Adhesion is one of the themes of this blog because biological systems have unparalleled mastery of surfaces and their interactions.  Barnacles, mussels and other marine invertebrates are worthy of a closer (phase I) look in order to understand the mechanisms and diversity of the glues they produce.  These glues are able to set while completely submerged.  They are strong, adhere well to dirty surfaces and appear to be very resistant to degradation.  Kristin Ödling of Göteborg University has taken a very close look at the production of cement proteins in larval barnacles.  She found four different types of cement granules. The route from inside to outside the cell is apparently powered by a sudden expansion in size of the granule that she attributes to osmotically induced swelling.

JEB Abstract

I have written about the Lotus effect and the ability of some surfaces to generate extreme contact angles in water droplets.  Here are a couple of images from BASF. They are working on sprays that would add this effect to surfaces.

The water droplets rest on the impregnated wood surface like mysterious blue pearls. But this is no conjuring trick: the wood has been treated with a BASFs nanoparticular surface coating , which has made its surface extremely water-repellent (superhydrophobic). This coating reduces the contact area between water and wood to a minimum. It also decreases the forces of adhesion, making the water droplets assume a globular form. Surfaces become self-cleaning and stay clean for a long time by applying nanostructures as they can be found on the leaves of the lotus plant.

The clean leaves of the lotus plant provided the inspiration for studies on the self-cleaning of surfaces. Botanist Professor Wilhelm Barthlott of Bonn University succeeded in explaining the lotus effect and utilizing it for technical applications. The self-cleaning process is based on the extremely water-repellent behavior of the leaf surface, also known as superhydrophobia. The water droplets form spherical globules and roll off the leaves even when they are only slightly inclined. Particles of dirt absorbed by the water are removed in the process, as we can see happening with this droplet on the leaf of the ancient Asiatic crop plant Colocasia esculenta. In this picture taken by Barthlott’s research team, we can also see the papillae on the cuticula. These papillae about 5 to 10 micrometers high are themselves coated by a fine nanostructure of wax crystals.

Click on the photos to see the source images.

Previously I ran across a Barrons article on a possible IPO for Biomimetic Therapeutics. Another article guessing that they might go public sent me off to learn more about the company. It certainly skirts my definition of biomimetic, they are using recombinant proteins in a matrix that promotes bone growth. That means the growth factor is not an imitation of the real deal but simply the real deal over expressed in bacteria so they can harvest lots of it. The matrix seems less an imitation of bone than a non-allergenic putty that seems to do no harm to the healing process. The matrix does not seem designed to bear load so much as fill gaps until the growth factor does its job.

The Company’s first product candidate, GEM 21S^® Growth-factor Enhanced Matrix, was recently approved by the FDA for the treatment of bone loss associated with advanced periodontal disease. GEM 21S combines the tissue growth factor rhPDGF-BB with the synthetic bone matrix, Beta-tricalcium phosphate (β-TCP).

They do have revenues though, so they are out ahead of many of the biotech start ups. I am more interested in the solutions that imitate the nature of bone. [1] [2]

News article

Biomimetic Therapeutics Web site

Phillip Ball finds some very intersting stuff. In a recently completed docotral dissertation and subsequent paper in a German language journal Bernhard Stamm has shown that it is possible to friction weld wood. Why is this interesting to us? Well, adhesion is an inherently interesting quality and biological adhesion systems are all the rage. The adhesion of one piece of wood to antoher is not dissimilar to the mechanism that holds a tree together. This method of liquifying the lignin in the wood and pressing two pieces together could revolutionize building.

Their tests on spruce and beech show that the wood starts to soften after a few seconds of rotary rubbing, as the temperature at the interface rises to about 320–350 °C. At this point, the surfaces start to smoke. The temperature peaks at 420–450 °C, when the surface wood is fully ‘molten’. At that stage the interface can be allowed to cool.

Furthermore the strength is nearly 40% of the strength of the original wood, easily sufficient for furniture and cabinetry. Nature Materials News and Views

Nacre, the material of molusc shells is a wonderfully tough material. That is, it takes a good deal of energy to cause it to fracture. This is because nacre is composed of thin sheets of ceramic interleaved with even thinner sheets of organic ‘glue’ Though one sheet is easy to fracture the crack immediately stops when it hits the soft, gluey interface, and it takes another load of energy to start the crack in the next layer. Manufacturing nacre-like materials has been a goal for 25 years and has been acheived with very limited success. A new method may change that, if it can be scaled up. Antoni Tomsia of Berkeley Lab’s Materials Sciences Division and a team of ressearhers there have used the properties of freezing salt water to make a layered composit. When sea water freezes, particulate matter runs ahead of the freezing front with only a few particles being actually trapped in ice. These particles are trapped in between layers of freezing ice crystals and so the result is a layered composite of water ice and particulates. By carefully controlling the freezing rate of a clay/seawater mix the team was able to control the thickness of the layers of mineral . When the water is freezing slowly the layers of particulate are relatively thick, on the order of tens or hundreds of micros.  When the temperature is dropped, freezing rate increases and there are more layers formed per millimeter – down to a 1 micron thick layer. Once the water is sublimated (Freeze dried) away this leaves a nicely layered ceramic. The final step is to allow a thin gluey material to trickle inot the pores in the material.

Berkeley Press Release

Science Magazine Abstract

I wrote a post on the sythesis of a bioengineered resilin a while ago.  This article is on the same research but is longer and more interesting than my post. 

The solid recombinant resilin features properties matching those of the natural version, Elvin says. The group is now working to better understand the material’s basic function so it can synthesize novel polymers that incorporate as building blocks the protein sequence responsible for elasticity.

Scientific American article

Speedo’s Fastskin suit cuts seconds off top swimmers times.  It is also an example of biomimicry in that the rough surface is supposed to be imimtating the tiny dermal denticles of sharks. The basic idea of the suit is that the little irregularities cause local micro-turbulence that decreases drag by allowing a quicker return to free stream velocity at a distance from the surface. 

I had thought that there was not very much experimental evidence that this system works, but I recently came across some really wonderful research on how the system functions. The suits are not very good mimics of sharks skin, but speedo has certainly commercialized a biomimetic product. More on the theory and experiments in a later post.

Random coverage

Secondary harmonic generation (SHG) is when the frequency of light that impinges on the surface of a material is doubled by some physical characteristic of the material.  The shifted light is emitted with a very different color than the input light.  These starch crystals from rice are showing SHG of incident red light.  The cool thing about this biomimetic generator is that the light can impinge over a wide range of angles.

Image info

An explanation of SHG

 I have highlighted several advances in the field of biomaterials that are aimed at replacing destroyed or degraded bone with synthetic materials.  An article in Nature Materials should make it clear that those methods which temporarily replace bone, providing a scaffold for later re-invasion by osteocytes are the best bet for biomimetics companies.  The material properties of bone, particularly its ability to withstand fracture, are complex and depend on the particular orientation of collagen in the mineralized matrix.

Does bone crack like a ceramic or like a polymer? The distinction isn’t clear-cut and various researchers have reported different toughening mechanisms depending on the experimental conditions. The main reason lies in the anisotropy of bone, and on the fact that the mechanism is dependent on the orientation of the crack propagation relative to the alignment of the collagen fibrils. Having performed controlled crack-propagation experiments, Herwig Peterlik and colleagues were able to reveal great differences in the values of crack energy for propagation in different directions. As the propagation of a crack changes from being aligned to being perpendicular to the collagen fibrils, the behavior changes from brittle to quasiductile.

Nature Materials Abstract

Two researchers from Arizona State University have applied for a patent on a method for integrating photonic systems with living tissue. The exact nature of the invention is well concealed by patent, but the research likely falls out of Pizziconi’s research on chlorosomes of cyanobacteria. I will peruse the primary literature for further news.  

One application of the proposed invention is the enhancement of well-known photoactive semiconductor devices, such as Si photovoltaic cells using nanoscale biophotonic constructs that are either acquired, harvested or otherwise manipulated in their natural or adapted state using the method and apparati described herein to achieve desired FoM performance characteristics

Patent Application