Layer Of Octacalcium Phosphate Research Articles

Interlayer expansion of octacalcium phosphate via forced oxidation of the intercalated molecules within its interlayers.

Octacalcium phosphate (OCP), a precursor to apatite, has a layered structure that allows various molecules to be intercalated within its interlayers. Previous research on the phase conversion process of OCP to apatite indicated that the layered structures typically collapse due to the shrinking of the OCP layers. In contrast, this study presents a novel phenomenon involving OCP layer expansion during phase conversion. This expansion is based on a forced oxidation process of the intercalated molecules within the hydrous layers of OCP. By introducing NaClO to an OCP interlayer containing dithiodiglycolic acid (DSG), the OCP layers are expanded. This process involves DSG decomposition through its reaction with NaClO. Specifically, the process occurs when a DSG-substituted OCP (containing disulfide bonds (-S-S-)) is immersed in a NaClO solution. This is the first study to report the expansion phenomenon during the phase conversion process from OCP to apatite, providing a new perspective to the conventional understanding that these layers only shrink.

Effect of pH of Coating Solution on Adhesion Strength of Hydroxyapatite and Octacalcium Phosphate Coatings on AZ31 Magnesium Alloy

Hydroxyapatite (HAp) and octacalcium phosphate (OCP) coatings were formed on a Mg-3Al-Zn (AZ31) alloy with a chemical solution deposition method using a Ca-EDTA solution at various pH levels. The adhesion strength of the coatings was examined using the pull-off method. The microstructures of HAp and OCP coatings were measured X-ray diffraction (XRD). The morphology and composition of the surface and cross section of the samples before and after the adhesion test were characterized using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and a 3D profilometer. The results showed that plate-like OCP crystals grew from a continuous OCP layer on the surface of the AZ31 substrate in the case of a pH 6.3 coating solution. At pH values of 7.5 and 8.6, the HAp coating showed a two-layer structure with a HAp rod-like outer layer and a HAp continuous inner layer. Regardless of the pH of the coating solutions, a very thin Mg (OH)2 intermediate layer was formed between OCP or HAp coating and substrate. The highest adhesion strength of the coatings was 6.7±0.5 MPa, achieved at a coating solution pH value of 7.5. A part of Mg (OH)2 layer remained on the substrate, indicating that the delamination occurred in the Mg (OH)2 intermediate layer. The primary particles in the inner layer formed at pH 7.5 was smaller than those at pH 8.6. This result indicates that the initial corrosion of substrate AZ31 at pH 7.5 was more rapidly than that at pH 8.6, presumably leading to the formation of mixed layer of Mg (OH)2 and calcium phosphate. Further investigation is necessary to understand the better adhesion strength at pH 7.5 than that at pH 8.6. This good adhesion could be due to the flawless and rod-like uniform crystal, which had the densest and finest structure on the surface.

Ammonium inhibition of the intercalation of dicarboxylic acid molecules into octacalcium phosphate layer by substitution

Octacalcium phosphate (OCP) is an attractive material for becoming the centerpiece of medical combination products as a layered calcium phosphate because it exhibits excellent biocompatibility and because various molecules can be intercalated between its layers. However, the factors that govern various events, such as molecular substitution into an OCP unit lattice, remain unclear. Herein, we focused on monovalent cations, including NH4+ and Na+, which are commonly used as agents to adjust the pH and ionic strength. This study aims to demonstrate the manner in which NH4+ inhibits the intercalation of thiomalate (SH–malate), which is an antirheumatic drug precursor, into the OCP unit lattice during SH–malate-substituted OCP (OCP–SH–malate) formation. With increasing NH4+ concentration, the amount of SH–malate substituted into the OCP unit lattice decreased without a change in the crystal morphology. This characteristic is undesirable for preparing OCP combination products because NH4+, which is commonly used in the buffer solutions, will strongly inhibit the intercalation of drug molecules into OCP.

Enhanced biocompatibility and improved osteogenesis of coralline hydroxyapatite modified by bone morphogenetic protein 2 incorporated into a biomimetic coating

Objectives(1) To determine whether the biocompatibility of coralline hydroxyapatite (CHA) granules could be improved by using an octacalcium phosphate (OCP) coating layer, and/or functionalized with bone morphogenetic protein 2 (BMP-2), and (2) to investigate if BMP-2 incorporated into this coating is able to enhance its osteoinductive efficiency, in comparison to its surface-adsorbed delivery mode. MethodsCHA granules (0.25 g per sample) bearing a coating-incorporated depot of BMP-2 (20 μg/sample) together with the controls (CHA bearing an adsorbed depot of BMP-2; CHA granules with an OCP coating without BMP-2; pure CHA granules) were implanted subcutaneously in rats (n = 6 animals per group). Five weeks later, the implants were retrieved for histomorphometric analysis to quantify the volume of newly generated bone, bone marrow, fibrous tissue and foreign body giant cells (FBGCs). The osteoinductive efficiency of BMP-2 and the rates of CHA degradation were also determined. ResultsThe group with an OCP coating-incorporated depot of BMP-2 showed the highest volume and quality or bone, and the highest osteoinductive efficacy. OCP coating was able to reduce inflammatory responses (improve biocompatibility), and also simple adsorption of BMP-2 to CHA achieved this. ConclusionsThe biocompatibility of CHA granules (reduction of inflammation) was significantly improved by coating with a layer of OCP. Pure surface adsorption of BMP-2 to CHA also reduced inflammation. Incorporation of BMP-2 into the OCP coatings was associated with the highest volume and quality of bone, and the highest biocompatibility degree of the CHA granules. Clinical significanceHigher osteoinductivity and improved biocompatibility of CHA can be obtained when a layer of BMP-2 functionalized OCP is deposited on the surfaces of CHA granules.

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

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.

The Influence of Biomimetic Deposition Ca-P Coatings on the Release of Simvastatin from TiO2Nanotube Array

In order to improve the capacity of simvastatin and extend the time of the release of the drug, this experiment adopts bionic-deposition to decorate a layer of octacalcium phosphate (OCP) on the face of TiO2 nanotube array,and respectively discusses what are the appropriate parameters of octacalcium phosphate (OCP) can be generated. Experiments show that loading a layer of octacalcium phosphate can extend the time of the release of the drug. In addition, the presence of simvastatin on the TiO2 nanotube array will be a certain influence on the morphology of octacalcium phosphate. However, simvastatin can be dissolved into the bionic fluid by using bionic deposition. Therefore, by step concentration soaking and then using this method to load OCP with simvastatin can effectively improve the amount of simvastatin loaded and extend drug release

Preparation of hydroxyapatite coating on CoCrMo implant using an effective electrochemically-assisted deposition pretreatment

Abstract A hydroxyapatite (HA) coating is efficiently generated on CoCrMo implant alloys by employing an electrochemically-assisted deposition (ECAD) pretreatment followed by chemical immersion in a supersaturated calcification solution. CoCrMo was electrochemically treated in a calcium- and phosphate-containing solution for short time. A thin layer about 200 nm thicknesses, consisting mainly of amorphous calcium phosphate, was formed on the surface of the CoCrMo after the ECAD pretreatment. After the chemical immersion for 2 h, a layer of octacalcium phosphate was formed on the surfaces. A layer of HA was formed after 72 h immersion. The effectiveness of these treatments was demonstrated by comparison with the alkaline treated CoCrMo. Results showed that the ECAD pretreatment highly enhanced the capability of formation of HA on the CoCrMo surface, while only a small amount of CaP islands were formed on CoCrMo through traditional chemical treatment. A tensile test showed that the coating tightly bonded to the substrate. This work has explored an effective ECAD pretreatment to activate CoCrMo implant surface for generating HA coating.

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.

Solid-state P-31 NMR study of octacalcium phosphate incorporated with succinate

Octacalcium phosphate (OCP) is an important model compound in the study of biomineralization. The octacalcium phosphate-succinate (OCPS) compound is prepared and characterized by (31)P solid-state NMR spectroscopy. Taking advantage of the fact that the crystal structures of OCP and OCPS are very similar, an NMR strategy based on the (31)P homonuclear double-quantum spectroscopy is developed to assign all the peaks observed in the (31)P magic-angle spinning spectrum of OCPS. On the basis of our experimental data, the molecular formula of OCPS is determined to be Ca(7.81)(HPO(4))(1.82)(PO(4))(3.61)(succinate)(0.56).zH(2)O, where z<or= 0.5. We find that mainly the phosphorus species at the P5 site will be displaced when succinate ions are incorporated to form the OCPS lattice. The stability of OCPS is significantly higher than OCP with respect to the hydrolysis reaction at high pH conditions. We conclude that the hydration layer of OCP is playing the key role in the structural transformation of OCP.

Electrolytic deposition of octacalcium phosphate/collagen composite coating on titanium alloy

Osteointegration of titanium or its alloy with bone can be greatly improved by calcium phosphate coatings, and further enhanced by an extracellular matrix protein layer such as collagen. In this study, an octacalcium phosphate (OCP)/collagen composite coating layer on Ti6Al4V substrate was prepared using electrolytic deposition method. A layer of OCP mineral consisting of flake-like crystals was first formed on the Ti6Al4V substrate. Subsequently, mineralized collagen fibrils were deposited on the former OCP layer. These collagen fibrils were interconnected and well adhered on the OCP layer so that they were immobilized. The microstructure of the composite coating varied with collagen concentration in the electrolyte. This study could offer a possibility of fabricating a desired surface matrix on orthopedic implants to enhance bone formation and fixation of implants.

In vitro transformation of OCP into carbonated HA under physiological conditions

Octacalcium phosphate (OCP) is a precursor phase during the in vivo mineralization of biological tissues. OCP can easily convert into hydroxyapatite (HA), which is the main inorganic constituent of human bone and teeth. In this study titanium alloys (Ti6Al4V) were coated with a crystalline OCP layer at 37 °C by using a supersaturated calcification solution (SCS). The in vitro bioactivity and mineralization behaviour was investigated by soaking the OCP coatings into simulated body fluid (SBF) for various time periods between 10 and 168 h. Samples were characterized by SEM-EDX, FT-IR- and XRD-analyses. In the early mineralization stages of OCP hydrolysis and partial dissolution of the crystals results in the formation of carbonated hydroxyapatite (CHA). The plate-shaped morphology of the OCP crystals remains unchanged and the thickness of the crystals increases with soaking time. After 100 h in SBF a continuous CHA layer grew upon the OCP coating proving the in vitro bioactivity of thus processed coatings. Thus, OCP coatings might enhance the osteoconductivity of orthopedic titanium based implants.

Effect of Silane-Coupling Treatment on Thermal Decomposition of Octacalcium Phosphate

Octacalcium phosphate (OCP) has a unique layered structure. The layered structure is feasible for novel organic-inorganic hybrids. We treated OCP powder with a silane-coupling agent, vinyltrimethoxysilane (VS), and examined its thermal properties. The VS was not incorporated in the hydrated layer of OCP but reacted only with the surface. The non-treated OCP (Pure-OCP) and treated OCP (OCP-VS) showed the almost same dehydration behavior when they were examined by thermogravimetry and differential thermal analysis. However, the different behavior in 010 diffraction peaks was observed in X-ray diffraction patterns when they were heated at 150°C. The treatment with VS retarded the decomposition of the layered structure of OCP. Some of the VS molecules in OCP-VS might have undergone the condensation reaction among the silanol groups in VS. Due to this VS network on the surface of OCP, the framework of the layer of OCP becomes stable. When Pure-OCP and OCP-VS heated at 150°C were aged under ambient conditions for 1 week, rehydration occurred in both samples. The VS introduced on OCP may provide a novel organic modification of OCP.

Electron Microscopy Analysis of the Central Dark Line Defect of the Human Tooth Enamel

ABSTRACTAfter some experimental results that indicated that HA is able to growth in an epitaxial way on the surface of OCP, it has been suggested that the central dark line (CDL) observed in the nanometric-sized grains of human tooth enamel corresponds to a one-unit-cell-thick layer of octacalcium phosphate (OCP). Based on this consideration, in this work we propose a model for CDL and we carried out the chemistry and structural analysis of the CDL with high resolution microscopy techniques such as Electron Energy Loss Spectroscopy (EELS) and Z-contrast (HAADF) with the aim of find the agreements and/or differences between the human tooth enamel HA and its CDL.

Fluoride analysis of apatite crystals with a central planar OCP inclusion: concerning the role of F- ions on apatite/OCP/apatite structure formation.

To study the roles of F- ions in the formation of apatite crystals embedding octacalcium phosphate (OCP) lamella in the center of apatite (Ap), a range of the Ap/OCP/Ap lamellar-mixed crystals were synthesized under various concentrations of fluoride ion (F-) from 0. 1-1.0 ppm at pH 6.5 and 37 degrees C. The products were analyzed for the F- incorporation, F- distribution, and the amount of OCP and Ap by chemical analysis, X-ray diffraction (XRD), electron probe microanalysis (EPMA), and nuclear magnetic resonance (NMR) techniques. The F- content and the amount of apatite in the crystalline product increased with an increase in the F- concentration in solution, whereas the amount of OCP and the yield of total product decreased. EPMA indicated that F- ions are distributed in the crystals almost homogeneously. The combined analysis suggested that a low-substituted fluoridated hydroxyapatite (FHAp) grew on a small amount of F--containing OCP or on a surface-reaction layer of OCP, which has accumulated a small amount of F-. The roles of F- ions were hypothesized as the reduction of the growth rate and/or the critical thickness in the a*-axis direction of OCP, the enhancement of hydrolysis of OCP, and the activation of the growth of FHAp, resulting in thinner OCP lamella and thicker apatite lamella in the a*-axis direction with an increase in F- concentration.

Zeolitic dehydration-rehydration of adipate-intercalated octacalcium phosphate

Octacalcium phosphate (OCP); Ca8(HPO4)2(PO4)4 · 5H2O) and adipate-intercalated OCP were investigated with respect to their dehydration-rehydration and related properties. The intercalation of adipate ions brought about increases in amount of zeolitic H2O and in limiting the dehydration temperature for retaining the zeolitic character. Infrared spectroscopic and differential scanning calorimetric data also supported the zeolitic character. The basal spacing (d100) of the OCP layer structure intercalated with and without adipate ions was contracted by dehydration and recovered by rehydration, and the variation in thed100 values was increased remarkably by the intercalation. The thermal stability of the layer structure was improved from 200 to 250° C to 400 to 450° C by the intercalation. Above these temperatures hydroxyapatite formed. The intermediately formed apatite could contain CO32− and possibly P2O74−.