Apatite Coatings Research Articles

Rapid Biomimetic Deposition of Drug-Loaded Apatite Coatings

In order to reduce the postoperative inflammation by the slow release of drugs at the beginning of implanting, drug-loaded apatite coatings and chitosan-apatite composite coatings on the NiTi alloy surface were prepared in the Simulated Body Fluid concentrated by five (5×SBF) under constant bubbling of carbon dioxide gas by biomimetic synthesis method. The composition and surface morphology of the coatings were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Additionally, a bacterial inhibition test was conducted for evaluating the drug slow release effects from the drug-loaded coatings. The results indicated that the porous apatite coatings with the flake structure could be deposited using the 5 times Simulated Body Fluid, and the drug-loaded chitosan-apatite composite coatings with better drug slow release effect were obtained. The incorporation of chitosan into the coatings could effectively control the drug release rate and was favorable for achieving better drug slow release effects.

Electrodeposited apatite coating for solid-phase microextraction and sensitive indirect voltammetric determination of fluoride ions

Electrodeposition was used to prepare a new solid phase microextraction (SPME) coatings. Two apatite SPME coatings, dicalcium phosphate dihydrate (DCPD or brushite) and hydroxyapatite (HAP) were validly and homogeneously one-step electrodeposited on glassy carbon electrode (GCE) under different conditions. The coatings were characterized by XRD, FTIR, SEM, CV and EIS. The apatite SPME coatings showed excellent and selective adsorbability to fluoride ions. A novel indirect voltammetric strategy for sensitive detection of fluoride was proposed using K3Fe(CN)6 as indicating probe. The detection principle of fluoride ions was based on the increment of steric hindrance after fluoride adsorption, which resulting in the decrease of the amperometric signal to Fe(CN)63−. The liner ranges were 0.5–20.0μmol/L for n-DCPD/GCE with the limit of detection of 0.14μmol/L and 0.1–50.0μmol/L for n-HAP/GCE with the limit of detection of 0.069μmol/L, respectively. The developed method was applied to the analysis of water samples (lake, spring and tap water) and the recovery values were found to be in the range of 90–106%.

Biomimetic deposition of apatite coatings on biomedical NiTi alloy coated with amorphous titanium oxide by microarc oxidation

The biomedical NiTi alloy was treated by microarc oxidation (MAO) in H3PO4 electrolyte using DC power supply. The amorphous titanium oxide coating with porous and rough structure was formed on NiTi alloy. The MAO treated NiTi was soaked in a simulated body fluid (1·0SBF) to investigate the biomimetic deposition of apatite on the surface of titanium oxide coated NiTi alloy. It was found that titanium oxide coated NiTi alloy shows an excellent apatite forming ability after soaking in a simulated body fluid (1·0SBF) for 28 days, while no apatite forming ability was observed on bared NiTi alloy, even though soaking time is up to 28 days. The Fourier transformed infrared and X-ray photoelectron spectroscopy results showed that apatite deposited on MAO treated NiTi is a kind of incorporated and Ca deficient apatite.

Enhanced bonding of biomimetic apatite coatings on surface-modified titanium substrates by hydrothermal pretreatment

The biomimetic coating method was employed by soaking the titanium substrates in a 1.5X simulated body fluid (1.5XSBF). Calcium was implanted on the cleaned titanium surfaces under four different hydrothermal conditions before exposure to SBF. For this purpose, the substrates were immersed in aqueous solutions of CaO at 0.02 or 0.2mol/L concentrations for 1 or 8h in the temperature-controlled hydrothermal chamber kept at 230°C. The effects of hydrothermal solution concentration and immersion time on the substrate surfaces were assessed in terms of coating integrity. All the modified substrates were able to develop B-type hydroxy-carbonate apatite coatings. It was found that the titanium substrates pretreated for 8h developed on their surfaces well-adhering and scattered Ca(OH)2 crystals that contributed to roughness. The apatite coatings on such substrates exhibited higher bond strength compared to the coatings on the relatively “smoother” substrates (i.e., pretreated for 1h). The mean values for tensile and shear strengths increased up to 22.4±3.2 and 9.7±2.7MPa, respectively, for the mechanical test specimens prepared by soaking the substrates, which were pretreated for 8h in the 0.2mol/L CaO solution, in the SBF for 2weeks.

How bone marrow-derived human mesenchymal stem cells respond to poorly crystalline apatite coated orthopedic and dental titanium implants

Due to the delayed and weak bone-implant integration in dental and orthopedic devices, there have been several attempts to enhance implant–bone interactions for rapid osseointegration. In this paper, the interactions of human bone marrow-derived stromal (mesenchymal) stem cells (hMSCs) with uncoated and coated titanium alloy implants with poorly crystalline apatite are studied. First the configuration and chemical composition of the apatite coatings and their deposition progress in different experimental conditions are investigated and discussed. Then, hMSCs are cultured on different substrates and cell attachment and proliferation are monitored and evaluated for different time intervals. Although the uncoated and coated substrates indicate good cell attachment, the differences in proliferation and morphology of the cells spread over the coated samples are significant. It is concluded that the coated samples improve the capability for accepting the cells in three-dimensional and slender shapes. The migration of hMSCs on both substrates are discussed. As such cell migration is directly associated to the osteoconduction, the findings confirm the hypothesis of enhancement in bone formation on the surface of biomimetically poorly crystalline apatite coated titanium implants. This in vitro study demonstrates that the coated samples are nontoxic and biocompatible enough for ongoing osteogenic studies in bone or dental defects in animal models in vivo.

The design and features of apatite-coated chitosan microspheres as injectable scaffold for bone tissue engineering

In this paper we developed two types of chitosan-based microspheres with and without biomimetic apatite coatings and compared their potential as injectable scaffolds for bone regeneration. The microspheres were obtained by emulsion cross-linking (E0) and coacervate precipitation (C0), respectively. They were then biomimetically coated with apatite to become E1 and C1 microspheres. The physicochemical properties and biocompatibility of the microspheres were characterized. Both E0 and C0 microspheres presented favorable ranges of diameter, density and Rockwell hardness. However, there were differences in the degree of cross-linking, shape, morphology, degradation rate, swelling rate, pH value after PBS immersion and the biocompatibility between E0 and C0. The apatite coating was successfully prepared for both C0 and E0, which enhanced the attachment, proliferation and differentiation of MC3T3-E1 cells. In conclusion, our results suggest the feasibility of using chitosan microspheres as a potential injectable scaffold. Both the preparation method and the biomimetic apatite coating contribute to their biological properties.

Incorporation of active ions into calcium phosphate coatings, their release behavior and mechanism

The dissolution and release of active ions from ion-doped apatites is currently gaining interest due to indications of a beneficial biologic response. The release of ions from apatite coatings is important because it influences the biological effect of these types of materials. In this study the ion release from three different ion-doped apatite coatings (iHA coatings), SrCaP, SiHA and FHA, has been studied. The coatings were prepared by a mineralization method based on immersion in modified PBS solutions containing additions of Sr, Si or F. The kinetics of ion release from the iHA coatings were studied in two different media with and without calcium and phosphate ions (phosphate buffer saline solution (PBS) and Tris–HCl). The amount of cumulative release of Sr, Si and F ions from the iHA coatings was SrCaP>SiHA>FHA in Tris–HCl, which could be also be related to the solubility for these iHA coatings. According to analysis using the Korsmeyer–Peppas model, the release of ions from the coatings was in most cases controlled by a combination of Fickian diffusion and dissolution of the coatings. The morphologies of the iHA coatings were not markedly changed after immersion in Tris–HCl. In the phosphate buffer solution, there was a concurrent redeposition of new apatite crystals on the surface of all of the iHA coatings, which means there were both a dissolution and a remineralization process acting, ultimately controlling the ion release rate.

Beta-tricalcium phosphate particles as a controlled release carrier of osteogenic proteins for bone tissue engineering

Beta-tricalcium phosphate (β-TCP) has been widely used as bone substitutes and delivery carriers of osteogenic proteins. However, low protein carrying capacity and agent burst release profiles of β-TCP limit their usage. This study investigates strategies to enhance protein carrying capacity of β-TCP particles with reduced initial burst by surface etching in citric acid solution or by creating apatite coatings with the simulate body fluid immersion approach. The release kinetics of protein from the modified β-TCP particles was investigated using Nel-like molecule-1 (Nell-1), a novel osteogenic protein, as a model protein. Although chemical etching treatments reduced the initial burst release of protein from the particles, a rapid burst release was observed with high protein dose. In contrast, the burst release of protein was significantly reduced by the apatite coating and a high protein dose was successfully delivered over a prolonged period from the apatite-coated particles. Protein release was further modulated by simultaneously delivering proteins from two different substrates: acid-etched and apatite-coated particles. The bioactivity of the protein was preserved during the loading procedure onto the particles. In addition, protein-loaded particles maintained biological activity in the lyophilized state over 4 weeks. These findings suggest that the protein carrying capacity of β-TCP can be modulated by surface modification, which has a potential for use as a protein carrier with controlled release.

Control of Surface Topography in Biomimetic Calcium Phosphate Coatings

The behavior of cells responsible for bone formation, osseointegration, and bone bonding in vivo are governed by both the surface chemistry and topography of scaffold matrices. Bone-like apatite coatings represent a promising method to improve the osteoconductivity and bonding of synthetic scaffold materials to mineralized tissues for regenerative procedures in orthopedics and dentistry. Polycaprolactone (PCL) films were coated with calcium phosphates (CaP) by incubation in simulated body fluid (SBF). We investigated the effect of SBF ion concentration and soaking time on the surface properties of the resulting apatite coatings. CaP coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and energy dispersive X-ray spectrometry (EDX). Young's modulus (E(s)) was determined by nanoindentation, and surface roughness was assessed by atomic force microscopy (AFM) and mechanical stylus profilometry. CaP such as carbonate-substituted apatite were deposited onto PCL films. SEM and AFM images of the apatite coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF solutions. Young's moduli (E(s)) of various CaP coatings were not significantly different, regardless of the CaP phase or surface roughness. Thus, SBF with high ion concentrations may be used to coat synthetic polymers with CaP layers of different surface topography and roughness to improve the osteoconductivity and bone-bonding ability of the scaffold.

Effect of Biomimetic Nanocrystalline Apatite Surface on Bone Ingrowth

The Success of Hydroxyapatite-Coated Acetabular Components Has Not Been Consistent. Plasma-Sprayed Hydroxyapatite Coatings Work Well on Nonporous Substrates but Do Not Coat the Inner Surfaces of Open-Porous Substrates. Solution Deposition Can Generate Consistent Bioceramic Coats on Porous Surfaces that More Closely Mimic the Trabecular Pattern and Biochemistry at the Bone Interface. we Compared Bone Response to the Following Implants: Porous-Coated Ti6al4v Cylinders with 1 of 3 Treatments: Plasma Sprayed with Hydroxyapatite (HA), Coated with a Solution-Deposited Biomimetic Apatite Coating (BA), and Untreated (Control). Bilateral Femurs in 36 Rabbits Were Implanted with One of the above Implants. Bone Ingrowth for HA and BA Surfaces Was Significantly Higher than that for Control Surfaces. No Fragmentation or Debris Production Was Evident in the Apatite Coat of the BA Group. A Biomimetic Coat of Solution-Deposited Apatite May Be Resistant to Coating Delamination and Particle Generation.

Rapid mineralization of porous gelatin scaffolds by electrodeposition for bone tissue engineering

In bone tissue engineering, rapid mineralization of polymeric scaffolds is of particular importance in protecting the encapsulated therapeutic drugs or growth factors from loss and degradation. Here, we present a simple and rapid approach to the fabrication of mineralized porous scaffolds for bone tissue engineering. In this approach, three-dimensional (3-D) porous gelatin scaffolds were firstly fabricated by freeze-drying followed by an electrodeposition process for mineralization. We show that a high-quality apatite coating on the gelatin scaffold could be achieved within a couple of hours by electrodeposition. Increasing the deposition voltage or electrolyte temperature favored to the formation of large amounts of apatite coatings with compositions dominated by the hydroxyapatite crystals, whereas the presence of ultrasonic field facilitated the production of homogeneous apatite coatings. Moreover, biological assays indicated that the mineralized scaffolds exhibited better support for the proliferation and osteoblastic differentiation of MC3T3-E1 cells over a neat gelatin scaffold, especially for the case of mineralized scaffolds by electrodeposition at 60 °C. Therefore, the method developed would be highly desired for the rapid mineralization of polymer scaffolds in which biological molecules were loaded for functional bone tissue engineering applications.

Strontium and Silicon Co-Doped Apatite Coating: Preparation and Function as Vehicles for Ion Delivery

New methods to improve the bone response to metallic implants are still emerging, ranging from surface modifications of the metal to coatings and drug delivery. One further development of coatings on implants is to incorporate bioactive ions in order to stimulate the bone response without the need of drug delivery. The aim of the current study is to prepare apatite coatings containing Sr and Si using a solution method, for the purpose of further optimising the bone response to metal implants. Titanium substrates were activated to induce the formation of coatings in modified PBS solutions. Soaking in PBS solutions with different concentrations of strontium and silicate at 37℃ or 60℃ produced coatings with different morphologies, thicknesses and compositions. Ion release experiments showed simultaneous release of Sr and Si from the coatings both in PBS and Tris-HCl. Analysis of the results using the Korsmeyer-Peppas model indicate that the release of ions from the coatings was a combination of Fickian diffusion and degradation of the coatings. This study shows that it is possible to coat Ti substrates with modified apatite with ion release functionality and thereby increase the possibilities for a tailored bone response in vivo.

Evaluation of Bone Regeneration of Apatite Coating Poly-L-lactide Scaffold in Rat Calvarial Defects

Evaluation of Bone Regeneration of Apatite Coating Poly-L-lactide Scaffold in Rat Calvarial Defects

The effect of vitamins to hydroxyapatite growth on porous polyurethane substrate

This work presents a study on the possibility of obtaining hydroxyapatite thin layers on porous polyurethane support using a modified coating method, which is based on a biomimetic technique. To investigate bone-like apatite coatings formation on polyurethane surface, two types of solutions such as supersaturated calcification solution (SCS) and modified SCS (M-SCS) were used. The modified supersaturated calcification solution was prepared with added at original SCS appropriate quantities of vitamin A and vitamin D2. The hydroxyapatite deposits are investigated by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) and ATR-IR spectroscopy. The presence of vitamins (A and D2) in M-SCS solution favours the formation of hydroxyapatite layer on polymeric substrate. The results obtained from SEM images have showed that porous polyurethane/hydroxyapatite scaffolds with estimated porosity of over 60% in an interconnected network, were produced under vitamins influence.

Electrostatic Spray Deposition of Biomimetic Nanocrystalline Apatite Coatings onto Titanium

AbstractTitanium (Ti) and its alloys are widely used to manufacture orthopedic and dental implants due to their excellent mechanical properties and corrosion resistance. Although these materials are bioinert, improvement of biological properties (e.g., bone implant contact) can be obtained by the application of a coating made of nanostructured apatite. The aim of this study was to investigate the applicability of the electrostatic spray deposition (ESD) technique for the deposition of nanostructured apatite coatings onto commercially pure (cp) Ti substrates at room temperature. To that end, poorly crystalline, nano‐sized, carbonate‐apatite plate‐like particles with dimensions similar to the nanocrystals present in bone were synthesized using wet‐chemical precipitation techniques and their physicochemical properties were subsequently characterized thoroughly. The apatite suspensions were optimized for the ESD process in terms of dispersion, aggregation, and stability. Furthermore, relevant ESD processing parameters, including nozzle‐to‐substrate distance, relative humidity in the deposition chamber and deposition time were varied in order to study their effects on coating morphology. Porous films made of agglomerates of nano‐sized apatite particles of ≈50 nm were generated, demonstrating the feasibility of the ESD technique for the deposition of thin apatite coatings with a nano‐sized surface morphology onto titanium substrates. The ability of these nanocrystals to bind therapeutic agents for bone diseases and the capability of ESD to produce coating at physiological conditions makes this work a first step toward the set‐up of coatings for bone implants based on surface‐activated apatite with improved functionality.

Preparation and Characterization of Bone-Like Apatite Coating on Ti6Al4V Spinal Fusion Devices

Sand-blasting treatment and chemically biomimetic growth are important methods improving the interface adhesion strength and formation of osteoconductive coatings for implants. In the present study, these methods were employed to generate bone-like apatite coating on Ti6Al4V spinal fusion devices. The surface morphology, elements and microstructure were analyzed using SEM, AFM, EDS, XRD and TEM. The results showed that bone-like apatite layer formed after sand blasting treatment and chemically biomimetic growth. Also the dimensional accuracy of device after the treatment could meet the implantation requirement of the device. The coating adhesion test suggests that rough surface after sand-blasting can improve the coating adhesion strength. The study will facilitate further the engineering application of chemically biomimetic growth in surface modification of Ti6Al4V implants and the medical application of spinal fusion device.

Magnesium Incorporation in Sol-Gel Derived Apatite Coating on Ti6Al4V Substrate

A series of the magnesium apatite coatings according to (Ca10-xMgx)(PO4)6(OH)2, where x = 0 to 2, was synthesized through a sol-gel dip-coating method. The roughness of the magnesium coatings increased as more magnesium incorporated into the coatings. The mechanical properties of the coatings were analyzed with Nanoindentor. The incorporation of magnesium decreased the hardness and the Young’s modulus of the coating. The X-ray Photoelectron Spectroscopy (XPS) analysis revealed that only part of magnesium was incorporated into the apatite structure while the rest existed in the form of MgO in the coating.

Photoluminescence in the characterization and early detection of biomimetic bone-like apatite formation on the surface of alkaline-treated titanium implant: State of the art

Photoluminescence (PL) property is particularly important in the characterization of materials that contain significant proportions of noncrystalline components, multiple phases, or low concentrations of mineral phases. In this research, the ability of biomimetic bone-like apatite deposition on the surface of titanium alloy (Ti6Al4V) substrates in simulated body fluid (SBF) right after alkaline-treatment and subsequent heat-treatment was studied by the inherent luminescence properties of apatite. For this purpose, the metallic substrates were treated in 5 M NaOH solution at 60 °C. Subsequently, the substrates were heat-treated at 600 °C for 1 h for consolidation of the sodium titanate hydrogel layer. Then, they were soaked in SBF for different periods of time. Finally, the possibility to use of PL monitoring as an effective method and early detection tool is discussed. According to the obtained results, it was concluded that the PL emission peak did not have any significant shift to the shorter or higher wavelengths, and the PL intensity increased as the exposure time increased. This research proved that the observed inherent PL of the newly formed apatite coatings might be of specific interest for histological probing and bone remodelling monitoring.

Apatite Coatings Deposited by DC Magnetron Sputtering

In this study, La-Si metallic coatings were synthesized by Direct Current Magnetron Sputtering of lanthanum and silicon targets in pure argon atmosphere. After the deposition stage, the ceramic apatite-structure coatings were obtained by thermal oxidation in air. The structural and chemical features of these films have been assessed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The electrical properties were determined by complex impedance spectroscopy in planar configuration. The films with a La/Si atomic ratio close to the apatite composition La9.33(SiO4)6O2 deposited on different substrates were initially amorphous. After thermal oxidation at 1173 K in air, the coating crystallised under the expected apatite structure. SEM observation revealed that the film compactness and thickness increased after thermal oxidation. The electrical measurements carried out under air as a function of temperature (1200 to 800 K) show only one contribution for the apatite layer on the Nyquist diagram. The electrical properties were controlled by the Arrhenius law with an activation energy (Ea = 0.7 eV) slightly lower than that of the literature data. The ionic conductivity is around 10-2 S.cm-1 at 1175K.

Effect of Electrochemical Parameters on the Morphology and Ca/P Ratios of Deposited Apatite Coatings on Metal and Alloy Substrates

Calcium phosphates were electrochemically deposited on stainless steel, titanium, and copper metal substrates with modified simulated body fluid of pH adjusted from 4 to 10 at 25 - 65 °C while maintaining cathodic potentials at -1.2 to -1.8 V (vs. SCE). The coatings were characterized by powder x-ray diffraction, scanning electron microscopy, and linear polarization corrosion method. X-ray diffraction show depositions in electrolytic solutions of pH below 8 contain hydroxyapatite along with a significant amount of impurities; however at pH 10 the deposit primarily consists of hydroxyapatite with little impurity, ideal for orthopedic implants. As the pH increases the morphology changes as shown with scanning electron microscopy, from an amorphous to a dense crystalline phase. Linear polarization and Tafel plot show surgical stainless steel has the most improvement in anticorrosion when coated with hydroxyapatite.