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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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April 28, 2017

Waxworm Eats Plastic

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The durability of plastic materials is both a benefit and a liability. Many plastics can withstand harsh weather, salt spray, ultraviolet light, and mechanical stress for years without visible effect. Unfortunately, this durability also means that when we are done with the plastic, it persists in our waste stream for years, resisting breakdown. A view of any public landfill will show mountains of plastic material. The well-publicized Great Pacific garbage patch, a swirling field of plastic debris estimated at a minimum size of the state of Texas to twice the size of the United States, is the result of years of floating plastic particulate debris accumulating under the influence of ocean currents. Although some photodegradation will occur in some plastics, the debris can persist for decades.

waxworm smaller still.jpgPerhaps the solution to plastic accumulation can be found in the lowly caterpillar.  A recent news article suggests that the waxworm, a caterpillar who evolved to consume beeswax as a food source, also appears to digest polyethylene, at least according to one researcher. Waxworms were transported in polyethylene shopping bags, and were able to reduce the bags to shreds in a few hours, with no visible signs of particulate debris. The researchers believe that the polyethylene was being converted to ethylene glycol (e.g. antifreeze), although more data is required. The question is, what are the chemicals or enzymes in the waxworm that allows this process, assuming the observations are correct? If they can be identified, can they be produced and applied on a larger scale to reduce the persistence of plastic debris? 

Posted by CatherineCerasuolo
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April 14, 2017

Born to Run...GCMS & DMA

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Running shoe technology has come a long way since Bill Bowerman, a running coach at the University of Oregon, first made prototypes by melting rubber into treads with a waffle iron in the 1960s, starting what would become Nike. As material technology improved, along with capabilities in analyzing running kinematics and physiology, shoe designs have gotten more complex, with complicated viscoelastic cushioning, designs to correct pronation, and lightweight materials to allow greater turnover speed. A book published in 2009, Born to Run, started a short but passionate trend backwards towards less cushioning and more minimalistic shoes. Since then, runners have cycled back towards more cushioned designs.

In preparation for the Boston Marathon on Monday, we decided to evaluate a few pairs of running shoes, comparing and contrasting at their viscoelastic properties and chemical properties.  Running shoes are typically made from various types of polymers, and may provide a great deal of cushioning, or very little at all! It is apparent that some of our samples have been used to run many miles, while others are more gently used.

Dynamic Mechanical Analysis 

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CPG used dynamic mechanical analysis (DMA) to measure the ability of the materials that make up the sole of the shoe to absorb and return mechanical energy. Storage modulus measurements are representative of the elastic portion of the stored energy, while the loss modulus measurements are representative of the viscous (or fluid-like) response of the material. Tan delta values may be interpreted as a “damping ratio,” characterizing the ability to which a material may absorb and dissipate energy. The above figure shows a comparison of the storage modulus, loss modulus, and tan delta for all shoe samples tested at a test frequency of 1Hz. 

Significant differences in storage modulus were observed among the tested samples. Generally, storage modulus values for shoe soles was significantly greater than the corresponding shoe’s insole, a measure of the increased stiffness of the sole and softer, more compliant nature of the insole. Significantly higher storage modulus values were observed for the “lightly used” Mizuno sole than for the “heavily used” Mizuno sole, suggesting that the mechanical properties (and underlying materials) have degraded with prolonged use and environmental exposure, likely due to permanent compression of the porous structure in the sole.

Tan delta values (representing damping) were higher for the insole as compared to the corresponding sole, providing a measure of the ability of these components to dissipate energy during running, ensuring a more comfortable running experience—an important factor over 26.2 miles!

HS-GC-MS

In order to perform a chemical comparison between the shoe samples, they were analyzed by headspace gas chromatography couple to mass spectrometry (HS-GC-MS). 

Measured chemicals may come from the constituent materials composing each sole, from environmental interferences[1] (all shoes were sampled from a mildly worn state), as well as from thermal degradation during the headspace heating and off gassing process.

Vibram

Some compounds identified in the Vibram sole include benzaldehyde, benzothiazole, decamethylcyclopentasiloxane, and BHT, suggesting the material contains significant silicone rubber elements. The benzothiazole is related to accelerators used for the crosslinking (vulcanization) of rubbers.

Nike

Some compounds identified in the Nike sole include n-butanol, α-methylstyrene, acetophenone, and butylated hydroxytoluene (BHT). These compounds suggest the sole is composed of a synthetic rubber rather than a natural rubber, due to the presence of styrene derivatives and possible degradation products. The BHT is likely added as an antioxidant to prevent material degradation during processing and usage. The n-butanol is likely used as a processing solvent during the rubber production.

Asics

Some compounds identified in the Asics sole include ethylhexanol, 1,2,3-trimethylbenzene, 2-pentyl-furan, acetophenone, 1-dodecene, 2,6-di-tert-butylbenzoquinone, and BHT. BHT is a widely used antioxidant and it is therefore not surprising to see its presence in each of the samples tested here.

Mizuno

Some compounds identified in the lightly used Mizuno sole include toluene, phenol, benzothiazole, acetophenone, and BHT. The toluene may be a residual solvent from rubber processing.

Headspace GC-MS is a valuable tool for exploring the chemical nature of polymeric samples, processing history, residual products, degradation products, and characterization of off-gassed species. Contact us for more information about HS-GCMS.

Read the full Born to Run...GCMS & DMA application note.


[1] A polite way of saying ‘foot odor’

Posted by CatherineCerasuolo
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