We report a kind of polymer ordered porous honeycomb structure film with enhanced mechanical strength and low density. The film is fabricated with polyimide as a basic structure and nano-clay as the enhanced layer in the honeycomb walls, which mimics the multi-scale structure of natural honeycombs. After examining the mechanical properties of the bio-inspired honeycomb structures with different contents of clay, we find that the hardness of the honeycomb films increases with increasing clay content, and reaches a maximum value of 0.037GPa on average, which is about 5 times that for the honeycomb film without clay. Because of the existence of the porous structure, the bulk density of the multiscale bio-inspired honeycomb structure films fabricated with the solution containing 0.9 wt% clay content is 35.7% of the honeycomb structure films fabricated with the solution without clay, and the apparent density of the honeycomb structure films fabricated with the solution containing 0.9 wt% clay content is 67.5% of the honeycomb structure films fabricated with the solution without clay, and the porosity increases by 45.6%. In addition, the study of the thermal properties indicates that the porous structure does not decrease the thermal stability of the original materials. Meanwhile, the introduction of the clay into the film can increase the thermal stability of the materials slightly. So this kind of multiscale bio-inspired honeycomb structure, with high mechanical strength, low density and excellent thermal stability, is considered to have wide applications in the areas of tissue engineering, aeronautical materials, separation films in lithium-ion batteries, and so on.

A novel endo-type beta-agarase gene, agaA, was cloned from a newly isolated marine bacterium, Agarivorans sp. LQ48. It encodes a protein of 457 amino acids with a calculated molecular mass of 51.2 kDa. The deduced protein contains a typical N-terminal signal peptide of 25 amino acid residues, followed by a catalytic module, which is homologous to that of glycoside hydrolase family 16. A sequence similar to a carbohydrate-binding module is found in the C-terminal region of the enzyme. The overall amino acid sequence shares a highest identity of 73% with the sequence of beta-agarase AgaB from Pseudoalteromonas sp. strain CY24. The mature agarase was highly expressed extracellularly in Escherichia coli. At pH 7.0 and 40 degrees C, the purified recombinant AgaA had a high specific activity of 349.3 micromol min(-1) mg(-1), a K(m) of 3.9 mg ml(-1), and a V(max) of 909.1 micromol min(-1) mg(-1) for agarose. The recombinant enzyme hydrolyzed the beta-1,4-glycosidic linkages of agarose, yielding neoagarotetraose and neoagarohexaose as the main products. Enzyme activity analysis revealed that the optimal temperature and pH of the recombinant AgaA were 40 degrees C and 7.0, respectively. Notably, AgaA still retained more than 95% activity after incubation at pH 3.0-11.0 for 1 h, a characteristic much different from other agarases reported. It is the first agarase identified to have so wide a pH range stability. This favorable property could make AgaA to be attractive to the food, cosmetic, and medical industrial applications.

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