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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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April 7, 2017

What plastic to use in your medical device?

whichway.jpgThe selection of a polymer for a medical device requires careful thought and knowledge of both the plastic and the target application, and how each will respond to the other. The range of choices of polymers for medical applications continue to increase as resin manufacturers synthesize novel homopolymers and copolymers, compounders create polymer blends and additives packages, and processors perform finishing steps such as crosslinking and surface treatments. Polymeric materials in medical devices range from rigid UHMWPE and PEEK, to flexible TPEs, films, and woven constructs, to soft hydrogels.

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What is the Target Application of Your Medical Device?

When we assist clients in selecting a polymer for their device, the project always starts with a detailed description of the target application. Will the device be an implant with longer than 30 days in the body, will it be in the body for less than 30 days, or will it never contact the patient directly but instead be used in a medical setting (such as packaging or the housing on an infusion pump)? If the device is an implant, is it intended to be permanent or is deliberate degradation desirable? If the latter, over what time scale? And of course, where in the body will the device be used?

Following these questions, we then ask about the device design to get a sense of what material properties will be important. For example, in a hip or knee component wear behavior is important, along with resistance to fracture due to impact loads. For a spinal rod, creep behavior under physiological loads is relevant. For a heart valve, fatigue resistance for millions of cycles is relevant. For a drug release device, the microstructure of the material is important as it can influence the release kinetics. If known, target material properties, such as tensile strength, modulus in the relevant loading condition, wear rates, or pore size, are listed as required specifications. This information is often the result of computer simulation of the design in its target application area. Often times, however, the required specifications or material behavior inputs for simulation are not known, and some initial guesses have to be made, to be verified later during screening tests.

As part of this discussion, the potential manufacturing process is considered, which will further aid in polymer identification. In some designs, injection molding is required, while others may require film extrusion, compression molding or fiber spinning. The use of additive manufacturing has further expanded the consideration of material selection. Storage life of the plastic is relevant for inventory control, as is secondary sources of the material. Lastly, the cleaning and disinfection/sterilization process has to be considered, since both can affect some polymer materials.

This approach helps define the required material specifications for the device. This list may grow as more information is gathered through screening tests, design verification tests, or even through validation testing.

Material Selection & Testing

We then begin assembling a list of candidate materials, normally starting with materials that meet the known property requirements. This material list can be filtered by materials that already have clinical use, ideally in the same or similar clinical area. Any clinically relevant information, such as testing performed to ISO 10993, is considered. There are many cases where an off-the-shelf solution does not exist, but a custom formulation or modification of an off-the-shelf solution can be provided.

After the list of candidate materials has been reviewed with the client, selected candidate materials will be ordered. At this point, we will often perform specific tests on the materials relevant to the client’s target application that are beyond the standard mechanical property tests provided by the resin manufacturer. These tests may include standard or custom fatigue tests, oxidation resistance tests, biocompatibility tests including leaching and extractables, or processability tests. Based on results of these tests, the list of candidate materials can be further reduced.

From this reduced list, we or the client will then make prototype assemblies of the target device, in order to test manufacturing processes and to evaluate the potential failure modes of the device with the candidate materials. Based on these results, the material criteria may be further modified, the design may be adjusted, or a candidate material may rise to the top.

Of course, the cost of the polymer is an important consideration. Depending on the anticipated volume and price point of the device, pricing considerations may be a primary criterion, or a secondary one. The actual polymer pricing depends heavily on volume and form factors.

During this whole process, we encourage the client’s production team to be involved, along with the design team, as both parties have unique understanding of their capabilities and requirements.

If you need assistance in developing a new medical device, or in evaluating alternate materials for an existing device, please contact us.

Posted by CatherineCerasuolo
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April 4, 2017

CPG Receives ISO 17025 Accreditation

A2LA-accredited-CPG.jpgCambridge Polymer Group is pleased to announce ISO/IEC 17025:2005 accreditation by the American Association for Laboratory Accreditation (A2LA).

ISO/IEC 17025:2005 is the international standard by which a testing laboratory’s commitment to quality and technical competence is evaluated. ISO 17025 includes ISO 9001 standards and adds higher level requirements, specific to testing laboratories. CPG underwent a thorough assessment of its quality management processes and competency to perform chemical testing. 

Cambridge Polymer Group achieved ISO/IEC 17025:2005 accreditation by demonstrating its compliance with the standard and A2LA accreditation requirements. This accreditation is further evidence of CPG's commitment to quality and technical expertise.  Our dedication to quality is an integral part of our strategy of being recognized as the premier contract research organization in North America, offering a full range of contract research services, excellent technical support and innovative products.

In addition to the ISO/IEC 17025:2005 accreditation, CPG is certified to ISO 9001:2015.

About A2LA

A2LA is the largest U.S.-based, multi-discipline accreditation body with over 35 years of experience providing internationally recognized accreditation services and quality training. A2LA’s world-class accreditation services encompass testing and calibration laboratories, medical testing laboratories, inspection bodies, proficiency testing providers, reference material producers and product certification bodies. Organizations are accredited to international standards and field-specific requirements developed with government and industry collaboration.

Posted by CatherineCerasuolo
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March 23, 2017

Mad as a March Basketball

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Every spring, Americans fall victim to a syndrome known as “March Madness.” Early onset symptoms include a loss of interest in regular activities, coupled with racing thoughts about the NCAA. Later stages are marked by a craving for CollegeHoopsNet.com posts, obsessive bracket picking, and frequent betting in office pools. Final stage is incessant streaming of tournament games, usually accompanied by a zombie-like stupor.

Whether March Madness causes an actual loss in the American GNP or whether it boosts productivity by providing the long term benefit of communal bonding remains controversial. Regardless, March Madness makes a notable impact on American life. We here at CPG sought to discover an environmental cause of this spring phenomenon.

Synthetic or Leather?  

Traditional basketballs were made with a leather cover. However, due to the effects of the harsh environmental conditions of outdoor courts, the new trend is synthetic or rubber materials. The NCAA regulation basketballs are required to be covered in leather or composite leather materials, given that these matches are held indoors on wood floors. The synthetic materials can provide more consistency between balls, better grip and handling, and do not need to be broken in prior to use; however, the leather balls will bounce better.

When the NBA switched to synthetic materials, the players were bothered by the decrease in rebound height and reverted back to the traditional leather balls. This habit of switching between synthetic and leather balls was certainly vexing for players, but was not likely to contribute to the afore-mentioned madness. We wanted to know more, so it was off to the lab with our basketballs.

HS-GCMS Determines Trace Volatile Compounds in Basketballs

Our FTIR and SEM analysis found no characteristics that should cause madness, so we turned to potential volatile compounds, some of which are known to cause hallucinations (see the Oracle of Delphi), and yes, madness. We were interested in the fingerprint of compounds present on the surface of a new and an old basketball. A commonly used technique for analysis of volatile compounds is head space gas chromatography (HS-GC-MS), a method we often use to look for residual solvents and trace volatile chemicals in materials.

The HS-GC-MS analytical method is especially powerful in determination of flavor and odor rendering compounds. A group of volatile compounds present only in the new basketball were identified by HS-GC-MS:

  • ethyl acetate, a compound with agreeable odor, which is present in confectionary, perfumes and fruits
  • methyl cyclohexane, an organic solvent detected at surprisingly high concentration
  • butylated hydroxytoluene (BHT) – an antioxidant commonly added to cosmetics, pharmaceuticals and rubber

Since BHT is used in many commonly used items outside of basketball, and ethyl acetate has an agreeable odor (no madness there), we move the methyl cyclohexane into a suspect category as a possible source of March Madness, although further testing would be required to determine a causal link, probably involving popcorn and televisions. Once we figure out how to screen for madness-induction from shoe squeaking or vuvuzelas, we will conduct a follow up study.

Read more in our March Madness application note.

Posted by CatherineCerasuolo
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March 15, 2017

CPG Researchers Receive Hip Replacement Positioning Patent

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CPG researchers, along with orthopedic surgeons from the Massachusetts General Hospital, received a U.S. patent for a low cost navigation system designed to assist surgeons in aligning the acetabular cup used in hip replacement surgeries. The USTPO issued the patent as number 9,554,731.

Hip replacements now have a possible life expectancy of over 20 years, the duration enhanced if the replacement is positioned correctly during implantation. After initial positioning on the operating table, the patient is secured with rigid posts or bags, and then covered in sterile drapes. Despite the restraints, the patient often moves, due to the sometimes drastic motions during surgery. The drapes make it difficult for the surgeon to find the true orientation of the hip, and even a small positioning error could lead to decreased implant longevity.

CPG's tool allows surgeons to overcome the challenge of the draped, moving patient without radical changes in surgical procedures. The device streams patient orientation data to either a monitor or hand-held device, reporting an acceptable range of position angles and warning of incorrect orientation. CPG's patented sensor is built on an adhesive pad, slightly larger than a quarter - cheap and disposable.

Optimize Your Patient Positioning

  • Improved implant position decreases wear and increases longevity.
  • Additional feedback is beneficial to all surgeons, but is especially helpful to low-volume and inexperienced surgeons.

This device is available for license. Please contact us for more information.

 

Posted by CatherineCerasuolo
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March 10, 2017

The Technology of Football Helmets

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We continue our discussion of polymers in sports equipment by looking at football helmets. The well-publicized dangers of head injuries have put helmet design back in the forefront of sports equipment manufacturers. Modern day football helmets bear little resemblance to the original leather helmets first introduced in the early 1900s. These leather helmets had no face guards, little padding, and were primarily used to protect the players’ ears. In the late 1930s, plastic helmets were introduced, which incorporated the chin strap for the first time. In the 1940s, the first face guards made their appearance, although they were much more minimal than the modern face guards seen today.

Material Composition of a Football Helmet

The mechanical requirements of football helmets requires a material that is lightweight, tough, and exhibits good impact strength. Most modern helmets use polycarbonate for the outer shell. Polycarbonate is a high impact resistant polymer that can be injection molded, painted, and can maintain its properties when subjected to cold temperatures, an important feature for teams playing in the northern states. Less expensive helmets sometimes use acrylonitrile-butadiene-styrene (ABS) copolymer, another impact resistant material.

The padding in helmets, critical for absorbing and dampening impact loads, is often made from nitrile-based foam, and reinforced with polyethylene foam. The pore size and chemistry of the foam will affect its viscoelastic response (modulus vs. frequency response), which is the most important behavior for a helmet application, so proper testing of potential materials is important, often requiring dynamic mechanical analysis.

Minimizing Impact Load

In addition to material selection, helmet design plays an important role in its ability to minimize direction transmission of impact load from the helmet to the athlete’s brain. Some helmet designs contain a hexagonal-shaped cutout near the forehead of the helmet. This cutout is a cantilever system which is intended to absorb some of the impact force.

Researchers are also considering integrated helmet-shoulder pad designs to further dissipate impact loads from the head down into the body. Accelerometers built into the helmets provide side-line monitoring of impact loads in players. 

Posted by CatherineCerasuolo
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March 8, 2017

Get Rich to Avoid Infections

The Antimicrobial Properties of Silver

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The phrase ‘blue bloods’ is associated with nobility or wealthy upper class. The etymology of the phrase has a few sources. One is that the pale skin associated with a non-laboring class of citizens allowed the blue veins to be better observed. A second, and more scientifically intriguing, source is that the silver cutlery, place settings, and goblets used by the wealthy and nobility imparted the users with a rich influx of silver ions, resulting in a healthy blue-ish patina on their skin.

Microbe Slayers in Medical Devices

Silver ions also impart some antimicrobial properties. Multiple researchers and companies have incorporated silver into wound dressings, salves, and medical devices to provide antimicrobial benefits. A potential issue of silver is that for efficacy against microbial agents, silver dose levels can often result in a toxic response in tissue. Fortunately for the 'blue bloods,' toxicity from ingested silver is fairly low, usually consisting of the cosmetic symptom of blue-grey skin. 

Skinny Silver For a Better Bandage

Research from the University of Wisconsin-Madison has led to the development of a wound dressing comprised of a porous polymer nanofilm that contains elemental silver nanoparticles. The nanofilm is less than one cell thick, and is very conformable to the wound surface, allowing intimate contact with the wound. This intimate contact allows better material localization to the skin cells rather than the wound fluid, allowing lower silver concentrations, which may address the issue of silver ion toxicity in the skin cells.

While in past centuries the upper class may have been the sole beneficiary of silver's antimicrobial properties, the University of Wisconsin-Madison researchers envision a day when silver nanoparticle band-aids are sold in drugstores. 

Posted by CatherineCerasuolo
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