Core Challenges in Filling High-Viscosity Liquids into Prefilled Syringes

Filling highly viscous drug solutions (e.g., viscosity >100 cP) presents significant technical challenges that drastically reduce the efficiency of conventional filling equipment. Key bottlenecks include:

· Difficulty in Defoaming: The liquid tends to entrain air bubbles, which are difficult to release naturally.

· High Flow Resistance: Results in substantial product residue and high material loss during transfer.

· Limited Sterile Filtration Capacity: High viscosity reduces membrane flux and increases the risk of filter clogging.

· Low Filling Accuracy: Unstable fluid control compromises dose precision.

· Bubble Generation During Stoppering: Mechanical movements disturb the liquid surface, increasing the risk of bubble formation.

These issues become especially critical when viscosity exceeds 5,000 cP (as seen with hyaluronic acid-based products), necessitating specialized processes and dedicated equipment to ensure production quality.

Vacuum Filling: A Critical Technology Pathway for High-Viscosity Liquids

Traditional positive-pressure filling often induces turbulence and entrapment of air bubbles. In contrast, vacuum filling technology overcomes these limitations by creating a controlled negative-pressure environment (adjustable from 0–50 kPa). It utilizes vacuum-assisted suction to enable smooth, laminar filling, effectively preventing foam generation.

Advantages of Vacuum Filling:

· Liquid is gently drawn into the needle under vacuum, minimizing shear forces.

· Integrated with Class 100 laminar airflow hoods to ensure sterile transfer.

· Independent control systems for vacuum filling and vacuum stoppering enhance sealing reliability.

This approach is particularly effective for sensitive, high-viscosity formulations where product integrity and sterility are paramount.

Key Structural Design and Fluid Management Optimization

To improve transfer efficiency and filling stability, the system incorporates the following customized components:

1. Reservoir and Distribution System

· Constructed from 316L stainless steel

· Designed with zero dead-leg geometry to minimize residual volume and facilitate cleaning

2. Metering Device

· High-precision ceramic piston pump with ±1% dosing accuracy

· Specifically engineered for reliable performance with high-viscosity fluids

3. Filling Needle Assembly

· Equipped with overload alarm and anti-splash structure

· Features a PEEK vacuum chamber sleeve, enabling stable operation under extreme viscosity conditions (up to 5,000+ cP)

4. Fully Servo-Controlled System

· Ensures high operational stability

· Achieves stopper insertion success rate >99%, critical for maintaining container closure integrity