Rapid synthesis of octacalcium phosphate

Abstract

The present innovation relates to biomaterials, particularly, to the synthesis method of octacalcium phosphate. The method can be applied in the commercial manufacturing of biomaterials for bone tissue regeneration or dental restoration as well as in drug delivery. The proposed method for the synthesis of octacalcium phosphate (OCP) bioceramic completes in less than one minute or not more than 5 minutes.

Description

[0001] RAPID SYNTHESIS OF OCTACALCIUM PHOSPHATE

[0002] DESCRIPTION

[0003]

[0001] The invention relates to the field of biomaterials, particularly the method to synthesize octacalcium phosphate (OCP) with a high specific surface area. The method can be applied in the commercial manufacturing of biomaterials for bone tissue regeneration or dental restoration, such as bioinks for 3D printing, calcium phosphate cements, bioceramics, composites and drug delivery systems.

[0004] Background of the art

[0005]

[0002] Hydroxyapatite is the most extensively studied bone substitute bioceramic. It has a close resemblance (chemically and structurally) with the minerals present in the bone. The main challenge associated with hydroxyapatite is that it does not break down in physiological conditions even after the regeneration of damaged bone [1]. Researchers are exploring options to accelerate the rate of reabsorption in the physiological environment and improve the biocompatibility of bone-forming cells by utilizing OCP, a precursor of hydroxyapatite.

[0006]

[0003] OCP acts as a precursor of biological apatite crystals in the hard tissues. The biological occurrence of OCP has been reported in dentine and urinary calculus [2] . The osteoconductivity of OCP is more than hydroxyapatite and tricalcium phosphate in terms of collagen formation [3], Precipitation and hydrolysis are the most common methods employed for the synthesis of OCP [4, 5]-

[0007]

[0004] Synthesis of OCP is governed by supersaturation, Gibbs free energy, common ion effect, molarity, pH, temperature, and mixing order / rate. A minor modification in these reaction parameters often leads to the formation of undesirable phases that compromises the purity of OCP [6].

[0008]

[0005] A direct wet precipitation method for the preparation of OCP is known. In this method dropwise addition of reagents for the synthesis of OCP was used. In the first reaction, 250 mb of calcium acetate solution (0.02M, 0.04 M) was added dropwise into 250 mb sodium acid phosphate solution (0.02 M, 0.04 M) at pH 5-6 and the temperature was maintained at 60 °C for 3 to 4 hours. In the second experiment, dropwise addition of phosphate solution into calcium solution at pH 5- 6 and the reaction was performed at 60 °C for 3 to 4 hours. Whereas in the third experiment either calcium solution was added dropwise into phosphate solution or vice versa. This reaction was divided into two parts: (a) 1-hour reaction at 70 °C and pH of 4.5 and (b) 1-hour reaction at 80 °C and pH of 4. Moreover, the reaction mixtures were either stirred or not stirred. The obtained precipitate was fdtered several times and dried at room temperature. The author has only mentioned the X-ray diffraction patterns of OCP samples synthesized at 60 °C whereas the X-ray diffraction of OCP at 70 °C and 80 °C is not available in the article [7], Using this method OCP was synthesized in 1 to 4 hours. The Ca / P ratio of OCP is 1.33 but in these experiments, the Ca / P ratio was 1. This leads to variations in the concentration of calcium and phosphate ions and affects the synthesis of OCP. Thus the precipitation of OCP was delayed and consumed more time for its synthesis.

[0009]

[0006] Based on the above described synthetic method, similarly obtained OCP having specific surface area of 25 m2 / g by mixing calcium acetate hydrate (0.04 M) and sodium dihydrogen phosphate (0.04 M). The calcium solution (250 m ) was slowly added to the phosphate solution (250 m ), this step was performed for 1 hour at a temperature of 67.5 °C with a stirring rate of 400 rpm [8], The Ca / P ratio used in this experiment was 1. This reduces the concentration of calcium and phosphate ions in the reaction mixture and affects the precipitation rate of OCP. As a result, formation of OCP was delayed and required more time for the completion of the reaction.

[0010]

[0007] In another article calcium acetate monohydrate (0.04 M) and sodium phosphate monobasic (0.03 M) were heated separately at different temperatures (50 °C, 60 °C, 70 °C). After attaining the desired temperature, both solutions were mixed in the micro-flow reactor at a flow rate of 10 mL / min. The mixing was performed at the pre-heated temperatures and then the reaction mixture was aged for 3, 6, and 12 hours at a similar temperature with a stirring rate of 70 rpm. No characteristic OCP peaks were noticed in the X-ray diffraction analysis of the samples obtained after mixing without aging. But the samples heated at 50 °C and aged for 3, 6, 12 hours revealed the presence of characteristic OCP peaks. In the case of batch reaction, calcium source (18 mb) was added dropwise into phosphate source (18 mb). The resultant mixture was maintained at 60 °C and aged for 3 hours with a stirring speed of 200 rpm [9],

[0011]

[0008] The addition of reagents using dose rate equipment and a slow stirring rate was found to be the major reason to synthesize OCP for a longer duration. Firstly, this study was performed on a micro-flow reactor that was capable of carrying out a low volume experiment. Even though the reaction volume was less, dose rate equipment was employed for adding calcium solution into phosphate solution. This reagent addition step was found to be time-dependent. Secondly, the stirring rate has been identified as a key factor affecting the synthesis of OCP. The stirring rate at which calcium and phosphate solutions are mixed is not mentioned. Due to improper mixing, OCP was not observed in the sample. Thus, an extended period of aging was done for different time intervals to initiate the formation of OCP.

[0009] To date, numerous attempts have been made for the synthesis of OCP but these methodologies are found to have high production costs, time-consuming and the entire reaction process takes from hours to days to complete. Moreover, the findings are unable to report precise reaction conditions for the preparation of OCP (Table 1).

[0012]

[0010] Specific surface area governs the drug adsorption ability of a material. The high specific surface area is considered as a beneficial parameter for the adsorption of drugs

[0010] ,

[0013] [Oi l] Hydroxyapatite with a high surface area acted as a promising material for drug delivery applications

[0011] .

[0014]

[0012] The adsorption of risecronate on the surface of hydroxyapatite and zinc substituted hydroxyapatite (ZnHA) was compared. The large surface area of ZnHA (86 m2 / g) resulted in higher adsorption of risecronate than hydroxyapatite (23 m?7g )

[0012] .

[0015]

[0013] The different specific surface area values of OCP reported in the literature are shown in Table 2.

[0016]

[0014] Therefore, there is still a great need for an efficient and fast method to synthesize OCP with a high specific surface area.

[0017] Table 1. An Overview of OCP synthesis conditions reported in the literature

[0018] *NA: Information not available

[0019] Table 2. Specific surface area of OCP

[0020] The object of the invention

[0021]

[0015] An object of the present invention is to develop a rapid and cost-effective method for the synthesis of OCP bioceramic, where at the same time OCP has a high specific surface area and can be applied in bone tissue regeneration or dental restoration such as bioinks for 3D printing, calcium phosphate cements, bioceramics, composites and drug delivery systems.

[0022]

[0016] Searching for a new synthesis process we unexpectedly discovered that the use of the wet route in combination with optimum reaction conditions notably reduces reaction time from days or hours to minutes and seconds. Summary of the invention

[0023]

[0017] OCP is prepared by the wet precipitation method. Stock solutions are prepared separately in deionized water.

[0024]

[0018] The term “stock solution” refers to solution made from calcium source and phosphate source.

[0025]

[0019] The term “calcium source” refers to calcium acetate hydrate .

[0026]

[0020] The term “phosphate source” refers to sodium dihydrogen phosphate dihydrate or potassium dihydrogen phosphate.

[0027]

[0021] The term “room temperature” refers to temperature 18-22 °C.

[0028]

[0022] The term “heated” refers to temperature 50-70 °C.

[0029]

[0023] The Ca / P ratio for the synthesis of OCP is ranging from 1 to 2, preferably from 1.2 to 1.4 or more preferably 1.3. The calcium source is mixed with the phosphate source. The volume ratio of both solutions can be 1: 1. The reaction is carried out at a temperature ranging from 40 °C to 80 °C, pH ranging from 4.0 to 6.0, preferably from 4.5 to 5.0.

[0030]

[0024] The term “mixing” refers to any type of mixing of liquids including stirring, and shaking. The mixing time is preferably from 5 seconds to 5 minutes.

[0031]

[0025] In one embodiment both calcium and phosphate sources are heated, in another embodiment, only the phosphate source is heated while the calcium source is kept at room temperature. Temperature plays a key role in controlling the phase purity, morphology, crystallinity, and rate of precipitation of octacalcium phosphate. Heating of reactants before mixing enhances the ion mobility, supersaturation, and decreases the solubility of OCP, leading to the rapid precipitation of OCP within minutes. The sample is separated by vacuum filtration or centrifugation or gravity filtration. The sample obtained after filtration can be dried in an incubator or lyophilization or hot air oven or at room temperature. The selected reaction conditions assist in obtaining OCP bioceramic.

[0032]

[0026] The OCP is prepared by wet precipitation comprising the following steps: a) heating phosphate and optionally calcium source in a range from 50 to 70 °C; b) mixing together a calcium source and a phosphate source, wherein the Ca / P molar ratio ranges from 1 to 2, a temperature range is from 40 to 80 °C with pH range from 4.0 to 6.0; c) mixing the resulting mixture for not more than 5 seconds to 10 minutes; d) separating the octacalcium phosphate precipitated in step c); e) drying the octacalcium phosphate obtained in step d).

[0033]

[0027] The mixing step c) can be done in less than 1 minute.

[0028] The term “high specific surface area” refers to specific surface area of dried OCP obtained after drying and ranging from 65 to 85 m2 / g, or preferably 69 to 85 m2 / g, or preferably 69 to 80 m2 / g, or more preferably 70 to 80 m2 / g.

[0034]

[0029] Brief description of the drawings:

[0035] Fig.l. X-ray diffraction pattern (a) and scanning electron microscopy image (b) of sample synthesized at 50 °C in less than 5 minutes.

[0036] Fig.2. X-ray diffraction pattern (a) and scanning electron microscopy image (b) of sample synthesized at 60 °C in less than 5 minutes.

[0037] Fig.3. X-ray diffraction pattern (a) and scanning electron microscopy image (b) of sample synthesized at 70 °C in less than 5 minutes.

[0038] Fig.4. X-ray diffraction pattern (a) and scanning electron microscopy image (b) of sample synthesized at 60 °C in less than 1 minute.

[0039] Fig.5. X-ray diffraction pattern (a) and scanning electron microscopy image (b) of sample synthesized at 60 °C in less than 5 minutes without heating calcium source.

[0040] Examples

[0041]

[0030] The following examples are intended to illustrate certain preferred embodiments of the invention and are not limiting in nature.

[0042]

[0031] Example 1. Sodium dihydrogen phosphate dihydrate solution (150 mb, 40 mM) and calcium acetate hydrate solution (150 mb, 53.2 mM) was heated separately at 50 °C. Calcium acetate hydrate solution was added into sodium dihydrogen phosphate dihydrate solution. The reaction was performed at pH 4.7 to 4.9 under mixing at a rpm ranging from 480 to 520. After adding calcium source, the resulting mixture was stirred for less than 5 minutes. Then the reaction mixture was filtered using a vacuum filter, washed with distilled water, frozen in liquid nitrogen and lyophilized. The sample obtained after lyophilization was analyzed by powder X-ray diffraction (Panalytical, Aeries, Netherlands) for phase identification, scanning electron microscope (Tescan, Bmo, Czech Republic) to analyze the surface morphology and Brunauer- Emmett-Teller (Quantachrome Instruments, Boynton Beach, Florida, United States of America) was employed for measuring specific surface area using nitrogen gas adsorption. X-ray diffraction pattern (Fig. la.) revealed pure OCP (98 to 100 %) phase. The characteristic peaks of OCP observed in X-ray diffraction pattern matched with the international centre for diffraction data (ICDD) card no. 00-026-1056. This confirmed that the diffraction maxima corresponds only to OCP and no other phases were identified. The scanning electron micrograph (Fig. lb) showed plate-like morphology and the specific surface area (Table 3) was found to be 69 m2 / g.

[0043]

[0032] Example 2. Sodium dihydrogen phosphate dihydrate solution (150 m , 40 mM) and calcium acetate hydrate solution (150 m , 53.2 mM) was heated separately at 60 °C. Calcium acetate hydrate solution was added into sodium dihydrogen phosphate dihydrate solution. The reaction was performed at pH 4.7 to 4.9 under mixing at a rpm ranging from 480 to 520. After adding calcium source, the resulting mixture was stirred for less than 5 minutes. Then the reaction mixture was filtered using a vacuum filter, washed with distilled water, frozen in liquid nitrogen and lyophilized. The characterization of the sample obtained after lyophilization was performed as mentioned in Example 1. X-ray diffraction pattern (Fig. 2a.) revealed pure OCP (98 to 100 %) phase. The characteristic peaks of OCP observed in X-ray diffraction pattern matched with the standard ICDD card no. 00-026-1056. This confirmed that the diffraction maxima corresponds only to OCP and no other phases were identified. The scanning electron micrograph (Fig. 2b) indicated that the surface of the sample was composed of plate-like structures whereas the specific surface area (Table 3) was found to be 72 m2 / g.

[0044]

[0033] Example 3. Sodium dihydrogen phosphate dihydrate solution (150 mb, 40 mM) and calcium acetate hydrate solution (150 mb, 53.2 mM) was heated separately at 70 °C. Calcium acetate hydrate solution was added into sodium dihydrogen phosphate dihydrate solution. The reaction was performed at pH 4.7 to 4.9 under mixing at a rpm ranging from 480 to 520. After adding calcium source, the resulting mixture was stirred for less than 5 minutes. Then the reaction mixture was filtered using a vacuum filter, washed with distilled water, frozen in liquid nitrogen and lyophilized. The characterization of the sample obtained after lyophilization was performed as mentioned in Example 1. X-ray diffraction pattern (Fig. 3a.) revealed pure OCP (98 to 100 %) phase. The characteristic peaks of OCP observed in X-ray diffraction pattern matched with the standard ICDD card no. 00-026-1056. This confirmed that the diffraction maxima corresponds only to OCP and no other phases were identified. The scanning electron micrograph (Fig. 3b) of the sample showed platy structures. The specific surface area (Table 3) of the sample was observed as 72 m2 / g.

[0045]

[0034] Example 4. Sodium dihydrogen phosphate dihydrate solution (150 mb, 40 mM) and calcium acetate hydrate solution (150 mb, 53.2 mM) was heated separately at 60 °C. Calcium acetate hydrate solution was added into sodium dihydrogen phosphate dihydrate solution. The reaction was performed at pH 4.7 to 4.9 under mixing at a rpm ranging from 480 to 520. After adding calcium source, the resulting mixture was stirred for less than 1 minute. Then the reaction mixture was filtered using a vacuum filter, washed with distilled water, frozen in liquid nitrogen and lyophilized. The characterization of the sample obtained after lyophilization was performed as mentioned in Example 1. X-ray diffraction pattern (Fig. 4a.) revealed pure OCP (98 to 100 %) phase. The characteristic peaks of OCP observed in X-ray diffraction pattern matched with the standard ICDD card no. 00-026-1056. This confirmed that the diffraction maxima corresponds only to OCP and no other phases were identified. The scanning electron micrographs (Fig. 4b) of the sample showed plate-like structures. The specific surface area (Table 3) of the sample was observed as 80 m2 / g.

[0046]

[0035] Example 5. To a heated (60 °C) sodium dihydrogen phosphate dihydrate solution (150 mL, 40 mM) the calcium acetate hydrate solution (room temperature) (150 mL, 53.20 mM) was added. The reaction was performed at pH 4.7 to 4.9 under mixing at a rpm ranging from 480 to 520. After adding calcium source, the resulting mixture was stirred for less than 5 minutes. Then the reaction mixture was filtered using a vacuum filter, washed with distilled water, frozen in liquid nitrogen and lyophilized. The characterization of the sample obtained after lyophilization was performed as mentioned in Example 1. X-ray diffraction pattern (Fig. 5a.) revealed pure OCP (98 to 100 %) phase. The characteristic peaks of OCP observed in X-ray diffraction pattern matched with the standard ICDD card no. 00-026-1056. This confirmed that the diffraction maxima corresponds only to OCP and no other phases were identified. The scanning electron micrograph (Fig. 5b) of the sample revealed the existence of plate / ribbon shaped structures whereas the specific surface area (Table 3) was found to be 73 m2 / g.

[0047] Table 3. Specific surface area of synthesized samples.

[0048] References

[0049] [1] Park, J. B. and Lakes, R. S (1992), Biomaterials- An Introduction, Plenum Press. [2] Indurkar, A., Choudhary, R., Rubenis, K., Loes, J., 2021. Advances in Sintering Techniques for Calcium Phosphates Ceramics. Materials 14, 6133. https: / / doi.org / 10.3390 / mal4206133

[0050] [3] Suzuki O, Shiwaku Y, Hamai R. Octacalcium phosphate bone substitute materials: Comparison between properties of biomaterials and other calcium phosphate materials. Dent Mater J 2020, 39, 187-99. https: / / doi.org / 10.4012 / dmj.2020-001.

[0051] [4] Suzuki O, Insley G. (eds): Octacalcium Phosphate Biomaterials Understanding of Bioactive Properties and Application. Woodhead Publishing, 2020, 1-342

[0052] [5] Monma H. Preparation of octacalcium phosphate by the hydrolysis of alpha-tricalcium phosphate. Journal of Materials Science, 1980, 15, 2428-34. https: / / doi.org / 10.1007 / BF00550744.

[0053] [6] Chow LC, Eanes ED. (eds): Octacalcium Phosphate. Monographs in Oral Science. Basel, Karger, 2001, 18, 94-111.

[0054] [7] LeGeros, R.Z., 1985, ‘Preparation of octacalcium phosphate (OCP): A direct fast method’, Calcified Tissue International, 37(2), 194-197.

[0055] [8] Suzuki, O., Nakamura, M., Miyasaka, Y., Kagayama, M., Sakurai, M., 1991. Bone Formation on Synthetic Precursors of Hydroxyapatite. Tohoku J. Exp. Med. 164, 37-50. https: / / doi.org / 10.1620 / tiem.164.37.

[0056] [9] Saengdet, P. (Milin) & Ogawa, M., 2021, ‘Directional growth of octacalcium phosphate using micro-flow reactor mixing and subsequent aging’, RSC Advances, 11(26), 15969- 15976.

[0057]

[0010] Wen, Y„ Li, J., Lin, H„ Huang, H„ Song, K„ Duan, K„ Guo, T„ Weng, J., 2021.

[0058] Improvement of Drug -Loading Properties of Hydroxyapatite Particles Using Triethylamine as a Capping Agent: A Novel Approach. Crystals 11, 703. htps: / / doi.org / 10.3390 / crystl l060703

[0059]

[0011] Du, M., Chen, J., Liu, K., Xing, H., Song, C., 2021. Recent advances in biomedical engineering of nano-hydroxyapatite including dentistry, cancer treatment and bone repair. Composites Part B: Engineering 215, 108790. htps: / / doi.Org / 10.1016 / j.compositesb.2021.108790

[0060]

[0012] Forte, L., Sarda, S., Combes, C., Brouillet, F., Gazzano, M., Marsan, O., Boanini, E., Bigi,

[0061] A., 2017. Hydroxyapatite functionalization to trigger adsorption and release of risedronate. Colloids and Surfaces B: Biointerfaces 160, 493-499. htps: / / doi.Org / 10.1016 / j.colsurfb.2017.09.055

[0062]

[0013] Graham, S. & Brown, P.W., 1993, ‘The low temperature formation of octacalcium phosphate’, Journal of Crystal Growth, 132(1-2), 215-225.

[0014] Bigi, A., Boanini, E., Borghi, M., Cojazzi, G., Panzavolta, S., Roveri, N., 1999. Synthesis and hydrolysis of octacalcium phosphate: effect of sodium polyacrylate. Journal of Inorganic Biochemistry 75, 145—151. https: / / doi.org / 10. 1016 / S0162-0134(99)00047-l

[0063]

[0015] Arellano-Jimenez, M.J., Garcia-Garcia, R. & Reyes-Gasga, J., 2009, ‘Synthesis and hydrolysis of octacalcium phosphate and its characterization by electron microscopy and X- ray diffraction’, Journal of Physics and Chemistry of Solids, 70(2), 390-395.

[0064]

[0016] Bigi, A., Boanini, E., Walsh, D., Mann, S., 2002. Morphosynthesis of Octacalcium Phosphate Hollow Microspheres by Polyelectrolyte-Mediated Crystallization This work was supported by MURST, the University of Bologna (Funds for Selected Research Topics), and the EPSRC (UK). Angew. Chem. Int. Ed. 41, 2163. htps: / / doi.org / 10.1002 / 1521-3773(20020617)41: 12<2163::AID-ANIE2163>3.0.CO;2-G.

[0065]

[0017] Forte, L., Torricelli, P., Boanini, E., Gazzano, M., Fini, M. & Bigi, A., 2017, ‘Antiresorptive and anti-angiogenetic octacalcium phosphate functionalized with bisphosphonates: An in vitro tri-culture study’, Acta Biomaterialia, 54, 419-428.

[0066]

[0018] Bigi, A., Bracci, B., Panzavolta, S., Iliescu, M., Plouet-Richard, M., Werckmann, J., Cam,

[0067] D., 2004. Morphological and Structural Modifications of Octacalcium Phosphate Induced by Poly- 1 -Aspartate. Crystal Growth & Design 4, 141-146. https: / / doi.org / 10.1021 / cg034078d

[0068]

[0019] Shelton, R.M., Liu, Y., Cooper, P.R., Gbureck, U., German, M.J. & Barralet, J.E., 2006, ‘Bone marrow cell gene expression and tissue construct assembly using octacalcium phosphate microscaffolds’, Biomaterials, 27(14), 2874—2881.

[0069]

[0020] Temizel, N., Girisken, G. & Tas, A.C., 2011, ‘Accelerated transformation of brushite to octacalcium phosphate in new biomineralization media between 36.5°C and 80°C’, Materials Science and Engineering: C, 31(5), 1136—1143

[0070]

[0021] Heydari, Z., Mohebbi-Kalhori, D. & Afarani, M.S., 2017, ‘Engineered electrospun polycaprolactone (PCL) / octacalcium phosphate (OCP) scaffold for bone tissue engineering’, Materials Science and Engineering: C, 81, 127-132.

[0071]

[0022] Sugiura, Y., Munar, M.L., Ishikawa, K., 2018. Fabrication of octacalcium phosphate foam through phase conversion and its histological evaluation. Materials Letters 212, 28-31. https: / / doi.Org / 10.1016 / j.matlet.2017.10.051

[0072]

[0023] Sugiura, Y., Ishikawa, K., 2018. Effect of Calcium and Phosphate on Compositional Conversion from Dicalcium Hydrogen Phosphate Dihydrate Blocks to Octacalcium Phosphate Blocks. Crystals 8, 222. https: / / doi.org / 10.3390 / crvst8050222

[0024] Sugiura, Y., Ishikawa, K., 2019. Fabrication of pure octacalcium phosphate blocks from dicalcium hydrogen phosphate dihydrate blocks via a dissolution-precipitation reaction in a basic solution. Materials Letters 239, 143-146. https: / / doi.Org / 10.1016 / j.matlet.2018.12.093

[0073]

[0025] Sugiura, Y., Munar, M.L., Ishikawa, K., 2018. Fabrication of octacalcium phosphate block through a dissolution-precipitation reaction using a calcium sulphate hemihydrate block as a precursor. J Mater Sci: Mater Med 29, 151. https: / / doi.org / 10.1007 / sl0856-018-6162-l

[0074]

[0026] Tripathi, G. & Miyazaki, T., 2021, ‘Spontaneous fabrication of octacalcium phosphate: synthesis conditions and basic characterizations’, Bulletin of Materials Science, 44(2), 163.

[0075]

[0027] Teterina, A.Y., Smirnov, I.V., Fadeeva, I.S., Fadeev, R.S., Smirnova, P.V., Minaychev, V.V., Kobyakova, M.I., Fedotov, A.Y., Barinov, S.M., Komlev, V.S., 2021, ‘Octacalcium Phosphate for Bone Tissue Engineering: Synthesis, Modification, and In Vitro Biocompatibility Assessment’, Int. J. Mol. Sci. 2021, 22, 12747.

[0076]

[0028] Loebenstein, W.V., 1965, ‘Progress Report on Surface Studies of Natural and Synthetic Bone Mineral and Teeth’, National Bureau of Standards Report, NBS Project 311.05-11- 3I1056I, NBS report 9078.

[0077]

[0029] Shiwaku, Y., Anada, T., Yamazaki, H., Honda, Y., Morimoto, S., Sasaki, K., Suzuki, O., 2012. Structural, morphological and surface characteristics of two types of octacalcium phosphate-derived fluoride-containing apatitic calcium phosphates. Acta Biomaterialia 8, 4417^425. https: / / doi.Org / 10.1016 / j.actbio.2012.07.041

[0078]

[0030] Suzuki, O., Yagishita, H., Amano, T., Aoba, T., 1995. Reversible Structural Changes of Octacalcium Phosphate and Labile Acid Phosphate. J Dent Res 74, 1764-1769. https: / / doi.Org / 10.1177 / 00220345950740110801

[0079]

[0031] Hiratsuka, T., Sato, K., Aoba, T., 2002. Thermodynamic and Kinetic Interpretation of Enamel Mineralization: Octacalcium Phosphate (OCP) as an Inevitable Intermediate Phase. Jpn J Oral Biol 44, 48-65. https: / / doi.org / 10.2330 / joralbioscil965.44.48

[0080]

[0032] Suzuki, O., Kamakura, S., Katagiri, T., Nakamura, M., Zhao, B., Honda, Y., Kamijo, R.,

[0081] 2006. Bone formation enhanced by implanted octacalcium phosphate involving conversion into Ca-deficient hydroxyapatite. Biomaterials 27, 2671-2681. https: / / doi.Org / 10.1016 / j.biomaterials.2005.12.004

Claims

CLAIMS1. A method for the synthesis of octacalcium phosphate (OCP) comprises the following steps: a) heating both phosphate and calcium source separately in a range from 50 to 70 °C; b) adding heated calcium source to heated phosphate source and mixing together, wherein the Ca / P molar ratio is 1 to 2, temperature range is from 40 to 80 °C with pH range from 4.0 to 6.0; c) mixing the resulting mixture for 5 seconds to 10 minutes; d) separating the octacalcium phosphate precipitated in step c); e) drying the octacalcium phosphate obtained in step d).

2. The method according to Claim 1 wherein the calcium source is calcium acetate hydrate.

3. The method according to Claim 1 wherein the phosphate source is selected from the group consisting of sodium dihydrogen phosphate dihydrate or potassium dihydrogen phosphate.

4. The method according to any of the previous claims, wherein the pH of step b) is in the range from 4.5 to 5.0.

5. The method according to any of the previous claims, wherein the temperature of step b) is in the range from 50 to 70 °C.

6. The method according to any of the previous claims, wherein the mixing in step c) is performed for a duration of less than 5 minutes, preferably less than 3 minutes, or even less than 1 minute.

7. Octacalcium phosphate obtained by a method of any of the preceding claims.

8. Octacalcium phosphate with a specific surface area in a range from 69 to 85 m2 / g preferably 69 to 80 m2 / g or more preferably 70 to 80 m2 / g.

9. The octacalcium phosphate according to claim 8 for use in bone tissue regeneration or dental restoration.

Images