MATERIALS | MEDICAL TUBING
Right: Radiopaque substances – whether a foreign body or, for instance, a catheter – can be located using X-rays
Optimised production Thomas Nick, director of medical and pharma sales at Collin Lab & Pilot Solutions, told delegates about optimising production of multiple micro- tubes on a single extrusion line. Micro-tubes are increasingly common – in
applications such as ‘lab-on-a-chip’ technology – and have helped researchers understand processes that were previously difficult to investigate. This, in turn, has driven further interest in applying micro- tubing to various scientific disciplines, he said. The tubes are typically produced under
cleanroom conditions. In one instance, four thermoplastic polyurethane (TPU) monolayer tubes – with an internal diameter of 0.43mm, outside diameter of 0.57mm and wall thickness of 70 microns – were produced on a single die and extruder at a line speed of 1.5 m/s, equating to an output of 360 m/min. Raw material flow was carefully controlled.
Granules were extruded through a single melt pump, then a die block – after which the tubes were cooled in a water bath, measured and wound onto reels. The line was an E20P from Collin with a maximum throughput of around 11 kg/hour. “The challenge [of a multi-tube die] is that the melt speed is the same at each outlet – even if one of the hollow fibres breaks or breaks off,” said Nick. Centring of the die inserts is performed manu-
ally, with an accuracy of +/- 10 microns. The die is simulated in the preliminary stage.
PTFE extrusion Sharan Thathand, engineering manager at Nord- son Medical, told delegates how PTFE extrusion can be improved by incorporating Tyflo ‘strike layer’ technology. “The challenge for catheter manufacturers
centres around the PTFE liner – which has a very low dynamic coefficient of friction – but low bondability with other materials in its natural state,” he said. To overcome this, the outer surface of the PTFE is chemically etched, which strips the fluorine molecules away from the carbon backbone of the PTFE. This results in the formation of organic molecules that allow adhesion to occur with other materials. Nordson says its Tyflo PTFE liner adds an
integrated ‘strike layer’, offering several benefits: improved adhesion between the PTFE and typical outer jackets (such as nylon and Pebax); less processing waste as a result of delamination; and increased shelf-life of etched PTFE liner compo- nents – due to protection by the strike layer.
16 PIPE & PROFILE EXTRUSION | Summer 2024
The strike layer material in the Tyflo liner is a functionalised styrene block copolymer, which Nordson says has no acute toxicity, irritation corrosion, skin sensitisation or mutagenicity. Thathand said that Tyflo offers higher peel force with both Pebax and nylon jackets – compared to a typical etched liner. This helps to reduce delamina- tion and improve patient safety, he said. The strike layer creates a melt-bondable surface that im- proves adhesion to both the liner and catheter jacket during the reflow process.
Laser catheter Timothy Searfoss, a senior engineer at US-based Oscor, presented details of a catheter device that can enhance cardiovascular treatment. Using pulsed sound cavitation, it enables precise cardio- vascular laser ablation of plaque without coming into contact with blood – which helps to treat ischemia.
Ischemia is a decrease in blood supply to organs
or tissue, caused by constricted or obstructed blood vessels. The catheter targets plaque build-up in the carotid, peripheral, and coronary arteries. The device is mounted on a catheter shaft, which is placed over a guide wire. The catheter itself has a maximum outer diameter of 0.355mm. It combines sound and laser technologies. Transducers at the catheter’s tip create a cavitation void. This tempo- rarily displaces blood, providing clear access to the arterial wall – allowing short laser pulses to remove plaque effectively. A high repetition rate of laser pulses helps to improve the efficiency of plaque removal. Laser pulses are delivered both radially and axially to the plaque on the inner wall of the
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IMAGE: SHUTTERSTOCK
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