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Zimmer, Inc. has received FDA clearance on their highly crosslinked, Vitamin E containing UHMWPE. The 510(k) application is for a hip liner, and is being marketed under the trademarked name "Vivacit-E" (pronounced 'vicacity').  Zimmer is advertising the new material in their Continuum acetabular shell system, shown above.

Link to 510(k)
Link to Zimmer Continuum Website

Medical device and instrumentation design and development usually requires testing the prototypes in a simulated environment. Interest in treatments involving patients with high fat content has led to requests for tissue models containing a large amount of simulated fat. Using their skills in custom polymer formulations, researchers at Cambridge Polymer Group have developed a simulated fat model for instrument testing and training. The fat model has a realistic feel, will not degrade, and can be prepared in a variety of shapes and thicknesses. Contact Cambridge Polymer Group for more details.

In the 10th Anniversary Issue of BoneZone, a trade journal focusing on arthroplasty, CPG staff were asked to write an article on the history and future of ultra high molecular weight polyethylene for use in total joint arthroplasties such as hip and knee replacements.  This article breaks down the history of UHMWPE as follows:

First generation of highly crosslinked UHMWPE
First introduced in the late 1990's, these materials were irradiation crosslinked with either gamma or electron beam radiation, with doses from 50 to 100 kGy. The post-processing on these materials either involved annealing (heating below the melting temperature) or melting (heating above the melting temperature) in an attempt to reduce the number of residual free radicals that could react with oxygen, leading to embrittlement.

Second generation of highly crosslinked UHMWPE
In response to implant design requiring improved mechanical properties, second generation crosslinked UHMWPE were introduced between 2005 to now (2012). These second generation materials did not use melting to reduce the effects of free radicals, but rather addressed free radicals through mechanical deformation, repeated annealing, or antioxidants.

Future generations of UHMWPE
It is likely that future generations of highly crosslinked UHMWPE will incorporate gradients in crosslink density, providing high crosslink on the bearing surfaces, and low crosslinking in the regions requiring high mechanical strength. Alternative antioxidants will likely be considered as well.

To see the full article, follow this link.

The environment of the upper gastrointestinal tract, including the stomach, can challenge materials placed into this environment. The pH environment can range from 1.5-2.0 prior to eating, but can spike up to pH~7 during and immediately after meals, requiring an hour or more to fall back to normal levels. Contrary to commonly held beliefs, the stomach does not continuously contain fluid, but only partially fills in anticipation of eating or drinking. The peristaltic action of the stomach grinds food against the stomach walls and itself, and enzymes act to help degrade food, along with the hydrochloric acid present in stomach acid.

Polymers sometimes find their way into the stomach environment, in the form of sutures, drug-release components, satiety treatments (e.g. balloons), and other temporary or permanent implants. Knowledge of how these materials will respond to the stomach environment will help to predict their performance. In some cases, the polymers are designed to respond to the stomach environment itself, swelling or deswelling in response to pH, salinity, temperature, or fluid content. In other cases, the polymer may degrade in response to these conditions.

Researchers at Cambridge Polymer Group have designed custom systems to simulate the stomach's environment. Using test methods with reference to ASTM D523, polymers systems are tested before and after model gastric fluid exposure to demonstrate the change in mechanical, chemical, and morphological properties.

Sol gel experiments are a useful technique to determine the amount of crosslinking in a polymer. In this technique, samples are weighed carefully, immersed in a specific solvent at a specific temperature, and allowed to swell for a period of time, typically 24 hours. After this immersion period, the samples are removed again and re-weighed. The sample is then dried and re-weighed. From these weight changes, the percentage of the material that is soluble  ('sol') and the crosslinked portion ('gel') can be determined. Additionally, the degree of crosslinking in the gel can be determined.

ASTM D2765 describes this technique for crosslinked polyolefins such as polyethylene. The standard calls for heating jars of xylene in an oil bath. With standard oil baths, it is very difficult to achieve a uniform temperature in both the oil bath and the sample jars within the required +/- 0.5C. Cambridge Polymer Group has modified this technique with individual heater sleeves for each jar, with isolated temperature control for each jar. With this approach, we can achieve much more precise and accurate temperature control, which results in more accurate sol/gel measurements.

CPG Sol/Gel heater sleeves and control system

CPG sol/gel temperature control station