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In this issue:

=> Human Exoskeleton and More Bone Repair Breakthroughs
=>  Ask Jim: How Much Free Styrene is Left in Typical Polystyrene?
=>  Highlights From the PSI Newsblog



Human Exoskeleton and More Bone Repair Breakthroughs


by Dale McGeehon
Exclusive to Polymer Solutions News
EvillCast

The wicked looking garment you see pictured here isn't Goth dance party attire but an orthopedic cast created by designer Jake Evill. It was made with a three-dimensional (3-D) printer. Even though the nylon cast has not yet been approved for medical use by the U.S. Food and Drug Administration (FDA), Evill is the talk of the town and one of several new polymer solutions we'll look at in this article.

The Problem With Plaster Casts

Do you remember the plaster casts kids wore 20 years ago? If you broke an arm or leg, your injured limb became a papier-mâché science project. Your doctor would dip a roll with plaster in some water and then proceed to wrap it around the broken bone. In minutes, it hardened into a slightly chalky cocoon.

Sure, your social status improved. Other kids wanted to sign it, or write or draw funny things on it that maybe you wished they hadn't. But bless you if you had an itch inside and couldn't scratch it. Bath time meant getting it wrapped in plastic or hanging it away from where the water could reach it.

And when the time came – finally – for the doctor to cut it off? Phew. What a stinky mess. All that dead skin couldn't flake off naturally, so it stayed, trapped within the cast, moist with sweat.

Enter Jake Evill and the Cortex Cast

The new nylon plastic lace cast designed by Jake Evill, a graduate student at Victoria University in Wellington, New Zealand, eliminates all those problems, reports MedCity News.

It's ventilated, allowing the skin to breath, and washable. It's also a strong brace, providing the most support at the point of fracture so that the broken bone is immobilized, allowing it to mend.

Evill's "cortex cast" is printed, ready to wear, and snaps closed with built-in fasteners, reports The New Zealand Herald. It can be worn discretely under a shirt, blouse, or jacket.

Evill was inspired when he broke his hand in what he sarcastically calls a "heroic rescue" of his friend during a fight, reports Liz Stinson for Wired UK. His hand required a traditional plaster cast for a few months.

"I was surprised by just how non-user friendly those cumbersome things are," Evill says. "Wrapping an arm in two kilos of clunky, and soon to be smelly and itchy, plaster in this day and age seemed somewhat archaic to me."

So Evill teamed with the university's orthopedic department to develop the concept. MedCity News explains further:

Patients being fitted for these braces would have an X-ray taken and then a scan of the injured arm or leg. A computer would assess the optimal pattern and structure for the cast. The honeycomb design would do away with the stinky, sweaty yuckiness that accompanies plaster and fiberglass casts and allow more breathing room for the skin.

Cortex Plastic Cast is Still In Development

The inspiration for Evill's so-called Cortex pattern came from a structure that forms the inner tissue of a bone called the trabecular. "It was this honeycomb structure that inspired the Cortex pattern because, as usual, nature has the best answers," Evill says. "This natural shape embodied the qualities of being strong whilst light just like the bone it is protecting within."

Once the cast was modeled, he sent it to a factory in the Netherlands where it was made with nylon plastic with a 3-D printer at a cost of $85. A typical Cortex cast would be only three millimeters thick and weigh less than 500 grams -- just over a pound.

A 3-D-printed cast takes longer to make than a plaster cast. Evill admits his cast is a work in progress. He is looking for collaborative partners and a hospital to host a pilot project. Perhaps this novel concept will soon be available to consumers. It is certainly inspiring orthopedic doctors rethink the traditional plaster cast.

Other Breakthroughs in Bone Repair

Evill's work is just one of many advancements in orthopedic medicine of late. For example, Oxford Performance Materials, based in South Windsor, CT, uses high-performance polymers with 3-D printing to create skull implants that can be designed and shaped for an individual's specific need. It received approval from the U.S. Food and Drug Administration last February.

Spanish researchers from the UPV/EHU-University of the Basque Country are developing biodegradable polymers, infused with bioglass, that could help badly broken bones heal without needing additional surgical procedures. As is often the case now, doctors have to put pins and bolts into shattered bones to mend them. When the bones heal, another surgical procedure is needed to remove the metal pins.

An Israeli company, RegeneCure, based in Jerusalem, has invented a polymer membrane that helps heal broken bones 40% faster than traditional methods. Sometimes doctors use autografts, where they take healthy bone from a donor and put it into the injury site, or use bone graft substitutes to fill a fractured gap. The new polymer membrane, on the other hand, can be formed into any geometric shape to wrap the damaged bone and can support bone drills and sutures. Its properties stimulate bone growth.

Polymers Solutions Incorporated can help companies and researchers determine whether their medical device or a polymer-based material meets industry standards or works properly. PSI's team of scientists can perform chemical analysis and physical testing of medical devices at any stage of their life cycle. In addition to testing medical devices, PSI also has extensive experience in analyzing implants, tissue engineering materials, drug delivery systems, and bone scaffolds. Quotes and consultations can be easily obtained.

Source: "Wow of the week: Could a 3-D printed cast become a disruptive medical device?" MedCity News, 7/6/13
Source: "Kiwi designer creates 3D-printed exoskeleton for broken bones," The New Zealand Herald, 7/5/13
Source: "This 3D printed cast could be the future of healing broken bones," Wired, 7/5/13
Source: "Modernizing the Plaster Cast with a 3D Printer," Mashable Video

Image by Jake Evill Design


Ask Jim: How Much Free Styrene is Left in Typical Polystyrene?


by James D. Rancourt, Ph.D., CEO of Polymer Solutions Incorporated
Exclusive to Polymer Solutions News
Resdiual Monomers

Ask Jim is a regular feature in Polymer Solutions News where PSI's Founder & CEO, Jim Rancourt, Ph.D., answers puzzlers about polymers submitted by readers. This month's question was submitted by Darren Macfarland who gets a $25 Starbucks gift certificate. Send your questions to askjim@polymersolutions.com.

Darren Macfarland with Hach Company asks:

"How much free styrene is left in typical polystyrene?"

Jim Rancourt replies:

Darren, thank you for your question! I will answer it on the most basic level but then also expand. Your question gets at a much bigger issue: residual monomers.

The amount of styrene left in a typical polystyrene depends on the manufacturer and on the application of the polystyrene. In general, you can expect to detect less than a few percent, and preferably much less than that. Also, consider that styrene is not the only monomer that may be left behind in a polystyrene sample.

Now, if I may expand as to why residual monomers need to be detected and understood. I will call this "Three Reasons Why You Should Sweat the Small Stuff".

  • Monomers Can Be a Health Hazard
  • Monomers Can Create Packaging Aesthetic Issues
  • Monomers Can Cause Taste and Odor Issues

Polymer materials are used extensively to manufacture components of medical devices, for packaging applications, and for a wide array of consumer products. Because polymers are large molecules manufactured by linking small molecule repeat units together, some level of residual un-reacted repeat units exist in all manufactured polymers. The repeat units are called "monomers" and their presence can be cause for concern.

Monomers Can Be a Health Hazard

Gum-like products can be manufactured using polyisoprene (rubber) as one of the components. A material safety data sheet (MSDS) for polyisoprene indicates this polymer to have a Health Rating of "0." This Health Rating means, "This material poses no significant risk to health."

From a health perspective the polyisoprene polymer has no harmful health effects. However, the residual monomers in gum products can include isoprene, isobutylene, and methyl chloride. Isoprene is an irritant, suspected mutagen, and suspected carcinogen having a HMIS Health Rating of 2. Isobutylene has a HMIS Health Rating of 1, and methyl chloride is a suspected carcinogen and suspected teratogen with a HMIS Health Rating of 2.

The Hazardous Materials Identification System (HMIS) is a numerical hazard rating that was developed by the American Coatings Association. It is a compliance aid for the OSHA Hazard Communication Standard.

HMIS Health Rating Description A Common Example
4 Life-threatening, major, or permanent damage may result from single or repeated overexposures (e.g., hydrogen cyanide). Nitric acid
3 Major injury likely unless prompt action is taken and medical treatment is given. Swimming pool chlorine/bleach
2 Temporary or minor injury may occur. Lacquer paint
1 Irritation or minor reversible injury possible. Methanol
0 No significant risk to health. Ethanol

When gum-like products are analyzed for residual monomers, low ppm range levels of isoprene, isobutylene, and methyl chloride are typically detected.

Monomers Can Create Packaging Aesthetic Issues

Line trimmers that are employed in lawn care applications use a monofilament string as the cutting device. The string can be manufactured using several types of polymer materials. One material that is used to make line trimmer string is polyamide (nylon 6).

Nylon 6 is manufactured using caprolactam monomer. Residual monomer acts as a plasticizer, a material that makes the string flexible. More plasticizer causes the string to be more flexible and softer than the same polymer with less residual monomer plasticizer.

A characteristic of monomer materials is that they can migrate out of the polymer during storage and use. The loss of monomer causes the nylon string to become stiffer than it originally was. Not only that, if the monomer migrates out of the line trimmer string while in the package, the packaging material can become discolored and have surface residues that detract from the appearance of the package and provide a poor impression to the consumer.

When nylon products are tested for residual monomers, amounts in the range of 6% or less are typically detected.

Monomers Can Cause Taste and Odor Issues

Polymers are used in a vast array of packaging applications, some very sophisticated and others seemingly simple. In all cases, residual monomers are of concern in food contact applications because the monomers can alter the taste of the food product. The monomers alter the taste of the food product by migrating into the food. "Extractables testing" determines the amount of monomers that a solvent can extract from packaging.

"Leachables testing" determines the amount of monomers that can leach from a container into a product. Some view the extractables content as a worst-case estimate of the potential leachable content.

For example, polystyrene is a material that is used to manufacture some beverage cups. Styrene is one of the residual monomers that is present in polystyrene.

When polystyrene resins intended for food applications are tested for residual monomers, amounts of less than 500 ppm are typically detected.

 

Detection of Monomers in Polymer Products

The three primary methods that Polymer Solutions uses to determine the chemical identity and amount of residual monomers in polymers are:

Gas chromatography coupled with mass spectrometry (GC-MS)

  • Useful for volatile chemicals
  • Detection range of 1 ppm or less

 

Liquid Chromatography (LC)

  • Useful for volatile, and nonvolatile soluble, chemicals
  • Detection limit of 0.05% or less

 

Nuclear Magnetic Resonance (NMR) Spectroscopy

  • Useful for volatile, and nonvolatile soluble, chemicals
  • Detection limit of 0.5% or less

 

Thanks for asking!

Jim Rancourt, Ph.D.

Image by CORE-Materials


Highlights From the Polymer Solutions Newsblog

The PSI Newsblog features original reporting on breaking news in the fields of plastics analysis, plastics testing, and plastics failure. Here are this month's most popular articles:

 

  1. Mouse Heart Regenerated With Human Stem Cells
    Researchers have succeeded in getting a mouse heart to beat again by rebuilding it with human stem cells. The breakthrough may have implications in regenerating human heart muscle.
  2. Dogs May Detect Signs of Cancer Sooner
    Dogs have been useful in sniffing out illegal perishables brought into a country, bombs, and survivors buried under rubble. Now, they may be helpful in chemical analysis detecting ovarian cancer.
  3. New Packaging Designs Solve User Problems
    Companies spend $150 billion annually on packaging trying to find ways to make products more consumer-friendly. New innovations and highlighted design changes that have solved some problems.
  4. Proper Packaging Reduces Food Waste
    Packaging fresh food makes it last longer. A packaging advocacy group in England has started a campaign called "The Good, The Bad and The Spudly," to counter negative publicity on packaging and help reduce food waste.
  5. Polymer Fights Drought Conditions
    Yes, now there's such a thing as "powdered water" -- and no, we're not talking about snow.

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