8. Plant Kingdom. Vascular plants transport water through their roots, shoots and leaves by means of a passive pumping system that is driven by the transpiration of water from the stomata of the plant's leaves.
In transpiration, water vapor is drawn from the leaf interior down a water potential gradient toward the outside air, much as a dry towel will wick away water from your skin.
This action powers water transport, but the cohesion of the water itself and its adhesion to the sides of the xylem in the plant is what helps water columns over 100 meters high defy the forces of gravity. In this mechanism there is an unbroken chain of hydrogen-bonded water molecules from the roots to the topmost leaves.
Researchers from Dalian University of Technology in China, have developed a micropump based on the principle of stomatal transpiration. Since flow rates based on micropore transpiration far exceed that of simple evaporation, the team used this "diameter law" to make a layered membrane with controllable micropores.
The micropump works on the principle of diffusion mentioned above and therefore requires no external energy to operate. It comprises three layers: the top layer is a 93 μm-thick PVC (polyvinylchloride) film with a group of slit-like micropores; the second layer is a PMMA (poly(methyl methacrylate)) sheet with adhesives to join the other two layers together; the third layer is a microporous membrane. Flow rates were controlled by the opening and closing of some of the micropores, and were both high and adjustable. Its simple structure, low fabrication cost and independence from a power source make it widely applicable to medical and manufacturing situations requiring quick, on-the-spot fluid pumping.
This is another great example of "surfing for free." Investigators have abstracted the principles of transpiration in order to construct a pump that is powered by the physical forces inherent in the material being manipulated. in this case, the tendency of fluids to flow from areas of high concentration to low.
9. Eukaryotes. Our living world can be divided into two basic cell types, Prokaryotes ("primitive" bacteria) and Eukaryotes (everything else).
Cilia, or tiny hairs, exist in many forms in the Eukaryotic world, including in our own windpipes, where they help sweep debris out of our lungs, and women's oviducts, where they help move the egg to the uterus. The cross-section of these hairs, whether on a protozoan membrane or in our windpipes, is remarkably similar.
Cilia are very handy to have. They sweep back and forth and either propel something, oarlike, through a fluid, or move loose material along their surface. They can also filter, and, of course, sense things; thanks, in no small part, to their high aspect ratio. Like all modular parts in nature, they get a lot done through strength of numbers, and damage to any one hair does not impede general operations.
Philseok Kim of the Wyss Institute for Biologically Inspired Engineering at Harvard, has designed a biomimetic system in which synthetic cilia are embedded in a hydrogel.
Hydrogels are water-loving mixtures of polymers and water that have a high shrink-swell capacity. The hydrogel can be made to respond to several different external stimuli and serve as an adjustable substrate for the cilia, causing them to project or to lie flat.
Indeed, hydrogels can be programmed into topographical patterns as intricate as opening and closing microflorets by controlling the volume and the conformation of the gel. The synthetic cilia are typically silicon nanostructures that have been created by the Bosch etching method, and these, too, have a multitude of patterns and characteristics possible.
Kim has proposed that these structures could be used as smart building membranes activated by temperature in order to improve energy efficiency. When building surfaces reached a temperature threshold, the transparent hydrogel would deploy the hairs on end. Each hair would possess a tiny deformable micromirror that would present its face to the exterior. Like the crowd at a football game that spells out messages in mosaic, the mirrors would form a continuous flat surface. This surface could now be tuned to control light and heat into the building.
There are scores of other potential applications for this technology, wherever dynamic, responsive surfaces would improve our lives. These include interior pipe surfaces that adjust flow characteristics according to the chemical composition of the liquid within them, fabric that can reverse its wetting properties, or structural members that change color according to the mechanical stress placed upon them. With the environmentally activated hydrogel as the engine and the nanostructure array as the translator of energy into mechanical work (and both separately programmable) there are many degrees of freedom in this system.
The bio-innovations here are many. The groundbreaking combination of two materials from separate research areas in order to solve problem contradictions is one. The hybrid system takes the best in tunability, responsiveness and reversibility from the hydrogel, and the range of mechanical behavior from the nanowires. Moreover, research into fabrication has made the flexible (hydrogel) more structured, and the rigid (nanostructure) more dynamic. This system also exhibits several other principles of bio-inspired design: Little things multiply up (emergence), surfing for free, and the use of a hierarchy of scales to solve a problem.
10. Animal Kingdom. Blood circulation systems in animals do many things -- distribute nutrients and enzymes, exchange oxygen and carbon dioxide, and regulate temperature, to name a few.
These circulatory systems also transport repair materials to wounds. When you cut yourself, platelets in your blood and the blood-clotting protein fibrinogen form a meshwork that traps red blood cells. Tissue-forming fibroblast cells collect in the area and white cells called neutrophils ingest the cell debris and foreign matter like dirt and germs. The clot gradually hardens to become a scab as the tissues heal beneath.
Self-healing materials is a major area of bio-inspired research, and there are many different approaches to the challenge, at the molecular, micro and macro levels. One macroscale approach has been pioneered by Professor Nancy Sottos and her team at the University of Illinois Urbana-Champaign. It involves the impregnation of plastics with a fine network of channels, each less than 100 millionths of a meter in diameter, that can be filled with liquid resins. These "micro-vascular" networks penetrate the material like an animal's circulation system, supplying healing agent to all areas, ready to be released whenever and wherever a crack appears.
The resins in the channels are placed under pressure and when a crack crosses a channel the liquid is drawn into the void and followed by a hardener. The pressurized system is an improvement over previous work that relied on embedded micro capsules of resin that were burst at the outset of a crack. The supply of repair material was too small and the reliance on diffusion alone too slow. The pumping system now allows for the repair of cracks up to a millimeter across, a tenfold increase.
Applications include the self-repair of vehicles and structures, and further refinements would include the integration of the pumping system into the material itself and increasing the multi-functionality of this synthetic vascular system, say making it do extra work as a hydraulic structural support system.
Congratulations to all our winning creatures! May we have the wisdom to use your lessons well.
CC-licensed photo at top of page of mantis shrimp via Wikimedia Commons.