Yao-Hung Tseng

Adsorption of a Statherin Peptide Fragment on the Surface of Nanocrystallites of Hydroxyapatite

Statherin is an active inhibitor of calcium phosphate precipitation in the oral cavity. For many studies of the interaction between statherin and hydroxyapatite (HAp), the samples are prepared by a direct mixing of statherin or its fragment with well-crystalline HAp crystals. In this work, the HAp sample is precipitated in the presence of peptide fragment derived from the N-terminal 15 amino acids of statherin (SN-15). The in situ prepared HAp crystallites are nanosized, leading to a significant increase of the peptide amount adsorbed on the HAp surface. The enhancement in NMR sensitivity allows, for the first time, the measurement of a two-dimensional 13C-13C correlation spectrum for a 13C uniformly labeled peptide sample adsorbed on mineral surface. The measurement time is about 18.5 h at a field strength of 7.05 T. Preliminary results suggest that there may exist two different mechanisms for the interaction between SN-15 and HAp. In addition to the one which will cause a conformational change near the N-terminal, SN-15 may also be absorbed on the HAp surface by simple electrostatic interaction, without any significant conformational changes of the peptides.

The origin of ZnO twin crystals in bio-inspired synthesis

A fabrication of uniform nacre-like hierarchical nanostructures of faceted ZnO twin-crystals was established by a hydrothermal route using gelatin as the structure-directing agent, zinc nitrate hexahydrate as the Zn source, and hexamethylenetetramine to control alkalinity. Early stage growth of ZnO twin-crystals was investigated by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A new formation mechanism is proposed. In the bio-inspired synthesis, Zn5(NO3)2(OH)8·2H2O nanoplatelets (10 to 20 nm in size) undergo orientated aggregation with gelatin to form Zn5(NO3)2(OH)8·2H2O/gelatin mesocrystalline nanoplates (150 to 400 nm in diameter and 20 to 50 nm in thickness). Surface re-crystallization of these nanoplates leads to two thin layers of ZnO separated by gelatin molecules. These double-layer nanoplates, negatively charged on both outer surfaces, are the cores of the twin-crystals. The dipolar Zn5(NO3)2(OH)8·2H2O nanoplates then stack on both sides of the double-layer nanoplates, followed by a phase transformation to ZnO. Eventually, twin-crystals are constructed in a manner reminiscent to that of an hourglass. The hexagonal morphology of the twin-crystals resulted from a late re-crystallization. The microstructure of the ZnO twin-crystals is very similar to the brick and mortar arrangement found in nacre. The present study is expected to shed light on the formation mechanism of many naturally occurring biominerals, as well as many other synthetic twin-crystals.

Dipole Field Guided Orientated Attachment of Nanocrystals to Twin‐Brush ZnO Mesocrystals

Mesocrystals of ZnO were synthesized hydrothermally by using gum arabic as a structure-directing agent. Their hierarchical structure has a unique twin-brush form consisting of vertically aligned nanorods in a single-crystal-like porous form. The formation mechanism of the twin-brush ZnO was investigated by quenching a series of samples at different times and examining them by TEM, SEM, and XRD. The alignment of ZnO crystal units can be modulated by adding simple salts such as KCl to change the units from nanorods to nanoplates. This can be explained by screening the dipolar force of the polar crystal. Local cathodoluminescence of twin-brush ZnO was used to follow the local structure changes.

Treatment of tooth fracture by medium energy CO2 laser and DP-bioactive glass paste: Thermal behavior and phase transformation of human tooth enamel and dentin after irradiation by CO2 laser

Acute trauma or trauma associated with occlusal disharmony can produce tooth crack or fracture. Although several methods are proposed to treat the defect, however, the prognosis is generally poor. If the fusion of a tooth fracture by laser is possible it will offer an alternative to extraction or at least serve as an adjunctive treatment in the reconstruction. The responses of soft tissues to lasers of different wavelengths are fairly well known, but the reactions of hard tissues are still to be understood. The purpose of this research was to study the feasibility of using a medium energy continuous-wave CO2 laser and a low melting-point bioactive glass to fuse or bridge tooth fractures. The present report is focused on the first part of the research, the analysis of changes in laser-irradiated human tooth enamel/dentin by means of X-ray diffractometer (XRD), Fourier-transforming infrared spectroscopy (FTIR), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and scanning electron microscopy (SEM). After CO2 laser irradiation, there were no marked changes in the X-ray diffraction pattern of the enamel when compared to that before laser treatment. However, a small peak belonging to α-TCP appeared at the position of 2θ=30.78°C. After being treated with CO2 laser, the dentin showed much sharper peaks on the diffraction patterns because of grain growth and better crystallinity. α-TCP and β-TCP were identified after laser treatment. In the FTIR analysis, an HPO4-2 absorption band was noted before laser treatment disappeared after the irradiation. No significant change in the absorption band of HPO4-2 was found on the FTIR curves of enamel after laser treatment. The results of DTA/TGA indicated that loss of water and organic materials occurred in both enamel and dentin after laser treatment. Under SEM, melting and resolidification occurred in both enamel and dentin by medium energy of CO2 laser. This implies that using a continuous-wave CO2 laser of medium energy density to fuse a low melting-point bioactive glass to the enamel/dentin is possible. We believe these phase changes and thermal data can make a useful guide for future studies on the thermal interaction and bridging mechanism between the bioactive glass and enamel/dentin under CO2 laser irradiation.

Solid-state P-31 NMR study of the formation of hydroxyapatite in the presence of glutaric acid.

We demonstrate that glutaric acid can be used to prepare nanorods of hydroxyapatite under hydrothermal condition at 100 °C with a Ca2+:glutaric acid molar ratio of 1:4. Frequency‐switched Lee–Goldburg irradiation is employed to obtain high‐resolution 31P{1H} correlation spectra of the reaction mixture at two different reaction periods, from which it is shown that octacalcium phosphate is the precursor phase of the final hydroxyapatite product. In addition, the spectra show that a substantial amount of water molecules is trapped between the glutaric acid and the hydroxyapatite surface, indicating that water molecules may play a prominent role in the noncovalent interaction of the glutaric acid and the HAp surface. Copyright