Views: 0 Author: Site Editor Publish Time: 2025-10-16 Origin: Site
In a complete drug delivery system, every detail matters — especially within the cartridge, the heart of the injection pen. Among all components, the rubber stopper plays a critical role in maintaining dose accuracy, sealing integrity, and injection smoothness. The length of the rubber stopper is one of the most influential yet often overlooked parameters that directly affect the mechanical behavior of the pen and the overall injection experience.
The rubber stopper serves as the dynamic sealing interface between the drug formulation and the pen’s mechanical drive system. During injection, it is pushed forward by the plunger rod, expelling the drug through the needle. Its dimensional precision, hardness, and elasticity directly influence the consistency and accuracy of each delivered dose.
Different stopper lengths create significant variations in internal pressure dynamics and friction resistance within the cartridge:
Shorter Stoppers (e.g., 5.5 mm – 6.0 mm)
Provide lower frictional resistance, resulting in smoother plunger movement.
Are ideal for low-viscosity formulations or pens designed for low injection force.
However, if too short, they may reduce sealing efficiency, leading to potential micro-leakage or air bubble formation over time.
Longer Stoppers (e.g., 6.5 mm – 7.0 mm or above)
Offer stronger sealing and dimensional stability, minimizing drug oxidation and ensuring long-term sterility.
Generate higher frictional resistance, which requires greater drive force from the injection mechanism.
Suitable for high-viscosity drugs such as peptides or GLP-1 analogs, where maintaining internal pressure is essential for accurate delivery.
The choice of stopper length must therefore balance mechanical compatibility with the drug’s chemical stability and the intended injection force profile.
Within the pen system, stopper length directly affects the torque, dose linearity, and user-perceived comfort:
A longer stopper increases the required drive torque, impacting the pen’s spring calibration and gear ratio design.
Inconsistent stopper dimensions can lead to variation in dose accuracy, particularly in multi-dose pens or low-force mechanical designs.
Precision engineering of the pen’s internal thread pitch and plunger rod engagement is essential to compensate for stopper dimension tolerances.
This interplay highlights why leading manufacturers conduct full-system compatibility validation between cartridge, stopper, and pen housing — ensuring optimal friction coefficients, dose accuracy, and user ergonomics under real-world conditions.
For end users, stopper performance translates into perceived injection smoothness and confidence during dosing. A pen that delivers too much resistance or inconsistent flow may discourage proper use, affecting treatment adherence.
From a regulatory standpoint, both ISO 11040 (cartridge systems) and ISO 11608 (needle-based injection systems) require manufacturers to validate component interactions — including stopper dimension, compression set, and lubricity — to ensure consistent performance and safety throughout the product’s shelf life.
At Sunrise Medical, each injection pen and cartridge system undergoes comprehensive mechanical compatibility testing using stoppers of different lengths, hardness grades, and coating materials (such as silicone oil or fluoropolymer coatings). This ensures every customized pen achieves optimal injection force balance, dose precision, and long-term stability across various formulations — from insulin and peptides to GLP-1 analogs.
The length of the rubber stopper is not a minor detail — it defines the entire mechanical equilibrium between cartridge and injection pen. Proper selection and validation ensure smooth operation, accurate dosing, and reliable user experience. By mastering these micro-level interactions, Sunrise Medical delivers fully optimized injection systems tailored to the needs of global pharmaceutical partners.
