Cambridge Polymer Group

October 30, 2014

Swedish warships and quality management systems

In the design of a new device, a good manufacturer will follow quality management principles to ensure the device meets the requirements of the end-user. What does this have to do with Swedish warships? History can provide us with useful lessons on quality management systems. The Vasa was a warship built in 1626 that holds the unfortunate reputation of sinking on her maiden voyage after sailing less than a mile. From a modern perspective, the construction and launch of the Vasa suffered from one primary problem. The lack of a quality management system during her design meant that a good design team was not assembled and new design concepts were not adequately tested and verified during construction. As a result, design changes were instituted “on the fly” after the nominal design freeze, and contradicting results from final verification tests were ignored, or never reached the right people. As a consequence, she was unable to meet the specifications required to be sea-worthy, and sank quickly when a gust of wind hit her when leaving Stockholm's harbor an incorrect weight balance resulting from overly complex superstructure. An adequate quality management system might have provided the checks and balances and gating necessary to any good design process, perhaps avoiding her sinking.

As an aside of a more polymeric nature, she was raised piece by piece from the sea floor in 1961, and currently sits in a museum in Stockholm, where she is in surprisingly good shape. She is being impregnated with polyethylene glycol as a preservative, although recent studies are suggesting that PEG application to wood in an acidic environment (the Vasa was in acidic water for centuries) will form formic acid, which could damage the wood.

Download full application note

October 9, 2014

Automatic Crack Length Measurements in Fatigue Testing

Plastic components subjected to cyclical loading cycles during their use can sometimes failure through fatigue crack formation. A plastic that shows good toughness in static testing may have brittle behavior when exposed to millions of fatigue cycles, particularly in parts with a sharp notch. Fatigue crack propagation testing helps to determine if a material is resistant to crack formation, and to compare different formulations of materials.

ASTM E647 describes the general protocol for fatigue crack propagation testing in materials using a pre-notched compact tensile specimen. The test requires simultaneous measurements of crack propagation after the application of tensile fatigue cycles. CPG engineers have developed an automated optical system that captures thousands of images of the propagating crack during the fatigue experiment from a dual camera system. The accompanying analysis software then determines the crack length in each image, outputting the da/dN vs. DK curve described in ASTM E647. The system provides a high density of data, in full compliance with E647, with greatly reduced labor.

More information on the system can be found here.

Contact CPG for more information on this system, which is available for purchase.

October 7, 2014

Detecting Potentially Harmful Contaminants in Medical Anesthesia

anesthesia mask.jpg

Many drugs used for the induction and maintenance of general anesthesia are volatile organic compounds that are delivered to the patient via inhalation. The low boiling point and high volatility of these compounds make them ideally suited for analysis by gas chromatography with mass spectroscopy (for example, as part of an in-process or QC check for material purity). Unfortunately, most commonly employed chromatographic methods are often unable to detect the presence of trace impurities due to limited instrument sensitivity. However, often the manufacturer is aware of the potential impurities or contaminants that may be present in a given anesthetic agent, and in such cases a targeted GC-MS method may be developed which maximizes sensitivity to these compounds. Cambridge Polymer Group has developed such chromatographic methods that can detect and quantify suspected anesthesia contaminants at levels in the parts per billion range.

Contact us for more information on this technique.

October 3, 2014

Recent Articles on Cleanliness of Medical Devices

Two articles recently appeared in Qmed that discuss medical device cleanliness. The first discusses the effects of cleanliness on the application of coatings on guidewires. Guidewires are used to help steer catheters and other cardiovascular equipment through blood vessels. PTFE is often applied to improve lubricity of the guidewires. When problematic flaking of the PTFE from guidewires was observed, Surface Solutions modified their cleaning process to help adhesion. Even contamination on the atomic level can interfere with adhesion of the PTFE, resulting in the need for ultraclean processing conditions.

The second article mentions the Sulzer InterOp recall, which was previously discussed in this blog. The article discusses manufacturing decisions in medical devices, including cleaning and sterilization, and how the materials used in the device need to be considered when selecting a sterilization modality.

September 22, 2014

Oxygen content in packaging

Vacuum packed dental mold.jpg

Manufacturers of medical devices and food products will often use packaging with a reduced oxygen level in the region of the product to minimize oxidation of the product and increase shelf-life. Inert gas, such as nitrogen or argon, may be flushed through the packaging, or vacuum may be pulled on the packaging.

Alternatively, an iron-based oxygen scavenger can be placed in the packaging. The packaging often uses a barrier film to inhibit the diffusion of oxygen through the packaging. This film is often a composite structure of multiple layers of plastics and metals.

Determination of the oxygen level in the packaging is a useful way to determine the efficacy of the
packaging process, and to monitor the packaging integrity over time. CPG has developed a technique to quantify the oxygen content in packaged components down to oxygen concentrations in the parts per million. This technique is discussed in this application note.

September 22, 2014

CPG staff cycle in Boston

Some of the staff at Cambridge Polymer Group and their spouses participated in Boston's annual Hub on Wheels, a 50 mile bike ride that winds through the Boston and its surrounding communities. The ride raises money for the Special Olympics, the Boston Parks and Recreation Fund, and Boston Bikes, an organization set up to encourage cycling in Boston.

September 9, 2014

Blame it on saliva

An article recently appeared that discuss the use of extensional rheometry to characterize natural polymer systems. The study, published in Food Hydrocolloids by Choi and co-workers, considers the effect of saliva on food products thickened with either xantham gum or carboxymethyl cellulose. These authors used a CaBER extensional rheometer, developed by Cambridge Polymer Group, to demonstrate that filament breakup kinetics of xantham gum is greatly influenced by the presence of saliva, whereas carboxymethyl cellulose is not as affected.

The significance of this study relates to the concept of psychorheology, or how our perception of a product can be influenced by its rheology. In the present study, the extensional viscosity can influence our perception of taste and flavor, as well as general mouth feel, when the xantham gum's viscosity is modified by the presence of saliva.

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