Eggshell derived hydroxyapatite microspheres for chromatographic applications by a novel dissolution - precipitation method

Hydroxyapatite ((Ca₁₀(PO₄)₆(OH)₂, HAp) based chromatography matrix has attracted great interest in the field of protein separation. However, researchers have been trying to combat the growing costs associated with the HAp matrix. In the present investigation, we utilized a cheap biological waste material, viz. eggshells, for the development of hydroxyapatite (HAp) resins and evaluated them for protein purification. Initially, the calcite of the eggshell carbonate was converted into metastable vaterite microspheres. The HAp microspheres (ECHAp) were then prepared from eggshell carbonate microspheres using a novel dissolution-precipitation process. Synthetic source calcium carbonate was also used to prepare HAp microspheres (CHAp) for comparison. The purity and morphology of the apatite microspheres were characterized using X-ray diffraction (XRD) method, Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and laser diffraction particle analysis. Although both the apatites have similar morphology, the ECHAp has a larger surface area of 33.8 m² g^?1 compared to CHAp of 17.27 m² g^?1 by surface area analysis method. A commercial HAp matrix (CHT) with similar properties was also studied for comparison. All the apatite microspheres were found to have a similar protein binding capacity for bovine serum albumin (BSA). But ECHAp showed better protein separation for BSA and lysozyme mixture compared to CHAp and CHT matrices. The ECHAp matrix was also found to be highly stable over 20 purification cycles. Hence, the eggshell waste seems to have the potential for HAp matrix by a novel carbonate route with ease of preparation and also an economical packing material for chromatographic purification of biomolecules.     

Construction of pH-responsive drug delivery platform with calcium carbonate microspheres induced by chitosan gels

Construction of simple and convenient platforms for controlled delivery of anti-cancer drugs is of great importance for medical science and pharmaceutics. Here, chitosan (CS) gels were used to induce the growth of calcium carbonate (CaCO₃) microspheres, and the resulting CaCO₃ microspheres were well dispersed within the three-dimensional (3D) network framework of the CS gels. The synthesized CaCO₃/CS composites were then examined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR) and X-ray diffractometry (XRD). Finally, the designed CaCO₃/CS composites were used for loading and controlled delivery of methotrexate (MTX), an anti-cancer drug. The encapsulation ratio of MTX calculated by UV–vis spectroscopy was approximately 78.8%. In addition, pH-responsive delivery of MTX from the CaCO₃/CS composites was successfully achieved due to the pH-sensitive property of CS, and the cumulative release of MTX could reach 93.3%, 86.6% and 77.6% at pH 8.5, 7.4 and 5.8, respectively.     

Inter-polymer complex microspheres of chitosan and cellulose acetate phthalate for oral delivery of 5-fluorouracil

Inter-polymer complexes (IPCs) of chitosan (CS) and cellulose acetate phthalate (CAP) have been prepared to develop spherical microspheres by a novel emulsion-solvent evaporation technique. The microspheres were used for the oral delivery of 5-fluorouracil (5-FU), an antimetabolite and antineoplastic agent, whose release time was extended up to 12 h. Formulations were prepared by varying the concentrations of CS, CAP and 5-FU. FTIR confirmed the formation of IPC, indicating no chemical interactions of 5-FU with the polymer matrix. Scanning electron microscopy suggested spherical shape of the microspheres with smooth surfaces. Average particle size measured by optical microscopy varied between 2.7 and 5.5 μm. Differential scanning calorimetry showed amorphous dispersion of 5-FU particles into the IPC matrix. Encapsulation efficiency as estimated by UV was dependent on polymer composition with the highest value of 96 %. Water uptake by the IPC microspheres was higher at higher concentration of CS in the matrix. In vitro drug release performed in pH 1.2 and pH 7.4 buffer media showed a dependence on compositions of CS, CAP and drug loading. Molar mass between cross-links (M _c) and cross-link density (d _x ) values of the polymer matrix calculated from swelling data indicated the formation of a dense matrix between CS and CAP; the matrix was able to control the release of 5-FU. The in vitro release data have been fitted to empirical equations to understand the nature of drug release mechanism.     

Fabrication,drug delivery kinetics and cell viability assay of PLGA-coated vancomycin-loaded silicate porous microspheres

Porous ceramic microspheres are a desirable substance for bone tissue reconstruction and delivery applications. This study focuses on Mg–Ca silicate microspheres encapsulated in biodegradable poly (lactic-co-glycolic acid) (PLGA) to serve as a biocompatible carrier for the controlled release of vancomycin hydrochloride. In this regard, diopside (MgCaSi₂O₆), bredigite (MgCa₇Si₄O₁₆), and akermanite (MgCa₂Si₂O₇) powders were synthesized by sol-gel and subsequent calcination methods. Then, porous akermanite, diopside and bredigite microspheres of 700–1000 μm in diameter were fabricated by using carbon porogen, droplet extrusion and sintering, then loaded with the drug and eventually coated with PLGA. The bare microspheres showed a considerable burst release mode of the drug into a physiological medium, whereas PLGA coating of the microspheres reduced the burst release level. To investigate effective mechanisms governing in the drug release from the carriers, the contribution of burst, degradation, and diffusion was analyzed by the sequential quadratic programming algorithm method. It was found that the relative contribution of diffusion to bioresorption is ranked as diopside > akermanite > bredigite, whereas PLGA coating dominates the diffusion mechanism. The dental pulp stem cells cytocompatibility MTT assay of the microspheres also showed that the drug loading deteriorates but PLGA coating improves the cell biocompatibility significantly. Comparatively, the biocompatibility of the PLGA-coated microspheres was ranked as akermanite > diopside > bredigite, as a result of a compromise between the release of the constituting ions of the ceramic carriers and vancomycin molecules. It was eventually concluded that PLGA-coated Mg–Ca silicate microspheres are promising candidates for drug-delivery bone tissue engineering and dental bone grafting applications.     

Facile synthesis,in vitro biocompatibility,and antibacterial activity of porous hollow hydroxyapatite microspheres

In this study, porous hollow hydroxyapatite (HAp) microspheres are prepared using chitosan microspheres as novel sacrificial templates and their microstructure, biocompatibility, and drug delivery properties are evaluated. Scanning electron microscope (SEM) observations show that HAp microspheres are spherical in morphology with a diameter of 100–300 μm and have a porous and core–shell structure. X-ray diffractometer patterns show that HAp microspheres consist of apatite phase. MTT assay indicates that HAp microspheres are biocompatible and have no significant cytotoxicity. SEM observations show that HAp microspheres support attachment and proliferation of osteoblast MC3T3-E1 cells. After being soaked in the solution of tetracycline hydrochloride (TH, model drug), HAp microspheres adsorb TH with an adsorption capacity of 47% to derive TH-loaded HAp microspheres. When exposed to two types of representative bacteria: Escherichia coli and Staphylococcus aureus, TH-loaded HAp microspheres maintain the biological activity of TH to inhibit the growth of bacteria.     

Preparation and characterization of chitosan-poly(acrylic acid) polymer magnetic microspheres

A modified method to prepare chitosan-poly(acrylic acid)(CS-PAA) polymer magnetic microspheres was reported in this paper. First, via self-assembly of positively charged CS and negatively charged Fe₃O₄ nanoparticles, magnetic CS cores with a large amount of Fe₃O₄ nanoparticles were successfully prepared. Subsequently, the AA monomers were polymerized on the magetic CS cores based on the reaction system of water-soluble polymer-monomer pairs. These polymer magnetic microspheres had a high Fe₃O₄ loading content, and showed unique pH-dependent behaviors on the size and zeta potential. From the magnetometer measurements data, the CS-PAA polymer magnetic microspheres also had superparamagnetic property as well as fast magnetic response. A continuous release of the entrapped ammonium glycyrrhizinate in such polymer magnetic microspheres occurred, which confirmed the potential applications of these microspheres for the targeted delivery of drugs.     

A novel SiCN@TiO2 core–shell ceramic microspheres derived from a polymeric precursor

A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO₂ nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO₂ core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO₂ microspheres with good spherical structure and uniform-dispersed TiO₂ surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO₂ core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO₂, SiC and Si₃N₄ crystalline phase, which were generated by polyvinylsilazane.     

Synthesis,antimicrobial, and release behaviors of tetracycline hydrochloride loaded poly (VInyl alcohol)/chitosan/ZrO2 nanofibers

Tetracycline hydrochloride loaded poly (vinyl alcohol)/chitosan/ZrO₂ (Tet‐PVA/CS/ZrO₂) hybrid nanofibers were fabricated via electrospinning technique. The representative weight ratio of PVA/CS at 3 : 1 was chosen to fabricate drug carrier PVA/CS/ZrO₂ nanofibers. The drug carrier showed a decrease in average diameter with the increase of ZrO₂ content at given conditions, and the nanofibers were uneven and interspersed with spindle‐shape beads with ZrO₂ content at 60 wt % and above. The networks linked by hydrogen and Zr–O–C bonds among PVA, CS, and ZrO₂ units resulted in the improving of thermal stability and decreasing of crystallinity of the polymeric matrix. Moreover, the incorporation of ZrO₂ endowed the fibers with ultraviolet shielding effect ranged from 200 to 400 nm. The Tet loading dosage had no obvious effect on the morphology and size of the medicated nanofibers at Tet content below 8 wt %, but interspersed with spindle‐shaped beads when Tet content increased to 10 wt %. The Tet‐PVA/CS/ZrO₂) nanofibers showed well controlled release and better antimicrobial activity against Staphylococcus aureus, and the Tet release from the medicated nanofibers could be described by Fickian diffusion model for M_t /M_∞< 0.6. These medicated nanofibers may have potential as a suitable material in drug delivery and wound dressing. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42506.     

Control of the Dissolution of Ca and Si Ions from CaSiO3 Bioceramic via Tailoring Its Surface Structure and Chemical Composition

Owing to their good osseointegration property, calcium silicate (CS) bioceramics have been extensively studied in recent years. Nevertheless, the excessively high environmental pH value of CS bioceramics will limit their clinical application. The purpose of this work is to reduce the dissolution of Ca and Si ions from the pure CS bioceramics by modifying its surface structure and chemical composition with Zn₂SiO₄ nanoparticles (Zn–CS bioceramic). The results indicated that the dissolution of Ca and Si ions from the CS substrate obviously decreased by the surface modification, and the pH value of the soaking liquid was also effectively controlled. SEM observation and EDS analysis showed that apatite mainly formed on the wall of the internal pores under the Zn‐containing porous surface layer when the Zn–CS bioceramic was soaked in the simulated body fluids (SBF). Moreover, cell adhesion assay proved that mouse osteoblast cells (MC3T3) well adhered and spread on the Zn‐containing porous surface layer, and the apatite formed on the surface of the Zn‐containing porous layer during the incubation process. Better bioactivity and the osseointegration property can be expected for Zn–CS bioceramic. The surface modification with Zn₂SiO₄ nanoparticles is a promising route to control the dissolution and environmental pH value of CS bioceramics.     

Evaluation of mechanical behavior,bioactivity, and cytotoxicity of chitosan/akermanite-TiO2 3D-printed scaffolds for bone tissue applications

This report aimed to evaluate the mechanical behavior, bioactivity, and cytotoxicity of novel chitosan/akermanite-TiO₂ (CS/AK/Ti) composite scaffolds fabricated using the 3D-printing method. The morphological and structural properties of these scaffolds were characterized by Fourier transform spectroscopy (FTIR) and scanning electron microscopy (SEM). The mechanical behavior was examined by measuring the compressive strength, while the bioactivity was estimated in the simulated body fluid (SBF), and also the cytotoxicity of the scaffolds was assessed by conducting cell culturing experiments in vitro. It was found that the mechanical properties were considerably affected by the amount of TiO_2. The scaffolds had the possessed bone-like apatite forming ability, which indicated high bioactivity. Furthermore, L929 cells spread well on the surface, proliferated, and had good viability regarding the cell behaviors. The outcomes confirmed that the morphological, biological, and mechanical properties of developed 3D-composite scaffolds nearly mimicked the features of natural bone tissue. In summary, these findings showed that the 3D-printed scaffolds with an interconnected pore structure and improved mechanical properties were a potential candidate for bone tissue applications.     

Fabrication and characterization of porous biphasic β-tricalcium phosphate/carbonate apatite alginate coated scaffolds

In this research, biphasic β-tricalcium phosphate/carbonate apatite (β-TCP/CO₃Ap) scaffolds incorporated with alginate were fabricated. Sodium alginate was extracted from local brown seaweed, Sargassum polycystum via calcium alginate process. Biphasic β-TCP/CO₃Ap scaffolds were fabricated by polymer reticulate method. β-TCP slurry was infiltrated into the polyurethane foam (PU) foam, then sintered up to 1300?°C, soaked for 4?h and immediately quenched in still air to form biphasic β-TCP/α-TCP scaffold. Biphasic β-TCP/α-TCP scaffold was then transformed to biphasic β-TCP/CO₃Ap scaffold by dissolution-precipitation reaction with 1?M of NaHCO₃ at 170?°C for 1, 3 and 5 days. Biphasic β-TCP/CO₃Ap scaffold from 5 days dissolution-precipitation reaction was chosen to incorporate with 1%, 3% and 5% of sodium alginate, respectively, as it has the highest composition of CO₃Ap phase. FTIR and FESEM analysis confirmed the presence of characteristic functional groups of sodium alginate. Mechanical strength of biphasic β-TCP/CO₃Ap scaffold improved by increasing the concentration of sodium alginate. The highest mechanical strength achieved was 26.38 kPa for biphasic β-TCP/CO₃Ap scaffold with 5% sodium alginate coating and it was chosen to further study with the addition of 1%, 3% and 5% microspheres. FESEM analysis confirmed the attachment of microspheres on the surface of alginate/biphasic β-TCP/CO₃Ap scaffold was successful.     

Bone-like forming ability of apatite-wollastonite glass ceramic

This research describes the preparation, characterisation and in vitro behavior of a bioactive glass ceramic containing 44.8 wt% apatite, 28.0 wt% wollastonite-2 M and 27.2 wt% of amorphous phase. The biomaterial was obtained by a specific thermal cycle process that caused the devitrification of the Ca₃(PO₄)₂-CaSiO₃ binary system's stoichiometric eutectic composition. Overall, the material combines the properties of a resorbable Si-Ca-rich glass, in addition to bioactive properties of wollastonite and apatite phases. The bioactivity of this material was studied by soaking the samples in a simulated body fluid (SFB) for 3, 7, 14 and 21 days at 36.5 °C. During the soaking, the amorphous phase and also wollastonite-2 M phase underwent steady dissolution by releasing Si and Ca ions into the SBF medium. After 7 days, a porous hydroxy-carbonate apatite (HCA) layer was formed at the SBF-glass ceramic interface. The micro-nanostructured apatite-wollastonite-2 M glass ceramics with improved mechanical properties, in comparison with the parent glass, could serve as a promising platform for hard tissue regeneration.     

Preparation,characterization, and salicylic acid release behavior of chitosan/poly(vinyl alcohol) blend microspheres

Blend microspheres of chitosan (CS) with poly(vinyl alcohol) (PVA) were prepared as candidates for oral delivery system. CS/PVA microspheres containing salicylic acid (SA), as a model drug, were obtained using the coacervation‐phase separation method, induced by addition of a nonsolvent (sodium hydroxide solution) and then crosslinked with glutaraldehyde (GA) as a crosslinking agent. The microspheres were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy. Percentage entrapment efficiency, particle size, and equilibrium swelling degree of the microsphere formulations were determined. The results indicated that these parameters were changed by preparation conditions of the microspheres. Effects of variables such as CS/PVA ratio, pH, crosslinker concentration, and drug/polymer (d/p) ratio on the release of SA were studied at three different pH values (1.2, 6.8, and 7.4) at 37°C. It was observed that SA release from the microspheres increased with decreasing CS/PVA ratio and d/p ratio whereas it decreased with the increase in the extent of crosslinking. It may also be noted that drug release was much higher at pH 1.2 than that of at pH 6.8 and 7.4. The highest SA release percentage was obtained as 100% for the microspheres prepared with PVA/CS ratio of 1/2, d/p ratio of 1/2, exposure time to GA of 5 min, and concentration of GA 1.5% at the end of 6 h. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microwave Sintering of Zirconia Materials: Mechanical and Microstructural Properties

Commercially, 3 mol% Y₂O₃‐stabilized tetragonal zirconia (70–90 nm) compacts were fabricated using a conventional and a nonconventional sintering technique; microwave heating in a resonant mono‐mode cavity at 2.45 GHz, at temperatures in the 1100–1400°C range. A considerable difference in the densification behavior between conventional (CS) and microwave (MW) sintered materials was observed. The MW materials attain a full density of 99.9% of the theoretical density (t.d.) at 1400°C/10 min, whereas the CS reach only 98.0% t.d. at the same temperature and 1 h of dwelling time. Therefore, the MW materials exhibit superior Vickers hardness values (16.0 GPa) when compared with CS (13.4 GPa).     

Novel blend microspheres of poly(vinyl alcohol) and succinyl chitosan for controlled release of nifedipine

Water-soluble succinyl chitosan (SCS) was synthesized by reacting succinic anhydride with –OH and –NH₂ reactive groups of chitosan (CS). The blend hydrogel microspheres were prepared from SCS with poly(vinyl alcohol) (PVA) by water-in-oil (w/o) emulsion cross-linking using glutaraldehyde (GA) as the cross-linking agent. Nifedipine (NFD), an antihypertensive drug having a plasma half-life of 2 h, was encapsulated giving encapsulation efficiency up to 92 % and its release was extended up to 12 h. Scanning electron microscopy (SEM) confirmed the spherical nature and smooth surfaces of the microspheres, while Fourier transform infrared spectroscopy (FTIR) confirmed succinylation of CS and chemical stability of NFD in the matrix. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) characterized the SCS and the blend hydrogel microspheres. X-ray diffraction (XRD) and DSC were also used to study the crystalline or amorphous nature of NFD. Swelling and in vitro release experiments performed in pH 1.2 and 7.4 buffer media showed a dependence of blend composition, extent of cross-linking and pH of the media. The mechanism of drug release as analyzed by an empirical equation, suggested non-Fickian trends.     

Evaluation of the La0.75Sr0.25Mn0.8Co0.2O3−δ system as cathode material for ITSOFCs with La9Sr1Si6O26.5 apatite as electrolyte

In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 °C.Apatite materials (La_10?xSr_xSi₆O_27?x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at 700 °C, a chemical and a dimensional stability for a pO₂ ranging from 10^?25 to 0.2 atm. A perovskite oxide (La_0.75Sr_0.25Mn_0.8Co_0.2O_3?δ) has been used as a cathode material.Symmetrical cathode/electrolyte/cathode cells were fabricated by stacking layers obtained by tape casting of apatite and perovskite powders and co-sintering at 1400 °C for 2 h in air.Impedance spectroscopy measurements were performed on these cells in order to determine the electrode resistance. It has been shown that the latter decreases with the porosity content of the cathode and with the use of a composite material (apatite/perovskite) instead of a simple perovskite.     

Effect of heparin coating on epichlorohydrin cross-linked chitosan microspheres on the adsorption of copper (II) ions

Epichlorohydrin cross-linked chitosan microspheres (CS) and chitosan–heparin polyelectrolyte complex microspheres (CSH) were used in the adsorption of copper (II) ions in aqueous solution. The chitosan microspheres were prepared by the phase inversion method. The use of a cross-linking agent improved the resistance to acidic medium. Polyelectrolyte complex microspheres were prepared by impregnating heparin in cross-linked chitosan microspheres. The microspheres were characterized by IR, TGA and DSC. A study on the effect of the pH on the adsorption of copper (II) ions showed that the optimum pH for both CS and CSH microspheres was 6.0. From a kinetic evaluation, it could be established that the adsorption equilibrium was achieved after 8 h for CS and 25 h for CSH microspheres. The adsorption isotherms were interpreted using Langmuir and Freundlich mathematical models. The results revealed that experimental data of CS was best adjusted by Langmuir model, with maximum capacity of surface saturation equal to 39.31 mg g⁻¹. On the other hand, Langmuir and Freundlich models provided a good fit for adsorption by CSH and the adsorption capacity was 81.04 mg g⁻¹. The interactions between copper (II) ions and both CS and CSH were confirmed by electron paramagnetic resonance spectroscopy, which revealed the formation of a square-planar complex with tetrahedral distortion on the surface of the adsorbents.     

Span 60 as a Microsphere Matrix: Preparation and in Vitro Characterization of Novel Ibuprofen-Span 60 Microspheres

Microspheres are a potential delivery system for controlled and sustained drug release. Polymeric microspheres are commonly prepared by the solvent evaporation technique whereas waxy microspheres by the melt dispersion technique. The goal of this study was to prepare a surfactant (Span 60)—Ibuprofen microspheres using both techniques. Ibuprofen‐Span 60 microspheres were fabricated with different drug to polymer weight ratios of 3:1, 1:1 and 1:3 and characterized by particle size, in vitro dissolution, infrared spectroscopy, x‐ray diffraction and scanning electron microscopy. The actual drug content increased with increasing the concentration of anti‐aggregating agent (polyvinylpyrolidone). The actual drug content and drug encapsulation efficiency was markedly higher in case of microspheres prepared by a solvent evaporation technique compared to that prepared by a melt dispersion one using the same theoretical drug content. The microspheres were spherical with irregular surfaces. The in vitro release showed no burst effect and incomplete drug release. The rate and total drug released from the microspheres prepared by a solvent evaporation technique are higher than those prepared by using the melt dispersion technique. FTIR rolled out the chemical changes of the drug in Span 60 microspheres. The X‐ray diffraction pattern of the microspheres prepared by using a solvent evaporation technique showed a decrease in the drug crystallinity. The drug crystallinity in microspheres prepared by the melt dispersion technique decreased with increasing the theoretical drug content. The drug entrapment mechanism is responsible for the changes in drug physicochemical properties and in vitro release.     

Synthesis and characterization of star-shaped poly (lactide-co-glycolide) and its drug-loaded microspheres

The star-shaped poly (lactide-co-glycolide) (PLGA) was synthesized via the ring-opening polymerization of d,l-lactide and glycolide, with pentaerythritol as a multifunctional initiator and stannous 2-ethyl hexanoate as a catalyst. The structures of these polymers were characterized by ¹³C-NMR spectroscopy, while the molecular weight and polydispersity index (PDI) were determined by gel permeation chromatography (GPC). The glass transition temperature (T _g) of copolymer was determined by differential scanning calorimetry (DSC). Bovine serum albumin (BSA) loaded microspheres were fabricated using star-shaped PLGA by a W/O/W double emulsion solvent evaporation method. The results of characterization demonstrated that the particle size of the PLGA microspheres were about 80–150 μm, the maximum loading capacity and encapsulation efficiency of BSA-loaded microspheres were 67.51 μg/(mg microspheres) and 78.39%, respectively, which were better than linear PLGA. The in vitro release profiles of BSA in phosphate buffer saline (PBS) lasted for 37 h. Drug release profiles can be affected by polymer molecular weight and the ratio of polymer to drug. The maximum release percentage was 80%.     

Time-dependent growth of biomimetic apatite on anodic TiO2 nanotubes

We report on the initial and later stages of apatite formation from simulated body fluid on titania with different surface morphologies (compact or nanotubular) and different crystal structures (anatase or amorphous). The nanotubular layers were fabricated by electrochemical anodization in fluoride-containing electrolytes. The study investigates the enhanced apatite deposition on titania nanotubes. In the initial stages of apatite growth, more nuclei are formed on the nanotubular surface than on flat compact TiO₂. While the crystallographic structure of the substrate plays a less important role than the morphology in the initial nucleation stages, it is of great importance in the later stages of apatite crystal growth. The nanotubular morphology combined with an anatase structure leads to the formation of apatite layers with a thickness of >6 nm in less than 2 days. No stable apatite layers can be observed on amorphous TiO₂ films, neither on compact nor on nanotubular substrates.XPS, FT-IR and XRD measurements reveal that carbonated hydroxyapatite (CHA) of low crystallinity is formed on annealed nanotubular and compact titania.Electrochemically grown and annealed TiO₂ nanotube arrays having anatase structure are expected to be a good precursor system for the formation of CHA and thus for the preparation of osseointegrative implants.