Kazushi Ohta

Electrophoretic Deposition of Hydroxyapatite Nanocrystal

Homogeneous nano-thin layer of hydroxyapatite (HAp) nanocrystals on the gold surface was fabricated by an electrophoretic deposition method (EPD); the HAp nanocrystals were dispersed into ethanol and the applied voltage was varied. The HAp nanocrystals were prepared by a wet method at 4 °C and 80 °C, which were characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The micro-thin layer of HAp nanocrystals was initially formed, and the ultrasonic treatments can remove the surplus nanocrystals from the surface. The nanostructure of the surface was investigated by atomic force microscopy and contact angle measurement. The thickness of coating layers was approximately 20nm and the root mean square (RMS) roughness was under 6.6 nm, which was clearly depended on the crystal sizes, applied voltages and applied times.

Interaction between hydroxyapatite and proteins by liquid chromatography using simulated body fluids as eluents

Hydroxyapatite (HAp) column chromatography for proteins using simulated body fluids (SBFs) as eluents was investigated in order to mimic the flow environment of human body fluid on the HAp surface in vivo. Acidic plasma proteins such as albumin, γ-globulin, and fibrinogen having carboxyl groups with a negative charge were suggested to adsorb at positively charged sites (Ca sites) on the HAp surface. These acidic plasma proteins were not even eluted at higher inorganic ion molarities of human body fluid. Whereas basic proteins such as papin, cytochrome c, and lysozyme were easily eluted at lower inorganic ion molarities of human body fluid due to existing Na+, Ca2 +, Mg2 + and (CH2OH)3CNH4+ ions in the eluents. The elution behavior of proteins using SBF in the presence or absence of glucose did not change. From these considerations, bone matrix proteins as acidic and neutral proteins would be considered an advantageous condition in order to adsorb on HAp in vivo.

Synthesis and Characterization of c-Axis Oriented Apatite Aggregates

The aggregates of c-axes oriented hydroxyapatite (HAp) cryst allites were synthesized by the hydrolysis of CaHPO 4·2H2O (DCPD) at 100 °C in 10mass% of NaOH solution. The HAp aggregate was of a plate-like form resembling DCPD. The me asur ments of X-ray diffraction pattern showed that the relative peak intensities of 002 and 004 diffractions incr eased with synthesis temperature. Some infrared peaks due to CO 3 were assigned to B-site substituted carbonate ions in HAp. From FE-SEM observation and XRD measurement, the crystallite s in the aggregate were kept in order and their c-axes were perpendicular to the wide surface of an original plate -like DCPD. Introduction Hydroxyapatite (Ca 10(PO4)6(OH)2, HAp) is the main inorganic component of hard tissues such as bone and tooth in human body and is also used as artificial bone [1], liquid chromat ographic packing [2] and scaffold for tissue engineering [3]. It is therefore impor tant to control surface reactivity of HAp crystals by controlling their morphology and aggregate. Few pa pers only were reported on the control of HAp crystal orientation, that is Langmuir-Blodgett (LB) [4] and electrochemical deposition methods [5] though many synthesis methods such as precipitation [6], hydrothe rmal [7], hydrolysis of salts [8-11] and sol-gel methods [12] have been developed. In the present pa p r, the synthesis of c-axes oriented HAp aggregates was tried on the basis of the hy drolysis of CaHPO4·2H2O (DCPD), i.e. 10CaHPO4·2H2O → Ca10(PO4)6(OH)2 + 20H2O + 10H + + 4PO4 . As regars this reaction, it is known that the atomic ratio of Ca /P v ries from 1.67 to 1.50, e.g. Ca10-x(HPO4)x(PO4)6-x(OH)2-x·nH2O (0≤x≤1) depending on chemical conditions in aqueous solutions [13], and Ca and PO 4 ions are partially replaced with other ions such as Na , Mg and CO3 2ions [14]. Materials and Methods HAp samples were prepared by the hydrolysis of DCPD (20g; Reagent grade, Kanto Chemical) in an aqueous solution (500ml; 10-30mass%) of NaOH (Reagent grade, Kanto Chem ical). The morphology of DCPD crystals was of a plate-like form and their m an particle size was 53μm. The solution was slowly stirred at a fixed temperature between 25 and 100 °C, and then the precipitates obtained were filtered, washed by distilled water and dried at 100 °C. Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 517-522 doi:10.4028/www.scientific.net/KEM.240-242.517

Evaluation of Pore Architecture in Hydroxyapatite/Collagen Scaffold Using Micro Computed Tomography

Hydroxyapatite/collagen (HAp/Col) composite scaffold with unidirectionally elongated pores (scaffold-U) was fabricated by the unidirectional solidification with ice growth and subsequent freeze-dry process. The pore architecture in the composite was evaluated by using scanning electron microscopy (SEM) and micro computed tomography (micro-CT) with a high resolution. The SEM observation showed that the scaffold-U had unidirectional pores elongated along the vertical direction (i.e. ice growth direction), however the horizontal cross-section showed quite different pore morphology: spindle-shaped pores with random direction. The 3-D micro-CT image of the scaffold-U simultaneously showed the microstructure of the unidirectionally elongated pore and the cross-sectional pore, indicating that the interconnected micropores were successfully fabricated along the ice growth direction. The micro-CT is a powerful tool for the visualization of 3-D pore structure.

Mesoporous Structure and Protein Adsorption Property of c-Axis Oriented Apatite Aggregates

Mesoporous HAp aggregates were composed of needle-like crystals that were aligned to the c-axes direction perpendicular to the flat surface of plate-like aggregates. The pore size distributions of the HAp aggregates increased with increasing heat treatment temperature e.g. 3-20 and 26-52 nm, respectively, before and after heat-treated at 600 °C. The adsorption proteins on the mesoporous HAp aggregates were investigated by liquid chromatography using the HAp aggregates as an adsorbent. Elution molarity ratios of acidic proteins on the mesoporous HAp aggregates before and after heat-treatment at 600 °C increased with increasing molecular weight in the order of ferritin > fibrinogen > catalase > albumin, whereas the elution molarity ratios of basic proteins were considerably lower than those of acidic proteins. These results suggested that penetration of the large size acidic proteins into the pore of the as-prepared mesoporous HAp aggregate was slightly inhibited but were the proteins could easily penetrate into the pore of the heat-treated mesoporous HAp aggregates and then were selectively adsorbed on the mesoporous wall consisting of the a-surface of the HAp aggregate. Conversely, the basic proteins could be adsorbed on the wide outer surface of the plate-like HAp aggregates. Therefore, the elution molarity ratios of basic proteins decreased with decreasing the specific surface area by the heat treatment, independent of the mesoporous structure.