State of the Art ePTFE Graft Manufacturing
Vascutek utilises computer controlled manufacturing and monitoring systems in its ePTFE production facility.
These systems ensure that an exact level of consistency and quality of product is achieved.
ePTFE Graft Production
1. PTFE Mixing
PTFE resin is mixed with an alcohol-based liquid, forming a PTFE paste.
2. Billet Formation
PTFE paste is then crushed into a solid structure (billet) using high pressure. The pressure is computer controlled to ensure a homogenous billet.
The billet is then placed into the extrusion equipment. Different extrusion heads and pins are used, depending upon which type of graft is being manufactured, for example a 6mm thin wall or a 7mm standard wall.
4. Alcohol Evaporation
The extruded PTFE is cut into short lengths and placed in a low temperature oven to allow the alcohol to evaporate. At this stage the PTFE has internal diameter and wall thickness parameters of the final product. The high pressure used in the extrusion process aligns the PTFE molecules in a longitudinal direction.
This process enables the conversion of extruded PTFE to expanded PTFE.
The short lengths of PTFE are placed into an oven and heated. This heating process softens the extruded PTFE. The short tubes are then stretched in a longitudinal direction at a pre-determined rate. The stretching process causes the tube to fibrillate. This results in a conversion from extruded PTFE to expanded PTFE. The computer controlled rate and ratio of stretching determines the inter-nodal distance (pore size) of the graft.
6. ePTFE Tape Wrapping
This process adds mechanical strength to the final expanded PTFE graft. An ePTFE tape is wrapped in a double layer onto the outer surface of the expanded PTFE tube using a laser guided system.
7. Reinforcing (Adding external support if required)
External spiral support is added to the graft (if required). The external spiral support provides kink and crush resistance and may be over the entire length of the graft, or have a central or end position.
8. Sintering (Cooking the expanded PTFE)
The expanded PTFE is next placed into the sintering oven. This is the most critical part of the entire production process as sintering stabilises the ePTFE and vastly improves the mechanical strength of the product.
Vascutek has developed a continuous conveyor sintering process where the ePTFE passes through a high temperature zone that causes the molecules to coalesce. The continuous conveyor sintering oven operates at temperatures in excess of 380°C with the hot zone being tightly controlled to within 3°C. This vastly reduces product variability seen in the traditional batch oven process used by other manufacturers.
9. Printing (adding the guideline)
All products are then printed with a guideline.
10. Gelatin Sealing (Process used with SEALPTFE™ and Taperflo™ product ranges)
Vascutek has developed a unique patented gelatin sealing process for its ePTFE products. This process coats the external surface of the graft with Vascutek’s proven gelatin sealant technology.
11. Cutting, Packaging & Sterilisation
At this stage, the grafts are cut to the desired length, packaged and then sterilised using Ethylene Oxide.
12. ePTFE Quality Control Procedures
Quality and consistency are paramount at every stage of ePTFE production.
From raw material checks to finished goods, Vascutek’s Quality Control Programme guarantees production excellence.
To ensure our finished products meet their exact design specifications, we remove multiple samples from each production batch and test these to destruction. The remainder of the batch is held in quarantine.
The testing schedule includes the following:
- Longitudinal tensile strength
- Suture retention (straight & oblique)
- Differential scanning calorimetery (DSC)
- Wall thickness measurements
- Internal diameter measurements
- Radial burst strength
- Peel strength (externally reinforced products)
- Peel strength (wrapped products)
Only after the samples have passed ALL tests, will the remainder of the batch be released for sale.
If the products fail to meet the quality contol acceptance limits for ANY of the tests – the whole batch will be rejected and destroyed.