The Nanotechnology Industry has been evolving at an exponential rate for three decades.  Since the 1970s, semiconductors and electrical circuits have been simplified immensely and made astronomically more efficient.  However, nanotechnology does not only lie within chips and wires, nanotechnology is often found in nature.  For example, a naturally occurring plant has the ability to repel all water due to its superhydrophobic properties (Lafuma et al 2003).  Scientists over the years have deemed such a characteristic interesting and have tried ever since to replicate it.  This is not the only example of naturally occurring nanotechnology, another being the gecko’s foot (Autumn 2003).  Scientists have, for years, tried to develop a material which captures the best traits of the extremely strong, extremely sticky surface of the gecko’s foot.  Nanotechnology is in nature and is being mimicked in order to develop more efficient, effective, and groundbreaking technologies.  These phenomena have  been occurring in nature for centuries and, until now, had no viable explanation.  Now, it is possible to explain why a gecko is able to hang upside down and why a leaf can resist all water.  Now, it is possible to analyze and learn from these naturally occurring phenomena.  Now, scientists can use what is learned from analyzing naturally occurring nanotechnology phenomena to develop technologies which would have otherwise been unheard of.  By learning from what has always been there to observe, it is possible to create some of the most innovative technologies ever known to man.

The lotus leaf is a naturally-occuring plant which is able to repel water (Lafuma et al 2003).  This phenomenon is explained in Lafuma’s article on superhydrophobicity.  â€œIt is well known that the roughness of a hydrophobic solid enhances its hydrophobicity.â€� (Lafuma et al 2003)  In the article, Lafuma suggests that the superhydrophobicity of the lotus leaf may be caused by the presence of certain features making the surface of the leaf rough.  For this reason, the leaf is often called “microtexturedâ€�.  Essentially, when water makes contact with the surface of the leaf, it is caught on the rough surface of the leaf which makes it superhydrophobic.  These beads are caught at a contact angle of approximately 160 degrees.  The only plausible flaw that has been found in the lotus leaf is that the leaf can, at times, have a superhydrophilic behavior (Cheng et al 2005).  This property, observed by researchers at Harvard University, has been marked as an obscurity and is currently under more research.  However, it is believed that this is dependent upon the angle at which the water makes contact with the leaf.  This duality is just one example of things scientists are learning about each day in attempts to replicate such natural phenomena.

Hydrophobicity is the property of an object to resist water.  Its opposite, hydrophilicity is the property of an object to absorb water.  There are two theories regarding hydrophobicity (Lafuma et al 2003).  These theories explain how the phenomenon of water resistance in the context of the lotus leaf works.  The first theory, according to Lafuma’s article, is that the microtextured surface of the lotus leaf causes an increased surface area.  This, in turn, allows the water to run off more easily.  The other theory regarding the leaf is that the microtextured surface allows air pockets to become trapped under water which falls onto the surface of the leaf.  This, in turn, causes the water to be resting on top of a bubble of air.  According to the laws of physics, water is repelled from the surface of the leaf and runs off.  Both theories are strong and supportive of each other.  The lotus leaf has an interesting duality which allows it to conditionally have hydrophobic traits and conditionally have hydrophilic traits.  This duality can be explained by the angle at which the water or other liquid contacts the surface of the lotus leaf.  According to research done by Yang-Tse Cheng and Daniel Rodak of Harvard University, the behavior exhibited by the leaf is dependent upon the contact angle.  If the water gets onto the surface of the leaf at a high angle, according to Cheng and Rodak, the surface will behave in a hydrophilic manner and amounts of water droplets may adhere to the surface of the leaf.  However, conversely, the leaf will exhibit hydrophobic traits if the contact angle is lower.  Cheng and Rodak explain this phenomenon using mathematics.

fs < 1/(1−cos ) [or fs > 1 / (1−cos )]

The mathematical expression above explains the relationship between the contact angle and the behavior exhibited between the contacting water and the surface of the lotus leaf.  In simple terms, while fs(fraction of surface areas) is not equal to 1/(1−cos ), the surface of the leaf will be hydrophilic.  If the fraction of surface areas is equal to 1/(1−cos ), the surface will be hydrophobic (Cheng et al 2005).

The lotus leaf has many practical applications connected to its ability to be either hydrophobic or hydrophilic.  Such information is extremely important in determining applications of such a material.  One application of this material, for example, might be self-cleaning surfaces.  The lotus leaf has the ability to be superhydrophobic.  This means that it will resist all water and absorb 0.00% of water which makes contact with it.  When water is rejected from the surface of the lotus leaf, it essentially grabs particles of dirt on its way and drags them along.  So, when water is poured on and rejected, the surface of the lotus leaf is often left cleaner than before water was applied, assuming that the leaf acted in a hydrophobic manner.  However, the duality of the lotus leaf is the most intriguing.  Scientists were able to study the duality of the lotus leaf and determine how to engineer materials which can behave in this manner, which is only one example of biomimicry in the nanotechnology industry.

Another intriguing behavior in nature is that of the gecko’s foot.  For years, scientists wondered how the generic reptilian gecko was able to invert itself and climb to extreme heights without falling.  According to the Brad Kloza, the gecko’s foot acts the way it does because of naturally-occurring van der Waals forces (Kloza 2003).  These extremely weak forces are caused when the outer-shell electrons of two atoms are momentarily on the same side of the electron.  For example, if they are both pointing at an angle of 180 degrees, attractive forces between the positive side of the first electron and the negative side of the second electron.  This force, while weak, is still significant when dealing with objects on the nanoscale.  The gecko’s foot works on the nanoscale, thus van der Waals forces are completely relevant.

The gecko’s foot works in a very complex way.  This complexity, however, makes the foot of the average gecko one of the most adhesive surfaces known to man.  The bottom of the gecko’s foot is covered with millions of nanoscale-sized hairs known as seta.  Setae are able to hold, according to observations, up to 20 milligrams of weight each.  A seta is approximately 200 billionths of a meter wide in size.  Combined with the millions of setae on the bottom of a gecko’s foot, the adhesive strength is approximately 400 Newtons.  This translates to approximately 90 pounds of weight able to be held by the seta on the bottom of just one foot of a gecko.  According to approximations made by many scientists, one million setae can fit on the surface of a dime.  90 pounds of weight can be held by an adhesive surface the size of a dime (Autumn 2003).  However, the strength of a the gecko’s foot cannot be fully attributed to the setae.  One of the most important parts of the gecko’s foot is beneath the surface of the foot.  Studied by morphologist Duncan Irschick, the tendons beneath the surface of the foot are also extremely strong and are what hold the setae in place.  For years, scientists did not think to look below the surface of the gecko’s foot and analyze what was keeping the setae in place.  Irschick was the first scientist to study geckos for a long period of time and draw such a conclusion.  The combined efforts between the attractive setae and the strong tendons beneath the surface of the foot are what make the gecko’s foot as adhesive as it is (Kuang 2013).  In addition to being one of the most adhesive surfaces known to man, it is also an extremely efficient.  The gecko’s foot not only works underwater and in a vacuum, but is also self-cleaning and leaves no residue behind when it releases its grip from another surface.

The gecko’s foot is essentially a super adhesive controlled by millions of nanoscale-sized hairs.  But, what exactly makes those hairs adhere to almost any surface on earth?  The forces that control how the setae behave with a surface upon contact are known as van der Waals forces.  These forces appear to be working between the setae and the contact surface.  In general terms, the forces can hold a negligible amount of weight.  However, if you put it into perspective, it is actually a very significant amount of weight.  The attraction force between an atom within the seta and an atom within the contact surface may be negligible.  However, when this attraction is present between loads of atom pairs within the seta and contact surface, the amount of attractive force begins to add up and become significant.  20 milligrams is not a lot of weight that can be held by the attractive forces between the seta and the contact surface.  But, 20 milligrams is the amount of weight that can be held by one seta on the foot of the gecko.  It is important to realize that, when you take into account the millions of setae on the gecko’s foot, the amount of attractive force is extremely high.  Setae are functional on nearly any surface on earth and work both inside a vacuum and underwater.  This behavior is what makes the gecko’s foot one of the most interesting naturally-occurring materials known to scientists today (Autumn 2003).

The intriguing behavior of the gecko’s foot has driven engineers across the world toward developing adhesive surfaces capable of holding a similar amount of weight as the gecko’s foot can.  The gecko’s foot, with its millions of attractive setae, is able to hold up to 90 pounds of weight without faltering.  Researchers at the University of Massachusetts Amhearst were able to develop an adhesive surface which mimics the surface of the gecko’s foot.  The surface, known as Geckskin, is able to hold approximately the same amount of weight as the gecko’s foot itself.  This measurement, of course, is proportional.  Essentially, the amount of weight which is able to be supported is dependent upon the amount of material which is making contact.  In an experiment using an index card-sized sample of Geckskin, the material was able to hold approximately 700 pounds of weight.  After the experiment, the material peeled away with no residue whatsoever, just as the gecko’s foot behaves.  While no material like Geckskin is currently available on the market, co-inventor Al Crosby believes that such a wondrous technology will soon be available to the general public.  Hopefully, Geckskin will show its face on the shelves of the free market soon (Kuang 2013).

The gecko’s foot and the lotus leaf are two of the most known examples of biomimicry.  The connection to nanotechnology from biomimicry is simple.  When humans see something in nature, they create it.  The science of looking at something as small as the gecko’s foot and then replicating it is nanoscience.  Between the gecko’s foot and the lotus leaf, engineers have spent loads of time attempting to engineer materials which allow humans to climb to extreme heights without falling or to jump into a pool of water without getting wet.  Part of the science is also taking into account the bad properties of a certain material and creating a material which has no flaws compared to its natural ancestor.  For example, the duality of the lotus leaf may not be desirable for something like a wetsuit.  So, part of the science would be to attempt to remove the hydrophilicity from the lotus leaf before making it into a wetsuit.  In the context of the gecko’s foot, Geckskin is designed to always be sticky no matter what.  The problem with this lies within the ability to selectively use the adhesive strength when needed.  Currently, Geckskin adheres to everything.  But, part of the science and innovation process might be to recognize the flaw of sticking to everything and make something that only sticks to any surface when the operator wishes it to.  Biomimicry and Nanotechnology is everywhere.  Some of the most important lessons in nanoscience can be learned from things that have been in existence for thousands of years.  From naturally-occurring materials such as the gecko’s foot, humans can discover how to climb to heights never before imagined.  Using lessons learned from nature, humans can exceed any expectation and defy any law of nature.

Works Cited