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1. Materials and Performance
Main Material: Medical-grade polyethylene (PE) is used; some products may use high-density polyethylene (HDPE), which possesses good biocompatibility, flexibility, and tear resistance.
Surface Treatment: The tube surface is typically coated with a hydrophilic coating (such as a PVP-based coating), which significantly reduces the coefficient of friction upon contact with water, minimizing damage to human tissue and improving operational smoothness.
2. Structural Design
Conical Tip Design: The distal (front) end is a tapered tip, with the outer diameter gradually decreasing along the axial direction to create a smooth transition, facilitating insertion into narrow body cavities (such as the ureter and blood vessels) and reducing puncture resistance.
Equal Diameter Section: Behind the conical tip is a tube of equal diameter, providing stable support and a passageway to ensure uniform force transmission during dilation.
Internal Channel: The tube has a hollow internal structure to accommodate the guidewire, enabling precise guidance.
3. Key Design Considerations
Tapered transition: The tapered design of the PE expansion tube is the core, and it is necessary to ensure sufficient taper and surface smoothness to balance expansion force and tissue protection.
Coating application: Hydrophilic coatings not only improve the user experience but also reduce the risk of postoperative complications such as mucosal edema and bleeding.
Material compatibility: The combination of materials between PE expansion tubes and sheaths (such as PTFE, PEBAX) must balance rigidity and flexibility to ensure smooth passage through complex cavities.
| Specification (Fr) | OD (mm) | ID (mm) | Common length (cm) | Cone length (mm) | Main materials | Surface treatment | Typical application scenarios |
|---|---|---|---|---|---|---|---|
| 6Fr | 2.0 | 1.0 | 10 / 13 | 10-15 | Medical PE/PP | Hydrophilic coating | Pediatric interventional procedures, delicate vascular puncture |
| 8Fr | 2.7 | 1.5 | 13 / 15 | 15-20 | Medical PE/PP | Hydrophilic coating | Peripheral vascular and ureteral guidance |
| 10Fr | 3.3 | 2.0 | 15 / 20 | 20-25 | Medical PE/PP | Hydrophilic coating | Percutaneous nephrolithotomy and biliary drainage |
| 12Fr | 4.0 | 2.5 | 20 / 25 | 25-30 | Medical PE/PP | Hydrophilic coating | Percutaneous nephrolithotomy and thoracic drainage |
| 14Fr | 4.7 | 3.0 | 25 / 30 | 30-35 | Medical PE/PP | Hydrophilic coating | Urology, Interventional Therapy |
| 16Fr | 5.3 | 3.5 | 30 / 35 | 35-40 | Medical PE/PP | Hydrophilic coating | Percutaneous nephrolithotomy, large instrument access |
| 18Fr | 6.0 | 4.0 | 35 / 40 | 40-45 | Medical PE/PP | Hydrophilic coating | Complex cavity dilation and endoscopic surgery |
| 20Fr | 6.7 | 4.5 | 40 / 45 | 45-50 | Medical PE/PP | Hydrophilic coating | Large cavity, special interventional surgery |
Size Matching: The outer diameter of the dilator must match the inner diameter of the target cavity or sheath, typically expanding in increments of 2 Fr to minimize tissue damage.
Length Selection: The length is selected based on the puncture depth and surgical path. For example, 20-30 cm is commonly used in percutaneous nephrolithotomy, and 10-15 cm is commonly used for peripheral vessels.
Coating Performance: Hydrophilic coatings significantly reduce insertion resistance, especially in sensitive tissues such as the ureter and blood vessels.
Material Hardness: PE material offers moderate hardness, balancing expansion force and flexibility; for higher rigidity, PP or composite PE materials can be selected.
A complete expanding sheath product is typically a kit, mainly composed of the following core components:
| Components | Materials | Function |
|---|---|---|
| Dilator (expansion tube) | Polyethylene (PE) / Polypropylene (PP) | It is used to expand cavities and create channels, and is the core component shown in the figure. |
| Sheath | Polytetrafluoroethylene (PTFE) / PEBAX / Stainless Steel | As the final channel carrier, it is usually composed of a multi-layered composite structure (inner PTFE lining, middle metal mesh, outer elastomer) to provide support and flexibility.。 |
| Connector / Handle | Polypropylene (PP) / Polycarbonate (PC) | It connects the expansion tube and the sheath, provides an operating grip point, and some parts have a locking mechanism. |
| Guide wire | 304 stainless steel with PTFE coating | Guide the expander and sheath to precisely reach the target location. |
| Other accessories | Such as hemostatic valves, locking caps, etc. | Used for sealing, locking, and auxiliary operations. |
