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MARINE BIOMIMETICS
INTRODUCTION - What is Biomimetics?
The Centre for Biomimetics at the University
of Redding concisely defines the science of biomimetics as "the abstraction of good design from nature." Another way to define it would be the intentional imitation of nature. The goal of this scientific field is to identify specific desirable qualities and attributes in biological systems and then use them in the design of new products.
Once again, then, we see that nature can serve as an important source of inspiration to foster
innovation. Industrial applications designers can exploit millions of years of tinkering and
tweaking by borrowing from nature's best designs and applying these to new problems and
situations.
A classic application of the principle of biomimetics can be seen in the invention of the revolutionary product Velcro®. Swiss engineer Georges de Mestral notes that he got the inspiration for this hook-and-loop fastening system after examining the burrs that clung to his dog's coat after their daily walk.
An Ocean of Inspiration
Marine systems, like all of nature, evolved over the span of millions of years, overcoming a multitude of survival challenges. Many of the solutions to these challenges are true
engineering marvels that arose under the same sorts of constraints facing today's human engineers
such as the need to maximize functionality while minimizing costs in energy and materials. In
addition to being time-tested and cost-efficient, the engineered structures devised by natural
systems are created using non-polluting processes that occur at biological temperatures -
something that can be said of only a few human-engineered industrial materials.
A familiar example of engineered systems successfully mimicking natural marine systems is the classic fusiform design of most maritime vessels. Tapered front and back ends and a fuller
mid-body is not only the rule of thumb in building such vessels, it is also the sleek hydrodynamic
body plan of swift pelagic animals like dolphins, tunas, and sharks.
Living marine systems are a rich source of inspiration for new biomimetic applications, as the
following examples demonstrate. From new surgical adhesives to enhanced fiber optics design to
the development of the next generation of artificial bone, marine organisms have been the source
of inspiration for a number of promising technical innovations.
 The Eyes Have It
In some instances, inspiration has come from logical sources. Such is the case with the Caribbean brittlestar Ophiocoma wendtii. Since this organism is known for its highly advanced compound eyes, it is not surprising that optics researchers from Bell Laboratories and Lucent Technologies find it interesting.
The arms of O. wendtii are covered with domes made of calcite crystal. In addition to providing structural
support and body armor, these 40- to 50-µm-diameter spherical crystals also act as an array of near-perfect
lenses that filter light and focus it onto underlying photoreceptor cells. The calcite lenses essentially
transform the entire upper surface of the brittlestar into a functional compound eye that can see its entire
surrounding environments.
This visual system appears to be unique to O. wendtii. The only other organisms known to have a
similar system are the extinct trilobites.
Though the image quality produced by this system is not yet known, researchers feel confident that information
about light, shadow, and directional movement is effectively conveyed. These are the essential bits of
information that would alert the brittlestar to the presence of would-be predators, giving them time to seek
cover.
Industry research scientists like Bell Laboratories and Lucent Technologies' Joanna Aizenberg [link:
http://www.bell-labs.com/org/physicalsciences/profiles/jaizenberg.html] recognize the near-perfect optical
properties of O. wendtii as more sophisticated than anything currently engineered by humans. Plastic microlenses similar (but inferior to) those of the brittlestar are responsible for transmitting signals along the optical fibers now used ubiquitously in communications systems. Successive generations of microlenses, improved based on insights gained through the biomimetic work of Dr. Aizenberg and others, may one day form the ÒcircuitryÓ of optical computers that process light instead of electrical impulses.
In 2003, the Bell/Lucent research group published work detailing a bio-inspired approach to growing
millimeter-sized single calcite crystals with sub-10-µm patterns and controlled crystallographic orientation.
It will be interesting indeed to see if a little-known cousin to the starfish ultimately leads to the
development of new and better microlens arrays.
References
Aizenberg J., Tkachenko A., Weiner S., Addad, L. and G. Hendler. 2001. Calcitic microlenses as part of the
photoreceptor system in brittlestars. Nature, 412:819-822.
Aizenberg J, Muller D.A., Grazul J.L., and D.R. Hamann. 2003. Direct Fabrication of Large Micropatterned
Single Crystals. Science 299:1205-1208.
Related Weblinks
"Brittle Star Features Calcite Lenses" (Photonics.com 11/01 news story)
http://www.photonics.com/spectra/tech/XQ/ASP/techid.1234/QX/read.htm
Glass Sponges, Fiber Optics and Better Buildings
Looking at the mechanics of a visual organism like Ophiocoma wendtii for insights into optics system design seems a logical
enough approach. On the other hand, finding similar insights by studying an eyeless animal from a primitive phylum that arose
millions of years before the first invertebrate eyes even existed would appear to be an exercise in futility.
Of course, appearances can be deceiving.
Joanna Aizenberg, the Lucent/Bell Labs materials scientist who headed up the O. wendtii research, has discovered that the body
of a deep-sea sponge ( Euplectella) contains organic structures that are strikingly similar to optical fibers used in modern
communication network. Notes Aizenberg, "Mother Nature's ability to perfect materials is amazing, and the more we study
biological organisms, the more we realize how much we can learn from them," says Aizenberg.
The sponge, with the common name of Venus' flower basket, is a member of a class of sponges called the "glass sponges" ( Class
Hexinactellida). The class is characterized by the presence of a skeleton composed of glass-like siliceous spicules. At the base of the sponge there
is a tuft of fibers used to anchor the sessile organism in place. These fibers range from two to seven inches in length and have
optical properties remarkably similar to man-made optical fibers (though they lack the degree of transparency modern
telecommunication networks demand). In addition, they possess attributes that the artificial optical fibers do not, including
the ability to be tied into tight knots without cracking. The presence of extensive organic cross bracing allows the fibers to
be tough without being brittle.
Of key importance, the Venus' flower basket manages to assemble these fibers at low temperatures, whereas the man-made fibers are produced at very high temperatures and with expensive equipment. These low temperatures allow the sponge to incorporate elemental sodium into its fibers and spicules, which enhances the materials' natural optical properties. In contrast, sodium cannot yet be incorporated into man-made optical fibers due to the high temperatures used to produce them.
In addition to its notable optical qualities, Aizenberg also sees in Euplectella a panoply of structural details that
correspond to well-established principles of mechanical engineering. Aizenberg and colleagues from Bell Labs, UC Santa Barbara's Collaborative Biotechnologies and Materials Research Laboratory,
and Germany's Max Planck Institute of Colloids and Interfaces identified seven distinct fundamental construction and
engineering principles exhibited by nature in the design of Euplectella.
References
Aizenberg J., Weaver J.C., Thanawala M.S., Sundar V.C., Morse D.E., and P. Fratzl. 2005. Skeleton of Euplectella sp.:
Structural Hierarchy from the Nanoscale to the Macroscale. Science 309:275-278.
Related Weblinks
Australian Museum Collections Deep-sea Glass Sponge Page
http://www.amonline.net.au/collections/marineinverts/sponge.htm
Research on Deep-Sea Sponge Yields Substantial Mechanical Engineering Insights (7/05 PhysOrg.com news story)
http://www.physorg.com/news5036.html
Mussel Adhesive, Surgical Superglue and Safer Medical Implants
Anyone who has ever tried to pry mussels off intertidal rocks or pilings can appreciate how tenaciously they attache to these surfaces. Blue mussels (Mytilis edulis) produce an intriguing group of mussel adhesive proteins (MAPs) that they use to form fibrous byssus threads for attachment. These proteins are the subject of a number of research efforts designed to better understand how they form one of nature's strongest glues as well as to develop bio-inspired biomedical and industrial applications derived from them.
The MAPs are secreted by the mussels as a fluid and then they undergo a chemical cross linking reaction that
hardens them to form solid adhesive plaques. The MAP plaques cure in the water to form durable bonds between the
mussels and their attachment surfaces.
Research into the nature of the MAPs, primarily by Phillip
Messersmith of Northwestern University, and associates, has revealed that both the adhesive and its cross linking characteristics are related to high concentrations of the amino acid L-3, 4- dihydroxyphenylalanine, also called DOPA. According to Messersmith, oxidation of DOPA induces the cross linking
between MAP proteins while unoxidized DOPA is believed to be responsible for substrate adhesion.
Adding to this picture is the work of Jonathan Wilker,
a chemistry professor at Purdue University. Wilker used spectroscopy to analyze the components of mussel adhesive and made the unexpected discovery that iron is also an important ingredient contributing to the adhesive strength of the natural glue. Mussels extract the iron from seawater and use it in the "curing" process to join fibrous MAP proteins together to form the solid mesh structure that makes up the mussel byssal threads.
Both Messersmith and Wilker are pursuing this biomimetic research to develop biomedical and industrial applications for synthetic protein-based glues based on that used by mussels. Among the goals of the Wilker research group is the development of a surgical adhesive. A good surgical glue needs to set even in a wet environment. It also has to form a strong bond with surrounding tissue while being biofriendly and nontoxic. A glue based on the type used by mussels is likely to possess all of these desirable traits.
The Messersmith research group is also working on biomedical applications for their MAP-based discoveries with several research projects underway to develop
synthetic polymers that mimic the composition and properties of mussel adhesive proteins and other natural adhesive proteins.
A key focus of these efforts is the development of safer and more effective implanted medical devices. Bacterial infection is a significant
problem associated with implanted medical devices. The Messersmith group's possible solution is to develop a special two-sided coating for the devices
based on synthetic MAPs. One side of this coating has adhesive properties allowing it to bond tightly to implant
surfaces while the other side is impregnated with a repellent to deter protein buildup as well as bacterial
biofilm formation. The deterrent the group has focused on is polyethylene glycol, a molecule with well-known
repellant properties. So far the group has successfully attached their adhesive/repellant complex to gold and
titanium surfaces, both of which are commonly used as implant materials. Preliminary studies examining
attachment to stainless steel and plastic surfaces have also shown promising results.
In addition to potential biomedical uses, the group is exploring the possibility of using mimetic MAP peptides to
adhere fouling-resistant polymer coatings onto surfaces to combat biofouling. This work is examined in the Environmental Research: Biomaterials section of this websiite.
References
Sever M.J., Weisser J.T., Monahan J., Srinivasan S., and J.J. Wilker. 2003. Metal-Mediated Cross-Linking in the
Generation of a Marine-Mussel Adhesive Angew Chem Int Ed Engl 16:448-50.
Hu B. and P.B. Messersmith. 2000. Protection of 3,4-dihydroxyphenylalanine (DOPA) for Fmoc solid-phase peptide
synthesis. Tetrahedron Letters 41: 5795-5798
Related Weblinks
Surgery Glue (3/31/04 ScienceCentralNews news story)
http://www.sciencentral.com/articles/view.php3?article_id=218392201&language=english
Chemists Crack Secrets of Mussels' Super Glue (Roland Piquepaille's Technology Trends 1/12/04 NSF Press Release)
http://www.nsf.gov/news/news_summ.jsp?cntn_id=100318
Compound Developed From Mussels May Lead To Safer, More Effective Medical Implants (4/8/03 ScienceDaily news
story)
http://www.sciencedaily.com/releases/2003/04/030408085244.htm
The Sensible Sea Cucumber
British military defense research is investigating the feasibility of an airfoil whose shape and stiffness are variable and reconfigurable on
demand. The materials design and construction is based on that seen in the skin of sea cucumbers.
Fibrous sea cucumber skin is a composite of collagen imbedded in a mucco-polysaccharide matrix. The skin can change its stiffness, which allows the
animal to soften, change shape, and then stiffen once more.
The ability to shift between rigid and semi-fluid degrees stiffness would allow for a degree of vibration control not achievable with current airfoil
technology.
Related Weblinks
Biomimetics: Copying Ideas From Nature Into Engineering (Website)
http://people.bath.ac.uk/en2pdd/Pete%20Site/biomimetic-report.htm
Mollusc shells, Seawater Slushies, and Improving Artificial Bones
Bone replacement is big business, with nearly a half-million knee or hip replacement procedures performed in the United States
each year. As the baby boomer generation continues to age these figures will no doubt increase.
Despite the prevalent need for such replacement procedures, current replacement joints remain poor facsimiles for natural bone
tissue. Real bone is capable of adapting to changing physiological conditions within the body, whereas current synthetic bone
is largely static. Current metal and ceramic replacement joints also often trigger inflammation and immune responses in
recipients. Ideally, the next generation of artificial bones would be more dynamic, and would also be capable of meshing with
surrounding organic tissue over time.
Researchers from the U.S. Department of Energy's Lawrence Berkeley National Laboratory
have been working on improving the structural aspects of artificial bone used in human transplant procedures. As part of this effort
investigators are successfully parlaying insights gleaned through observation of two different marine phenomena - shell
deposition in molluscs and the physics of seawater freezing.
In January, 2006, The Berkley Lab published details of a synthetic bone-like composite that mimics the structure of the
nacreous layer of molluscan shells. Nacre, commonly called "mother of pearl," is an
organic-inorganic composite material secreted by specialized epithelial cells in the mantles of some shell-forming mollusks that forms the smooth and often iridescent innermost layer of the molluscan shell. The nacre composite consists of layers or
inorganic aragonite crystal (a form of calcium carbonate CaCO 3, the key ingredient in reef-building corals) crystal and the fibrous protein conchiolin, within a
carbohydrate matrix.
The composite's combination of hardness and elasticity imbues nacre with strength and resilience as well as light weight —
properties that are highly desirable in a variety of engineered materials. Duplicating the structural and performance
characteristics of nacre in manmade ceramic materials proved to be a formidable task, however. Mimicking the architecture of
nacre across multiple scales of resolution had the Berkley Lab researchers stumped.
Then they thought about sea ice.
As seawater freezes, crystals of pure ice are formed while dissolved salts are expelled from the crystals and into the
interstitial spaces (channels) between them. As the freezing process continues, layers of ice crystals form that are separated
by layers composed of salt and other impurities. The Berkley Lab research group sees similarities between this layered
structure and the composite construction seen in molluscan nacre.
The group hypothesized that freezing could be used to similarly order a suspension of hydroxyapatite, the mineral component of bone, into a layered composite. As experiments bore out, freezing the mixture indeed produced a layered composite in
which the hydroxyapatite was arranged into wafers within the channels between the ice crystals that formed.
When the interstitial ice is then removed via sublimation (direct conversion from solid to vapor state), what remains is a
porous hydroxyapatite scaffolding that is a very good facsimile of nacre and may soon become the next generation of artificial
bone. Natural bridges that form between some of the layers in the scaffolding help to make it four times as strong and
fracture resistant as the porous hydroxyapatite ceramics now being used in artificial bone.
Further research revealed that if the scientists accelerated the rate of freezing they could create ever thinner
layers, ultimately obtaining hydroxyapatite wafers less than one micron thick.
The ideal synthetic bone would actively promote the regeneration of living bone tissue at the replacement site. The Berkley Lab researchers believe one way to do this would be to fill the interstitial spaces of the hydroxyapatite scaffolding with an organic polymer designed to break down over the course of several weeks. As it does so, it would release embedded antibiotics and compounds that stimulate bone growth. New porosity would be created as the polymer degrades and bone cells would be stimulated to grow and proliferate within the scaffolding of the artificial bone, ultimately fusing new natural bone and synthetic bone at the replacement site.
References
Deville S., Saiz E., Nalla R.K., and A.P. Tomsia. 2006. Freezing as a Path to Build Complex Composites. Science 311:515-8.
Related Weblinks
Secrets of the Sea Yield Stronger Artificial Bone (1/31/06 Berkley Lab press release)
http://www.lbl.gov/Science-Articles/Archive/MSD-artificial-bone.html
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