Silicate-substituted Hydroxyapatite Research Articles

Effect of silver ion and silicate group on the antibacterial and antifungal properties of nanosized hydroxyapatite

Hydroxyapatite is one of the most widely used materials in biomedical applications in reparative and regenerative medicine. Doping of nanosized hydroxyapatite improves its bioactive properties, and thus, the synthesis of different types of nanohydroxyapatite with antimicrobial activity is a perspective route of modern materials science. In this study, undoped hydroxyapatite (HAp), hydroxyapatite doped with silver (HAp with 0.1, 0.5 and 1 mol% Ag+ ions), and silicate-substituted hydroxyapatite doped with silver (Si-HAp with 0.1, 0.5 and 1 mol% Ag+ ions) nanoparticles (NPs) were synthesized by microwave-assisted hydrothermal technique and sintered at 450 °C. The structural properties and composition of obtained hydroxyapatite NPs were investigated using X-ray powder diffraction (XRPD), Fourier-transformed infrared spectroscopy (FT-IR), and Energy-dispersive X-ray spectroscopy (EDS). The morphology of synthesized nanosized powders was detected using the high-resolution transmission electron microscopy (HRTEM) technique. The results of XRPD for all synthesized nanosized powders confirmed the presence of hydroxyapatite crystal structure. The FT-IR spectra confirmed the presence of functional groups characteristic of the hydroxyapatite structure. The EDS analysis of obtained materials has shown the presence of Ca, P, O, Si, and Ag elements. Significant differences in size and morphology of the obtained particles were found using HRTEM. The particles have an elongated, rod-like shape with subtle differences. Moreover, HAp doped with 1 mol% Ag+ ions and Si-HAp doped with 1 mol% Ag+ ions nanosized powders showed antibacterial activity in comparison to pure hydroxyapatite both against gram-positive and gram-negative bacterial strains (Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecalis). These two types of hydroxyapatite NPs also demonstrated antifungal activity against reference strains of Candida albicans, Candida kruzei, and Candida tropicalis, with stronger activity observed for Si-HAp doped with silver.

Effect of Physicochemical Surface Properties of Silicon-Substituted Hydroxyapatite on Angiogenesis.

Synthetic hydroxyapatite (HA) is a widely studied bioceramic for bone tissue engineering (BTE) due to its similarity to the mineral component of bone. As bone mineral contains various ionic substitutions that play a crucial role in bone metabolism, the bioactivity of HA can be improved by adding small amounts of physiologically relevant ions into its crystal structure, with silicate-substituted HA (Si-HA) showing particularly promising results. Nevertheless, it remains unclear how distinct material characteristics influence the bioactivity due to the intertwined nature of surface properties. A coculture methodology was optimized and applied for in vitro quantification of the biological response. Initially, HA and Si-HA samples were produced and characterized. To compare the bioactivity of the samples, a method was developed to measure interactions in an increasingly complex environment, first including fibronectin (FN) adsorption and subsequently cell adhesion in mono and coculture using primary human osteoblasts (hOBs) and human dermal microvascular endothelial cells (HDMECs), with and without FN precoating. An experimental set-up was designed to assess to what extent different surface features of the samples contribute to the induced biological response. An 8-nm gold sputter coating was applied to eradicate the electrochemical differences and polishing and abrading was used to reduce the differences in surface topographies. Overall, 1.25 wt% Si-HA exhibited most nanoscale variations in surface potential. In terms of bioactivity, 1.25 wt% Si-HA samples induced the highest osteoblast attachment and vessel formation. Additionally, in vitro vessel formation was established on Si-HA surfaces using a hOB:HDMEC cell ratio of 70:30 and a methodology was established that enabled the assessment of the relative effect of topographical and electrochemical features induced by silicon substitution in the HA lattice on their bioactivity. It was found that the difference in the amount of protein attached to HA and 1.25 wt% Si-HA after 2 h was affected by topographical differences. Conversely, electrochemical differences induced different vessel-like structure formation in coculture with a FN precoating. Without an FN precoating, both topographical and electrochemical differences dictated the differences in angiogenic response. Overall, 1.25 wt% Si-HA surface features appear to induce the most favorable protein adsorption and cell adhesion in mono and coculture with and without FN precoating.

Multifunctional platform for future applications in cell and tissue engineering based on silicate phosphate hydroxyapatite co-doped with Li+, Eu3+ and Gd3+ ions

Although hydroxyapatite has established itself as a promising biomaterial for the simultaneous diagnosis and treatment of bone defects, several physicochemical properties can be further refined to achieve a specialized theranostic platform for cell and tissue engineering. In this context, we synthesized silicate-substituted hydroxyapatites co-doped with Li+, Eu3+, and Gd3+ ions (abbr. as Si-HAp-LEG) using a microwave-assisted hydrothermal method. The aim was to create a combination of dopants to stimulate bone regeneration (Li+ ion) while enabling bioimaging (Eu3+ and Gd3+ ions). Structural and morphological assessments included, e.g., XRPD (X-ray Powder Diffraction), HR-TEM (High-resolution Transmission Electron Microscopy) imaging, and BET (Brauner-Emmet-Teller) analysis. Unit-cell parameters were estimated via Rietveld refinement. The luminescence properties (emission, excitation spectra, and emission kinetics) were recorded depending on the varying Li+-ion concentration. The cytocompatibility of biomaterials was tested using hBMSCs (multipotent human bone-marrow mesenchymal stromal cells). In vitro assays evaluated biomaterials’ effects on morphology, metabolic activity (Alamar blue assay), and transcriptomic activity (RT-qPCR). The results indicate that co-doping with Li+, Eu3+, and Gd3+ ions introduces distortions while preserving the crystal structure of hydroxyapatite. Additionally, the cells maintained proper morphology and ultrastructure, internalizing biomaterials without significant cytotoxicity. The biomaterials also triggered the expression of key transcriptional factors. Si-HAp-LEG biomaterials, particularly LEG-222 and LEG-221, exhibit desired physicochemical and biological features, rendering them highly bioactive and promising for cell and tissue engineering applications.

New silicate-substituted hydroxyapatite materials doped with silver ions as potential antifungal agents

BackgroundHydroxyapatites (HAp) are widely used as medical preparations for e.g., bone replacement or teeth implants. Incorporation of various substrates into HAp structures could enhance its biological properties, like biocompatibility or antimicrobial effects. Silver ions possess high antibacterial and antifungal activity and its application as HAp dopant might increase its clinical value.ResultsNew silicate-substituted hydroxyapatites (HAp) doped with silver ions were synthesized via hydrothermal methods. The crystal structure of HAp was investigated by using the X-ray powder diffraction. Antifungal activity of silver ion-doped HAp (with 0.7 mol%, 1 mol% and 2 mol% of dopants) was tested against the yeast-like reference and clinical strains of Candida albicans, C. glabrata, C. tropicalis, Rhodotorula rubra, R. mucilaginosa, Cryptococcus neoformans and C. gattii. Spectrophotometric method was used to evaluate antifungal effect of HAp in SD medium. It was shown that already the lowest dopant (0.7 mol% of Ag+ ions) significantly reduced fungal growth at the concentration of 100 µg/mL. Increase in the dopant content and the concentration of HAp did not cause further growth inhibition. Moreover, there were some differences at the tolerance level to Ag+ ion-doped HAp among tested strains, suggesting strain-specific activity.ConclusionsPreformed studies confirm antimicrobial potential of hydroxyapatite doped with silver. New Ag+ ion-HAp material could be, after further studies, considered as medical agent with antifungal properties which lower the risk of a surgical-related infections.

Effects of annealing in vacuum on the microstructure of silicon-containing calcium phosphate films deposited on a ZrNb alloy by radio-frequency magnetron sputtering

Coatings were deposited on the surface of a ZrNb alloy by radio-frequency magnetron sputtering using targets consisting of either pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA). The coated ZrNb samples were heated in a vacuum furnace at a pressure of 5 × 10−5 Torr and temperature 700 °C for 2 h. Precursor powders of silicate-substituted HA [Ca10(PO4)6−x(SiO4)x(OH)2−x, x = 0, 0.5, or 1.72] were used to fabricate the targets for sputtering. The aim of this study was to analyze the effect of Si addition to HA on crystallization behavior and structure of the resulting films using transmission electron microscopy and electron diffraction patterns of selected sites. The average thickness of the films was in the range of 175–345 nm. The Si substitution in HA played a major role in the mechanisms of coating formation and crystallization behavior, which influenced the structure and crystallinity of the layers deposited by radio-frequency magnetron sputtering. Moreover, the results indicate that surface-induced crystallization of the deposited thin films is more pronounced than internal crystallization. A possible mechanism underlying the observed decrease in the crystallization rate with the increasing silicate content in the HA-based films is discussed.

The Study of Nanosized Silicate-Substituted Hydroxyapatites Co-Doped with Sr2+ and Zn2+ Ions Related to Their Influence on Biological Activities.

Nanosized silicate-substituted hydroxyapatites, characterized by the general formula Ca9.8-x-nSrnZnx(PO4)6-y(SiO4)y(OH)2 (where: n = 0.2 [mol%]; x = 0.5-3.5 [mol%]; y = 4-5 [mol%]), co-doped with Zn2+ and Sr2+ ions, were synthesized with the help of a microwave-assisted hydrothermal technique. The structural properties were determined using XRD (X-ray powder diffraction) and Fourier-transformed infrared spectroscopy (FT-IR). The morphology, size and shape of biomaterials were detected using scanning electron microscopy techniques (SEM). The reference strains of Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa were used to assess bacterial survivability and the impact on biofilm formation in the presence of nanosilicate-substituted strontium-hydroxyapatites. Safety evaluation was also performed using the standard cytotoxicity test (MTT) and hemolysis assay. Moreover, the mutagenic potential of the materials was assessed (Ames test). The obtained results suggest the dose-dependent antibacterial activity of nanomaterials, especially observed for samples doped with 3.5 mol% Zn2+ ions. Moreover, the modification with five SiO4 groups enhanced the antibacterial effect; however, a rise in the toxicity was observed as well. No harmful activity was detected in the hemolysis assay as well as in the mutagenic assay (Ames test).

ВЛИЯНИЕ СОСТАВА КРИСТАЛЛОХИМИЧЕСКОЙ СТРУКТУРЫ КАЛЬЦИЙ-ФОСФАТНОГО НАНОКОМПОЗИТА НА ФОРМИРОВАНИЕ ЭЛЕКТРОПОВЕРХНОСТНЫХ И КИСЛОТНО-ОСНОВНЫХ СВОЙСТВ

The single-phase modified nanostructured hydroxyapatites and biomimetic calcium-phosphate nanocomposite (BMHAP) doped by silicate and carbonate anions are synthesized by chemical precipitation in aqueous solutions. The chemical composition of the obtained samples is studied by energy dispersive X-ray spectroscopy using a scanning electron microscope. It is shown that the obtained molar ratios are close to the design values in all samples. The influence of different modifying ions in the crystal-chemical structure of hydroxyapatite (HAp) on the electrosurface properties of the synthesized products has been studied. Unmodified hydroxyapatite, silicate-substituted hydroxyapatite, and BMHAP particles are found to carry a negative charge in an aqueous suspension at pH = 7, while carbonate-substituted HAp particles had a positive charge. It is revealed that the introduction of silicate and carbonate anions into the HAp structure is accompanied by an increase in negative values of the zeta-potential from -1.05 to -4.29 mV. The change in the distribution of active centers on the surface of modified nanostructured hydroxyapatites is studied by the adsorption of acid-base indicators method with pKax in the range from -0.3 to +12.8. In contrast to stoichiometric hydroxyapatite, in BMHAP the neutral Bronsted centers prevails, and their concentration is 48.38 mmol-eq/g

Investigation of Physicochemical Properties of the Structurally Modified Nanosized Silicate-Substituted Hydroxyapatite Co-Doped with Eu3+ and Sr2+ Ions.

In this paper, a series of structurally modified silicate-substituted apatite co-doped with Sr2+ and Eu3+ ions were synthesized by a microwave-assisted hydrothermal method. The concentration of Sr2+ ions was set at 2 mol% and Eu3+ ions were established in the range of 0.5–2 mol% in a molar ratio of calcium ion amount. The XRD (X-ray powder diffraction) technique and infrared (FT-IR) spectroscopy were used to characterize the obtained materials. The Kröger–Vink notation was used to explain the possible charge compensation mechanism. Moreover, the study of the spectroscopic properties (emission, emission excitation and emission kinetics) of the obtained materials as a function of optically active ions and annealing temperature was carried out. The luminescence behavior of Eu3+ ions in the apatite matrix was verified by the Judd–Ofelt (J-O) theory and discussed in detail. The temperature-dependent emission spectra were recorded for the representative materials. Furthermore, the International Commission on Illumination (CIE) chromaticity coordinates and correlated color temperature were determined by the obtained results.

Theranostic Applications of Nanostructured Silicate-Substituted Hydroxyapatite Codoped with Eu3+ and Bi3+ Ions-A Novel Strategy for Bone Regeneration.

In this paper, nanocrystalline silicate-substituted hydroxyapatites (nSi-HAps) codoped with Eu3+ were functionalized with Bi3+ ions. Biomaterials were synthesized using a microwave-assisted hydrothermal method and heat-treated at 700 °C. The concentration of Eu3+ ions was established at 1 mol %, and the concentration of Bi3+ was in the range of 0.5-2 mol %. The physicochemical properties of the obtained biomaterials were determined using previously established methods, including X-ray powder diffraction, scanning electron microscopy techniques, and IR spectroscopy. Particle sizes obtained in this study were in the range of 22-65 nm, which was established by the Rietveld method. The luminescence properties of the Eu3+ ion-doped silicate-substituted apatite were recorded depending on the bismuth(III) concentration. The cytocompatibility of obtained biomaterials was tested using the model of mouse pre-osteoblasts cell line, that is, MC3T3-E1. We showed that the obtained biomaterials exerted anti-apoptotic effect, reducing the number of early and late apoptotic cells and decreasing caspase activity and reactive oxygen species accumulation. The transcripts levels of genes associated with apoptosis confirmed the anti-apoptotic effect of the biomaterials. Increased metabolic activity of MC3T3-E1 in cultures with biomaterials functionalized with Bi3+ ions has been observed. Moreover, the determined profile of osteogenic markers indicates that the obtained matrices, that is, Eu3+:nSi-HAp functionalized with Bi3+ ions, exert pro-osteogenic properties. The biological features of Eu3+:nSi-HAp modified with Bi3+ ions are highly desired in terms of functional tissue restoration and further efficient osteointegration.

Quanfima: An open source Python package for automated fiber analysis of biomaterials.

Hybrid 3D scaffolds composed of different biomaterials with fibrous structure or enriched with different inclusions (i.e., nano- and microparticles) have already demonstrated their positive effect on cell integration and regeneration. The analysis of fibers in hybrid biomaterials, especially in a 3D space is often difficult due to their various diameters (from micro to nanoscale) and compositions. Though biomaterials processing workflows are implemented, there are no software tools for fiber analysis that can be easily integrated into such workflows. Due to the demand for reproducible science with Jupyter notebooks and the broad use of the Python programming language, we have developed the new Python package quanfima offering a complete analysis of hybrid biomaterials, that include the determination of fiber orientation, fiber and/or particle diameter and porosity. Here, we evaluate the provided tensor-based approach on a range of generated datasets under various noise conditions. Also, we show its application to the X-ray tomography datasets of polycaprolactone fibrous scaffolds pure and containing silicate-substituted hydroxyapatite microparticles, hydrogels enriched with bioglass contained strontium and alpha-tricalcium phosphate microparticles for bone tissue engineering and porous cryogel 3D scaffold for pancreatic cell culturing. The results obtained with the help of the developed package demonstrated high accuracy and performance of orientation, fibers and microparticles diameter and porosity analysis.

A new approach to spectroscopic and structural studies of the nano-sized silicate-substituted hydroxyapatite doped with Eu3+ ions.

Nanocrystalline silicate-substituted hydroxyapatites Ca10-xEux(PO4)4(SiO4)2(OH)2 (where x = 0.5, 1.0, 2.0, 5.0 mol%) doped with Eu3+ ions were synthesized using a microwave assisted hydrothermal method and heat-treated in the temperature range from 700 to 1000 °C. The concentration of optically active Eu3+ ions was established in the range of 0.5-5 mol% to investigate the preference of occupancy sites. The structural and morphological properties of the obtained biomaterials were determined by using XRD (X-Ray Powder Diffraction), TEM (Transmission Electron Microscopy) and SEM (Scanning Electron Microscopy) techniques as well as infrared (IR) spectroscopy. The average particle sizes were calculated to be in the range from 20 nm to 80 nm by the Rietveld method. The charge compensation mechanism in europium(iii)-doped silicate-substituted hydroxyapatite was proposed in the Kröger-Vink-notation. The luminescence properties (the emission, excitation spectra and emission kinetics) of the Eu3+ ion-doped apatite were recorded depending on the dopant concentration. The existence of Eu2+ ions was confirmed by the emission spectra.

Pre-osteoblast cell colonization of porous silicon substituted hydroxyapatite bioceramics: Influence of microporosity and macropore design

Silicate-substituted hydroxyapatite scaffolds containing multiscale porosity are manufactured. Model parts containing macropores of five cross-sectional geometries (circle, square, rhombus, star and triangle) and two sizes are shaped by microstereolithography. Three open microporosity contents (0.5, 23 or 37 vol%) are introduced in the ceramic. MC3T3-E1 pre-osteoblasts are seeded onto these scaffolds. Analysis of cell colonization inside the macropores after 7 and 14 days of cultivation shows that the cellular filling is proportional to the macropore size and strongly influenced by macropore shape. Straight edges and convex surfaces are detrimental. High aspect ratios, the absence of reentrant angles and the presence of acute angles, by creating concavities and minimizing flat surfaces, facilitate cell colonization. Rhombus and triangle cross-sections are thus particularly favorable, while square and star geometries are the least favored. An increase in the microporosity content strongly impairs cell growth in the macropores. The data are statistically analyzed using a principal components analysis that shows that macro- and microtopographical parameters of scaffolds must be collectively considered with correlated interactions to understand cell behavior. The results indicate the important cell sensing of topography during the initial step of cell adhesion and proliferation and evidence the need for an optimized scaffold design.

A comparative study of the dissolubility of pure and silicon substituted hydroxyapatite from density functional theory calculations.

Introduction of silicon into hydroxyapatite (HA) is one of the effective ways to modulate the bioactivity of HA-based biomaterials. The bulk and surface structures of silicate-substituted HA (Si-HA) were characterized by using density functional theory calculations. The energetically favorable structures were identified from a number of candidate structures. Particular attention was paid to the surface structures of Si-HA, whose bioactivity is closely relevant to their surface atoms. Compared to the surface of pure HA, the Si-HA surface has similar surface energy but different charge distribution. Under the implicit solvent model, the exposed calcium/oxygen atoms become more positive/negative in net charge, resulting in a considerable change in the surface electrostatic potential at van der Waals distances. However, changes in the dissolution of surface calcium ions are not remarkable, as depicted by their activation energy leaving from the surface. Our calculations reveal that the surface structures and properties of HA were changed to some extent by silicate substitution, which provides some hints for understanding the experimentally observed changes in bioactivity and biodegradability of Si-HA that still remain controversial in many aspects.

Functionalization of phosphocalcic bioceramics for bone repair applications

This work is devoted to the processing of bone morphogenetic protein (BMP-2) functionalized silicate substituted hydroxyapatite (SiHA) ceramic spheres. The motivation behind it is to develop injectable hydrogel/bioceramic composites for bone reconstruction applications. SiHA microspheres were shaped by spray drying and thoroughly characterized. The silicate substitution was used to provide preferred chemical sites at the ceramic surface for the covalent immobilization of BMP-2. In order to control the density and the release of the immobilized BMP-2, its grafting was performed via ethoxysilanes and polyethylene glycols. A method based on Kaiser's test was used to quantify the free amino groups of grafted organosilanes available at the ceramic surface for BMP-2 immobilization. The SiHA surface modification was investigated by means of X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy and thermogravimetry coupled with mass spectrometry. The BMP-2 bioactivity was assessed, in vitro, by measuring the luciferase expression of a stably transfected C3H10 cell line (C3H10-BRE/Luc cells). The results provided evidence that the BMP-2 grafted onto SiHA spheres remained bioactive.

Use of a fluorescent probe to monitor the enhanced affinity of rh-BMP-2 to silicated-calcium phosphate synthetic bone graft substitutes under competitive conditions

A comparative investigation was undertaken on 1–2mm sized granules of two forms of synthetic bone graft substitute (SBG) with identical pore structure but varied bulk chemistry, stoichiometric hydroxyapatite (HA) and silicate substituted (0.8wt% Si) hydroxyapatite (SA), to assess the influence of SBG chemistry on the relative affinity of an osteogenic growth factor (GF), recombinant human bone morphogenetic protein-2 (rhBMP-2). A previously described novel fluorescent probe, fluoresceinthioureidoaminocaproic acid (FTCA), was covalently attached to rhBMP-2 to give FTCA-rhBMP-2 and facilitate the quantitative monitoring of GF uptake and release from the two chemistries of SBG. The relative affinity of rhBMP-2 for the HA and SA granules was assessed at a physiologically relevant concentration of 300ngmL−1 from three (increasingly complex) environments; phosphate buffered saline (PBS), minimum Eagles' medium (MEM) and serum supplemented MEM (SCEM) in order to closely mimic clinical bone repair procedures. The results demonstrated that rhBMP-2 affinity to SBGs was highly sensitive to both SBG chemistry and the composition of the local environment. Under the most physiologically relevant competitive conditions of SCEM, rhBMP-2 showed greater affinity to SA (P<0.05) such that 50% of the rhBMP-2 in solution was adsorbed to the SA granules after only 15min, as compared to 30% adsorbed to the HA granules. Subsequent investigation of the desorption of adsorbed GF from the SBGs demonstrated that a significantly higher percentage of the adsorbed rhBMP-2 was desorbed from HA as compared to SA granules. Together, these observations suggested that at physiologically relevant concentrations and conditions, rhBMP-2 has a greater affinity to silicate-substituted hydroxyapatite as compared to stoichiometric hydroxyapatite, which may in part explain the enhanced osteoconductivity and reported osteoinductivity for silicate-substituted hydroxyapatite based SBGs.

Silicates in orthopedics and bone tissue engineering materials.

Following the success of silicate-based glasses as bioactive materials, silicates are believed to play important roles in promoting bone formation and have therefore been considered to provide a hydroxyapatite (HAP) surface layer capable of binding to bone as well as potentially being a pro-osteoinductive factor. Natural silicate minerals and silicate-substituted HAPs are also being actively investigated as orthopaedic bone and dental biomaterials for application in tissue engineering. However, the mechanisms for the proposed roles of silicate in these materials have not been fully understood and are controversial. Here, we review the potential roles of silicate for bone tissue engineering applications and recent breakthroughs in identifying the cellular-level molecular mechanisms for the osteoinductivity of silica. The goal of this article is to inspire new ideas for the rational design of third-generation cell-and gene-affecting biomaterials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2090-2102, 2017.

Is the Expression of RUNX2 and Osterix Upregulated by Silicate Substituted Hydroxyapatite?

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Tendon cells cultured on electrochemically coated hydroxyapatite and silicate-substituted hydroxyapatite substrates

Tendon cells cultured on electrochemically coated hydroxyapatite and silicate-substituted hydroxyapatite substrates

Effects of silicate and carbonate substitution on the properties of hydroxyapatite prepared by aqueous co-precipitation method

This research was conducted to investigate the effects of silicate and carbonate substitutions in hydroxyapatite (HA) on phase retention, physical properties, and in vitro biological response. A wet chemical method was employed to synthesize silicate-substituted HA (Si-HA) and carbonate-substituted HA (CHA). It was shown that the presence of silicate and carbonate ions in the HA lattice increases the specific surface area and Ca/P molar ratio. In addition, the substitution also resulted in a reduction in the crystallinity of the HA powder and promoted better bioactivity of the sintered body. This was confirmed through in vitro cell culture experiment which revealed that the osteoblast cells adhered well on the surface of the ceramic and that ionic-substituted HA exhibited better cell performance than the control HA. (C) 2015 Elsevier Ltd. All rights reserved.

Silicate-substituted carbonated hydroxyapatite powders prepared by precipitation from aqueous solutions

The powders of silicate-substituted carbonated hydroxyapatites were prepared by a precipitation method from aqueous alkaline solutions with a varied sodium silicate content. With the use of physicochemical techniques, it was established that the solid phase included to 7.36 wt % silicate ions and to 7.34 wt % carbonate ions under the test conditions. The nature of processes occurring on the thermal treatment of the samples depends on the Ca/P and Ca/(P + Si) molar ratios and the concentration of SiO4 groups. A study of the behavior of solid phases on contact with a solution of NaCl (0.9 mol %) showed that the rates of dissolution of all of the silicon-containing samples were higher than that of unsubstituted hydroxyapatite species by a factor of 2–4 because of the active participation of silicates in the resorption of the materials.