Lessons from Nature

The word nanotechnology is a relatively new word, but it is not an entirely new field. Nature has gone through evolution over the 3.8 billion years since life is estimated to have appeared on Earth. Nature has many materials, objects, and processes which function from the macroscale to nanoscale. Understanding the functions provided by these objects and processes can guide us to imitate and produce nanomaterials, nanodevices, and processes. Biologically inspired design, adaptation or derivation from nature is referred to as biomimetics. The term biomimetics is relatively new; however, our ancestors looked to nature for inspiration and the development of various materials and devices many centuries ago. There are a large number of objects, including bacteria, plants, land and aquatic animals, seashells, and spider web, with properties of commercial interest.

Several billions years ago, molecules began organizing into complex structures that could support life. Photosynthesis harnesses solar energy to support plant life. Molecular ensembles present in plant leaves, which include light-harvesting molecules such as chlorophyll, arranged within the cells (on the nanometer to micrometer scales), capture light energy and convert it into the chemical energy that drives the biochemical machinery of plant cells. Live organs use chemical energy in the body. This technology is being exploited for solar energy applications.

Some natural surfaces, including the leaves of water-repellent plants such as lotus, are known to be superhydrophobic and self-cleaning due to hierarchical roughness (microbumps superimposed with nanostructure) and the presence of a wax coating. Roughness-induced superhydrophobic and self-cleaning surfaces are of interest in various applications, including self-cleaning windows, wind-shields, exterior paints for buildings and navigation ships, utensils, roof tiles, textiles, and applications requiring a reduction of drag in fluid flow, e.g., in micro/nanofluidics. Superhydrophobic surfaces can also be used for energy conversion and conservation.

The leg attachment pads of several creatures, including many insects (e.g., beetles and flies), spiders, and lizards (e.g., geckoes), are capable of attaching to a variety of surfaces and are used for locomotion.

Biological evolution over a long period of time has led to the optimization of their leg attachment systems. The attachment pads have the ability to cling to different smooth and rough surfaces and detach at will.

This dynamic attachment ability is referred to as reversible adhesion or smart adhesion. Replication of the characteristics of gecko feet would enable the development of a superadhesive polymer tape capable of clean, dry adhesion which is reversible. (It should be noted that common manmade adhesives such as tape or glue involve the use of wet adhesives that permanently attach to surfaces.) The reusable gecko-inspired adhesives have the potential for use in everyday objects such as tapes, fasteners, and toys, and in high technology such as microelectronic and space applications.

Many aquatic animals can move in water at high speeds with low energy input. Drag is a major hindrance to movement. Most shark species move through water with high efficiency and maintain buoyancy. Through its ingenious design, their skin turns out to be an essential aid to this behavior by reducing friction drag and autocleaning ectoparasites from their surface.

The very small individual tooth-like scales of shark skin, called dermal denticles, are ribbed with longitudinal grooves, which result in water moving very efficiently over their surface. The scales also minimize the collection of barnacles and algae. Boat, ship, and aircraft manufacturers are trying to mimic shark skin to reduce friction drag and minimize the attachment of organisms to their bodies. In addition, mucus on the skin of aquatic animals, including sharks, acts as an osmotic barrier against the salinity of seawater and protects the creature from parasites and infections. It also acts as a drag-reducing agent.

A remarkable property of biological tissues is their ability for self-healing. In biological systems, chemical signals released at the site of a fracture initiate a systemic response that transports repair agents to the site of an injury and promotes healing. Various artificial self-healing materials are being developed. Human skin is sensitive to impact, leading to purple-colored marks in areas that are hit. This idea has led to the development of coatings indicating impact damage. Other lessons from nature include the wings of flying insects, abalone shell with high-impact ceramic properties, strong spider silk, ultrasonic detection by bats, infrared detection by beetles, and silent flying of owls because of frayed feathers on the edges of their wings.

(Bhushan B. Springer Handbook of Nanotechnology – Würzburg, 2010)