Dried implant composition and injectable aqueous implant formulation

Abstract

A dried implant composition for preparing an injectable aqueous implant formulation that is extrudable through a tapering system and a gauge 18 cannula, including a mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve; an injectable aqueous implant formulation, wherein the injectable aqueous implant formulation is obtainable by hydration and homogeneous mixing; a process for preparing the injectable aqueous implant formulation; and a kit for preparing the injectable aqueous implant formulation.

Claims

1. A syringe containing a dried mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve, whereby the w/w ratio of the nanocrystalline hydroxyapatite particles to the naturally crosslinked fibrous collagen material is from 1.8 to 4.5.

2. An injectable aqueous implant formulation, wherein the injectable aqueous implant formulation comprises 25-45 w/w % of a dried implant composition consisting essentially of a mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve, whereby the w/w ratio of the nanocrystalline hydroxyapatite particles to collagen is from 1.8 to 4.5, homogenized in a pharmaceutically acceptable aqueous vehicle, wherein the injectable aqueous implant formulation having properties such that it is extrudable through a tapering system and an 18 gauge (0.838 mm inner diameter) 25.4 mm long cannula with a force not exceeding 60 N.

3. The injectable aqueous implant formulation of claim 2, wherein the formulation comprises 30-40 w/w % of the dried implant and having properties such that it is extrudable through a tapering system and an 18 gauge (0.838 mm inner diameter) 25.4 mm long cannula with a force not exceeding 40 N.

4. The injectable aqueous implant formulation of claim 2, wherein the dried implant composition has a w/w ratio of the nanocrystalline hydroxyapatite particles to collagen of from 2.5 to 4.2.

5. A ready to use syringe containing the injectable aqueous implant formulation of claim 2.

6. A kit for preparing the injectable aqueous implant formulation of claim 2 comprising: a) a syringe equipped with a mixing device and containing: a dried implant composition consisting essentially of a mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve, whereby the w/w ratio of the nanocrystalline hydroxyapatite particles to collagen is from 1.8 to 4.5; a tapering system; and a gauge 18 (0.838 mm inner diameter) 25.4 mm long cannula; and b) a container filled with an appropriate amount of a pharmaceutically acceptable aqueous vehicle.

7. The kit of claim 6, wherein the container comprising the pharmaceutically acceptable aqueous vehicle is a syringe with a cannula.

8. A process for preparing the injectable aqueous implant formulation of claim 2 comprising: providing a dried implant composition consisting essentially of a mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve, whereby the w/w ratio of the nanocrystalline hydroxyapatite particles to collagen is from 1.8 to 4.5; rehydrating and homogeneously mixing 25-45 w/w % of the dried implant composition in the pharmaceutically acceptable aqueous vehicle.

9. The process of claim 8, comprising rehydrating and homogeneously mixing 25-45 w/w % the dried implant composition in a syringe equipped with a mixing device.

10. The process of claim 8, wherein providing the dried implant composition comprises the following steps: (a) preparing nanocrystalline hydroxyapatite particles having a size of 50 to 200 μm; (b) preparing milled naturally crosslinked fibrous collagen material by a process comprising an alkaline treatment, an acid treatment and a treatment by organic solvents, and mincing the naturally crosslinked fibrous collagen material into fragments that pass through a 0.5 mm sieve to obtain the milled naturally crosslinked fibrous collagen material; (c) adding the milled naturally crosslinked fibrous collagen mixing obtained in (b) to an aqueous solution, vigorously mixing the aqueous solution such as to obtain a collagen slurry, adding the nanocrystalline hydroxyapatite particles having a size of 50 to 200 μm prepared in (a) to the collagen slurry, and vigorously mixing, at a pH from 4.2 to 7.5 to obtain a mixed composition, (d) drying the mixed composition containing the nanocrystalline hydroxyapatite particles and collagen obtained in (c) to obtain a dried implant composition; and (e) sterilizing by gamma- or X-ray irradiation the dried implant composition obtained in (d).

11. The method of claim 2, wherein the pharmaceutically acceptable aqueous vehicle is sterile water, a sterile isotonic saline solution, blood or fractions thereof.

12. A method of implanting the injectable aqueous implant formulation of claim 2 into an implantation site by extruding the injectable aqueous implant formulation through a tapering system and a gauge 18 cannula positioned in the implantation site.

13. The method of claim 12, further comprising, before said implanting: a) providing a dried mixture of nanocrystalline hydroxyapatite particles derived from natural bone having a size of 50 to 200 μm and fragments of naturally crosslinked fibrous collagen material that pass through a 0.5 mm sieve, whereby the w/w ratio of the nanocrystalline hydroxyapatite particles to collagen is from 1.8 to 4.5; and b) rehydrating 25-45 w/w % of the dried mixture in a pharmaceutically acceptable aqueous vehicle and mixing to form the injectable aqueous implant formulation.

14. The method of claim 13, wherein the dried mixture has a w/w ratio of the nanocrystalline hydroxyapatite particles to collagen of from 2.5 to 4.2.

15. The method of claim 13, wherein the nanocrystalline hydroxyapatite particles have a size from 100 to 180 μm.

16. The method of claim 13, wherein the dried mixture has been sterilized by gamma- or X-ray irradiation.

17. The method of claim 13, wherein in the dried implant composition the naturally crosslinked fibrous collagen material is selected from the group consisting of porcine dermis and porcine peritoneum or pericardium membrane.

18. The method of claim 13, wherein the pharmaceutically acceptable aqueous vehicle is sterile water, a sterile isotonic saline solution, blood or fractions thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in further detail with reference to illustrative examples of preferred embodiments of the invention and the accompanying figures in which:

(2) FIG. 1 represents the Medmix syringe mixing system (MEDMIX, SP 003-00M-02/B, catalogue number 507211), (1) being the syringe containing the dry biomaterial, (2) being the syringe cap with an open bore luer outlet, which is compatible with any luer cannula, (3) being the open bore cap to close the syringe during the mixing process, (4) being the mixing device, which is a flexible mixer once the plunger has been removed and (5) being the plunger, that can be removed to mix the material in the syringe and can be reset afterwards to push out the material.

(3) FIG. 2 is a copy of the Medmix mixing procedure as set out in the Operating Instruction which is attached to the Medmix syringe mixing system.

(4) FIGS. 3A and 3B represent the extrusion curves of the injectable aqueous implant formulations obtained by rehydrating and homogeneously mixing dried implant compositions 2 and 4 in the examples with isotonic saline (curves (1) and (3)) or fresh human blood (curves (2) and (4)), respectively.

(5) FIG. 4 is a microscopy image using a CV1000 confocal spinning disk microscope with excitation by 561 nm laser illumination of injectable aqueous implant formulation 4 obtained by rehydrating and homogeneously mixing dried implant composition 4 (prepared in Example 6) with human blood: the grown MC3T3 CytoLight Red cells are visualised in bright.

(6) FIG. 5 represents on the left-hand-side a scanning electron micrograph (SEM) of nanocrystalline hydroxyapatite particles derived from natural bone and on the right-hand-side a SEM of synthetic beta-TCP particles.

DETAILED DESCRIPTION

(7) The following examples illustrate the invention without limiting its scope.

Example 1 Preparation of the Raw Materials

(8) 1) Preparation of Hydroxyapatite Fine Particles Having a Size of 100 to 150 μm or 125 to 180 μm

(9) Hydroxyapatite bone mineral fine particles were produced from cortical or cancellous bone as described in Examples 1 to 4 of U.S. Pat. No. 5,417,975, using an additional sieving step between 100 and 150 μm or 125 to 180 μm, respectively. Alternatively, hydroxyapatite bone mineral fine particles were produced by grinding Geistlich Bio-Oss® Small Granules (available from Geistlich Pharma AG, CH-6110, Switzerland), careful impaction using a piston and an additional sieving step between 100 and 150 μm or 125 to 180 μm, respectively.

(10) The above prepared hydroxyapatite bone mineral fine particles having a size of between 100 and 150 μm or 125 to 180 μm were stored in glass bottles until use.

(11) 2) Preparation of Collagen A

(12) Porcine hides were ground in a meat grinder to pieces of 1 to 20 mm. The water was removed using a water soluble solvent such as an alcohol or a ketone. The collagen fibres were defatted using a chlorinated hydrocarbon such as dichloroethane or methylene chloride or a non-chlorinated hydrocarbon such as hexane or toluene. After removing the solvent, the collagen was treated with a strong inorganic base at a pH above 12 for a period of 6 to 24 hours and treated with a strong inorganic acid at a pH of 0 to 1 for a period of 1 to 12 hours. The excess acid was removed by rinsing with water and the suspension was homogenized to a 0.5 to 2% homogenous suspension of collagen fibres in the presence of a swelling regulator such as an inorganic salt. The suspension was dried by freeze-drying and the dry collagen fibres of the sponge obtained was successively cleaned with different organic solvents such as alcohols, ethers, ketones and chlorinated hydrocarbons, the solvents being then evaporated under vacuum to a solvent residue of less than 1%.

(13) 1×1 cm pieces of the cleaned collagen sponge were cut by hand using scissors. The cut pieces were further minced by using first a cutting mill which includes a sieve of 0.5 to 4.0 mm, then a centrifugal mill (Retsch, ZM200) with a 0.5 mm sieve including trapezoid holes. The scissor cut pieces were alternatively milled directly with the centrifugal mill.

(14) Collagen A consisting of naturally crosslinked fibrous collagen fragments that pass through a 0.5 mm sieve was thus obtained.

(15) 3) Preparation of Collagen B

(16) The peritoneal membranes from young pigs were completely freed from flesh and grease by mechanical means, washed under running water and treated with 2% NaOH solution for 12 hours. The membranes were then washed under running water and acidified with 0.5% HCl. After the material had been acidified through its entire thickness (about 15 min) the material was washed until a pH of 3.5 was obtained. The material was then shrunk with 7% saline solution, neutralised with 1% NaHCO.sub.3 solution and washed under running water. The material was then dehydrated with acetone and degreased with n-hexane.

(17) The material was dried using ethanol ether and milled with a cutting mill (e.g. Pulverisette 25 from Fritsch: see fritsch.de./produkte/mahlen/schneidmuehlen/pulverisette-25 or SM300 from Retsch: retsch.de/de/produkte/zerkleinern/schneidmuehlen.htlm) which includes a trapezoidal sieve of 0.5 to 1.0 mm.

(18) The cut collagen fibre segments were further minced by using a centrifugal mill (Retsch, ZM200) with a 0.5 mm sieve including trapezoid holes.

(19) Collagen B consisting of naturally crosslinked fibrous collagen fragments that pass through a 0.5 mm sieve was thus obtained.

Example 2 Drying and Sterilization of Mixed Compositions Containing Hydroxyapatite Particles and Collagen

(20) The mixed compositions containing hydroxyapatite particles and collagen (obtained as described in Examples 3 to 8 below) were dried by freeze-drying or air drying under reduced pressure and sterilized by gamma-ray or X-ray irradiation.

(21) 1) Freeze-Drying

(22) From the 50 ml syringe the mass was filled up in 1 ml Cyclic Olefin Copolymer (COC) syringes from back side. Approximately 0.5 ml volume was filled up per 1 ml syringe. The syringes were stored closed from both sides for 5 hours in a fridge at 4° C. Then the syringes were opened on both sides and put on a metal plate in the lyophilisator, each syringe being in a lying down position such as have a large surface of contact with the metal plate. Then the following lyophilisation program was initiated:

(23) 1. Freezing in 7 hours to −40° C.

(24) 2. Holding 4 hours at −40° C.

(25) 3. Primary drying at −10° C. and 850 μbar during 20 hours

(26) 4. Secondary drying at +20° C. and 100 μbar during 6 hours

(27) Alternatively, the viscous collagen-hydroxyapatite mass was not freeze-dried in syringes, but on stainless steel plates or in small stainless steel forms of less than 25 mm in diameter and less than 10 mm in depth. The dry obtained material after freeze drying was crushed into particles of 0.1 to 2 mm in size by using a centrifugal mill (Retsch, ZM200) with 1.5 mm up to 10 mm sieves. Crushing by a mill led to smaller hydroxyapatite particles in the reconstituted end product.

(28) Alternatively, for crushing the viscous collagen-hydroxyapatite mass was extruded out of a standard luer outlet of a syringe and formed as straight lines on stainless steel plates. Then the material was freeze dried as such.

(29) 2) Air Drying

(30) The viscous collagen-hydroxyapatite mass e.g. formed as straight lines was alternatively dried by air in a vacuum oven at 30° C. and 10 mbar for 24 hours. The dried straight lines were broken into 5 to 10 mm long sticks by hand. The granulated material or the small sticks was then filled in a 3 ml syringe mixing system (MEDMIX, SP 003-00M-02/B, catalogue number 507211) with syringe cap with open bore luer and open bore cap (MEDMIX, CP 000-76M/D, catalogue number 506964).

(31) 3) Sterilization

(32) The dried implant composition obtained by lyophilisation or air drying under reduced pressure was sterilized in the syringe by gamma-ray or X-ray irradiation with 27-33 kGy.

(33) The water content in the dried product just after sterilisation was 3-7%, as measured by Karl Fisher titration.

Example 3 Preparation of Dried Implant Composition 1 Containing Hydroxyapatite Particles Having a Size of 100 to 150 μm or 125 to 180 μm and Collagen A, with a w/w Ratio of Hydroxyapatite to Collagen of 4.0

(34) Preparation of the Collagen-Hydroxyapatite Composition

(35) Water and hydrochloric acid (2M) were mixed in a beaker with a spatula. The milled collagen A obtained in Example 1 was added and carefully pushed into the liquid to wet all the collagen. The beaker was closed with a screw lid and the water-collagen slurry was homogenously mixed by Speedmixer (CosSearch GmbH, Speedmixer DAC400.1FVZ) during 4 minutes with 2500 rpm. The collagen slurry was slightly heated up during the mixing procedure. Then the collagen slurry was cooled for 30 minutes in the fridge at 4° C.

(36) The collagen slurry was mixed again by Speedmixer during 2 minutes with 2500 rpm. Then the hydroxyapatite bone mineral fine particles having a size of between 100 and 150 μm or 125 and 180 μm prepared in Example 1 were added in the beaker with the collagen slurry and the mass was mixed by Speedmixer during 2 minutes with 2000 rpm. The resulting pH was around 4.5.

(37) The material quantities used in the experiments above are specified in the following table:

(38) TABLE-US-00001 Material Net weight [g] Water 6.36 HCl 2 mol/l 0.64 Collagen A 0.60 Hydroxyapatite 2.40 particules 100-150 μm or 125-180 μm

(39) Drying of the Hydroxyapatite-Collagen Composition

(40) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(41) Dried implant composition 1 containing hydroxyapatite particles having a size of 100 to 150 μm or 125 to 180 μm and collagen A with a w/w ratio of hydroxyapatite to collagen of 4.0 and giving a pH of 4.5 after rehydration with demineralised water performed as described in Example 9, was thus obtained.

Example 4 Preparation of Dried Implant Composition 2 Containing Hydroxyapatite Particles Having a Size of 125 to 180 μm and Collagen B, with a w/w Ratio of Hydroxyapatite to Collagen of 4.0

(42) Preparation of the collagen-hydroxyapatite composition

(43) The milled collagen B obtained in Example 1 was carefully pushed into demineralized water to wet all the collagen. The beaker was closed with a screw lid and the water-collagen slurry was homogenously mixed by Speedmixer during 1 minute with 2500 rpm. The collagen slurry was then heated up to 70° C. in a water bath during 4 hours. Then the collagen slurry was cooled for 30 minutes at ambient temperature or in a fridge or in a water bath.

(44) The collagen slurry was mixed again by Speedmixer during 2 minutes with 2500 rpm. Then the hydroxyapatite bone mineral fine particles having a size of between 125 and 180 μm prepared in Example 1 were added in the beaker with the collagen slurry and the mass was mixed by Speedmixer during 2 minutes with 2000 rpm. The resulting pH was 6.2.

(45) The material quantities used in the experiments above are specified in the following table:

(46) TABLE-US-00002 Material Net weight [g] Water 6.36 Collagen B 0.60 Hydroxyapatite 2.40 particles 125-180 μm

(47) Drying of the Hydroxyapatite-Collagen Composition

(48) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(49) Dried implant composition 2 containing hydroxyapatite particles having a size of 125 to 180 μm and collagen B with a w/w ratio of hydroxyapatite to collagen of 4.0 and giving a pH of 6.2 after rehydration with demineralised water performed as described in Example 9, was thus obtained.

Example 5 Preparation of Dried Implant Composition 3 Containing Hydroxyapatite Particles Having a Size of 125 to 180 μm and a Mixture of 2 Parts of Collagen A for 1 Part of Collagen B, with a (w/w) Ratio of Hydroxyapatite to Collagen of 2.67

(50) Preparation of the Collagen-Hydroxyapatite Composition

(51) Water and hydrochloric acid (2M) were mixed in a beaker with a spatula. The milled Collagen B obtained in Example 1 was carefully pushed into the liquid to wet all the collagen. The beaker was closed with a screw lid and the water-collagen slurry was homogenously mixed by Speedmixer during 2 minutes with 2500 rpm with a resulting pH between 0.9 and 1. The collagen slurry was then heated up to 70° C. in a water bath during 20 minutes. Then the collagen slurry was cooled down for 30 minutes in a water bath at 25° C.

(52) The milled collagen A obtained in Example 1 was added and carefully pushed into the collagen slurry to wet all the collagen. Then the slurry was mixed by Speedmixer during 4 minutes with 2500 rpm.

(53) Finally, the hydroxyapatite bone mineral fine particles having a size of between 125 and 180 μm prepared in Example 1 were added in the beaker with the collagen slurry and the mass was mixed by Speedmixer during 2 minutes with 2000 rpm. The resulting pH was around 4.5.

(54) The material quantities used in the experiments above are specified in the following table:

(55) TABLE-US-00003 Material Net weight [g] Water 6.08 HCl 2 mol/l 0.62 Collagen A 0.60 Collagen B 0.30 Hydroxyapatite 2.40 particles 125-180 μm

(56) Drying of the Hydroxyapatite-Collagen Composition

(57) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(58) Dried implant composition 3 containing hydroxyapatite particles having a size of 125 to 180 μm and a mixture of 2 parts of collagen A for 1 part of collagen B, with a (w/w) ratio of hydroxyapatite to collagen of 2.67, and giving a pH of 4.5 after rehydration with demineralised water performed as described in Example 9, was thus obtained.

Example 6 Preparation of Dried Implant Composition 4 Containing Hydroxyapatite Particles Having a Size of 125 to 180 μm and a Mixture of 2 Parts of Collagen A for 1 Part of Collagen B, with a w/w Ratio of Hydroxyapatite to Collagen of 2.67

(59) Preparation of the Collagen-Hydroxyapatite Composition

(60) The milled Collagen B obtained in Example 1 was carefully pushed into demineralized water to wet all the collagen. The beaker was closed with a screw lid and the water-collagen slurry was homogenously mixed by Speedmixer during 1 minute with 2500 rpm. The collagen slurry was then heated up to 70° C. in a water bath during 20 min. Then the collagen slurry was cooled down for 30 minutes in a water bath at 25° C.

(61) The milled collagen A obtained in Example 1 was added and carefully pushed into the collagen slurry to wet all the collagen. Then the slurry was mixed by Speedmixer during 4 minutes with 2500 rpm.

(62) Finally, the hydroxyapatite bone mineral fine particles having a size of between 125 and 180 μm prepared in Example 1 were added in the beaker with the collagen slurry and the mass was mixed by Speedmixer during 2 minutes with 2000 rpm. The resulting pH was 6.0.

(63) The material quantities used in the experiments above are specified in the following table:

(64) TABLE-US-00004 Material Net weight [g] Water 6.70 Collagen A 0.60 Collagen B 0.30 Hydroxyapatite 2.40 particles 125-180 μm

(65) Drying of the Hydroxyapatite-Collagen Composition

(66) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(67) Dried implant composition 4 containing hydroxyapatite particles having a size of 125 to 180 μm and a mixture of 2 parts of collagen A for 1 part of collagen B, with a w/w ratio of hydroxyapatite to collagen of 2.67, and giving a pH of 6.0 after rehydration with demineralised water performed as described in Example 9, was thus obtained.

Example 7 Preparation of Dried Implant Composition 5 Containing Hydroxyapatite Particles Having a Size of 125 to 180 μm and Collagen A, with a w/w Ratio of Hydroxyapatite to Collagen of 4.0

(68) Preparation of the Collagen-Hydroxyapatite Composition

(69) The milled Collagen A was carefully pushed into demineralized water to wet all the collagen. The hydroxyapatite bone mineral fine particles having a size of between 125 and 180 μm prepared in Example 1 were added and the beaker was closed with a screw lid. The water-collagen-hydroxyapatite slurry was homogenously mixed by Vortex mixer during 1 minute and a scoop during 1 minute.

(70) The resulting pH was 6.1.

(71) The used material quantities are described in the following table:

(72) TABLE-US-00005 Material Net weight [g] Water 7.0 Collagen A 0.60 Hydroxyapatite 2.40 particles 125-180 μm

(73) Drying of the Hydroxyapatite-Collagen Composition

(74) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(75) Dried implant composition 5 containing hydroxyapatite particles having a size of 125 to 180 μm and collagen A, with a w/w ratio of hydroxyapatite to collagen of 4.0, and giving a pH of 6.1 after rehydration with demineralized water performed as described in Example 9, was thus obtained.

Example 8 Preparation of Dried Implant Composition 6 Containing Hydroxyapatite Particles Having a Size of 125 to 180 μm and Collagen A, with a (w/w) Ratio of Hydroxyapatite to Collagen A of 2.0

(76) Preparation of the Collagen-Hydroxyapatite Composition

(77) The milled Collagen A was carefully pushed into demineralized water to wet all the collagen. The hydroxyapatite bone mineral fine particles having a size of between 125 and 180 μm prepared in Example 1 were added and the beaker was closed with a screw lid. The water-collagen-hydroxyapatite slurry was homogenously mixed by Vortex mixer during 1 minute and a scoop during 1 minute.

(78) The resulting pH was 5.8.

(79) The used material quantities are described in the following table:

(80) TABLE-US-00006 Material Net weight [g] Water 7.0 Collagen A 1.0 Bio-Oss 125-180 μm 2.0

(81) Drying of the Hydroxyapatite-Collagen Composition

(82) Drying by freeze-drying or air drying under reduced pressure and sterilization was performed as described in Example 2.

(83) Dried implant composition 6 containing hydroxyapatite particles having a size of 125 to 180 μm and collagen A, with a (w/w) ratio of hydroxyapatite to collagen of 2.0, and giving a pH of 5.8 after rehydration with demineralised water performed as described in Example 9, was thus obtained.

Example 9 Preparation of a Ready-to-Use Syringe Containing an Injectable Aqueous Implant Formulation by Rehydration of the Dried Implant Composition in the Syringe

(84) 1) Preparation of a ready to use syringe containing an injectable aqueous implant formulation obtained by rehydration and homogeneous mixing of the dried implant composition a) Using a 3-way stopcock valve Luer-Lok adapter and a 1 ml syringe 2) Dried, sterile hydroxyapatite-collagen compositions in the 1 ml product syringe were rehydrated by using a 3-way stopcock valve Luer (Luer-Lok) adapter (BD Connecta, 3-way stopcock, catalog number 394600), Vaclok syringes (Qosina, Vaclok syringe, catalog number C1097) and a normal single use supplementary syringe 1 ml (Luer-Lok). The liquid to rehydrate the collagen was demineralised water, an isotonic saline solution, a PBS solution of pH 7.4 containing 150 mM sodium phosphate buffer (prepared by dissolving NaH.sub.2PO.sub.4 in demineralised water and adjusting the pH with sodium hydroxide), or blood. The weight of the dry biomaterial (dried implant composition obtained in one of Examples 3 to 8) in the syringe was known or was measured. An amount of rehydrating liquid was filled in the supplementary syringe such as to obtain an injectable paste containing by weight 38% dry biomaterial. The product syringe was then connected to the 3-way stopcock valve and the 180° counterpart of the 3-way stopcock valve was closed by a closing cap. At the third position (90° from the product syringe) of the 3-way stopcock valve a 60 ml Vaclok Syringe was connected to the system. Air was evacuated from the product syringe by pulling the plunger of the Vaclok Syringe and locking at 50 ml volume. Then the 3-way valve was rotated by 180° to keep the vacuum in the product syringe, whereas the Vaclok Syringe was replaced by the supplementary syringe filled with liquid. Then the 3-way valve was rotated by 180°. Due to the vacuum, the liquid automatically flowed into the product syringe and wetted the product. To ensure the complete liquid transfer into the product syringe the plunger of the product syringe was drawn back. The material was rested for 30 seconds to enable hydration before the material was pushed from the product syringe into the supplementary syringe and back, this sequence repeated 40 times to obtain a homogeneously mixed material. After the mixing procedure the 3-way stopcock valve was replaced by the applicator which is a tapering system and a blunt end 18 gauge (inner diameter 0.838 mm) 25.4 mm long cannula. The reconstituted injectable aqueous implant formulation obtained by rehydration and homogeneous mixing of each of the dried implant compositions 1 to 6 with demineralised water had a pH near to the pH measured before lyophilisation, namely about 4.5, 6.2, 4.5, 6.0, 6.1 and 5.8, respectively. b) Using a 3 ml Medmix syringe mixing system Alternatively the particles of the dried material were rehydrated with demineralised water, an isotonic saline solution, a PBS solution of pH 7.4 containing 150 mM sodium phosphate buffer or blood, in the Medmix syringe mixing system (MEDMIX, SP 003-00M-02/B, catalog number 507211) with syringe cap with open bore luer and open bore cap (MEDMIX, CP 000-76M/D, catalog number 506964), represented in FIG. 1 in which (1) is the syringe containing the dry biomaterial, (2) is the syringe cap with an open bore luer outlet, which is compatible with any luer cannula, (3) is the open bore cap to close the syringe during the mixing process, (4) is the mixing device, which is a flexible mixer once the plunger is removed, (5) is the plunger, that can be removed to mix the material in the syringe and can be reset afterwards to push out the material. The Medmix mixing procedure set out in FIG. 2 was followed. To get an optimal result, after step 4 the plunger is pushed 3 times in order to push the liquid into the material to wet it and perform the mixing step (step 6) for 60 seconds. All the air is removed in step 8. 3) Extrusion test

(85) The extrudability of the reconstituted injectable aqueous implant formulation obtained was tested with a tension and pressure testing device (Zwick & Roell, BT1-FR2.5TS.D14). The ready to use syringe prepared above was placed vertically in a syringe holding and the plunger was pressed down from the machine while the force of pressing the product out of the syringe through the applicator comprising a tapering system and a blunt end 18 gauge (inner diameter 0.838 mm) 25.4 mm long cannula (Nordson EFD, Precision Tip 18GA 1″, catalog number 7018110), was measured with the following program: Force till resistance: 0.1 N Speed till resistance: 100 mm/min Testing speed: 1 mm/s, position controlled End of testing: force limit, 150 N Force sensor: 200 N

(86) For all tested injectable implant formulations obtained by rehydration and homogeneous mixing with demineralised water, an isotonic saline solution or a PBS solution, notably for injectable implant formulations, which were prepared from dried implant compositions 1 to 6, the measured force did not exceed 40 N. For all tested injectable implant formulations obtained by rehydration and homogeneous mixing with blood, notably for injectable implant formulations, which were prepared from dried implant compositions 1 to 6, the measured force did not exceed 45 N.

(87) For injectable implant formulations obtained by rehydration and homogeneous mixing with demineralised water, an isotonic saline solution or a PBS solution, which were prepared from dried implant compositions 1, 2, 3, 5 and 6 the measured force did not exceed 20 N.

(88) For injectable implant formulations obtained by rehydration and homogeneous mixing with blood, which were prepared from dried implant composition 1 (containing hydroxyapatite particles having a size of 100 to 150 μm or 125 to 180 μm and collagen A, with a w/w ratio of hydroxyapatite to collagen of 4.0) and dried implant composition 2 (containing hydroxyapatite particles having a size of 125 to 180 μm and collagen B, with a w/w ratio of hydroxyapatite to collagen of 4.0), the measured force did not exceed 25 N.

(89) See FIGS. 3A and 3B, which represent the extrusion curves of the injectable implant formulations obtained by rehydrating and homogeneously mixing dried implant compositions 2 and 4 with isotonic saline or fresh human blood, respectively. In FIG. 3A, (1) and (2) are the extrusion curves of dried implant composition 2 (containing hydroxyapatite particles having a size of 125 to 180 μm and collagen B, with a w/w ratio of hydroxyapatite to collagen of 4.0) rehydrated with isotonic saline and fresh human blood, respectively. In FIG. 3B, (3) and (4) are the extrusion curves of dried implant composition 4 (containing hydroxyapatite particles having a size of 125 to 180 μm and a mixture of 2 parts of collagen A for 1 part of collagen B, with a w/w ratio of hydroxyapatite to collagen of 2.67) rehydrated with isotonic saline and fresh human blood, respectively.

Example 10 Biocompatibility: In Vitro Test on Growth of Two Bone Forming Cell Lines in the Injectable Aqueous Implant Formulation of the Invention

(90) The cells from: MC3T3 CytoLight Red, a prosteoblast cell line originating from mouse calvaria (ATCC CRL-2593) that was transduced to express red fluorescent protein in the cytoplasm using Cytolight Red Lentivirus (Essen Bioscience), or MG63 (cell line derived from human osteosarcoma)
were tested for their ability to colonize the injectable aqueous implant formulation of the invention as follows.

(91) Those cells were cultivated under conditions recommended by the supplier, namely for MC3T3 Cytolight Red cells: culture in aMEM (GIBCO) supplemented with 10% fetal bovine serum (FBS, Lubio), 1% Penicillin-Streptomycin (GIBCO) and 0.5 μg/ml Puromycin (Sigma) and for MG63 cells: culture in DMEM (GIBCO) supplemented with 10% FBS (Lubio), 1% Penicillin-Streptomycin (GIBCO). A layer of those cells was introduced into wells of a multiwall plate and about 1 ml of biomaterial was added on top of the layer of cells in each well using 3 ml Medmix syringes containing injectable implant formulations 1 to 4 obtained by rehydrating and homogeneously mixing dried implant compositions 1 to 4 (prepared in examples 3 to 6) with human blood or an isotonic saline solution. The cells were cultivated for 8 days.

(92) Those experiments showed for each of injectable implant formulations 1 to 4 colonization of the biomaterial by each the MC3T3 CytoLight Red and M63 cell lines. See FIG. 4, which is a microscopy image using CV1000 confocal spinning disk microscope (Yokogawa) with excitation by 561 nm laser illumination of injectable aqueous implant formulation 4 obtained by rehydrating and homogeneously mixing dried implant composition 4 (prepared in Example 6) with human blood: the grown MC3T3 CytoLight Red cells are visualised in bright.

(93) Those experiments show that bone forming cells can grow in vitro in the injectable aqueous implant formulation of the invention. This demonstrates the high biocompatibility of that injectable aqueous implant formulation which provides upon implantation a matrix very close to the natural in vivo environment in which regeneration takes place.