Thin Hydroxyapatite Research Articles

Nano-crystalline pulsed laser deposition hydroxyapatite thin films on Ti substrate for biomedical application

Hydroxyapatite (HA) thin coating has been coated on titanium substrates by pulsed laser deposition (PLD). Structural and morphological studies by transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed. The HA film is polycrystalline and irregular with a range size of particulates from 100 nm to 1 μm. Adhesion of the HA films to the Ti substrates was excellent as observed by cross-scanning electron microscopy (X-SEM) and transmission electron microscopy (XTEM). The residual stresses state determined on uncoated Ti substrates was compressive. After deposition of thin PLD HA on titanium substrates at 400°C the residual stress state was in a very low tensile state.

Sol–gel derived hydroxyapatite coatings on titanium substrates

The oscillatory micromovements at the interface between the implant and the bone induce fretting wear and sometimes, fatigue cracks, causing early failure of the joint prosthesis. Hydroxyapatite films were formed using a sol–gel method from an organic precursor solution. The average film thickness was found to be 1.0μm. Composite coatings containing HA doped with ZrO2 were also formed. Hydroxyapatite (HA) and composite films of HA and ZrO2 formed on commercial titanium substrates using an organic precursor solution by sol–gel route, were tested for fretting wear using a ball-on-flat fretting apparatus. The moderately lower values of the coefficient of friction (0.4–0.5) and morphology of the wear pits for considerably long cycles of fretting indicate strong bonding of the HA coating to the titanium surface. The interface shear strength of a thin hydroxyapatite film on commercial purity titanium has been evaluated using a substrate straining method. The maximum interfacial strength was about 570 and 678MPa, for the pure HA and composite films, respectively, on the highly polished surface. However, the maximum interfacial strength was found to be about 263MPa on the oxidized surface.

Apatite formability of boron nitride nanotubes

This study investigates the ability of boron nitride nanotubes (BNNTs) to induce apatiteformation in a simulated body fluid environment for a period of 7, 14 and 28 days. BNNTs,when soaked in the simulated body fluid, are found to induce hydroxyapatite (HA)precipitation on their surface. The precipitation process has an initial incubation period of ∼ 4.6 days. The amount of HA precipitate increases gradually with the soaking time. Highresolution TEM results indicated a hexagonal crystal structure of HA needles. No specificcrystallographic orientation relationship is observed between BNNT and HA, which is dueto the presence of a thin amorphous HA layer on the BNNT surface that disturbs a definiteorientation relationship.

Microstructure and Toughness Mechanism of Tooth

Tooth is a kind of biomaterial in nature. It behaves favorable strength, stiffness and fracture toughness, which are closely related to its fine microstructure. The observation of scanning electron microscope (SEM) on a mature tooth shows that the tooth is a kind of natural bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The observation also shows that the hydroxyapatite layers consist of long and thin hydroxyapatite sheets and that all the hydroxyapatite sheets are arranged in a kind of parallel distribution. The maximum pullout energy of the hydroxyapatite sheets, which is closely related to the fracture toughness of the tooth, is investigated based on the representative model of the parallel distribution. It shows that the long and thin shape as well as the parallel distribution of the hydroxyapatite sheets increase the maximum pullout energy and enhance the fracture toughness of the tooth.

Residual stress distribution in ceramic/metal systems by nondestructive techniques

The bio-ceramic coatings on metallic implants are proposed to be a solution for combining the mechanical properties of the metal with the necessarily bioactive character of the ceramic layer, leading to a better integration of the entire implant.In this paper, the determination of residual stresses in such systems by non-destructive methods is presented for a mock-up of an implant constituted by two different biomedical ceramic/metal systems: (i) titanium dental implants and (ii) porcelain crown. Stress distributions are reported in: (i) a thin hydroxyapatite coating (50μm) deposited by plasma-spray ceramic films on titanium alloy as well as (ii) a multilayer consisting of a layer (1.8mm) of glassy-ceramic and opaque ceramic (0.35mm), normally Porcelain- Fused- to- Metal on a palladium substrate (1.6mm).

Studies of bacterial adhesion on TiN, SiO 2–TiO 2 and hydroxyapatite thin layers deposited on titanium and Ti6Al4V alloy for medical applications

The Staphylococcus epidermidis biofilm formation on titanium or titanium alloy, coated with TiN, SiO 2–TiO 2 and electrodeposited hydroxyapatite, was tested. Surfaces of titanium, Ti6Al4V alloy or TiN, modified with SiO 2–TiO 2 layer, were found to be highly resistant to bacterial adhesion. Only small amounts of bacterial cells were observed on matrices coated by thin hydroxyapatite films, deposited on both SiO 2–TiO 2 and TiN + SiO 2–TiO 2 interlayers. Biological tests showed that the biofilm formed massively on polished and ground titanium and titanium alloy surfaces, also those covered with TiN, but not on those modified with SiO 2–TiO 2 nanofilm.

The biocompatibility of HA thin films deposition on anodized titanium alloys

A thin hydroxyapatite (HA) film was deposited on anodized titanium for the biocompatibility by RF sputtering method. The anodized titanium has improved its bioactivity further by the HA deposition on the anodized titanium surface. TiO 2 layer with 0.2 ~ 0.5 μm diameter pore size was formed on the Ti surface by anodization. HA film deposited surface showed that the pore size and number decreased compared with non-HA deposited surface. The corrosion resistance of HA deposited/anodized Ti was higher than that of the non-treatment Ti alloy in Hank's solution, indicating better protective effect. From the results of cell culture using MTT assays, the best cell proliferation showed in HA deposited surface after anodization of Ti surfaces compared with another surface treatment.

Antibacterial properties of Ag-doped hydroxyapatite layers prepared by PLD method

Thin hydroxyapatite (HA), silver-doped HA and silver layers were prepared using a pulsed laser deposition method. Doped layers were ablated from silver/HA targets. Amorphous and crystalline films of silver concentrations of 0.06 at.%, 1.2 at.%, 4.4 at.%, 8.3 at.% and 13.7 at.% were synthesized. Topology was studied using scanning electron microscopy and atomic force microscopy. Contact angle and zeta potential measurements were conducted to determine the wettability, surface free energy and electric surface properties. In vivo measurement (using Escherichia coli cells) of antibacterial properties of the HA, silver-doped HA and silver layers was carried out. The best antibacterial results were achieved for silver-doped HA layers of silver concentration higher than 1.2 at.%.

Surface Observation of Thin Hydroxyapatite-Coated Implants at 80 Months After Insertion

We observed surfaces and cross sections of thin hydroxyapatite (HA)-coated implants produced by the thermal decomposition method in a patient attending our clinic who underwent implant removal at 80 months due to fracture of the implants. On the implant surfaces of the removed sample, most of the HA had dissolved, and extensive osseointegration was observed where Ti had closely bonded to bone. This indicated that the HA coated on the implant surfaces had disappeared and osseointegration had been established where Ti directly bonded to the bone. In addition, calcium titanate (CaTiO(3)) and HA layers formed by the thermal decomposition method showed no desorption. The results clearly indicate the positive clinical potential of thin HA-coating by the thermal decomposition method.

Screwy microstructure of hydroxyapatite sheets of shank bone

Scanning electron microscope (SEM) observation shows that a shank bone is a kind of bioceramic composite consisting of inorganic hydroxyapatite and organic collagen protein. The hydroxyapatite possesses laminated microstructure and the each hydroxyapatite layer is composed of numerous long and thin hydroxyapatite sheets. The hydroxyapatite sheets in an arbitrary hydroxyapatite layer make an almost fixed angle with the hydroxyapatite sheets in their adjacent hydroxyapatite layers which compose a kind of particular screwy microstructure. The maximum pullout energy of the screwy microstructure, which is closely related to the fracture toughness of the bone, is theoretically investigated and compared with that of the parallel microstructure of the sheets. It shows that the maximum pullout energy of the screwy microstructure is markedly larger than that of the parallel microstructure, which is experimentally verified.

INTERSECTANT MICROSTRUCTURE OF HYDROXYAPATITE SHEETS OF SHANKBONE

Bone possesses excellent mechanical properties, which are closely related to its favorable microstructures optimized by nature through millions of years. In this work, a scanning electron microscope (SEM) was used to observe the microstructures of a shankbone. It showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The hydroxyapatite layers are further composed of long and thin hydroxyapatite sheets. The hydroxyapatite sheets in different hydroxyapatite layers distribute along different orientations, which composes a kind of intersectant microstructure. The maximum pullout force of the intersectant microstructure was investigated and compared with that of 0° microstructure with their representative models. The result indicated that the maximum pullout force of the intersectant microstructure is markedly larger than that of the 0° microstructure, which was experimentally verified.

A new cementless total hip arthroplasty with bioactive titanium porous‐coating by alkaline and heat treatment: Average 4.8‐year results

A method has been developed for creating a bioactive coating on titanium by alkaline and heat treatment, and shown that it forms a thin layer of hydroxyapatite (HA) on the surface of implants when soaked in simulated body fluid. A series of 70 cementless primary total hip arthroplasties using this coating technique on a porous titanium surface was performed, and followed up the patients for a mean period of 4.8 years. There were no instances of loosening or revision, or formation of a reactive line on the porous coating. Although radiography just after operation showed a gap between the host bone and the socket in over 70% of cases, all the gaps disappeared within a year, indicating the good osteoconduction provided by the coating. Alkaline-heat treatment of titanium to provide a thin HA coating has several advantages over plasma-spraying, including no degeneration or absorption of the HA coating, simplicity of the manufacturing process, and cost effectiveness. In addition, this method allows homogeneous deposition of bone-like apatite within a porous implant. Although this was a relatively short-term study, treatment that creates a bioactive surface on titanium and titanium alloy implants has considerable promise for clinical application.

Microstructure and Toughness Mechanism of Shank Bone

Scanning electron microscope (SEM) observation was performed and showed that shank bone is a kind of bioceramic composite consisting of laminated hydroxyapatite and organic materials. The hydroxyapatite layers are parallel with the surface of the bone and consist of numerous thin and long hydroxyapatite sheet fibers. The hydroxyapatite sheet fibers in different hydroxyapatite make a little angle with each other and compose a kind of screwy microstructure. The maximum pullout force of the screwy microstructure was investigated and compared with that of parallel microstructure. It shows that the maximum pullout force of the screwy microstructure is markedly larger than that of the parallel microstructure, which was experimentally validated.

Hydroxyapatite-Sheet Parallel Microstructure of Shinbone

Bone is a natural biomaterial. It behaves favorable strength, stiffness and fracture toughness, which are closely related to its eximious microstructure. Scanning Electron Microscope (SEM) observation on a shinbone showed that the bone is a bioceramic composite consisting of laminated hydroxyapatite and collagen matrix. The hydroxyapatite layers are parallel with the surface of the bone and consist of long and thin hydroxyapatite sheets. The observation also showed that the hydroxyapatite sheets in different hydroxyapatite layers also parallel with each other, which composes a hydroxyapatite-sheet parallel microstructure. The maximum pullout energy of the parallel microstructure was investigated based on its representative model. It was shown that the long and thin shape of the hydroxyapatite sheets in the parallel microstructure is profitable to increase the maximum pullout energy and enhance the fracture toughness of the bone.

Longitudinal Observation of Thin Hydroxyapatite Layers Formed on Anodic Oxide Titanium Implants after Hydrothermal Treatment in a Rat Maxilla Model

Purpose: Highly crystalline thin hydroxyapatite (HA) layers deposited on the surface of commercially pure titanium (cpTi) by discharge anodic oxidation and hydrothermal treatment (SA treatment) enhance the value of cpTi as endosseous implants in clinical dentistry. In particular, the SA treatment affects the osteoconductive properties of cpTi. Determining whether this HA layer retains its chemical stability during osseous wound healing is crucial for its use in implants. In this study, we characterized the morphological, chemical, and structural features of HA layers on SA-treated cpTi implants in rat maxilla.Materials and methods: SA-treated cpTi implants (diameter: 1.0 mm, length: 2.0 mm) were placed in the maxilla of 8-week-old Wistar rats. After 14, 21, and 28 days, the maxilla were harvested and the implant surfaces were analyzed by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and x-ray photoelectron spectroscopy (XPS).Results: SEM analysis revealed precipitated HA crystals on the implant surface; the crystals had a typical single hexagonal columnar shape and they were highly crystalline. Implantation up to 28 days changed neither the morphology nor the crystalline features of the thin HA layer. EPMA revealed an even distribution of P and Ca in the HA layers before and after implantation in the maxilla, while XPS indicated no change in the binding energies of P and Ca in the HA crystals.Conclusion: The thin HA layer formed on the SA-treated cpTi implants remained stable during the process of jaw bone formation.

Longitudinal Observation of Thin Hydroxyapatite Layers Formed on Anodic Oxide Titanium Implants after Hydrothermal Treatment in a Rat Maxilla Model

Longitudinal Observation of Thin Hydroxyapatite Layers Formed on Anodic Oxide Titanium Implants after Hydrothermal Treatment in a Rat Maxilla Model

Surface Modification Enhances Osteoblast Behavior and Bone Formation on Thin Hydroxyapatite Layers Deposited Using a Novel Anodization-Hydrothermal Treatment on Commercially Pure Titanium Endosseous Implants

In the present study, we assessed the effects of commercially pure titanium (cpTi) by anodic oxidation and hydrothermal treatment (SA-treated cpTi) on osteoblastic differentiation and interfacial bone formation through parallel in vitro and in vivo investigations. Osteoblast cells were cultured on SA-treated cpTi disks for 5, 7, 10, and 14 days. Bone matrix mineralization was assessed by EPMA. The levels of collagen I, alkaline phosphatase, osteocalcin, osteopontin, bone sialoprotein, and β-actin mRNA were analyzed using RT-PCR. In addition, SA-treated cpTi implants were placed in the mandibles of beagles for 14 days, and then examined histologically by light microscopy. Widespread Ca and P signals were observed early in the in vitro culturing period, and mRNA expression was up-regulated in cells that were in contact with the SA-treated cpTi. The bone-to-implant contact formed at the mandible SA-treated cpTi implant sites involved direct contact of the implant with the surrounding bone tissue. These results demonstrate the potential of SA-treated cpTi surfaces for enhancing surface-specific expression of osteoblastic phenotypes and for inducing changes in bone matrix gene expression.

Preparation and characterization of hydroxyapatite coatings on human enamel by electrodeposition

Thin hydroxyapatite (HA) coatings, approximately from 1 μm to 10 μm in thickness, had been prepared on human enamel by electrodeposition with the current density of 0.5 mA/cm 2 at 55 °C in 1 h. They exhibited an acicular morphology and had a tight contact with the substrate by scanning electron microscope and transmission electron microscope observation. The comparison was made between the enamel specimens with HA coatings in this study and the sound enamel. In this comparison, while the Vickers micro-hardness showed a similar value, the antibacterial activities improved significantly after the formation of HA coatings. In conclusion, electrodeposition was proved to be an effective method for preparing HA coatings on human enamel and could be considered as a promising method to restore the initial enamel lesions in clinic.

Investigation to the Cross Microstructure of Hydroxyapatite Sheets of a Cannon Bone

Bone possesses excellent mechanical properties, which are closely related to its favorable microstructures optimized by nature through many centuries. In this work, a scanning electron microscope (SEM) was used to observe the microstructures of a cannon bone. It showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The hydroxyapatite layers are composed of long and thin hydroxyapatite sheets. The hydroxyapatite sheets in different hydroxyapatite layers distribute along different orientations, which composes a kind of cross microstructure. The maximum pullout force of the cross microstructure was investigated and compared with that of the 0° microstructure with their representative models. The result indicated that the maximum pullout force of the cross microstructure is markedly larger than that of the 0° microstructure.

Effects of Thin Hydroxyapatite Coating on Initial Response of Osteoblast-Like Cells

To combine the bioinert titanium with the biological active coating of hydroxyapatite [HA, Ca10(PO4)6(OH)2] a new pulsed laser deposition(PLD) method was applied. The initial osteoblast-like MC3T3-E1 cell response to this thin HA coated(<1μm) surface was compared with non-coated surfaces. Cell responses on four different pure titanium surfaces, such as smooth titanium, HA coated smooth titanium, rough titanium and HA coated rough titanium, were compared. Cell morphology and attachment were examined by scanning electron microscopy after 6, 24 and 72 hrs of culture, cell proliferation by MTS assay after 3, 7 and 14 days. The differentiation of the cells was analyzed by real time PCR up to 21 days. The cells were well spread and attached on all surfaces and showed more irregular shapes on the HA coated specimens. They proliferated continuously on all specimens up to 14 days. Smooth surface specimens showed better cell proliferation than rough ones after 7 days, and the HA coated specimens demonstrated slightly greater MTS activity than the non-coated groups after 14 days. The surface topography affected cell proliferation initially however; there was no significant difference afterwards. Thin HA coating influenced the expression of some genes related with cell differentiation.