The Basics Of Silicone Tubing

Flexible elastomers are critical to the development of new and innovative medical devices, providing sealing, gasketing, and fluid transfer properties not possible with most other materials. Silicone elastomers in particular have played a major role in the materials development portion of this initiative. By using inputs not typically associated with allergenic responses, and avoiding introduction of migratory plasticizers, silicone elastomers have expanded in areas traditionally served by lower cost materials such as PVC and latex.

Silicone tubing is typically used in applications such as catheters, drains, feeding tubes, and peristaltic pumps where biological compatibility is a key requirement. Manufacturers considering silicone for these types of applications can choose from special grades that meet stringent health agency requirements, such as USP Class VI and ISO 10993.

Most silicone tubing used in the healthcare industry is manufactured using a continuous extrusion process with hot air vulcanizing ovens to thermally cure the tubing. Size can range from extremely fine capillaries for optical surgery to 3-in. diameter tubing for high-pressure exhaust hose. In addition to conventional tubing, more complex designs involving fabric or wire reinforcement are possible as well as multi-lumen tubing having several distinct transport sections within the same construction.

Unlike thermoplastics such as PVC, which are processed by heating to a melt with subsequent cooling to the final form, silicones are thermoset materials that are chemically crosslinked and therefore tend to be more resistant to deformation. Traditionally, most extruded silicone rubber tubing is vulcanized using organic peroxide curing agents. However, platinum curing systems have become more popular because of their high purity and low level of extractables, since there are limited cure “by-products.”

While dimensional tolerances on ID and wall thickness for extruded tubing can be held to within several thousandths of an inch, cyclical variation is possible with a continuous extrusion process. Liquid injection-molded silicone elastomers offer an alternative for making high quality, cost-effective parts and have recently been used to make a silicone rubber tube for disposable peristaltic-pump cartridges used for enteral feeding. Liquid silicone elastomers are two-component, platinum cured, pumpable silicones that can be molded and cured at elevated temperatures using injection-molding machines that process thermoset materials. In contrast to extrusion, molding allows for complex part geometry and exacting dimensions resulting in improved pump-delivery accuracy. Closely controlling the tube geometry may enable creative new pump designs with improved portability and excellent fluid delivery performance. As a result, liquid silicone elastomers provide tubing manufacturers with additional options to consider in many future tubing applications.