.2 and the temperature of the chamber is gradually increased to 35 C. and the pressure adjusted to 75 bar.

[0155] After drying, the pressure is decreased very slowly (60 minutes to return to the atmospheric pressure). Results are illustrated in FIG. 1 (first and third line).

[0156] The morphology of the composite is assessed by scanning electron microscopy (FIG. 1, third line) and compared to the second line (Example 2) and the first line (the reference ceramic).

[0157] The two first pictures illustrate the modifications of porous network of the initial ceramic due to addition of polymer and the modifications of porous structure to the corresponding two first pictures of Example 2 due to the immersion of the treated composite into absolute ethanol before drying. It can be observe a more porous organic structure with pore sizes more important than those obtain in example 2 (composite without washing in ethanol).

[0158] The third picture of Example 3 highlights carbonated nanocrystals formed by precipitation during supercritical CO.sub.2 treatment. These crystals formed after chemical reaction between carbonates and ionic species contained in SBF solution used to form the gel are located on the surface of polymer network as well as inside polymer matrix forming porous network.

EXAMPLE 4

Composite BCP/Gelatin+SrCl.SUB.2./Treatment Solution: SrCl.SUB.2.+SBF(0.9)/Washing with Ethanol Before CO.SUB.2 .Drying

[0159] Ceramic cubes with dimension 3 mm*3 mm*3 mm (0.293 g) consist in 65% hydroxyapatite (HA) and 35% tricalcium phosphate (TCP). Their total porosity is between 60 and 85% and the pore size is between 150 and 400 m. A gelatin hydrogel containing: 3 g gelatin, 0.3 g SrCl.sub.2 and 100 ml water is introduced as describe in previous examples into porous network of ceramics.

[0160] A solution A is prepared from 0.207 g K.sub.2HPO.sub.4, 0.2637 g CaCl.sub.2, 3 g SrCl.sub.2, 5.46 g TRIS buffer dissolved in 1l of deionised water. The pH is adjusted to 7.4 using HCl.

[0161] The composites are placed into a container with solution A. The amount of solution A used is that corresponding to L/S=2. The assembly is then placed in the chamber of a supercritical CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The temperature of the chamber is gradually increased to 50 C. and the pressure adjusted to 100 bar. After 30 hours of treatment, the pressure is reduced to atmospheric pressure and the assembly is removed from the enclosure.

[0162] As in example 3, the composites are removed from the enclosure chamber and immersed into absolute ethanol during 20 minutes. This operation is realized 2 times with fresh ethanol solution. The composites are then placed into the reactor enclosure of the CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The enclosure chamber is full and emptied 2 times. Then, the chamber is filled in full with liquid CO.sub.2 and the temperature of the chamber is gradually increased to 35 C. and the pressure adjusted to 75 bar.

[0163] After drying, the pressure is decreased very slowly (60 minutes to return to the atmospheric pressure). As previously described (in examples 2 and 3), the composites exhibit interconnected porosity as well as nanocrystals loaded within the polymer network.

EXAMPLE 5

Composite TCP/(PLA+Chloroform)+(SBF0.9+MgCl2+Water) Emulsion/No Treatment Solution/Washing with Acetone Before CO.SUB.2 .Drying

[0164] Ceramic cubes with dimension 3 mm*3 mm*3 mm (0.295 g) consist in 100% tricalcium phosphate (TCP). Their total porosity is between 60 and 85% and the pore size is between 150 and 400 m.

[0165] Preparation of the organic phase: A solution A is prepared by dissolving 1 g of poly(d,l-lactic acid) (PURASORB PDL02A) in 3.45 g of chloroform. A solution B is prepared introducing 30 mg MgCl.sub.2 in 100 ml of SBF(0.9) solution.

[0166] A coarse emulsion is prepared by mixing under stirring 2.7 g of solutions A and 2.1 g of solution B. The mixture is then introduced into the ceramic network as previously described under vacuum.

[0167] The composites are introduced in the chamber of supercritical dryer. The chamber is filled to two thirds with liquid CO.sub.2. The composite is washed 2 times with liquid CO.sub.2 to remove the chloroform and form the polymer network. A third filling is performed but this time, the chamber is raised to 45 C. and 100 bar in order to achieve the supercritical state of CO.sub.2. The elimination of chloroform allows to form a polymer network filled with the aqueous solution (SBF+MgCl.sub.2). The amount of water is sufficient (43.75% of the solvent constituting the emulsion with L/S=0.43) :the treatment is carried out without additional treatment solution. The composites are maintained under these conditions for 5 hours and then the pressure and temperature are restored to the normal. When the processing is complete, the composites are removed from the chamber and then washed 2 times in an acetone solution. The washing with acetone allows to remove the water and promotes drying and structuration of three-dimensional network of polymer. Composites are introduced one last time inside the dryer to be dried using CO.sub.2 in supercritical conditions (45 C.-100 b). The composites exhibit interconnected porosity and many apatite nanocrystals on the surface of the ceramic. The polymer, unlike the previous examples did not appear to have penetrated the entire network of porous ceramics and remains dispersed on the surface of the ceramic. It presents nanocristaux precipitated on its surface.

EXAMPLE 6

Composite BCP/(PLA+Chloroform)+(SBF0.9+MgCl2+Water) Emulsion/SBF+MgCl2+Water Treatment Solution/Washing with Acetone Before CO2 Drying

[0168] Ceramic cubes with dimension 3 mm*3 mm*3 mm (0.275 g) consist in 65% hydroxyapatite (HA) and 35% tricalcium phosphate (TCP). Their total porosity is between 60 and 85% and the pore size is between 150 and 400 m.

[0169] Preparation of the organic phase: A solution A is prepared by dissolving 1 g of poly(d,l-lactic acid) (PURASORB PDL02A) in 3.45 g of chloroform. A solution B is prepared introducing 30 mg MgCl2 in 100 ml of SBF(0.9) solution.

[0170] A coarse emulsion is prepared by mixing under stirring 2.7 g of solutions A and 2.1 g of solution B. The mixture is then introduced into the ceramic network as previously under vacuum.

[0171] The composites are introduced in the chamber of supercritical dryer. The chamber is filled to two thirds with liquid CO.sub.2. The composite is washed 2 times with liquid CO.sub.2 to remove the chloroform and form the polymer network. A third filling is performed but this time, the chamber is raised to 45 C. and 100 bar in order to achieve the supercritical state of CO.sub.2. The elimination of chloroform is used to form a polymer network filled with the aqueous solution (SBF+MgCl2).

[0172] The composites are placed into a container with solution B. The amount of solution B used is that corresponding to L/S=2. The assembly is then placed in the chamber of a supercritical CO.sub.2 dryer. The chamber temperature is raised to a temperature of 5 C. and then the chamber is filled in full with liquid CO.sub.2. The temperature of the chamber is gradually increased to 45 C. and the pressure adjusted to 100 bar. After 30 hours of treatment, the pressure is reduced to atmospheric pressure and the assembly is removed from the enclosure.

[0173] When the processing is complete, the composites are removed from the chamber and from the treatment solution and then washed 2 times in an acetone solution. The washing with acetone allows to remove the water and promotes drying and structuration of three-dimensional network of polymer. Composites are introduced one last time inside the dryer to be dried using CO.sub.2 in supercritical conditions (45 C.-100b). The result obtained is quite similar to those describe above, that is to say: the polymer remains positioned on the surface of the ceramic with the presence of precipitated nanocrystals. The ceramic has a large amount of apatite nanocrystals.