Calcium Phosphate Films Research Articles

New insights into the influence of mineral surface transformation on the flotation behavior of anhydrite/apatite

Apatite is generally associated with calcium-containing minerals such as anhydrite, which are difficult to separate due to their similar surface characteristics. In this study, the influence of anhydrite on the flotation behavior of apatite in a fatty acid system was systematically investigated using micro-flotation tests, solution chemical calculations, and surface chemical analyses based on the theory of flotation solution chemistry. The single and mixed mineral flotation experiments revealed that an increasing concentration of anhydrite in the mixed ore system rises, apatite flotation is inhibited while anhydrite flotation is activated. The solution chemical calculation results demonstrated that in the mixed system of anhydrite/apatite, the surface dissolution of anhydrite in the pulp will change the solution chemistry environment, resulting in a drastic decrease in the number of surfaces located ions on the apatite surface and inhibiting its flotation. Furthermore, when the pH of the solution exceeds 4.3, the surface of anhydrite transformed to apatite, promoting anhydrite flotation. The results of the X-ray photoelectron spectroscopy (XPS) analysis further confirmed that the phosphate ions dissolved by apatite were adsorbed on the anhydrite surface at pH= 9, forming calcium phosphate films. Based on the above test results, a novel flotation process was designed to realize the selective flotation of apatite from anhydrite-rich phosphate ores. This study can serve as a theoretical foundation and a practical reference for the separation of calcium-containing minerals.

Effects of annealing in vacuum on the microstructure of silicon-containing calcium phosphate films deposited on a ZrNb alloy by radio-frequency magnetron sputtering

Coatings were deposited on the surface of a ZrNb alloy by radio-frequency magnetron sputtering using targets consisting of either pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA). The coated ZrNb samples were heated in a vacuum furnace at a pressure of 5 × 10−5 Torr and temperature 700 °C for 2 h. Precursor powders of silicate-substituted HA [Ca10(PO4)6−x(SiO4)x(OH)2−x, x = 0, 0.5, or 1.72] were used to fabricate the targets for sputtering. The aim of this study was to analyze the effect of Si addition to HA on crystallization behavior and structure of the resulting films using transmission electron microscopy and electron diffraction patterns of selected sites. The average thickness of the films was in the range of 175–345 nm. The Si substitution in HA played a major role in the mechanisms of coating formation and crystallization behavior, which influenced the structure and crystallinity of the layers deposited by radio-frequency magnetron sputtering. Moreover, the results indicate that surface-induced crystallization of the deposited thin films is more pronounced than internal crystallization. A possible mechanism underlying the observed decrease in the crystallization rate with the increasing silicate content in the HA-based films is discussed.

Calcium phosphate composites to synergistically promote osteoconduction and corrosion resistance on bone materials via plasma polymerized hexamethyldisilazane coatings

A facile and effective plasma polymerized hexamethyldisilazane (ppHMDSZ) combining with calcium phosphate (Ca-P) coating to promote osteoconduction meanwhile provide resistance to corrosion is developed in this study. The composites of Ca-P and ppHMDSZ thin films were deposited on bone substitutes to investigate the osteoblast compatibility. The amount of the Ca-P coatings was modulated with a linear deposition rate of 7.37 μg/(cm2∙cycle) by alternative immersion cycles (1, 2, 5, and 10) in solutions containing calcium and phosphate, measured by quartz crystal microbalance (QCM). Importantly, cell behaviors including cell adhesion, proliferation, and functional activity responded positively toward the surface wettability and roughness of the Ca-P layers. Moreover, the human osteoblast cells (hFOB1.19) revealed excellent compatibility on the stainless steel coated with Ca-P/ppHMDSZ composite films. The combination of bioceramics and corrosion resisting plasma polymerized HMDSZ films showed a synergistic effect on the biocompatibility and osteoconductive for bone tissue engineering applications.

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.

Electrochemically Deposited Calcium Phosphate Coatings Using a Potentiostat of In-house Design and Implementation

Abstract The effect of growth conditions and post treatments on the properties of calcium phosphate films electrodeposited by a potentiostat of the authors’ design and construction is presented. The electrolyte used was formed with 0.025 M (NH4)H2PO4 and 0.042 M Ca(NO3)2.4H2O, and its pH was kept at 5. A voltametric analysis was performed to determine the necessary potential values to obtain the films. Additionally, the temperature of the electrolyte was varied to determine its influence on the properties of the deposited films. The films were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The films deposited at -1.4 V and -1.7 V present the brushite phase. The thermal post-treatment favored the formation of octagonal calcium phosphate in amorphous phase, while the basic treatment provided the OH- groups necessary for the formation of hydroxyapatite. The low cost potentiostat implemented presents excellent characteristics for obtaining films with similar characteristics to those obtained with a conventional potentiostat.

Laser-Induced Forward Transfer with Optical Stamp of a Protein-Immobilized Calcium Phosphate Film Prepared by Biomimetic Process to a Human Dentin

The rapid and area-specific printing of calcium phosphate with superior biocompatibility and osteoconductivity is a useful technique for the surface functionalization of biomedical devices. We recently demonstrated the laser-induced forward transfer (LIFT) of a brittle calcium phosphate film onto a soft and shock-absorbing polydimethylsiloxane (PDMS) substrate. In this work, a new LIFT using an optically transparent PDMS-coated stamp, which we hereafter call LIFT with optical stamp (LIFTOP), was introduced to achieve the transfer of brittle films to harder substrates. Cell adhesion protein fibronectin-immobilized calcium phosphate films (Fn-CaP) were prepared on the optical stamp through a biomimetic process. Then, the irradiation of a single laser pulse transferred the Fn-CaP film from the optical stamp onto relatively hard substrates, polyethylene terephthalate and human dentin. As a result of this LIFTOP process, Fn-CaP microchips with a shape corresponding to the laser beam spot were printed on the substrates. Cross-sectional observation of the interface between the Fn-CaP microchip and the dentin substrate revealed good attachment between them without obvious gaps for the most part.

Influence of Crystallographic Texture on the Corrosion Product Morphology and Corrosion Rate of AZ31 Plate in Simulated Body Fluid

This paper investigates the effect of crystallographic texture on the corrosion product morphology and corrosion behavior of AZ31 magnesium alloy after immersion in simulated body fluid for 3 days. The microstructure and macrotexture analyses are performed through optical microscopy and x-ray diffraction methods, respectively. The polarization test evaluated the corrosion, and the FESEM electron microscope equipped with EDS was used to investigate the morphology of the corrosion products. According to the results, the morphology of calcium phosphate deposit as a corrosion product at the surface with basal texture was a porous cauliflower shape. In contrast, the calcium phosphate deposit at the surface of the nonbasal texture was uniform and nanoworm-like. The corrosion rate at the basal texture surface was higher than the nonbasal one, which is attributed to the difference in the morphology of calcium phosphate film.

Deposition of biphasic calcium phosphate film on laser surface textured Ti–6Al–4V and its effect on different biological properties for orthopedic applications

Abstract The present study reports laser surface texturing (LST) of Ti–6Al–4V using a Nd-YAG laser with a particular set of parameters and three different overlapping factors (OF): 0%, 25% and 50%. Biphasic calcium phosphate (BCP) film was deposited on bare as well as textured Ti–6Al–4V specimens by using radio frequency (RF) sputtering. The simultaneous effect of texturing as well as BCP coating on different physical and biological properties was investigated. The study revealed that the surface wettability of bare Ti–6Al–4V enhanced after laser texturing (as contact angle reduced from 89° to 71°-77°). It was further improved upon BCP deposition to make the Ti–6Al–4V superhydrophilic (contact angle ≈ 17°-21°). It was also observed that the surface roughness of bare Ti–6Al–4V significantly increased from Ra ≈ 94 nm to Ra ≈ 0.98–1.84 μm for different micro-dimpled texture substrates. The dimensions of micro-dimpled texture did not change after BCP deposition; however, a non-uniform film is deposited with increase in surface roughness. Protein adsorption was found as a function of surface hydrophobicity, which increased from 5.3 to 7.11 μg/cm2 with the rise in hydrophobicity of modified surfaces. Compared to bare Ti–6Al–4V and BCP deposited bare-Ti-6Al–4V surfaces, the BCP deposited textured surfaces exhibit higher number of well spread MG63 osteoblast cells. For the same surface chemistry, increase in surface area (roughness) improves cellular behavior. With texturing of the substrate, the cell adhered percentage and average cell area improved significantly and BCP-(50% OF)–Ti–6Al–4V was found to have the maximum cell spreading and proliferation. Overall, these findings revealed that a micro-dimpled textured surface followed by BCP film deposition strategy improved the physio-chemical properties of surfaces such as surface roughness and wettability. This in turn enhanced the bioactivity, cell adhesion and proliferation of bone cells (MG63) on modified Ti–6Al–4V surfaces and based on the results we envisage that can be potentially used for orthopedic and dental applications.

Effect of TiO2 addition on adhesion and biological behavior of BCP-TiO2 composite films deposited by magnetron sputtering.

The present investigation focuses on the deposition of biphasic calcium phosphate (BCP) and titania (TiO2) composite films on Ti-6Al-4V substrates using radio frequency (RF) magnetron sputtering. Three different compositions such as 100% BCP, 25% TiO2-75% BCP and 50% TiO2-50% BCP films were fabricated, and the physical, mechanical and biological behaviors of the films were analyzed. Post deposition, the films were annealed at 700°C for 2h to induce the crystallinity and to study its effect on different properties. The wettability was found to be 95°(±3°) for 100% BCP, 73°(±2°) for 25% TiO2-75% BCP and 35°(±1°) for 50% TiO2-50% BCP films, indicating improvement in wettability with an increase of TiO2 weight percent in the composite films. The value of critical load (Lc2) for 100 BCP film improved from 8.7N to 14.8N (25 TiO2-BCP) and >19N (50 TiO2-BCP film), indicating improvement in bonding strength with TiO2 addition. The fetal bovine serum (FBS) adsorption decreased from 7.11±0.25 to 4.42±0.17μg/cm2 with TiO2 weight percent from 0 to 50%. Cell adhesion and proliferation significantly improved in 100% BCP, 25% TiO2-75% BCP and 50% TiO2-50% BCP films as compared to uncoated Ti-6Al-4V. The maximum cell proliferation was found on the surface of 50% TiO2-50% BCP film (210.1±6.5%) after 6days of incubation. However, after annealing all the films exhibited less cell adhesion and cytocompatibility presumably due to change in composition. Globular apatite structure was observed on all modified surfaces after 7days immersion in simulated body fluid (SBF); however, the growth rate was higher for 50 TiO2-BCP films. All these results revealed that the addition of TiO2 in BCP film (without annealing) is advantageous for improving the bonding strength as well as the bioactivity of implants, which can be used for long-term dental and orthopedic applications.

Fabrication and bioresorbability of Ag- and Ta-containing amorphous calcium phosphate films formed on titanium substrates by RF magnetron sputtering

Silver (Ag)- and tantalum (Ta)-containing amorphous calcium phosphate (ACP) coating films were fabricated on titanium substrates by radiofrequency magnetron sputtering for biomedical applications. The sputtering targets were hot-pressed into 10 mol% Ag-containing ß-tricalcium phosphate sintered compacts with and without 8 mol% Ta. The fabricated ACP coating films were dense and smooth, with all elements distributed homogeneously along the depth direction. In addition, Ag existed as ions in the ACP regardless of the presence of Ta. The resorbability of the Ag-containing ACP coating films in simulated body fluids was suppressed by the addition of Ta. The concentration of detected Ag ions was higher in diluted nutrient broth solution than in Tris-HCl solution.

Fabrication of porous scaffold by ternary combination of chitosan, gelatin, and calcium phosphate for tissue engineering

Recently, 3D porous scaffolds using naturally derived polymers, i.e. chitosan (CHN), gelatin (GLN), and their blends have attracted attentions for tissue engineering applications. Research on the use of polymers and ceramic composites has been performed to improve biocompatibility of tissue scaffolds. However, calcium phosphate (CaP) coating on CHN/GLN blend scaffolds has not been well studied. In this study, we fabricated CHN/GLN films and scaffolds at various CHN/GLN blending ratios (100/0, 75:25, 50/50, 25/75, and 0/100) and established optimal CaP coating method on CHN/GLN blends. Increase in GLN content promoted both surface hydrophilicity and Ca/P ratio. The prepared CHN/GLN scaffolds displayed highly porous architecture with elastic nature. The effect of increase in GLN content on osteoblast proliferation was evident but no significant impact on alkaline phosphatase (ALP) activity. When the CHN/GLN scaffold was coated with CaP film, ALP activity was dramatically improved, and the 75/25 scaffold showed the highest ALP level among all CHN/GLN scaffolds. The present study demonstrated that the combination of CHN, GLN, and CaP coating can generate synergistic effects on the improvement of bioactivity of CHN/GLN scaffold and can be further used for the fabrication of hard tissue scaffolds.

Effect of Growing Conditions and Post Treatments on Calcium Phosphate Films Obtained by Electrode Position

The effect of growing conditions and post treatments in electrodeposited calcium phosphate films on 316 L stainless steel is presented. The concentration and pH of electrolyte solution and the potential values for the electrodeposition process were determined based on a study of cyclic voltammetry curves. The electrolyte concentration was fixed at 0.025 M ((NH4) H2PO4) and 0.042 M (Ca(NO3)2.4H2O), choosing a pH = 5 as the better condition for the films deposition. In addition, the electrolyte temperature was varied between room temperature and 60°C to determine the influence of this parameter on the deposited films. Films were characterized using Fourier Transform Infrared Spectroscopy, X-ray diffraction and Scanning electron microscopy equipped with energy dispersive spectroscopy. The as deposited films at -1.2 V and -1.7 V exhibit the dicalcium phosphate dihydrate phase (Brushite) while thermal post treatment favor the formation of octacalcium phosphate in amorphous phase, and basic treatment tend to produce the Hydroxyapatite phase. The suggested mechanism for the HAp phase formation, after the basic treatment, consists in providing the necessary OH- groups to complete the synthesis process.

Osteoblast-like Cell Growth and Differentiation Behaviors on the Phospholipid Vesicle-Interacted Calcium Phosphate Films

Osteoblast-like Cell Growth and Differentiation Behaviors on the Phospholipid Vesicle-Interacted Calcium Phosphate Films

Characteristics of RF-Sputtered Thin Films of Calcium Phosphate on Titanium Dental Implants

Hydroxyapatite (HA) coatings on titanium have been investigated for many years, and have demonstrated advantageous biocompatibility in dental implants. Animal experiments have demonstrated that the biological response to plasma-sprayed HA-coated implants shows disadvantages in terms of adherence, thickness uniformity, and long-term osseointegration effects. Determining how to resolve the degradation problem of HA in the body by improving osseointegration and stability in alveolar bones has become an increasingly researched topic. The present study investigated the film characteristics and dissolution properties of calcium phosphate (CaP) coatings obtained by radio-frequency (RF) sputtering of a self-developed atmospheric plasma spray (APS) HA target. The experimental parameters varied, including RF power (60–250 W), sputtering time (15–120 min), and substrate roughness (0.4–4 μm). Analyses were conducted using synchrotron X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), white light interferometry, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (EDS). EDS analysis showed that the Ca/P ratio increased as the discharge power was increased. The analysis results also showed that a lower surface roughness resulted in higher crystallinity, because a larger surface-free energy was attained during sputtering. In-plane texturing has been proven when HA films are sputtered onto substrates of varying roughness, within appropriate deposition parameters. FTIR analysis revealed the presence of the principal PO43- bonds in the deposited calcium phosphate films. The CaP films induced calcium phosphate precipitation when immersed in simulated body fluid (SBF), suggesting that, based on in vitro bioactive behavior, the proposed combined surface modification can be used in dental implants.

Fabrication of Phospholipid Vesicle-Interacted Calcium Phosphate Films with Sterilization Stability

The development of a calcium phosphate (CP) coating technique on tissue culture poly(styrene) (TCPS) is important in biomedical fields. In this study, the CP hybridized with l-α-phosphatidylcholine phospholipid vesicle (PV) was formed on TCPS as the film state for suggesting the unique CP/PV hybrid films. The film formation was conducted by the following two different processes: (i) the CP deposited on PV was prepared in a simulated body fluid (SBF) and subsequently casted on TCPS to form the films, and (ii) the CP was precipitated in SBF on the pre-prepared PV films on TCPS. These films were denoted as “CP/PV-Bef” and “CP/PV-Aft” films. The stability of the CP/PV hybrid films against the sterilization processes (ethanol, UV/ozone, and autoclave treatments) and subsequent immersion process in a phosphate buffer saline (PBS) was also demonstrated. As a result, the CP/PV hybrid films were successfully coated on TCPS through the mediation by PV with preserving the vesicle structure. The morphologies and phys...

Strontium doped calcium phosphate coatings on poly(etheretherketone) (PEEK) by pulsed electron deposition

Herein the preparation of Sr2+-doped calcium phosphate (CaP) coatings on poly(etheretherketone) (PEEK) substrates by pulsed electron deposition (PED) was investigated. Hydroxyapatites (HA) substituted with tailored amounts of Sr2+ up to 9wt% were synthesized to generate the deposition targets. Dense and uniform amorphous CaP films having Sr/Ca molar ratios close to that of targets were achieved. The roughness and the wettability of the bare PEEK were significantly enhanced after coating deposition. The presence of Sr2+ led to a slight increase of the particles size while it did not mainly affect the RMS of the coatings that consisted of nanostructured aggregates of globular shape. After a mild annealing treatment at 130°C for 6h, the amorphous coatings transformed into nanocrystalline HA films incorporating Sr2+ having Sr/Ca molar ratios close to those of the as-deposited films. The annealing did not affect the topography and the roughness of the coatings, while improved the hardness of the films un-doped and doped at low-extent. This study shows that PED is feasible technique to coat PEEK implants with CaP films with control over the Sr/Ca ratio, which could improve bone fixation and in vivo stability especially under osteoporotic conditions thanks to the anabolic effect of Sr2+.

Effects of Electrolyte Concentration on Formation of Calcium Phosphate Films on Ti–6Al–4V by Electrochemical Deposition.

Nano-sized calcium phosphate film was formed on Ti–6Al–4V alloy using simple electrochemical deposition. Pre-treatment of Ti–6Al–4V alloy was carried out by galvanostatic treatment step which acted as anchorage for growth of the hydroxyapatite during subsequent pulsed electrochemical deposition process at 40 and 85 °C. The phase and morphologies of deposited calcium phosphate were influenced by the electrolyte temperature and electrolyte ratio (Ca/P). The nano needle-like precipitates were formed under 1.67 Ca/P ratio in solution. The needle-like deposits were transferred to the plate-like precipitates in the case of Ca-deficient or Ca-rich electrolyte.

In-situ ellipsometric study of calcium phosphate biomineralisation on organic thin films

In this study, in-situ ellipsometry and scanning electron microscopy (SEM) were used to follow the growth kinetics of calcium phosphate (CaP) films on zein and hexadecanoic acid (HDA) layers self-assembled at the air-liquid interface. The duration of the mineral film induction period was heavily dependent on the organic template used, presence or absence of Mg2+, solution pH and concentration. In a standard simulated body fluid (SBF) solution at 20°C and pH 7.4, CaP film growth occurred after an induction period of 40 min for HDA and 100 min for zein. In the absence of Mg2+ the mineralisation induction period was reduced, for only the zein protein, to 50 min. At pH 6, HDA and zein-induced CaP films started forming after 100 min and 180 min, respectively. No induction period was observed when the SBF concentration was doubled, with immediate CaP growth observed for both HDA and zein. This study shows the effect of biomineralisation conditions on the growth of CaP with the organic template playing an important role. Knowledge of the factors that influence mineral growth processes is of importance in areas of biomineralisation and controlled crystal growth.

Fabrication of Bioactive Cobalt-Chromium Alloys by Incorporation of Apatite Nuclei

Micrometer-sized pores were formed on the surface of cobalt-chromium (Co-Cr) alloys by sandblasting method. In order to provide bioactivity to the Co-Cr alloys, the alloys were soaked in SBF and heated. By this treatment, amorphous calcium phosphate film was formed on the Co-Cr alloys. Apatite-forming ability of the specimens was evaluated by using SBF.

Role of magnesium on the biomimetic deposition of calcium phosphate

Biomimetic depositions of calcium phosphate (CaP) are carried out using simulated body fluid (SBF), calcifying solution and newly developed magnesium containing calcifying solution. Calcium phosphate has a rich phase diagram and is well known for its excellent biocompatibility and bioactivity. The most common phase is hydroxyapatite (HAp), an integral component of human bone and tooth, widely used in orthopedic and dental applications. In addition, calcium phosphate nanoparticles show promise for the targeted drug delivery. The doping of calcium phosphate by magnesium, zinc, strontium etc. can change the protein uptake by CaP nanocrystals. This work describes the role of magnesium on the nucleation and growth of CaP on Ti and its oxide substrates. X-ray diffraction studies confirm formation of HAp nanocrystals which closely resemble the structure of bone apatite when grown using SBF and calcifying solution. It has been observed that magnesium plays crucial role in the nucleation and growth of calcium phosphate. A low magnesium level enhances the crystallinity of HAp while higher magnesium content leads to the formation of amorphous calcium phosphate (ACP) phase. Interestingly, the deposition of ACP phase is rapid when magnesium ion concentration in the solution is 40% of calcium plus magnesium ions concentration. Moreover, high magnesium content alters the morphology of CaP films.