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This paper compares the synthesis of tricalcium phosphate (TCP) (β-Са3(РО4)2) and Са3–хNa2х(PO4)2 substituted calcium phosphates (x = 0.5 and 1: solid solution A and β-CaNaPO4 sodium rhenanite, respectively) via precipitation and by a sol–gel process in ethylene glycol (EG). We have determined the phase composition of the synthesized phosphate powders and studied their micromorphology. Slow addition of ammonium (di)hydrogen phosphate to calcium ethylene glycolate at temperatures above 110°C leads to precipitation of crystalline β-TCP (with an average particle size under 200 nm) from the solution. In the synthesis of sodium calcium substituted phosphates, solvolysis of the sodium phosphates prevents congruent precipitation and requires correction of solution composition. The powder precipitated from a solution of sodium ethylate and calcium ethylene glycolate in EG (molar ratio above 2) crystallizes at 800°C in the rhenanite structure (particle size under 500 nm). In sol–gel synthesis, triethyl phosphate (TEP) was used as a phosphate component. For gelation, we used TEP solvolysis in EG and the formation of ester polymers as a result of reaction between citric acid and EG (Pechini process). The gel thermolysis products obtained between 600 and 800°C contained considerable amounts of residual carbon. The particle size characteristics and sinterability of the calcium phosphate powders precipitated from solutions in EG allow them to be used for filling photosuspensions that are employed in the fabrication of osteoconductive bioceramics with the use of stereolithographic 3D printing.

The problem of producing biodegradable implants based on calcium phosphate porous ceramics is being solved. Highly porous ceramics with a uniform distribution of pores of a specified size is fabricated by slip casting from a suspension containing tricalcium phosphate Ca3(PO4)2 and polymeric granules 50–100 μm in size in amounts of 20 and 50 vol %, respectively, followed by heat treatment. For the chosen sintering parameters, the porosity of the ceramics is not lower than 40% and its tensile strength and biocompatibility satisfy the corrsponding requirements.

In view of the wide use of titanium dioxide, more and more approaches to 3D printing of materials based on it have recently been developed, the most promising if which remains stereolithography 3D printing owing to high resolution and low power consumption. It was studied how the degree of crystallinity of titanium dioxide affects both the properties of the obtained suspensions for stereolithography 3D printing, and the sinterability of the printed bulk materials. It was shown that the use of amorphous titanium dioxide as a precursor increases the fraction of the inorganic phase in the suspension, which leads to a significantly smaller shrinkage in sintering. Despite the high critical energy of polymerization and the low photosensitivity of the produced suspensions, the use of amorphous titanium dioxide enabled one to completely remove the polymer binder by high-temperature annealing without significant deformation of the printed samples.

The review covers problems related to development and application of a new type of “smart” medical materials, mainly, for regeneration of bone tissue that are capable of creating additional stimuli influencing the regeneration process. Application of ferroelectric and magnetoelastic materials is discussed, including their use as sensors and actuators. Physical and materials science principles of development, along with examples of using composite magnetoelectric materials of the piezoelectric/magnetoelastic type as magnetically controlled scaffolds creating local electric fields, are analyzed.

Technologies for the 3D printing of metallic powders are being increasingly extensively used around the world as alternatives to casting and machining to manufacture components of complex shapes and prototypes. Silicon-alloyed aluminum alloys are the most widely used materials in the selective laser melting technologies, which is caused by the price of these alloys and their high manufacturability for the layer-by-layer fused deposition, owing to their low susceptibility to hot cracking under thermal and shrinkage stresses. High rates of cooling the melt facilitate the formation in the material of ultradispersed silicon-containing phases, which results in increased strength. In the article, exemplified by two cast alloys (AK7ch and AK9ch), the speeds of the process of building up the products by the selective laser melting technology have been determined at a laser-beam power of 300 and 325 W and an energy density within the range 89–32 J/mm3. It is shown that, for the AK9ch alloy, lower porosity values are achieved within the investigated energy density range when compared with the AK7ch alloy and better mechanical properties of the alloy with a higher silicon content are achieved within the range of lower laser-beam energy densities than for the alloy with a lower silicon content. The mechanical properties of the materials produced under the optimal selective laser melting conditions comply with the most stringent requirements for the mechanical characteristics of the castings of the AK7ch alloy upon heat treatment.

Hybrid materials designed for the regeneration of bone defects and consisting of a resorbable ceramic base (tricalcium phosphate, TCP) coated with a layer of hydrophilic biodegradable polymer have been developed. Biocompatibility of the ceramics was evaluated through in vitro tests using cultures of human skin fibroblasts. To increase the therapeutic potential, the created model structures were saturated with the antitumor drug doxorubicin within the composition of the coating of UV-polymerizable hydrogel based on polyacrylamide/polyethylene glycol diacrylate (PAA/PEGDA). The kinetics of drug release was studied by spectrophotometry using saline. The studied hybrid constructs had low cytotoxicity. Saturation of the structures with the antitumor drug resulted in its prolonged release. The results demonstrate the technological feasibility of creating osteoconductive implants based on calcium phosphates suitable for local delivery of antitumor drugs.

We have assessed the informativeness of X-ray diffraction patterns in the form of a halo, characteristic of metallic alloys prepared by liquid quenching (melt spinning) (using an Fe78P20Si2 alloy as an example) and oxide films grown on unheated substrates by ion beam sputtering of targets with an appropriate composition (LiNbO3 and Ca10(PO4)6(OH)2). Simulation results for X-ray diffraction patterns of expected crystalline phases with allowance for the size effect in diffraction demonstrate that a model halo agrees well with the halos observed in X-ray diffraction patterns of the samples under study. Observed correlations lead us to conclude that, inherent in rather large crystals, coherence of elastically scattered waves is lost in the structures considered here because of the random mutual orientation of crystalline nuclei of the corresponding phases with ultimately small dimensions. For this reason, translational symmetry, limited by the ultimately small dimensions of mutually misoriented crystallites, is the most transparent characteristic of the nature of such (quasi-amorphous) structures for systems with strong interatomic bonding.

Methods were presented to synthesize tricalcium phosphate Ca3(PO4)2 (TCP), calcium pyrophosphate Ca2P2O7 (CPP), and TCP/CPP composites in nonaqueous media in the temperature range 25–300°C. It was shown that solvo- and ionothermal synthesis methods can give phosphates of complex composition. The phase composition, micromorphology, and particle size distribution of the obtained powders and their evolution during synthesis were described. The synthesis at 110°C while slowly adding ammonium hydrophosphate to a solution of calcium ethylene glycolate in ethylene glycol gives a nanocrystalline β-TCP powder with an average size of aggregates of platy crystals of 150 nm and a distribution width of 50 nm. The morphological characteristics and sinterability of the powders synthesized in solutions in ethylene glycol make them suitable for producing macroporous ceramics by stereolithography 3D printing methods.

The synthesis of double phosphates based on calcium and alkali metals from different two-phase mixtures was studied. The phase relationships in the CaO–K2O–P2O5 and CaO–Na2O–P2O5 system were clarified, especially the phase transition temperature in potassium rhenanite CaKPO4. It was shown that some compounds that are mentioned in the literature, in particular, CaK2P2O7, CaNa2P2O7, CaK4(PO4)2, and CaNa4(PO4)2, cannot be obtained at 1000–1200°C at normal pressure. The densification and recrystallization were investigated during the reaction sintering of selected two-phase mixtures. Reaction sintering of a mixture of Ca3(PO4)2 and CaK4(PO4)2 gives CaKРO4 ceramic with a density of 78% (linear shrinkage of the sample is 5%); when sintering a mixture of K2CO3 and Ca2P2O7, the density of ceramic was 62% with a linear shrinkage of 15%. The reaction sintering of sodium-containing mixtures made it possible to obtain dense ceramics (density above 90%, linear shrinkage more than 6.5%) from a mixture of CaNa4(PO4)2 and Ca3(PO4)2. The experimental features of the reaction sintering of calcium and potassium/sodium double phosphates are discussed from the point of view of volume change during the course of the reaction. Another aspect that determines the density and microstructure of ceramics is the phase transformation of α → β in alkali metal rhenanites CаMPO4.

The powder of hydrated calcium pyrophosphate Ca2P2O7 ⋅ xH2O containing potassium chloride KCl as a by-product was synthesized at room temperature from 0.5 M aqueous solutions of calcium chloride CaCl2 and potassium pyrophosphate K4P2O7 at a ratio of Ca/P = 1. The particle size of the powder with a shape close to isometric was 100–200 nm after synthesis and 0.5–1.0 μm after heat treatment at 700°C. Upon heating, KCl was retained in the powder up to 600°C, participating in the formation of new phases: potassium/calcium double pyrophosphate K2CaP2O7 and chlorapatite Ca3(PO4)3Cl in the range of 500–700°C and then K-substituted tricalcium phosphate Ca10K(PO4)7 at 800°C. The hydrated calcium pyrophosphate powder containing KCl as a by-product can be recommended for the manufacture of biocompatible multiphase ceramic materials, and the powder after heat treatment at 800°C can be used to obtain biocompatible materials using chemical bonding reactions.

Hydrogels filled with CaHPO4 · 2H2O and Ca8(HPO4)2(PO4)4 · 5H2O were synthesized from the acrylate derivatives of poly(ethylene glycol) by the photopolymerization method. The swelling behaviour of the filled and unfilled hydrogels in water was studied. The solubility of the photoinitiator in water and in the monomers was estimated.

Production of ceramic materials based on various calcium phosphates is a multistep process, which includes preparing a substance in a splintered state (powder or suspension), molding a sample or product using one of the available methods, and sintering. A given phase composition, microstructure, and shape of the sample are formed during sintering, which are properties necessary for the intended use of the material. All stages of the production of phosphate-based materials are performed, as a rule, by predetermined chemical reactions. The chemical transformations occurring at different stages of the production of ceramic materials based on calcium phosphates are examined in the present review.

—The substructure of hydroxyapatite ceramics produced by cold-pressing nanocrystalline hydroxyapatite powder, followed by annealing for 1–12 h at 1150°C, has been studied by transmission electron microscopy, and the hardness and modulus of elasticity of the ceramics have been determined using nanoindentation. The results demonstrate that the compaction process leads to coalescence of nanoparticles of the starting powder, which ensures a minimum hardness of the compact with a 50% relative density. The hardness and modulus of elasticity of HA ceramics increase with increasing firing time as a consequence of improvement of its substructure (an increase in grain size and a decrease in pore size and density).

—A standard series of ceramic scaffolds for bone tissue regeneration with Kelvin architecture was developed, providing matrix water permeability not less than 900 Darcy and relative rigidity of matrices of not more than 0.2. The possibility of producing bioceramic scaffolds is shown using stereolithographic 3D printing of light-cured slurries containing a mixed calcium sodium phosphate Ca2.5Na(PO4)2 composition. A production technology of bioceramic scaffolds is developed and tested, including the development of photocurable slurries; 3D printing modes are also worked out, as well as conditions of heat treatment of printed models and sintering. The proposed methods of stereolithography formation followed by heat treatment of printed models make it possible to produce ceramic scaffolds with lateral resolution no worse than 50 μm and 50 μm layering. The dimensions of the bioceramic scaffold differ from the reference dimensions of the initial model by no more than 10%; the degree of macroporosity is not less than 70% and the pore size is 500 μm. It is shown that the obtained bioceramic scaffolds are compatible with the human fibroblast cell culture, are not cytotoxic, do not contain components inhibiting fibroblast adhesion, spreading, and proliferation, and can be used in tissue engineering.

A new alloplastic high-permeable material based on tricalcium phosphate with Kelvin architectonics created by stereolithographic 3D-printing was studied in vivo. A monocortical defect of the femur was modeled in rats and the material was implanted into the defect area. In 24 weeks, the animals were euthanized and histological examination of the defect area was performed. One femur fracture with fixator migration was recorded after implantation of the studied material and the reference chronOS synthetic material. The studied material demonstrated better osteoconductive properties then traditional osteoplastic material, which was seen from greater number of bone trabeculae and their area in the defect area.

The introduction of 10 – 50% (by weight) brushite powder, preheated at 50° and then fired at 1200°C, into a permeating suspension based on hydroxyapatite powder heat-treated at 800°C results in partial decomposition of hydroxyapatite to the α- and β-modifications of tricalcium phosphate. The presence of a tricalcium phosphate phase in calcium phosphate foam ceramic promotes an increase of the porosity from 40 to 60% and the resorption with significant static strength reduction from 3 – 7 to 0.3 MPa.

—A new method for obtaining the nanoscale hydroxyapatite with low crystallinity from aqueous solution of calcium malate Ca(C4H5O5)2 and ammonium hydrophosphate (NH4)2HPO4 at room temperature, molar ratio Ca/P = 1.67, and pH 9 was proposed. After synthesis and drying, the sample was a transparent composite with a matrix from the by-product of the reaction of organic nature containing nanoscale particles of calcium phosphate. The phase composition of the sample after thermal treatment at 900°C was represented by calcium hydroxyapatite.

The process of removing an organic component from composites (photopolymer/calcium phosphate) with complex architecture, which are obtained by 3D-printing in order to create personalized bioceramic implants, was studied. Ceramic materials with complex pore-space organization were obtained by stereolithographic printing. It is shown that the degree of polymerization of the composite influences the final density of the calcium phosphate ceramic materials with complex architecture.

The mechanical characteristics are studied for macroporous composite implants on the basis of β‑Ca/PO4)2/polylactide and β-Ca/PO4)2/polycaprolactone obtained by means of thermal-extrusion 3D printing. The effect of the degree of filling exerted on the strength, Young’s modulus, and the characteristics of the material destruction is described for the polymer, as well as for the three-dimensional structure filled with phosphate cement.

An a priori approach for the analysis of the architecture of osteoconductive bioceramic implants has been proposed. The most permeable products have been achieved in the case of the Kelvin architecture and the gyroid. The promising implant architecture is chosen to be the Kelvin model with a porosity of 70% and the pore sizes of 750 μm. The permeability of this architecture calculated to be 987 darcy for water approaches the value of trabecular bone tissue. It is found that the most rigid model among the architectures studied is the model with diamond architecture, while the most compliant are the Kelvin model and gyroid.

In this work, biocomposites based on hydrogels filled with calcium phosphates were fabricated using DLP method of 3D printing for the treatment of bone defects. The possibility to tune the functional properties of hydrogels such as degradation, swelling, and mechanical behavior by using a mixture of monomers with different functionality and different calcium phosphates was shown. Mechanical properties, photopolymerization, swelling behavior, and microstructure of hydrogels based on a mixture of poly(ethylene glycol) methacrylate/poly(ethylene glycol) diacrylate (PEGMA/PEGDA) monomers with different composition were studied. It was found that the usage of α-tricalcium phosphate (α-TCP) powder as a filler for hydrogels allowed to increase the filler fraction up to 60 ​wt% in comparison with octacalcium phosphate (OCP) and brushite (10 ​wt%) without significant thickening of photosuspension for DLP printing. Finally, the main parameters of DLP printing for biocomposites based on PEGMA/PEGDA hydrogels were found, and the macroporous biocomposite filled with 60 ​wt% α-TCP with gyroid structure was obtained.

The fabrication method of macroporous ceramics based on Ca3(PO4)2 from photocured water-oil emulsions has been proposed. The conditions for obtaining porous ceramic structures with a pre-determined pore size in the range of 2—50 μm and their volume of more than 56% were determined. The main problems of this method are discussed, and the solution methods are proposed. The strength characteristics of the created porous ceramic structures are described.

Powder mixtures prepared by mechanical activation from synthetic hydrated acidic calcium phosphates Ca(H2PO4)2 · H2O and CaHPO4 · 2H2O were used to obtain resorbable ceramic in the system Ca (PO3)2–Ca2P2O7. The phase composition of the ceramic after firing in the interval 700 – 1000°C was represented by biocompatible and bioresorbable phases: calcium polyphosphate Ca(PO3)2, tromelite Ca4P6O19, and calcium pyrophosphate Ca2P2O7. The obtained materials can be used to fabricate resorbable implants for regenerative treatment of defects of bone tissue.

Based on theoretical and experimental analysis of ionic equilibria in buffer solutions, we have found conditions for octacalcium phosphate (OCP), Ca8(HPO4)2(PO4)4 ∙ 5H2O, synthesis. Succinate-substituted OCP, Ca8(HPO4)2–хSucx(PO4)4 ∙ 5H2O, with x = 0.8–0.9 has been synthesized at pH 5.5 and t = 60°C in 3 h via α-TCP hydrolysis in a 0.25 M succinic buffer solution. The synthesis product is more stable to thermolysis than is pure OCP: the apatite-like product is stable up to 630°C. The succinate@OCP powder has been used as a filler for poly(ethylene glycol)diacrylate-based hydrogel in producing a composite implant by stereolithographic 3D printing.

X-ray amorphous powder was synthesized from a water solution of calcium acetate and a mixed-anionic $$ \left({\mathrm{HPO}}_4^{2-}/{\mathrm{CO}}_3^{2-}\right) $$ water solution, including ammonium hydrophosphate and ammonium carbonate, at room temperature without pH regulation. The powders synthesized from the mixed-anionic $$ \left({\mathrm{HPO}}_4^{2-}/{\mathrm{CO}}_3^{2-}\right) $$ solution can be recommended for fabricating composite materials with a polymer matrix or for obtaining ceramic containing tricalcium phosphate and calcite phases with firing temperature not exceeding 600°C.

Ceramic materials in the Na2O–CaO–P2O5 system have been produced using powder mixtures containing calcium hydrogen phosphates (monetite/brushite: CaHPO4/CaHPO4 ∙ 2H2O) and sodium salts (Na2CO3 ∙ H2O, Na4P2O7 ∙ 10H,O, and NaPO3). These salts were used as precursors to the following high-temperature phases: Сa2P2O7, Na2O, Na4P2O7, and NaPO3. The amount of the salts in the powder mixtures was such that the oxide composition of the ceramics corresponded to 10 mol % sodium oxide for each mixture in the Na2O–CaO–P2O5 system. The powder mixtures were prepared using mechanical activation in acetone, which was accompanied by monetite rehydration to brushite. X-ray diffraction characterization showed that, after firing, the phase composition of the ceramics produced from the powder mixtures thus prepared lay in the Сa2P2O7–NaCaPO4–Na2СaP2O7–Са(РО3)2 phase field. The resultant ceramic materials contain biocompatible and bioresorbable phases and can be recommended for bone implant fabrication.

Brushite (CaHPO4 · 2H2O) powder has been synthesized in aqueous 1.0 M solutions of calcium nitrate dipotassium hydrogen phosphate, and disodium hydrogen phosphate at a Ca/P ratio of unity, without adjusting the pH of the reaction. After synthesis and drying, the fraction of a reaction by-product (NaNO3, KNO3, or their mixture) in the powder was about 20 wt %. After firing at temperatures from 800 to 1000°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and Na2HPO4 consisted of β-Ca2P2O7 and β-NaCaPO4. After firing at temperatures from 900 to 1100°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and K2HPO4 consisted of Са10К(РО4)7 and СаК2Р2О7. The ceramic composites produced in this study can be recommended as materials for resorbable bone implants.

Brushite cement obtained from α-Ca3(PO4)2 and orthophosphoric acid in the presence of Mg(H2PO4)2 with compressive strength of 18 MPa was armored with a framework with the Kelvin architecture made of polylactide by thermoextrusion 3D printing. It is shown that armoring of cement with polylactide framework allows one not only to increase the compressive strength of such a structure (up to 35 MPa) but also to significantly improve its deformability (up to 15%).

The rheological properties of highly concentrated calcium phosphate suspensions for producing bioceramic with complex shape by means of slip casting and 3D-printing were investigated. Macroporous bioceramic with gyroid architecture was prepared by casting water slips into polymer molds with gyroid geometry, which were fabricated by thermal-extrusion and stereolithographic 3D-printing. The limitations of this technology in reproducing fine details as compared with direct 3D-stereolithography of ceramic suspensions are indicated.

Highly permeable macroporous implants of various architectures for bone grafting have been fabricated by thermal extrusion 3D printing using highly filled β-Ca3(PO4)2/poly(D,L-lactide) (degree of filling up to 70 wt %) and β-Ca3(PO4)2/poly(e-caprolactone) (degree of filling up to 70 wt %) composite filaments. To modify the surface of the composite macroporous implants with the aim of improving their wettability by saline solutions, we have proposed exposing them to a cathode discharge plasma (2.5 W, air as plasma gas) in combination with subsequent etching in a 0.5 M citric acid solution. It has been shown that the main contribution to changes in the wettability (contact angle) of the composites is made by the changes produced in their surface morphology by etching in a low-temperature plasma and citric acid. An alternative approach to surface modification of the composites is to produce a carbonate hydroxyapatite layer via precipitation from a simulated body fluid solution a factor of 5 supersaturated relative to its natural analog (5xSBF).

Calcium phosphate powder was synthesized from calcium formiate Ca(CHO2)2 and ammonium hydrophosphate (NH4)2 HPO4 with Ca/P ratio in the initial water solutions equal to 1. The phase composition of the powders synthesized from 0.5M solutions was represented by brushite CaHPO4 · 2H2O and octacalcium phosphate Ca8(HPO4)2 (PO4)6 · 6H2O. After firing at 1100°C the phase composition of the powder was represented by calcium pyrophosphate β-Ca2P2O7 and tricalcium phosphate β-Ca3 (PO4)2. The synthesized powder can be used to obtain biocompatible resorbable biphase ceramic materials and composites with a polymer matrix.

A calcium phosphate powder has been synthesized from aqueous 0.25, 0.5, and 1.0 M calcium lactate and ammonium hydrogen phosphate solutions atat a Ca/P = 1, without pH adjusting. According to X-ray diffraction data, the as-synthesized powder consisted of brushite (CaHPO4 · 2H2O) and octacalcium phosphate (Ca8(HPO4)2(PO4)4 · 5H2O). After heat treatment in the range 500–700°C, the powders were gray in color because of the destruction of the reaction by-product. The powders heat-treated in the range 500–700°C consisted largely of γ-Ca2P2O7. The ceramics prepared from the synthesized powders by firing at 1100°C consisted of β-Ca2P2O7 and β-Ca3(PO4)2.

A composite bioceramic with density at least 80% of the theoretical value was obtained from thermolyzed octacalcium phosphate (OCP). The treatment temperatures of OCP were 450, 600, and 700°C. The ceramic was obtained by firing thermolyzed powders at maximum temperature 1000, 1050, and 1100°C with soaking for 3, 6, and 9 h. Samples obtained from OCP treated at 450°C demonstrate the highest strength in bending (up to 125 MPa).

Osteoconductive ceramic implants based on Ca3–x M2x (PO4)2 (M = Na, K) double phosphates and having the Kelvin structure, tailored macropore size (in the range 50–750 μm), and a total porosity of 70–80% have been produced by stereolithographic 3D printing. We demonstrate that, to maintain the initial geometry of a model and reach sufficiently high strength characteristics of macroporous ceramics (compressive strength up to 9 MPa and fracture toughness up to 0.7 MPa m1/2), the polymer component should be removed under specially tailored heat treatment conditions. Based on our results on polymer matrix destruction kinetics, we have found heat treatment conditions that ensure a polymer removal rate no higher than 0.1 wt%/min and allow one to avoid implant cracking during the firing process.

This paper examines the physicochemical properties and microstructure of brushite calcium phosphate cements possessing strength acceptable for application in surgery (15–20 MPa) and ensuring an optimal acidity (pH 6.5–7.5) of solutions in contact with them. Holding in a physiological saline produces significant changes in the microstructure of the cement relative to that before immersion in the solution: it causes a transformation of the most soluble components into platelike hydroxyapatite crystals.

We have studied the formation of octacalcium phosphate (OCP) in various buffer solutions. Brushite hydrolysis in acetate and succinate buffer solutions at 60°C and pH 5.75 ensures rapid synthesis of pure OCP and substituted OCP (sOCP), which allows a rather large amount of this phosphate (at least 10 g in a single synthesis run) to be obtained in 50–60 min. The observed differences in phase composition between the OCP and sOCP thermolysis products make it possible to obtain biphasic ceramic composites of various kinds: β-TCP/β-CPP (Ca/P = 1.33) in the case of OCP and β-TCP/HA (Ca/P = 1.54) in the case of sOCP. Ceramics with a density of 80% of theoretical density and higher produced using the OCP precursors synthesized in this study have a uniform microstructure, possess the desired microporosity, and are potentially attractive for further advances in the field of bioresorbable osteoplastic materials.

On the basis of mixtures of Ca3(PO4)2(α-TCP)/CaO and α-TCP/CaMPO4 powders (M = Na, K), self-hardening pastes are prepared whose treatment with solutions of sodium bicarbonate and calcium chloride results in the production of chemically bonded composites containing the phases of hydroxyapatite (HA) and calcium carbonate, as well as TCP and HA. The resulting materials can be used both as relatively dense composites (up to 75%) for osteoplasty and in the casting of settable ceramic slurries in plastic molds of special geometry for obtaining osteoconductive macroporous ceramics.

Amorphous hydrated calcium phosphate powder was synthesized at room temperature from aqueous solutions of polyphosphoric acid and calcium acetate with addition of ammonia water solution. Synthesized powder remains amorphous after heat in the temperature range 200–500 °C. Phase composition of powder and compacted powder samples after firing at 800 °C consists of calcium polyphosphate (β-Ca(PO3)2), tromelite (Ca4P6O19) and calcium pyrophosphate (β-Ca2P2O7). Synthesis of amorphous hydrated calcium phosphate powder with the ion-exchange stage for preparing an aqueous solution of polyphosphoric acid can be recommended as a simple way of production of powdered precursor for biocompatible bioresorbable phosphate ceramics containing calcium polyphosphate, tromelite and calcium pyrophosphate.

The present review describes approaches to the preparation of powder formulations for production of calcium phosphate ceramic materials. In order to mold semifinished powder items by means of various methods powder formulations, comprising synthetic powders and fabrication binders, are used.

Chemical modification of the surface of basalt glass fiber has been considered, including diffusion-mode oxidation without formation of new crystalline phases and ion-exchange lithium enrichment. The effect of such a modification on the appearance of new surface formations during the hardening of composites that consist of the modified fiber and model nonorganing binding materials (mixtures of Ca3SiO5 and Ca3Al2O6 with water) has been analyzed. It has been shown that both ion-exchange lithium enrichment and diffusion-mode oxidation change the composition and the morphology of hydrosilicate and hydroaluminate particles that are formed on the surface from “individual hydraulically active phase–water” mixtures. They have also been shown to change the morphology of the very fiber that is in contact with the liquid phase of the binding material.

Ceramic based on calcium phosphates is obtained from powders synthesized from water solutions of calcium nitrate, ammonium hydrophosphate, and ammonium pyrophosphate as well as from a mixed-anionic solution containing simultaneously ammonium pyro- and orthophosphate in the molar ratio (NH4)2HPO4/(NH4)4P2O7 = 1. The ceramic obtained contains biocompatible bioresorbable phases and can be used to make implants used in regenerative methods for the treatment of bone tissue defects. This represents the first time synthesis from mixed-anionic solutions is used to obtain powders of calcium phosphates with significant quantities of each anion.

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during “wet” synthesis by CO 3 2− carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin–spin relaxation) of the NO 3 2− nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion–cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

Powder mixtures are considered containing ammonium hydrophosphate and calcium carbonate intended for preparing biocompatible porous ceramic in the CaO–P2O5 system. Pore formation on heating in workpieces based on the powder mixtures in question occurs due to occurrence of gas liberation in the presence of melt in the NH3–H2O–CO2–CaO–P2O5 or CO2–CaO–P2O5 systems. Gas phase formation is due to liberation of gaseous water and ammonia, thermal hydrolysis of calcium polyphosphate, decomposition of calcium carbonate, and oxidation of carbonized organic compounds remaining within a powder mixture in the form of associated calcium carbonate synthesis reaction product.

3D printing based on multiphoton absorption is playing a growing role in biomedical engineering and regenerative medicine. Multiphoton lithography is a 3D printing approach that is based on the multiphoton absorption process. The review focuses on the use of multiphoton lithography to create microneedles, microfluidic devices, nanoprobes, filters, and tissue engineering scaffolds with sub-micrometer scale features. The fundamental requirements of the multiphoton absorption process are described. Efforts to increase the processing rate as well as understand the bioresorbability of multiphoton lithography-created structures are discussed. Improvements to the biocompatibility of the polymers and photoinitiators used in multiphoton lithography are considered. The multiphoton lithography process offers unique opportunities to process tissue engineering scaffolds with small-scale features.