Control of air residue in syringe packaging

Update:27 Jan 2021

In theory, it is impossible to be bubble-free when prod […]

In theory, it is impossible to be bubble-free when producing syringe packaging, because even under the lowest vacuum, there will still be some air molecules remaining in the syringe packaging. If the best process conditions are used, the bubbles may be so small that they are invisible to the naked eye. The size of the remaining bubbles mainly depends on the vacuum in the syringe and the filling level during operation. The amount of dissolved gas is negligible.


For example, using the traditional vacuum stopper method: Fill a 1ml (long) syringe with 0.75ml of water-based product, and press the stopper at a pressure of 100mbar, and a bubble with a diameter of 2mm will be generated (based on 1000mbar pressure). As the gas is dissolved in the product, the volume of bubbles can be reduced by about 10%.


Generally speaking, low vacuum, low friction, high filling level, high gas solubility, and the use of push rods will reduce the residual gas space in the syringe injection package. In this way, it seems that the use of high-vacuum vacuum plugging methods (such as 1mbar or 2mbar) can solve the problem of residual bubbles, but the problem is far from simple. This is important because a decrease in pressure will also decrease the boiling point of the liquid. The boiling point of water under 10mbar is 9°C. Product boiling is very dangerous, because this will increase the chance of the plugging device being contaminated, and the product may also splash to the outer edge of the syringe and rubber stopper. This shows that the boiling point of the product under low pressure is the limit of the operating vacuum, and the situation of alcohol products is even worse. Generally speaking, the pressure in the syringe package must be significantly higher than the vapor pressure of the product.


Some high-viscosity products (such as hyaluronic acid) allow lower pressures, so that the amount of air remaining will be reduced. Bubble-free processing was already possible in the early 1990s. In some special occasions, such as suspension or emulsion vaccines, they need to be mixed before use, because these products will be stratified during storage, and the existence of bubbles helps to improve the mixing of products by shaking effect. In addition, keeping a certain amount of residual gas is also conducive to heat sterilization and adapting to pressure and temperature changes during air transportation.


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