Zhefeng Xu

Synthesis and luminescence properties of Eu(III)-doped nanoporous silica spheres.

Europium (III) (Eu(3+))-doped nanoporous silica spheres were synthesized, and the states of Eu(3+) ions in the silica framework structure were investigated. The ordered nanopores were preserved with the doping at the Eu(3+) molar concentration to Si up to 10 mol%, and the O-Si-O and Si-OH groups in the structures were clearly rearranged with the doping, indicating the interaction of Eu(3+) with the O atoms. The significant morphological changes in the spheres were observed with the doping. The photoluminescence spectral shapes due to the transitions of (5)D(0)-(7)F(1) and (5)D(0)-(7)F(2) were indicative of the presence of the Eu(3+) in an environment of a low symmetry. It was found that the Eu(3+) was located inside the silica framework to electrostatically interact with the environmental O atoms, which would prevent the aggregation among Eu(3+) ions to show the efficient luminescence. Therefore, the interactions between the Eu(3+) ions and silica framework structures in the spheres were successfully clarified.

Synthesis of luminescent nanoporous silica spheres functionalized with folic acid for targeting to cancer cells.

Luminescent europium(III)-doped nanoporous silica nanospheres (Eu:NPS) were successfully synthesized, and a folate N-hydroxysuccinimidyl ester (FA-NHS) molecule as a targeting ligand for cancer cells was immobilized on the nanosphere surfaces through mediation of the 3-aminopropyltriethoxysilane (APTES) adlayer. The ordered nanopores were preserved by the immobilization, and the specific surface area decreased only with the APTES immobilization, suggesting that the FA-NHS was predominantly immobilized on the outer surface of the nanopores. The photoluminescence of the nanospheres functionalized with folic acid (FA) exhibited a characteristic peak due to the interactions (e.g., energy transfer) between FA and Eu(3+), and further the orange luminescence could be clearly detected by fluorescence microscopy in air and water. Furthermore, the nanospheres highly dispersed in cell culture medium exhibited nontoxicity in the cellular proliferation stages of the Hela cancer cells and NIH3T3 fibroblasts and specifically bind to the Hela cells. The nanospheres after the binding and uptake also showed intense luminescence from the outer/inner cell surfaces for the culture time of 4 days. Therefore, the luminescent FA-functionalized Eu:NPS nanospheres could be used for specific targeting and imaging abilities for cancer cells.

Immobilization of folic acid on Eu3+-doped nanoporous silica spheres.

Folic acid (FA) was immobilized on Eu(3+)-doped nanoporous silica spheres (Eu:NPSs) through mediation of the 3-aminopropyltriethoxysilane adlayer. The ordered nanopores of Eu:NPS were preserved by the immobilization. The FA-immobilized Eu:NPSs showed the characteristic photoluminescence peak due to interactions between the FA molecules and Eu(3+) ions, and highly dispersed stability in phosphate buffered saline.

Rapid oriented fibril formation of fish scale collagen facilitates early osteoblastic differentiation of human mesenchymal stem cells

We studied the effect of fibril formation of fish scale collagen on the osteoblastic differentiation of human mesenchymal stem cells (hMSCs). We found that hMSCs adhered easily to tilapia scale collagen, which remarkably accelerated the early stage of osteoblastic differentiation in hMSCs during in vitro cell culture. Osteoblastic markers such as ALP activity, osteopontin, and bone morphogenetic protein 2 were markedly upregulated when the hMSCs were cultured on a tilapia collagen surface, especially in the early osteoblastic differentiation stage. We hypothesized that this phenomenon occurs due to specific fibril formation of tilapia collagen. Thus, we examined the time course of collagen fibril formation using high-speed atomic force microscopy. Moreover, to elucidate the effect of the orientation of fibril formation on the differentiation of hMSCs, we measured ALP activity of hMSCs cultured on two types of tilapia scale collagen membranes with different degrees of fibril formation. The ALP activity in hMSCs cultured on a fibrous collagen membrane was significantly higher than on a non-fibrous collagen membrane even before adding osteoblastic differentiation medium. These results showed that the degree of the fibril formation of tilapia collagen was essential for the osteoblastic differentiation of hMSCs.

Preparation of copper–graphite composite particles by milling process:

The fabrication of copper–graphite composites by a milling process was investigated using a centrifugal ball mill. The copper particles were homogeneously milled in a graphite vessel, and the reaction time was varied. Scanning electron microscopy images clearly revealed that a fragment of graphite ground by the copper particle adheres to the copper particle surface, indicating the formation of a copper–graphite composite. The composite graphite amount per 1 g of copper particles increased to 0.46 mg at the milling time 5 min, and subsequently decreased to 0.25 mg at 60 min, indicating the suitable milling-time for the interfacial adhesion. When using only the copper particles, the naturally oxidized layer on the surface decreased with milling. On the other hand, when using only the graphite, the characteristic graphite structure is disrupted and the defect structure increased with milling. Thus, the new copper surface generated by milling strongly reacts with the defect structure of the graphite. It is suggested that the interfacial bonding between the copper and graphite was attributed to a Van der Waals attraction and/or binding force due to oxygen atoms located at the interface.

Mechanochemical fabrication of iron–graphite composites

The fabrication of iron–graphite composites was investigated using a milling process. Based on the milling time of the process, the average particle size of the host iron particles decreased to 10 µm. The size of the graphite particles decreased to a nanometer scale, resulting in the graphite strongly adhering to the iron surfaces. Raman spectra revealed that the graphite aromatic ring structure disappeared and the iron near-surface layer was changed to iron oxide phases. The dangling bond of the fragmented graphite combined with the oxidized iron surface by interfacial binding to efficiently form the interfacial composites.

Mechanochemical surface modification of carbon fibers using a simple rubbing method

A simple rubbing treatment was used to mechanochemically modify the surface of polyacrylonitrile-based carbon fibers and its effect on their surface structure and functional groups was studied using several surface characterization techniques. To control the mechanochemical effect, the shear forces accompanying rubbing were kept constant. Scanning electron microscopy tests and the peak positions and widths of the main Raman spectroscopy bands indicated that there were no morphological changes to the carbon fibers following rubbing. In contrast, X-ray photoelectron spectroscopy showed an increase in oxygen-containing functional groups; in addition to hydroxyl species, the main groups introduced were alkoxide, carbonyl, and carboxyl groups. The ratio of carboxyl groups on the carbon fiber surface increased with the shear force magnitude, indicating carbon surface oxidation. The difference between the Raman and X-ray photoelectron spectroscopy results indicates that the modification was confined to the first few atomic layers; therefore, this rubbing method is capable of producing efficient mechanochemical surface modification of carbon fibers. This technique is simple, is relatively inexpensive, and is applicable to carbon fiber-reinforced plastic processing techniques.

Prediction of mechanical properties on zinc system alloys and their application to high temperature lead-free solder

The effectiveness of the electronic parameter was evaluated in order to predict the mechanical properties of zinc system alloys for high temperature application. Firstly, the relation of ultimate tensile strength or elongation and s-orbital energy level (Δ Mk) of already reported Zn system multicomponent alloys were investigated. According to this relation, the lead-free Zn-Al-Sn system alloys have been proposed in order to satisfy both the tensile strength of 200 MPa and elongation of 5 %. Promising compositions of alloys were Zn-4Al-7Sn, Zn-10Al-0.5Sn and Zn-10Al-2Sn in mass % and their Δ Mk values were 0.079, 0.080 and 0.089, respectively. Proposed alloys showed tensile strength of 195-225 MPa depending on increment of Δ Mk values, and elongation of 4.5-5.1 %. The optimization of compositions on Zn alloys was found to be speedy and precisely achieved using the Δ Mk parameter. The proposed alloys also showed liquidus temperatures of 645-700K, indicating that the high temperature lead-free solders can be applied for power semiconductor devices packages, etc. In addition, the contact angles between Cu plate and the proposed alloys Zn-4Al-7Sn, Zn-10Al-0.5Sn and Zn-10Al-2Sn at 973 K in the Ar stream are 33.8°, 73.5°and 50.1°, respectively.