Hydroxyapatite Films Research Articles

Effect of pulsed electron beam treatment on the physico-mechanical properties of hydroxyapatite-coated titanium

The effect of the pulsed electron beam (PEB) treatment on the structure and morphology of the hydroxyapatite (HA) coating deposited on the surfaces of titanium substrates by radio frequency magnetron sputtering was elucidated. The structure, composition and morphology of the samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results collected from SEM experiments demonstrated that the HA film was smooth and featureless. The samples were irradiated by PEB using an electron beam energy density of 0.1Jcm−2, electron beam pulse duration of 50μs, pulse repetition frequency of 5Hz, and number of pulses N=50 and N=150. After PEB treatment with N=50, the coating exhibited a much finer uniform surface morphology, playing a crucial role in the enhancement of the mechanical properties of the HA-coated titanium substrate. The surface of the HA film treated with N=150 was still smooth and featureless. The XRD data demonstrated that PEB treatment of HA films produced only a slight decrease in the HA phase content. The combination of these two techniques opens the possibility of preparing high quality HA layers.

Nanoscale analysis of calcium phosphate films obtained by RF magnetron sputtering during the initial stages of deposition

In the present work, we investigated the nanostructure of calcium phosphate films formed during the initial stages of deposition (between 30 and 240s; deposition rate of 3.7nm/min) by radio-frequency magnetron sputtering. The sputtering deposition parameters and the plasma energy were previously adjusted to produce nearly stoichiometric nanocrystalline hydroxyapatite films after 180min. Grazing-incidence X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the films formed in the initial stages were composed of an amorphous calcium phosphate phase with a Ca/P ratio Ca/P=1.60±0.12, which is close to that of hydroxyapatite. Using high-resolution transmission electron microscopy, we demonstrated that the films were not a unique amorphous phase. An additional phase composed of dense calcium phosphate nanospheres was found in all periods and investigated. The nanospheres grew in size as the deposition time increased, and small nanospheres were always observed. This observation suggests the continuous formation of nanospheres at the surface of the film. Nanocrystalline regions were revealed by electron diffraction and high-resolution electron microscopy after a deposition of 60s with a corresponding film thickness of 3.7nm. Electron energy-loss spectroscopy analysis comparing individual nanospheres to the amorphous calcium phosphate layer showed differences in the oxygen K edge, suggesting a difference in the chemical bonding of the oxygen species. Nanospheres were observed in association with isolated crystals, suggesting that the nanospheres may participate in the crystallization of hydroxyapatite according to a heterogeneous nucleation process.

Preparation and Characterisation of Hydroxyapatite Coatings on Nanotubular TiO2 Surface Obtained by Sol-Gel Process.

Hydroxyapatite (HA) coating on titanium dioxide (TiO2) nanotubular surface has been developed to complement the defects of both TiO2 and HA. A sol-gel processing technique was used to coat HA on TiO2 nanotubular surface. All the titanium discs were blasted with resorbable blast media (RBM). RBM-blasted Ti surface, anodized Ti surface, and sol-gel HA coating on the anodized Ti surface were prepared. The characteristics of samples were observed using scanning electron microscopy and X-ray photoemission spectroscopy. Biologic responses were evaluated with human osteosarcoma MG63 cells in vitro. The top of the TiO2 nanotubes was not completely covered by HA particles when the coating time was less than 60 sec. It was demonstrated the sol-gel derived HA film was well-crystallized and this enhanced biologic responses in early stage cell response.

Synthesis of piroxicam loaded novel electrospun biodegradable nanocomposite scaffolds for periodontal regeneration.

Development of biodegradable composites having the ability to suppress or eliminate the pathogenic micro-biota or modulate the inflammatory response has attracted great interest in order to limit/repair periodontal tissue destruction. The present report includes the development of non-steroidal anti-inflammatory drug encapsulated novel biodegradable chitosan (CS)/poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) electro-spun (e-spun) composite nanofibrous mats and films and study of the effect of heat treatment on fibers and films morphology. It also describes comparative in-vitro drug release profiles from heat treated and control (non-heat treated) nanofibrous mats and films containing varying concentrations of piroxicam (PX). Electrospinning was used to obtain drug loaded ultrafine fibrous mats. The physical/chemical interactions were evaluated by Fourier Transform Infrared (FT-IR) spectroscopy. The morphology, structure and pore size of the materials were investigated by scanning electron microscopy (SEM). The thermal behavior of the materials was investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Control (not heat treated) and heat treated e-spun fibers mats and films were tested for in vitro drug release studies at physiological pH7.4 and initially, as per requirement burst release patterns were observed from both fibers and films and later sustained release profiles were noted. In vitro cytocompatibility was performed using VERO cell line of epithelial cells and all the synthesized materials were found to be non-cytotoxic. The current observations suggested that these materials are potential candidates for periodontal regeneration.

Electrochemical growth of composite hydroxyapatite coatings for controlled release

An electrochemical method was used to load ionic molecules into hydroxyapatite (HA) coatings during electrochemical synthesis. A metal cathode surface was first electrochemically coated with a thin layer of HA. Then, a second electrochemical coating step was conducted with non-reactive ionic molecules added to the synthesis solution. The loading and release from the HA films are driven in large part by the sign and valence of charge on the ionic additive. Cationic additives are attracted to the cathode surface and effectively loaded to form composite HA films, while anionic species are repelled from the cathode and not effectively incorporated. Divalent cations are released more slowly than monovalent cations. This simple method may be used to create drug eluting bioactive coatings for controlled release. The loading and release of streptomycin, a common antibiotic, was measured as a representative pharmaceutical example.

Hydrophobic coatings for prevention of dental enamel erosion

The protective effect of a hydrophobic surface against acid erosion was validated in the present work using octadecyltrichlorosilane (OTS) on hydroxyapatite films (HA) and on dental samples. The acid erosion was firstly evaluated on films made of HA and fluorapatite (HAF), and subsequently on films of HA coated by OTS. Our results have shown that the two first films were completely eroded during this evaluation and that no significant erosion was observed for the last film. Indeed, teeth coated with OTS showed no erosion at all after seven days of exposure to citric acid. The evaluation was based on QCM-D measurements, SEM images and water contact angle characterization. The results validate that a hydrophobic surface may be an effective tooth protector against acid erosion.

Effect of silicate doping on the structure and mechanical properties of thin nanostructured RF magnetron sputter-deposited hydroxyapatite films

Silicon-doped hydroxyapatite-based (Si-HA) coatings were deposited via radio frequency (RF) magnetron sputtering on the surface of titanium that was treated with a pulsed electron beam. This study aimed to evaluate the effect of Si doping on the structure and mechanical properties of thin HA films. The content of the silicon was 1.2 and 4.6at.% for the coatings prepared using the Si-HA precursor powders with a chemical formula Ca10(PO4)6−x(SiO4)x(OH)2−x where, x=0.5 and 1.72. Pure HA (Ca10(PO4)6(OH)2) coatings were deposited for comparison. The as-deposited films were analysed with respect to their composition, state of chemical binding and microstructure using XPS, FTIR, XRD, and SEM. We hypothesized that the addition of Si would affect the mechanical features of the coatings due to microstructure changes. The effect of the introduction of Si on the nanohardness and the Young's modulus as well as the adhesion strength and scratch resistance of the HA coating was investigated using nanohardness testing and a scratch test, respectively. Examination of the coating microstructure using SEM and AFM revealed that Si doping influenced the surface morphology and led to a smaller grain size. The tendency to form an amorphous structure also increased with an increase in the Si content. A monotonous decrease in both the nanohardness and the elastic modulus was observed with an increase in the Si content. A maximum nanohardness of ~7GPa was obtained for the Si-free HA coating, whereas the hardness decreased to ~4.3GPa for the films with a Si content of 1.2at.%. The addition of 4.6at.% Si to the HA coating resulted in a reduction in the elastic modulus, whereas the nanohardness was very similar to that of the uncoated substrate. The adhesion behaviour of the coatings demonstrated different responses. In the case of pure HA coatings, failure occurred due to the low cohesion of the coating, whereas the crystalline Si-HA coatings with a Si content of 1.2at.% deformed plastically without crack formation and without detaching from the titanium substrate, which resulted in a greater coating stability.

Vesicular delivery of crystalline calcium minerals to ECM in biomineralized nanoclay composites

The mechanisms of mineralization and new bone formation were explored in newly formed extracellular matrix in a nanoclay based composite. Nanoclay films were prepared by intercalating the clays with amino acids and using the amino acids for mineralization of hydroxyapatite. The biomineralized hydroxyapatite (HAP) inside nanoclay galleries or in situ HAP/clay was further used to make films (substrates) using polycaprolactone (PCL) that were seeded with mesenchymal stem cells in a two-stage seeding process. SEM imaging experiments performed on PCL/in situ HAPclay composite films seeded with human MSCs indicated formation of matrix vesicles. The vesicles appear to emerge from the cells that are adhered to the nanoclay HAP films and also deposited in the extracellular space. Vesicles are also observed to be embedded in the cells or under the surface of cells. Crystalline structures with Ca and P were found inside vesicles. The Ca/P ratios obtained using energy dispersive spectroscopy indicate values ranging from below 0.7 to the stoichiometric HAP value of 1.67. The Ca/P ratios were obtained to be closer to the stoichiometric value for single seeding experiments as compared to the double seeding experiments indicating more new bone formation in double seeding experiments. New bone formation with bone mimetic mineralization is thus observed on the in situ HAP nanoclay PCL samples. Hence the PCL/in situ HAPclay composites besides being osteoinductive are also capable of providing a favorable micro-environment for cell dependent processes involved in bone mineral formation.

Ultrathin film coating of hydroxyapatite (HA) on a magnesium–calcium alloy using RF magnetron sputtering for bioimplant applications

A thin film of hydroxyapatite (HA) was coated on a magnesium–calcium (Mg–Ca) alloy using radio frequency (RF) magnetron sputtering. The thickness of the HA coating was in the range of 550–750nm. In vitro degradation behaviour of the HA coated alloy was evaluated in simulated body fluid (SBF) using electrochemical methods. The ultrathin film coating has significantly improved the degradation resistant of the alloy. The polarisation resistance (Rp) of the coated alloy was more than two-order of magnitude higher and the corrosion current density (icorr) reduced by ~98% as compared to the base alloy.

Effect of SiC interlayer between Ti6Al4V alloy and hydroxyapatite films.

Bioactive coatings are frequently used to improve the osseointegration of the metallic implants used in dentistry or orthopaedics. Among different types of bioactive coatings, hydroxyapatite (Ca10(PO4)6(OH)2) is one of the most extensively used due to its chemical similarities to the components of bones and teeth. In this article, production and characterization of hydroxyapatite films deposited on Ti6Al4V alloy prepared by magnetron sputtering were reported. Besides, SiC was deposited on substrate surface to study the interlayer effect. Obtained coatings were annealed at 600 °C for 30 and 120 min in a mixed atmosphere of N2 + H2O vapours with the heating rate of 12 °C min(-1). The effects of SiC interlayer and heat treatment parameters on the structural, mechanical and corrosion properties were investigated. After heat treatment process, the crystalline hydroxyapatite was obtained. Additionally, cell viability tests were performed. The results show that the presence of the SiC interlayer contributes a decrease in surface roughness and improves the mechanical properties and corrosion performance of the hydroxyapatite coatings. Biological properties were not affected by the presence of the SiC interlayer.

Low-temperature crystallization and high-temperature instability of hydroxyapatite thin films deposited on Ru, Ti, and Pt metal substrates

We investigated the crystallinity, orientation, and stability of hydroxyapatite (HAp) thin films on structural materials including SiO2 and metals (Ru, Ti, and Pt). The HAp films were deposited by electron cyclotron resonance (ECR) plasma sputtering with an Xe sputtering gas under simultaneous flow of H2O vapor. The HAp films as-crystallized during deposition and solid-phase crystallized by post annealing were analyzed with X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman scattering. The lowest solid-phase crystallization temperatures were 350°C on Ru, 300°C on Ti, and 300°C on Pt. These crystallization temperatures are much lower than those on silicon and SiO2 substrates (550°C). For HAp films as-crystallized at temperatures above 400°C, the elements out diffused and reacted with substrates. Precipitation of CaO was observed for HAp films deposited on SiO2 and Ru substrates. Diffusion of PO43− into SiO2 and Ru-catalyzed decomposition of HAp crystals are suggested for the mechanism. When deposited on Pt substrates, CaPt2O4 alloy byproducts were created for solid-phase crystallized films and CaPt2 alloy byproducts were created for as-crystallized films, indicating reaction of Ca atoms with Pt substrates.

Hydroxyapatite Thin Films with Giant Electrical Polarization

It is demonstrated that hydroxyapatite, a type of calcium phosphate commonly found in bone tissue, retains surprisingly large stored charge when synthesized electrochemically from aqueous solution. Thin films of hydroxyapatite formed on titanium and stainless steel electrodes were found to display giant polarization with quasi-permanent stored charge in excess of 70 000 microcoulombs per square centimeter. The polarization of the hydroxyapatite film develops during synthesis as a result of field-induced changes in concentration of ionic reactants in the electrical double layer near the electrode surface. This novel mechanism of polarization during synthesis provides much larger stored charge than what is possible by postsynthesis poling of ferroelectric or electret materials. The polarized hydroxyapatite films on titanium are shown through in vitro experiments to hold promise in stimulating bone growth and may enable new applications in ion exchange separations, drug delivery, or energy storage.

Morphological Study of HAP Coated Alumina by Sol-Gel Method for Orthopedic Implants

Hydroxyapatite (HAP) Ca10(PO)6(OH)2is widely used as a bioactive ceramics since it forms a chemical bonding to bone. The dominant requirement for the development of HAP coatings on metallic implants is the preparation of stoichiometric material with required chemical and phase composition (Ca/P molar ratio 1.67). In this work the preparation of HAP films by sol-gel method on alumina and its characterization are described. The coating was done using dip-coating method, starting from a colloidal suspension of hydroxyapatite. Compound formation of HAP is confirmed using GIXRD. By Energy Dispersive X-Ray spectroscopy (EDX) analysis Ca/P ratio of the HAP was found to be 1.657 which is very close to the stoichiometric value of 1.67. The FTIR spectra of the coatings were used to determine the presence of chemical species of the coatings. Surface Characterization has been carried out using SEM & AFM techniques. Wettability study has been carried out using OCA and it was found that hydrophobicity decreases with the increase in HAP thickness. Corrosion studies have been carried out using electrochemical analyzer (ECA) in Ringer solution and best corrosion resistance was observed for the thickest sample. The paper discusses the variations in surface morphology using SEM, AFM & EDX and its effect on biocompatibility.

Electrical properties of hydroxyapatite

Abstract Despite being one of the mostly studied biomaterials for orthopedic, dental, protein purification and stem cell applications, electrical properties of hydroxyapatite has received only limited attention. Since the prediction in 2005 of the possibility of piezo and pyroelectricity in hydroxyapatite several theoretical and experimental works in this field may lead to new understandings of electrical behaviors of calcified tissues in vertebrates. Also, the ability of creating discrete electrostatic domains on nanocrystalline films of hydroxyapatite will open the possibility of understanding how surface charge influences biological interactions. The outlook for future endeavours in this field will be discussed.

Osteogenic Responses to Zirconia with Hydroxyapatite Coating by Aerosol Deposition

Previously, we found that osteogenic responses to zirconia co-doped with niobium oxide (Nb2O5) or tantalum oxide (Ta2O5) are comparable with responses to titanium, which is widely used as a dental implant material. The present study aimed to evaluate the in vitro osteogenic potential of hydroxyapatite (HA)-coated zirconia by an aerosol deposition method for improved osseointegration. Surface analysis by scanning electron microscopy and x-ray diffraction proved that a thin as-deposited HA film on zirconia showed a shallow, regular, crater-like surface. Deposition of dense and uniform HA films was measured by SEM, and the contact angle test demonstrated improved wettability of the HA-coated surface. Confocal laser scanning microscopy indicated that MC3T3-E1 pre-osteoblast attachment did not differ notably between the titanium and zirconia surfaces; however, cells on the HA-coated zirconia exhibited a lower proliferation than those on the uncoated zirconia late in the culture. Nevertheless, ALP, alizarin red S staining, and bone marker gene expression analysis indicated good osteogenic responses on HA-coated zirconia. Our results suggest that HA-coating by aerosol deposition improves the quality of surface modification and is favorable to osteogenesis.

Crystalline nano-coatings of fluorine-substituted hydroxyapatite produced by magnetron sputtering with high plasma confinement

A radio-frequency magnetron sputtering technique operating in right-angle geometry (RAMS) with high plasma confinement was revised to produce thin films (15–570nm) of fluorine-substituted hydroxyapatite, FHA, adapted to be used as nano-coatings for biomedical implants. An electron temperature of Teff≈9.0eV and a plasma electron density of 1.2×1015m−3 assured the nucleation of an amorphous fluorine-substituted hydroxyapatite phase on Si and Ti surfaces. With the aid of a Langmuir probe, the RAMS plasma energy was tuned to control the coating stoichiometry and the ratio between the crystalline and amorphous phases. The energy delivered over time from the bombardment of ions and electrons transformed the amorphous calcium phosphate phase into crystalline fluorine-substituted hydroxyapatite. The crystalline films were obtained at room temperature. The partial substitution of OH− for F− in the HA structure was confirmed by X-ray diffraction using synchrotron radiation in grazing-incidence mode, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. High-resolution transmission electron microscopy carried out on cross-section film samples prepared by a focused ion beam (FIB) technique revealed that the film ultrastructure was composed of columnar crystals oriented perpendicularly to the substrate surface. The crystals were connected to the substrate surface by ordered nanolayers, indicating the existence of a continuous binding between the two materials. This work demonstrates that the RAMS technique is able to produce FHA nano-coatings with controlled chemical compositions and structures on metallic implants for clinical applications.

パウダージェットデポジションによるハイドロキシアパタイト膜形成に関する研究

The authors have proposed a new dental treatment method by using powder jet deposition (PJD) technique to make coatings on human teeth. The method utilizes hydroxyapatite (HA), which is the main element of human hard tissue, as a restoration material. The coating process is achieved by high speed impacts of the particles on a tooth, and it can be carried out under room temperature and the atmospheric pressure. The thick PJD film is obtained through the accumulation of fractured parts of particles. This study focuses on the microstructures of the HA particles and the deposited film. To investigate the effect of particle crystal structures, two types of HA particles were produced: one (Type A particle) is covered with an amorphous surface, whose thickness is approximately tens of micrometers; the other one (Type B particle) is a type of complete-crystal-growth particles, which are produced by heating the particle A at 230°C for 12 hours. The film fabrication experiments were performed with these particles and machined areas were observed with a scanning electron microscope. It was found that the fabricated film with Type A particles was spalled during blasting. In contrast, the fabricated HA film with Type B particles is well deposited without film spalling. To further investigate the microstructures of the HA film, observations with a transmission electron microscope were conducted. The dark field image of the film with a Type A particle implies that the created HA layer consists of HA crystals of one to tens of nanometers. The bright field image indicates that cracks of approximately 300 nm generated in the film. Thus the mechanical strength of the film fabricated using the Type A particle is not strong enough against the subsequent particle impacts and the pressure of blasted air. In contrast, cracks were not observed in the film created with the Type B particle.

Hybrid biocomposite with a tunable antibacterial activity and bioactivity based on RF magnetron sputter deposited coating and silver nanoparticles

In this work, we describe fabrication techniques used to prepare a multifunctional biocomposite based on a hydroxyapatite (HA) coating and silver nanoparticles (AgNPs). AgNPs synthesized by a wet chemical reduction method were deposited on Ti substrates using a dripping/drying method followed by deposition of calcium phosphate (CaP) coating via radio-frequency (RF) magnetron sputter-deposition. The negatively charged silver nanoparticles (zeta potential −21mV) have a spherical shape with a metallic core diameter of 50±20nm. The HA coating was deposited as a dense nanocrystalline film over a surface of AgNPs. The RF-magnetron sputter deposition of HA films on the AgNPs layer did not affect the initial content of AgNPs on the substrate surface as well as NPs size and shape. SEM cross-sectional images taken using the backscattering mode revealed a homogeneous layer of AgNPs under the CaP layer. The diffraction patterns from the coatings revealed reflexes of crystalline HA and silver. The concentration of Ag ions released from the biocomposites after 7 days of immersion in phosphate and acetate buffers was estimated. The obtained results revealed that the amount of silver in the solutions was 0.27±0.02μgmL−1 and 0.54±0.02μgmL−1 for the phosphate and acetate buffers, respectively, which corresponded well with the minimum inhibitory concentration range known for silver ions in literature. Thus, this work establishes a new route to prepare a biocompatible layer using embedded AgNPs to achieve a local antibacterial effect.

Inorganic-organic thin implant coatings deposited by lasers.

The lifetime of bone implants inside the human body is directly related to their osseointegration. Ideally, future materials should be inspired by human tissues and provide the material structure-function relationship from which synthetic advanced biomimetic materials capable of replacing, repairing, or regenerating human tissues can be produced. This work describes the development of biomimetic thin coatings on titanium implants to improve implant osseointegration. The assembly of an inorganic-organic biomimetic structure by UV laser pulses is reported. The structure consists of a hydroxyapatite (HA) film grown onto a titanium substrate by pulsed-laser deposition (PLD) and activated by a top fibronectin (FN) coating deposited by matrix-assisted pulsed laser evaporation (MAPLE). A pulsed KrF* laser source (λ = 248 nm, τ = 25 ns) was employed at fluences of 7 and 0.7J/cm(2) for HA and FN transfer, respectively. Films approximately 1500 and 450 nm thick were obtained for HA and FN, respectively. A new cryogenic temperature-programmed desorption mass spectrometry analysis method was employed to accurately measure the quantity of immobilized protein. We determined that less than 7 μg FN per cm(2) HA surface is adequate to improve adhesion, spreading, and differentiation of osteoprogenitor cells. We believe that the proposed fabrication method opens the door to combining and immobilizing two or more inorganic and organic materials on a solid substrate in a well-defined manner. The flexibility of this method enables the synthesis of new hybrid materials by simply tailoring the irradiation conditions according to the thermo-physical properties of the starting materials.

Chemical properties of hydroxyapatite deposited through electrophoretic process on different sandblasted samples

Abstract An implantable material based on titanium (Ti6Al4V) was sandblasted in order to be deposited with a thin film of hydroxyapatite. Two samples of the alloy, in a shape of a bar with 10 mm diameter and 20 mm length, were subjected to mechanical treatment. After deposition of the hydroxyapatite through electrophoresis process, the samples were analyzed by scanning electron microscopy. The nature and chemical properties of thin films formed on Ti-based substrate were investigated with electrochemical impedance spectroscopy based on the extremely high polarization resistance of the material. The results revealed the formation of a homogeneous layer on the surface of the metallic substrate. The layer composed of TiO2 and hydroxyapatite provided a high corrosion protection.