Small-diameter mandrels are commonly used in the manufacturing of endovascular catheters, for the purpose of retaining inside diameter dimensions and tolerances. Upon completion of manufacturing, these mandrels are removed, leaving a precision catheter shaft.
Mandrels can be comprised of metal, such as copper, or polymers such as acetals. Processing temperatures associated with the specific catheter materials being utilized typically determine the type of mandrel required. Catheters that use polyimide or PTFE layers often require oven curing at temperatures exceeding melt temperatures of polymer mandrels, and therefore require metal mandrels. Materials that do not require high-temperature oven processing can often utilize polymer mandrels.
The use of polymer mandrels has proliferated in recent years due to the increase in catheter innovations and demand for thin-walled, tight tolerance designs. The most common application for polymer mandrels is the production of braid reinforced catheter shafts. These mandrels maintain inside diameter shapes and tolerances during extrusion of the thermoplastic inner layer, stainless steel braided overcoat, and extruded thermoplastic overcoat. Such constructions are common for cardiovascular diagnostic catheters.
Polymer mandrels also have been used for the manufacturing of independent components for braid reinforced catheter shafts, such as thin-walled polymer tubes and stainless steel braided tubes. These components are manually assembled and thermally fused to provide complex constructions with discrete properties along the catheter shaft. Such constructions are common in cardiovascular and neurovascular guide catheters.
Lastly, polymer mandrels are used to produce thin-walled, small-diameter tubing with tight tolerances that cannot otherwise be produced using free-form extrusion. For example, polymer marker bands used on balloon catheters are cut from thin-walled polymer tubing with high loadings of tungsten filler to enhance visibility under fluoroscopy. This material is too heavy to retain shape during free-form extrusion and requires support by a mandrel of the inside diameter.