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Molded capillary tubing used in a range of medical and diagnostic applications, including drug delivery, is typically fabricated from thermoplastics. The Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University, both located in Aachen, Germany, are exploring a process that would optimize the micromolding of tubing with integrated functional features using liquid silicone rubber (LSR). The technology could offer a better alternative to thermoplastics, say researchers.

Norbert Sparrow

August 26, 2014

3 Min Read
Emerging medical LSR molding technology enables single-step process, improved product functionality

Molded capillary tubing used in a range of medical and diagnostic applications, including drug delivery, is typically fabricated from thermoplastics. The Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University, both located in Aachen, Germany, are exploring a process that would optimize the micromolding of tubing with integrated functional features using liquid silicone rubber (LSR). The technology could offer a better alternative to thermoplastics, say researchers.

The biocompatibility of LSR, along with its sterilizability and chemical resistance, make it a highly desirable material for medical applications. By combining gas-assist injection molding (GAIM) and projectile injection technology (PIT) with LSR micromolding, researchers believe that they can improve upon existing products. In particular, the technology will allow molders to form elastic micro-sized hollow tubing that won't buckle as easily as its straight elastic counterparts, explains Daniel Kaltbeitzel, Dipl.-Ing., Medical Engineering, at IKV. Other advantages over thermoplastics include the material's lower viscosity and the aforementioned biocompatibility, he adds.

The use of GAIM/PIT would enable the production of hollow parts in a single-step process and allow the molding of complex geometries with additional integrated functional elements, says Kaltbeitzel. "Conventional injection molding of hollow bodies is usually restricted to cylindrical parts or ducts with sharp edges, which always interfere with the internal flow of media," he told PlasticsToday. To achieve rounded edges in hollow parts using traditional techniques requires highly complex tooling.

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"By using GAIM/PIT, it is possible to form hollow parts with a continuous smooth inner wall using a less complex mold incorporating a GAIM plant to provide the blowing agent," says Kaltbeitzel. In PIT, a solid projectile is placed on the injector to displace the melt. GAIM achieves the same objective without the use of a solid projectile.

PIT produces parts with thinner and more-consistent walls than GAIM and can lead to a reduction in manufacturing costs, cooling time, and part weight, says Kaltbeitzel.

The research team has built a variable test mold for an ultra-small injection molding machine to investigate micro-scale LSR processing using PIT. The use of various inserts ensures that parts with outer diameters between 1 and 4 mm can be tested. The injector technology integrated into the standard mold unit with a closable and switchable injector also allows the use of both GAIM and PIT with projectile diameters of 0.5 to 3 mm in a single mold.

As the project moves forward, the research team will investigate the influence of various process parameters on micro-injection LSR moulding and determine variations that may be caused by the fluid injection technology and different projectile materials.

"Of course, other materials such as thermoplastic elastomers need to be investigated, as well," adds Kaltbeitzel, "and they may perform just as well as LSR, at least in terms of processing and maybe biocompatibility."

He also acknowledges that the cost-benefit ratio might not be advantageous compared with thermoplastics. But that is a discussion for another day, after the proof of principle has been conducted and possible applications have been explored, Kaltbeitzel says.

The work is funded as a Joint Industrial Research project via the Confederation of Industrial Research Associations by the German Federal Ministry for Economic Affairs and Energy.

Norbert Sparrow

Norbert Sparrow is Senior Editor at PlasticsToday. Follow him on twitter @norbertcsparrow and Google+.

About the Author(s)

Norbert Sparrow

Editor in chief of PlasticsToday since 2015, Norbert Sparrow has more than 30 years of editorial experience in business-to-business media. He studied journalism at the Centre Universitaire d'Etudes du Journalisme in Strasbourg, France, where he earned a master's degree.

www.linkedin.com/in/norbertsparrow

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