Clippings

Damage and Fluctuations Induce Loops in Optimal Transport Networks

Phys. Rev. Lett. 104, 048704 (2010): Damage and Fluctuations Induce Loops in Optimal Transport Networks.

Leaf venation is a pervasive example of a complex biological network, endowing leaves with a transport system and mechanical resilience. Transport networks optimized for efficiency have been shown to be trees, i.e., loopless. However, dicotyledon leaf venation has a large number of closed loops, which are functional and able to transport fluid in the event of damage to any vein, including the primary veins. Inspired by leaf venation, we study two possible reasons for the existence of a high density of loops in transport networks: resilience to damage and fluctuations in load. In the first case, we seek the optimal transport network in the presence of random damage by averaging over damage to each link. In the second case, we seek the network that optimizes transport when the load is sparsely distributed: at any given time most sinks are closed. We find that both criteria lead to the presence of loops in the optimum state.

TreeHugger published a review of the research at Awesome Biomimicry: Leaf Veins Inspire New Model for Water and Electricity Distribution Networks.  While distribution networks based on simple tree-like branching are efficient, they are not resilient in that failure at a point will block access to the parts of the network past that point.  The paper above (subscription required) explores various reasons for loops found in the veins of dicotyledon leaves, including resilience and load fluctuations.

Water may not run uphill, but it practically flies off new surface

University of Florida News - Water may not run uphill, but it practically flies off new surface.

Engineering researchers have crafted a flat surface that refuses to get wet. Water droplets skitter across it like ball bearings tossed on ice. The inspiration? Not wax. Not glass. Not even Teflon. Instead, University of Florida engineers have achieved what they label in a new paper a “nearly perfect hydrophobic interface” by reproducing, on small bits of flat plastic, the shape and patterns of the minute hairs that grow on the bodies of spiders.

Researchers led by professor Wolfgang Sigmund of the University of Florida based their design on the discovery that spider hairs are not uniform, but vary in length and form.  The team has been able to develop a plastic surface that repels both water and oil due to its physical (rather than chemical) properties.  Although the Lotus Effect also repels water due to its nano-structure, Sigmund's surfaces appear to be even more hydrophobic and can repel oil.  Applications include food packaging, windows, solar cells and boat hulls.

Sigmund's work has been published at Artificial Hairy Surfaces with a Nearly Perfect Hydrophobic Response (subscription required).

Thanks to Biomimicry: Chemical-Free Water-Blocking Material Inspired By Spider Hair for the pointer!

Underwater Bugs in Medicine - Caddisfly Silk Inspires Scotch Tape Solution for Surgeries : TreeHugger

Underwater Bugs in Medicine - Caddisfly Silk Inspires Scotch Tape Solution for Surgeries : TreeHugger.

[The] caddisfly larva, or a rock roller as it is also known ... while in larva state, lives underwater and creates its own "shell" by spinning a sticky silk that collects sand grains. Scientists are using this as an inspiration for a biomimetic solution in surgery, hoping to create a synthetic version that can be used as an adhesive tape-like suture.

Russel Stewart leads a team at the University of Utah that is studying how caddisfly silk differs from that of moths and butterflies in both chemistry and structure.  Phosphates and electrical charges appear to be important in making the proteins water-soluble in water (allowing the silk to be spun) and sticky underwater.  The team believes that the arrangement of the electrical charges can turn the proteins insoluble, resulting in a stable silk fibers.

Potential applications include a surgical tape that can be used to close internal incisions rather than using sutures.