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High-strength and high-modulus polyimide fiber is a kind of high-performance organic fiber rapidly developing in recent years. Taking advantage of its high strength and toughness and being combined with carbon fiber, it is expected to make a balance between stiffness and toughness, so as to afford a kind of structural composite with high strength and toughness. In this study, a series of hybrid fiber reinforced composites were prepared with high-strength and high-modulus PI fiber and carbon fiber as reinforcements. The effects of stacking sequence and hybrid ratio on the tensile, compressive and flexural properties and failure modes of the composites were systematically investigated. Experimental results showed that tensile, compressive and flexural properties of the hybrid composites were markedly improved compared with polyimide fiber composite, while failure strain and failure energy were superior to those of the carbon fiber composites. The flexural properties were largely affected by the stacking sequence. Hybrid composites with carbon fiber as the compressive side showed higher flexural strength, while the ones with carbon fiber as both compressive side and tensile side had higher flexural modulus.

Natural killer (NK) cells and cytolytic T lymphocytes (CTL) have been implicated as important effectors of antiviral defense. We previously isolated a novel antibacterial polypeptide, which was identified as high mobility group nucleosomal-binding domain 2 (HMGN2), from human mononuclear leukocytes. This study examined the antiviral activity of HMGN2 against human hepatitis virus B. HMGN2 was isolated and purified from the acid soluble proteins of the human THP-1 cell line, and identified by mass spectrum, Western blot and antibacterial assay. The hepatitis B virus (HBV)-transfected HepG2.2.15 cell line was used in the in vitro assay system. In the range of 1-100 microg/ml HMGN2, no cytotoxicity for HepG2.2.15 cells was detected by MTT assay. When incubated with HMGN2 at 1-100 microg/ml for 72 or 144 h, there was a significant reduction in hepatitis B e antigen (HBeAg) and hepatitis B surface antigen (HBsAg) expression, which were detected by ELISA, and a significant reduction in HBV DNA copies, which was determined by the real time quantitative PCR, in the supernatant of HepG2.2.15 cells. Northern and Southern blot analysis also showed that the levels of the HBV 3.5 kb and the 2.4/2.1 kb mRNA species and HBV replicative intermediate DNA were significantly reduced in the HMGN2-treated HepG2.2.15 cells. These results indicated that HMGN2 protein could markedly inhibit HBV protein expression and replication in vitro.