Sep. 29, 2025
Prefilled syringes offer unparalleled convenience in drug storage and administration, seamlessly combining a primary container and a delivery device. However, this convenience must be underpinned by an uncompromising commitment to one critical factor: seal integrity. The syringe's seal is the primary guardian of a drug's safety, stability, and potency from the production line to the point of use. This article delves into how the design and rigorous testing of prefilled syringes ensure this vital seal, safeguarding pharmaceutical products.
A prefilled syringe is an integrated system typically composed of a barrel (管套), plunger rod (推杆), piston (活塞), tip cap (护帽), and often a dose-setting ring. The synergy of these components creates a robust barrier against external threats. The core of the seal lies at two critical junctions: the tip cap and the piston.
The Tip Cap (护帽): This component is the first line of defense. After drug filling, the tip cap is securely fastened over the barrel's opening. Its primary function is to prevent drug leakage and, more importantly, to create a hermetic barrier against microbial and particulate contamination from the external environment throughout the product's shelf life.
The Piston and Plunger Rod (活塞与推杆): The piston, driven by the plunger rod, acts as the dynamic seal within the barrel. After filling, the piston is positioned to create a tight seal against the barrel's inner wall. This interface prevents the drug from leaking back and protects it from air and moisture ingress, ensuring the formulation remains stable and uncontaminated.
To ensure these mechanisms work flawlessly, specific standards and rigorous tests are mandated. In China, for example, the standard T/CVDA 1—2019 "Veterinary Prefilled Plastic Mammary Infusers" provides a clear testing protocol that underscores the industry's commitment to quality. The general test流程 is as follows:
Preparation: A representative sample of syringes is taken.
Water Filling: The syringe barrel is filled halfway with water.
Piston Insertion: The piston is inserted into the barrel.
Air Removal and Capping: The tip cap is removed to allow air expulsion and then immediately re-applied to seal the opening.
Pressure Application: A defined axial force (e.g., 30N) is applied via the plunger rod for a set duration (e.g., 30 seconds).
Leak Inspection: The syringe is meticulously inspected for any signs of leakage at both the tip cap seal and the piston-barrel interface.
This stringent testing simulates the stresses of transport and storage, validating that the syringe assembly can maintain its integrity under pressure.
A compromised seal can lead to drug leakage, concentration changes, microbial growth, and oxidation—all of which directly undermine a drug's efficacy and safety. This is especially crucial for sensitive biologics, viscous formulations delivered via a paste syringe, or products packaged in a multidose syringe intended for several uses. For a precise dosing syringe for paste, a faulty seal can alter the viscosity and homogeneity of the product, leading to inaccurate dosing. Similarly, the complex mechanism of a dial a dose syringe relies on a stable internal environment to ensure each incremental dose is accurate throughout its use.
The seal integrity of a prefilled syringe is not a minor feature but a fundamental requirement. Through precision engineering of components like the tip cap and piston, and adherence to rigorous, standardized testing protocols, manufacturers can guarantee the integrity of the drug within. For pharmaceutical companies, choosing a prefilled syringe supplier with a proven commitment to robust seal validation is a critical step in ensuring patient safety, maintaining drug efficacy, and protecting brand reputation in the market.
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