MATERIALS | MEDICAL TUBING
Right: Junkosha says that its peelable heat shrink tubing is available with inside diam- eters to 0.18mm
Some of the main issues are concerned with soluble polymers, soluble additives and water- absorbing polymers, he said. In each case, an equilibrium constant (K) gives a measure of where a physical or chemical process comes to equilib- rium, at a given temperature. “K is constant for a given temperature – so when
temperature changes, K will be different,” he said. The effect of temperature is exponential, and a rule says that a 10°C rise effectively doubles the rate of change – though Herrild says: “Be careful when applying this rule.” He says that procedures to control K can include speeding up the line – to ensure a shorter contact time – or using a spray rather than a water bath. In one specific case, Teel was approached by a customer to compound an active ingredient into a polymer matrix. The polymer matrix was then extruded into a dosing form factor – which was required to have a very specific dose per unit Teel’s approach was to get the safety data sheet (SDS) and technical data sheet (TDS) on the additive and polymer, test the solubility, then perform lab-scale runs and test the results. This process showed that the additive was not
very water-soluble. In this case, as it dissolved it created an endothermic reaction – meaning that the water needed to be cold. From a process perspective, it meant having a short line, using cold water and running at a fast rate. “Pre-development testing of materials and their
interactions with water is critical to development,” said Herrild. “Once a stable process is developed, lock it down to control the end product.”
Shrinking fast Miniaturisation is a key trend within medical tubing – and this will require extra effort from extruders of medical tubing said Joe Rowan, president and CEO of Junkosha USA. Catheters for neurovascular applications, for
instance, require the use of smaller and smaller tubes in order to reduce pain and trauma. Devel- oping such products goes hand in hand with “omni present customer needs” – including total cost of ownership, higher quality and a faster time to prototyping. “And everything is secondary to patient safety,”
he said. Rowan said the Junkosha helps to fulfil a number of ‘unmet customer needs’ with its products. One example he cites is peelable heat shrink tubing (PHST) – which he says is available with inside diameters down to 0.18mm. Another is tapered micro-catheters. Here, a tapered mandrel ensures that the end that is inserted into the body is slightly narrower than the ‘proximal’ end – mak- ing it easier to push in. Junkosha has also made a series of micro-cathe- ters with thinner walls – which “reduces the real estate within the lumen while maintaining strength and robustness”.
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