Application of bone graft particles in preparation of porous bone graft material

Abstract

The present invention relates to the use of bone graft particles in the preparation of a porous bone graft material comprising an acid-containing self-setting adhesive composition. The bone graft particles have a porous core, the outer surface of which is at least partially covered by an outer layer. The core comprises a core material selected from the group consisting of a heterograft, a bone xenograft, and a bone allograft, or mixtures thereof. And the outer particle layer comprises carbonate.

Description

[0001] The present invention relates to the use of bone graft particles in the preparation of a porous bone graft material.

[0002] Generally, bone tissue regeneration is achieved by filling a bone repair site with a bone graft. Over time, the bone graft is incorporated by the host, and new bone remodels the bone graft.

[0003] Bone grafts can be heterografts, xenografts, autografts or allografts having mechanical properties similar to bone.

[0004] In oral surgery and orthopaedics, synthetic bone repair materials based on hydroxyapatite (HA) and / or tricalcium phosphate (TCP) are widely used. Depending on the indication, they can be applied as granules or prefabricated blocks. US 6,511,510 relates to a calcium phosphate porous ceramic material obtained by a sintering process. The use of granular materials allows the treatment of a wide range of indications. For granular materials, the ceramic block material is subsequently processed by steps such as friction, percussion and sieving (WO 04 / 054633). Although granular materials are suitable for a wide range of indications in terms of size and area, their applicability for treating large bone defects is limited because they tend to migrate and are thus encapsulated. The enhanced volume defined by the applied granules may collapse and fail to guide bone regrowth to its original size. US 7,012,034 describes a block-shaped bone augmentation material based on porous β-tricalcium phosphate.

[0005] In a typical periodontal surgical bone repair procedure, an incision is made in the gingival tissue to expose a bone defect adjacent to the tooth root. Once the defect and the root have been debrided, a bone repair material suspended in a suitable carrier is placed. The gingival tissue is then closed, holding the repair material in place. Optionally, a barrier material can be utilized to keep the repair formulation in contact with the defect. Thus, the bone repair material in periodontal surgery needs to have a formulation that can be easily shaped according to the size and shape of the defect.

[0006] WO 2004 / 011053 proposes a formulation having a putty consistency. Similarly, EP 1 490 123 describes a kneadable and flexible bone replacement material based on granular calcium phosphate and a hydrogel. When applied to the defect site, the formulation remains adhered to the defect site without migrating or overexpanding.

[0007] US2020147260 discloses an interconnected porous calcium carbonate body in which the sulfate ion component of the anion component of calcium sulfate as a raw material inorganic compound and the anion component of sodium carbonate as an electrolyte are replaced. These particles are combined with other inorganic compounds including phosphoric acid.

[0008] US2013122057 discloses cements containing certain small molecule amino acid phosphates (such as phosphoserine) and certain polyvalent metal compounds.

[0009] US2022 / 023493A1 discloses a viscous composition containing a polyvalent metal salt, an osteoinductive factor, and β-TCP granules, which exists in the form of an aqueous solution or suspension and can be hardened in situ. Although the material has excellent adhesion properties, it is very dense and blocks the pores of the β-TCP granules, having a negative impact on bone integration.

[0010] Therefore, the problem of the present invention is to provide a bone graft material that allows good bone integration.

[0011] This problem is solved by the particles of claim 1. Further preferred embodiments are the subject matter of dependent claims 2 to 15.

[0012] Surprisingly, it has been found that the bone graft particles of the present invention can be used to prepare a porous bone graft material comprising an acid-containing self-setting binder composition. They have a porous core, and the outer surface of the porous core is at least partially covered by an outer layer. Preferably, at least 50% of the outer surface is covered by the outer layer. The core contains a core material selected from the group consisting of bone allografts, bone xenografts, and bone allografts or mixtures thereof, and the outer layer contains carbonate.

[0013] Once the particles of the present invention come into contact with the acid-containing self-setting binder composition, the carbonate in the outer layer of the particles begins to form carbon dioxide bubbles, which prevent the self-setting binder composition from flowing into the pores. In addition, the bubbles also form additional pores in the self-setting binder composition during curing, thereby forming a porous scaffold. Despite the high porosity, the bone graft material still has sufficient stability to prevent movement, and it is strong enough to withstand the forces within the implantation site, i.e., resist mechanical stress. In addition, due to the viscosity of the acid-containing self-setting binder composition, the particles do not migrate and remain at the application site. In addition, since the bone graft material is in a putty state, the bone graft material can be shaped in about 1 to 2 minutes and can occupy voids of different shapes. Therefore, the particles of the present invention allow the preparation of a porous bone graft material that ensures the stability of the graft site, while also having optimal resorption kinetics and thus promoting bone formation.

[0014] The use of the coated bone graft particles of the present invention allows the obtaining of a bone graft material having a large number of open pores, which promotes the angiogenesis, healing, and remodeling of bone. A large number of open pores are beneficial for the adhesion and invasion of osteoblasts.

[0015] The term "carbonate" includes primary carbonates (i.e., salts of bicarbonate (HCO3 - ) and secondary carbonates (HCO32- ) salts.

[0016] The term "self-setting" refers to the ability of a material to solidify and harden due to the mixing of solid and liquid components.

[0017] The term "bone allograft substitute" refers to a synthetic, inorganic, biocompatible bone substitute that does not contain animal or human components.

[0018] The term "bone xenograft" represents particles derived from animal bone tissue. Preferably, the porous or spongy part of an animal joint ball is used to prepare bone xenografts. Regarding the pore structure, it has been shown that using animals (preferably adult cattle) is particularly suitable for extracting the spongy parts of leg and arm joints because the trabecular structure is well-developed and there are large areas with the same pore structure.

[0019] As used herein, the term "bone allograft" refers to bone that includes cortical bone and / or cancellous bone, which is recovered from another individual and processed for implantation into a living patient, including, for example: fibular wedge; humeral wedge; tibial wedge; fibular trapezoidal wedge; humeral trapezoidal wedge; femoral trapezoidal wedge; fibular shaft and ring; humeral shaft and ring; and femoral shaft and ring; and substantially intact bone grafts, including, for example, proximal and distal femur, femoral head; and small cut bone grafts, including, for example, cancellous cubes, iliac crest wedges, and Cloward positioning sheaths.

[0020] In the context of the present invention, the term "pore" refers to and includes any void in a material, and includes voids of any size and shape. For example, pores include substantially spherical voids, substantially rectangular voids, and elongated voids or channels having any cross-sectional shape including non-linear or irregular shapes. In particular, the term pore includes nanopores, micropores, and macropores as defined below.

[0021] The particles of the present invention stimulate tissue formation and tissue ingrowth, and therefore preferably contain pores of different sizes in the range of 1 nm to 1500 microns, most preferably having an average pore size between 500 nm and 1000 microns. Even more preferably 1 micron to 500 microns. Thus, the material can include nanopores from 1 nm to 100 nm, micropores from 100 nm to 1 micron, and macropores greater than 50 microns.

[0022] Preferably, not only is at least a part of the outer surface of the porous core covered with carbonate, but also at least a part of the pore surface is covered with carbonate. It is believed that any self-setting bioadhesive that enters the pores of the particles will trigger gas formation and thus be pushed out of the pores due to increased pressure.

[0023] In one aspect of the present invention, the weight ratio of the particulate carbonate to the core material is from 15:100 to 1:100, preferably from 8:100 to 2:100, and most preferably from 4:100 to 2:100. It can be seen that said ratio has a significant effect on bubble formation. A ratio between 4:100 and 2:100 results in larger pores and significant volume growth.

[0024] Preferably, the core material of the particles of the present invention is a bone allograft selected from the group consisting of hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, tetracalcium phosphate, anhydrous dicalcium phosphate, dicalcium phosphate dihydrate, amorphous calcium phosphate, calcium-deficient hydroxyapatite, calcium sulfate, and bioactive glass. The advantages of said materials are their biocompatibility, safety, and efficacy in periodontal regeneration and guided bone regeneration.

[0025] Preferably, the carbonate present in the outer layer of the particles of the present invention is selected from the group consisting of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, calcium carbonate, strontium carbonate, and magnesium carbonate. All of said carbonates are biocompatible. Optimal results can be obtained using carbonates selected from sodium bicarbonate, ammonium bicarbonate, and sodium carbonate, especially using sodium bicarbonate. They all have good solubility in water. This allows for rapid and inexpensive coating of the particles, for example by mixing them with an aqueous solution containing said carbonate. Preferably, the carbonate concentration is adjusted according to the core material to prevent blocked pores in the final product.

[0026] In one aspect of the present invention, the core of the particles has a porosity of at least 50%, preferably at least 60%, and most preferably from 65% to 80%. Due to the presence of carbonate on its surface, and optionally also on the pore surface, the pores remain open, which allows for very rapid wicking, infiltration, and absorption of blood, which is a key requirement for good bone integration.

[0027] In one embodiment of the present invention, the porosity is distributed over a wide range of effective pore diameters. The particles can simultaneously have nanoporosity, microporosity, and macroporosity. Preferably, nanoporosity, microporosity, and macroporosity can occur simultaneously and can be interconnected. In a preferred embodiment of the present invention, the average pore diameter of the particles is from 200 μm to 1000 μm, preferably from 600 μm to 900 μm, resulting in excellent bone integration.

[0028] The porosity can be measured by helium pycnometry. This process is known to those skilled in the art and determines the density and true volume of a sample by measuring the change in pressure of helium in a calibrated volume.

[0029] Preferably, the average particle size of the bone graft granules is from 0.1 mm to 3.0 mm, preferably from 0.5 mm to 2.0 mm. Preferably, granules with an average particle size of 0.5 mm to 1.0 mm are used for smaller bone defects. The use of such granules results in better surface contouring, especially in aesthetic areas. Granules with an average particle size of 1.0 mm to 2.0 mm are preferably used for larger bone defects as they enable better vascularization.

[0030] Preferably, the acid-containing self-setting binder composition comprises an aqueous solution and a self-setting powder, the self-setting powder comprising at least two different components, namely a polyvalent metal salt and phosphoserine.

[0031] Preferably, the polyvalent metal salt contained in the self-setting binder powder comprises tetracalcium phosphate or tricalcium phosphate, preferably α-tricalcium phosphate. α-TCP is more soluble in the body's bone material, which can increase its absorption rate and shorten the healing process.

[0032] Preferably, the content of phosphoserine is from 20% by weight to 50% by weight of the self-setting binder powder, preferably from 20% by weight to 30% by weight of the self-setting binder powder.

[0033] Preferably, the content of the polyvalent metal salt is from 50% by weight to 90% by weight of the self-setting binder powder, preferably from 70% by weight to 80% by weight of the self-setting binder powder.

[0034] On the other hand, there is provided a method for preparing a porous bone graft material by mixing an acid-containing self-setting binder composition with the granules of the present invention at the start of the curing process, i.e., at the start of the curing reaction. As previously mentioned, the self-setting binder composition comprises an aqueous solution and a self-setting binder powder. The granules of the present invention can be premixed with the self-setting binder powder before adding the aqueous solution, or they can be added directly after mixing the aqueous solution and the self-setting powder. Once the aqueous solution and the self-setting binder powder come into contact, curing begins. The self-setting binder composition has an initial adhesion phase during which it has adhesive properties for 1 to 3 minutes, after which the material becomes putty-like. At this stage, carbon dioxide bubbles form on the surface of the granules and optionally on the surfaces of the pores of the porous core of the granules. The bubbles prevent the self-setting binder composition from entering the pores of the granules. In addition, the bubbles also form additional pores in the self-setting binder composition during curing, thereby forming a porous scaffold. Limited manipulation of the bone graft material within the same time allows for the removal of excess portions. The bone graft material reaches initial setting completely in about 15 minutes after mixing. However, the material continues to cure and harden, completing 90% within 24 hours.

[0035] This bone graft material can withstand a combined tensile and shear stress of up to 3 MPa, similar to the strength of human cancellous bone. Due to the particles of the present invention, the scaffold has high osteoconductivity and bioactivity, and ultimately the bone graft material can be replaced by new bone. In addition, over time, the load-bearing responsibility is transferred to the new tissue, thus maintaining mechanical integrity.

[0036] Another aspect of the present invention relates to a kit for preparing a porous bone graft material, which comprises:

[0037] a) A first component A, which comprises an aqueous solution, and

[0038] b) A second component B, which comprises an acid-containing self-setting binder powder, and the self-setting binder powder preferably comprises at least a polyvalent metal salt and phosphoserine, and

[0039] c) A third component C, which comprises the particles of the present invention.

[0040] In the kit, component A, component B, and component C are stored in separate compartments, so they are physically separated from each other. The separation of the three compartments allows for the provision of a ready-to-use system with a long shelf life.

[0041] Alternatively, the kit may only comprise two components, namely

[0042] a) A first component A, which comprises an aqueous solution, and

[0043] b) A second component B, which comprises an acid-containing self-setting binder powder and the particles of the present invention, wherein the self-setting binder powder preferably comprises at least a polyvalent metal salt and phosphoserine.

[0044] Therefore, in this embodiment, the acid-containing self-setting binder powder and the particles are premixed as component B, which is physically separated from the liquid component A (i.e., the aqueous solution), and thus they are stored in two different compartments.

[0045] Both kits allow for the direct in-situ preparation of a porous bone graft material before use. Therefore, the separate components are physically separated from each other and are not mixed until use.

[0046] Preferably, the acid-containing self-setting binder composition comprises phosphoserine (most preferably L-phosphoserine) as the acid. L-phosphoserine is a component of many endogenous proteins, especially osteopontin (bone sialoprotein), and is a normal metabolite found in human body fluids. It has a high affinity for apatite with a relatively low crystallinity, indicating that it plays an important role in the mineralization process.

[0047] In the context of the present invention, the term aqueous solution refers to water which may additionally contain additives such as salts. Preferably, it is distilled water or a solution comprising water and saline (an aqueous solution of 0.9 wt% NaCl).

[0048] In another aspect of the present invention, Component A of the kit further comprises an acidifying agent selected from the group consisting of hydrochloric acid, ascorbic acid, citric acid, malic acid, tartaric acid, maleic acid, succinic acid, fumaric acid, acetic acid, formic acid and propionic acid or mixtures thereof, preferably citric acid. The presence of the acidifying agent enhances the in-situ formation of carbon dioxide on the surface of the particles and thus results in a higher porosity of the final product.

[0049] Preferably, the polyvalent metal salt contained in the kit of the present invention comprises tetracalcium phosphate or tricalcium phosphate, preferably α-tricalcium phosphate.

[0050] Preferably, Component B of the kit further comprises calcium silicate which also promotes bone formation.

[0051] The porous bone graft material of the present invention is preferably used for treating bone defects such as voids, gaps or cracks in order to fill the bone defect. Preferably, the bone defect is a large bone defect because such bone defects are particularly difficult to treat using conventional bone graft materials. In one embodiment of the present invention, the bone defect is selected from the group consisting of alveolar ridge augmentation and extraction socket restoration. In another embodiment of the present invention, the bone defect is selected from the group consisting of calvarial bone defect, osteochondral defect, vertebral fracture, intervertebral spinal fusion, posterolateral spinal fusion and iliac crest defect repair.

[0052] Another aspect of the present invention relates to a method for treating a bone defect, the method comprising directly applying the porous bone graft material to the bone defect site after mixing an acid-containing self-setting adhesive composition and the particles of the present invention, thereby repairing the bone defect.

[0053] According to some embodiments of the present invention, the method for repairing a bone defect further comprises shaping the porous bone graft material in the bone defect site, which can be carried out, for example, with a spatula.

[0054] According to some embodiments of the present invention, the method for repairing a bone defect further comprises allowing the porous bone graft material to solidify and cure, thereby forming a solidified bone graft material. Examples:

[0055] Preparation of saturated sodium bicarbonate solution

[0056] In a falcon tube, 4 g of sodium bicarbonate was added to 10 ml of water and dissolved while stirring the container (shaking by hand). The solution was left to stand for 30 minutes and then stirred again to ensure that as much sodium bicarbonate as possible was dissolved in the water. Then the falcon tube was left to stand until the undissolved sodium bicarbonate solidified at the bottom of the tube. When coating the particles, only the saturated solution was used, without using the undissolved sodium bicarbonate.

[0057] Coating of the particles

[0058] 0.27 g of Cerabone particles supplied by Straumann, Basel were added to a 1.5 ml Eppendorf tube. 250 μl of saturated sodium bicarbonate solution was added so that the liquid just covered the particles. Then the Eppendorf tube was opened and left overnight at 55 °C to evaporate the water. What remained were dry Cerabone particles coated with sodium carbonate.

[0059] Mixing with the self-setting binder

[0060] 0.5 g of a self-setting binder powder containing 76% α-TCP (Innotere GmbH) and 24% serine phosphate (Merck) was mixed with 200 μl of a citric acid solution (15%) using a spatula. Once the mixture was homogeneous, the particles were added while continuing to mix with the spatula to distribute the particles evenly. Then the mixture was transferred to an Eppendorf tube (see Figure 1 ) and allowed to cure.

[0061] Results:

[0062] Pore formation started immediately after mixing the self-setting binder with the particles. In the cross-section cut ( Figures 2A and 2B ), it could be seen that the particles were surrounded by or adjacent to pores.

[0063] Experiment 2: Sodium carbonate vs sodium bicarbonate

[0064] The particles were impregnated with solutions containing three different concentrations instead of the saturated solution.

[0065] Three different concentrations of stock solutions containing NaHCO3 were prepared:

[0066] - 96 g / L

[0067] - 48 g / L

[0068] - 24 g / L

[0069] Three different concentrations of stock solutions containing Na2CO3 were prepared:

[0070] - 96 g / L

[0071] -48 g / L

[0072] -24 g / L

[0073] For the preparation of the impregnated granules, 0.27 g of Cerabone (botiss) was placed in a 1.5 mL Eppendorf tube and 250 μL of the stock solution was added. Subsequently, the prepared sample was placed at room temperature with the lid open to allow the water to evaporate.

[0074] The following observations were made:

[0075] The optimal amount of water for the preparation of the mixture containing granules and self-setting binder powder increased compared to the mixture containing only the self-setting binder powder. The optimal amount of water for the NaHCO3 granules was found to be 175 μl to compensate for the water "consumption" of the granules. The optimal amount of water for the Na2CO3 granules was found to be 200 μl to compensate for the water "consumption" of the granules.

[0076] During the experiment, an unexpected correlation was found between the amount of NaHCO3 and Na2CO3 and the formation of bubbles. It was found that this was related to the hygroscopicity of the granules. The more carbonate deposited on the surface of the granules (i.e., the more concentrated the stock solution), the more the sample dried during the curing process. Therefore, during solidification, the granules coated with a larger amount of carbonate appeared drier, resulting in smaller pores and less volume increase.

[0077] For the granules and self-setting binder powder coated with Na2CO3 prepared with 200 μl of water, the optimal porosity was obtained at a low carbonate concentration (24 g / L), and it was also found that this was the overall best sample (Figure 3a).

[0078] For the granules / and self-setting binder powder coated with NaHCO3 prepared with 175 μl of water, the optimal concentration was found to be a medium concentration (48 g / L). However, the difference was not as obvious as that of the Na2CO3 sample (Figure 3b).

Claims

1. Use of bone graft particles in the preparation of a porous bone graft material comprising an acid-containing self-setting binder composition, wherein, The bone grafting particles have a porous core, the outer surface of which is at least partially covered by an outer layer, and wherein the core contains a core material selected from the group consisting of xenografts, bone xenografts, and bone allografts or mixtures thereof, characterized in that the outer layer contains carbonate.

2. The use according to claim 1, wherein, The surface of the pores is at least partially coated with carbonate.

3. The use according to any one of the preceding claims, wherein, The weight ratio of carbonate to core material of the particles is from 15:100 to 1:100, preferably from 8:100 to 2:100, most preferably from 4:100 to 2:

100.

4. Use according to any one of the preceding claims, wherein, The xenograft is selected from the group consisting of hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, tetracalcium phosphate, anhydrous dicalcium phosphate, dicalcium phosphate dihydrate, amorphous calcium phosphate, calcium-deficient hydroxyapatite, calcium sulfate, and bioactive glass.

5. Use according to any one of the preceding claims, wherein the core has a porosity of at least 50%, preferably at least 60%, most preferably 65% to 80%.

6. Use according to any one of the preceding claims, wherein, The carbonate is selected from the group consisting of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, calcium carbonate, strontium carbonate, and magnesium carbonate, preferably sodium bicarbonate, ammonium bicarbonate, and sodium carbonate, most preferably sodium bicarbonate.

7. Use according to any one of the preceding claims, wherein, The average particle size of the bone grafting particles is from 0.1 mm to 3.0 mm.

8. Use according to any one of the preceding claims, wherein, The average pore size of the bone grafting particles is from 200 μm to 1000 μm, preferably from 600 μm to 900 μm.

9. A method for preparing a porous bone grafting material by mixing an acid-containing self-setting binder composition with the particles according to any one of the preceding claims at the start of the curing process.

10. The method according to claim 9, wherein, The acid-containing self-setting binder composition comprises an aqueous solution and an acid-containing self-setting binder powder, wherein the acid-containing self-setting binder powder preferably contains at least a polyvalent metal salt and phosphoserine.

11. A kit for preparing a porous bone grafting material, comprising a) a first component A, which comprises an aqueous solution, b) a second component B, which comprises an acid-containing self-setting binder powder, wherein the acid-containing self-setting binder powder preferably contains at least a polyvalent metal salt and phosphoserine, and c) the particles according to any one of claims 1 to 9.

12. A kit for preparing a porous bone grafting material, comprising a) a first component A, which comprises an aqueous solution, and b) a second component B, which comprises an acid-containing self-setting binder powder and the particles according to any one of claims 1 to 9, wherein the acid-containing self-setting binder powder preferably contains at least a polyvalent metal salt and phosphoserine.

13. The kit according to claim 11 or 12, wherein, The component A further comprises an acidifying agent selected from the group consisting of hydrochloric acid, ascorbic acid, citric acid, malic acid, tartaric acid, maleic acid, succinic acid, fumaric acid, acetic acid, formic acid, and propionic acid or mixtures thereof, preferably citric acid.

14. The kit according to any one of claims 11 to 13, wherein The acid-containing self-setting binder powder further comprises calcium silicate.

15. Use of the porous bone grafting material according to any one of claims 1 to 9 for the treatment of bone defects, preferably large bone defects.

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