RU2700770C2 - Method for making matrices based on low-temperature modifications of calcium phosphates for bone engineering - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medicine and concerns composite materials for plastic reconstruction of damaged bone tissues. Proposed method for making matrices based on low-temperature modifications of calcium phosphate (CP) for bone engineering involves 3 stages. At first step, article is shaped to required degree by layer filling of granules or powders α-tricalcium phosphate (α-TCP) into a mold, the parameters of which correspond to parameters of the end product, and impregnation of each layer until complete impregnation with a solution of the composition: 1.5M sodium acetate, 0.15M L-glutamic acid, orthophosphoric acid to pH 4.75, obtaining a bulk matrix of 5–20 wt. % dicalcium phosphate dihydrate (DCPD), 80–95 wt. % tricalcium phosphate (TCP). At the second stage, the volumetric matrix formed at the first stage is maintained in a buffer solution of the following composition: 1.5M sodium acetate, 0.15M L-glutamic acid, 0.035M calcium chloride, orthophosphoric acid to pH 5.5, at temperature of 35±2 °C, at a weight ratio of material to liquid of 1/100, respectively, for minimum of 168 hours to obtain a bulk matrix of 80–100 wt. % DCPD and 0–20 wt. % TCP. At the third stage, the three-dimensional matrix formed at the second step is held in a buffer solution of the following composition: 1.5M sodium acetate, 0.035M calcium chloride, under conditions of temperature 35±2 °C, at material to liquid weight ratio of 1/100 for at least 168 hours respectively to obtain a bulk matrix of 80–100 wt. % octacalcium phosphate (OCF) and 0–20 wt. % TCF.

EFFECT: technical result is the technology of creating volumetric products based on low-temperature modifications of FC for use in medicine when performing operations for replacement of bone tissue defects.

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Description

The invention relates to materials used in medicine for bone engineering as matrices having biocompatibility and osteoconductivity and can be used in the technology of 3D molding and / or 3D printing of ceramic matrices. A method for layer-by-layer construction of bulk structures based on dicalcium phosphate dihydrate (DCPD) and octalcium phosphate (OCF) is proposed, which is based on the chemical transformation of the starting material under the action of a buffer system. By their strength characteristics and porosity, the samples are not inferior to their counterparts.

Calcium phosphate-based materials used in bone medicine as matrices have biocompatibility and osteoconductivity. The creation of materials based on DCPD and OKF is possible using methods based on the processes of phase transformations under the action of buffer solutions at temperatures not exceeding 37 ° C.

The advantages of materials based on DCPD and OCP can be attributed to a high rate of biodegradation in body fluids, the formation of material at physiological temperatures and the possibility of application in areas with low regenerative potential.

The closest to materials based on OKF according to the method of execution and the result of the proposed method is RF patent No. 2596504 A method for producing ceramics based on octalcium phosphate, in which the final product can be granules, blocks and coatings based on OKF. As an initial object, ceramic volumetric matrices based on α-tricalcium phosphate (α-TCP) can be used, obtained by sintering powders or granules, which can be transformed into blocks of the OKF composition according to the technology described in the patent.

The technology described in the patent allows the formation of granules up to 2 mm in size, as well as volumetric blocks of the composition of the OKF. Often, when performing operations to replace bone defects, the use of granules is not possible due to the lack of the possibility of their fixation in the defect volume, the inability to bear mechanical loads and the possibility of their washing out of the defect area by various biological flows. The creation of volumetric blocks of the OKF composition, according to the technology, is possible only when using the formed ceramic block of the α-TKF composition by pressing and sintering methods, which does not allow the formation of complex forms of matrices due to the impossibility of obtaining them by pressing.

The task to which our invention is directed is to create a technology for the layer-by-layer formation of complex-shaped volumetric matrices of the final OKF composition by chemical bonding of individual granules or powder particles under the action of buffer solution A _{g 4.75} and the possibility of applying the developed approach to the formation of volumetric matrices by three-dimensional inkjet printing. Also, modifying the composition of solutions for carrying out transformation processes by introducing calcium cations helps minimize the processes of primary dissolution of the initial FA due to the presence of cations necessary for crystallization in the initial solution, which contributes to the minimum change in the shape of the sample, which is possible due to dissolution of its surface.

The technical result of the invention is the technology of creating bulk products based on low-temperature modifications of FC for use in medicine when performing operations to replace defects in bone tissue, which is achieved by chemical bonding of individual particles (granules or powders) of α-TKF under the action of a buffer system with subsequent processing, resulting in to a change in the phase composition in the OCF, an increase in the total porosity and strength.

Porous samples were obtained using spherical granules of α-TCP (Komlev VS, Barinov SM, Koplik EV A method to fabricate porous spherical hydroxyapatite granules intended for time-controlled drug release // Biomaterials 2002. V. 23. I. 16. P. 3449 -3454) and buffer solutions. The formation of bulk ceramic samples is carried out due to the phase transformation of α-TCP, filled into a form corresponding to the parameters of the final product, under the action of an aqueous buffer solution of 1.5 M sodium acetate, 0.15 M L-glutamic acid adjusted to pH 4.75 _phosphoric acid (solution A _{g 4.75} ). A layer of α-TKF granules with a thickness of not more than 500 μm is _poured into the _mold and impregnated with a solution of _{4.75 g} until the granules are completely impregnated at room temperature 25 ± 2 ° С. After the procedure is repeated until the form is completely filled. The result of the interaction of the material of the granules and the buffer liquid is the formation of crystals of DCPD, holding individual granules together and giving strength to the final matrix. The compressive strength of the final samples does not exceed 2 MPa, and the composition corresponds to 5-20 mass. % DKFD, 80-95 mass. % TCP.

Further exposure of the formed sample in a buffer solution of 1.5 M sodium acetate, 0.15 M L-glutamic acid and 0.035 M calcium chloride adjusted to pH 5.5 with _phosphoric acid (solution A _{g 5.5} ), with a sample weight / mass ratio liquid equal to 1/100, for a minimum of 168 hours, at a temperature of 35 ± 2 ° C and constant low-intensity stirring in a shaker incubator. This processing step is aimed at increasing the compressive strength due to the complete transformation of the residual α-TCP into DCFD. Upon completion of the process, the compressive strength increases to 12 MPa, the composition corresponds to 80-100 mass. % DKFD and 0-20 mass. % TCP.

The creation of a matrix of the OKF composition is realized by exposing the bulk DCPD product in a buffer solution of 1.5 M sodium acetate and 0.035 M calcium chloride (solution A), with a sample mass / liquid mass ratio of 1/100, for a minimum of 168 hours, at temperature 35 ± 2 ° С and constant low-intensity stirring in a shaker incubator. Due to the processes of recrystallization and diffusion, an OKF structure is formed on the basis of the initial DCPD, while the shape of the final sample does not change, the minimum compressive strength is 8 MPa, and the composition of the sample corresponds to 80-100 mass. % OKF and 0-20 mass. % TCP. The application of the technology steps is possible for the formation of bulk ceramic matrices by the method of powder three-dimensional printing, the initial material for which will be granules of α-PCF with a diameter of up to 100 μm, and the buffer solution with a binder liquid (ink).

An example of obtaining sample No. 1. The formation of the volumetric matrix of the composition of the OKF takes place in three stages:

Stage 1. Granules of α-TCP fractions of 100-300 μm are poured into a cylindrical layer with a thickness not exceeding 0.5 mm Using a 1 ml syringe, droplet impregnation of the granule layer is carried out with buffer solution A _{g 4.75} at room temperature 25 ± 2 ° C until the liquid is distributed throughout the entire volume of the layer. The next layer of granules is backfilled with a thickness not exceeding 0.5 mm, and also impregnated with a solution. The procedure is repeated until the required height of the sample is reached, after which the sample is removed from the mold and dried at 35 ° C for 24 hours. Then ten times washing in distilled water followed by drying at 35 ± 2 ° C follows. The result of the stage is a volumetric matrix of 5-20 mass. % DKFD, 80-95 mass. % α-TCP. An example of a sample obtained by this method and its microstructure are presented in Figure 1. Figure 1 (A) shows cylindrical samples obtained by the proposed technology using α-TCP particles of various sizes. Figure 1 (B) shows the microstructure of samples subjected to chemical bonding, from which it is seen that the initial spherical granules dissolve in the process, and new plate-shaped DCPD crystals form on their surface, which grow from the surface toward adjacent granules, growing inside the granule material thereby bonding individual particles, giving the final shape and strength.

Stage 2. Formed sample composition of 5-20 mass. % DKFD, 80-95 mass. % α-TCP is placed in buffer A _g5.5 , containing sodium acetate, L-glutamic acid, calcium chloride and phosphoric acid, in the ratio of 1 g of sample weight per 100 ml of solution, and maintained with constant stirring and a temperature of 35 ± 2 ° C in a shaker incubator. This is followed by a tenfold washing in distilled water, followed by drying at 35 ± 2 ° C. The result of this stage is a volumetric matrix of 80-100 mass. % DKFD and 0-20 mass. % TCP. The microstructure of the final sample is shown in Figure 2 (A, B).

Stage 3. Sample composition of 80-100 mass. % DKFD and 0-20 mass. % TCF is placed in buffer solution A, containing sodium acetate and calcium chloride, in a ratio of 1 g of the sample mass per 100 ml of solution, and maintained with constant stirring at a temperature of 35 ± 2 ° С in an incubator shaker. This is followed by a tenfold washing in distilled water, followed by drying at 35 ± 2 ° C. The result of the stage is a volumetric matrix of 80-100 mass. % OKF and 0-20 mass. % TCP. The microstructure of the final sample is shown in Figure 3 (A, B).

Claims (1)

A method of manufacturing matrices based on low-temperature modifications of calcium phosphates for bone engineering, characterized in that it includes 3 stages, the first of which gives the desired shape to the product by layer-by-layer filling of granules or powders of α-tricalcium phosphate (α-TCP) into a form whose parameters correspond to the parameters the final product, and soaking each layer until it is completely impregnated with a solution of the composition: 1.5 M sodium acetate, 0.15 M L-glutamic acid, phosphoric acid to a pH of 4.75, to obtain a volumetric matrix composition 5-20 wt.% dicalcium phosphate dihydrate (DCPD), 80-95 wt.% tricalcium phosphate (TKF); at the second stage, the bulk matrix formed at the first stage is maintained in a buffer solution of the composition: 1.5 M sodium acetate, 0.15 M L-glutamic acid, 0.035 M calcium chloride, phosphoric acid to pH 5.5, at a temperature of 35 ± 2 ° C, with a ratio of the mass of material to liquid 1/100, respectively, for a minimum of 168 hours to obtain a volumetric matrix of 80-100 wt.% DKFD and 0-20 wt.% TKF; at the third stage, the bulk matrix formed at the second stage is exposed in a buffer solution of the composition: 1.5 M sodium acetate, 0.035 M calcium chloride, at a temperature of 35 ± 2 ° C, with a ratio of the mass of material to liquid 1/100, respectively, for a minimum of 168 hours to obtain a bulk matrix of 80-100 wt.% octacalcium phosphate (OCF) and 0-20 wt.% TCF.

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