Lati Industria Thermoplastici (Vedano Olona / Italy; www.lati.com) is collaborating with contract sterilisation specialist Gammarad Italia (Bologna / Italy; www.gammarad.it) in the testing of gamma irradiation on polymers used in the manufacture of medical devices and packaging. The companies said that sterilisation by irradiation is effective and does not cause significant temperature increases, which can cause damage in autoclaving, and that materials can be treated while already in the final package. The research also includes some materials intended for contact with food, as these are also widely used in biomedical and pharmaceutical applications.

The focus of the collaboration is on materials used in diagnostic medical devices for in vitro analysis, laboratory equipment and medical equipment and disposable products for dialysis, extracorporeal circulation (syringes, separation devices and collection tubes), respiratory devices, packaging and pharmaceutical products for human and veterinary use, and aseptic food packaging.

For testing, Lati selected a number of its thermoplastic compounds that have proven resistant to gamma irradiation while maintaining the required technical, aesthetic, and certification properties. These include sulphonates “Lasulf” polysulphone (PSU) and “Lapex R” polyphenylsulphone (PPSU), bio-based “Latigea” B01 PLA, “Larton” PPS, “Latamid” and “Latigloss” PA66 and “Latene” HT cyclic olefin copolymer (COC). Three different irradiation doses were used in the tests – 30, 60 and 150 kGy (the kilogray is an SI measurement unit of absorbed radiation dose of ionising radiation) – and the variation of a number of properties was evaluated including mechanical, thermal, colour, odour, and dimensional stability. The 30 kGy dose is normally used for sterilisation of medical devices, pharmaceuticals and packaging. The 60 kGy dose is used both in irradiation chemistry for the modification of material properties, cross linking and sterilising and antiviral treatments, while the 150 kGy dose is used only in irradiation chemistry in the modification of material properties.

Mechanical decay and thermal decay were measured and, other than PLA at extremely high levels of irradiation, the materials showed no significant changes in the tests. None of the tested materials showed a reduction in elongation at break at 30 kGy.

Yellowing, darkening, and change in transparency depended on the chemistry of the polymer, Lati said. This parameter is important as during medical procedures as operators must be able to quickly identify the device by colour. PPSU, PLA and PPS showed no significant colour changes and all of the tested materials remained dimensionally stable while showing no change in odour. PPSU and PPS did not undergo any mechanical, thermal or chromatic change when exposed to the three levels of irradiation, the companies concluded.