ePTFE (or expanded polytetrafluoroethylene) has been used as an implantable material for over 30 years in a wide variety of medical and dental applications including arterial grafts, facial plastic surgery, orthopedic joint implants, sutures, chorda of tendineae in the heart, reconstruction or augmentation for cosmetic purposes.
Why is ePTFE used so extensively in the medical and dental fields?
ePTFE is a form of PTFE created with through mechanical expansion of extruded PTFE that has a mesh-like structure. It is flexible, soft, strong, and porous. ePTFE’s porosity is incredibly important in these applications as it allows the body’s own tissue to grow into the material and bond with it to keep it where it needs to be. ePTFE is also non-biodegradable, biologically inert, and non-toxic with very low rejection rates or allergy problems.
Are ePTFE implants permanent?
ePTFE implants can certainly be removed if necessary, however most implants created with ePTFE are permanent and non-migrating. It is the recommended choice for facial implant procedures because it is inert with very low risk of complications or adverse reaction from the body. ePTFE can promote tissue in-growth, that will reduce implant migration, erosion, and scaring.
How is ePTFE’s porosity created and how does that affect its performance?
As we stated above, the porosity of this material is very important. In order to create ePTFE’s porous structure, the extruded profile will be mechanically expanded, then followed by amorphic locking, or “sintering”, of the expanded structure.
There is a direct correlation between the material’s fiber length and the volume density – the greater the mechanical expansion, the longer the fiber length, and the lower the volume density. Non-porous PTFE has a volume density of 2.15 g/c cm, while IPE is able to expand to a volume density from less than 0.3g/cubic cm to over 1.0 g/cubic cm. The measurement of the fiber length (which is also called Internodal Distance or IND) is not a measurement of the pore size; it is actually a measurement of the fiber length as measured with SEM or high end microscopy. Those familiar with ePTFE implanted products will reference the internodal distance as related to various cellular responses to ePTFE material implantation. IPE has the processing capabilities of producing internodal distances of < 10 microns to >80 microns.
How does the porosity affect the strength of the profile?
As the porosity of ePTFE changes, the physical strength properties also change. The resins used as well as the ePTFE expansion process itself will increase the material’s tensile strength. The main reason for the increase is that the crystallinity of ePTFE can be 95% or higher as compared to the 40-50% crystallinity of PTFE products. There are also various patented methods that can be applied to ePTFE processing that further increase the strength of the material.
How do you select the correct porosity?
Ensuring the correct material porosity and material thickness in order meet various functional requirements is incredibly important to take into consideration when designing with ePTFE.
| The higher the porosity (lower volume density or the higher the internodal distance) the ePTFE material will become: | The lower the porosity (higher volume density or shorter internodal distance) will be: |
| -Softer -More compressible -Higher flexural capabilities -Lower tensile strengths -Higher air permeability -Greater tissue in-growth or endothelization of implanted products | -Stiffer -Resist compression -Lower flexural capabilities -Higher tensile strengths -Lower air permeability -Reduced tissue in-growth or endothelization of implanted products |
What specific implants are we talking about here?
There are several common types of implants that are created with ePTFE – including single layer non-reinforced, multi-layer PTFE reinforced, and thermally formed ePTFE.
Multi-layer reinforced ePTFE can be carved or formed which is used for facial implants including cheeks, chin, and nose in cosmetic and reconstructive procedures. It is used to create parts for:
- Facial implants
- Submalar implants
- Malar implants
- Chin implants
- Premaxilla implants
- Nasal implants
- Dorsal nasal implants
- Nasal labial fold implants
- Lip implants
- Scar fill
- And many more
Another application for expanded PTFE (ePTFE) is in the use during various dental surgical procedures and surgical grafting. In the correct product density and configuration. This material can be used as barrier membranes to prevent bacterial growth and epithelial migration or provide tissue scaffold for reconstruction. These membranes can be used with or without reinforcement, which can help the membrane maintain the desired shape.
What other medical or dental applications is ePTFE used for?
A few other uses include, but are not limited to:
1.) Medical instrument covers for highly articulating robotic or flexible bending sections. Typically the ePTFE is used in a tubular form that covers or protects internal laser-cut metal frame bending sections to reduce tissue damage, reduce insertion forces of instruments into the body with its high lubricity, and prevents kinking or bunching seen in other polymer covers.
2.) In non-supported tubular constructions like aeration or de-aeration tubing. The tubing porosity should be selected to provide the appropriate flow rate through the tubing wall. ePTFE is used in these applications due to its ability to be hydrophobic under low pressures while still being highly flexible.
3.) Standard vascular bypass or graft tube applications. There are a lot of different configurations of vascular graft tubing available and each design may indicate difference in the internal or external porosity. Changes in the porosity can either limit or promote tissue in-growth on different surfaces of the ePTFE tubing. A majority of these tubes would have a volume density of .45-.75g/c cm or a 20-40 micron internodal distance. Since the tissue in-growth properties should be the main consideration in the design of this tubing, the diameter and wall thickness will be required to prevent kinking or collapse of this tubing during use based on the tubing internodal distance. For example, a larger tube diameter would require a thicker final tube wall as compared to a smaller diameter which can have a proportionately thinner wall.
How can IPE help you?
IPE manufactures and distributes custom profile extrusions made from a variety of melt thermoplastic materials and our Fluoroflex™ porous polytetrafluoroethylene (ePTFE). Our FluoroFlex™ ePTFE is the ideal material for medical and dental components. The material is biocompatible, hydrophobic, flexible, resistant to virtually all chemicals, and withstands extreme temperatures. When looking for a highly flexible, lubricious, chemically inert, hydrophobic plastic for critical applications, very few non-woven plastics can meet or exceed the flexural properties needed in typical medical implants like our FluoroFlex™.
We are committed to understanding your specific project requirements and will tailor a development program to your time frame, costs, and project needs. As an ISO 13485 registered company, we place a strong emphasis on quality. Our facility includes a Class 10,000 clean room for projects with stringent cleanliness standards. With more than 20 years of custom extrusion experience, we apply our extensive knowledge to every project and will optimize your custom extrusion for aesthetics, cost, and/or functionality.
For more information please visit our website at www.ipeweb.com, send us a request for quote, or contact us to get started on your next project.
