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Engineers are increasingly turning to so-called smart fluids to solve complex mechanical problems. One specific type of smart fluid is the magnetorheological fluid (MR fluid) which greatly increases its viscosity to the point of becoming a viscoelastic solid when subjected to a magnetic field. Importantly, the yield stress and viscosity of the fluid when in its active state can be controlled very accurately by varying the magnetic field intensity. CPG has recently developed an MR fluid testing apparatus that integrates with a standard shear rheometer made by TA Instruments.

The MR fixture mounted on a TA Instruments AR-G2 shear rheometer

CPG has developed a hardware and software add-on that enables a current commercial shear rheometer to test magnetorheological fluids across temperature and field strengths relevant for a wide range of industries. The MR fixture leverages existing rheometer hardware and uses a parallel plate geometry in a controlled magnetic field over a wide temperature range while monitoring conventional shear viscosity parameters such as stress, strain and viscosity in steady or dynamic shearing modes. The high power magnet of this instrument provides the ability to characterize magnetorheological fluids through the spectrum of magnetic flux ranging from -1 to +1 Tesla, or more and across a broad temperature range.

The MR fixture is sold through TA Instruments. Contact Cambridge Polymer Group for more details.

Schematic diagram of sample shearing zone of MR fixture

The FDA has just issued a new draft document detailing if medical device manufacturers who have a product previously cleared by the 510(k) process, and have made changes to that product, have to refile another 510(k) for that product. The two main questions that a device manufacturer must ask about their revised device are as follows:

1. Have the changes significantly affected the safety or efficacy of the device?
2. Has there been a major change or modification in the intended use of the device?

If the answer is yes to either of these questions, then a resubmittal of the 510(k) application may be necessary. The predicate for the resubmittal should be the cleared and marketed device on which the modifications have been made, as opposed to a competitor device or another device marketed by the manufacturer. Changes are not limited to material or design, but also to manufacturing process changes that meet one of the above two questions. Packaging, labeling, and sterilization modality are included in these criterion.

More information can be found on the FDA web site

Psychorheology is a term that is familar to the food industry, having been used for many years. Its use in other areas, such as consumer products, is slowly starting to make its way into the common lexicon. Psychorheology is the relationship between instrumental data and sensory data. Sensory data may include 'mouth-feel', warmness, and richness. Consumer products companies often conduct panel studies on their developmental products. An assembled panel of consumers will test different formulations of hand creams, and then will fill out forms ranking the creams in terms of smoothness, thickness, slimyness, stringiness, warmth, and a variety of other sensory perceptions. While these rankings are very important to marketing and development people, it would be beneficial to R&D staff to be able to assign these characteristics to new formulations without the time and cost of assembling the panels. By assembling a database of quantitative, instrument-based numbers that are associated with the panels' more qualitative perceptions, the researcher can a priori tell how their new formulation will be perceived.

One single test is usually insufficient for this type of analysis. Rheology, or the study of fluid motion, is most commonly employed, as it provides information on viscosity, elasticity, and other properties that scale with sensory perception. However, other tests are employed. For example, smoothness or slimyness is usually associated with coefficient of friction, with slimyness also associated with the rheological properties of the material. Stickiness is a property associated with both tack and extensional flow properties, whereas stringiness is more associated with extensional flow properties alone. The gel-like behavior associated with high quality shampoos is related to the yield stress properties of the material; the material will retain its form under gravitational conditions, but will flow when sheared between the hand and scalp.

Cambridge Polymer Group assists clients with designing a testing suite to characterize the psychorheological characteristics of their materials, with the intent of finding testing conditions that distinctly separate formulations that have shown a sensory separation in field testing. With these suites, we then characterize the client's formulations, forming a database of properties, from which R&D staff from many divisions within the company can select components to achieve a specific sensory experience.

Throughout our history, we have worked on a variety of interesting projects for our clients and our own internal research. Projects have included cleaning systems for ships, hydrogels for biomedical applications, psychorheology of food products, and synthetic tissue models. We have posted case studies on our web site for prospective clients to see the range of projects on which we have worked. Click here to go to our case studies.

On June 9-8, 2011, the FDA hosted a workshop to discuss issues involved in the re-processing of re-usable medical devices, such as endoscopes and orthoscopic shavers. The purpose of the workshop was to establish what guidance documents should be established to ensure that reusable devices are being properly cleaned and disinfected/sterilized to ensure patient safety. Representatives from hospitals, regulatory, reprocessors, OEMs, and testing labs discussed the state of instructions for use, cleaning testing and validation, and the risks associated with poor cleaning.

Cambridge Polymer Group presented the most recent work performed at ASTM on standards targeted towards improving medical device cleanliness, and participated in a panel discussion of what future standards will be required.

The archived webcast of the conference can be found on the FDA website. A summary of the discussion can be found here.

CPG presentation on ASTM activities in Medical Device Reprocessing