PENAFLOR TANIA

Apatite nanoparticles are biocompatible nanomaterials, so their film formation on biodevices is expected to provide effective bonding with living organisms. However, the biodevice-apatite interfaces have not yet been elucidated because there is little experimental evaluation and discussion on the nanoscale interactions, as well as the apatite surface reactivities. Our group has demonstrated the biomolecular adsorption properties on a quartz crystal microbalance with dissipation (QCM-D) sensor coated with apatite nanoparticles, demonstrating the applicability of apatite nanoparticle films on devices. Therefore, it is important to clarify the biodevice-apatite nanointerfaces by characterizing their physicochemical properties. This research aims to control the apatite nanoparticle surfaces using different types of pH adjusters as well as to investigate biodevice-apatite interfaces. In this study, tetramethylammonium hydroxide, sodium hydroxide, and potassium hydroxide were used to adjust the pH during the synthesis of apatite nanoparticles. As a result, it was found that the ratio of Ca-deficient hydroxyapatite phase to B-type carbonate ion-substituted hydroxyapatite phase could be controlled by adjusting the OH- concentration and that the formation of B-type carbonate ion substituted hydroxyapatite phase was demonstrated in terms of the charge compensation because hydrogen phosphate ion in the non-apatitic layer would be diffused and substituted inside the apatite core structure by the replacement of carbonate ion. By contrast, the phosphate ions in the core structure were moved and contained in the non-apatitic layer, and the proportion of phosphate ions in the non-apatitic layer increased. The surface changes of the nanoparticles provide an effective biodevice surface coating. It was observed that the thickness of the electrophoretically deposited nanoparticles clearly increased with the proportion of phosphate ions in the non-apatitic layer. Furthermore, the formation of the hydration layer with immersion in biological fluid was evaluated. It was inferred that the water molecules in the hydration layer interacted with the substituted ions and remained as nonfreezing water layer on the top surface of the nanoparticles, while the abundant phosphate ions newly interacted with the water molecules in the non-apatitic layer, thus increasing the proportion of intermediate water. These results indicated that the hydrogen phosphate and phosphate ions were retained in the non-apatitic layer on the top surfaces of apatite nanoparticles, so that the thickness of the electrophoretically deposited film and the weight fraction of the hydrated layer can be controlled by the component ratio of phosphate ions in the non-apatitic layer. It is expected that surface coating technology using apatite nanoparticles will be applied for biodevices.

Biological hydroxyapatite (HA) contains the different minor ions which favour its bio-reactivity in vivo. In this study, the preparation of HA particles containing both silicate and carbonate ions under the presence of sodium silicate was investigated, and the physicochemical properties were evaluated according to the contents and states of silicate and carbonate ions. The increment in the silicate ion reduced the crystallinity and expanded the crystalline size along with a-axis. Solid-state29 Si–NMR spectra indicated the increase in the adsorption of oligomeric silicate species on the HA particle surfaces in addition to the substitution state of silicate ions, suggesting the occurrence of the surface coating of silicates on the surfaces. The possible states of carbonate and silicate ions at the HA surfaces will provide the bioactivity.

Alpha-tricalcium phosphate (α-TCP), which can be converted to calcium-deficient hydroxyapatite (HA) by hydrolysis reaction, has been researched as a bone filling. Although the composites of α-TCP with various organic molecules can exhibit a novel functionality, the reaction based on the addition of the interactive organic molecules has not been understood. Investigation of the hydrolysis conversion process under various conditions can lead to the elucidation of the biomineralization process. In this study, we investigated the hydrolysis conversion of α-TCP to HA in the presence of orotic acid (Ort). As a result, the conversion rate from α-TCP to HA at the reaction time of 3 h was improved to be more than five times as compared to that in the absence of Ort. Moreover, the addition of Ort promoted the crystal growth and suppressed the crystal growth in the m-plane direction. Furthermore, the mechanism for promoting HA formation is assumed to be related to the molecular structure of Ort, which is capable of forming the interactions between carboxylate and Ca2+ ions.

We successfully synthesized the photofunctionalized octacalcium phosphate (OCP) with layered structures and high biosafety. Specifically, two systems of europium(III) ion (Eu3+)-doped OCP particles (OCP:Eu) and succinate (Suc)-modified OCP:Eu particles (Suc-OCP:Eu) were synthesized by substituting an Eu3+ ion with a Ca2+ ion of OCP while maintaining the layered structures. The OCP:Eu and Suc-OCP:Eu (crystal shape sizes: ca. 0.4-1.0 μm) exhibited the strong luminescence based on the f-f transition of the Eu3+ ion, and the luminescence intensity and quantum efficiency increased with increasing the initial Eu molar concentration to Ca+Eu up to 10 mol %, indicating the suppression of the concentration quenching by the layered structures. The intensity and efficiency of Suc-OCP:Eu were about 1.3 times as high as the OCP:Eu, indicating that the hybridization with Suc ions leads to the enhancement of the luminescent properties. The sustained release of the Suc ion from Suc-OCP:Eu in simulated body fluid (SBF) was achieved for more than 168 h, and the release rates at the immersion time of 168 h were 85, 60, and 20% for the Suc-OCP:Eu at the initial molar concentrations of Eu to Ca+Eu of 0, 5, and 10 mol %, respectively. Moreover, the intensity, efficiency, and layer structure of Suc-OCP:Eu were maintained by the immersion time of 168 h. Thus, the effect of the hybridization with Suc ions on the luminescence properties of the Eu3+ ion, and that of the doping on the release of the Suc ion in SBF was clarified. We achieved the synergistic functions of both photofunctions and organic molecules in the layered structure of the biocompatible OCP, and the sustained release of organic molecules in biological solution.

The Zn−substituted HAp NPs were successfully synthesized at the initial molar ratios of (Ca+Zn)/P at 1.67 and 2.00, providing the stoichiometric Zn:HAp and carbonate Zn:CHAp NPs and the maximum Zn ion substitution in the structure is ca. 5 mol% by the XRF analysis. The 10.0−Zn:HAp and 10.0−Zn:CHAp NPs contain 0.76 and 0.68 wt% of Zn at the maxima, respectively, which is safety for cells in the animal body. The increase in the Zn ion concentration significantly induced the carbonate ion including. The crystalline size decreased with the increasing Zn ion substitution, indicating the suppression of the crystal growth by the Zn ion addition to resultantly increase the specific surface area. TEM observation clearly indicated that the needle-like shape nanoparticles were changed to the particulate shapes with increasing the Zn ion substitution to form aggregation form with the mesostructures. Thus, the morphological control by the Zn−substitution in stoichiometric and carbonate HAp NPs was successfully achieved. The Zn:HAp and Zn:CHAp NPs were deposited on the Ti-PDMS by an EPD technique obtaining an uniform and transparent Zn:HAp and Zn:CHAp NPs. The fibroblasts on the Zn−substituted HAp NP films exhibited good adhesion/spreading. In particular, the Zn:CHAp NP films are very cytocompatible. By the antibacterial test, the viable E. coli DH5α reduction was significantly observed in the films with the higher Zn amounts. Resultantly, the 5.0 and 10−Zn:CHAp NP films. Furthermore, all the nanoparticle films electrically plated on a Ti-PDMS substrate give no cytotoxicity, and the Zn:CHAp NP films significantly provided the bioactive properties for fibroblast ingrowth, suggesting the effect of Zn and carbonate ions on the cytocompatibility. Summarizing, The Zn:HAp and Zn:CHAp NP films with the optimized cytocompatible and antibacterial properties were successfully prepared as the Ti-PDMS surface modification technique.[Doctoral thesis] Doctoral supervisor: Dr. Motohiro Tagaya