Posts Tagged ‘material properties’

Beautiful flowers in small packages

20 May, 2013 2 comments
The latest addition to my collection...

The latest addition to my collection…

Anyone who has seen my home knows that I have a bit of a… hmm… obsession with orchids. To control my orchid intake, I meter my purchases to buying more plants only after I have either mastered or killed my latest orchid purchase. This has resulted in nearly 20 pots of these gorgeous plants with orchid “spa treatment days” (i.e., deep watering days) lasting hours at a time. So you can probably imagine the enthusiasm with which I embraced a recent article from the journal Science, in which Harvard researchers Wim L Noorduin and colleagues proclaim that they have discovered how to create predictable complex nano- and microstructures via biomineralization techniques, and then demonstrate this by creating micro-flowers!

Self-assembly of complex forms occur regularly in nature as a result of dynamic interactions with the surrounding environment. Many of these structures have a stunning beauty to them, with snowflakes being one of the most well-known examples of this phenomenon. The claim that no two snowflakes are alike is based on the understanding that the basic shape of a snowflake is guided by a combination of atmospheric temperature and humidity. However, its individuality is “crafted” as it falls through the atmosphere, tracing unique paths and being exposed to different air patterns as its shape shifts with each tumble, spin, pitch and glide, and twirl.

"Diatom Circle" by Graham P. Matthews (

“Diatom Circle” by Graham P. Matthews (

Another, perhaps lesser-known example is the shells of diatoms, a type of algae that is characterized as being encased in a shell formed of silica. These silica shells often exhibit a remarkable level of complexity, being extremely porous to permit gas and nutrient exchange with the surrounding environment.

What makes them of particular interest to physicists and materials scientists is their ability to repeatedly produce these intricate and complex shells through self-assembly with such accuracy that the identification and classification of these creatures can be guided by the patterns and placements of their pores.

Until recently, the study of how these patterns emerge has focused on looking at the chemical compositions and material properties of complex microsystems, or has worked on defining the initial conditions required to generate these forms. While the understanding that complex structures are usually created as a result of dynamic interactions with the surrounding environment is well-accepted, how these complex structures form through self-assembly had never yet reached the point of being something scientists could predict.

So Noorduin and co-authors set off undaunted to discover how dynamic environmental interactions can be used to generate predictable, patterned precipitation in synthetic systems, to create self-assembled complex structures… repeatedly (i.e., in a predictable manner).

Micro flowers grown in a beaker!

Micro flowers grown in a beaker! (Image by W.L. Noorduin)

It turns out that the secret to growing complex structures is to subject the solution to a dynamically-changing environment, one that responds to its growing shape. The images to the left are scanning electron micrographs that have been artificially colored, but aren’t they beautiful?

It’s important to realize that while Noorduin and colleagues did produce these flowers as a beautiful demonstration of their technique, that all of this isn’t purely just for fun and games. Rather, if we can harness the basic principles guiding self-assembly, especially that of biomineralization, this will change the face of how nano- and micromaterials are made.

As of now, our go-to method for creating nanomaterials is by using lithography techniques, through which 3D structures are laboriously etched. Not only is this slow, it is also very, very expensive. Using the methods this group is developing, it will soon become possible to mass-manufacture complex materials for drug delivery, development of catalysts for chemical production, micro-circuitry, etc., by mechanisms of self-assembly.

The possibilities are truly… endless.

Bionics in 1999

9 November, 2010 2 comments

The Fly-O-Rama created in the Dickinson Lab to study how flies maneuver during flight, by tethering fruit flies to a metal rod and giving them a virtual world to react to (see photo below for a tethered fly's eye view!).

I was rummaging through my electronic library today and came across a paper had I read over and over again in 1999 as a new graduate student with a nearly insatiable appetite. I am now realizing that it was right around the time this paper was published, that the seed of biomimetics was planted in my head. This article is written by a then faculty member at UC Berkeley (now at Cal Tech), by the name of Michael Dickinson. Even then, as a fairly new professor, it was clear that Dickinson was a rapidly rising star — one with amazing vision and a force to contend with. As the head of a fly neurobiology and flight lab, he was a pioneer in understanding the mechanisms of fly flight using self-created contraptions such as RoboFly and Fly-O-Rama, pictured above. I hope you enjoy and are inspired by this article as much as I was.

Photo courtesy of M Dickinson

Wispy weeping willows

23 September, 2010 1 comment

I consider myself to be among the lucky few in Philadelphia that get to both live in the city and also live on a large plot of land. My home is built on a 0.6 acre lot that is flanked on three sides by dense “forests” (i.e., unmaintained growth). This forest consists of quite the diverse flora, including introduced maples, pines, black walnut, cherry, and sycamore, as well as an understory dominated by a nearly equal mix of matted wild rose briars and poison ivy.

A gorgeous weeping willow tree that holds very little resemblance to our skinny backyard companion.

The centerpiece of our yard, and Rob’s pride and joy, is a rather Sideshow Bob-like weeping willow tree. Last winter, the unusual amounts of heavy, wet snow broke one of its primary branches off the main trunk, such that what used to be the crown of the tree draped over our lawn for easily 5-6 months before we finally managed to remove it. The lanky trunk and wispy branches that make the willow “weep”, combined with the thin halo of leaves form a deceivingly delicate facade on an incredibly tenacious plant. This enormous, 2 foot diameter branch actually began to heal itself during the course of the 5-6 months it braced itself against the ground! By the time we chopped the branch off in the spring, as it threatened to take down the rest of the tree in its fight to survive, it was sending out new branches and had actually even tried to root a section of itself to the ground!

The aggressive roots of willows are one of their most simultaneously beloved and hated traits. Those who hate the willow tree roots complain about the nearly magical ability for the roots to detect the presence of water, even through metal pipes, and will gradually bore their way through, repeatedly clogging pipes. In fact, there is even a blog dedicated to one such incident of a swamp willow that clogged water intake pipes, and continued to clog them even after the trees were chopped down!

swamp willow roots in pipe

An intake pipe clogged full with swamp willow tree roots.

Those who love the root’s determined hydrophilic nature plant these trees close to rivers, streams, and lakes, to control erosion on embankments. The complex root system wraps the soil, holding it in place, while presenting a zen-like tree above ground for all to admire.

The properties of roots are highly complex. They are very weak resisting compressive and bending forces, excelling in their tensile strength. In other words, roots are strongest when you are trying to play tug-of-war with them, which is precisely why they can be hard to pull out of the ground!

It turns out that the way the roots hold the soil in, is through a process known as edaphoecotropism — quite the mouthful to simply say “stress-avoidance”. In effect, wherever there are particularly high resistive or sheer forces, roots will turn and move down the path of least resistance. In short, what this means is that wherever there is a sheer plane in soil (i.e., one layer of soil moving relative to another), when the root reaches this layer of sheer, it will turn and orient itself parallel to the direction of sheer. Interestingly, what this does is transfer the sheer forces of the soil to tension in the roots, by means of friction of the soil along the entire length of the root. This tension causes the root to lengthen and deform, further increasing the surface area exposed to friction and making the pull out even more difficult.

A potential fruitful area of continued study would be to examine the precise mechanisms of edaphoecotrophism. We already utilize ideas of tensile reinforcement in many familiar materials such as clothing and fibreglass plates. However, I suspect that if we can harness the means of edaphoecotrophism from its sensory or even mechanistic perspectives, we may have some potential innovations for the fields of robotics or artificial growth of stronger construction materials.

Want to read more on soil reinforcement? Check out Simon and Bennett. 2004. Riparian Vegetation and Fluvial Geomorphology. American Geophysical Union.

A tent like a leaf

14 September, 2010 1 comment

Sketches for a biomimetic tent by Ondrej Vaclavik

I happened to come across these sketches tonight for a biomimetic tent designed by Ondrej Vaclavik, a graduate from Prague’s Academy of Arts, Architecture, and Design.

Top view of tent

A top view rendering of the biomimetic tent. Note the clear leaf-like veins!

The structures for this tent are modeled after a leaf, with the veins forming the primary support structures for the tent. Despite the obvious beauty of this structure, it nonetheless is not immediately clear if this offers any added functionality. For example, is it lighter or stiffer? Does it shed water more effectively or deal with wind storms? Alternatively, is this a tent simply constructed for its beauty and to invoke emotions of oneness with the surrounding environment?

Irrespective of this, the design reminded me of tent caterpillars (and other similar insects) that actually will stick two or more leaves together to form a shelter while they pupate. My best guess is that the leaves provide more camouflage than protection, although I could imagine that there could be additional environmental advantages conferred from being wrapped in live, respiring leaves, possibly for temperature or humidity control.

Tent caterpillar cocoon wrapped in leaves (from

Can this design be taken a step further: Are there certain repeatable patterns to the way the leaves or folded and stuck together that can be predictable based on the structural properties of the leaves? Are there any properties to the cell structure and their patterns relative to the veins that can be adapted for addressing construction challenges or for increasing the efficiency/organization of transport?

Interestingly, Mr. Vaclavik also has designed other rather slick looking products inspired by biological shapes, for example, this “cactus juicer”, shown below.

Cactus juicer

A juicer shaped like a cactus. The edges of the ellipses extract the juice, which is then funneled into the cup below.

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