Hydroxyapatite Lattice Research Articles

Luminescent Tb3+/Sm3+ co-doped hydroxyapatite nanoparticles as an imaging probe in N2a cells

This work reports the synthesis of hydroxyapatite (HAp) nanoparticles co-doped with trivalent terbium (Tb3+) and samarium (Sm3+) ions by a surfactant free chemical precipitation method. Co-doping enables to combine the optical properties of Tb3+ and Sm3+ ions. Characterization techniques like X-Ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), energy dispersive X-ray spectroscopy (EDX) were used to determine the crystalline and structural properties. These studies confirmed that the lanthanide ions Tb3+ and Sm3+ were successfully doped onto the HAp lattice. The photoluminescence emission spectra exhibited intense emissions from both the lanthanide ions. The Sm3+ photoluminescence spectra showed enhanced emission,indicating that energy is being transferred from the Tb3+ to Sm3+ ions. To examine the cell viability, N2a cellswere subjected to the MTT cytotoxicity assay. As demonstrated by the cell imaging on N2a cells, the synthesised nanoparticles are ideal candidates for fluorescent labelling using lanthanide ions. Furthermore, thestrong cytocompatibility of Tb3+/Sm3+ co-doped hydroxyapatitesuggests that it is a promising nanoscale biomaterial.

Effects of copper on hydroxyapatite thin films by pulsed laser deposition on silicon

AbstractThis study deals with the effect of Cu on hydroxyapatite (HAp) thin films on silicon substrates prepared by pulsed laser deposition (PLD) technique for Cu concentrations ranging from 0 to 0.8 wt.%. Fourier transform infrared spectroscopy and Raman spectroscopy provide additional evidence of HAp in the films, which exhibit characteristic HAp bands such as the 960 cm−1 phosphate ion band. The X‐ray diffraction patterns confirm the presence of HAp, without copper‐related peaks, suggesting that it is not incorporated into the HAp lattice, which is present as an amorphous phase. X‐ray photoelectron spectroscopy confirms the presence of Cu on the HAp thin films, possibly related to the adsorption of Cu2+ on HAp surfaces through electrostatic or interactions with (PO4)3− groups. Atomic force microscopy shows that the roughness of the films varies depending on the presence or absence of copper ions. Finally, density functional theory and kinetic Monte Carlo simulations explain the effects of atomic diffusion on roughness and HAp clustering. These changes correlate with the contact angle values, indicating the formation of hydrophobic films due to copper inclusions.

Ancient and modern bone diagnosis: Towards a better understanding of chemical and structural feature alterations

Chemical and structural alterations hold great importance in the field of diagenesis. Attenuated Total Reflectance − Fourier Transform Infrared Spectroscopy (ATR-FTIR) is a valuable method for examining bio-apatite composition changes. Infrared spectroscopy (IR) and X-ray diffraction (XRD) were employed to analyze both modern and archaeological bone specimens. Organic and mineral component changes in modern and ancient samples were investigated. Ancient bone samples were collected from two archaeological sites in Jordan, dating back to the Iron and Byzantine ages. IR results indicated that collagen cross-links and mineral maturity are higher in modern bones compared to ancient bones. Additionally, the crystallinity index is higher in modern bones than in archaeological bones, while the carbonate to phosphate ratio (C/P) is lower in modern bones than in ancient ones. Curve fitting was applied to reveal the carbonate substitution inside the hydroxyapatite lattice within the IR region from 850 to 890 cm−1. A2-type carbonates (identified as υ2 of CO32−) denote hydroxyl site substitution, and B-type carbonates represent a substitution to the phosphate site. The full width at half maximum (FWHM) of the peak at 604 cm−1 from IR spectra reveals that crystallinity is higher in modern bones, as confirmed by the FWHM of the (002)-apatite pattern in XRD. Statistical analysis was conducted to validate these findings, ensuring the robustness of the results. Finally, the results obtained in this investigation align with previous literature reports regarding ATR-FTIR ratios. This suggests that modern bones have better crystallinity compared to ancient bones. Furthermore, the ATR-FTIR ratios indicate that the hydroxyl and phosphate sites of modern bones undergo more substitution than older bones. The findings of this study not only enhance our understanding of the diagnostic processes in archaeological bone specimens but also have broader implications for fields such as archaeology, anthropology, and forensics, where the analysis of bone composition and structural changes can provide valuable insights into the history and characteristics of ancient remains.

Substitution of europium (III) in hydroxyapatite lattice for luminescence applications: Integrating experimental and theoretical insights

Europium(III) (Eu3+/Eu(III)) substitution in the hydroxyapatite (HAp) lattice imparts luminescence properties, enabling its application in diagnostics and bioimaging. Despite numerous experimental studies, there has been a lack of comprehensive discussion on the substitution behavior and local structural stability of Eu3+ within HAp. In this study, experimental and first-principles investigations were integrated to explore and understand the substitution of Eu3+ in HAp. Optimization of various HAp models revealed the dependency of Eu3+ substitution site on the charge compensation mechanism. Eu3+ prefers the Ca(2) site when OH is converted to O and the Ca(1) site in the presence of a Ca vacancy. Phonon calculations showed that temperature influences charge compensation and site preference, favoring OH to O compensation and Eu3+ in Ca(2) at higher temperatures and Ca vacancy and Eu3+ in Ca(1) at lower temperatures. Electronic structure simulations explained that the luminescence in Eu(III)-substituted HAp primarily arises from charge transfer between Eu3+ and O atoms, supported by experimental photoluminescence measurements. Correspondence between simulations and experimental photoluminescence data emphasizes the reliability of the computational approach in this study. The integration of insights from experimental and simulation results enhances the understanding of substitution of Eu3+ in the HAp lattice, providing valuable guidance for designing and optimizing HAp-based luminescent and optical materials.

Mechanical properties of additively manufactured lattice structures composed of zirconia and hydroxyapatite ceramics

Ceramic lattices hold great potential for bone scaffolds to facilitate bone regeneration and integration of native tissue with medical implants. While there have been several studies on additive manufacturing of ceramics and their osseointegrative and osteoconductive properties, there is a lack of a comprehensive examination of their mechanical behavior. Therefore, the aim of this study was to assess the mechanical properties of different additively manufactured ceramic lattice structures under different loading conditions and their overall ability to mimic bone tissue properties.Eleven different lattice structures were designed and manufactured with a porosity of 80% using two materials, hydroxyapatite (HAp) and zirconium dioxide (ZrO2). Six cell-based lattices with cubic and hexagonal base, as well as five Voronoi-based lattices were considered in this study. The samples were manufactured using lithography-based ceramic additive manufacturing and post-processed thermally prior to mechanical testing. Cell-based lattices with cubic and hexagonal base, as well as Voronoi-based lattices were considered in this study. The lattices were tested under four loading conditions: compression, four-point bending, shear and tension.The manufacturing process of the different ceramics leads to different deviations of the lattice geometry, hence, the elastic properties of one structure cannot be directly inferred from one material to another. ZrO2 lattices prove to be stiffer than HAp lattices of the same designed structure. The Young’s modulus for compression of ZrO2 lattices ranges from 2 to 30GPa depending on the used lattice design and for HAp 200MPa to 3.8GPa. The expected stability, the load where 63.2% of the samples are expected to be destroyed, of the lattices ranges from 81 to 553MPa and for HAp 6 to 42MPa.For the first time, a comprehensive overview of the mechanical properties of various additively manufactured ceramic lattice structures is provided. This is intended to serve as a reference for designers who would like to expand the design capabilities of ceramic implants that will lead to an advancement in their performance and ability to mimic human bone tissue.

The Incorporation of Zinc into Hydroxyapatite and Its Influence on the Cellular Response to Biomaterials: A Systematic Review.

Zinc is known for its role in enhancing bone metabolism, cell proliferation, and tissue regeneration. Several studies proposed the incorporation of zinc into hydroxyapatite (HA) to produce biomaterials (ZnHA) that stimulate and accelerate bone healing. This systematic review aimed to understand the physicochemical characteristics of zinc-doped HA-based biomaterials and the evidence of their biological effects on osteoblastic cells. A comprehensive literature search was conducted from 2022 to 2024, covering all years of publications, in three databases (Web of Science, PUBMED, Scopus), retrieving 609 entries, with 36 articles included in the analysis according to the selection criteria. The selected studies provided data on the material's physicochemical properties, the methods of zinc incorporation, and the biological effects of ZnHA on bone cells. The production of ZnHA typically involves the wet chemical synthesis of HA and ZnHA precursors, followed by deposition on substrates using processes such as liquid precursor plasma spraying (LPPS). Characterization techniques confirmed the successful incorporation of zinc into the HA lattice. The findings indicated that zinc incorporation into HA at low concentrations is non-cytotoxic and beneficial for bone cells. ZnHA was found to stimulate cell proliferation, adhesion, and the production of osteogenic factors, thereby promoting in vitro mineralization. However, the optimal zinc concentration for the desired effects varied across studies, making it challenging to establish a standardized concentration. ZnHA materials are biocompatible and enhance osteoblast proliferation and differentiation. However, the mechanisms of zinc release and the ideal concentrations for optimal tissue regeneration require further investigation. Standardizing these parameters is essential for the effective clinical application of ZnHA.

Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

Carbonate hydroxyapatite is the common derivative of hydroxyapatite found in living systems. It is the building block of most hard tissues, including the teeth and bones. A vast majority of the applications of this versatile material focus on its biomedical applications, which is attributable to its closeness to biological apatites. Hydroxyapatite is a strong precursor to carbonate apatite in nature, and many experiments show that both are similar in a few respects. A significant divergence point is carbonate's obvious impact on its physicochemical properties and concomitant applications. The inclusion of carbonate ions into the lattice of hydroxyapatite results in morphological and physicochemical changes that vary with the method of synthesis and extent of substitution. The unique crystal structure, improved surface area, and porous morphology of carbonate hydroxyapatites also make it useful for catalysis and environmental remediation as adsorbents for heavy metals. This review briefly examines carbonate hydroxyapatite, its synthesis, its modification, and its characterization. It also highlights its biomedical applications while drawing attention to its non-medical potential.

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.

Ordering of oxygen vacancies in hydroxyapatite under electron irradiation

Understanding the mechanisms of radiation induced defect generation is essential for assessment of materials to be used in nuclear environments. In the current work, we investigate the effect of 10 MeV electron irradiation on the generation and possible ordering of defects/oxygen vacancies in hydroxyapatite (HAP) powders. Comprehensive analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) and Raman spectra establish that (a) HAP has a high level of structural stability even after exposure to electron irradiation; (b) irradiation leads to the generation of surface defects/oxygen vacancy predominantly in the PO43− polyanion site, particularly in part of asymmetric bonding within the P–O bonds and (c) there is noticeable evidence for an ordered arrangement of oxygen vacancies within the HAP irradiated at 1 MGy dose. These radiation-induced defects, such as oxygen vacancies, can migrate within the HAP lattice, leading to formation of defect/oxygen vacancies clusters which ultimately results in the ordering tendency of oxygen vacancies within the lattice. The observed ordering, as evidenced by the photoluminescence intensities, aligns with the sequence HAP-1MGy > HAP-20MGy > HAP, providing further support for the presence of ordered oxygen vacancies.

Formation of Oxygen Vacancies in Cr3+-Doped Hydroxyapatite Nanofibers and Their Role in Generating Paramagnetism

AbstractWe demonstrate that doping hydroxyapatite (HAp) with Cr3+ ions induces oxygen vacancies, contributing to paramagnetism. Cathodoluminescence and photoluminescence analyses reveal increased oxygen vacancy formation in $${\text{O}}{\text{H}}^{-}$$ OH - and $${\text{P}}{\text{O}}_{4}^{3-}$$ PO 4 3 - groups with rising Cr3+ concentrations, highlighted by stronger cathodoluminescence emissions at 2.57 and 2.95 eV and the photoluminescence emission at 3.32 eV. Raman spectroscopy shows new modes at 900 and 970 cm−1, indicating distortion of the v1 vibrational mode due to Cr3+ substitution at Ca(II) sites of the HAp lattice. X-ray photoelectron spectroscopy confirms Cr3+ in the HAp:Cr. Magnetometry reveals a shift from diamagnetism in pure HAp to increasing paramagnetism in HAp:Cr with higher Cr3+ content, achieving 0.0460 emu/g at 10 kOe with concentrations higher than 2.9 at.%. This paramagnetism is attributed to Cr3+ ions and singly ionized oxygen vacancies $$V^{\prime}_{{\text{O}}}$$ V O ′ aligning along an external magnetic field, with $$V^{\prime}_{{\text{O}}}$$ V O ′ formation linked to $${\text{PO}}_{4}^{{3}-}$$ PO 4 3 - replacement by $${\text{PO}}_{3}^{{2}-}$$ PO 3 2 - in HAp.

Site preference and local structural stability of Bi(III) substitution in hydroxyapatite using first-principles simulations.

Bismuth (Bi(III)) substitution in hydroxyapatite (HAp) lattice confers unique properties such as antibacterial, catalytic, radiosensitization, and conductive properties while preserving the innate bioactivity. Understanding the local structural changes upon Bi3+ substitution is essential for controlling the stability and optimizing the properties of HAp. Despite numerous experimental studies, the precise substitution behaviors, such as site preference and structural stability, remain incompletely understood. In this study, the substitution behavior of Bi(III) into the HAp lattice with formula of Ca9Bi(PO4)6(O)(OH) was investigated via first-principles simulation by implementing density functional theory. Energy calculations showed that Bi3+ preferentially occupies the Ca(2) site with an energy difference of ∼0.02 eV per atom. Local structure analysis revealed higher bond population values and an oxygen coordination shift from 7 to 6 for the Ca(2) site, attributed to the greater covalent interactions and its flexible environment accommodating the bulky Bi3+ ion and its stereochemically active lone pair. This work provides the first comprehensive investigation on Bi3+ ion substitution site preference in HAp using first-principles simulations.

Abalone shell-derived Mg-doped mesoporous hydroxyapatite microsphere drug delivery system loaded with icariin for inducing apoptosis of osteosarcoma cells.

Hydroxyapatite (HAP) porous microspheres with very high specific surface area and drug loading capacity, as well as excellent biocompatibility, have been widely used in tumour therapy. Mg2+ is considered to be a key factor in bone regeneration, acting as an active agent to stimulate bone and cartilage formation, and is effective in accelerating cell migration and promoting angiogenesis, which is essential for bone tissue repair, anti-cancer, and anti-infection. In this study, abalone shells from a variety of sources were used as raw materials, and Mg2+-doped abalone shell-derived mesoporous HAP microspheres (Mg-HAP) were prepared by hydrothermal synthesis as Mg2+/ icariin smart dual delivery system (ICA-Mg-HAP, IMHA). With increasing of Mg2+ doping, the surface morphology of HAP microspheres varied from collapsed macroporous to mesoporous to smooth and non-porous, which may be due to Mg2+ substitution or coordination in the HAP lattice. At 30% Mg2+ doping, the Mg-HAP microspheres showed a more homogeneous mesoporous morphology with a high specific surface area (186.06 m2/g). The IMHA microspheres showed high drug loading (7.69%) and encapsulation rate (83.29%), sustained Mg2+ release for more than 27 days, sustained and stable release of icariin for 60 hours, and good responsiveness to pH (pH 6.4 > pH 5.6). In addition, the IMHA delivery system stimulated the rapid proliferation of bone marrow mesenchymal stem cells and induced apoptosis in MG63 cells by blocking the G2 phase cycle of osteosarcoma cells and stimulating the high expression of apoptotic genes (Bcl-2, caspase-3, -8, -9). This suggests that the abalone shell-based IMHA may have potential applications in drug delivery and tumour therapy.

Physicochemical characterization and cell behavior of porous hydroxyapatite ceramics doped with Ag ions: Fluorescence quenching in fluorescence-labeled cells

Mouse preosteoblast cells were found to adhere well to and spread on the surface of porous Ag-doped hydroxyapatite (HAp) ceramics fabricated using a small amount of Ag. Ag particles were deposited on the surfaces of the HAp ceramics fabricated by doping Ag in large amounts. These Ag-doped samples were more hydrophobic owing to the loss of OH ions from HAp lattices with increasing the amount of added Ag. The cells adhered to the hydrophobic surface even in the presence of cytotoxic Ag particles. Consequently, the equilibrium between the hydrophobicity of the surface and cytotoxicity of Ag particles determines cell adhesion. Additionally, fluorescence quenching did not occur in cells stained for nuclei (blue) and fibronectin (red), but in cells stained for actin (red and green), in the presence of Ag particles. Charge transfer from actin protein molecules to Ag particles enabled quenching because the Ag particles exerted the heavy-atom effect.

Selenium- and/or copper-substituted hydroxyapatite: A bioceramic substrate for biomedical applications.

Atomic substitution or doping of a bioceramic material hydroxyapatite (HA) with specific ions is an appealing approach for improving its biocompatibility and activity, as well as imparting antibacterial properties. In this study, selenium- and/or copper-substituted hydroxyapatite powders were synthesized by an aqueous precipitation method and using the freeze-drying technique. The molar concentrations of constituents were calculated based on the proposed mechanism whereby selenium (Se4+) ions partially substitute phosphorus (P5+) sites, and copper (Cu2+) ions partially substitute (Ca2+) sites in the HA lattice. Dried precipitated samples were characterized using Inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR) and Field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX). Accordingly, substitution of Se4+ and/or Cu2+ ions took place in the crystal lattice of HA without the formation of any impurities. The presence of sulphur (S2-) ions in the hydroxyapatite was detected by ICP-OES in all samples with copper substituted in the lattice. The cytotoxicity of the powders on osteoblastic (MC3T3-E1) cells was evaluated in vitro. Selenium substituted hydroxyapatite (SeHA), at the concentration (200μg/mL), demonstrated higher populations of the live cells than that of control (cells without powders), suggesting that selenium may stimulate the proliferation of these cells. In addition, the copper substituted hydroxyapatite (CuHA) and the selenium and copper substituted hydroxyapatite (SeCuHA) at the concentrations (200 and 300μg/mL) and (200μg/mL), respectively demonstrated better results than the unsubstituted HA. Antimicrobial activity was assessed using a well-diffusion method against Streptococcus mutans and Candida albicans, and superior results has obtained with SeCuHA samples. Presented findings imply that selenium and/or copper substituted modified hydroxyapatite nanoparticles, may be an attractive antimicrobial and cytocompatible substrate to be considered for use in a range of translational applications.

A tailored hydroxyapatite/magnesium silicate 3D composite scaffold: Mechanical, degradation, and bioactivity properties

Today, hydroxyapatite (HA)-based composite scaffolds are widely studied, but there is a lack of a doping method that can simultaneously improve the mechanical strength, degradation rate, and bioactivity of HA scaffolds. In this paper, the amorphous magnesium silicate (MS) with a low melting point is selected as the doping phase of HA. The hydroxyapatite/magnesium silicate composite was fabricated using photocuring technology. In addition, at high temperatures, ionic substitution can occur between the magnesium silicate glass phase and the HA lattice. Therefore, a new phase with a pinning effect can be obtained at the grain boundary and the magnesium silicate can further improve the biocompatibility of HA scaffolds. In the sintering process, the magnesium silicate was melted to a liquid state, and then the sintering temperature of the scaffold was reduced for grain refinement. The morphological analysis shows that MS doping is an important factor for grain refinement, which has been reduced from 12 μm to 6 μm. Furthermore, the formation of new diopside and whitlockite phases with a pinning effect has been observed at the grain boundaries. Specifically, the compressive stress of the composite scaffold is increased by 59.15% compared to the pure HA scaffold. However, the soaking and cell experimental findings show that the composite scaffold has a better degradation rate, cell activity, and bone induction. Finally, this study found that a composite scaffold with improved mechanical strength, degradation performance, and biocompatibility can be obtained with the addition of magnesium silicate as the doping phase of HA with 30 wt% of.

Antibacterial activity of silver doped hydroxyapatite toward multidrug-resistant clinical isolates of Acinetobacter baumannii

Bacteria Acinetobacter baumannii is a persistent issue in hospital-acquired infections due to its fast and potent development of multi-drug resistance. To address this urgent challenge, a novel biomaterial using silver (Ag+) ions within the hydroxyapatite (HAp) lattice has been developed to prevent infections in orthopedic surgery and bone regeneration applications without relying on antibiotics. The aim of the study was to examine the antibacterial activity of mono-substituted HAp with Ag+ ions and a mixture of mono-substituted HAps with Sr2+, Zn2+, Mg2+, SeO32- and Ag+ ions against the A. baumannii.The samples were prepared in the form of powder and disc and analyzed by disc diffusion, broth microdilution method, and scanning electron microscopy. The results from the disc-diffusion method have shown a strong antibacterial efficacy of the Ag-substituted and mixture of mono-substituted HAps (Sr, Zn, Se, Mg, Ag) toward several clinical isolates. The Minimal Inhibitory Concentrations for the powdered HAp samples ranged from 32 to 42 mg/L (Ag+ substituted) and 83–167 mg/L (mixture of mono-substituted), while the Minimal Bactericidal Concentrations after 24 h of contact ranged from 62.5 (Ag+) to 187.5–292 mg/L (ion mixture). The lower substitution level of Ag+ ions in a mixture of mono-substituted HAps was the cause of lower antibacterial effects measured in suspension. However, the inhibition zones and bacterial adhesion on the biomaterial surface were comparable. Overall, the clinical isolates of A. baumannii were effectively inhibited by substituted HAp samples, probably in the same amount as by other commercially available silver-doped materials, and such materials may provide a promising alternative or supplementation to antibiotic treatment in the prevention of infections associated with bone regeneration. The antibacterial activity of prepared samples toward A. baumannii was time-dependent and should be considered in potential applications.

Adsorption of l-buthionine sulfoximine on Bi(III) and Eu(III) co-substituted hydroxyapatite nanocrystals for enhancing radiosensitization effects

Cancer theranostics combines therapeutic and diagnostic capabilities into a single system to treat cancer efficiently. Biocompatible nanomaterials can be engineered to exhibit cancer theranostic functions, for instance radiosensitization and photoluminescence. In this study, trivalent Bi and Eu ions were co-substituted into the lattice of hydroxyapatite (Bi(III):Eu(III) HAp) to develop a cancer theranostic nanocrystal. Bi provides radiosensitization capabilities while Eu imparts photoluminescence properties. To complement the radiotherapeutic function, l-buthionine sulfoximine (l-BSO) was adsorbed onto the nanocrystal surface. l-BSO inhibits the biosynthesis of cellular antioxidants, which can enhance radiosensitization effects. The Bi(III):Eu(III) HAp nanocrystals were prepared via a hydrothermal method. Structural and compositional analyses showed that both Bi and Eu ions were substituted into the HAp lattice. l-BSO was adsorbed onto the surface via electrostatic interactions between the charged carboxyl and amino groups of l-BSO and the surface ions of the nanocrystals. The adsorption followed the Langmuir isotherm model, implying a homogeneous monolayer adsorption. The l-BSO adsorbed Bi(III):Eu(III) HAp nanocrystals were found to have negligible cytotoxicity except the setting with l-BSO adsorbed amounts of 0.44 μmol/m2. This l-BSO amount was found to be high enough to elicit cytotoxicity due to l-BSO being released and causing excessive antioxidant depletion. Gamma ray irradiation clearly activated the cytotoxicity of the samples and increased the cell death rate, confirming radiosensitization abilities. At a constant amount of nanocrystals, the cell death rate increases with l-BSO concentration. This indicates that l-BSO can enhance the radiosensitization effect of the Bi(III):Eu(III) HAp nanocrystals.

Biological Response of Human Gingival Fibroblasts to Zinc-Doped Hydroxyapatite Designed for Dental Applications-An In Vitro Study.

This study aimed to investigate the biological response induced by hydroxyapatite (HAp) and zinc-doped HAp (ZnHAp) in human gingival fibroblasts and to explore their antimicrobial activity. The ZnHAp (with xZn = 0.00 and 0.07) powders, synthesized by the sol-gel method, retained the crystallographic structure of pure HA without any modification. Elemental mapping confirmed the uniform dispersion of zinc ions in the HAp lattice. The size of crystallites was 18.67 ± 2 nm for ZnHAp and 21.54 ± 1 nm for HAp. The average particle size was 19.38 ± 1 nm for ZnHAp and 22.47 ± 1 nm for HAp. Antimicrobial studies indicated an inhibition of bacterial adherence to the inert substrate. In vitro biocompatibility was tested on various doses of HAp and ZnHAp after 24 and 72 h of exposure and revealed that cell viability decreased after 72 h starting with a dose of 31.25 µg/mL. However, cells retained membrane integrity and no inflammatory response was induced. High doses (such as 125 µg/mL) affected cell adhesion and the architecture of F-actin filaments, while in the presence of lower doses (such as 15.625 µg/mL), no modifications were observed. Cell proliferation was inhibited after treatment with HAp and ZnHAp, except the dose of 15.625 µg/mL ZnHAp at 72 h of exposure, when a slight increase was observed, proving an improvement in ZnHAp activity due to Zn doping.

Structural Changes in Ceramic Carbonized Hydroxyapatite as a Result of Long-Term Storage at Room Temperature

Carbonated hydroxyapatite (CHA) is the basic mineral component of animal and human bone. Therefore, it is widely used in medicine to repair bone defects. In orthopedic surgeries, ceramic implants are usually used as a biologically active defect filler. In the lattice of CHA carbonate ions can occupy two non-equivalent positions - A and B. A position corresponds to the position of OH- anions in the lattice of hydroxyapatite (HA), and B - PO43-. It is well known that substitution of B-positions with carbonate groups leads to significant distortions of HA lattice, which causes microstresses and crystalline defects in it. Therefore, CHA ceramics as a result of sintering is characterized by significant internal stresses whose relaxation at room temperature can lead to a change in both its phase composition and biological activity. By methods of chemical and X-ray structural analysis, infrared spectroscopy and electron scanning microscopy the ageing process of pressed CHA at room temperature, sintered in an atmosphere of dry carbon dioxide at temperatures 800÷1200 °C was studied. The phase composition and structure of freshly prepared and aged for two years ceramic samples were compared. It is shown that relaxation of internal stresses arising during sintering of presses causes plastic deformation of crystallites accompanied by redistribution of carbonate ions from B to A-position. As a result, displacement of OH- ions from channel (A) positions and decomposition of B-type CHA on CaO and A-type CHA becomes energetically advantageous.

Thermal Stability of Iron- and Silicon-Substituted Hydroxyapatite Prepared by Mechanochemical Method

In this study, hydroxyapatite with the substitution of calcium cations by iron and phosphate by silicate groups was synthesized via a mechanochemical method. The as-prepared compounds have the general formula Ca10−xFex(PO4)6−x(SiO4)x(OH)2−xOx/2 with x = 0–1.5. The thermal stability of the as-prepared compounds was studied by ex situ annealing of powders in a furnace. It has been established that, at 800 °C for x ≤ 0.5, a partial decomposition of the substituted apatites occurs with the formation of the β–Ca3(PO4)2 phase. At high “x” values, the formation of this phase starts at the lower temperature of 700 °C, followed by the formation of Fe2O3 at 900 °C. The introduction of iron and silicate ions into the hydroxyapatite lattice was shown to decrease its thermal stability.