Biphasic calcium phosphate coating on cobalt-base surgical alloy during investment casting

The biphasic calcium phosphate (BCP) yields higher bioactivity and efficiency than the Hydroxyapatite (HA) alone. The HA/β-TCP ratio significantly affects BCP bioactivity as well as the extent of BCP resorption. In this study, the BCP coating on ASTM F-75 cobalt base alloy during the investment casting process was investigated. For this purpose, molten metal was poured at 1,470°C into previously coated investment molds preheated to 750, 850, 950, 1,050°C in order to investigate the effect of mold preheating temperatures on coating phase transformations. For in vitro evaluation, samples were immersed in the simulated body fluid (SBF) at 37°C for 4 weeks and characterized by XRD, SEM, EDS, and optical microscopy. The weight percentages of HA and β-TCP of the specimens were calculated to find that the HA/β-TCP ratio significantly depended on the mold preheating temperature as it caused changes in the dissolution behavior of BCP coating and the bone-like apatite precipitation on coating during in vitro evaluation.     

Biomimetic calcium phosphate coatings on nitric-acid-treated titanium surfaces

This study describes biomimetic calcium phosphate (Ca-P) coatings formation under simulated physiological conditions on Ti surfaces that go through nitric acid treatment (NT). In the present study, nitric acid treatment was used to treat Ti specimens so that Ti specimens could have the ability to induce Ca-P formation. After careful selection of the NT parameters, Ca-P coatings success fully formed on the nitric-acid-treated Ti surfaces in a supersaturated calcium phosphate solution (SCPS) and in the simulated body fluid (SBF). Before NT, the Ti specimen should go through mixed acid etching to increase its surface roughness because rough surfaces lead to good adherence between coatings and substrates. Amorphous Ca-P coatings were formed on the Ti surfaces by immersing the NT Ti specimens in SBF, while octacalcium phosphate (OCP) coatings were formed in the SCPS after 3 days of immersion. The study firstly proved that nitric acid treatment is not only just for surface passivation but also is another bioactive treatment as an alternative to the alkaline treatment and two-step method. The experimental results also confirmed that the conventional nitric acid treatment of a titanium surface does not increase the titanium oxide on the Ti surfaces. However, extending the nitric acid treatment time and enhancing the nitric acid treatment temperature help to increase Ti surface ability of Ca-P induction in simulated physiological environments. Ti specimens that had 600 min of NT at 60 °C had the best Ca-P induction ability under biomimetic conditions.     

Biomimetic calcium phosphate coating on Ti wires versus flat substrates: structure and mechanism of formation

Biomimetic calcium phosphate (Ca–P) coatings improve the osteoconductivity of orthopedic implants and show promise as slow delivery systems for growth factors. This paper compares the structure and composition of biomimetic coatings on flat titanium coupons and on Ti wires/thin pins that are often used as model implants in small animal in vivo models. Ca–P coatings were grown on alkali-treated Ti substrates using a two-step deposition procedure. The coatings on wires consisted of a surface layer of octacalcium phosphate (OCP) and a layer of Ca-deficient hydroxyapatite (CDHA) underneath. The coating thickness and the proportion of CDHA decreased with increasing wire diameter. The coatings on flat coupons were the thinnest, and were comprised almost entirely of OCP. A mechanism of successive formation of the CDHA and OCP phases based on the interplay between nucleation, growth and hydrolysis of OCP crystals as a function of changing local supersaturation is proposed.     

Micromorphological effect of calcium phosphate coating on compatibility of magnesium alloy with osteoblast

Abstract

Octacalcium phosphate (OCP) and hydroxyapatite (HAp) coatings were developed to control the degradation speed and to improve the biocompatibility of biodegradable magnesium alloys. Osteoblast MG-63 was cultured directly on OCP- and HAp-coated Mg-3Al-1Zn (wt%, AZ31) alloy (OCP- and HAp-AZ31) to evaluate cell compatibility. Cell proliferation was remarkably improved with OCP and HAp coatings which reduced the corrosion and prevented the H₂O₂ generation on Mg alloy substrate. OCP-AZ31 showed sparse distribution of living cell colonies and dead cells. HAp-AZ31 showed dense and homogeneous distribution of living cells, with dead cells localized over and around corrosion pits, some of which were formed underneath the coating. These results demonstrated that cells were dead due to changes in the local environment, and it is necessary to evaluate the local biocompatibility of magnesium alloys. Cell density on HAp-AZ31 was higher than that on OCP-AZ31 although there was not a significant difference in the amount of Mg ions released in medium between OCP- and HAp-AZ31. The outer layer of OCP and HAp coatings consisted of plate-like crystal with a thickness of around 0.1 μm and rod-like crystals with a diameter of around 0.1 μm, respectively, which grew from a continuous inner layer. Osteoblasts formed focal contacts on the tips of plate-like OCP and rod-like HAp crystals, with heights of 2–5 μm. The spacing between OCP tips of 0.8–1.1 μm was wider than that between HAp tips of 0.2–0.3 μm. These results demonstrated that cell proliferation depended on the micromorphology of the coatings which governed spacing of focal contacts. Consequently, HAp coating is suitable for improving cell compatibility and bone-forming ability of the Mg alloy.     

Biomimetic calcium phosphate crystal mineralization on electrospun cellulose-based scaffolds

Novel cellulose based-scaffolds were studied for their ability to nucleate bioactive calcium phosphate crystals for future bone healing applications. Cellulose-based scaffolds were produced by electrospinning cellulose acetate (CA) dissolved in a mixture of acetone/dimethylacetamide (DMAc). The resulting nonwoven CA mats containing fibrils with diameters in the range of 200 nm to 1.5 μm were saponified by NaOH/ethanol for varying times to produce regenerated cellulose scaffolds. Biomimetic crystal growth nucleated from the fiber surface was studied as a function of surface chemistry. Regenerated cellulose scaffolds of varying treatments were soaked in simulated body fluid (SBF) solution. Scaffolds that were treated with CaCl(2), a mixture of carboxymethyl cellulose (CMC) and CaCl(2), and NaOH and CaCl(2), were analyzed using X-ray photoelectron spectroscopy, X-ray powder diffraction, and scanning electron microscopy to understand the growth of bioactive calcium phosphate (Ca-P) crystals as a function of surface treatment. The crystal structure of the nucleated Ca-P crystals had a diffraction pattern similar to that of hydroxyapatite, the mineralized component of bone. The study shows that the scaffold surface chemistry can be manipulated, providing numerous routes to engineer cellulosic substrates for the requirements of scaffolding.     

A study on hot deformation behavior of Ni-42.5Ti-7.5Cu alloy

To investigate the hot deformation behavior of the Ni-42.5Ti-7.5Cu (wt%) alloy, hot compression tests were carried out at the temperatures from 800 °C to 1000 °C and at the strain rates of 0.001 s⁻¹ to 1 s⁻¹. The results show that the occurrence of dynamic recrystallization (DRX) is the dominate restoration mechanism during the hot deformation of this alloy. There is an increase in peak and steady state stresses with decreasing the deformation temperature and increasing the strain rate. The experimental results were then used to determine the constants of developed constitutive equations. There is a good agreement between the measured and predicted results indicating a high accuracy of developed model. Zener–Hollomon (Z) parameter, calculated based on the developed model, indicates that DRX was postponed when the logarithm of the Zener–Hollomon parameter fell around 33 at strain rate of 0.001 s⁻¹ and temperature of 900 °C. This phenomenon can be regarded as the interactions between solute atoms and mobile dislocations. The established constitutive equations can be used to predict and analyze the hot deformation behavior of Ni-42.5Ti-7.5Cu alloy.     

Effects of protein incorporation on calcium phosphate coating

The incorporation of proteins into calcium phosphate (Ca–P) coatings is expected to alter their properties. The aim of this work is, therefore, to study the effect of protein concentration on the formation of Ca–P film. A biodegradable blend of corn starch/ethylene vinyl alcohol (SEVA-C) was used as substrate and bioactive glass (45S5 Bioglass^®) was used as a nucleating agent. Bovine serum albumin (BSA) and α-amylase were added, separately, at a concentration of 0.5, 1, and 5 mg/mLto simulated body fluid (SBF) solutions, at the nucleation stage.The incorporation of protein molecules was shown to affect the properties of Ca–P coatings in terms of morphology, composition and crystallinity. Both proteins seem to inhibit in some extent and/or retard the growth of Ca–P nuclei at 0.5 and 5 mg/mL concentrations. FTIR analyses revealed the presence of phosphate and carbonate groups, confirming the formation of a Ca–P layer. The characteristic groups of protein molecules were also detected on the IR spectra, which indicate the efficient incorporation of the proteins into the coatings. When α-amylase was added to the SBF solution the production of reducing sugars was detected, proving the retention of enzyme activity. These results suggest the carrier potential of Ca–P coatings for the sustained delivery of other biologically active proteins and consequently with a strong potential for inducing bone tissue regeneration.     

Calcium phosphate coating on magnesium alloy for modification of degradation behavior

Magnesium alloy has similar mechanical properties with natural bone, but its high susceptibility to corrosion has limited its application in orthopedics. In this study, a calcium phosphate coating is formed on magnesium alloy (AZ31) to control its degradation rate and enhance its bioactivity and bone inductivity. Samples of AZ31 plate were placed in the supersaturated calcification solution prepared with Ca(NO₃)₂, NaH₂PO₄ and NaHCO₃, then the calcium phosphate coating formed. Through adjusting the immersion time, the thickness of uniform coatings can be changed from 10 to 20 μm. The composition, phase structure and morphology of the coatings were investigated. Bonding strength of the coatings and substrate was 2–4 MPa in this study. The coatings significantly decrease degradation rate of the original Mg alloy, indicating that the Mg alloy with calcium phosphate coating is a promising degradable bone material.     

Porous calcium phosphate ceramics prepared by coating polyurethane foams with calcium phosphate cements

Porous calcium phosphates have important biomedical applications such as bone defect fillers, tissue engineering scaffolds and drug delivery systems. While a number of methods to produce the porous calcium phosphate ceramics have been reported, this study aimed to develop a new fabrication method. The new method involved the use of polyurethane foams to produce highly porous calcium phosphate cements (CPCs). By firing the porous CPCs at 1200 °C, the polyurethane foams were burnt off and the CPCs prepared at room temperature were converted into sintered porous hydroxyapatite (HA)-based calcium phosphate ceramics. The sintered porous calcium phosphate ceramics could then be coated with a layer of the CPC at room temperature, resulting in high porosity, high pore interconnectivity and controlled pore size.     

Blood compatibility of zinc–calcium phosphate conversion coating on Mg–1.33Li–0.6Ca alloy

Magnesium alloys as a new class of biomaterials possess biodegradability and biocompatibility in comparison with currently used metal implants. However, their rapid corrosion rates are necessary to be manipulated by appropriate coatings. In this paper, a new attempt was used to develop a zinc-calcium phosphate (Zn-Ca-P) conversion coating on Mg-1.33Li-0.6Ca alloys to increase the biocompatibility and improve the corrosion resistance. In vitro blood biocompatibility of the alloy with and without the Zn-Ca-P coating was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed from the hemolysis test, the dynamic cruor time test, blood cell count and SEM observation of the platelet adhesion to membrane surface. The results showed that the Zn-Ca-P coating on Mg-1.33Li-0.6Ca alloys had good blood compatibility, which is in accordance with the requirements for medical biomaterials.     

Formation mechanism of calcium phosphate coating on micro-arc oxidized magnesium

A calcium phosphate coating was prepared on the surface of micro-arc oxidized magnesium by a chemical method. The microstructure evolution of the coating was characterized by X-ray diffraction, Fourier-transformed infrared spectroscopy and scanning electron microscopy. The results showed that Ca₁₀(PO₄)₆(OH)₂ (HA) was firstly formed on the surface of micro-arc oxidized magnesium, followed by flake-like CaHPO₄·2H₂O (DCPD). The solution pH and Ca²⁺ concentration had intense influence on the formation of calcium phosphate coating. Acidic Ca²⁺ enrichment solution was favourable for HA formation on the surface of micro-arc oxidized magnesium. High concentration of HPO₄²⁻ and low concentration of Ca²⁺ in acidic solution improved the formation of DCPD coating.     

Hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition

The aim of this study was to investigate the hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition. The Ti-35Nb-xZr ternary alloys contained from 3 wt.% to 10 wt.% Zr content were manufactured by arc melting furnace. Hydroxyapatite (HA) coatings were prepared by electron-beam physical vapor deposition (EB-PVD) method, and crystallization treatment was performed in Ar atmosphere at 300 and 500 °C for 1 h. The coated surface morphology of Ti-35Nb-xZr alloy was examined by FE-SEM, EDX and XRD, respectively. In order to evaluate the corrosion behavior, the tests were performed by potentiodynamic, cyclic polarization and AC impedance test. All the electrochemical data were obtained using a potentiostat. The Ti-35Nb-xZr alloys exhibited equiaxed structure with β phase, the peak of β phase increased with Zr contents. The hardness and elastic modulus of Ti-35Nb-xZr alloys decreased as Zr content increased. The HA coated layer was approximately 150 nm and Ca/P ratio of HA coated surface after heat treatment at 500 °C was around 1.67. The HA thin film consisted of small droplets with spherical shape by crystallization. From the anodic polarization curves, HA coated and heat treated Ti-35Nb-10Zr alloy showed higher corrosion potential than other samples. HA coated film on the Ti-35Nb-10Zr alloy can be shown high polarization resistance by crystallization.     

Study of a hydraulic calcium phosphate cement for dental applications

Calcium phosphate-based cements (CPCs) have attracted much interest because of their good osteoconductivity for bone reconstruction. We obtained CPCs by mixing calcium bis-dihydrogenophosphate monohydrate (MCPM) and calcium oxide with water or sodium phosphate buffers (NaP) as liquid phase. Cement samples with different calcium-to-phosphate ratios (Ca/P), liquid-to-powder ratios (L/P) and liquid phases were analyzed by X-rays diffraction (XRD), pH-metry, extensometry and calorimetry. Antibacterial activity on two bacterial strains (Streptococcus mutans, Lactobacillus acidophilus) and a polycontaminated bacterial inoculum was also studied using the agar diffusion method. The best mechanical properties (25 MPa) corresponded to Ca/P ratios between 1.67 and 2.5, a 1 M sodium phosphate buffer pH 7, as liquid phase and a L/P ratio of 0.6 ml g^-1. The final setting time increased with the Ca/P ratio. The setting expansion, around 1–2%, depended on the Ca/P and L/P ratios. The inner temperature of the cements rose to 45° during setting then decreased rapidly. The injectability was 100% up to 3.5 min and then decreased. It increased with increasing the L/P ratio but to the detriment of the compressive strength and setting time. XRD analysis indicated that the setting reaction led to a mixture of calcium hydroxide and calcium-deficient hydroxyapatite even for a Ca/P ratio of 1.67. Consequently, the pH of the surrounding fluids rose to 11.5–12 during their dissolution. Bacterial growth inhibition was only clearly observed for Ca/P2. This bioactive calcium phosphate cement can potentially be employed for pulp capping and cavity lining as classical calcium hydroxide-based cements, but it is not usable, in the present formulation, for root canal filling because of its short setting time.     

Biomimetic transformations of amorphous calcium phosphate: kinetic and thermodynamic studies

The biomimetic synthesis and phase transformation of XRD amorphous calcium phosphate were studied by application of kinetic, chemical and spectral (XRD and IR) methods and thermodynamic simulations. Two SBFs (SBFc and SBFr), differing in their HCO₃ ⁻ and Cl⁻ ion contents, were used in the maturation studies. It has been proven that the biomimetic maturation accelerated the phase transformation of less thermodynamically stable amorphous calcium phosphate to poorly crystalline hydroxyapatite. Several regularities have been found: (i) kinetic reasons determined the biomimetic precipitation of XRD-amorphous calcium deficient phosphate (ACP); (ii) the precipitated ACP always contained impurities due to co-precipitation, ion substitution and incorporation phenomena; (iii) the increased content of HCO₃ ⁻ ions in the surrounding microenvironments increased the rate of phase transformation and the concentration of MeHCO₃ ⁺ (Me = Ca, Mg) species in the solution, but the solubility of CaCO₃ has only been decreased and its precipitation accelerated, thus playing a crucial role in the process under study.     

Effect of commercial mouthwashes on the corrosion resistance of Ti-10Mo experimental alloy

The purpose of this work was to evaluate the effect of three commercial mouthwashes on the corrosion resistance of Ti-10Mo experimental alloy. Experiments were made at 37.0 ± 0.5^∘ C in a conventional three-compartment double wall glass cell containing commercial mouthwashes. Three mouthwashes with different active ingredients were tested: (I) 0.05% sodium fluoride + 0.03% triclosan; (II) 0.5 g/l cetylpyridinium chloride + 0.05% sodium fluoride; (III) 0.12% chlorohexidine digluconate. The assessment of the individual effect of active ingredients was studied by using 0.05% sodium fluoride. Commercially pure titanium (CP Ti) was used as control. Microstructures from Ti-10Mo experimental alloy and CP Ti were also evaluated using optical microscopy. Ti-10Mo as-cast alloy shows the typical rapidly cooled dendrites microstructure (β phase) while CP Ti has exhibited a metastable martensitic microstructure. Electrochemical behavior of dental materials here studied was more affected by mouthwash type than by Ti alloy composition or microstructure. In both alloys passivation phenomenon was observed. This process may be mainly related to Ti oxides or other Ti species present in spontaneously formed film. Small differences in passive current densities values may be connected with changes in film porosity and thickness. Protective characteristics of this passive film are lower in 0.05% sodium fluoride + 0.03% triclosan mouthwash than in the other two mouthwashes tested.     

Biomimetic self-assembly of calcium phosphate templated by PNIPAAm nanogels for sustained smart drug delivery

Poly(N-isopropylacrylamide) (PNIPAAm)/calcium phosphate (CaP) hybrid nanocomposites with dual-responsive controlled drug delivery property have been prepared by in-situ biomineralization process. Poly(acrylic acid) (PAA) is used as a crystal growth additive to control the morphology of the hybrid nanocomposites. The interaction between PAA and Ca²⁺ contributes to the formation of homogeneous and robust nanocomposites. Vitamin B₂ release behavior is found to be pH- and thermal-responsive. Additionally, the release profiles are sustained with the introduction of CaP, indicating that CaP nanocrystallines could decrease the permeation of the encapsulated drug effectively. The results suggest that the prepared hybrid nanocomposites can be used as “smart” nanoscale materials for sustained dual-responsive drug delivery.     

An electrodeposition method of calcium phosphate coatings on titanium alloy

Calcium phosphates coatings were deposited onto titanium alloy discs via en electrodeposition method. Titanium alloy discs were blasted with calcium phosphate particles, then etched in a mixture of nitric and fluoric acids and rinsed in demineralized water. The titanium alloy disc (cathode) and platinum mesh (anode) were immersed in a supersaturated calcium phosphate electrolyte buffered at pH 7.4 and connected to a current generator. The microstructure, chemical composition and crystallinity of the electrodeposited coatings were studied as function of time 10–120 min, temperature 25–80°C, current density 8–120 mA/cm², magnesium and hydrogen carbonate amounts (0.1–1 mM). Uniform calcium phosphate coatings were obtained in 30 min but coating thickness increased with deposition time. Raising the temperature of electrolyte resulted in more uniform coatings as ionic mobility increased. Low current density was preferable due to hydrogen gas evolving at the cathode, which disturbed the deposition of calcium phosphate crystals on titanium. The amounts of magnesium and hydrogen carbonate ions affected both the homogeneity and morphology of the coatings. This study showed that the electrodeposition method is efficient for coating titanium with osteoconductive calcium phosphate layers.     

Biomimetic apatite coating on magnetite particles

Apatite-coated magnetite particles have been prepared using a novel biomimetic method. This method consisted of immersing magnetite particles in simulated body fluids (SBF, 1.5 SBF) along with disk-shaped sintered wollastonite. Different routes were followed: 7 days of immersion in SBF or 1.5 SBF and 7 or 28 days using a re-immersion method. The magnetic properties were evaluated both before and after the biomimetic process. A bone-like apatite layer was formed on all the samples tested and not a significant change was observed on their original magnetic behavior. These bioactive and superparamagnetic particles may be potential materials for bone cancer treatment.