MEDICAL TUBING | MATERIALS
Emerging materials and techniques – from bioabsorbable polymers to ‘transitional extrusion’ – are helping to improve the production of medical tubing. Lou Reade reports
Extrusion offers healthy future for medical tubing
Delegates at the recent Medical Tubing conference in Berlin, organised by AMI, learnt about some of the challenges of producing these intricate products. Brian Dillon, principal polymer engineer at Boston Scientific in Ireland, pointed out the importance of bioabsorbable polymers – which degrade in the body over time. These are used as the basis for a number of medical devices, including stents. A number of polymers can be applied here, including the L-version of polylactic acid. This polymer is referred to as PLLA (or poly L-lactic acid). It has a number of properties that are useful for making medical tubing, he said, which are strongly influenced by molecular weight and percentage crystallinity. He told delegates that extrusion conditions have a big influence over the properties of the final tubing product. He is part of a team that studied
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the use of microbore extruders for processing the material. The research was published in the journal Polymers. In the research, high molecular weight (medical
grade) PLLA was processed using low shear microbore extrusion machinery. The material had a low moisture content (less than 100ppm) and was used to make tubes of 1.9mm outside diameter and 0.6mm wall thickness. Dillon pointed out the importance of resin
drying, in a material that was highly susceptible to thermal degradation and melt fracture. The tubing produced was tested by a variety of methods, including gas chromatography, DSC, tensile tests and DMA. Extrusion processing – including drying – caused molecular weight loss of at least 17%, said the researchers. “Longer melt residence times results in greater
September 2019 | PIPE & PROFILE EXTRUSION 13
Main image: Stents are manufactured by extruding polymer with a wire support structure
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