RU2580728C1 - Method of producing single-phase crystalline silicon-substituted hydroxyapatite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a process of preparation of crystalline silicon-substituted hydroxyapatite (Si-HA), which can be used in orthopedics and dentistry. Si-HA is received by deposition method from extracellular fluid model solution by preparing a solution with the following composition: CaCl₂ - 3.7424 g, MgCl₂ - 0.6092 g, K₂NRO₄ - 2.8716 g, NaHCO₃ - 4.5360 g, Na₂SO₄ - 0.0144 g, NaCl - 8,8784 g at pH 7.40±0.05, by adding to it of modified sodium silicate in a molar ratio of Ca/ (P + Si) 2.00÷2.50 in the shape of Na₂SiO₃, by letting it settle for 48 hours, by filtering, washing and drying at a temperature of 80±5 °C for 5 hours.

EFFECT: invention allows to obtain a monophasic nanocrystalline (with an average crystal size of 6-7 1/10 nm) Si-HA having enhanced bioactivity in a medium that simulates the extracellular fluid of a human body.

1 cl, 5 dwg, 3 tbl

Description

The invention relates to medicine, namely to a method for producing crystalline silicon-substituted hydroxylapatite, which can be used in orthopedics and dentistry.

Due to the fact that hydroxylapatite Ca ₁₀ (PO ₄ ) 6 (OH) ₂ (HA) is a mineral analogue of the bone component, materials based on them are used to create artificial substitutes for human bone tissue. One way to solve this problem is the synthesis of nanosized hydroxylapatite followed by heat treatment below the sintering temperature. Therefore, to obtain nanoscale HA, methods based on the precipitation of hydroxylapatite from alkaline aqueous solutions of reagents containing calcium ions and phosphate ions in a stoichiometric ratio are most widely used today. [one].

Along with this, the results of recent clinical trials have shown that the prepared materials using HA with advantages have a number of disadvantages: low rate of bioresorption and osteoinduction, high value of the observed activation energy. Chemical modification of hydroxylapatite is the main method for controlling the biological activity of a material made on its basis. The introduction of silicon, in contrast to unmodified GA, causes a significantly higher biological response, which may be due to the Si-inducing change in the properties of the material. When silicon is introduced into the HA crystal structure, the effective charge of the material surface changes, which is associated with the specific arrangement of silicate ions relative to phosphate ions in the crystal lattice of silicon-substituted hydroxylapatite (Si-HA). This was confirmed in tests conducted in vivo, where it was found that protein adsorption, attachment of osteoblast cells, specific cellular reactions (type I collagen synthesis, activation of alkaline phosphatase) and, accordingly, mineralization of young bone matrix [2, 3]. In view of the data obtained, the modification of GA is a promising and relevant task. Si-HA can be represented by the formula: Ca ₁₀ (PO ₄ ) ₆ -x (SiO ₄ ) x (OH) ₂ -x,

where x is the degree of substitution

A known method of producing silicon-substituted hydroxylapatite by precipitation from an aqueous solution of reagents [1]. When obtaining silicon-containing hydroxylapatite by the method of precipitation from aqueous solutions, the following reactions are most often used:

10Са (ОН) ₂ + (6-х) Н ₃ PO ₄ + xSi (OR) ₄ → Са ₁₀ (РО ₄ ) 6-x (SiO ₄ ) x (OH) ₂ -х +

+ 4xROH + (18-x) H ₂ O,

where R = Et, n-Pr, Ac.

The synthesis is carried out at temperatures of 60 ÷ 80 ° C, pH 9 ÷ 11 is supported by an ammonia solution, sometimes an inert gas is used to suppress the absorption of carbon dioxide synthesis product from air. The material is prepared according to GA stoichiometry, provided that silicon replaces the position of phosphorus in the crystal lattice, and the molar ratio Ca / (P + Si) is 1.67. The HA precipitate was heat treated at 1100 ° C for 2 hours in air. The disadvantage of this method, on the one hand, is the low degree of substitution of silicon x <1, which corresponds to a silicon content of 0.8-1.5 wt.% In the material, and on the other hand, the appearance of impurity phases, for example, calcium oxide or tricalcium phosphate after heat treatment when using higher degrees of substitution, for example, for x> 1.

The closest in technical essence and the achieved result is the method (RF patent No. 25000040) for producing a monophasic crystalline silicon-substituted hydroxylapatite, which involves the synthesis of Si-HA by precipitation at a pH of at least 9 from reagents containing phosphoric acid, calcium hydroxide and tetraethylorthosilicate. Moreover, the reagents are introduced into the reaction mixture, provided that the molar ratio of Ca / P in the range from 2.0 to 2.5. A composition is prepared from a 0.08-0.16% aqueous solution of calcium hydroxide and tetraethylorthosilicate. A solution of orthophosphoric acid with 10-20% concentration is poured at a rate of 0.2-0.8 ml / min, per liter of an aqueous solution of calcium hydroxide / tetraethylorthosilicate composition. Settled to complete the phase formation process, precipitate is isolated and dried. Heat treatment is carried out at a temperature not lower than 300C, but not more than 400C. This method allows to obtain polycrystalline pure or monophasic silicon-substituted hydroxylapatite, consisting of particles with a size of 0.010-0.012 μm (or 10-12 nm, respectively), having a relatively high dissolution rate and the ability to extract sufficient amounts of silicon in solution. The advantage of silicon-substituted hydroxylapatite of this solution is its higher solubility compared to ceramic silicon-substituted hydroxylapatite and ordinary unmodified hydroxylapatite, as well as a higher yield of silicon upon contact with the solution. When keeping silicon-substituted hydroxylapatite in physiological saline, the concentration of calcium ions remains unchanged or increases. This compares favorably with hydroxylapatites with a low level of silicon substitution, for which the calcium content in physiological saline decreases during the same period of time. The advantages of this Si-HA include the absence of side phases in the form of calcium oxides, tricalcium phosphates (TCF) during calcination at high temperatures. The main disadvantages of this method is that the synthesis is carried out at pH far from the normal physiological values of the human body. Also, this sample does not repeat the structure of the human bone, there is no carbonate group in it. In the synthesis, tetraethoxysilane (TES) is used as a carrier reagent for silicon ions, which forms ethyl alcohol during hydrolysis, resulting in poisoning of living tissues, in contrast to sodium silicate, in which sodium hydroxide will be the hydrolysis product.

An object of the invention is to provide a method for producing monophasic nanocrystalline silicon-substituted hydroxylapatite with increased bioactivity in a medium simulating human extracellular fluid.

The specified technical result is achieved by the fact that the proposed method for producing a monophasic crystalline silicon-substituted hydroxylapatite by precipitation from a model solution of extracellular fluid, in which a solution of the composition is prepared: CaCl ₂ - 3.7424 g, MgCl ₂ - 0.6092 g, K ₂ HPO ₄ - 2.8716 g, NaHCO ₃ - 4.5360 g, Na ₂ SO ₄ - 0.0144 g, NaCl - 8.8784 g at pH 7.40 ± 0.05, add modified sodium silicate in a molar ratio Ca / (P + Si) 2.00 ÷ 2.50 in the form of Na ₂ SiO ₃ , defend for 48 hours, carry out filtering, washing and dry at t = 80 ± 5 ° C for 5 hours.

The method includes the following new features:

- synthesis is made from a solution as close to physiological as possible;

- the pH of the medium during synthesis corresponds to physiological values;

- sodium silicate is used as a silicon promoter;

- to increase bioactivity, there is no need to conduct heat treatment.

The mode of sedimentation for 48 hours, filtration, washing and drying at t = 80 ± 5 ° C for 5 hours was selected experimentally based on the condition of complete removal of adsorption water. After this, the precipitate was separated from the cake filter into an agate mortar and ground with a pestle until a homogeneous powder was obtained.

Moreover, the inventive method allows to obtain:

stoichiometric monophasic Si-HA with an average crystal size of 6.0-7.1 nm, having increased bioactivity;

stable monophasic product of the formula Ca ₁₀ (PO ₄ ) ₆ -x (SiO ₄ ) x (OH) _2- x, where 0.50 <x <5.00% wt.,

One of the problems in Si-HA synthesis is the selection of the mass content of silicon in the sample.

The XRD results showed that all samples synthesized in the medium of a model solution of extracellular fluid with varying concentrations of silicate ions are single-phase and are hydroxylapatite. In FIG. Figure 1 shows the diffraction patterns of samples of hydroxylapatite modified with Na ₂ SiO ₃ : I - C Si ref. 0.5%; II - With Si, ref 2.5%; TPP: III - With Si, ref 0.5%; IV - With Si, ref 2.5%. These diffraction patterns contain HA reflections at 25.8 ° (002), 31.7 ° (211), 32.2 ° (112) and 32.9 ° (300) (Fig. 1). It should be noted that the diffraction patterns corresponding to solid phases with different sources of silicate groups of Na ₂ SiO ₃ have a similar appearance. The crystallite sizes of the obtained unmodified HA were 6.3 nm, for Si-HA - 6.0–7.1 nm, which indicates the formation of compounds in the nanocrystalline state.

Table 1 shows the concentration of ions in model solutions that are close in electrolyte composition to extracellular fluid, mmol / L. This table is used for the preparation of synthesis solutions.

Table 2 presents the crystal lattice parameters of the formed solid phases.

These parameters are increased in comparison with unmodified hydroxylapatite (HA), which confirms the possible replacement of various sized orthophosphate ions with a silicate ion (Si-O distances = 1.66 Å, P-O = 1.55 Å [4]). An increase in the parameter indicates that the silicate ion predominantly occupies the position of the phosphate ion in the structure of HA, and not the hydroxyl ion [5].

In FIG. 2. The IR spectra of hydroxylapatite samples modified are presented: 1 - Na ₂ SiO ₃ C Si ref 0.5%; 2 and 3 - TPP С Si ref. 0.5 and 2.5%. The IR spectra of the samples obtained in the presence of silicate ions contain absorption bands characteristic of hydroxylapatite.

имеют высокое сродство к молекулам воды, вследствие чего происходит гидратация. Ввиду того что ГА синтезирован в воздушной среде, в процессе его образования из атмосферы воздуха сорбируется углекислый газ и в решетке локализуются ионы карбоната в положении фосфатного иона, которым в ИК-спектрах соответствуют полосы поглощения деформационных колебаний С-O связей иона

при 875 см^-1 и валентных колебаний при 1422-1457 см^-1 [6].The structure of the HA is determined by the following bands: 1040-1080 (ν ₃ ), 960, 840 (ν ₂ ), 602, 574 (ν ₄ ) and 473 (ν ₂ ) cm ^-1 , corresponding to vibrations of phosphate groups, a wide band at 3440-3570 cm ^-1 corresponds to deformation vibrations of OH ^- groups and stretching vibrations of adsorbed water. The high intensity of this peak in modified GA is due to the fact that

have a high affinity for water molecules, resulting in hydration. Due to the fact that GA is synthesized in air, carbon dioxide is sorbed from the atmosphere during its formation and carbonate ions are localized in the lattice in the position of a phosphate ion, which correspond to absorption bands of deformation vibrations of CO bonds of the ion in the IR spectra

at 875 cm ^-1 and stretching vibrations at 1422-1457 cm ^-1 [6].

на

в структуре ГА, что приводит к искажению

тетраэдра, в результате чего происходит изменение параметров элементарной ячейки. Таким образом, данные ИК-Фурье-спектроскопии находятся в согласии с результатами РФА.In the IR spectra there is an absorption band of low intensity vibration of the bonds of the silicate group at 511 cm ^-1 , due to deformation vibrations of Si-O bonds. The absorption band of the vibration of the Si — O bond at 945 cm ⁻¹ overlaps with the absorption band corresponding to the vibration of the P — O bond at 960 cm ⁻¹ . The presence of these signals on the spectrum indicates the substitution

on

in the structure of GA, which leads to distortion

tetrahedron, as a result of which the unit cell parameters change. Thus, the data of IR Fourier spectroscopy are in agreement with the results of XRD.

Table 3 presents data on the concentration of silicate ions in the solid phase, the compositions of the solid phases obtained by chemical analysis of the supernatant.

Their content increases significantly with an increase in the initial concentration of silicate ions to 5% in the system. The Ca / P ratio in the synthesized compounds exceeds a preset value of 1.67, which is typical for stoichiometric hydroxylapatite, and corresponds to the phase of calcium-excess HA. This indicates a decrease in the amount of phosphate ions in the obtained solid phases, which, in our opinion, is associated with the replacement of phosphate groups by silicate groups.

In FIG. Figure 3 shows the kinetic curves of the dissolution of Si-HA in hydrochloric acid at t = 37 ° C. The bioactivity of the material was checked by dissolving the same sample weighed in different solvents (HCl, 0.9% NaCl, Tris-HCl buffer) at 37 ° C (Fig. 3-5). It was found that samples in which sodium silicate is used in the synthesis have greater resorbability than a material that does not contain an addition of silicate ions.

Literature

1. Soin A.V., Evdokimov P.V., Veresov A.G., Putlyaev V.I. Synthesis and study of anion-modified apatites // International scientific journal "Alternative Energy and Ecology" - 2007 - T. 1 - No. 45 - p. 130-132.

2. Pietak A.M., Reid J.W., Stott M.J., Sayer M. Silicon substitution in the calcium phosphate bioceramics // Biomaterials 2007; 28: 4023-4032.

3. Portera A.E., Patela N., Skepperb J.N., Besta S.M., Bonfielda W. Comparison of in vivo dissolution processes in hydroxyapatite and silicon-substituted hydroxyapatite bioceramics // Biomaterials 2003; 24: 4609-4620.

4. Solonenko A.P., Golovanova O.A. Thermodynamic modeling of the processes of formation of calcium orthophosphates. // J. Butlerov Communications. 2011.Vol. 24 No. 2. S. 106-112.

5. Malovskaya E.A., Golovanova O.A., Panova T.V., Gerk S.A., Osintsev V.A. Crystallization of calcium phosphates from prototypes of biological fluids on bone samples. // J. Butlerov Communications. 2013.Vol. 36 No. 10. S. 21-28.

6. Solonenko A.R., Golovanova O.A., Hydroxyapatite-Brushite ixtures: Synthesis and Physicochemical Characterization // J. Inorganic Chemistry 2014, Vol. 59, No. 1, pp. 12-20.

Claims (1)

A method of obtaining a monophasic crystalline silicon-substituted hydroxylapatite by precipitation from a model solution of extracellular fluid in which a solution of the composition is prepared: CaCl ₂ - 3.7424 g, MgCl ₂ - 0.6092 g, K ₂ HPO ₄ - 2.8716 g, NaHCO ₃ - 4.5360 g, Na ₂ SO ₄ - 0.0144 g, NaCl - 8.8784 g at pH 7.40 ± 0.05, add modified sodium silicate in a molar ratio Ca / (P + Si) of 2.00 ÷ 2.50 in the form of Na ₂ SiO ₃ , stand for 48 hours, filter, wash and dry at t = 80 ± 5 ° C for 5 hours.

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