Researchers from the Paul Scherrer Institute (PSI), the University of Basel and the pharmaceutical company Roche have shown that storing pre-filled syringes at adversely high temperatures can clog the injection needle. They accomplished this by illuminating the injection needles of such syringes with neutrons.
“Neutrons are optimally suited for this problem because they penetrate the metal needle almost unimpeded but are deflected from their straight path by hydrogen atoms as they occur, for example, in water,” PSI researcher Christian Grünzweig said in a statement. “So if some of the liquid medication gets into the metal injection needle, we can make it visible with neutrons.”
The researchers also produced a three-dimensional image of a clogged syringe by capturing many neutron images of the same syringe from different angles and then putting them together digitally on a computer. The resulting image clearly shows slanting cracks running through the material inside the needle. This can only mean “that the plug in the needle is solid – that in this case, the liquid portion has actually evaporated”, explained PSI researcher David Mannes.
The researchers conducted tests on 60 pre-filled syringes: they stored half of them properly at 5 degrees Celsius for 10 days, and the other half at 40 degrees Celsius. The neutron images showed zero medicinal substance inside the needles of the syringes that had been kept cool. In contrast, medicinal liquid had partially or completely intruded into the needle in 28 of the 30 warm-stored syringes.
