When a medical product or device is being manufactured, it is important that the correct type of material is used. In most instances, polymers have a mucher greater advantage for these types of products than what metal has because of the fact that the saline solution that is found inside of the human body is very hostile to all metals. That being said, metals are not subject to the same level of degradation that the great majority of polymers are.
The plastics that are used for the purpose of injection moulding fit into three distinct classifications.
- Elastomers / Rubbers – those materials that are considered to be rubbers have elastomeric properties. This means that they have the ability to be stretched and then will go back to their original size and shape once the stress being applied to them is released.
- Thermosets – these materials are polymers that have been cross linked and are both intractable and rigid. They are made up of a molecular network that is 3 dimensional. These materials cannot be melted down again, as when they are exposed to extreme heat, rather than melt, they degrade.
- Thermoplastics – with branched or linear polymers, thermoplastics can be melted down with heat. Because of this, these materials can be molded into various shapes and removed via traditional techniques. For instance, wax has the ability to be molded into a range of different shapes.
Polyethylene is a plastic that is used throughout the world for a wide range of applications, both medical and none medical. In fact, it is so widely used that it represents as much as 34 percent of all the plastic that is used globally. Because it is resistant to most chemicals, absorbs very little moisture, and is resistant to impact, it is the ideal choice to make plastic medical components. Additionally, it does not retain potentially harmful bacteria or fade over time. It is for all of these reasons that it is used for the purpose of making medical implants.
The thermoplastic polypropylene is used for a range of different applications within the medical industry. This is because it is resistant to most chemicals and is very rugged. It is these properties that make the material ideal for use in medical equipment and protective packaging. Once done with, polypropylene can be made into small plastic pellets that are then recycled into new plastic products, thus keeping it out of landfill sites.
Polystyrene is a commonly used plastic within the medical industry for laboratory containers, such as petri dishes, microplates, and test tubes. All of these products are made via the process of injection moulding. After this, it is sterilized vua the use of the colorless and flammable gas ethylene oxide and or irradiation. The reason for its wide use is that this material is relatively inexpensive compared with other plastics and has a tensile strength that is very high. However, it does have a low melting point, and is a poor barrier for water vapour and oxygen.