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July 19, 2017

Balls That Can Walk on Water

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As children, we learn that to skip a stone across a lake or puddle, we need to have a fairly flat stone. We also learn that a ball thrown at a pool, usually at one’s brother, tends to bury itself into the water rather than skipping. The makers of the Waboba (which stands for ‘water bouncing ball’) have made an interesting use of the viscoelastic nature of polymers to cross the line between a thrown ball and a skipping stone. Look at various videos on-line of the Waboba, and you will see that a thrown Waboba will skip across a flat body of water with equal, or some would say, more enthusiasm than a stone. And it is less painful to catch on the other side.

So how does it work? Unlike balls that are rigid and inflexible, the Waboba will deform and flatten when subjected to a compressive force. When a ball is thrown at a shallow angle into the water, it generates a depression in the water as the entrance force ejects water out of the flat layer. If the ball is inflexible, it will present a small surface area to the backside of the depression in the water, causing the ball to penetrate into the water and eventually sink. A flat stone, on the other hand, presents a larger surface area, allowing the stone to plane on the backside of the water depression and fly out of the depression.

The Waboba enters the water as a spherical ball, but then flattens as the compressive forces generated by the kinetic energy of the thrown ball being counteracted by the resistance of the water. The flattened ball then behaves like the flat stone, and planes out of the water depression. The designers of the Waboba needed to work out the proper range of compressive properties. Interestingly, the harder the ball is thrown into the water, the more it should flatten and hence achieve greater planing behavior.

This important research was conducted 5 years ago by Tadd Truscott, a professor at BYU, who clearly recognized the critical need of explaining why, from strict engineering principles, toys are fun. Videos of Dr. Truscott’s work can be found here, with stills from the video shown below.

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Stone entering water, creating depression.

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The stone rides up the back of the depression and flies out.

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A rigid ball entering the water, creating a depression.

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The smaller surface area pushes the ball deeper into the water.

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Waboba entering the water, flattening under the compressive force of the ball hitting the back of the water depression.

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The Waboba exiting the water depression and resuming its more spherical shape.

Posted by CatherineCerasuolo
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July 17, 2017

Who You Gonna Call?

It isn’t only Ghostbusters that have to worry about being slimed! Last Friday, chaos ensued when 3,400 kg of hagfish were accidentally deposited on a highway in Oregon.

This slimy traffic accident reminded us of work we performed a few years ago in collaboration with Prof Douglas Fudge on understanding quite what is going on when these animals are disturbed.  These evolutionary throwbacks are generally considered the vultures of the deep sea, feeding off carcasses and debris at the bottom of the ocean.  Their skin is often used as a faux eel-skin, but to an engineer the most fascinating aspect of this animal is the slime it produces.  When attacked, the animal responds by generating copious amounts of slime; although relatively small animals, they can generate gallons of gel almost instantaneously. 

It turns out these animals have evolved this spectacular defense based on two physiological components.  There are 150-200 slime glands spaced along the body of the animal.  In each gland are thread cells of about 150 microns in size, but composed of a single wrapped 1-3 micron filament that is 10 -20 cm long.  Along with this cell are high molecular weight mucous glycoproteins in vesicles.  These components expand rapidly upon exposure to water; the vesicles provide an elastic gel-like matrix, while the fibers entangle and hold the gel together.

We performed rheology on hagfish glycoproteins in an attempt to understand the assembly and gelation mechanisms (presented at the Society of Rheology in 2003) with evidence of a yield stress and elasticity, and a strong salt influence.  In the end though, perhaps the most interesting aspect is the manner in which the hagfish clears itself – it simply ties itself in a knot and “slides” the gel off itself.   

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Posted by CatherineCerasuolo
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June 9, 2017

Phoenicopterus Ruber Plasticus

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We are approaching the 60th anniversary of a very important milestone that coupled the unpresuming plastic industry with the world of kitsch: the development of the pink plastic lawn flamingo.  The lawn flamingo was invented by the appropriately and presciently-named Donald Featherstone. Mr. Featherstone, after graduating from the Worcester Art Museum, took a job with a plastic lawn ornament manufacturer in Leominster, MA, a town 1 hour from Cambridge Polymer Group’s headquarters. Leominster has a long history in plastic production, earning the nickname ‘Comb City’ based on its production of celluloid-based combs in the late 1800s. Injection molding also got its start in Leominster, pioneered by Samuel Foster, who made, amongst other items, injection molded sunglasses that go by the name ‘Foster Grants’.  Lastly, Leominster can claim to be the home of Tupperware, the happily burping container system still in vogue.

So pink plastic lawn flamingos were a natural fit for Leominster. Fittingly, Mr. Featherstone received an Ig Nobel Prize for his work in 1996, an award that celebrates both invention and humor, with a smattering of sarcasm. As an interesting aside, Mr. Featherstone and his wife wore matching outfits for 35 years; not terribly relevant, but interesting. Although Mr. Featherstone left this mortal coil in 2015, we are comforted knowing the world he left is a bit pinker and more plasticky.  The flamingos continue to appear in modern culture and on the bolder homeowner’s lawn. Students at the University of Wisconsin were treated to the sight of over 1000 plastic flamingos adorning Bascom Hill on campus in 1979, courtesy of the student government. This event prompted Madison, WI, home of the UW campus, to name the lawn flamingo its official bird in 2009.

So join the plastics world in thanking Mr. Featherstone for this unassuming but important contribution.

Posted by CatherineCerasuolo
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June 2, 2017

Developing a Thicker Skin

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Development of synthetic tissue models has been gaining speed over the past decades as materials, designs, and processing techniques have become more sophisticated. Polyurethane and silicone organ models adorn the desktops of many scientists and physicians, and serve as useful anatomical images and guides. For actual surgical technique development and training, these rigid materials sometimes do not accurately replicate the behavior of biological tissue. Alternative materials, most notably hydrogels, can function well in this role. The highly hydrated nature of hydrogels can give them the feel, elasticity, and cutting behavior of native tissue, and they can often be prepared in form factors that mimic the native organs. CPG has been developing custom tissue models for over 20 years for clients based on its proprietary hydrogel formulations.

Skin is a challenging organ to model, since it has unusual elasticity and frictional behavior when compared to other tissues, such as muscle and fat. Beyond just mechanical behavior, researchers are keenly interested in skin models that help assess biological safety requirements. The standard approach for biological safety is normally an animal model (rat, rabbit), but public resistance to animal testing has pushed for development of non-animal based models. L’Oreal is using additive manufacturing techniques to make films of skin models derived from human keratinocytes, producing a model that is histologically similar to the human epidermis. Intended to allow L’Oreal to test their skin products, the EpiSkin™ model is proposed for tests in involving irritation, UV exposure, DNA damage, and other parameters.

A company local to Boston, MatTek, has also been producing EpiDerm™ skin models for several years by culturing human keratinocytes.

These technologies present an exciting platform for reproducible, clinically-relevant skin testing without the need for animal models.

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Posted by MaryOsward
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May 25, 2017

Minimizing Risk in Medical Device Material Selection

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Are you selecting materials for use in a medical device and feeling overwhelmed by the dizzying array of material options?  In this webinar, Dr. Brian Ralston shares the process CPG uses to help clients select and test materials to minimize risk and maximize safety, efficacy, and prospects for regulatory approval. 

Brian Ralston, Ph.D., P.E., researches and consults on the analysis and processing of polymeric materials and their physical and chemical behavior in products, with a focus on biomedical devices. His expertise spans numerous analytical methods including mechanical, thermal and chemical characterization, failure analysis, design assessment, fractography, statistics, accelerated aging, and development of novel test methods and fixtures.

This webinar is targeted towards:

  • Medical device manufacturers
  • Medical device engineers
  • Process engineers
  • Quality engineers
  • Regulatory personnel

Duration: 30 minutes

MINIMIZING RISK IN MEDICAL DEVICE MATERIAL SELECTION

Wednesday, May 31, 3 p.m., Eastern Standard Time

To register, click here

Posted by CatherineCerasuolo
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May 22, 2017

It Is All About Size

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Ethylene gas, hexane, paraffin wax, and polyethylene all have the same chemical building block, namely an ethylene group (CH2-CH2). The difference in properties in these materials comes from the number of ethylene groups that make up a single molecule. Ethylene gas has a single group (or repeat unit), hexane has 3, and polyethylene can go up in excess of 70,000 repeat units. As the number of repeat units increase, the molecule moves from the idea of a rigid linear rod to a floppy random coil. When placed with other ethylene molecules of comparable size, the chains entangle, which causes the material to transition from a liquid to a solid, as the entangled chains resist disentanglement until sufficient energy, usually in the form of heat, is applied. Some portions of the chains will also align to form crystal structures, which further solidify and rigidify the material.

Although some techniques exist to count the number of repeat units in a material, such as MALDI, molecular weight is normally determined by inferred techniques that look at the size of the individual polymer chain in solution. The size of the chain depends both on its molecular weight and the solvent environment it is placed in (a better solvent and improved temperature will tend to expand the polymer chain more). As shown below, a rigid rod molecule’s size is the number of repeat units multiplied by the length of each repeat units. Most polymers will occupy space as a coil, shown on the right, with a size (the radius of gyration, Rg) dictated by the equation shown below for a good solvent. 

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Researchers have derived relationships between measured properties of polymer solutions, such as viscosity, light diffraction, and osmotic pressure, to determine molecular weights. These techniques all report a mean value of molecular weight. Most polymers have a distribution of molecular weights, as the polymerization process will yield shorter and longer chains around the nominal desired chain length. Gel permeation chromatography (GPC) is a technique that allows determination of the distribution of molecular weights.

In GPC, a dilute solution of polymeric material is prepared using a good solvent for the polymer. This solution is passed through a chromatography column that contains a porous structure that is sized to allow penetration of smaller polymer chains while excluding the larger ones, which effectively separates the polymer chains by size as they exit the column. A detector (or multiple detectors) measures the quantity of the polymer chains at each elution time, forming a concentration vs. elution time plot. A series of calibration standards are injected through the same column, and the molecular weight vs. elution time is determined. By converting elution time to molecular weight for the unknown sample, a molecular weight distribution plot can be determined. As may have been obvious, the actual molecular weights are not measured; rather, the size of the polymer chains are, with the assumption that the size scales with molecular weight. 

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CPG provides GPC analysis on a variety of polymer types, including water soluble, organic soluble, high temperature (for polyolefins), and biologic materials. We can also perform testing using viscometry detectors and light scattering.

Posted by CatherineCerasuolo
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May 18, 2017

Cobalt Brew: Frothy Foam, Sick Heart

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The normal effects of beer consumption are well known.  The ethanol in beer enters the blood stream and eventually makes it to the brain, where the ethanol molecules can sit between brain cells and interfere with neurotransmission, the electrochemical process that controls the activities in the brain, such as body movement, communication, and general thought processes. Too much beer, or ethanol, in a short period of time can interfere with neurotransmission to the point that the imbiber loses control of one or more of these brain processes, leading to classic signs of drunkenness (unsteadiness, impulse control issues, memory lapses, and potential unconsciousness). Excessive drinking for prolonged periods of time can also lead to heart disease, generically termed cardiomyopathy, which is any disease that impairs the ability of the heart to circulate blood effectively.

Heart Disease Spike in Beer Drinkers

A study conducted in 1965 in Quebec and Nebraska of beer drinkers who showed unusually high levels of cardiomyopathy resulted in an unexpected source of drinking-related issues with the heart. In Omaha, Nebraska, in a study of 50 patients, a spike in cardiomyopathy was observed starting in 1964. A similar trend was observed in Quebec around the same time. During interviews, clinicians learned that both sets of patients were frequent beer drinkers, and that each set of patients were drinking the same beer local to their area. The one complicating factor in the Quebec case was that Montreal beer drinkers had access to the same brand of beer, but did not have the spike in cardiomyopathy. Clinicians discovered that breweries in both Omaha and Quebec started adding cobalt sulfate to the beer to stabilize the foam. This practice was employed to counter issues with beer foam dissipation in inadequately cleaned glasses due to poor rinsing of  detergent by the bar staff (yet another issue). 

Too Much of a Trace Metal

Cobalt is a metal commonly used in alloys, and is also part of the metabolism mechanism in all animals. However, too much cobalt can cause issues, such as interference with the Krebs cycle and aerobic cellular respiration. Studies where guinea pigs were administered cobalt into the myocardium resulted in diminished contractions of the papillary muscle.[1]  The clinicians felt that the beer drinkers in Quebec and Omaha were exposed to higher than normal levels of cobalt, which resulted in their cardiomyopathy.

So why the difference between Montreal and the rest of Quebec? For the larger breweries, such as those found in Montreal, separate batches were made for draft beer and bottled beer. Since the bottled beer normally was not put in glasses, no cobalt sulfate was added, hence fewer beer drinkers were exposed to high levels of cobalt sulfate. For smaller breweries, such as those found in Quebec, single batches were made for both draft and bottle, resulting in high levels of cobalt sulfate in both forms of beer. Researchers coined the phrase ‘beer drinkers’ cardiomyopathy’ based on this study.[2] Cobalt sulfate adulteration of beer was discontinued after this study came out.

Trace analysis of metals, such as cobalt, is normally measured in food and polymer products with inductively coupled plasma mass spectroscopy (ICP-MS). Contact CPG for assistance in trace metals analysis in your materials.


[1] Kaufmann, Fleckenstein, Plueger Arch. Ges. Physiol., 282, p 290, (1965).

[2] Morin, Daniel, Canad. Med. Ass. J.,  vol 97, p. 926 (1967).

Posted by CatherineCerasuolo
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