Black Bioceramics: Combining Regeneration with Therapy

Bioceramics have been developed from bioinert to bioactive or biodegradable materials in the past few decades. However, at present, traditional bioceramics are still mainly used in bone tissue regeneration and dental restoration. In this work, a new generation of “black bioceramics,” extending the applications from tissue regeneration to disease therapy, is presented. Black bioceramics, through magnesium thermal reduction of traditional white ceramics, including silicate-based (e.g., CaSiO₃, MgSiO₃) and phosphate-based (e.g., Ca₃(PO₄)₂, Ca₅(PO₄)₃(OH)), are successfully synthesized. Due to the presence of oxygen vacancies and structural defects, the black bioceramics possess photothermal functionality while maintaining their initial high bioactivity and regenerative capacity. These black bioceramics show excellent photothermal antitumor effects for both skin and bone tumors. At the same time, they have significantly improved bioactivity for skin/bone tissue repair in vitro and in vivo. These fascinating properties award the black bioceramics with profound applications in both tumor therapy and tissue regeneration, which should greatly promote the scientific relevance and clinical application of bioceramics, representing a promising new direction of cell-instructive biomaterials.     

Polyfunctional bioceramics based on calcium phosphate and M-type hexagonal ferrite for medical applications

Magnetic biologically active ceramics based on calcium phosphate with a content of M-type hexagonal ferrite (HF) particles varying from 10 to 50 wt % has been synthesized and characterized. It has been found that the ceramics synthesized consists of a biocompatible carbonated hydroxyapatite (CHA) with the matrix containing M-type HF particles, leading to the magnetic characteristics of the ceramics synthesized being significantly higher than those of iron-oxide-modified bioglass ceramics used in medicine.     

Dielectric characteristics of biocompatible Ca10(PO4)6(OH)2 ceramics

The temperature dependence of the dielectric permittivity and losses of biocompatible Ca₁₀(PO₄)₆(OH)₂ ceramics were studied in a temperature range from 20 to 500°C. An approach to the interpretation of anomalies (bending points) observed in the dielectric characteristics of the ceramic samples is proposed, which takes into account features of the crystal structure of calcium hydroxyapatite and the defects formed in the course of thermal treatments.     

Bioactivity and mineralization of hydroxyapatite with bioglass as sintering aid and bioceramics with Na3Ca6(PO4)5 and Ca5(PO4)2SiO4 in a silicate matrix

Hydroxyapatite and Bioglass^®-45S5 were sintered together creating new ceramic compositions that yielded increased apatite deposition and osteoblast differentiation and proliferation in vitro compared to hydroxyapatite. The sintered products characterized by X-ray diffraction, revealed hydroxyapatite as the main phase when small quantities (1, 2.5 and 5 wt.%) of bioglass was added. Bioglass behaved as a sintering aid with β-TCP (Ca₃(PO₄)₂) being the minor phase. The amount of β-TCP increased with the amount of bioglass added. In compositions with larger additions of bioglass (10 and 25 wt.%), new phases with compositions of calcium phosphate silicate (Ca₅(PO₄)₂SiO₄) and sodium calcium phosphate (Na₃Ca₆(PO₄)₅) were formed respectively within amorphous silicate matrices. In vitro cell culture studies of the ceramic compositions were examined using bone marrow stromal cell (BMSC). Cell proliferation and differentiation of bone marrow stromal cells into osteoblasts were determined by Pico Green DNA assays and alkaline phosphatase (ALP) activity, respectively. All hydroxyapatite–bioglass co-sintered ceramics exhibited larger cell proliferation compared to pure hydroxyapatite samples. After 6 days in cell culture, the ceramic with Ca₅(PO₄)₃SiO₄ in a silicate matrix formed by reacting hydroxyapatite with 10 wt.% bioglass exhibited the maximum proliferation of the BMSC's. The ALP activity was found to be largest in the ceramic with Na₃Ca₆(PO₄)₅ embedded in a silicate matrix synthesized by reacting hydroxyapatite with 25 wt.% bioglass.     

The kinetics of calcium deficient and stoichiometric hydroxyapatite formation from CaHPO4·2H2O and Ca4(PO4)2O

Isothermal calorimetry was performed on intimate mixtures of CaHPO₄·2H₂O and Ca₄(PO₄)₂O constituted at Ca/P molar ratios of 1.50 and 1.67 to form the hydroxyapatite compositions Ca₉HPO₄(PO₄)₅OH and Ca₁₀(PO₄)₆(OH)₂, respectively, at complete reaction. The temperature range investigated was 15–70°C. The effects of the reaction temperature on the rates of heat evolution during hydroxyapatite formation were determined. Reactions were carried out utilizing a liquid-to-solids weight ratio of 1.0. A two-stage reaction mechanism was observed regardless of the Ca/P ratio as indicated by the presence of two reaction peaks in the plots of the rates of heat evolution against time. An Arrhenius relationship was found between the rate and temperature for each reaction stage for both compositions. Apparent activation energies of 120 and 90 kJ/mol (Ca/P=1.67) and 118 and 83 kJ/mol (Ca/P=1.50), respectively, were calculated for the first and second reaction peaks. An Arrhenius relationship was also found between the time of maximum rate and temperature. The following qualitative reaction mechanism is proposed for each of the two reaction stages for both compositions studied. The first stage involves the complete consumption of CaHPO₄·2H₂O and the partial consumption of Ca₄(PO₄)₂O to form a noncrystalline calcium phosphate and nanocrystalline hydroxyapatite. During the second stage the remaining Ca₄(PO₄)₂O reacts with the noncrystalline calcium phosphate to form the final product, stoichiometric or calcium deficient hydroxyapatite.     

Biomorphous porous hydroxyapatite-ceramics from rattan (<Emphasis Type="Italic">Calamus Rotang</Emphasis>)

The three-dimensional, highly oriented pore channel anatomy of native rattan (Calamus rotang) was used as a template to fabricate biomorphous hydroxyapatite (Ca₅(PO₄)₃OH) ceramics designed for bone regeneration scaffolds. A low viscous hydroxyapatite-sol was prepared from triethyl phosphite and calcium nitrate tetrahydrate and repeatedly vacuum infiltrated into the native template. The template was subsequently pyrolysed at 800°C to form a biocarbon replica of the native tissue. Heat treatment at 1,300°C in air atmosphere caused oxidation of the carbon skeleton and sintering of the hydroxyapatite. SEM analysis confirmed detailed replication of rattan anatomy. Porosity of the samples measured by mercury porosimetry showed a multimodal pore size distribution in the range of 300 nm to 300 μm. Phase composition was determined by XRD and FT-IR revealing hydroxyapatite as the dominant phase with minimum fractions of CaO and Ca₃(PO₄)₂. The biomorphous scaffolds with a total porosity of 70–80% obtained a compressive strength of 3–5 MPa in axial direction and 1–2 MPa in radial direction of the pore channel orientation. Bending strength was determined in a coaxial double ring test resulting in a maximum bending strength of ~2 MPa.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Enhanced dielectric constant and structural transformation in Fe-doped hydroxyapatite synthesized by wet chemical method

We report the synthesis of single-phase Fe-doped hydroxyapatite (HAp) [Ca_10?xFe _x (PO₄)₆(OH)₂ (0.0?≤?x?≤?0.3)] and enhanced dielectric constant of HAp with Fe doping. Rietveld analysis shows the change in x-axis-oriented lattice constant a in Fe-doped x?=?0.1 and 0.3 compositions in comparison with parent HAp, while z-axis-oriented lattice constant c does not show any considerable change. Analysis of absorbance data shows two new symmetric stretching peaks for Fe-doped x?=?0.1 and x?=?0.3 compositions, which are not present in parent HAp. Magnetic measurements show paramagnetic behaviour of all Fe-doped samples at 300 K. Fe-doped Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows increase in impedance in the presence of 500 Oersted (Oe) applied magnetic field in comparison with impedance in the absence of magnetic field. Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows increase in dielectric constant in comparison with parent HAp in frequency range 5–35 MHz. Fe-doped Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows?~?970% colossal magnetoimpedance at 100 Hz and?~?200% at 20 MHz frequency.     

The effect of mechanical activation on the synthesis of biocompatible Ca10(PO4)6(OH)2

The effect of mechanical activation on the course of reactions involved in the synthesis of calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ was studied; the composition, crystallographic parameters, spectroscopic characteristics, and dielectric properties of the products were determined. The role of the composition of initial components on the rate of synthesis is analyzed.     

Effects of polarization on crystallization of calcium phosphate

The acceleration effects of polarized lead zirconate titanium (Pb(Ti,Zr)O₃, PZT) on the crystallization of calcium phosphate were demonstrated when PZT plates were immersed in saturated solutions of hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂). Moreover, it is indicated that polarization also had influences on the orientation of the deposited crystals because crystalline layers of OCP (Ca₈H₂(PO₄)₆·5H₂O) were found on the negatively charged surfaces of PZT.     

Red long-lasting phosphorescence (LLP) in β-TCP type Ca9.5Mn(PO4)7 compounds

Mn-ion doped calcium phosphates namely Ca₅(PO₄)₃(OH) hydroxyapatite (HAP), β-Ca₃(PO₄)₂ (β-TCP) as well as Ca_9.5Mn(PO₄)₇ whitlockite were synthesized and the optical properties of the Mn²⁺ cations were investigated. Annealing under reducing atmosphere enhances the emission of the divalent manganese species. Electron paramagnetic resonance (EPR) and optical spectroscopies confirm that Mn²⁺ ions are the active species. Orange and red emissions occur respectively for the Mn:HAP and Mn:TCP. For this latter, long-lasting phosphorescence (LLP) coming from the Mn²⁺ emission (⁴T₁ → ⁶A₁ transition) is observed at 640 nm but it appears that the traps depths are either two shallow or too deep to lead to an efficient long-lasting emission.     

Resorption of Ca<Subscript>3 – <Emphasis Type="Italic">x</Emphasis></Subscript>M<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> (M = Na,K) Calcium Phosphate Bioceramics in Model Solutions

The resorbability of bioceramics in the Ca₃(PO₄)₂–CaNaPO₄–CaKPO₄ system is evaluated in an approach involving thermodynamic assessment of solubility and investigation of the dissolution kinetics in model media, in particular in citric acid solutions. Thermodynamic calculation indicates high solubility of the Ca₅Na₂(PO₄)₄, α-CaМPO₄, β-CaKPO₄, and β-СаK_0.6Na_0.4PO₄ phases. Investigation of the dissolution kinetics of ceramics has made it possible to identify two distinct types of behavior of resorbable materials in weakly acidic solutions: with fast resorption kinetics in the case of the phases based on nagelschmidtite solid solutions and α-CaМPO₄ disordered high-temperature solid solutions, and with a nearly constant, relatively low dissolution rate and a high solubility limit in the case of β-СaK_{1 – x}Na _x -based phases.     

Substitution of manganese and iron into hydroxyapatite: Core/shell nanoparticles

The bioceramics, hydroxyapatite (HAP), is a material which is biocompatible to the human body and is well suited to be used in hyperthermia applications for the treatment of bone cancer. We investigate the substitution of iron and manganese into the hydroxyapatite to yield ceramics having the empirical formula Ca_9.4Fe_0.4Mn_0.2(PO₄)₆(OH)₂. The samples were prepared by the co-precipitation method. The formation of the nanocrystallites in the HAP structure as the heating temperatures were raised to obtain a glass–ceramic system are confirmed by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) and electron spin resonance (ESR). TEM images show the core/shell structure of the nanoparticles, with the core being formed by the ferrites and the shell by the hydroxyapatite. The ED patterns indicate the nanoparticles formed at 500 °C have an amorphous structure while the nanoparticles formed at 1000 °C are crystalline. ESR spectroscopy indicated that the Fe³⁺ ions have a g-factor of 4.23 and the Mn²⁺ ions have a g-factor of 2.01. The values of the parameters in the spin Hamiltonian which describes the interaction between the transition metal ions and the Ca²⁺ ions, indicate that the Mn²⁺ ion substitute into the Ca²⁺ sites which are ninefold coordinated, i.e., the Ca(1) sites.     

Synthesis and Structure of Magnesium-Substituted Hydroxyapatite

Magnesium-substituted calcium phosphates with the general formula Ca_{10 – x} Mg _x (PO₄)₆(OH)₂ (x & 1) are synthesized and characterized by IR spectroscopy and x-ray diffraction. The magnesium ion is found to destabilize the structure of hydroxyapatite: increasing the Mg content from 1 to 10 at. % (in terms of metals) reduces the temperature of the hydroxyapatite–whitlockite transition.     

Hyrdoxyapatite Coatings on Titanium

Some ceramics, including calcium phosphates and certain glasses and glass‐ceramics, form an important class of bioactive materials that are used extensively in repair and reconstruction of diseased or damaged parts of the musculoskeletal system. The similarity between synthetic hydroxyapatite (HA) (Ca₁₀(PO₄)₆(OH)₂) and the mineral phase of bone and tooth made HA one of the earliest materials to be used to impart osteoconductive (bone‐bonding) properties to the surface of biocompatible, metallic implants. HA and other calcium phosphate surfaces are used primarily to cause early stabilization of the implant in the surrounding bone through the formation of a direct bond and enhanced bone apposition. Although bioactive ceramics are used in several compositions and forms, the focus here is on the use of HA coatings in metallic implants. The coatings made by commercially available plasma‐spray and other techniques are compared to those made recently by surface‐mediated biomimetic routes.     

Extraction and characterisation of apatite- and tricalcium phosphate-based materials from cod fish bones

Apatite- and tricalcium phosphate-based materials were produced from codfish bones, thus converting a waste by-product from the food industry into high added-valued compounds. The bones were annealed at temperatures between 900 and 1200 °C, giving a biphasic material of hydroxyapatite and tricalcium phosphate (Ca₁₀(PO₄)₆(OH)₂ and β-Ca(PO₄)₃) with a molar proportion of 75:25, a material widely used in biomedical implants. The treatment of the bones in solution prior to their annealing changed the composition of the material. Single phase hydroxyapatite, chlorapatite (Ca₁₀(PO₄)₆Cl₂) and fluorapatite (Ca₁₀(PO₄)₆F₂) were obtained using CaCl₂ and NaF solutions, respectively. The samples were analysed by several techniques (X-ray diffraction, infrared spectroscopy, scanning electron microscopy and differential thermal/thermogravimetric analysis) and by elemental analyses, to have a more complete understanding of the conversion process. Such compositional modifications have never been performed before for these materials of natural origin to tailor the relative concentrations of elements. This paper shows the great potential for the conversion of this by-product into highly valuable compounds for biomedical applications, using a simple and effective valorisation process.     

An analysis of the phase transitions in biocompatible Ca10(PO4)6(OH)2

The results of investigations of the physical and chemical properties of calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ were summarized with a view to the synthesis and processing of this compound. Based on these data, the effects of steric factors, crystal structure defects, and composition on the phase transitions accompanying the thermal treatment of this substance are analyzed.     

Hydroxyapatite-Carboxymethyl Cellulose Nanocomposite Biomaterial

An organic-mineral composite of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanoparticles and carboxymethyl cellulose (CMC) is synthesized via coprecipitation from a solution containing CaCl₂, aqueous ammonia, (NH₄)₂HPO₄, and CMC. The composition and microstructure of the composite and the lattice parameters and particle size of the hydroxyapatite are determined using x-ray diffraction, chemical analysis, IR spectroscopy, scanning and transmission electron microscopy techniques, electron diffraction, and x-ray microanalysis. The hydroxyapatite nanoparticles are shown to form agglomerates about 200 nm in size. The interaction between the nanoparticles and CMC macromolecules leads to the formation of a pore structure potentially attractive for biomedical applications.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 592–599.Original Russian Text Copyright © 2005 by Zakharov, Ezhova, Koval, Kalinnikov, Chalykh.     

XANES analysis of calcium and sodium phosphates and silicates and hydroxyapatite–Bioglass®45S5 co-sintered bioceramics

Bioglass®45S5 was co-sintered with hydroxyapatite at 1200 °C. When small amounts (< 5 wt.%) of Bioglass®45S5 was added it behaved as a sintering aid and also enhanced the decomposition of hydroxyapatite to β-tricalcium phosphate. However when 10 wt.% and 25 wt.% Bioglass®45S5 was used it resulted in the formation of Ca₅(PO₄)₂SiO₄ and Na₃Ca₆(PO₄)₅ in an amorphous silicate matrix respectively. These chemistries show improved bioactivity compared to hydroxyapatite and are the subject of this study. The structure of several crystalline calcium and sodium phosphates and silicates as well as the co-sintered hydroxyapatite–Bioglass®45S5 bioceramics were examined using XANES spectroscopy. The nature of the crystalline and amorphous phases were studied using silicon (Si) and phosphorus (P) K- and L_2,3-edge and calcium (Ca) K-edge XANES.Si L_2,3-edge spectra of sintered bioceramic compositions indicates that the primary silicates present in these compositions are sodium silicates in the amorphous state. From Si K-edge spectra, it is shown that the silicates are in a similar structural environment in all the sintered bioceramic compositions with 4-fold coordination.Using P L_2,3-edge it is clearly shown that there is no evidence of sodium phosphate present in the sintered bioceramic compositions. In the P K-edge spectra, the post-edge shoulder peak at around 2155 eV indicates that this shoulder to be more defined for calcium phosphate compounds with decreasing solubility and increasing thermodynamic stability. This shoulder peak is more noticeable in hydroxyapatite and β-TCP indicating greater stability of the phosphate phase. The only spectra that does not show a noticeable peak is the composition with Na₃Ca₆(PO₄)₅ in a silicate matrix indicating that it is more soluble compared to the other compositions.     

Synthesis and cytocompatibility of manganese (II) and iron (III) substituted hydroxyapatite nanoparticles

Manganese (II) and iron (III) substituted hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) nanoparticles were synthesized using wet chemical method. All samples were single-phase, non-stoichiometric and B-type carbonated hydroxyapatite. Compared with pure HA, Mn²⁺ substituted (MnHA) and Fe³⁺ doped HA (FeHA) did not demonstrate significant structure deviation. Since ion exchange mechanism was applied for the synthesis process, the morphology and particle size were not significantly affected: all samples were elongated spheroids of around 70 nm. The presence of Fe and Mn was confirmed by energy dispersive X-ray spectroscopy (EDX) while the concentrations were quantified by inductively coupled plasma (ICP). Fe³⁺ ions were more active than Mn²⁺ ions in replacing Ca²⁺ ions in HA lattice structure. The magnetic property of HA was modified by substitution with Fe. The Fe5 (Fe_added/Ca_added = 5% by molar ratio) was paramagnetic while pure HA was diamagnetic. Results of extraction assay from cells cultured in extracted medium for 72 h suggested that both MnHA and FeHA were non-cytotoxic to osteoblast cells. Meanwhile, the presence of Fe³⁺ ions in HA demonstrated significant positive effect on osteoblast cells, where the cell number on Fe5 pellets was twice that of pure HA and MnHA samples.