Posted by: Prospector PJ2 OCT 2013
A syringe that changes colour has been designed to tackle the 1.3 million deaths caused every year by unsafe injections. The World Health Organization estimates that up to 40 per cent of the 40 billion injections given annually are delivered with reused and unsterilised syringes.
David Swann, of the University of Huddersfield, has designed a “behaviour-changing syringe” using relatively cheap methods used in the food industry — inks that react to carbon dioxide and packaging filled with nitrogen. Once a syringe is opened and exposed to the air, the user has a 60-second treatment window before it turns bright red. A faceted barrel design means the piston breaks if someone tries to replace it.
Products that change colour use a number of reactions. Thermochromic products are triggered by temperature changes, photochromic products react to ultraviolet light, hydrochromic changes are caused by water, and piezochromic materials change colour under pressure.
Thermochromic products are of two types — liquid crystals and leuco dyes. Liquid crystals, used in products such as forehead thermometers, can be highly sensitive, but require specialised manufacturing and are more expensive than leuco dyes.
Scientists have recently developed this liquid crystal technology to help spot problems with ultrasound equipment used to treat muscle damage. It can detect “hotspots” where the treatment is focusing sound waves in a way that could make the patient’s muscle strain or ligament damage worse. A thermochromic display for metered dose inhalers has been patented that responds to temperature changes in the inhaler due to expansion of propellant on use. This would display the number of doses remaining.
Thermochromic leuco dyes require a temperature change of about 3C to change colour, and activation temperatures range from low refrigeration to temperatures above the pain threshold. They are used in a wide range of inks and plastics, and can be used to warn about a high temperature safety hazard, for example.