The Dry Sliding Wear Properties of Nano-Sized TiCp/Al-Cu Composites at Elevated Temperatures.

Nano-sized ceramic particle reinforced aluminum composites exhibit excellent room-temperature mechanical properties. However, there is limited research on the dry sliding wear behavior of those composites at elevated temperatures, which should be one of the major concerns on elevated temperature applications. Here the Al-Cu composites reinforced with nano-sized TiCp were fabricated. The dry sliding wear behaviors of the nano-sized TiCp/Al-Cu composites at various temperatures (140-220 °C) and loads (10-40 N) with different TiCp contents were studied, and the results showed that the nanocomposites exhibited superior wear resistance. For instance, the relative wear resistance of the 0.5 wt.% nano-sized TiCp/Al-Cu composite was 83.5% higher than that of the Al-Cu matrix alloy at 180 °C under 20 N, and was also 16.5% higher than that of the 5 wt.% micro-sized TiCp/Al-Cu composite, attributed to the pronounced Orowan strengthening effect of nanoparticles. The wear rates of the nanocomposites were always lower than those of the Al-Cu matrix alloy under the same test condition, which increased with the increase in temperature and load and with the decrease in TiCp content.

[Detection and functional analysis of CD-4+ CD-25+ regulatory T cells in the peripheral blood of patients with generalized aggressive periodontitis].

OBJECTIVE: To investigate the changes of proportion and suppression function of CD-4+ CD-25+ regulatory T cells in the peripheral blood of patients with aggressive periodontitis. METHODS: Flow cytometric analysis was used to detect the frequency of CD-4+ CD-25+ regulatory T cells in the peripheral blood of 16 patients with generalized aggressive periodontitis and 17 patients with chronic periodontitis, as well as 17 periodontal healthy controls. Furthermore, CD-4+ CD-25+ regulatory T cells and CD-4+ CD-25- T cells were separated from peripheral blood of each enrolling subject using magnetic cell sorting technology. The direct suppression effect of CD-4+ CD-25+ regulatory T cells on CD-4+ CD-25- T lymphocytes proliferation was performed by the mixed lymphocytes reaction and measured by 3H-thymidine radioactive assay. RESULTS: The patients with generalized aggressive periodontitis had a lower frequency of CD4+ CD-25+ regulatory T cells (9.71 +/- 4.01)% in the peripheral blood than periodontal healthy controls [(14.72 +/- 3.51)%] and chronic periodontitis patients [(17.01 +/- 5.16 )%], P < 0.05. A significant decrease was found in the suppression function of CD-4+ CD-25+ regulatory T cells from peripheral blood of patients with generalized aggressive periodontitis when co-cultured with CD-4+ CD-25- T lymphocytes in the proportion of 2 : 1, 1 : 1 and 1 : 2 as compared with chronic periodontitis patients and periodontal healthy controls (P < 0.05). CONCLUSIONS: Diminished numbers and decreased suppression function of CD-4+ CD-25+ regulatory T cells were found in patients with generalized aggressive periodontitis.

[Bioassay of the soluble human tumor necrosis factor receptor I recombinant plasmid expression in vitro].

OBJECTIVE: To detect the expression of recombinant plasmid PcDNA3.1-sTNFRI in vitro and evaluate the bioactivity of expressed sTNFRI. METHODS: CHO cells were transfected with recombinant plasmid PcDNA3.1-sTNFRI by liposome. sTNFRI in cell culture supernatant was detected by ELISA and sTNFRI blockage of TNF-alpha cytotoxicity in L929 cells evaluated by MTT assay. RESULTS: The expression of sTNFRI in transfected cell culture supernatant was higher than control groups (P < 0.001). The expressed sTNFRI could significantly neutralize TNF-alpha cytotoxicity in L929 cells. CONCLUSIONS: These results showed that the recombinant plasmid PcDNA3.1-sTNFRI can be expressed in mammalian cells and the recombinant sTNFRI has biological function.

[Construction of eukaryotic expression clone for human amelogenin].

OBJECTIVE: To construct-the eukaryotic expression clone for human amelogenin. METHODS: Total RNA was isolated from human fetal tooth buds. RT-PCR was used to amplify the amelogenin encoding region, and the amplified fragment for human amelogenin was inserted into eukaryotic expression vector PcDNA 3.1. The positive clones were selected and analyzed by restriction endonuclease mapping and DNA sequencing. RESULTS: 570 bp fragment was produced by RT-PCR; it was of the same size as expected based on human ameloginin mRNA encoding area length. The sequence of the inserted fragment from the recombinant clone PcDNA 3.1-AMG was consistent with that of AMELX from GenBank with one mismatch on 485 from G to C, without affecting the amino acid sequence. CONCLUSION: The eukaryotic expression clone PcDNA 3.1-AMG was successfully constructed with the properly inserted DNA sequence encoding mature human amelogenin.