Structure Of Calcium Phosphate Research Articles

Effect of heat-treatment temperature on the structure of calcium phosphate synthesized by wet precipitation

In this work, nanometric calcium phosphate (CaP) was synthesized by wet chemical precipitation using Ca(OH)2 and H3(PO4). The subsequent heat treatment was carried out varying from 25 °C to 1000 °C, to study the changes caused in the structure of the final product through XRD, FTIR, Fluorescence, Raman, UV–Vis, DLS, Zeta Potential, SEM and TEM/EDS analyses. Cell viability was measured via MTS assays. XRD showed that the crystallinity of the synthetic calcium phosphate obtained increases with increasing heat-treatment temperature, getting close to the structure of hydroxyapatite. In the FTIR, Raman and UV–vis spectroscopic analyses, carbonate removal from the synthesized CaP structure at high heat-treatment temperatures was observed. Samples T800 and T1000 showed greater fluorescence. DLS measurements revealed the formation of aggregates at heat-treatment temperatures lower than 800 °C. According to the Zeta Potential measurements, T1000 is the most stable colloid (−28.4 ± 1.4 mV). The thermal treatment also affected the morphology of the samples, and nanowhiskers, nanorods and nanocubes were observed. In addition, the viability assay revealed that a decrease in particle sizes in CaP samples led to a decrease in metabolic activity, showing that the correct choice of particle size is the key to producing compounds that favor cell proliferation, making it a promising material for bone tissue engineering.

Stearic Acid Treatment Enhancing Corrosion Resistance of Biomimetic-Deposited Calcium Phosphate Dihydrate Coating on Medical Degradable Magnesium Alloy.

Magnesium (Mg) alloys, a degradable material, have been studied for medical applications due to their excellent mechanical and chemical properties. However, their applications are limited by rapid corrosion. In this work, stearic acid and sodium stearate were used to treat the silane-induced calcium phosphate dihydrate coating to improve its protection for the Mg alloy further without changing the bone-like structure of calcium phosphate. The different effects of stearic acid treatment and sodium stearate treatment were compared. Electrochemical test and immersion test results confirmed that the corrosion resistance of the stearic acid-treated composite coating was greatly enhanced with a reduced corrosion current density by 3 orders of magnitude and hydrogen evolution reduced to 1/25 after 14 days. The stearic acid-treated coating also exhibited improved in vitro biocompatibility corroborated by promoted cell viability and better cell morphology.

Hydrothermal growth of biomimetic calcium phosphate network structure on titanium surface for biomedical application

Calcium phosphate (CaP) coating-modified titanium (Ti) surfaces have been developed to improve the biological activity and osseointegration of Ti-based implants. However, these coatings always lack three-dimensional micro/nanostructures mimicking bone tissue. To fabricate hierarchical CaP coating structures and enhance the bioactivity of Ti implants, this study developed a novel hydrothermal method for preparing biomimetic three-dimensional CaP network structures on alkali-treated Ti surface with the assistance of oleic acid. Moreover, the growth mechanism of the CaP network structure was investigated, and its biocompatibility was evaluated by co-culture with preosteoblasts. The coatings were mainly composed of HA nanowires, which grew vertically along the titanate nanowires and further self-assembled into macropores. Compared to the pristine Ti surface, this hierarchical network structure showed superior hydrophilicity, elevated roughness, and improved cell attachment, proliferation, and osteogenic differentiation. Furthermore, this CaP structure demonstrated significantly higher alkaline phosphatase (ALP) activity and upregulated the expression of osteopontin (OPN) and osteocalcin (OCN) in comparison with similar titanate structures, suggesting improved bioactivity of the hierarchical CaP network structure. These improvements were probably attributed to hierarchical micro/nanostructure and CaP chemistry. The above findings indicate that this method effectively fabricates hierarchical CaP network structures on Ti-based substrates, which construct a favorable microenvironment for inducing osteogenic differentiation.

The effect of pulsed electron irradiation on the structure, phase composition, adhesion and corrosion properties of calcium phosphate coating on Mg0.8Ca alloy

The influence of pulsed electron irradiation (PEI) on the surface morphology, structure, phase composition, adhesion and corrosion properties of micro-arc coatings with β-tricalcium phosphate (β-TCP) particles on Mg0.8Ca alloy has been studied. When modifying the PEI coating with an energy density of 10 J/cm2, a melted layer is formed up to the substrate, as well as a denser transition layer between the coating and the substrate. At the same time, the surface layer of the coating is enriched with Ca and P due to the fusion of β-TCP particles and an increase in the adhesive strength of the coating is observed. With the help of potentiodynamic polarization curves, EIS test, and localized electrochemical analysis performed by SVET and SIET methods, a lower corrosion activity of this coating was established in comparison with the initial, unmodified state.

Zinc additions in calcium phosphate system. Phase behavior, microstructural and mechanical compatibility during sequential heat treatments

The study investigates the structural and mechanical stability of the calcium phosphate - ZnO composites during sequential heat treatments. The composites were synthesized through a solution based co-precipitation technique by varying the precursor concentrations. The characterization results infer the Zn2+ insertion in calcium phosphate and moreover the isostructural phase of β-Ca3(PO4)2 → Ca19Zn2(PO4)14 is preserved until 1300 ℃. The upsurge in Zn2+ concentration ensure the presence of apatite trace at 1300 ℃. Zn2+ inclusion tends to the alter the calcium phosphate structure, mainly by delaying the allotropic β → α-Ca3(PO4)2 conversion until 1300 ℃. Zn2+ prefers to accommodate at Ca2+(4), and Ca2+(5) sites of Ca19Zn2(PO4)14 lattice, while the Zn2+ ions exceeding the saturation limit crystallize as ZnO. The structural distortion of PO4 bands due to the inclusion of Zn2+ concentration is verified from FTIR and Raman results. Zn2+ play a crucial role in the microstructural features and density of the resultant calcium phosphate system thus displaying the constant distribution of grains and resilient solidity in the system. Low ZnO content tends to boost the Youngs modulus and hardness while an inverse trend is noticed in case of high ZnO content.

Spheroid co-culture of BMSCs with osteocytes yields ring-shaped bone-like tissue that enhances alveolar bone regeneration

Oral and maxillofacial bone defects severely impair appearance and function, and bioactive materials are urgently needed for bone regeneration. Here, we spheroid co-cultured green fluorescent protein (GFP)-labeled bone marrow stromal cells (BMSCs) and osteocyte-like MLO-Y4 cells in different ratios (3:1, 2:1, 1:1, 1:2, 1:3) or as monoculture. Bone-like tissue was formed in the 3:1, 2:1, and 1:1 co-cultures and MLO-Y4 monoculture. We found a continuous dense calcium phosphate structure and spherical calcium phosphate similar to mouse femur with the 3:1, 2:1, and 1:1 co-cultures, along with GFP-positive osteocyte-like cells encircled by an osteoid-like matrix similar to cortical bone. Flake-like calcium phosphate, which is more mature than spherical calcium phosphate, was found with the 3:1 and 2:1 co-cultures. Phosphorus and calcium signals were highest with 3:1 co-culture, and this bone-like tissue was ring-shaped. In a murine tooth extraction model, implantation of the ring-shaped bone-like tissue yielded more bone mass, osteoid and mineralized bone, and collagen versus no implantation. This tissue fabricated by spheroid co-culturing BMSCs with osteocytes yields an internal structure and mineral composition similar to mouse femur and could promote bone formation and maturation, accelerating regeneration. These findings open the way to new strategies in bone tissue engineering.

Chitosan/Calcium-Coated Ginsenoside Rb1 Phosphate Flower-like Microparticles as an Adjuvant to Enhance Immune Responses

Simple SummaryThe field-level control over IBD is primarily via vaccination. The development of high effective IBV vaccine has drawing great attentions worldwide. Herein, the GRb1 was encap-sulated into Calcium phosphate and chitosan core-structure nanoparticles microspheres, which con-stitute a novel system for nanoparticle delivery (GRb1/IL-4@CS/Cap). The new nano-adjuvant de-livery system could induce the activation of chicken dendritic cells ( DCs ), with up-regulate the expression of MHC II and CD80, and increase the production of IL-1β and TNF-α. At the same time, it can trigger higher levels of IBDV-specific IgG and higher IgG2a/IgG1 ratio, and promote the production of IFN-γ, TNF-α, IL-4, IL-6, IL-1α, and IL-1βand other cytokines in chicken serum after vaccination, it provides an effective adjuvant system for the development of chicken IBDV attenu-ated vaccine.Infectious bursal disease (IBD) is a highly contagious immunocompromising disorder that caused great economic losses in the poultry industry. The field-level control over IBD is primarily via vaccination. The development of a highly effective IBV vaccine has drawn great attention worldwide. Chitosan/Calcium Phosphate (CS/CaP) nanoparticle was a newly developed effective biological delivery system for drug and antigen. Ginsenoside Rb1 is one of the main bioactive components of ginseng root extract, which has antioxidant, anti-inflammatory and immunological enhancement effects. Until now, the combined effect of CS/CaP and ginsenoside Rb1 on the chicken immune response had remained unknown. In this study, the GRb1 and IL-4 were encapsulated into Calcium phosphate and chitosan core structure nanoparticles microspheres (GRb1/IL-4@CS/CaP), and the effect of a newly developed delivery system on an infectious bursal disease virus (IBDV) attenuated vaccine was further evaluated. The results demonstrated that GRb1/IL-4@CS/CaP treatment could induce the activation of chicken dendritic cells (DCs), with the upregulated expression of MHCII and CD80, and the increased production of IL-1β and TNF-α. Importantly, GRb1/IL-4@CS/CaP could trigger a higher level of IBDV-specific IgG and a higher ratio of IgG2a/IgG1 than the traditional adjuvant groups, promoting the production of cytokine, including IFN-γ, TNF-α, IL-4, IL-6, IL-1α, and IL-1β, in chicken serum after 28 d and 42 d post-vaccine. Taken in all, GRb1/IL-4@CS/CaP could elicit prolonged vigorous immune responses for IBDV attenuated vaccine in chicken, which might provide an effective adjuvant system for avian vaccine development.

Enhanced Piezocatalysis by Calcium Phosphate Nanowires via Gold Nanoparticle Conjugation.

Piezocatalytic materials have considerable application potential in wireless therapy. Most of these applications require biocompatible nanomaterials for in vivo targeting and control of intracellular processes. However, the piezocatalytic performance of a material decreases at a nanometer size regime, and most of the biocompatible materials have poor piezocatalytic efficiency. In particular, hydroxyapatite or calcium phosphate-based nanomaterials have weak piezocatalytic properties that limit the biomedical application potential. Here, we show that anisotropic shape and Au nanoparticle conjugation can enhance the piezocatalytic property of a calcium phosphate nanomaterial by 10 times and the performance approaches that of the bulk/nanoparticle form of well-known BaTiO3. The colloidal form of calcium phosphate nanowires/nanorods/nanospheres (2-5 nm diameter and 30-1000 nm length) and their Au nanoparticle (5-8 nm) composites are prepared, and their piezoelectric properties have been investigated with piezoresponse force microscopy. It has been observed that the anisotropic nanowire structure of calcium phosphate can enhance the piezoelectric property by 2 times and Au nanoparticle conjugation can enhance it up to 10 times with a piezoelectric constant value of 72 pm/V, which is close to the value of the bulk/nanoparticle form of BaTiO3. This enhanced piezoelectric property is shown to enhance the piezocatalytic reactions by 10 times. The approach has been used to design colloidal nano-bioconjugate for selective labeling of cancer cells, followed by wireless cell therapy via medical-grade ultrasound-based intracellular reactive oxygen species generation. The developed approach and material can be extended for wireless therapeutic applications and for controlling intracellular processes.

Selenite Substituted Calcium Phosphates: Preparation, Characterization, and Cytotoxic Activity.

The aim of this study was to prepare a biomimetic selenium substituted calcium phosphate system for potential application in osteosarcoma therapy. Calcium phosphate (CaP) systems substituted with selenite ions were prepared by the wet precipitation method, using biogenic CaCO3 (derived from cuttlefish bone), CO(NH2)2-H3PO4, and Na2SeO3·5H2O as reagents. Starting reaction mixtures were prepared based on the formula for selenite-substituted hydroxyapatite, Ca10(PO4)6-x(SeO3)x(OH)2, with Ca/(P + Se) molar ratio of 1.67 and Se/(P + Se) molar ratio of: 0, 0.01, 0.05, and 0.10, respectively. The prepared CaP powders were characterized by Fourier transform infrared spectrometry, elemental analysis, scanning electron microscopy, X-ray powder diffraction analysis and Rietveld refinement studies. Phase transformation and ion release were analyzed during 7 days of incubation in simulated body fluid at 37 °C. The metabolic activity of healthy and osteosarcoma cell lines was assessed by cell cytotoxicity and viability test. The as-prepared powders were composed of calcium-deficient carbonated hydroxyapatite (HAp), octacalcium phosphate (OCP), and amorphous calcium phosphate (ACP). Along with the selenite substitution, the presence of Sr2+, Na+, and Mg2+ was detected as a result of using cuttlefish bone as a precursor for Ca2+ ions. Inductively coupled plasma mass spectrometry analysis showed that the Se/(P + Se) molar ratios of selenite substituted powders are lower than the nominal ratios. Heat treated powders were composed of HAp, α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). Doping CaP structure with selenite ions improves the thermal stability of HAp. The powder with the Se/(P + Se) molar ratio of 0.007 showed selective toxicity to cancer cells.

Dissolution, bioactivity behavior, and cytotoxicity of 19.58Li2 O·11.10ZrO2 ·69.32SiO2 glass-ceramic.

Glass and bioactive glass-ceramic can be used in several applications. In bone growth where good bone/biomaterial adhesion was required, bioactive coatings for implants can improve bone formation. The glass and glass-ceramics of the LZS (Li2 O-ZrO2 -SiO2 ) system are very interesting because of their mechanical, electrical, and thermal properties. Very recently, their biological response in contact with human osteoblast has been evaluated. However, despite several initiatives, there are still no studies that systematically assess this system's bioactivity, dissolution, and cytotoxicity in vitro. This work aims to investigate the dissolution, bioactivity behavior, and cytotoxicity of LZS glass-ceramic. LZS glass-ceramics were produced from SiO2 , Li2 CO3, and ZrSiO4 by melting followed by quenching. The obtained glass frits were milled and uniaxially pressed and heat-treated at 800 and 900°C and submitted to physical-chemical, structural and mechanical characterization. Their dissolution behavior was studied in Tris-HCl, while bioactivity was performed in simulated solution body fluid (SBF). The cytotoxicity test was performed using glass-ceramic in direct contact with mesenchymal stem/stromal cells (SC) isolated from human exfoliated deciduous teeth. Structural and microstructural analyzes confirmed bioactivity. The results show that it was possible to produce bioactive glass-ceramic from LZS, proven by the formation of new calcium phosphate structures such as hydroxyapatite on the surface of the samples after exposure to SBF. The SC viability test performed indicated that the materials were not cytotoxic at 0.25, 0.5, and 1.0mg/ml. The glass-ceramic system under study is very promising for a medicinal application that requires bioactivity and/or biocompatibility for bone regeneration.

Properties of CaP coatings produced by reactive RF-magnetron sputtering in a mixture of nitrogen and noble gases

Calcium phosphate coatings are widely used to increase the biocompatibility of metal implants. Nowadays various dopants in the structure of calcium phosphate coatings are actively studied. Nitric oxygen is known as an essential mediator of blood flow. Its presence in the structure of calcium phosphate coating can stimulate angiogenesis and promote osseointegration of the implant. This article is dedicated to the study of morphology and physico-chemical properties of the calcium phosphate coatings formed via reactive RF-$$$magnetron sputtering of hydroxyapatite in the mixture of noble gases (Ne, Ar and Xe) and nitrogen with the same volume concentrations. There is a decrease in grain size and an increase in roughness with the growth of the atomic mass of noble gas in the mixture with nitrogen. The Ca/P ratio also decreases with the increase in the atomic mass of noble gas. Coatings formed in Ne + N2 and Xe + N2 gas mixtures are characterized by higher surface free energy in comparison with the ones formed in Ar + N2. It allows us to suggest that the coatings formed in Ne + N2 and Xe + N2 are more biocompatible than ones formed in Ar + N2, however, additional studies are needed to prove it.

Structure and formation of amorphous calcium phosphate and its role as surface layer of nanocrystalline apatite: Implications for bone mineralization

We provide a critical review of the chemical composition and structure of synthetic and biogenic (bone/dentin mineral) nanocrystalline hydroxy-carbonate apatite (HCA). Such particles exhibit a “core–shell” organization, where an ordered HCA core is coated by a surface layer, whose nature is best captured by amorphous calcium phosphate (ACP), which is known to be a precursor phase of synthetic HCA, but whose role of bone/dentin mineralization has remained a most controversial subject. After reviewing the structure of each HCA and ACP component, as well as the most recent findings on their in vitro formation mechanisms, we examine the core–shell HCA organization further, with a focus on the disordered surface (“shell”) domain. In most of recent literature, the surface portion is often referred to as the “hydrated surface layer”, but without identifying its shared chemical and structural features of (synthetic) ACP. Unfortunately, that missing surface-layer/ACP equivalence obscures that the surface layer at the synthetic/biogenic nanocrystallites may simply constitute a remnant of the ACP phase from which the ordered HCA “core” nucleated. Although many topics reviewed herein have been investigated for more than six decades, several remain unsettled and heavily debated. Notably, decades-old articles offer suggestions that have passed unnoticed by the younger generations of researchers; we contrast and discuss both the latest and early contributions of this field, as well as highlighting several unsettled topics that should be revisited to improve our understanding of the ACP and HCA structures and in vitro/in vivo formation mechanisms.

The features of aliovalent substitution in anionic and cationic sublattices of apatite-related calcium phosphate

We investigated the features of complex substitution in anionic (PO43–CO32–) and cationic (Ca2+M+, M+ – Na, K) sublattices of apatite-type calcium phosphate during wet precipitation. The nanoparticles (10–35 nm) of apatite-related calcium phosphates were prepared from the aqueous solutions of the system М+–Ca2+–CO32––PO43––NO3– at determined molar ratios Ca2+/PO43–=1.67, CO32–/PO43–=1.0 and М+/PO43–=3.0 and 6.0 at the temperature of 250C. The positions of characteristic vibrations of carbonate groups in the FTIR spectra of the prepared samples in the regions of 1500–1400 cm–1 and 880–870 cm–1 confirmed the realization of partial substitution of РО43– by CО32– (B-type) in apatite-type structure. Results of elemental analysis indicated that the presence of potassium cations in the initial solution promoted the anionic substitution in calcium phosphate structure. The study of the activity of the synthesized carbonate-containing calcium phosphates in vitro revealed their tendency to gradual dissolution without a significant effect on the pH of the medium, which indicates the prospects of the synthesized samples in bone engineering.

Influences of strontium on the phase composition and lattice structure of biphasic calcium phosphate

Hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are widely used in bone graft materials, because they have excellent biocompatibility. However, the degradation rates of HAp and β-TCP do not match the rate of osteogenesis, which limits their clinical applications. Therefore, forming biphasic calcium phosphate (BCP) is a promising method to control the biodegradation rate of the material. In addition, strontium (Sr) is an important element that promotes osteogenesis and inhibits bone absorption. Therefore, this study focused on the effects of Sr in the as-synthesized BCP with varied Sr concentrations of 1, 5, and 15 mol%, which are synthesized by chemical precipitation and a high-temperature calcination method. In this study, we assume that Sr is doped into Ca(5) of β-TCP and Ca(1) & Ca(2) of HAp during the Rietveld refinement. On the basis of the Rietveld refinement results obtained from X-ray diffraction (XRD) patterns, with increasing Sr concentration, the mass percentage of HAp decreases first, which is due to the distortion of the HAp structure, resulting in a decrease in HAp stability and phase variation from HAp to β-TCP. However, when the concentration of Sr reaches 15 mol%, the mass percentage of HAp increases, which may be because of the phase transformation from β-TCP to calcium-deficient apatite by the diffusion of Ca. In addition, the increase in the lattice constants and volumes indicates that Sr has been successfully doped into the crystal lattices of both β-TCP and HAp, since the ion radius of Sr2+ (0.113 nm) is larger than the ion radius of Ca2+ (0.099 nm). As shown in the X-ray photoelectron spectroscopy (XPS) results, the intensities of Sr3d and Sr3p increase with increasing Sr concentrations, which indicates that Sr is not only on the surface of the sample but also in the crystalline structures of both β-TCP and HAp.

Influence of adding Pluronic F127 in the electrolyte on the morphology, structure and biofilm adhesion of calcium phosphate coatings

In this work, we have investigated the addition of Pluronic F127 (PF127) into the electrolyte solution on the structure, morphology and antibacterial growth of calcium phosphate (CaP) coatings synthesized by an electrochemical method on Ti substrate. Different parameters of the deposition process were investigated, which were temperature, time and PF127 wt%. The coatings were characterized by X-ray diffraction (XRD), gravimetric analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In vitro antimicrobial assays against S. aureus were performed. XRD analysis confirmed the formation of dicalcium phosphate dihydrate (DCPD) or anhydrous dicalcium phosphate (DCPA) and octacalcium phosphate (OCP). The structure and morphology depended mainly on PF127 wt% and deposition temperature in lower deposition time. Interestingly, structure and morphology were not influenced by adding PF127 at higher deposition time using higher PF127 concentrations. The morphology by SEM changed from plate-like to fiber by varying the PF127 concentration as well as blocks at higher temperatures. Moreover, all coatings were crystalline, uniform and crack-free. Antibacterial assays showed that biofilm formation was prevented when a coating of PF127 is deposited on the surface. Bacterial growth depended on the phase and morphology of washed coatings. Thus, the structure, morphology and consequently bacterial growth resistance can be tailored by the use of PF127 in the electrochemical processing at shorter deposition times.

Nanostructure of calcium phosphate films synthesized by pulsed laser deposition under 1 Torr: Effect of wavelength and laser energy

In this study, we investigated aspects about the nanostructure of calcium phosphate films formed by pulsed laser deposition under a high-pressure gas (argon) environment (1 Torr) that are not addressed in the literature by using infrared and green laser sources. The plume generated from an ablated hydroxyapatite target was deposited directly over transmission electron microscopy (TEM) grids during 120 s to allow for the use of TEM techniques to investigate the morphology, composition and structure of deposited films from the micron to the nanoscale. The films were found to comprise five different calcium phosphate structures: (1) unstructured amorphous thin film formed by the deposition of ions and molecules over the substrate, (2) dense nanoparticles (<20 nm) formed over the substrate, (3) low Ca/P ratio spherical particles (<400 nm) formed on the way to the substrate, (4) rich Ca/P ratio ring-shaped particles (>400 nm) ejected from the target and (5) crystalline particles (~500 nm) removed from the target. Although all samples presented these five structures, the morphology, abundance and size population were all different. This work opens a window to elucidate the complex mechanism underlying calcium phosphate film deposition and growth by pulsed laser deposition.

Study of Hydroxyapatite Nano-particles synthesized using sono-chemical supported hydrothermal method

Hydroxyapatite or Calcium Phosphate hydroxide [Ca10(PO4)6(OH)2, HA] is a multi-functional material having complex structure of Calcium phosphate which comprises the major inorganic part of mammalian hard tissues. It is widely utilized in biomedical and non-biomedical fields either in a pure, doped or composite form. As application of this material truly depends on the synthesis route, HA nano-particles were first synthesized using conventional sono-chemical method, hydrothermal method and combinative technique (i.e. sono-chemical supported hydrothermal method) and named as sample ‘S’, sample ‘H’ and ‘S + H’ respectively. Then, as the combinative technique gave better results, three samples were synthesized using different sonication time i.e 10 min., 20 min. and 30 min. prior to hydrothermal treatment and named as 10 HA, 20 HA, 30 HA respectively. Analysis of XRD data confirmed the presence of HA as major phase in all the samples (JCPDS card No.09-432). Crystallite size first decreased and then again start increasing with the increment in sonication time. SEM micrographs showed agglomerated particles. Agglomeration might be caused due to Ostwald ripening during drying process. From analysis of UV–VIS spectra, energy band gap of all the samples was found in UV-C region. It was also found that band gap energy increases slightly with sonication time. Therefore, this material can be utilized as photocatalyst material in UV-C (200–280 nm) region as well as for targeted drug delivery. FT-IR spectra of samples synthesized by combinative technique confirmed the presence of all elementary functional groups in synthesized samples and intensity of carbonate groups or nitrate groups decreases with increment in sonication time. Future studies will be carried out for decrement in band gap of HA for photocatalytic applications in UV-A to visible region.

Salt partition, ion equilibria, and the structure, composition, and solubility of micellar calcium phosphate in bovine milk with added calcium salts

Increasing dietary calcium has been suggested to have a range of health benefits, such as reducing the risk of osteoporosis and hypertension. However, producing calcium-fortified products is challenging due to the destabilizing effect caused by added calcium. We provide new data on the effect of adding either calcium gluconate or calcium lactate at up to 50 mM on the partition of salts and the structure and solubility of micellar calcium phosphate (MCP). The empirical chemical formula of the MCP in milk with added calcium was Ca(HPO4)0.6(PO4)0.267, similar to that previously reported for the MCP in native bovine casein micelles. Ion equilibria calculations showed that the solubility of the MCP was decreased as measured by an increase in negative logarithm of the solubility constant (pKS) from 6.8 to 7.3 ± 0.1 and 7.5 ± 0.1 for milk with added calcium gluconate and calcium lactate, respectively. No substantial change in the amorphous structure of the MCP was observed by either X-ray powder diffraction or infrared spectroscopy of dried casein micelles as a result of added calcium. The conclusion is that the added calcium caused an increase in the concentration of the MCP and decreased its solubility without changing its amorphous structure or chemical composition.

Characterization of Hybrid Bio-Ceramic Hydroxyapatites Reinforced by Expanded Perlite-TiO2-ZrO2-MgO-P2O5

Background: Hydroxyapatite, which is naturally and synthetically available, is often used as a biomaterial because of its similarity to bone. Aim: In this study, Natural hydroxyapatite powder, synthesized from sheep bone, and synthetic hydroxyapatite were used as matrix. Materials and Methods: Hybrid bio-ceramic composites were obtained by adding 5 wt. % expanded perlite-TiO2-ZrO2-MgO-P2O5 to both matrixes. The bio-ceramic materials which were mixed with mechanical mixer for 30 minutes were pressed with hydraulic press under 25 MPa pressure and sintered at 900°C for 1 hour. Density, micro-hardness, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis were performed to determine characteristics of the samples. Results: As a result, it was identified that the micro-hardness of natural hydroxyapatite was higher. In addition, the increase in micro-hardness values of ZrO2-reinforced samples was higher than the TiO2-reinforced samples. Conclusion: Hydroxyapatite, calcium silicate, calcium phosphate structures were observed in XRD analysis. Micro-pores were observed in TiO2-reinforced samples while more dense structures were observed in ZrO2-reinforced samples.

Tetracalcium phosphate and biphasic tetracalcium phosphate/tricalcium phosphate powders' effects evaluation on human osteoblasts.

Calcium ions levels in bone niches have been demonstrated to severely influence new bone formation. Osteoinductive scaffolds containing calcium have been largely studied to control the release of calcium in bone regeneration and tissue engineering purpose. The aim of the present study was, firstly, to synthesize two different resorbable calcium phosphate-based powders, thought to be reservoirs of calcium ions, and secondary, to investigate their effects on human osteoblasts, in order to develop a suitable titanium coating material. Tetracalcium phosphate (A450) and biphasic tetracalcium phosphatae/tricalcium phosphate (A850) powders were prepared with an innovative method. The presence of calcium phosphate structures was chemically confirmed with XRD. Furthermore, powders macroscopic aspect was observed with a stereomicroscope. For in-vitro experiments, human osteoblastic cells were cultured in the presence of A450 and A850, and assayed for viability and metabolic activity through Crystal Violet and MTT, respectively. Our synthesis led to the formation of calcium phosphates in both samples, even though A850 presented a higher level of crystallinity and a more powdery aspects than A450. Both the samples enhanced the viability of cultured cells, inhibiting cell metabolic activity in the case of A850, which furthermore showed to be internalized by cells. We developed two different kind of calcium phosphate-based powders and we tested their effect on human osteoblasts, underlying the possibility of use calcium phosphate-based coatings to enhance cell response on implantable materials.