How To Select The Stiffness of Pebax Medical Flexible Multi-lumen Tubing

I. Hardness Grades and Characteristics of Medical-Grade Pebax Multi-Lumen Tubing

1.1 Hardness range of Pebax materials

Medical-grade Pebax (polyether block amide) is a core material for minimally invasive interventional devices. It offers a wide Shore hardness range—from 25D to 72D—allowing for hardness adjustment without the need for plasticizers, and complies with USP Class VI and ISO 10993 biocompatibility standards. Common medical-grade designations include 2533MED, 3533MED, 4533MED, 5533MED, 6333MED, and 7233MED; higher numerical values ​​indicate greater material hardness and a higher proportion of nylon segments, resulting in enhanced support and rigidity.

1.2 Differences in core performance across hardness grades

Low-hardness grades (25D–35D) are dominated by polyether segments, offering excellent flexibility and conformability; they feature a small minimum bending radius, allowing them to navigate complex, tortuous human body lumens while minimizing irritation to the vascular endothelium. Medium-hardness grades (40D–50D) strike a balance between flexibility and support, offering outstanding resilience and kink resistance—making this the most commonly used range for multi-lumen catheters. High-hardness grades (63D–72D) contain a high proportion of nylon segments, providing high column strength, superior pushability, and excellent kink resistance, making them suitable for use as the proximal support section of a catheter.

II. Two Core and Reliable Factors in Hardness Selection

2.1 Clinical Application Scenarios and Interventional Pathways

The complexity of the interventional route is the primary factor in selecting the hardness grade. For devices navigating tortuous blood vessels or narrow lumens, ensuring smooth passage is paramount, so a lower hardness grade should be chosen. Conversely, for proximal segments requiring a stable delivery platform and capable of withstanding significant thrust, a high-hardness material is necessary to prevent buckling (instability and bending). The hardness at body temperature must also be considered; Pebax material softens slightly at 37°C, so a performance margin should be allowed during selection.

2.2 Requirements for Pipe Structure and Mechanical Properties

The number of cavities, wall thickness, and reinforcement layer design of multi-cavity tubes directly affect hardness adaptation. The multi-cavity structure itself increases the overall rigidity of the tube. If there are many cavities and the wall thickness is thin, it is recommended to choose a lower hardness substrate to balance the overall flexibility. For multi-cavity tubes with braided or spring-wound reinforcement layers, the metal layer already provides support, and the outer layer can use a lower hardness Pebax to optimize surface compliance. Furthermore, burst pressure, fatigue life, and other indicators are also positively correlated with hardness; for high-pressure fluid transportation scenarios, the hardness level needs to be appropriately increased.

2.3 Sterilization and Long-Term Use Stability

Pebax materials are resistant to various sterilization methods, including ethylene oxide and gamma rays, but the aging resistance varies among different hardness grades. For long-term indwelling multi-lumen tubes (such as drainage tubes and infusion ports), hardness stability in bodily fluid environments needs to be considered; medium-to-high hardness grades offer better resistance to creep and deformation, making them less prone to deformation over long-term use. For short-term interventional devices, flexibility can be prioritized, and lower hardness grades should be selected.

III. Hardness Selection Recommendations for Different Scenarios

3.1 Vascular interventional multi-lumen tubes

For interventional devices such as multi-lumen catheters and coronary microcatheters that require passage through tortuous blood vessels, a hardness of 25D-45D is recommended for distal insertion to ensure both Abercrombie & Fitch (Abercrombie & Fitch) tracking and vascular safety. For the proximal insertion segment, a high-hardness of 63D-72D can be used to improve the efficiency of force transmission. For balloon dilation catheters and angiography catheters, a medium-hardness range of 35D-55D is recommended to balance filling pressure resistance and flexibility.

3.2. Multilumen tubes for drainage and infusion

For multi-lumen tubes used in cavities such as abdominal drainage tubes and three-lumen working tubes, a hardness range of 35D-55D is recommended. This ensures that the tube body is not easily kinked or blocked, while also reducing irritation to tissues and mucous membranes. For special multi-lumen tubes with pressure monitoring cavities, to ensure sensing accuracy, it is recommended to select a hardness of 45D or higher to reduce the interference of tube compression deformation on measurement results.

3.3 Endoscopes and multi-lumen tubes for cavities

For endoscope forceps and laparoscopic instrument tubes that require frequent bending and friction, a hardness of 40D-63D is recommended to balance wear resistance and bending flexibility. For operating channels that require repeated bending, medium-hardness Pebax with excellent resilience is preferred to reduce permanent deformation after repeated bending and extend instrument lifespan.

IV. Common Misconceptions and Precautions in Product Selection

The most common misconception in material selection is blindly pursuing high or low hardness. Excessive hardness can easily lead to cavity damage and a stiff operating feel; insufficient hardness results in insufficient pushing force and a tendency for twisting and bending. In practical applications, a segmented variable hardness design is often used, gradually adjusting the hardness along the tube's axis to achieve the optimal combination of near-end support and far-end flexibility.

Furthermore, material selection must be considered in conjunction with processing technology compatibility. Different hardness grades have significantly different extrusion temperatures and drying parameters. Lower hardness grades have lower melting temperatures, while higher hardness grades require higher processing temperatures. The production stage needs to adjust process parameters accordingly to avoid material degradation leading to hardness shifts.