Hydroxyapatite Films Research Articles

Application of Solution Plasma Surface Modification Technology to the Formation of Thin Hydroxyapatite Film on Titanium Implants

Hydroxyapatite (HA) coatings on titanium implants enhance rapid bone formation around the implant due to their osteoconductive property. The present study aimed to achieve a thin and uniform HA film coating on titanium implants by solution plasma treatment (SPT). Commercially pure titanium and porous titanium disks were employed. A pulse plasma generator was used on the disks for 30 min. Morphologic and crystallographic features of the deposited films were examined by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). To evaluate the wettability of the disks, water droplet (20 µL) surfaces were measured using a contact angle analyzer. The initial attachment of osteoblast-like cells (MC3T3E1) on the titanium substrates before and after solution plasma treatment was evaluated by counting the number of attached cells after incubation for 4 h. After immersion in the mineralizing solution for up to seven days, no crystals were observed on the polished-Ti surface. A more uniform and dense precipitation of round and grown crystals with diameters of approximately 1–5 µm was observed on Ti-SPT. XRD clearly showed that the precipitated crystals on titanium disks were HA. The contact angle of the polished-Ti increased with time (θ = 37°–51°). The surface of the Ti-SPT remained hydrophilic (θ ˂ 5°) after up to 30 days of aging. The number of attached cells on the Ti-SPT after aging for 30 days remained above 85% of that on the Ti-SPT without aging. SPT in a mineralizing solution can be used to acquire a homogenous precipitation of HA on porous-surfaced titanium implants.

Effect of thermal treatment on structure, phase and mechanical properties of hydroxyapatite thin films grown by RF magnetron sputtering

Hydroxyapatite (HA) thin films with a Ca/P ratio of 1.69 and approximately 500 nm in thickness were deposited by radio frequency magnetron sputtering on Ti-6Al-4 V substrates at 100 °C and a working pressure of 0.5 Pa. The obtained coatings were thermally treated at 400 and 700 °C in argon atmosphere and characterized in terms of elemental and phase composition, morphology, structure and mechanical properties by energy dispersive x-ray spectroscopy, scanning electron microscopy, atomic force microscopy, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and nanoindentation. It was found that the thermal treatments increase the crystallinity although induce residual tensile stresses formation in the HA coatings, which are greater at high temperatures. Nevertheless, enhances in the mechanical properties: hardness (H), elastic modulus (E) and adhesion strength for the heat treated at 400 °C samples compared to the as-deposited coatings were obtained. Values of 7.45 ± 0.6 GPa (H), 115 ± 10 GPa (E) and a critical load of 175 ± 4 mN were measured for those thermally treated samples at 400 °C.

Multiscale connections between morphology and chemistry in crystalline, zinc-substituted hydroxyapatite nanofilms designed for biomedical applications

Hydroxyapatite (HA), Ca10(PO4)6(OH)2, is a key material used to manufacture thin, bioactive coatings on metal implants for hard tissue regeneration. Technical challenges in their fabrication include control of the coating structure and chemical composition, as well as managing surface activation via ionic substitution. In this study, 15 – 216 nm-thick zinc-doped HA (ZnHA) thin films were grown via magnetron sputtering at room temperature. The effect of substituting Zn2+ for Ca2+ on the ultrastructures of the HA films was analyzed during several stages of film growth. Infrared vibrational scattering scanning near-field optical microscopy (s-SNOM) using the ultra-broad-band IR beam from synchrotron radiation was compared with Fourier transform infrared spectroscopy in attenuated total reflectance (FTIR/ATR) to reveal the close relationships between local topography and the chemical compositions of the film surface and the bulk of the film. The energy delivered via ionic bombardment induced the formation of complex structures: island-shaped nanoparticles of amorphous zinc-doped calcium phosphate, coalescent islands, disordered non-stoichiometric ZnHA nanoparticles, and long-range structures of nearly stoichiometric and crystalline ZnHA. Grazing incidence X-ray diffraction (GIXRD) from synchrotron radiation, X-ray photoelectron spectroscopy (XPS), focusing ion beam (FIB), and high-resolution transmission electron microscopy (HRTEM) confirmed Zn substitution into the HA lattice. Zinc was distributed homogeneously within the film structure (1.6 at%) but its concentration increased slightly on the film surface. The bulk of the film consisted of crystalline, columnar ZnHA domains oriented perpendicular to the substrate surface while the regions near the film/substrate interface were preferentially disordered and non-stoichiometric.

Size Control Synthesis of Hydroxyapatite Plates and Their Application in the Preparation of Highly Oriented Films

Hydroxyapatite (HAp) plates were successfully synthesized using dodecanedioic acid (DDDA). Following the preparation of an ethanolic solution of DDDA, solutions of calcium and phosphate were added in succession to produce a white slurry upon mixing. Subsequent processing of this slurry under hydrothermal conditions provided HAp plates of various sizes. Indeed, the plate size could be changed by varying the quantity of DDDA employed in the synthesis, with larger particles being obtained in the presence of larger quantities of DDDA. It was confirmed that a calcium–DDDA complex (Ca-DDD, calcium dodecanedioate) was formed upon mixing of the DDDA and calcium solutions. The observed morphological control could potentially be accounted for by the formation of Ca-DDD. More specifically, during crystal growth, Ca-DDD plays the role of a nucleation substrate (template), a pH buffer, and a calcium reservoir. Finally, we demonstrated that the obtained HAp plates could be employed to prepare a HAp film with high cryst...

Effect of Doubled Sandblasting Process and Basic Simulated Body Fluid Treatment on Fabrication of Bioactive Stainless Steels.

In our recent study, we aimed to impart hydroxyapatite (HA)-forming to bioinert stainless steels (SUS316L). The surfaces of SUS316L specimen were treated by a sandblasting process using alumina grinding particles with 14.0 or 3.0 μm for average particle size, respectively. In addition, a doubled sandblasting process (DSP) using the 14.0 μm particles and subsequently 3.0 μm ones were also conducted. Compared with the case of the 14.0 μm particles, the 3.0 μm particles were available to increase the surface roughness and the surface area of the specimen. Moreover, these values were further increased in the case of the DSP. These specimens were soaked in simulated body fluid (SBF) at pH = 8.4, 25 °C and were directly heated in the solution by electromagnetic induction. By this treatment, formation of CaP was induced on each specimen. These materials performed high HA-forming ability in SBF. Average bonding strength of the HA film formed on them in SBF was increased depending on the increase of surface roughness and surface area. These results indicated that sandblasting condition was an important factor to improve interlocking effect related to the increase of the surface roughness and the surface area.

Biomineralization behavior of electrophoretic-deposited hydroxyapatite-tricalcalcium phosphate biphasic composite

Hydroxyapatite (HA) and tricalcium phosphate (TCP) coatings have been widely used as bonding layers on implants in the medical applications. In this research, nano-powders of HA is synthesized via aqueous sol-gel route. TCP is obtained by controlled heat treatment of HA phase at 700 °C. After that, these nano-powders are electrophoretically deposited on stainless steel substrates by applying 60 V for 5 min. Also, biphasic composite of these nano-powders are prepared at various HA/TCP ratios. The phase purity of HA and TCP are confirmed by means of X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis. Differential thermal analysis and thermogravimetry (DTA/TG) clearly demonstrate the thermolysis and phase formation for each phase. Fourier transformed infrared (FTIR) spectroscopy represents through elimination of unwanted ions. The electrophoretic deposition behavior of HA/TCP biphasic as well as single phase samples are compared and biomineralization test is performed by simulated blood fluid solution. The electrophoretic behavior of the samples dramatically changes by increasing the TCP content due to its larger particle. The HA films show higher thickness and lower porosity, which are gradually changes by increasing TCP content. In terms of biomineralization, suitable growth occurs in all samples. However, the most appreciable growth is taken place in HA:TCP ratio of 25:75 wt%. These results show that the biphasic HA/TCP coatings, if appropriately applied on implants by simply controlling the electrophoretic deposition parameters, can enormously improve the grafting process by combining the TCP reactivity to form porous structure and providing required species and the HA biocompatibility and strength to bond to adjacent tissues.

Simultaneous detection of Pb2+, Cu2+ and Hg2+ by differential pulse voltammetry at an indium tin oxide glass electrode modified by hydroxyapatite

A novel electrochemical sensor basing on an indium tin oxide (ITO) glass electrode modified by hydroxyapatite (HAp) film was fabricated by electrodeposited method for simultaneous detection of Pb2+, Cu2+ and Hg2+ using differential pulse voltammetry (DPV). Various experimental parameters such as supporting electrolyte and pH were optimized. Under the optimal conditions, the electrode needs no accumulate time. The electrode showed linear correlation in the ranges of 1 × 10−7 to 1 × 10−6 M and 3 × 10−6 to 1 × 10−5 M for Pb2+, 1 × 10−7 to 1 × 10−6 M and 1 × 10−6 to 1 × 10−5 M for Cu2+, and 1 × 10−7 to 1 × 10−5 M for Hg2+. The limits of detection (S/N = 3) were 1 × 10−12, 1 × 10−12, 8 × 10−8 M for Pd2+, Cu2+ and Hg2+, respectively. Meanwhile, the developed electrode showed excellent anti-interference capabilities and selectivity with other heavy metal ions and common ions. The electrode has been successfully applied to the detection of above heavy metal ions in tap water. Above all, two major detection mechanisms of developed electrode were also researched in this work. The mechanism of filling Ca deficiency due to that the radiuses of Pb2+ and Cu2+ are similar to Ca2+, so Pb2+ and Cu2+ can fill in the deficiency. That is why the detection limits of Pb2+ and Cu2+ are much lower than Hg2+. When Ca deficiency has been almost filled, the detection of Pb2+ and Cu2+ based on the mechanism of surface adsorption. Because the radius of Hg2+ is not similar to Ca2+, Hg2+ cannot fill in the deficiency. The detection of Hg2+ mainly based on the mechanism of surface adsorption. The OH− on the surface of HAp plays a major role in the adsorption of heavy metal ions.

The Nature of the Nonsingularity of Inner Interfaces in Hydroxyapatite Ceramics

The morphology of inner interfaces in hydroxyapatite (HA) based calcium phosphate ceramics has been studied by transmission electron microscopy. Grain boundaries in the ceramics have been shown to have a vicinal character, which is related to the mechanism of secondary recrystallization in the material: layer growth of grains via sequential motion of elementary steps on planes corresponding to the $$\{ 1\bar 100\} $$ HA prism faces, which grow through transitions of atoms from adjacent grains that are in contact through their planes with large Miller indices. The recrystallization process may be accompanied by a “collision” of vicinal growth surfaces of grains with relatively large misalignment angles and the formation of grain boundaries nanofaceted by prism planes of adjacent grains. The recrystallization process in such a case should be expected to continue in the grain with a smaller nonsingularity of the growth front. Grain boundaries may allow for a match between planes differing in Miller indices, ndh1k1l1 ≈ mdh2k2l2, and the formation of grain-boundary Pumphrey dislocations, which compensate for the size mismatch between interplanar spacings and/or misalignment of the planes. The observed characteristic grain match configurations are typical of both ceramics produced by sintering HA powders and HA films produced by ion sputtering.

Control of hydroxyapatite film orientation by RF magnetron sputtering.

Hydroxyapatite (HAp) is compatible with bone tissue and used as a bone prosthetic material especially for the implants coating. The c-axis of biological apatite (BAp) in bone is mainly oriented along the bone axis direction due to the mechanical stress produced in this direction. Then, the coating of implant with c-axis parallel oriented HAp thin film is expected to improve the healing speed. In this study, fabrication of oriented HAp thin films was performed by using a RF magnetron sputtering technique. The control of the HAp orientation in the film was achieved by changing the gas conditions, distance and angle between the target and substrate during sputtering.

Hydroxyapatite coatings on Mg-Ca alloy prepared by Pulsed Laser Deposition: Properties and corrosion resistance in Simulated Body Fluid

Magnesium (Mg) alloys are very promising biocompatible materials for biodegradable biomedical implants, however, the main problem in using them is their fast degradation in the conditions of human body. In this work, we coated Mg-Ca (calcium) alloy substrate with hydroxyapatite (HA) to improve its resistance to corrosion and to control the in vitro degradation. Pulsed Laser Deposition technique was applied to deposit HA coatings. Their properties were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy, high resolution transmission electron microscopy, Vickers microhardness, and Tafel plot electrochemical technique. The substrate temperature was ranged in the interval from room up to 400 °C. According to the obtained results, the recommended substrate temperatures are 200–300 °C, since higher ones lead to the HA decomposition. Furthermore, the HA films deposited at 200 and 300 °C show good corrosion resistance in Simulated Body Fluid. The obtained coatings are promising for a perspective use in biomedical implant applications.

Correlation between structural and mechanical properties of RF magnetron sputter deposited hydroxyapatite coating

In the present study hydroxyapatite (HA) thin films with a,b-plain and c-plain preferential orientation were prepared by means of RF-magnetron sputtering with water vapor addition into a working gas atmosphere to investigate the influence of microstructural features on mechanical performance of the coating at nanoscale. The mechanical properties of the HA coatings textured along a,b- and c-axes by nanoindentation conclusively highlight that elastic modulus, H/E ratio, H3/E2 parameter and percent of elastic recovery are determined by preferential orientation of the film. Nanoindentation reveals that the HA films exhibiting (300) texture possess commensurate nanohardness and lower elastic modulus compared to (002) oriented films, indicating that the former films possess higher resistance to cracking. The (002) and (300) textured coatings exhibited a nanohardness of 4.7 ± 2.0 GPa and 4.4 ± 2.2 GPa, respectively. The elastic modulus of the HA film with (300) and (002) preferential orientation was 75 ± 40 GPa and 103 ± 40 GPa, respectively. The HA coating with (300) texture showed a higher percentage of elastic recovery of 92% within unloading than that of the (002) textured film (69%).

Effect of bioglass addition on the properties of HA/BG composite films fabricated by pulsed laser deposition

In order to improve the osteoconduction of metallic implants, bioactive films are often coated on the implant surfaces. In this paper, hydroxyapatite (HA) and bioglass (BG) composite films on Ti alloy were fabricated by pulsed laser deposition, and the effect of bioglass addition on the film properties was analyzed. Results show that the composite films are composed of crystalline HA, β-TCP and amorphous bioglass. The addition of bioglass decreases the crystallinity of the whole film and increases the Ca/P and Si/Na atomic ratio change rate. However an appropriate addition of bioglass can increase the adhesion strength to substrate and induce the c-axis orientation growth of HA. The composite film with 20 wt% bioglass exhibits excellent osteoconduction and can be considered as a prospective competitor for bone implantology applications.

Enhanced Photocatalytic Activity of TiO2 Nanoparticles Supported on Electrically Polarized Hydroxyapatite.

Fast recombination of photogenerated charge carriers in titanium dioxide (TiO2) remains a challenging issue, limiting the photocatalytic activity. This study demonstrates increased photocatalytic performance of TiO2 nanoparticles supported on electrically polarized hydroxyapatite (HA) films. Dense and thermally stable yttrium and fluorine co-doped HA films with giant internal polarization were synthesized as photocatalyst supports. TiO2 nanoparticles deposited on the support were then used to catalyze the photochemical reduction of aqueous silver ions to produce silver nanoparticles. It was found that significantly more silver nanoparticles were produced on polarized HA supports than on depolarized HA supports. In addition, the photodegradation of methyl orange with TiO2 nanoparticles on polarized HA supports was found to be much faster than with TiO2 nanoparticles on depolarized HA supports. It is proposed that separation of photogenerated electrons and holes in TiO nanoparticles is promoted by the internal polarization of the HA support, and consequently, the recombination of charge carriers is mitigated. The results imply that materials with large internal polarization can be used in strategies for enhancing quantum efficiency of photocatalysts.

Electrophoretic deposition of hydroxyapatite-shrimp crusts nanocomposite thin films for bone implant studies.

Hydroxyapatite-shrimp crusts nanocomposite thin films were deposited on titanium substrates by electrophoretic technique, under different preparation conditions, for bone implant applications. Fourier transform infrared spectrometer, atomic force microscope, X-ray diffraction (XRD), optical microscope, and scanning electron microscope were employed to characterise the synthesised films. Vickers' micro-hardness measurements revealed a value of 502 HV for the hydroxyapatite films and 314.55 HV for the nanocomposite films. XRD results confirmed the polycrystalline nature of the hydroxyapatite and hydroxyapatite-shrimp nanocomposite films. The in-vitro bioactivity test of the synthesised films in simulated body fluid showed very low dissolution rate. Antibacterial activity of synthesised films was investigated against E. coli bacteria.

In Vitro and In Vivo Osteogenic Activity of Titanium Implants Coated by Pulsed Laser Deposition with a Thin Film of Fluoridated Hydroxyapatite.

To enhance biocompatibility, osteogenesis, and osseointegration, we coated titanium implants, by krypton fluoride (KrF) pulsed laser deposition, with a thin film of fluoridated hydroxyapatite (FHA). Coating was confirmed by scanning electron microscopy (SEM) and scanning probe microscopy (SPM), while physicochemical properties were evaluated by attenuated reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Calcium deposition, osteocalcin production, and expression of osteoblast genes were significantly higher in rat bone marrow mesenchymal stem cells seeded on FHA-coated titanium than in cells seeded on uncoated titanium. Implantation into rat femurs also showed that the FHA-coated material had superior osteoinductive and osseointegration activity in comparison with that of traditional implants, as assessed by microcomputed tomography and histology. Thus, titanium coated with FHA holds promise as a dental implant material.

Electrophoretic Deposition of Hydroxyapatite Film Containing Re-Doped MoS₂ Nanoparticles.

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS2 (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

Pore Shape Changes and Apatite Formation on Zn and Si Ion-Doped HA Films of Ti-6Al-4V After Plasma Electrolytic Oxidation Treatment.

In this study, pore shape changes and apatite formation on zinc (Zn) and silicon (Si) ion-doped hydroxyapatite (HA) films of Ti-6Al-4V by plasma electrolytic oxidation (PEO) treatment has been investigated by several techniques. The PEO films and the Ti-6Al-4V surface after immersion in SBF were observed by X-ray spectroscopy, field-emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. The number of pores decreased as Zn ion concentration increased from 5Zn to 10Zn. The maximum size of pores were increased from 5Zn to 20Zn concentration, whereas, the minimum size of pores decreased. The amount of bone-like apatite formation for the 5Zn/5Si sample was higher than those of other samples immersed in SBF.

The Effect of Hydroxyapatite Coatings on the Passivation Behavior of Oxidized and Unoxidized Superelastic Nitinol Alloys

Nitinol alloys have been used in various biological applications due to their superior properties. In this study, a bipolar pulsed current electrodeposition technique was applied to produce a hydroxyapatite (HA) film on the Nitinol alloy. Also, the protection performance of the coating was evaluated on both abraded and thermochemically modified alloy. According to obtained data, reducing the electrocrystallization rate by the pulse deposition technique can promote HA formation on both abraded and modified substrates. Based on scanning electron microscopy and high-resolution transmission electron microscopy data, the HA coatings revealed a flake-like morphology and each flake was composed of nano-crystalline grains. Atomic force microscopy images revealed that flakes on the abraded substrate were smaller in size than that of the modified alloy. Comparing the corrosion resistance of the bare substrates revealed that the modified alloy has a higher corrosion resistance than the abraded alloy and the modified surface is well passivized during anodic polarization in Ringer’s solution. However, this condition is reversed after the deposition of HA film. It seems that because of the lower crystallization sites on the abraded alloy, the produced HA film is denser and more protective against the corrosive mediums as compared to the coating on the modified alloy. Although the HA coating can improve the bioactivity of both substrates, the resulted film on the oxidized alloy is porous and deteriorates the implant permanence in the vicinity of body fluids.

Durable Self-Cleaning Coatings for Architectural Surfaces by Incorporation of TiO₂ Nano-Particles into Hydroxyapatite Films.

To prevent soiling of marble exposed outdoors, the use of TiO2 nano-particles has been proposed in the literature by two main routes, both raising durability issues: (i) direct application to marble surface, with the risk of particle leaching by rainfall; (ii) particle incorporation into inorganic or organic coatings, with the risk of organic coating degradation catalyzed by TiO2 photoactivity. Here, we investigated the combination of nano-TiO2 and hydroxyapatite (HAP), previously developed for marble protection against dissolution in rain and mechanical consolidation. HAP-TiO2 combination was investigated by two routes: (i) sequential application of HAP followed by nano-TiO2 (“H+T”); (ii) simultaneous application by introducing nano-TiO2 into the phosphate solution used to form HAP (“HT”). The self-cleaning ability was evaluated before and after prolonged exposure to simulated rain. “H+T” and “HT” coatings exhibited much better resistance to nano-TiO2 leaching by rain, compared to TiO2 alone. In “H+T” samples, TiO2 nano-particles adhere better to HAP (having flower-like morphology and high specific surface area) than to marble. In “HT” samples, thanks to chemical bonds between nano-TiO2 and HAP, the particles are firmly incorporated in the HAP coating, which protects them from leaching by rain, without diminishing their photoactivity and without being degraded by them.

Nanoparticles Deposition on Mini-implants for Osseo-integration and Antibacterial Properties Improvement

In last few years, researchers focused on improvement of lifespan of dental mini-implants by coating them with nanopoarticles for a better osseo-integration, which also possesses antibacterial properties. Once their surface is coated with nanoparticles type silver dopped hydroxyapatite makes them durable and safe by a good integration into tissue and by preventing bacterial infections. It is well known that a particular problem with medical devices such as dental mini-implants is bacterial colonization. For this reason the use of nanoparticles coated mini-implants is a measure to prevent or to treat infections caused by microbial agents present in oral cavity. Our study considers the possibility of using silver doped hydroxyapatite thin films on titanium mini-implants as an osseo-integration and antibacterial component. Therefore several physic-chemical analyses were performed in order to determine their properties and to open new perspectives to develop nanoparticulated thin films as coatings for orthodontic mini-implants.