What are dilator and sheath extrusions?
Dilators and sheaths are a pair of extruded components included in a vascular introducer set. An introducer set contains devices used to access blood vessels for the insertion of vascular catheters. After a needle is inserted through the skin and into the blood vessel, the dilator and sheath are passed together into the blood vessel.
The long tapered tip of the dilator acts to stretch the opening in the skin and blood vessel to allow for the insertion of the larger sheath. The dilator is then removed, leaving only the sheath inserted into the blood vessel, providing a port through which a variety of catheters can be inserted.
Some introducers incorporate a proximal seal to allow catheters to be repeatedly inserted and removed while preventing blood from escaping. Other introducers are designed to split in half and peel away after insertion, leaving behind only the catheter device.
What polymers are dilator and sheath sets commonly comprised of and why?
Polypropylene – The stiffest of the polymers used, it is commonly used for insert molded connectors and dilators requiring high strength, such as those used in bariatric applications. It is the least lubricious of the polymers listed here, but is more lubricious than common elastomers used for catheters. It easily accepts color pigments and radiopaque fillers, and is among the least expensive polymers available.
Polyethylene – High density (HDPE) and low density polyethylene (LDPE) are moderately stiff polymers with durometers of approximately 50D and 40D respectively. HDPE, LDPE, or a blend of the two, may be used for standard dilators and sheaths. Polyethylene has good lubricity and easily accepts color pigments, radiopaque fillers and is among the least expensive polymers available.
FEP – The softest of the polymers used, it is used to produce sheath components where lubricity is important. FEP is a melt extrudable fluorinated polymer with very good lubricity, second only to ETFE (PTFE is the most lubricious fluoropolymer but it is not melt processable). Radiopaque fillers and color pigments are more difficult to incorporate in FEP, and it is much more expensive than polypropylene or polyethylene.
ETFE – With higher stiffness than FEP, it is commonly used to produce sheath components where lubricity is most important and higher stiffness required. ETFE is the most naturally lubricious extrudable polymer. Like FEP, it is incorporating radiopaque fillers and color pigments presents some challenges and it is much more expensive than polypropylene or polyethylene and comparable to FEP.
What materials are used as radiopaque fillers for dilator and sheath sets?
Barium Sulfate was the first radiopaque filler widely used in medical formulations. It is a relatively inexpensive white powder that has excellent process stability. High loadings are required for comparable radiopacity to other fillers. Because it has poor tinting strength, it is relatively easy to color.
Bismuth Subcarbonate offers greater radiopacity that barium sulfate and can be added in less quantity to achieve comparable results. It is a white powder with high tinting strength, thus limiting color matching in some instances. It is limited by processing temperatures (yellows at 400 F) and in some polymers (not compatible with thermoplastic polyurethanes).
Bismuth Trioxide also offers excellent radiopacity in comparably lower loadings and is compatible with most polymers. It is yellow in color and can turn brown at elevated processing temperatures, limiting color matching. Gritty surfaces in finished parts limit use in thin wall and critical surface components.
Bismuth Oxychloride provides excellent radiopacity and is compatible with a wide range of polymers. It is more temperature stable than bismuth subcarbonate. White ‘platelet-like’ particles provide a smooth, pearlescent finish on components. This can provide limitations to exact color matches.
Tungsten is a very heavy metal powder that is compatible with virtually all polymers at very high loadings by weight. It is dark gray in color and produces a matte finish in high concentrations, providing substantial restrictions for color matching.
Polymer compounds with tungsten can be very abrasive on processing equipment. However, it is a filler of choice in very thin-walled devices where radiopacity is critical.
What medical devices, body parts or procedures is this commonly used in?
The use of introducer dilators and sheaths is common for intravascular catheter applications. A wide variety of sizes are available for common procedures such as central lines.
Unique and innovative catheters may require a custom introducer set that is matched to the size and application technique of the catheter device.
Why is Barty the best choice for this product?
Barty has been one of the leader in introvention medical devices for several years. Our engineers are experts in the right materials and technologies to give high-performance results you can trust. Talk with a Barty engineer or sales representative and find out how we can put our expertise to work for you.