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Pre-filled
syringes

Sterility alone does not protect a PFS.

A pre-filled syringe is a hermetically sealed container with a movable plunger. During thermal sterilization, the liquid expands, part of it vaporizes, dissolved gases are released and the gas already present in the headspace increases in pressure.

An aqueous solution expands by approximately 6% when heated from ambient temperature to 121°C, while the volume of a glass syringe increases by only about 1%. The container expansion is therefore insufficient to compensate for the internal volume increase, and the resulting pressure acts directly on the plunger.

Some plunger movement is physically unavoidable. If it is not correctly governed, however, it can lead to product loss, water entrainment in the outer plunger grooves, compromised sterility maintenance or complete plunger expulsion.


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PRESSURE IS PART OF
PRODUCT PROTECTION.

The thermal expansion of the liquid cannot be prevented. The process must instead balance the pressure developing inside the syringe with the counterpressure applied externally throughout heating, exposure and cooling.

This balance cannot be defined for a generic sealed container. It depends on the injectable solution, fill volume, available headspace, dissolved gases, syringe material, plunger characteristics and initial plunger position.

Key pillars of Fedegari steam-air counterpressure sterilization technology for pre-filled glass syringes
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We model the behaviour of the complete filled syringe and translate it into a dedicated pressure profile.

The objective is not to prevent plunger movement completely, but to keep it within acceptable limits throughout the cycle

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CHARACTERIZING THE FILLED SYRINGE

Process development starts from the complete PFS configuration. Product properties, fill volume, headspace and closure geometry determine how pressure will develop and how much movement the system can accommodate.

DEVELOPING THE COUNTERPRESSURE PROFILE

During heating, chamber pressure progressively increases to counteract the rising internal pressure. During cooling, it is maintained above the decreasing internal pressure to support the controlled return of the plunger. The profile is developed phase by phase to avoid both excessive outward movement and excessive return during cooling.

VERIFYING THE COMPLETE OUTCOME

Validation cannot stop at microbiological lethality. The process must also demonstrate controlled plunger displacement, acceptable final plunger position, absence of product loss and preservation of the relevant product and container attributes.

PRESSURE CONTROL
In saturated steam sterilization, pressure governs steam conditions. Controlling pressure supports temperature uniformity and repeatable process behavior. 
±0.5°C UNIFORMITY
Temperature standard deviation is a key indicator of process behavior. The tighter the deviation, the greater the stability and repeatability across the entire load. 
DRY-LOADS
Critical components 
emerge sterile, dry and ready for immediate use. 
CANISTER PROVEN
We support advanced  canister-based transfer strategies while preserving filter integrity, drying performance and sterile transfer conditions.

FREQUENTLY ASKED QUESTIONS

Why does the plunger move during PFS sterilization?

Heating causes the liquid and gases inside the sealed syringe to expand, generating pressure against the movable plunger. Some displacement is unavoidable, but its extent and subsequent return must be controlled.

Why is headspace important?

Headspace provides room for the volume changes occurring inside the syringe. Insufficient available space increases plunger displacement and the risk of product loss or expulsion.

Why is an air-steam process used?

Air-steam sterilization allows chamber pressure to be controlled independently from temperature. Counterpressure can therefore be adjusted to balance the pressure developing inside the PFS without changing the required sterilization temperature.

Can the same counterpressure profile be used for every PFS?

No. The required profile depends on the formulation, fill volume, headspace, dissolved gases, syringe material and closure characteristics. It must be developed for the complete product-container configuration.

What must PFS sterilization validation demonstrate?

Validation must confirm microbiological effectiveness together with controlled plunger behaviour, acceptable final positioning, product retention and preservation of the relevant product and container attributes.

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THE CUBE HAS MORE THAN THREE FACES

Explore how Fedegari has approached sterile process challenges across different industries, applications and manufacturing environments.

 

WHITE PAPER AND RESEARCH

Technical depth, documented and made accessible. A growing collection of papers and research contributions developed from real application experience across industries, processes and manufacturing environment.

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It is a way of working.

A global network designed to keep Fedegari close to the customer, close to the process and close to the decisions that make sterile manufacturing safer, more reliable and more valuable over time.