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Focus on cells

Bayer MaterialScience AG : 07 September, 2004  (Company News)
A doctor is performing a skin cancer screening and she's found a small mole that looks suspicious. To be on the safe side, she cuts out a small sample of tissue under local anaesthetic and sends it to a pathological laboratory for further examination.
The histological examination is quite a feat of logistics, because the specialist labs have to perform and evaluate a large number of tests. Examination under the microscope is the most important aspect when it comes to determining the results and the correct staining of the sample material plays a crucial role in this.

Thankfully, highly specialized machines, such as the Shandon Varistain® Gemini automatic stainer manufactured by Thermo Electron Corporation of Runcorn, UK, which offers an exceptionally high throughput of samples, can be entrusted with this demanding task. And polyurethanes from Bayer MaterialScience AG´s Baydur® range are also playing an important part in this process – their robustness and dimensional stability will help this cost-effective lab robot to achieve high levels of performance long into the future.

Tissue samples sent by the doctor to a histology lab have to undergo extremely labor-intensive pretreatment. After fixation in formaldehyde solution, the biological material is generally dehydrated, hardened in paraffin wax, cut into wafer-thin sections and stained for examination under the microscope. The pathologist can choose between various methods, which can, for instance, highlight certain cell elements such as collagen and nuclei or help make bacteria, fungi or even certain carcinomas visible. That means that even the staining process can be extremely complex. The tissue samples have to be introduced in succession into various dishes with staining reagents following a precise timetable.

The Shandon Varistain® Gemini can store up to 50 freely definable staining programs using 32 staining dishes in its memory and execute the programs fully automatically and in parallel. Automatic staining devices are therefore complex machines that, as high-tech investment goods, need to have a long service life. Nevertheless, they are only manufactured in relatively small quantities as they serve a highly specialized market.

Engineers developing the Shandon Varistain® Gemini faced the challenging task of achieving maximum functionality and sturdiness, while at the same time making the manufacturing process as uncomplicated as possible and cutting costs. Polyurethane processor Rim Plastics Technology Ltd. of Basildon, UK, rose to this challenge by using polyurethanes from Bayer MaterialScience. For example, the doors and the top deck of the device, which measures 700 x 700 x 80 mm, are made of Baydur® 110. This is a polyurethane that, in addition to exceptional surface quality, also offers excellent stiffness even with thin walls. The upper casing is made of Baydur® 60, a versatile engineering polymer suitable for producing sandwich structures with a high stiffness-to-weight ratio.

The top deck of the product, which only weighs approx. 5 kg, was originally manufactured as an aluminum casting, but using Baydur® 110 means production is now far simpler. What's more, the upper casing walls differ greatly in thickness, from 5 up to 30 mm. Polyurethane integral skin foams like Baydur® 60 are better suited for such geometries than the majority of rival materials because of their excellent flowability. Polyurethane integral skin foams are produced in molds from liquid components that expand and cure, and their flowability enables low-cost molds made of aluminum to be used. This quickly pays dividends, particularly when it comes to producing high-quality moldings in small and medium-sized series.

This idea gave birth to the design of an additional central component for the Shandon Varistain® Gemini, the turntable which contains the actual staining reagents. In addition to its resistance to solvents such as xylene and its cost-effectiveness, the enormous design possibilities offered by Baydur® 110 were an important factor that weighed in this material's favor, since the turntable has an extremely complex geometry, with a whole host of indentations, undercuts and apertures.

This derived from the need to pick up containers filled with fluid securely and store them in a stable manner. However, it is also due to the computer-aided design adaptations that guarantee exceptional creep resistance – even in intensive use over many years.

Despite its complexity, this component can be manufactured particularly cost-effectively using a multi-part mold whose slide bars are moved manually. Consequently, polyurethanes from Bayer MaterialScience, with their robustness, dimensional stability and economical RIM processing technology, make a massive contribution toward ensuring that an investment in the high-performance Shandon Varistain® Gemini remains secure long into the future. And they also indirectly help keep costs down in today's efficient health care systems.
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