High-density polyethylene (HDPE) is a long, linear hydrocarbon chain. Its high density is achieved by having a high crystallinity, which is typically attributed to a high molecular weight and linear molecules. This material is often used for dilators and introducers because of its low cost and easy processing. It is also used for heatshrink tubing used for the assembly of devices.
Polyolefins are the simplest of polymers, containing only carbon and hydrogen atoms. Because of their chemical structure, they are relatively inert and resistant to many solvents. Polyolefins are also fabricated from readily available feedstock, making them inexpensive. This combination of chemical inertness and low cost makes polyolefins ideal for most packaging applications. They are also commonly used in dilators and introducers.
Polyolefins are beneficial because they are inexpensive yet biocompatible when formulated correctly. For example, UHMWPE, or Ultra High Molecular Weight Polyethylene, is often used as a solid lubricant in joint replacement prosthetics.
Low-density polyethylene (LDPE) is a long, branched hydrocarbon chain. Its low density occurs because the branching in the molecules does not allow for a high degree of crystallinity. This material is often used for dilators and introducers. It is also used for heatshrink tubing used for the assembly of devices.
Linear low-density polyethylene (LLDPE) is a short, linear hydrocarbon chain. Its low density occurs because its chains and branches are small, allowing only small crystals to form. These small branches result in a lower yield stress, as the chains are less entangled with each other. The advantage in choosing LLDPE is that the tubing made with it will be extremely flexible, much more so than with any other polyolefin.
Medium-density polyethylene (MDPE) is a blend of HDPE and LDPE, providing a product with a stiffness somewhere between the two. MDPE is ideal when customizing dilators to an end-user’s preferences.
Polypropylene (PP) is a hydrocarbon chain with methyl “pendant” groups. These “pendants” provide higher stiffness and help resist stress cracking better than the polyethylenes mentioned above. It is because of those properties that polypropylene is ideal for stiff packaging tubing.