To ensure easy administration the plunger as well as the barrel in a pre-filled syringes, cartridges and other devices are lubricated with silicone oil. A homogeneous distribution of the silicone oil, on the barrel of a pre-filled syringe is preferable.
ISO 11040-4 and -6 both Annex E for example provides detailed information on the gliding force of empty syringe barrels to assess the quality and consistency of silicone oil lubrication within the inner syringe barrel.
Quality and function of the silicone layer is is therefore only measured indirectly. Furthermore, this critical quality aspect is also influenced by the diameter of the plunger, orifice of the cannula and the barrel as well as of the viscosity of the filling of the syringe. Weighing before and after spraying on gives the amount of silicone oil.
Silicone oil layer amount (weight) and silicone oil layer homogeneity can be quickly assessed and documented with
a cutting-edge device called the Layer Explorer. The measurement is highly accurate repeatable and non-contact and preserves the silicone layer for further tests. As seen in many examples, silicone oil once applied forms not a static but a rather dynamic layer. Re-distribution of silicone by gravity is observed and can be visualized by the Layer Explorer device. Furthermore the corrugation of the Silicone layer and the formation of up to 50 µm sized silicone mountains with a height of up to 1,300 nm are observable over longer storage times. Therefore the age of a syringe as well as storage conditions impact on the silicone layer can be measured by the Layer Explorer.
Interaction with the drug also affects the layer and changes its uniformity and therefore the performance of the device. This is well known for spray-on siliconized syringes, but also an important quality factor baked-on cartridges.
Determine the quality relevant factors of baking on siliconization in your process: stirring of the emulsion, pre-washing, baking time