Toughness and transparency are important properties for the constituents of intravenous lines. However, chemical properties and biocompatibility are paramount for medical grade plastics, which, compared to normal grades, have to comply with a barrage of regulatory tests. This is achieved by extra care at manufacture to minimise polymerisation residues and careful selection of additives such as antioxidants and plasticisers.
I had a recent stay in hospital following emergency surgery. I had the opportunity to observe at first hand the not insignificant contribution that plastics made to my recovery. The skill of the surgeon, the expertise of the medical clinicians and the superb nursing care were major factors. However, the proliferation of tubing attached to me also had a role to play, along with flow controllers, infection minimising gloves and aprons and not forgetting the sterile packaging.
When it comes to medical implants, intuitively you might expect that the most inert plastics, such as PTFE, would have most success. However, the body tends to reject anything totally inert. It prefers thermoplastics with some compatibility with human tissue, either from the thermoplastic’s chemical structure or by appropriate chemical modification.
Bioengineers are now finding that, in addition to chemical compatibility, nano-scale surface texture holds the key to biocompatibility. Some nano-scale patterns can kill off cells while other patterns encourage cell growth, particularly bone cell growth. This opens up the possibility of plastics implants for repair of diseased bones.