Spiral Honeycomb Microstructured Bacterial Cellulose for Increased Strength and Toughness.

Natural materials, such as nacre and silk, exhibit both high strength and toughness due to their hierarchical structures highly organized at the nano-, micro-, and macroscales. Bacterial cellulose (BC) presents a hierarchical fibril structure at the nanoscale. At the microscale, however, BC nanofibers are distributed randomly. Here, BC self-assembles into a highly organized spiral honeycomb microstructure giving rise to a high tensile strength (315 MPa) and a high toughness value (17.8 MJ m-3), with pull-out and de-spiral morphologies observed during failure. Both experiments and finite-element simulations indicate improved mechanical properties resulting from the honeycomb structure. The mild fabrication process consists of an in situ fermentation step utilizing poly(vinyl alcohol), followed by a post-treatment including freezing-thawing and boiling. This simple self-assembly production process is highly scalable, does not require any toxic chemicals, and enables the fabrication of light, strong, and tough hierarchical composite materials with tunable shape and size

Prevalence of helminth parasites in digestive tract of Persian sturgeon (Acipenser persicus) broodstocks southeast of the Caspian Sea

We collected 100 specimens of Persian sturgeon brood stocks propagated in Shahid Marjani Fish Culture Center to study internal parasites during March, April and May 2005. The center is located in the southeast of the Caspian Sea. Three different parasite species were recovered from digestive tract (stomach and intestine) of the fish. Cucullanus sphaerocephalus, Skrjabinopsolus semiarmatus showed the highest incidence and highest mean intensity (with prevalence of 80% and 55% respectively) but Leptorhynchoides plagicephalus had the lower prevalene 2 %. The prevalence of S. semiarmatus and C. sphaerocephalus were higher in males than in females whereas the intensity of these parasites was higher in females than in males. Statistical analysis of data showed a significant relationship between the occurrence of S. semiarmatus and the sex of the fish. There was a significant relationship between the occurrence of C. sphaerocephalus and the length of the fish (P 6 0.05). Forty nine percent of the fish had less than 10 worms. It was also found that the internal parasites of A. persicus in the southeast of the Caspian Sea are the same as those found in the southwest but the diversity of parasites were fewer in the former