Crystalline Hydroxyapatite Research Articles

Development of novel nano-hydroxyapatite doped with silver as effective catalysts for carbon monoxide oxidation

A series of novel silver-containing catalysts were synthesized, characterized by X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy, N2 adsorption-desorption isotherms, thermogravimetric analysis and then tested for the oxidation of carbon monoxide (CO). The microwave-hydrothermal method was a useful synthesis pathway to structurally incorporate low amounts of silver (2.5–5.0 atomic percentage) to hydroxyapatite (HA) lattice, preserving the crystalline structure of the HA. Specific surface area and particle size (diameter) of the obtained materials were about 52–55 m2/g and 19–47 nm, respectively. Silver-catalysts showed higher catalytic activities than the unmodified HA sample at temperatures between 600 and 850 °C. The best catalytic results were achieved at around 700–800 °C with silver-containing HA samples. However, due to the significant decrease in the crystallinity of the materials exposed to 800 °C; then, 700 °C was established as the best thermal condition for producing CO2 and preserving the HA crystalline structure.Furthermore, cyclic tests demonstrated that silver-containing HA catalysts perform CO oxidation for 3 h through several consecutive catalytic tests at 700 °C without losing neither their activity nor their structural properties, evidencing their high thermal stability under the CO-O2 atmosphere. Thus, the highest reaction rate values (rCO2) were obtained with HA containing 2.5% of silver at 700 °C during the five cycles performed, positioning it as a promissory catalyst with high activity during the CO oxidation at high temperatures. The proposed reaction mechanism was established using these silver-doped materials. This work constitutes the first assessment to add low amounts of silver to increase the activity of this kind of catalytic materials for the CO oxidation reaction.

CaSiO3-HAp Structural Bioceramic by Sol-Gel and SPS-RS Techniques: Bacteria Test Assessment.

The article presents an original way of getting porous and mechanically strong CaSiO3-HAp ceramics, which is highly desirable for bone-ceramic implants in bone restoration surgery. The method combines wet and solid-phase approaches of inorganic synthesis: sol-gel (template) technology to produce the amorphous xonotlite (Ca6Si6O17·2OH) as the raw material, followed by its spark plasma sintering–reactive synthesis (SPS-RS) into ceramics. Formation of both crystalline wollastonite (CaSiO3) and hydroxyapatite (Ca10(PO4)6(OH)2) occurs “in situ” under SPS conditions, which is the main novelty of the method, due to combining the solid-phase transitions of the amorphous xonotlite with the chemical reaction within the powder mixture between CaO and CaHPO4. Formation of pristine HAp and its composite derivative with wollastonite was studied by means of TGA and XRD with the temperatures of the “in situ” interactions also determined. A facile route to tailor a macroporous structure is suggested, with polymer (siloxane-acrylate latex) and carbon (fibers and powder) fillers being used as the pore-forming templates. Microbial tests were carried out to reveal the morphological features of the bacterial film Pseudomonas aeruginosa that formed on the surface of the ceramics, depending on the content of HAp (0, 20, and 50 wt%).

Synthesis and characterization of the novel 80S bioactive glass: bioactivity, ‎biocompatibility, cytotoxicity

In this research, the 80S bioactive glass with different Ca/P ratios was prepared by the sol-gel route. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transforms infrared spectroscopy (FTIR) were used to study the apatite structure and shape. According to the results, the 78SiO2–17P2O5–5CaO bioglass showed a higher rate of crystalline hydroxyapatite (HA) on its surface in comparison with the other bioglasses. After 3 days of immersion in the SBF solution, spherical apatite was formed on the 78SiO2–17P2O5–5CaO surface, which demonstrated high bioactivity. A statistically significant promotion in proliferation and differentiation of G292 osteoblastic cells was also observed. Regarding its optimal cell viability and bioactivity, the 78SiO2–17P2O5–5CaO bioactive glass could be offered as a promising candidate for bone tissue applications.

Synthesis and Characterization of Hydroxyapatite Produced From Egg Shells; A Micellar Templated Approach

In the present study hydroxyapatite (HA) powder has been synthesized using egg shells as source of calcium. The synthesis has been carried out using CTAB, surfactant micelles as templates through hydrothermal approach. The phase purity and crystallinity of synthesized powder synthesized was conducted using FTIR and XRD analysis respectively. Whereas, FESEM and TEM analysis was conducted to observe morphology of synthesized sample. Results indicated synthesis of low crystalline HA nanopowders with rodlike morphology.

In vitro bioactivity of silicophosphate glasses doped with ZnO, SrO or CuO

Silicophosphate glasses with variable divalent ion dopants (Zn2+, Sr2+ or Cu2+) were prepared via melt annealing route. Parent and doped glasses were thermally heat-treated through a two-step regime to be converted into their glass–ceramic derivatives. Fourier transform infrared (FT-IR) spectral data were recorded for parent glasses and their glass–ceramics derivatives to identify the structural building units which reveal vibrational bands due to both main phosphate and some silicate groups and to verify the bioactivity behavior after immersion in diluted phosphate solution. X-ray diffraction studies indicate the formation of different phosphate and silicate crystalline phases in the derived glass–ceramics which varied with the type of dopant oxide. SEM investigations of the glass–ceramics before and after immersion in phosphate solution showed multicomponent microcrystalline textures in the studied micrographs before immersion. Nodular-shaped microcrystalline features were identified after immersion in phosphate solution referring to the formation of crystalline hydroxyapatite. The undoped glass–ceramic is identified to crystallize in almost equal silicate and phosphate phases, while with the dopant ZnO, SrO or CuO, the crystalline phases are only of phosphates, while the silicate phase is assumed to be retained in the surrounding remaining vitreous boundaries.

Photocatalytic HA deposition on TiO2 of Ti-0.2Pd surface immersed in simulated body fluid

Effect of photocatalysis on apatite formation on Ti-0.2Pd alloy when the metal is immersed in a physiological solution is investigated. The surface of Ti-0.2Pd was treated by a method of thermal oxidation at 400 and 600 °C in air. Immersion tests of Ti-0.2Pd pieces in a simulated body fluid (SBF containing 27 mM HCO3−) at 37 °C for 14 days under ultraviolet (UV) irradiation and in dark environment were carried out. Glancing angle X-ray diffraction and Fourier transform infrared spectroscopy were used to examine the crystallinity and composition of the deposition. Two different morphologies of carbonated hydroxyapatite (HA) deposition: spherical flower shape and dot shape are found formed on the samples. Spherical flower-shaped HA has higher crystallinity and higher Ca/P ratios (1.2–1.4) which are related to the effect of photocatalysis. Dot shaped HA with lower crystallinity and lower Ca/P ratio (0.8–1.0) is found formed on most dark immersed pieces. This work suggests the UV irradiation causes the change of the morphology and crystallinity of HA but has no effect on the quantity of HA formed on Ti-0.2Pd. The chemical composition of the deposition produced on Ti-0.2Pd under UV lighting is closer to that of a crystallized HA compared to that formed in dark.

Investigation of Physico-mechanical Behavior, Permeability and Wall Shear Stress of Porous HA/PMMA Composite Bone Scaffold

Hydroxyapatite (HA)-based composite bone scaffolds are developed using solvent casting particulate leaching technique by varying the weight percentages of HA from 50 to 70% (w/w) in polymethyl methacrylate matrix. The chemical properties of the developed scaffolds are investigated by XRD analysis which shows the presence of crystalline HA and traces of β-TCP in the scaffolds. The microstructure of the scaffolds is studied by the SEM micrographs, which show porous morphology with an average pore size of 119 ± 18–148 ± 23 µm and a maximum pore size of 148 ± 23 µm for HA 50 scaffold. The highest porosity of 75 ± 2.0% is recorded for HA 50 scaffold by conducting liquid displacement test and a maximum compressive strength of 6.26 ± 0.53 MPa is recorded for HA 60 scaffold by performing uniaxial compression test of the scaffolds. The permeability and wall shear stress (WSS) of the scaffolds are investigated by computational fluid dynamics (CFD). The CFD analysis is performed in a fluid domain developed by Boolean operations on the CAD model of the scaffold developed using micro-computed tomography-based 3D image acquisition technique by Mimics V1. Results show that the permeability increases and WSS decreases with an increase in the porosity of the scaffolds. However, both permeability and WSS obtained for the developed scaffolds are within the limit prescribed for the growth of bone tissues. It is concluded that scaffolds with 60 wt% of HA exhibit the best combination of porosity, permeability and compressive strength making it suitable for bone tissue engineering applications.

Fabrication of c‐plane‐oriented hydroxyapatite film on amorphous SiO2 substrate

AbstractWe investigated a fabrication technique of c‐plane‐oriented hydroxyapatite (HA) crystalline film on low‐cost amorphous SiO2 substrates to apply the orientation‐controlled HA crystal to disposal biochips. An experiment was conducted by the pulsed laser deposition method. We showed that a high‐quality HA crystalline film was grown using a fluorapatite (FA) buffer layer, which was self‐oriented on amorphous SiO2. A relationship between an FA‐film thickness and the HA quality was examined with an aim of minimizing a toxic risk of F to biomolecules, even if it was eluted from FA. It was found that the thickness of the FA film could be reduced to about 7.5 nm, at the same time, the crystallinity and smoothness of HA were also excellent. A crystal growth model of FA on the amorphous SiO2 was also studied. We considered that highly reactive F in a laser‐ablated plume substituted for O on the substrate surface, which became a migration trap, causing three‐dimensional island growth as FA crystal nuclei. This model consistently agreed with a series of experimental results.

Low-Cost Hydroxyapatite Powders from Tilapia Fish

Synthetic hydroxyapatite {HAp, Ca10(PO4)6(OH)2} is a bioactive and biocompatible material widely used in healthcare for bone implants and grafts, due to its chemical and structural similarity with biological hydroxyapatite present in bone tissues. In this work, HAp was processed by calcination of tilapia fish bones from fish reared in net tanks and slaughtered at the age of 360 days. The bones were cleaned and dried, calcined at 900°C for 8 h and submitted to high energy milling for 8 h, to produce HAp powder. The thermogravimetric analysis and differential thermal analysis (TGA-DTA), dynamic light scattering (DLS), x-ray diffraction (XRD), Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR), Raman spectroscopy and scanning electron microscopy (SEM), were techniques used to characterize the material produced. The results indicate that the methodology employed is effective for the production of nanostructured HAp powder, with particle size ranging from 600 nm to 1200 nm and grain size between 0.25 and 1.1 µm (evaluated by SEM in one piece of calcined bone). TGA-DTA analysis indicates complete removal of organic components at temperatures above 600°C. XRD analysis and refinement by the Rietveld method indicated the presence of a single crystalline phase, HAp, with a Ca/P ratio of 1.66. The results obtained by Raman spectroscopy and FTIR-ATR show the presence of characteristic vibrational bands of HAp. In conclusion, the results of this work showed that the methodology used allowed the production of a natural and crystalline hydroxyapatite, with a Ca/P molar ratio of 1.66, with potential for use in bone reconstruction.

Synthesis and characterization of hydroxyapatite from duck eggshell modified silver by gamma radiolysis method

Crystalline hydroxyapatite (HA) prepared from duck eggshell using the precipitation method. Duck eggshell used because it has higher calcium oxide (CaO) purity than another eggshell. The amount of duck eggshell calcinated to obtain calcium precursor then dropped with phosphoric acid wisely. The hydroxyapatite result modified with a silver (HA-Ag) using gamma radiolysis reduction. Hydroxyapatite powder added with an alcoholic silver ion precursor and followed by high energy gamma irradiation. This modification is to increase the antibacterial activity of hydroxyapatite for further medical applications. The results of the bacterial inhibitory test, showed the largest antibacterial clear zone in 25 kGy irradiation dose of HA-Ag. HA and HA-Ag characterized by FTIR, XRD, SEM and EDX. All characterization result support the forming of pure hydroxyapatite and the presence of a silver particle.

Impact of Glutamate Carboxylation in the Adsorption of the α-1 Domain of Osteocalcin to Hydroxyapatite and Titania.

One proposed mechanism of implant fouling is attributed to the nonspecific adsorption of non-collagenous bone matrix proteins (NCPs) onto a newly implanted interface. With the goal of capturing the fundamental mechanistic and thermodynamic forces that govern changes in these NCP recognition domains as a function of γ-carboxyglutamic acid (Gla) post-translational modification and surface chemistry, we probe the adsorption process of the most commonly occurring NCP, osteocalcin, onto a mineral and metal oxide surface. Here, we apply two enhanced sampling methods to independently probe the effects of post-translational modification and peptide structure on adsorption. First, well-tempered metadynamics was used to capture the binding of acetyl and N-methylamide capped glutamic acid and Gla single amino acids onto crystalline hydroxyapatite and titania model surfaces at physiological pH. Following this, parallel tempering metadynamics in the well-tempered ensemble (PTMetaD-WTE) was used to study adsorption of the α-1 domain of osteocalcin onto hydroxyapatite and titania. Simulations were performed for the α-1 domain of osteocalcin in both its fully decarboxylated (dOC) and fully carboxylated (OC) form. Our simulations find that increased charge density due to carboxylation results in increased interactions at the interface, and stronger adsorption of the single amino acids to both surfaces. Interestingly, the role of Gla in promoting compact and helical structure in the α-1 domain resulted in disparate binding modes at the two surfaces, which is attributed to differences in interfacial water behavior. Overall, this work provides a benchmark for understanding the mechanisms that drive adsorption of Gla-containing mineralizing proteins onto different surface chemistries.

Effect of a Sodium Fluoride-Releasing Rubber Cup on Hydroxyapatite Crystallinity of Human Enamel: FTIR Spectroscopy Analysis

Fluoride application is an important strategy to reduce demineralization and enhance remineralization in human teeth. This study aimed to evaluate the effect on enamel hydroxyapatite (HA) crystallinity (C) of a sodium fluoride-releasing rubber cup compared to a non-fluoride rubber cup, using Fourier Transformed Mid Infrared Spectroscopy (FTMIR) analysis. First class direct composite restorations were performed in ten sound extracted molars. Teeth were then divided into two groups (n=5): Control group, polished with non-fluoride rubber cup (noFHA), for 10 s; Tested group, polished with a sodium fluoride-releasing rubber cup (FHA), for 10 s. Samples were scraped off on the treated surfaces with abrasive paper and the dust was analyzed using FTMIR. Spectra were acquired in the range of 4000-400 cm-1 and each spectrum represented the average of 5 measurements. Phosphate (PO4) vibration at 604 cm-1 was used to analyze C: the full width at half maximum (FWHM) of noFHA was lower than the one of FHA; thus, sodium fluoride, contained in the rubber cup, increased C. The absorption at 1090 cm-1 can be considered an additional marker of C, indeed the peak of FHA was higher than the one of HA and noFHA, thus suggesting increasing and stabilizing of the enamel C. In conclusion, the tested sodium fluoride-releasing rubber cup could be an effective polishing system since it not only allows to polish the tooth surface, but also improves the C of enamel HA, thanks to the quick bond done by fluoride.

The pH Level Influence on Hydroxyapatite Phase Composition Synthesized with Hydrothermal Method

This paper reports the pH level influence on hydroxyapatite phase composition synthesized with hydrothermal method in Ca(OH)2-H3PO4, Ca(NO3)2-(NH4)2HPO4-NH4OH, Ca(OH)2-NH4H2PO4.The obtained samples were studied with X-Ray diffraction, Fourier Transform Infrared (FTIR) and Raman spectroscopy. The one phase Ca5H2O13P3 high crystallinity hydroxyapatite was synthesized with hydrothermal method at pH equal to 11. The crystallinity degree was calculated from the X-Ray diffraction pattern and became 0.96. The increasing pH level from 7 to 11 provides obtaining one phase hydroxyapatite at pH level 11 instead the two phase Ca9.04(PO4)6(OH)1.68, CaHPO4 at pH level 9 and CaPO3(OH), Ca(OH)2 at pH level 7.

Nano-size hydroxyapatite extracted from tilapia scale using alkaline heat treatment method

In biomedical research, hydroxyapatite (HAp) has been commonly used as the coating materials, filler and as a drug delivery system. This is mainly due to the similarity of the chemical composition of HAp to human bone and teeth that make it have excellent bioactivity and biocompatibility. Hence, the recovery of HAp from a natural resource such as from the animal scale and bone is a promising alternative to produce natural HAp, which is much similar to the human bone. Thus, in this research, the nano-size HAp was extracted from tilapia fish scale using alkaline heat treatment. The fish scale was pre-treated with 0.1% HCl to deproteinize the scale prior to the alkaline heat treatment. The alkaline heat treatment was performed in two stages to ensure complete removal of the organic compound from the tilapia scale. Upon completing the procedure, off white HAp powder was obtained. The HAp powder was characterised using X-ray diffraction analysis (XRD), field emission scanning electron microscopy analysis (FESEM), energy dispersive spectroscopy (EDS), and fourier-transform infrared spectroscopy (FTIR). The XRD pattern demonstrated that the obtained powder was a pure crystalline HAp. The FESEM micrograph revealed that the HAp powder exhibited rod shapes with a size ranged between 50 and 60 nm width and 30–200 nm length. The EDS result revealed that the extracted HAp powder had a Ca/P ratio of 1.74, which was higher compared to stoichiometric HAp. Lastly, the corresponding functional groups of PO43- and CO32– were identified using FTIR were corresponded to the HAp functional group. In summary, the natural HAp extracted from the tilapia scales using alkaline heat treatment method has the potential to be used as biomaterials for the biomedical implant.

Synthesis, microstructure and mechanical properties of tricalcium phosphate–hydroxyapatite (TCP/HA) composite ceramic

Tricalcium phosphate-hydroxyapatite (TCP/HA) is an important composite ceramic ubiquitously applied in biomedicine research. In this work, a novel design and synthesizing method for preparation of TCP/HA composites is proposed consisting in suspension mixing amorphous calcium phosphate (ACP) and hydroxyapatite (HA) ceramic powders with different weight ratios, and their compaction under a uniaxial pressure of 200 MPa and sintering at 1150 °C for 2 h. The obtained sintered bodies exhibited optimum hardness and fracture toughness of 5 GPa and 1.27 MPa m1/2, and values significantly improved as compared with those obtained with the traditional mechanical mixing method. The mechanical enhancement mechanism was mainly attributed to the good ACP and HA phase dispersion and ACP crystallization. SEM and HRTEM observations showed the suspension mixing method to allow amorphous spherical ACP and crystalline rod-like HA particles with size around 50 nm to uniformly disperse at the nano scale in the composite powder, which contributes to the excellent sinter ability. Furthermore, XRD results indicate that after sintering, nearly 100% of amorphous spherical ACP transformed to the crystalline β-TCP, which results in the nanoparticle shrinkage, porosity reduction and composite densification.

Osteogenic potential of human mesenchymal stem cells on eggshells-derived hydroxyapatite nanoparticles for tissue engineering.

Nanocrystalline hydroxyapatite (HAp) was synthesized from biowaste eggshells through sonication followed by the heat treatment. Calcium oxide as a precursor moiety for the synthesis of HAp was obtained through the heat treatment of eggshells at 900°C for 3 hr. The prepared HAp was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The appearance of the FTIR absorption peaks in between at 516-1031 and 3,636 cm-1 shows phosphate and hydroxyl groups in prepared HAp, respectively. The XRD-patterns indicate the formation of HAp started within 5 min of sonication. The SEM morphologies suggested that the synthesized HAp was highly crystalline and compact. We tested the elemental analysis of the synthesized HAp through X-ray fluorescence spectroscopy and inductively coupled plasma mass spectroscopy. The higher Ca/P ratio has observed in heat-treated HAp. These results show that heat treatment facilitates the formation of highly crystalline and compact HAp. Cytotoxicity and osteogenic potential of human mesenchymal stem cells (hMSCs) were also evaluated in the presence of HAp. No significant cytotoxicity was noted in the presence of HAp, suggested their biocompatibility. Enhanced osteogenesis of hMSCs occurred with HAp powder, confirming the feasibility in the treatment of osteogenesis. Thus, synthesized HAp has the potential to use a biomaterial in tissue engineering applications for bone tissues.

Characterization of Catla catla and Oreochromis niloticus fish scales derived hydroxyapatite scaffolds for regenerative medicine

Naturally derived biomaterials have been preferred since decades for the tissue regeneration to repair, replace, and improve the tissues/organs functionality. In the present study, the synthesis of raw fish scales derived hydroxyapatite scaffolds (FSHA) was carried out from two fish species namely, Catla (Catla catla) and Tilapia (Oreochromis niloticus). The control were chemically synthesized hydroxyapatite from gradual mixing of Ca(NO3)2 4H2O (0.40 M) and (NH4)2 HPO4 (0.24 M) solutions at room temperature, with maintaining pH at 11 with NH4OH. The raw powder was utilized to develop porous scaffold by using sacrificial template by sintering at 800 °C for two hours. The commercially available hydroxyapatite (sHA) were compared for the study as control. Further all group of powder and scaffold samples were characterized for their physico-chemical properties. The crystallinity and the compound purity, along with the chemical bond analysis were estimated by XRD and FTIR analysis. TGA was carried out to determine the thermal stability of the FSHA when subjected to temperature range 20–1000 °C. The morphological characterization of porosity and elemental composition and existence of other trace elements were carried out FESEM-EDS. The XRD analysis confirmed the synthesis of crystalline hydroxyapatite from fish scales and FTIR data indicated the presence of bonds supporting the cell-biomaterial interaction. The thermal stability of the developed fish scale derived scaffolds showed support towards physiological conditions. Thus, the performed study with the raw fish scales derived hydroxyapatite scaffolds and compared with synthetic hydroxyapatite as standard seems relevant towards the application for tissue regeneration.

Calcification Microstructure Reflects Breast Tissue Microenvironment

Microcalcifications are important diagnostic indicators of disease in breast tissue. Tissue microenvironments differ in many aspects between normal and cancerous cells, notably extracellular pH and glycolytic respiration. Hydroxyapatite microcalcification microstructure is also found to differ between tissue pathologies, including differential ion substitutions and the presence of additional crystallographic phases. Distinguishing between tissue pathologies at an early stage is essential to improve patient experience and diagnostic accuracy, leading to better disease outcome. This study explores the hypothesis that microenvironment features may become immortalised within calcification crystallite characteristics thus becoming indicators of tissue pathology. In total, 55 breast calcifications incorporating 3 tissue pathologies (benign – B2, ductal carcinoma in-situ - B5a and invasive malignancy - B5b) from archive formalin-fixed paraffin-embedded core needle breast biopsies were analysed using X-ray diffraction. Crystallite size and strain were determined from 548 diffractograms using Williamson-Hall analysis. There was an increased crystallinity of hydroxyapatite with tissue malignancy compared to benign tissue. Coherence length was significantly correlated with pathology grade in all basis crystallographic directions (P < 0.01), with a greater difference between benign and in situ disease compared to in-situ disease and invasive malignancy. Crystallite size and non-uniform strain contributed to peak broadening in all three pathologies. Furthermore, crystallite size and non-uniform strain normal to the basal planes increased significantly with malignancy (P < 0.05). Our findings support the view that tissue microenvironments can influence differing formation mechanisms of hydroxyapatite through acidic precursors, leading to differential substitution of carbonate into the hydroxide and phosphate sites, causing significant changes in crystallite size and non-uniform strain.

Anisotropic Epitaxial Behavior in the Amorphous Phase-Mediated Hydroxyapatite Crystallization Process: A New Understanding of Orientation Control.

The precise control of crystallization is a key in the construction and engineering of crystalline materials, especially in biomineralization. Although it is generally accepted that biomineral crystals have evolved from their amorphous precursors, there are intense debates about crystallographic orientation control. By using in situ high-resolution transmission electron microscopy, we herein reveal that hydroxyapatite (HAP) is produced through its epitaxial growth from amorphous calcium phosphate with a preferential c-axis orientation. Abnormally but interestingly, this anisotropic epitaxial crystallization priority along the c-axis is not affected by the existing HAP crystalline substrate, which is exactly the same on either {002} or {100} facets. Molecular dynamics simulations suggest this preference is correlated with the interfacial energetic controls at the amorphous-crystalline transition frontier. The orientation control of biominerals here shows the key role of the interface energy, rather that the organic molecules or matrices, which provides a complementary understanding of the general c-axis orientation control of HAP in various biomineralization cases and aids in the development of an alternative strategy for crystallization control of functional materials.

Fabrication of C-plane Oriented Hydroxyapatite Film on Amorphous SiO2 Substrate

We investigated a fabrication technique of c-plane oriented hydroxyapatite (HA) crystalline film on low cost amorphous SiO2 substrates to apply the orientation-controlled HA crystal to disposal biochips. An experiment was conducted by the pulsed laser deposition (PLD) method. We showed that a high quality HA crystalline film was able to be grown by using a fluoroapatite (FA) buffer layer, which was self-oriented on amorphous SiO2. A relationship between a FA film thickness and the HA quality was examined with an aim of minimizing a toxic risk of F to biomolecules, even if it was eluted from FA. It was found that the thickness of the FA film could be reduced to about 7.5 nm, at the same time, the crystallinity and a smoothness of HA were also excellent. A crystal growth model of FA on the amorphous SiO2 was also studied. We considered that highly reactive F in a laser-ablated-plume substituted for O on the substrate surface, which became a migration trap, causing 3-dimensional island growth as FA crystal nuclei. This model consistently agreed with a series of experimental results.