Amorphous Calcium Phosphate Layer Research Articles

Damage evaluation of HAp-coated porous titanium foam in simulated body fluid based on compression fatigue behavior

Although pure Ti is nontoxic, alloying elements may be released into the surrounding tissue when Ti alloys are used, and this can cause cytotoxicity. Therefore, this study performed the damage evaluation of hydroxyapatite (HAp)-coated porous Ti components subjected to cyclic compression in a simulated body fluid (SBF). The HAp coating layer was deposited on the surface of porous Ti by electrophoresis, and a dense and homogeneous coating morphology was observed on the surface of the porous Ti. To specify damage types of HAp coating in situ, acoustic emission (AE) measurements and microscopic observations were simultaneously conducted during compressive fatigue loading tests to detect the specific failure mode. Compression tests revealed that the interfacial strength between the HAp coating and porous Ti was higher than the yield strength of the porous body (7–9 MPa). The AE signals were detected only in the plastic deformation stage of porous Ti, which indicated that they were generated because of plastic deformation/fractures in the porous body. Compressive fatigue tests revealed that no significant HAp coating damage occurred when the applied maximum stress was within the elastic limit of porous Ti in air. In contrast, the HAp coating exhibited delamination at the initial stage of cyclic loading at all stress levels in SBF, while the fatigue limit of the coated porous substrate, 2 MPa, was not affected by the SBF medium. Though the delamination of the HAp coating in SBF occurred during the early stages of fatigue loading, the amorphous calcium phosphate layer was recovered partly through re-precipitation from SBF. The AE signals from the delamination of the HAp coating or fracture in porous Ti could be identified using the peak voltage and frequencies. As microscopic observations were limited to certain parts of the porous body, AE signals were clustered according to the types of failure. The clustered AE signals were successfully correlated with the fatigue behavior of porous Ti. Corrosion fatigue was determined to be the primary mechanism for the delamination of the HAp coating on porous Ti in SBF.

On the amorphous layer in bone mineral and biomimetic apatite: A combined small- and wide-angle X-ray scattering analysis

The occurrence of an amorphous calcium phosphate layer covering the crystalline apatite core has been suggested to be an intrinsic feature of both bone mineral and synthetic biomimetic analogs. However, an exahustive quantitative picture of the amorphous-crystalline relationship in these materials is still missing. Here, we present a multiple scale modelling that combines small-angle X-ray scattering (SAXS) and synchrotron wide-angle X-ray total scattering (WAXTS) analyses to investigate the amorphous-crystalline spatial interplay in bone sample and biomimetic carbonated nano-apatites. SAXS analysis indicates the presence of a single morphology consisting of tiny nanoplates (NPLs) and provides a measure of their thickness (falling in the 3–5 nm range). WAXTS analysis was performed by developing atomistic models of apatite NPLs incorporating lattice strain, mostly attributed to the carbonate content, and calculating the X-ray patterns using the Debye Scattering Equation. Upon model optimization, the size and strain parameters of the crystalline platelets were derived and the amorphous component, co-existing with the crystalline one, separated and quantified (in the 23–33 wt% range). Notably, the thickness of the apatite core was found to exhibit nearly null (bone) or minor (< 0.5 nm, biomimetic samples) deviations from that of the entire NPLs, suggesting that the amorphous material remains predominantly distributed along the lateral sides of the NPLs, in a core-crown-like arrangement. The lattice strain analysis indicates a significant stiffness along the c axis, which is comparable in bone and synthetic samples, and larger deformations in the other directions. Statement of SignificanceCurrent models of bone mineral and biomimetic nanoapatites suggest the occurrence of an amorphous layer covering the apatitic crystalline nanoplates in a core-shell arrangement. By combining X-ray scattering techniques in the small and wide angle regions, we propose a joint atomic-to-nanometre scale modelling to investigate the amorphous-crystalline interplay within the nanoplates. Estimates are extracted for the thickness of the entire nanoplates and the crystalline core, together with the quantification of the amorphous fraction and apatite lattice strain. Based on the thickness matching, the location of the amorphous material mostly along the edges of the nanoplates is inferred, with a vanishing or very thin layer in the thickness direction, suggesting a core-crown-like arrangement, with possible implications on the mineral surface reactivity.

Low-temperature fabrication of titania layer on 3D-printed 316L stainless steel for enhancing biocompatibility

Petal-like titania layer was obtained on the 3D-printing 316L stainless steel substrate by two-step method at low temperature. Liquid phase deposition (LPD) method was used to prepare the fluorine-containing titania transition layer as step 1, not only improving the binding force with the substrate, but also contributing to the deposition of the second bioactive layer obtained by hydrothermal method in step 2. The samples were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), X-ray fluorescence (XRF) and static state contact angle. The XRF result indicated that the fluorine could be effectively concealed by Petal-like layer in step 2. And the wettability test showed that the as-treated samples were hydrophilic. Furthermore, the calcium-deficient amorphous calcium phosphate (ACP) layer was induced on the as-treated samples via being soaked in 1.5 times simulated body fluid (1.5SBF) solution within 3 days. Meanwhile, the biocompatibility results showed that the adhesion morphology and the quantity of osteoblasts on the sample treated by two-step method were better than the other sample groups. In a word, this two-step method is expected as a novel approach to improve the biocompatibility of the 3D-printing customized biomedical stainless steel.

Bioactivity and Cell Compatibility of β-Wollastonite Derived from Rice Husk Ash and Limestone.

The aim of this study was to prepare β-wollastonite using a green synthesis method (autoclaving technique) without organic solvents and to study its bioactivity. To prepare β-wollastonite, the precursor ratio of CaO:SiO2 was set at 55:45. This mixture was autoclaved for 8 h and later sintered at 950 °C for 2 h. The chemical composition of the precursors was studied using X-ray fluorescence (XRF), in which rice husk ash consists of 89.5 wt % of SiO2 in a cristobalite phase and calcined limestone contains 97.2 wt % of CaO. The X-ray diffraction (XRD) patterns after sintering showed that only β-wollastonite was detected as the single phase. To study its bioactivity and degradation properties, β-wollastonite samples were immersed in simulated body fluid (SBF) for various periods of time. Throughout the soaking period, the molar ratio of Ca/P obtained was in the range of 1.19 to 2.24, and the phase detected was amorphous calcium phosphate, which was confirmed by scanning electron microscope with energy dispersive X-ray analysis (SEM/EDX) and XRD. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the peaks of the calcium and phosphate ions increased when an amorphous calcium phosphate layer was formed on the surface of the β-wollastonite sample. A cell viability and proliferation assay test was performed on the rice husk ash, calcined limestone, and β-wollastonite samples by scanning electron microscope. For heavy metal element evaluation, a metal panel that included As, Cd, Pb, and Hg was selected, and both precursor and β-wollastonite fulfilled the requirement of an American Society for Testing and Materials (ASTM F1538-03) standard specification. Apart from that, a degradation test showed that the loss of mass increased incrementally as a function of soaking period. These results showed that the β-wollastonite materials produced from rice husk ash and limestone possessed good bioactivity, offering potential for biomedical applications.

Amorphous surface layer versus transient amorphous precursor phase in bone - A case study investigated by solid-state NMR spectroscopy.

Questions still persist on the structural organization of bone and biomimetic apatites. The existing model proposes a core/shell structure, with an amorphous surface layer coating a crystalline bulk. The accuracy of this model is still debated because amorphous calcium phosphate (ACP) environments could also arise from a transient amorphous precursor phase of apatite. Here, we provide an NMR spectroscopy methodology to reveal the origin of these ACP environments in bone mineral or in biomimetic apatite. The 1H magnetization exchange between protons arising from amorphous and crystalline domains shows unambiguously that an ACP layer coats the apatitic crystalline core of bone et biomimetic apatite platelets.

Enhancement of adhesion bonding between titanium metal and electrodeposited calcium phosphate

A novel hydroxyapatite/rutile coating was prepared on a titanium substrate. Initially, an amorphous calcium phosphate coating layer was electrochemically deposited on a Ti substrate. The surface morphology, chemical composition and phase identification of the coatings were investigated by the X-ray diffraction and scanning electron microscopy associated with an energy dispersive spectrometer. Annealing at 700°C for 3 hrs. transforms the amorphous calcium phosphate layer into well-crystallized hydroxyapatite (HAP) and the Ti metal surface into rutile. The developed HAP/rutile composite surface layer became denser and better adhering with the substrate than the initially formed amorphous calcium phosphate. The adhesion bond strength and the hardness of the coating were extremely raised by thermal annealing.

Accelerated cell-surface interlocking on plasma polymer-modified porous ceramics

Excellent osseointegration of permanent implants is crucial for the long lasting success of the implantation. To improve the osseointegrative potential, bio-inert titanium alloy surfaces (Ti6Al4V) are modified by plasma chemical oxidation (PCO®) of the titanium-oxide layer to a non-stoichiometric, amorphous calcium phosphate layer. The native titanium-oxide film measuring only a few nanometers is converted by PCO® to a thick porous calcium phosphate layer of about 10μm. In a second step the PCO surface is combined with a cell adhesive plasma-polymerized allylamine (PPAAm) nano film (5 and 50nm). Independent of the PPAAm coating homogeneity, the human osteoblast-like MG-63 cells show a remarkable increase in cell size and well-developed filopodia. Analyses of the actin cytoskeleton reveal that the cells mold to the pore shape of the PPAAm-covered PCO, thereby establishing a strong attachment to the surface. Interestingly, we could demonstrate that even though our untreated PCO shows excellent hydrophilicity, this alone is not sufficient to facilitate fast cell spreading, but the positive surface charges mediated by PPAAm.This multilayer composite material guarantees enhanced interlocking of the cells with the porous surface.

Fast degradation PLLA/apatites composites with high content of mineral phase for bone regeneration.

Event Abstract Back to Event Fast degradation PLLA/apatites composites with high content of mineral phase for bone regeneration. Diego Souza1 and Luiz Henrique Catalani1 1 Instituto de Química - USP, Departamento de Química Fundamental, Brazil Introduction: Since hydroxyapatite (HA) is the main mineral component of bones and teeth, it is widely used as biomaterial[1]. In the last decade, biocomposites of poly(L-lactide) (PLLA) and HA have attracted much attention due its ability to exhibit osteoinductive and osteoconductive properties, biodegradability and adequate mechanical strength[2]. However, its clinical use is limited owing to its slow biodegradation. Moreover, the low miscibility of HA in the polymer phase renders composites of low mineral content. Hence, other fast degradation calcium phosphates (CPs), such as calcium deficient hydroxyapatite (CDHA), β-tricalcium phosphate (β-TCP) and octacalcium phosphate (OCP) have been considered as HA substitute[3]. This work aims at the production fast degradation PLLA composites with high content of alternative CPs as mineral phases, such as CDHA, β-TCP and OCP, as well as to study their bioactivity properties. Results: In order to improve the dispersion of the mineral phase in the polymeric matrix, lauryl chloride was used to functionalize the surface of CPs and improving the interfacial adhesion of the particles. As a result, biocomposites containing up to 40wt% of mineral phase were produced. The bioactivity of the biocomposites was assayed in vitro using a solution of Simulated Blood Fluid (SBF)[4]. After 28 days of immersion in SBF, the formation of an amorphous calcium phosphate layer was observed on the surface of the substrate PLLA/HA; while for the biocomposites containing CDHA or CDHA/ β-TCP (7: 3) the minerals were composed of flake crystals. Increase of bone-like minerals was observed on surface of the substrate PLLA/OCP, these findings indicate that the deposited CP layer coating the surface of electrospun fibers containing OCP was in a more advanced stage of nucleation. Figure 1: SEM images of electrospun PLLA/apatites-laurate 40 wt% after incubation in SBF for 28 days: (a) HA; (b) CDHA; (c) CDHA/TCP (7:3); (d) OCP. The cell viability on all the samples was measured by MTT assay. While pure PLLA presented cell viability around 80%, as compared to control (PS plate) biocomposites containing 40% of funcionalized apatite showed over 100% of cell viability. These results show that these materials are not only atoxic but can help cell proliferation. Figure 2:Viability of NIH/3T3 fibroblasts on PLLA and PLLA/apatites-laurate 40%wt nanofibrous scaffolds. The different biocomposites were tested for adhesion and proliferation assays of NIH/3T3 fibroblasts using MTT assay. The biocomposites showed similar increase in cell proliferation, but after 15 days they promoted higher cell proliferation compared to pure PLLA electrospun fibers. Figure 3: Proliferation of NIH/3T3 fibroblasts on the control PLLA and PLLA/apatites-laurate 40%wt nanofibrous scaffolds as a function of culture time. Conclusions: The bicomposites high mineral phase (up to 40%) were produced. Electrospun mat of PLLA/OCP-laurate 40 wt% presented higher bioactivity in contact with SBF than similar composites containing HAD, HAD/TCP (7:3) or HA. However all CPs biocomposites in this study provided similar increase in cell proliferation, as compared to PLLA. These new materials are proposed as fast degradation CPs biocomposites for bone and teeth applications. FAPESP (Projeto 2011/21442-6); Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq

Nanoscale analysis of calcium phosphate films obtained by RF magnetron sputtering during the initial stages of deposition

In the present work, we investigated the nanostructure of calcium phosphate films formed during the initial stages of deposition (between 30 and 240s; deposition rate of 3.7nm/min) by radio-frequency magnetron sputtering. The sputtering deposition parameters and the plasma energy were previously adjusted to produce nearly stoichiometric nanocrystalline hydroxyapatite films after 180min. Grazing-incidence X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the films formed in the initial stages were composed of an amorphous calcium phosphate phase with a Ca/P ratio Ca/P=1.60±0.12, which is close to that of hydroxyapatite. Using high-resolution transmission electron microscopy, we demonstrated that the films were not a unique amorphous phase. An additional phase composed of dense calcium phosphate nanospheres was found in all periods and investigated. The nanospheres grew in size as the deposition time increased, and small nanospheres were always observed. This observation suggests the continuous formation of nanospheres at the surface of the film. Nanocrystalline regions were revealed by electron diffraction and high-resolution electron microscopy after a deposition of 60s with a corresponding film thickness of 3.7nm. Electron energy-loss spectroscopy analysis comparing individual nanospheres to the amorphous calcium phosphate layer showed differences in the oxygen K edge, suggesting a difference in the chemical bonding of the oxygen species. Nanospheres were observed in association with isolated crystals, suggesting that the nanospheres may participate in the crystallization of hydroxyapatite according to a heterogeneous nucleation process.

Preparation, in vitro mineralization and osteoblast cell response of electrospun 13-93 bioactive glass nanofibers.

In this study, silicate based 13-93 bioactive glass fibers were prepared through sol-gel processing and electrospinning technique. A precursor solution containing poly (vinyl alcohol) and bioactive glass sol was used to produce fibers. The mixture was electrospun at a voltage of 20 kV by maintaining tip to a collector distance of 10 cm. The amorphous glass fibers with an average diameter of 464±95 nm were successfully obtained after calcination at 625 °C. Hydroxyapatite formation on calcined 13-93 fibers was investigated in simulated body fluid (SBF) using two different fiber concentrations (0.5 and 1 mg/ml) at 37 °C. When immersed in SBF, conversion to a calcium phosphate material showed a strong dependence on the fiber concentration. At 1mg/ml, the surface of the fibers converted to the hydroxyapatite-like material in SBF only after 30 days. At lower solid concentrations (0.5 mg/ml), an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite phase after 7 days of immersion. The XTT (2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide) assay was conducted to evaluate the osteoblast cell response to the bioactive glass fibers.

Preparation and in vitro characterization of electrospun 45S5 bioactive glass nanofibers

Bioactive glasses are widely used in biomedical applications due to their ability to bond to bone and even to soft tissues. In this study, 45S5 bioactive glass fibers were prepared through sol–gel processing and electrospinning technique. A precursor solution containing poly vinyl alcohol and bioactive glass sol was used to produce fibers. The mixture was electrospun at a voltage of 20kV by maintaining tip to a collector distance of 8cm. The fibers with an average diameter of 337±81nm (before calcination) were successfully obtained. Results showed that the crystalline phase of the fibers was largely influenced by the calcination temperature. Hydroxyapatite formation on calcined 45S5 fibers was investigated in simulated body fluid (SBF) using different fiber/SBF (F/S) ratios (0.5, 1, 2 and 10mg/ml) at 37°C. When immersed in SBF, conversion to a calcium phosphate material showed a strong dependence on the F/S ratio. At high solid concentration (10mg/ml), surface of the fibers could not be converted to the HA-like material in SBF after 30 days. At lower solid concentrations (2, 1 and 0.5mg/ml) an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite.

Structural characterization of nanostructured hydroxyapatite–iron oxide composites

Nanostructured hydroxyapatite (HA)–iron oxide composites obtained by a wet-chemical method through co-precipitation were investigated with respect to the changes induced in the samples structure by progressive addition of iron, by thermal treatments carried out at 450°C, 550°C and 700°C, and by incubation in simulated body fluid. The structural changes were analyzed by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and magic angle spinning nuclear magnetic resonance (MAS-NMR). After heat treatments, crystalline HA was developed in all samples, even in larger amount in those with iron, showing that iron acts as a catalyzer for HA development. The MAS-NMR results show as well that only a part of the iron atoms are uniformly incorporated in the HA structure by replacing calcium. EPR results support that an important part of iron atoms are disposed in regions rich in iron that behave like superparamagnetic or magnetic particles distributed in HA matrix. The analyses carried out on 550°C treated samples, after three days of immersion in SBF, point out a decrease of HA crystallite size and the appearance on particles surface of a new amorphous calcium phosphate layer.

Effect of magnesium ion incorporation on the thermal stability, dissolution behavior and bioactivity in Bioglass-derived glasses

There is a strong discrepancy in the literature regarding the effect of magnesium on bioactive glasses. Hence the present study is focused on the physical and chemical behavior of the “golden standard” 45S5 glass and magnesium-containing bioactive glasses developed here to evaluate their reactivity and in vitro bioactivity. The aim of this study was to analyze the influence of CaO replacement by MgO, especially its effect on the rate of formation of the apatite-like layer at the glass surface, the reaction kinetics between the glasses and simulated body fluid (SBF-K9) and on the glass stability against devitrification during heating. Five melt-derived bioactive glasses of the system 24.3Na2O–26.9(xCaO−(1−x)MgO)–46.3SiO2–2.5P2O5 (x=1; 0.875; 0.75; 0.625 and 0.5) were synthesized with CaO progressively replaced by MgO. Their thermal stability on heating was characterized by DSC analysis. Their degradation and ability to form an apatite-like layer were evaluated through in vitro tests by immersion in SBF-K9; FTIR, ion selective electrode analysis and by solid state nuclear magnetic resonance (NMR) spectroscopy. Our results indicate that magnesium plays an important role in the stability of this glass family, defined as the difference between the glass transition temperature Tg and crystallization temperature Tx. The lower Tg observed in the MgO-rich glasses and insignificantly changed solubilities, as well as the 29Si NMR results suggest that in this glass system MgO does not act as a network intermediate or former oxide, but as network modifier, as we expected. Dissolution kinetics, FTIR, and solid state 31P and 1H MAS-NMR consistently indicate that partial replacement of CaO by MgO in the bioglass does not influence the rate at which the initial amorphous calcium phosphate (ACP) layer is precipitated when the glass is exposed to SBF. In contrast it greatly reduces the rate of conversion of this precursor phase to the crystalline hydroxycarbonate apatite (HCA)-layer.

In vitro reactivity of Cu doped 45S5 Bioglass® derived scaffolds for bone tissue engineering.

Cu-doped 45S5 bioactive glasses with varying Cu contents were fabricated and used to process 3D porous scaffolds via the foam replica technique. Cu-doping results in the weakening of the glass network and a decrease in its glass transition temperature. Acellular in vitro studies revealed very high bioactivity independent of Cu doping as indicated by the fast formation of a carbonated hydroxyapatite layer (CHA) on scaffold surfaces after immersion in simulated body fluid (SBF). The kinetics of the glass-ceramic scaffold's transition to an amorphous calcium phosphate layer (ACP) and the crystallisation of CHA were explored by FT-IR and SEM analyses. The elemental distribution in the scaffold/fluid interface region was monitored by the advanced micro-PIXE-RBS (particle induced X-ray emission/Rutherford backscattering spectrometry) method. Cu-containing glasses showed slower release of Si, Ca and P from the scaffold periphery, whereas traces of Cu were found incorporated in the CaP layer on the scaffold surface. Cu release kinetics from the scaffolds in SBF were found to depend on culturing conditions while highest Cu concentrations of ∼3.1 ppm and ∼4.6 ppm under static and quasi-dynamic conditions, respectively, were observed. Since Cu exhibits potential angiogenic and osteogenic properties, the Cu-containing scaffolds are suggested as promising materials for bone tissue engineering applications.

Crystallization of hydroxyapatite during hydrothermal treatment on amorphous calcium phosphate layer coated by PEO technique

Surface modification of titanium implants is recently considered by several researchers. In this study, PEO was performed over commercially Ti-6Al-4V alloy pellets in an aqueous electrolyte containing calcium acetate (C.A.) and calcium glycerphosphate (Ca–GP) with a Ca/P molar ratio of 6.8, and applying current density of 0.212A/cm2, frequency of 100Hz and duty ratio of 60% for 4min. In the next step, hydrothermal treatments were carried out for various durations and at different temperatures inside an autoclave chamber containing a NaOH solution with pH of 11.5. XRD and SEM results confirmed formation of needle-shaped HAp after all hydrothermal conditions. Maximum intensity of HAp peaks was observed for the hydrothermally treated sample at 190°C for 15h. Moreover, crystallinity degree of HAp was increased by increasing hydrothermal duration and temperature. According to the SEM line scan analysis of cross section of the PEO coated sample after hydrothermal treatment at 190°C for 15h, it seems that Ca+2 and [PO4]−3 ions from internal layer of amorphous coating diffuse to the coating surface and dissolve into the solution during hydrothermal treatment, and finally precipitate on the outer layer of coating as needle-shaped HAp.

In vitro assessment of degradation and bioactivity of robocast bioactive glass scaffolds in simulated body fluid

In this study porous three-dimensional scaffolds of borate (13-93B3) bioactive glass were prepared by robocasting and in vitro degradation and bioactivity was evaluated. Grid like scaffolds with interconnected pores was assembled using robotic deposition technique which is a direct ink writing method. After binder burnout, the constructs were sintered for 1h at 560°C to produce scaffolds (porosity≈60%) consisting of dense glass struts (300±20μm in diameter) and interconnected pores of width 580±20μm. Hydroxyapatite formation on borate bioactive glass scaffolds was investigated in simulated body fluid (SBF) using three different scaffold/SBF (S/S) ratios (1, 2 and 10mg/ml) at 37°C. When immersed in SBF, degradation rate of the scaffolds and conversion to a calcium phosphate material showed a strong dependence to the S/S ratio. At high solid concentration (10mg/ml) surface of the glass scaffolds converted to the calcium rich amorphous calcium phosphate after 30 days. At lower solid concentrations (2 and 1mg/ml) an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite.

Effect of a bioactive glass-ceramic on the apatite nucleation on titanium surface modified by micro-arc oxidation

The aim of this work was to evaluate the ability of a bioactive glass-ceramic to induce the apatite nucleation on the titanium oxide layer produced by micro-arc oxidation. “In vitro” tests were carried out on a simulated body fluid solution in two different manners: one group was soaked in the SBF, while the other group was soaked together with the bioactive glass-ceramic. Results revealed that after 7days, the specimens soaked in SBF were covered with an amorphous calcium phosphate layer, while the specimens soaked in SBF plus glass-ceramic formed a crystalline apatite layer, suggesting thus, that the glass-ceramic provides silanol groups that accelerated the hydroxyapatite apatite precipitation on the anodic TiO2 layer.

Bioactivity modulation of Bioglass® powder by thermal treatment

Abstract A discussion of the effects of Bioglass ® powder crystallisation on the in vitro bioactivity in simulated body fluid (SBF) is presented. Starting from Bioglass ® powder, different glass–ceramics were obtained by thermal treatments between 580 °C and 800 °C, with variable crystallisation content (from 10 to 92 wt%). All samples (glass and glass–ceramics) showed apatite formation at their surface when immersed in SBF. In case of the glass and the samples with lowest crystallinity, the first step of apatite formation involved a homogenous dissolution followed by an amorphous calcium phosphate (CaP) layer precipitation. For the samples with a high crystallisation content, heterogeneous dissolution occurred. For the first time, the Stevels number of the amorphous phase is used to explain the possible dissolution of the crystalline phase present in materials with a similar chemical composition of the Bioglass ® . All samples presented at 21 days of immersion in SBF B-type hydroxycarbonate apatite crystals.

Crystallization and Ability of Hydroxyapatite Formation in Some Trivalent Oxides Containing Na-Ca-Silicate Glass-Ceramics

The formation of glass-ceramics based on Na2O- CaO-silicates containing P2O5 with minor additives of some trivalent oxides (e.g. La, In, Ga, and Al), has been investigated. Different crystalline phases including sodium- orthosilicate containing lanthanum, or aluminum were formed together with Na2Ca2Si3O9 ,N aInSi 2O6 ,a nd Na3Ga2Si3O10. The nature and mechanism of HA formed in the glass-ceramics are considered. In general, the presence of trivalent oxides in the glass-ceramics progres- sively reduced the ability to form a calcium phosphate layer on the surfaces of the materials. The addition of In2O3 decreased the crystallization of the hydroxyapatite layer. However, in the presence of either Ga2O3 or Al2O3 only the amorphous calcium phosphate layer was formed after the immersion of the crystallized specimens in the SBF solution.

Nucleation and growth of octacalcium phosphate on treated titanium by immersion in a simplified simulated body fluid

A simplified simulated body fluid solution (S-SBF) was used to study the kinetics and mechanism of nucleation and growth of octacalcium phosphate (OCP) on the surfaces of alkali and heat-treated titanium samples. After the alkali and heat treatments, the samples were soaked in S-SBF for periods varying up to 24 h. A thin layer of poorly crystallized calcium titanate was formed after 15 min of immersion, allowing for the deposition of another layer of amorphous calcium phosphate (ACP). After 2.5 h of immersion, OCP nuclei were observed on the surface of the ACP layer. After 5 h of immersion in S-SBF solution, the specimens were completely covered with a homogeneous plate-like layer of OCP. Analyses by transmission electron microscopy revealed that nucleation and growth of OCP occurred concomitantly to the crystallization of ACP in hydroxyapatite (HA). This transformation took place by solid-state diffusion, forming a needle-like HA structure underneath the OCP film.