J.-M. Yang

Influence of 8DSS Peptide on Nano-mechanical Behavior of Human Enamel

Aspartate-serine-serine (DSS) repeats are abundant in naturally occurring proteins that are critical for tooth formation. We recently developed octuplet repeats of aspartate-serine-serine (8DSS) peptides to promote the nucleation of calcium phosphate carbonate from free ions. In this paper, we report a possible role of 8DSS in promoting mineral deposition onto human enamel. Human enamel specimens were demineralized, exposed briefly to 8DSS solution, and then exposed to simulated body fluid that favors mineral deposition. At various stages of treatment, nano-mechanical behaviors, namely, hardness and elastic modulus, were determined by nano-indentation. Nano-indentation results showed that 8DSS treatment effectively improved the mechanical and elastic properties of demineralized enamel. The values of hardness and elastic modulus for the 8DSS-treated enamel were significantly higher than those of surfaces without 8DSS treatment. Furthermore, 8DSS peptides promoted the uniform deposition of nano-crystalline calcium phosphate carbonate over demineralized enamel surfaces and reduced surface roughness of demineralized enamel.

Influences of ionic concentration on nanomechanical behaviors for remineralized enamel

This study evaluates the influences of 8DSS peptide and ionic concentrations of simulated body fluid on remineralization behaviors. The polished enamel specimens were acid-demineralized, exposed briefly to 8DSS peptide solution, and then immersed into simulated body fluid (SBF) that favors mineral deposition. At various stages of treatment, nanohardness and elastic modulus were determined by nanoindentation. The results show that the nanomechanical properties of the acid-demineralized enamel were greatly improved as increasing the ionic concentrations of SBF due to the acceleration of mineral deposition. Additionally, the demineralized enamel, treated with 8DSS peptide and immersed into SBF×2 solution, possesses the highest values of nanohardness and elastic modulus resulting from the combinative effects of surface roughness, morphology, microstructure and crystallinity of the newly formed nanocomposite of calcium phosphate carbonate and hydroxyapatite. The formation of pores in the subsurface induced a reduction in the nanomechanical properties for the enamel subjected into SBF×3 solution.

Reinforcement/Matrix Interaction in Sic Fiber-Reinforced Ni 3 a1 Matrix Composites

The interfacial reaction characteristics of two different types of SiC fibers with Ni3Al (Ni-Al-Cr-Zr-B) matrix have been investigated. The microstructure and chemical compositions across the reaction zones have been analyzed quantitatively using microscopy and electron probe microanalysis. In both types of SiC/Ni3Al composites, it was found that Ni was the dominant diffusing species responsible for the overall reaction. The C-rich layer outside the SCS-6 fiber provided an incubation period, but could not stop the inward diffusion of Ni. It could, however, effectively stop the diffusion of Al, Zr, and Cr. No significant increase in reaction zone thickness after exposure at temperatures below 900/degree/C for up to 100 hours was observed. When the C-rich layer was depleted, a rapid increase in reaction zone thickness and the formation of multilayer reaction products occurred. In the case of Sigma/Ni3Al composite, extensive reaction between the fiber and the matrix occurred at all the temperatures studied. Diffusion barrier coating for both types of fibers is required to develop nickel aluminide matrix composites. 17 refs., 3 figs.

Mechanical Properties and Deformation Mechanisms of an A1 2 O 3 Fiber-Reinforced Nial Matrix Composite

The mechanical behavior of a continuous Al 2 O 3 fiber-reinforced NiAl matrix composite was investigated. The interfacial mechanical properties were measured at room temperature using a fiber pushout test. Tensile test was conducted at room and elevated temperatures. Four-point bending creep test was also conducted at 700 °C. The key microstructural parameters controlling the mechanical behavior and fracture processes were identified. The effect of fiber surface coating on the interfacial properties and mechanical behavior of the composite was also studied.

Effects on Hardness and Elastic Modulus for DSS-8 Peptide Treatment on Remineralization of Human Dental Tissues.

Dental remineralization may be achieved by mediating the interactions between tooth surfaces with free ions and biomimetic peptides. We recently developed octuplet repeats of aspartate-serine-serine (DSS-8) peptide, which occurs in high abundance in naturally occurring proteins that are critical for tooth remineralization. In this paper, we evaluated the possible role of DSS-8 in enamel remineralization. Human enamel specimens were demineralized, exposed briefly to DSS-8 solution, and then exposed to concentrated ionic solutions that favor remineralization. Enamel nano-mechanical behaviors, hardness and elastic modulus, at various stages of treatment were determined by nanoindentation. The phase, microstructure and morphology of the resultant surfaces were characterized using the grazing incidence X-ray diffraction (GIXD), variable pressure scanning electron microscopy (VPSEM), and atomic force microscopy (AFM), respectively. Nanoindentation results show that the DSS-8 remineralization effectively improves the mechanical and elastic properties for demineralized enamel.

Influence of DSS-8 on the remineralisation of Dentine

Dental remineralization may be achieved by mediating the interactions between tooth surfaces with free ions and biomimetic peptides. We recently developed octuplet repeats of aspartate-serine-serine (DSS-8) peptide, which occurs in high abundance in naturally occurring proteins that are critical for tooth remineralization. In this paper, we evaluated the possible role of DSS-8 in dentin remineralization. Human dentin specimens were demineralized, exposed briefly to DSS-8 solution, and then exposed to concentrated ionic solutions that favor remineralization. Dentin nano-mechanical behaviors, hardness and elastic modulus, at various stages of treatment were determined by nanoindentation. The phase, microstructure and morphology of the resultant surfaces were characterized using grazing incidence X-ray diffraction, variable pressure scanning electron microscopy, and atomic force microscopy, respectively. Nanoindentation results show that DSS-8 remineralization effectively improves the mechanical and elastic properties of native dentin. Moreover, the hardness and elastic modulus for the DSS-8 treated dentin were significantly higher than surfaces remineralized without DSS-8.

Fracture and Fatigue Resistance of Ag/Ta-coated SCS-6/Ti 3 Al Composites

The effect of a Ag/Ta coating on the fracture resistance of a notched SCS-6 fiber-reinforced Ti 3 Al matrix composite under both static and fatigue loading was investigated. The crack propagation patterns and damage mechanisms under various loading conditions were characterized and compared with the uncoated composite counterparts. The results show that the Ag/Ta-coated composites exhibit typical mode-I failure patterns under both static and fatigue loading, while mixed mode-I & H failure patterns were observed in the uncoated SCS-6/Ti-25-10 composite. Localized interfacial debonding, matrix cracking and fiber fracture in the crack wake were the responsible damage mechanisms for the Ag/Ta-coated SCS-6/Ti-25-10 composite. Extensive interfacial debonding, crack splitting and branching, however, were found to be the dominant mechanisms in the uncoated SCS-6/Ti-25-10 composite.