How are PVC laryngeal mask airway cuff connectors manufactured

There are two mainstream manufacturing methods for laryngeal mask cuff connectors: injection molding (producing hard or semi-rigid connectors, which is the dominant method) and, in a minority of older models, integral molding via PVC dip molding. Typically, the connector and the cuff balloon are bonded together during a subsequent assembly step, though in a few cases, they are integrally molded. Medical-grade soft PVC must meet ISO 10993 biocompatibility standards and possess thermal stability to prevent the release of HCl due to thermal decomposition at high temperatures.

 

1. Raw Material Preparation
Medical-grade soft PVC pellets: PVC resin + plasticizer (DOP/DOA) + calcium-zinc heat stabilizer + lubricant; must be medical-grade and compliant with ISO 10993.
- Pre-drying: Dry at 60–70°C for 2–3 hours to remove moisture and prevent bubbles or silver streaks.
- Note: PVC has a narrow processing window; temperatures exceeding 190°C easily cause degradation, yellowing, and the release of hydrogen chloride. This can corrode the mold, so the mold requires chrome plating for corrosion resistance.

 

2. Mold
- Cavity and Core: S136 mirror-finish mold steel with cooling channels; the connector features steps, barbs, and slots (for mating with the cuff airbag), requiring a slider-based core-pulling mechanism.
- Gate: Side gate or point gate; the gate should ideally be located away from sealing surfaces to prevent flash from compromising the seal.
- Shrinkage Rate: Approximately 1.0–1.3% for soft PVC; the mold design must incorporate a shrinkage allowance.

 

3. Injection Molding Parameters (Medical-Grade Soft PVC)
- Mold closing and clamping;
- Barrel temperature: 160–180°C; nozzle temperature: 170–185°C (do not exceed 190°C);
- Multi-stage injection: Fill at low speed to prevent air entrapment; apply sufficient holding pressure to eliminate sink marks;
- Mold cooling: Circulating water cooling; ensure thorough cooling and setting (insufficient cooling of soft PVC leads to deformation);
- Mold opening and part ejection.

 

4. Post-processing (in cleanroom)
- Trim gates and remove flash/burrs;
- Ultrasonic cleaning / purified water cleaning;
- Full dimensional inspection: outer diameter, inner diameter, slot depth, and mating tolerances;
- Leakage testing (sampling): pressure test for leaks after assembling the connector and cuff;
- Assembly: connector + laryngeal mask cuff.

 

Two methods:
1) Sleeve-and-bond with medical-grade PVC adhesive: The PVC tube of the cuff balloon is inserted into the connector's slot, medical-grade adhesive is applied, and the joint is cured;
2) Heat welding: Localized heating melts and fuses the PVC, leaving no adhesive residue; this method is commonly used for high-end laryngeal masks.

After completion, the products undergo clean packaging and EO sterilization.

 

A metal mandrel is dipped into liquid PVC plastisol, heated in an oven to gel and cure, and then demolded to produce a soft PVC part integrating the connector and cuff.
- Advantages: No weld lines; uniform wall thickness.
- Disadvantages: Poor dimensional accuracy; difficult to form precise locking slots or stepped features. Rarely used for connectors nowadays; primarily used for the airbag body itself.

 

 

1. Risk of thermal degradation: Temperature control is critical for PVC; overheating causes yellowing and plasticizer leaching, compromising biocompatibility. Molds require corrosion-resistant chrome plating, and residual PVC material must be purged from the screw during machine downtime.
2. Dimensional fit precision: The connector mates with the cuff balloon; tolerances must be strictly controlled, as excessive clearance leads to air leaks, while insufficient clearance makes assembly difficult.
3. Bonding/Welding reliability: The connection between the connector and the cuff balloon is a PVC-to-PVC joint; the choice of adhesive, as well as heat-sealing temperature and pressure, directly determine whether separation or air leakage occurs during clinical use.
4. Cleanliness: All molding and post-processing operations must take place in an ISO Class 7 cleanroom; the presence of debris or flash is prohibited to prevent entry into the airway.

 

Injection-molded connectors: High precision; capable of forming features such as locking slots, barbs, and stepped profiles; controllable wall thickness with the ability to selectively increase thickness; high production efficiency, making them suitable for mass production; widely used as the standard connector for laryngeal mask cuffs.
Dip-molded connectors: Low precision; suitable for simple cylindrical shapes; wall thickness is controlled by the duration of the dipping process; low production efficiency with long cycle times; rarely used for connectors, though the process is commonly employed for the balloon body itself.