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November 17, 2017

Turkey-Inspired Supraballs

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It’s that time of year when the turkey takes center stage, er, table. Although many claim Ben Franklin lobbied for the turkey to become the United States’ national symbol, Franklin was taken out of context. Franklin neither publicly championed the turkey nor opposed the bald eagle, and he characterized the turkey as “a little vain and silly.” Although the wild turkey was never a candidate for national symbolism, it has played a significant role in the culture of many Native American tribes, from sacred warrior to fabric to favorite meal.  Wild turkey was important to European settlers as well; historical record puts wild turkey on the menu at the first Plymouth Thanksgiving, unlike pumpkin pie, potatoes and cranberry sauce, which wouldn’t have been available to the Pilgrim colonists.

Better Color Through Chemistry

In addition to these cultural and culinary roles, Meleagris gallopavo has another claim to fame. Turkey feathers have inspired an international team of researchers to create a new type of structural coloring, a nanoparticle made of melanin and silica, called a “supraball.” Changing the thickness of the silica shell surrounding the melanin core determines the shade and intensity of color.

Chemical pigments, produced by the absorption of light by molecules, fade as they break down. Structural colors, created by the scattering of light by nanostructures, are resistant to bleaching and are less dependent on toxic materials than pigments. Although structural colors have obvious advantages to chemical pigments, obstacles remain to the mass production of structurally colored materials.

Many structural colors are iridescent and not practical for wide-angle displays. Non-iridescent structural colors often lack adequate color saturation due to incoherent scattering. Although a partial “solution” for non-iridescent colors has been found, it is not scalable; core-shell nanoparticles with a shell refractive index (RI) comparable to water have been used to tune core spacing to attain optimal scattering for non-iridescent colors, but only in solution.

The discovery of the supraball technique could overcome these challenges. Supraballs tune core spacing without the need for a solution, and yield a full spectrum of colors. Additionally, the reverse emulsion process used to create the supraballs is simple and scalable. The nanoparticles cluster into supraballs at room temperature in water and octanol, and can be extracted as a powder.

Paint It Black

Melanin is a dark biological pigment found in skin, hair, feathers (including turkey), scales, eyes, and some internal membranes. The use of melanin, with its high RI and broadband absorption of lights, increases the brightness and saturation of the supraballs. The spacing between the balls of melanin produces different colors, although only from normal distance; under a microscope, the supraballs are black.

The low RI clear silica shell forces the melanin cores farther apart or closer together, depending on the thickness of the shell.  This color tuning technique, using high-RI cores and low-RI shells to increase reflectance and brighten colors, was inspired by the hollow, high RI contrast melansomes of wild turkeys, and the hexagonal nonclose-packed melansomes of green-winged teal (see below).

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Researchers believe this technology can be replicated at the industrial scale, and has many potential applications. Since melanin can dissipate 90% of UV radiation, supraballs could be used to color UV-resistant inks. Supraballs could also be used in paints, plastics, coatings, and, since melanin is biocompatible, cosmetics and food.

Posted by CatherineCerasuolo
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November 16, 2017

Cranberry Polymers

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Some of us dread Thanksgiving - the prospect of awkward political discussions, family dysfunction, and, last but not least, the debate over home-made vs. canned cranberry sauce. This annual cranberry conflict seems like a subject fit for a Seussian Butter Battle sequel. Many households solve the problem by offering both a thick, homemade sauce and a can-shaped, store-bought jelly. In either version of the cranberry condiment, pectin polymerization plays a vital role.

Pectin Polymerization

Regardless of whether the sauce is made in the kitchen or factory, the first step is dissolving sugar in water. Once the sugar is dissolved, it is safe to add the cranberries. Heating the berries before adding the sugar will result in a runny pink liquid, unappealing to all.

Cranberries contain a great deal of pectin, a naturally occurring polymer found in the cell walls of plants. When the berries are heated, their cell walls pop open and break apart, releasing the pectin. Pectin is usually attracted to water molecules; however, if most of the water molecules are already bonded to sugar molecules, pectin polymers will bind to other pectin polymers, giving your cranberry concoction more structure. The linked pectin increases the viscosity of the sauce, thereby thickening it in a fashion similar to gravy.

Cooking the sauce for longer will release more pectin, increasing the stability of the sauce, and resulting in a more gelled dish.

Pectin has been used by the food and beverage industry for years as a gelling agent, a thickening agent, and a colloidal stabilizer. The pharmaceutical and biotechnology industries are also discovering applications for pectin; its distinctive properties allow it to be used as a matrix for drug delivery or cell/protein entrapment.

Cranberry is a Type-A Fruit

The American cranberry, one of only three fruits native to North America, contains large amounts of A-type proanthocyanidins (PACs). Cranberry proanthocyanidins are a varied group of polymeric structures made up of flavan- 3-ols, ranging greatly in size and structure. Unlike most other fruits which contain B-type PACs, cranberry’s A-type PACs have been shown to impede bacterial adhesion to cellular or biomaterial surfaces. Recent research published in Nature:Scientific Reports demonstrates that cranberry PACs interfere with bacteria’s ability to spread and become virulent.

So let’s all stop fighting about the preferred viscosity of our turkey condiment, and be thankful that the cranberry is a red beacon of hope in our war on drug resistant bacteria.

Posted by CatherineCerasuolo
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November 6, 2017

Crosslinked Polymers Guest Star on The CW's Flash

Elongated Man: Silly Putty Vs. Rubber Band 

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Warning: This blog post contains spoilers from Season 4, Episode 4 of DC Comics/The CW's The Flash.

“Elongated Journey Into Night" introduces Ralph Dibny, a former cop turned private investigator, recently endowed with superhuman stretching abilities by a dark matter bus accident. Dibny doesn't know how to control his newly acquired powers and can't shrink his limbs back to normal after being stretched off a six story building. Team Flash takes Dibny to S.T.A.R. Labs for diagnosis and treatment.

Dr. Harry Wells: The dark matter has polymerized Dibny’s cells.

Dr. Caitlin Snow: You’re saying the walls of every cell in his body have elasticized?

Harry: I’m saying that they’ve formed an unbreakable bond on the atomic level and they stretch these cells and stretch these cells...Like Silly Putty!

CPG scientists, choosing not to take artistic license into account, provide a scientific rebuttal, and anxiously await notification of a writer’s credit from The CW.

CPG's Response

From a molecular structure point of view, Silly Putty is an incorrect analogy, since the crosslinking bonds formed in Silly Putty are transient boron-linkages that readily de-form and reform under extensional deformation, and are hence breakable.

Silly Putty is best described as visco-elastic, having both viscous and elastic properties. If Dibny were truly like Silly Putty, he would eventually settle into a shallow, liquid-like pool due to the viscous behavior of Silly Putty. 

A better analogy for Dibny would be a rubber band, which has covalent bonds which are more permanent, and hence ‘unbreakable’. Rubber bands are primarily elastic, meaning they can stretch but then retain their normal shape once the stress is removed.

More troublesome in this clinical description of Dibny is the idea that his cells have undergone polymerization, which presumably means that each cell has become covalently bonded to another cell. Would this be the case, Dibny would effectively have become a crosslinked system, which would resist, rather than encourage, elastic deformation.

Dibny's Treatment: Crosslinking or Depolymerization?

In an attempt to return Dibny's overextended extremities to regular sizes, Snow synthesizes a crosslinking serum:

Caitlin: Drink this...It’s a serum of sulfur, zinc oxide and steric acid to crosslink your polymerized cells.

Dibny: You did it! I’m cured!!!

Caitlin: Well, not cured. All I did was introduce a stabilizing enzyme to reset your body to default shape through vulcanization.

CPG's Response

Interestingly, none of the serum components described by Caitlin are an enzyme. Stearic acid is a wax-like compound derived from animal and vegetable fats, and would play no role in crosslinking. Zinc oxide would also play no role in crosslinking, but would help Dibny avoid sunburn.

However, the sulfur mentioned is used in vulcanization of rubber, which crosslinks the rubber so that it can be used in tires, so it is sort of in line with Caitlin’s crosslinking statement. However, high temperatures are required for vulcanization (normally in excess of 150°C), so Dibny would have other issues beyond an unusual level of cellular stretchiness.

From the diagnosis above, however, Dibny’s problems are not due to the need for more crosslinking, but rather less crosslinking. So Dibny really needs a depolymerization process. For this, we would recommend either a peroxide-based catalyst, an unhealthy dose of ultraviolet light, a good amount of heat, or lots of mechanical deformation, all of which could cause depolymerization.

Posted by CatherineCerasuolo
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November 3, 2017

Da Vinci and Plastic

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Following our previous blog on the potential first report of a plastic in Capri around 30 A.D., the recent publication of Walter Issacson's biography of Leonardo Da Vinci prompted us to query whether this prolific inventor and student of materials dabbled in plastic technology. We, of course, were not the first to think of this, and there is some evidence that Da Vinci did plastically dabble.

As originally reported by the Discovery Channel, the director of the Museo Ideale in the Tuscan town of Vinci, Da Vinci’s birthplace, believes that Leonardo’s copious notes in his Codices contain recipes for synthetic materials. Allessandro Vezzosi, the director and Da Vinci scholar, found experiments in Da Vinci’s notes where he combined glues derived from animal and vegetable sources with organic fibers, and coated these mixtures onto animal organs and the leaves of cabbages or lettuces.

When Vezzosi repeated these experiments, the hardened layer was removable from the vegetable matter or organ tissue, and resembled BakeLite, a phenol-formaldehyde based thermoset developed in the early 1900s and considered to be one of the first widespread synthetic plastics. Da Vinci’s notes further describe incorporating pigments into his mixtures, perhaps making one of the first master-batch compounded resins. Vezzosi suggested that the resulting materials were tough enough to resist breakage when dropped on the floor, and could have been used to make vases, cups, and knife handles, all items that incorporate modern plastics.

Sadly, none of Da Vinci’s plastic cups or utensils survive today, if indeed they were ever created. In addition to the historical significance, they would have presented a wonderful opportunity for a long-term shelf-aging study. Similarly, given Da Vinci’s interest in the human anatomy, one speculates what would have happened if Da Vinci had tried his hand at an artificial knee using his resin.

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Posted by CatherineCerasuolo
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October 31, 2017

A Bit of a Stretch

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Given that today is Halloween, this blog entry started with the question of what is the most popular candy? For Massachusetts, the home of Cambridge Polymer Group, that candy is Starburst.[1] Starburst bears a loose association with taffy, which is a candy made by stretching a heated mass of sugar. The act of pulling taffy introduces small air bubbles into the molten sugar, which makes the mixture softer and improves the texture.

Do the Taffy Math

3rodtaffystretcher.jpgYou have likely seen a taffy stretcher at a candy shop. I always thought it was for show, but it turns out that it is a necessary process to make the taffy. Pulling taffy by hand is challenging, given the temperature of the material, the viscoelasticity, and the number of required pulls. What I hadn’t also realized was the complex math that these confectioners were practicing in front of us. As discussed by Jean-Luc Thiffeault, from the University of Wisconsin, taffy pulling is modeled by topological dynamics, and is associated with the dilatation of pseudo-Anosov maps.[2]

I know; I was excited to hear about this association as well, but even more so when I heard that they give a nod to the special integer relationships of Golden and Silver ratios.  Any budding theoretical rheologist would grow faint. What this means, essentially, is that the taffy is stretched exponentially overtime. Thiffeault’s article touches on the interesting patent fights that occurred in the 1920s over taffy stretcher designs, going all the way up to the Supreme Court.

Mixing Polymer Melts

The relevance to our work at Cambridge Polymer Group is the mixing of viscoelastic materials, such as polymer solutions and melts, and pharmaceutical compounds. Standard mixing processes used for Newtonian solutions (think sugar mixing into water) do not apply to viscous materials, which requires a great deal more energy and benefit from a combination of shear and extensional flows. Optimization of mixing procedures is key, since polymers and pharmaceutical compounds can be sensitive to heat and mechanical deformation; finding the optimal mixing conditions can preserve the original properties.

So ponder those pseudo-Anosov maps next time you have a salt-water taffy, and consider how this popular candy, at least in Massachusetts, has benefited the plastics and pharma industry. Note: salt water is not a taffy ingredient. The name is allegedly a joke made by a Atlantic City candy shop owner whose taffy was soaked during a storm.

 


[1] https://www.usatoday.com/story/news/nation/2016/10/20/most-popular-halloween-candy/92473320/

[2] Thieffeault, “A mathematical history of taffy pullers,” https://arxiv.org/pdf/1608.00152.pdf (2016).

Posted by CatherineCerasuolo
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October 20, 2017

Move a Mussel

Biofouling, the adhesion of sea life to ships' hulls, is a serious problem for all marine vessels. The sticky stowaways significantly increase the hull's friction; the resulting drag decreases boat speed and increases fuel consumption by up to 40%. In the past, the most effective solution was to dry-dock the boat and manually remove the sea life, which is expensive and labor intensive. In addition to the financial toll of increased fuel usage and dry dock cleaning, marine fouling also contributes to the spread of invasive species.

Anti-Fouling Biocides vs. Non-Toxic Hydrogel

Many commercial anti-fouling agents are composed of toxic chemicals. The obvious drawbacks to a toxic approach are water pollution and the poisoning of non-fouling species. Additionally, anti-fouling biocides need to be replaced frequently, and do not always work well. 

The US Naval Coastal Systems Station contracted Cambridge Polymer Group to develop a slow-dissolving hydrogel formulation to clean ships' hulls underwater. Applied by divers using gun applicators, the hydrogel eliminates the need for dry dock manual removal. Simple dilution of the hydrogel makes it safe for marine life, providing a non-toxic, affordable solution for boat cleaning.

Mussel Attachment Issues

But what if the fouling itself could be prevented? Recently, Harvard researchers unveiled a lubricant-infused coating which stops mussels from attaching to underwater surfaces. Mussels are some of the worst biofouling offenders; they have evolved to stick under the severest of marine conditions. As part of that adaptation, mussels secrete adhesive filaments called byssal threads. These threads are tipped with adhesive plaques which remove water molecules from the wet surface, allowing the plaques to bind to it.

The researchers' lubricant-infused polymer coating fools the mussel into sensing the hull's surface as too soft for attachment. This trick discourages the mussel from secreting its adhesive filaments, preventing attachment of the mussel's foot. Even if a mussel attempts to deploy its byssal threads, this Slippery Liquid Infused Porous Surface (SLIPS) stops the threads from binding. Co-first author Shahrouz Amini speculates the liquid overlayer of the lubricant-infused surfaces resists displacement by mussels' adhesive proteins.

The amazing adhesive ability of mussels does have positive applications. UC Santa Barbara researchers have developed stronger, more durable dental fillings using catechols, the same chemical groups used by the mussel to promote adhesion on wet surfaces (wet surfaces except for SLIPS, that is). Purdue researchers have inserted catechol into a biomimetic polymer, creating an underwater adhesive that outperforms many commercial adhesives.

Posted by CatherineCerasuolo
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October 12, 2017

Leachable Studies of Medical Devices in Complex Biological Environments

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 Thursday, October 12, 2:10 p.m. EST

Adam Kozak, a senior research scientist at Cambridge Polymer Group, presents "Leachable Studies of Medical Devices in Complex Biological Environments" at Eurofins Lancaster Laboratories' Extractables and Leachables Symposium for Drugs and Devices in Pennsylvania.

Detailed Extractables/Leachables Studies

Extractables and leachables studies usually follow a two-step program. In the first step, an exaggerated extraction is conducted using simple solvent conditions more aggressive than those anticipated to be realized in a clinical setting in order to determine to determine the complete extraction profile and to identify the potential extraction compounds, desired or undesired. In the second step, a leaching study is conducted that attempts to simulate the clinical environment of the target application. The simulated leaching environment often comprises a more complex biological matrix than those used for extraction, which in turn complicates the chemical analysis assays used to identify and quantify the leaching materials. In this presentation, we show examples of studies that required a more detailed testing assay to identify and quantify compounds coming from implanted medical devices.

Biography

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Adam Kozak specializes in the chemical and mechanical analysis of polymer materials and medical devices. He has substantial experience in the use of gas chromatography-mass spectroscopy (GC-MS) for leachables and extractables analysis, trace impurity/contaminant analysis, residual monomer content, unknown compound identification, migration levels, deformulation, and odor analysis by headspace GC-MS and other chromatographic techniques.

Posted by CatherineCerasuolo
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