Most medical tubing is made of clear and sometimes colored-plastic lines used on IV sets and other hospital fluid-management chores. But what if an application calls for something more rigid, nonmagnetic, or capable of handling higher temperatures? Composites and liquid crystal polymers can be manufactured with properties for tasks that conventional plastic tubes cannot handle. Composites, for instance, can replace traditional stainless, aluminum, and other thermoplastic materials including PEEK. They can also be tailored to almost any engineering job. And liquid-crystal polymers can be extruded into tubing suitable for high pressure and high temperature tasks.

Composites such as the Polymed line from Polygon Co., Walkerton, Ind., (polygoncompany.com) are said to work well in thin-walled applications, including single and multilumen cannulas. Composites also have dielectric insulating capabilities, radioluscense (does not block x-rays), high strength-to-weight ratios, and corrosion resistance. Plus, they can be sterilized.

Performance characteristics of composites improve on those of thermoplastic materials and competitive metals. What's more, structural configurations perform like metal but with properties of a composite. The tubing has been used in laparoscopic surgical procedures and external orthopedic components.

Composites made with continuous fibers show higher strength than that of filled, short fiber, or long-fiber thermoplastics formed by injection molding or extrusion. The company adds that most Polymed tubes are used where metals must be shielded or coated to prevent capacitance coupling.

The tubes come as braided, circumferentially wound, or unidirectional. Diameters range from 3 to 20 mm with walls as thin as 0.23 mm.

Liquid crystal polymers are usually extruded into medical tubing for unusual properties such as a tolerance for temperatures up to about 400F. According to manufacturer Precision Extrusion, Glen Falls, N.Y. (precisionextrusion.com), its patented rotating extrusion die generates a biaxial orientation of polymers that overcomes the structural limitations of conventionally extruded LCP tubing.

The material is unusual because its attributes fall between those of a conventional liquid and a solid crystal. A liquid crystal, for instance, may flow like a liquid, but the arrangement of its molecules is similar to that of a crystal. There are many different types of liquid crystals which can be distinguished by their optical properties. The grade of LCP and the wall thickness determine the strength of the tubing. Kevlar is one well known example of the material.

LCP tubes can provide significant cost and performance advantages. For instance, the tubing typically costs from 30 to 60% less than fiber-reinforced composites with similar properties.

Precision Extrusion says manipulating manufacturing parameters provides the stiffness, compressive strength, and other properties needed for particular applications. An LCP tubing, for example, can be one third the thickness of a tube formed from polycarbonate yet have equivalent stiffness. These tubes typically have twice the crush resistance of conventional plastic tubing.

A few properties for a liquid-crystal polymer

A few properties of Polymed