First and foremost the material chosen for infusion catheters must be compatible with the infusate. Information regarding material compatibility can be found. The polymers most often used in preclinical and clinical practice are silicone, polyurethane (PU), polyethylene (PE), polyvinylchloride (PVC), PTFE, and nylon. Flexibility, durability, chemical compatibility, biocompatibility and thrombogenicity are the characteristics to evaluate when choosing between them. Silicone and PU are the two most often used for IV infusion based on these criteria.
In general, silicone is more porous than polyurethane and not as durable. Many researchers prefer silicone because it less rigid to the touch and therefore may be less injurious to vessel endothelium. Polyurethane is a thermoplastic and catheters and tubing are extruded. Extruding allows for easy tapering and adjustment of the softness or hardness of the catheter. Catheter tips may be extruded smaller and softer at the tip and larger and more durable outside of the vessel where kinking and abrasion are more likely. Because PU is a thermoplastic, it softens when warmed (by the body or blood) and stiffens when cooled. Catheters therefore will be stiffer outside of the body than they will inside the vessel. Because it is stronger than silicone catheter walls made with PU can be made thinner providing a larger internal diameter than silicone catheter of the same size. This provides better flow and may lessen the chances of clotting-off.
An important fact to remember is that all polyurethane is not the same. There are hundreds of polyurethane elastomers available in the market today. Many articles have been written that compare catheter materials or catheter treatments to one another but fail to identify the quality or formulation of the PU that was studied. The key is to always use a polyurethane that has been scrutinized to the fullest extent. SAI only uses polyurethane formulations in their catheters that have been tested at the highest level.