Hydroxyapatite Microcrystals Research Articles

Morphology evolution of Hydroxyapatite: Synergistic effects and water treatment application

Shuttle/flower-like hydroxyapatie crystals have been fabricated by a simple hydrothermal treatment under the combined action of sodium citrate and a pluronic triblock copolymer (F127). The morphology characterization results demonstrate that the hierarchical flower-like hydroxyapatite microcrystals are evolved from the one-dimensional hydroxyapatie nanoshuttles. The effects of the additives and hydrothermal time on the morphology are studied. Based on the experiment results, this work presents a possible growth mechanism for the hydroxyapatite morphology. Remarkably, the adsorption experiments results exhibit that the HAP microflower have fast adsorption ability for heavy metal ions.

Hydroxyapatite surface-functionalized monolithic column for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid

To date, hydroxyapatite (HAP) based monoliths were mainly fabricated by directly doping of HAP, which suffered from less effective coverage of HAP. Herein, a HAP surface-functionalized monolithic column (HAP@PDA@UF) has been prepared by in-situ biomineralization and applied as sorbent for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid. A polydopamine coating was first generated on the surface of the parent urea-formaldehyde resin monolith; and then HAP microcrystals were further grew on the polydopamine coating to achieve this preparation. SEM, EDAX, FTIR, XPS and mercury intrusion method were utilized for the characterization of the HAP@PDA@UF monolith, and provided evidences of this successful preparation. The selective extraction mechanism of the HAP@PDA@UF monolith was investigated by the optimization of methanol percentage in the sampling solution, phosphate concentration in the eluent. Other crucial factors, including sampling and elution flow rate, and collection time span, were also optimized for the desired SPME performance. Under the optimal conditions, the proposed method showed low LODs of 0.1 μg/mL, satisfactory recoveries of 79.6%-92.5% with RSDs less than 2.7%, and good reproducibility with RSD less than 6.9%, which demonstrated the excellent application of the HAP@PDA@UF monolith, and its potential as a promising selective sorbent for bisphosphonates.

ИЗУЧЕНИЕ МЕТОДОМ ЭЛЕКТРОННОГО ПАРАМАГНИТНОГО РЕЗОНАНСА ВЛИЯНИЯ ФИЗИКО-ХИМИЧЕСКИХ И СТРУКТУРНЫХ ХАРАКТЕРИСТИК КОСТНОЙ ТКАНИ НА ПРОЦЕССЫ ОСТЕОИНТЕГРАЦИИ ДЕНТАЛЬНЫХ ИМПЛАНТАТОВ С РАЗЛИЧНОЙ МИКРОСТРУКТУРОЙ ПОВЕРХНОСТИ

Aim. Study by the method of electronic paramagnetic resonance (EPR) physical- chemical and structural features of bone tissue and their effect on the processes of osseointegration during dental implantation using implants with different macro-microstructure of the surface.
 Material and methods. The experimental study was conducted on 7 Vietnamese visobryu-pig mini-pigs. Under anesthesia, implants with different macro-microstructures of the surface (SLA, RBM, ) were installed under the methods of direct and delayed implantation. At different dates of the experiment, after the appropriate anesthesia, the gentle method was to remove implants with small fragments of periemplant bone tissue. Macro-drugs of bone tissue of the jaws after sawing on blocks and extraction of implants, as well as appropriate preparation, were investigated by the method of stationary electronic paramagnetic resonance.
 Results. As a result of the study it was revealed that the insertation of the implant into the jaw bone leads to structural changes in the surrounding bone implant. After prior exposure, the EPR spectrums, caused by different types of paramagnetic centers, were observed in the samples studied. Two types of centers, , have been identified. and F is the center. The spectrum of the second type reflects the presence in hydroxiapatites of lattice defects associated with isomorphism, and, . The findings suggest that one of the reasons for the higher content of free radicals (SR) in bone tissue derived from radiation, after dental implantation is the weakening of chemical bonds, greater mobility of fragments that make up its structure. It must be assumed that the high content of SR in the bone in the postoperative period is nothing but a result of the disruption of the mineralization process, which is accompanied by the replacement of phosphate groups with carbonate ions that are free-radicalized. It has also been revealed that the structural integrity of the bone depends to a large extent on the degree of orderliness of microcrystals of hydroxyapatite. According to EPR, the most favorable bone recovery (the process of osseointegration) occurs when using implants with a surface, .
 Conclusions. EPR research of native and carbonate radicals is a unique tool for studying the physical and chemical and structural features of bone tissue and their role in the process of osseointegration of implants. The speed of osseointegration for implants with different microstructures of the surface varies. EPR can be used as an additional method to control the integration of implants into bone tissue.

Hydroxyl Groups Induce Bioactivity in Silica/Chitosan Aerogels Designed for Bone Tissue Engineering. In Vitro Model for the Assessment of Osteoblasts Behavior.

Silica (SiO2)/chitosan (CS) composite aerogels are bioactive when they are submerged in simulated body fluid (SBF), causing the formation of bone-like hydroxyapatite (HAp) layer. Silica-based hybrid aerogels improve the elastic behavior, and the combined CS modifies the network entanglement as a crosslinking biopolymer. Tetraethoxysilane (TEOS)/CS is used as network precursors by employing a sol-gel method assisted with high power ultrasound (600 W). Upon gelation and aging, gels are dried in supercritical CO2 to obtain monoliths. Thermograms provide information about the condensation of the remaining hydroxyl groups (400–700 °C). This step permits the evaluation of the hydroxyl group’s content of 2 to 5 OH nm−2. The formed Si-OH groups act as the inductor of apatite crystal nucleation in SBF. The N2 physisorption isotherms show a hysteresis loop of type H3, characteristic to good interconnected porosity, which facilitates both the bioactivity and the adhesion of osteoblasts cells. After two weeks of immersion in SBF, a layer of HAp microcrystals develops on the surface with a stoichiometric Ca/P molar ratio of 1.67 with spherulite morphology and uniform sizes of 6 μm. This fact asserts the bioactive behavior of these hybrid aerogels. Osteoblasts are cultured on the selected samples and immunolabeled for cytoskeletal and focal adhesion expression related to scaffold nanostructure and composition. The initial osteoconductive response observes points to a great potential of tissue engineering for the designed composite aerogels.

Loss of β-Actin Leads to Accelerated Mineralization and Dysregulation of Osteoblast-Differentiation Genes during Osteogenic Reprogramming.

Actin plays fundamental roles in both the cytoplasm and the cell nucleus. In the nucleus, β‐actin regulates neuronal reprogramming by consolidating a heterochromatin landscape required for transcription of neuronal gene programs, yet it remains unknown whether it has a role in other differentiation models. To explore the potential roles of β‐actin in osteogenesis, β‐actin wild‐type (WT) and β‐actin knockout (KO) mouse embryonic fibroblasts (MEFs) are reprogrammed to osteoblast‐like cells using small molecules in vitro. It is discovered that loss of β‐actin leads to an accelerated mineralization phenotype (hypermineralization), accompanied with enhanced formation of extracellular hydroxyapatite microcrystals, which originate in the mitochondria in the form of microgranules. This phenotype is a consequence of rapid upregulation of mitochondrial genes including those involved in oxidative phosphorylation (OXPHOS) in reprogrammed KO cells. It is further found that osteogenic gene programs are differentially regulated between WT and KO cells, with clusters of genes exhibiting different temporal expression patterns. A novel function for β‐actin in osteogenic reprogramming through a mitochondria‐based mechanism that controls cell‐mediated mineralization is proposed.

Scanning electron microscopy for blood micro-crystals in aortic stenosis patients.

BackgroundMicro-crystals of calcium phosphate have been detected on the aortic valve of patients with aortic stenosis using scanning electron microscopy. It is not known whether crystalisation is specific to heart valve tissue or a general blood-derived process.MethodsTo this end we modified the method to determine whether calcium phosphate micro-crystals were present in the blood of patients with aortic stenosis. The method was first validated by adding synthetic calcium phosphate hydroxyapatite micro-crystals to healthy volunteer blood samples and determining the lower limit of detection. Then the method was used to examine the blood of 63 patients with echocardiographically confirmed aortic stenosis and 69 unaffected controls undergoing echocardiography for other reasons. Serum calcium and phosphate were measured and the calcium phosphate product compared in cases and controls.ResultsIn the validation study, synthetic hydroxyapatite micro-crystals were identified down to a lower concentration limit of 0.008mg/mL. In the experimental study no particles were identified in any patient, with or without aortic stenosis, even though serum calcium phosphate was higher in cases compared with controls 2.6mmol/L (2.58–2.77) versus 2.47mmol/L (2.36–2.57), p = 0.005 for the difference.ConclusionThe results of our study confirm a positive association between serum calcium phosphate and aortic stenosis, but indicate that the calcium phosphate particles found in valve tissue do not precipitate freely in the blood.

Bioactive composites of hydroxyapatite/polyvinylpyrrolidone for bone regeneration applications

The implantation of bioactive composites for bone repair applications has recently gained the attention of many research groups. The present paper introduces a method for grafting of polyvinylpyrrolidone on the surface of hydroxyapatite (CaHAp) microcrystals by wet precipitation method to manufacture new composite scaffolds with suitability for bone tissue engineering. After grafting with the polymer, the degree of CaHAp crystallinity decreased, and its thermal behavior changed indicating a strong interaction between them. Homogenous clusters of CaHAp particles within the polymeric matrix were observed in combination with an increase in the roughness of the resulting structures. Bioactivity of the composites was tested using MTT assay; a higher viability of the seeded cells was observed relative to those cultured with CaHAp powder.

Osteoblast Differentiation and Bone Matrix Formation In Vivo and In Vitro.

We review the characteristics of osteoblast differentiation and bone matrix synthesis. Bone in air breathing vertebrates is a specialized tissue that developmentally replaces simpler solid tissues, usually cartilage. Bone is a living organ bounded by a layer of osteoblasts that, because of transport and compartmentalization requirements, produce bone matrix exclusively as an organized tight epithelium. With matrix growth, osteoblasts are reorganized and incorporated into the matrix as living cells, osteocytes, which communicate with each other and surface epithelium by cell processes within canaliculi in the matrix. The osteoblasts secrete the organic matrix, which are dense collagen layers that alternate parallel and orthogonal to the axis of stress loading. Into this matrix is deposited extremely dense hydroxyapatite-based mineral driven by both active and passive transport and pH control. As the matrix matures, hydroxyapatite microcrystals are organized into a sophisticated composite in the collagen layer by nucleation in the protein lattice. Recent studies on differentiating osteoblast precursors revealed a sophisticated proton export network driving mineralization, a gene expression program organized with the compartmentalization of the osteoblast epithelium that produces the mature bone matrix composite, despite varying serum calcium and phosphate. Key issues not well defined include how new osteoblasts are incorporated in the epithelial layer, replacing those incorporated in the accumulating matrix. Development of bone in vitro is the subject of numerous projects using various matrices and mesenchymal stem cell-derived preparations in bioreactors. These preparations reflect the structure of bone to variable extents, and include cells at many different stages of differentiation. Major challenges are production of bone matrix approaching the in vivo density and support for trabecular bone formation. In vitro differentiation is limited by the organization and density of osteoblasts and by endogenous and exogenous inhibitors.

Morphology control of hydroxyapatite microcrystals: Synergistic effects of citrate and CTAB

Using hydrothermal treatment and with the synergistic regulating effects of citrate and CTAB, various 3D hierarchical superstructure of hydroxyapatite (HAp) microcrystals were synthesized by simply adjusting the Ct/CTAB ratio and calcium–citrate complex (CC) morphology. The resulting superstructure was characterized using X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM) etc. With the shape transformation of CC from sphere-like colloid, nano-needle to lamellar-like particles, the final products were hollow spheres, bunched-like microrods and nanorod clusters, respectively. A possible mechanism for the formation of HAp hierarchical microstructure was proposed.

Remineralisation of enamel surface by biomimetic Zn-carbonate containing toothpaste

Consumption of acid foods and drinks and other factors causing enamel wear are responsible of the daily enamel loss and degradation. In order to contrast these effects, some toothpastes have been showed to possess different properties of remineralisation and/or repair of the enamel surface. The aim of the study was to evaluate whether the use of a toothpaste containing Zn-carbonate hydroxyapatite (CHA) microcrystals may exert remineralisation/repair effects of the enamel surface. Two groups of patients, aged between 18 and 75 years, used for 8 weeks a Zn- CHA nanocrystals toothpaste (experimental group) and a potassium nitrate/sodium fluoride toothpaste (active control group). At the end of this period, scheduled extractions were performed in five subjects for each group. Negative controls consisted on two subjects treated with non-specified fluoride toothpaste. Teeth were processed for morphological and chemical-physic superficial characterizations by means of Scanning Electronic Microscopy with Elementary analysis, X-Ray Diffraction analysis and Infrared analysis. The results showed that use of a Zn-CHA nanocrystals toothpaste may lead to a remineralization/repair of the enamel surface, by deposing a hydroxyapatite-rich coating. On the other hand, the use of both a nitrate potassium/sodium fluoride and non-specified fluoride toothpastes do not appreciably change the enamel surface. In conclusion, this study demonstrates that the toothpaste containing Zn-CHA nanostructured microcrystals, differently from nitrate potassium/sodium fluoride and non-specified fluoride toothpastes, may promote enamel superficial repair by means of the formation of a protective biomimetic CHA coating.

Carboxymethyl cellulose—hydroxyapatite hybrid hydrogel as a composite material for bone tissue engineering applications

Natural bone is a complex inorganic-organic nanocomposite material, in which hydroxyapatite (HA) nanocrystals and collagen fibrils are well organized into hierarchical architecture over several length scales. In this work, we reported a new hybrid material (CMC-HA) containing HA drown in a carboxymethylcellulose (CMC)-based hydrogel. The strategy for inserting HA nanocrystals within the hydrogel matrix consists of making the freeze-dried hydrogel to swell in a solution containing HA microcrystals. The composite CMC-HA hydrogel has been characterized from a physicochemical and morphological point of view by means of FTIR spectroscopy, rheological measurements, and field emission scanning electron microscopy (FESEM). No release of HA was measured in water or NaCl solution. The distribution of HA crystal on the surface and inside the hydrogel was determined by time of flight secondary ion mass spectrometry (ToF-SIMS) and FESEM. The biological performance of CMC-HA hydrogel were tested by using osteoblast MG63 line and compared with a CMC-based hydrogel without HA. The evaluation of osteoblast markers and gene expression showed that the addition of HA to CMC hydrogel enhanced cell proliferation and metabolic activity and promoted the production of mineralized extracellular matrix.

Hardness and the nature of microplasticity of hydroxyapatite

The hardness of thin (1.0–4.0 μm) hydroxyapatite (HA) coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown on Ti and Si by rf magnetron sputtering has been studied using nanoindentation. In all of the coatings, deformation was observed to have an elastoplastic nature. The hardness of the nanocrystalline coatings corresponds to medium hardness values of HA microcrystals. The structure of the nanocrystalline coatings has been studied by high-resolution transmission electron microscopy in the indent zone and away from it. Comparison of the hardness values of coatings with different structures and analysis of the intragranular structure leads us to assume a nondislocation mechanism of plastic deformation. Its nature is interpreted in terms of a cluster representation of the structure of HA and amorphous calcium phosphates and cluster-boundary sliding in the course of deformation.

Surface Design and Water Vapor-Adsorption Characteristics of Biomimetic Composite Materials Derived from Salmon Resource

Biomimetic composites of hydroxyapatite (HAp) and collagen with fast bio-absorption and good biocompatibility were designed utilizing salmon bone and skin at 283-293 K and pH 7.5-7.9 by a dissolution-precipitation method. Simultaneously, dissolved-precipitated HAp (dp-HA) was prepared at pH 9-10 using the calcined bone. The HAp/collagen composites (HA-C) were constituted by Ca2+-deficient HAp, I type-collagen and gelatin. At the synthetic temperature of 283 K, collagen fiber and HAp microcrystals were seen, while at 293 K, frock like-agglomerated particles or fiber like-oriented columnar ones were observed depending on the composition ratio (H/C) of HAp to collagen. Specific surface areas and total pore volumes for the HA-C synthesized at 293 K clearly increased with increasing the H/C, although there were micro-and-meso-pores in the pore diameters of 3-30 nm. Concerning water vapor-adsorption isotherms at 298 K for the HA-C powders, hysteresis-curves of the amounts of water vapor adsorbed (V) were recognized in the adsorption-desorption processes. The V values increased with increasing the H/C under the low relative pressures (P/PS) of 0-0.3 that mean monolayer-adsorption of water molecule. However, for H/C=2.2, the V values were the highest under the high P/PS of 0.70-0.90 that mean multilayer-adsorption and the biggest hysteresis-curve was found under the P/PS of 0.45-0.60, suggesting that the HA-C (H/C=2.2) powder not only adsorb water molecule on the surfaces but also absorb one into the crystal structure. Accordingly, the biomimetic HA-C powders will be applied as water-absorbable adsorption materials for cosmetic products or bone-regeneration therapy.

Surface structure and biocompatibility of demineralized dentin matrix granules soaked in a simulated body fluid

Demineralized dentin matrix (DDM) granules with excellent biocompatibility were easily prepared using unnecessary human teeth by a new cooling-pulverizing and demineralizing technique. Extracted human teeth were pulverized together with saline ice at 12,000rpm-rotation number of a ZrO2 blade for 30s in a ZrO2 vessel. The pulverized granules exhibited the particle size distribution of 0.5–2mm that was efficient for regeneration of alveolar bone. The (Ca/P) ratios of the granules were 1.60–1.66, which were close to the stoichiometric value of 1.67 for standard hydroxyapatite (HAp). Small amounts of Na+ and Mg2+ ions present at less than 1% were detected. The pulverized granules were dissolved with stirring under 500rpm for 10–60min in 2.0%-HNO3 solutions to obtain partial or complete DDM granules. As the dissolution time increased, crystallinity of HAp phase lowered and asperity on surfaces of the granules became outstanding due to elution of mineral components. At the dissolution of 60min, the pulverizing granules were completely demineralized and the weight decreased to about one-fifth. To improve surface activity of the DDM granules without denaturation of bone growth factors, the DDM granules were soaked at 309.5K and pH 7.40 in a simulated body fluid (SBF). HAp microcrystals were gradually precipitated on surfaces of the DDM granules with increasing the soaking time. Different morphology of the precipitates was observed, depending on the demineralization situation of the pulverized granules. For the DDM with low dissolution efficiency of 42%, porous bone-like apatites at 24h after the soaking and fiber-oriented aggregates at 144h were recognized. The bioactive DDM granules were implanted into the subcutaneous tissues of the back region of rats. At 4 weeks after the implantation, bio-absorption by comparatively small amounts of multi-giant cells was recognized around the surface layers of DDM granules.

EDTA-Assisted Self-Assembly of Fluoride-Substituted Hydroxyapatite Coating on Enamel Substrate

Reconstructed layers containing ordered enamel-like structures of fluoride-substituted hydroxyapatite (FHAp) microcrystals were constructed on a human enamel surface using ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) as the mediating agent under near-physiological conditions (pH 6.00, 37 °C, 1 atm). The effects of initial pH value, fluoride concentration, as well as reaction time on the formation of the FHAp microcrystals, including their microarchitectural structure, crystalline phase, chemical components, and hardness properties, were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Vickers microhardness measurements. The results of these in vitro experiments indicated that EDTA induced the assembly of hexagonal prismlike FHAp microcrystals along their c-axis direction, and the microcrystals further amalgamated with the extended reaction time. In addition, fluoride ions were found to play a critical role in the formation of hexagonal FHAp microcrystals. Interestingly, after reaction for 5 days, the Vickers microhardness of the new layer (347–370 VHN) was harder than that of natural tooth. On the basis of the experimental evidence, a mesoscale self-assembly mechanism was proposed to explain the growth of FHAp microcrystals.

A Biomimetic Material with a High Bio-responsibility for Bone Reconstruction and Tissue Engineering

A biomimetic composite was prepared using type-I collagen as the matrix, and particles of sol–gel-derived bioactive glass (58S), hyaluronic acid and phosphatidylserine as additives. The material has an interconnected 3-D porous structure with a porosity > 85%. When incubated in simulated body fluid (SBF), the composite induced the formation of microcrystals of bone-like hydroxyapatite (HA), suggesting good bioactive properties. During the in vitro cell-culture experiment, MC3T3-E1 cells adhered to, migrated and spread on the surface of the porous composite. The material was employed to repair a 10-mm defect in a rabbit's radius. The composite was gradually degraded within 8 weeks and replaced by new bone. After 12 weeks, the bone marrow cavity was restored and the Haversian canal was noted from the histological observation. The biomimetic composite is a potential scaffold material for bone reconstruction and bone tissue engineering.

Shape-controlled synthesis of F-substituted hydroxyapatite microcrystals in the presence of Na 2EDTA and citric acid

We present a facile strategy for the shape-controlled synthesis of F-substituted hydroxyapatite (FHAp) microcrystals based upon using a combination of Na 2EDTA and citric acid (CA). Novel, well-defined FHAp microcrystals of various shapes, such as hexagonal disks with predominant (0 0 0 1) faces, hexagonal shuttles, hexagonal prisms, icosahedrons, and hexagonal microrods with tunable aspect ratios, were fabricated. In particular, FHAp hollow microcrystals with tunable shapes were fabricated directly without using any additional template. The central features of our approach are the use of both Na 2EDTA and CA as two distinct chelating reagents and the use of substitution ions (F −) itself as a growth inhibitor for the FHAp crystals. F − ions were found to play a critical role in the formation of hexagonally shaped FHAp microcrystals, and in the one-pot formation of hollow microcrystals, which relies on the addition order of F − ions in the synthesis.

Long‐term results of disodium etidronate treatment in pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare disease with alveolar microliths mainly composed of calcium phosphate. The gene responsible for the disease is SLC34A2, which encodes a type-IIb sodium phosphate cotransporter, has been described recently. Treatment of this disease is not clearly defined. Disodium etidronate is a member of bisphonates and it has been administered in these patients due to its inhibitory effect on the precipitation of hydroxyapatite microcrystals. Here, clinical and radiological improvement of two patients with PAM who were treated with disodium etidronate for 9 and 11 years, respectively, are presented. The pathogenetic mechanism of this treatment on the genetic basis of disease is discussed.

Micro-CT studies on 3-D bioactive glass–ceramic scaffolds for bone regeneration

The aim of this study was the preparation and characterization of bioactive glass–ceramic scaffolds for bone tissue engineering. For this purpose, a glass belonging to the system SiO 2–P 2O 5–CaO–MgO–Na 2O–K 2O (CEL2) was used. The sponge-replication method was adopted to prepare the scaffolds; specifically, a polymeric skeleton was impregnated with a slurry containing CEL2 powder, polyvinyl alcohol (PVA) as a binding agent and distilled water. The impregnated sponge was then thermally treated to remove the polymeric phase and to sinter the inorganic one. The obtained scaffolds possessed an open and interconnected porosity, analogous to cancellous bone texture, and with a mechanical strength above 2 MPa. Moreover, the scaffolds underwent partial bioresorption due to ion-leaching phenomena. This feature was investigated by X-ray computed microcomputed tomography (micro-CT). Micro-CT is a three-dimensional (3-D) radiographic imaging technique, able to achieve a spatial resolution close to 1 μm 3. The use of synchrotron radiation allows the selected photon energy to be tuned to optimize the contrast among the different phases in the investigated samples. The 3-D scaffolds were soaked in a simulated body fluid (SBF) to study the formation of hydroxyapatite microcrystals on the scaffold struts and on the internal pore walls. The 3-D scaffolds were also soaked in a buffer solution (Tris–HCl) for different times to assess the scaffold bioresorption according to the ISO standard. A gradual resorption of the pores walls was observed during the soakings both in SBF and in Tris–HCl.

Electron microscopy of biomaterials based on hydroxyapatite

Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300–500 μm in diameter. Sintering of hydroxyapatite crystals at a temperature of 870°C for 2 h or at 1000°C (for 3 h) + 1200°C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870°C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200°C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 μm. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200°C.