Co-extrusion presses two or more materials through a single die, resulting in one piece. It requires two or more extruders, each providing a pre-measured quantity of molten plastics for the end product. Co-extruded tubing serves many purposes in the medical market, particularly with medical devices. Co-extruded tubes can contain internally hardened tubes within a flexible tube-wires, coils and cables embedded in plastics – or multi-colored and x-ray contrast striped tubes.
Three distinct areas of co-extrusion include multi-layer extrusion, extruding wires and fibers within plastics tubing walls, and the coating/extrusion of plastics over wires.
Multi-layer extrusion
Co-extrusion in its simplest form is the ability to offer a tubing solution in which the inner and outer layers offer different functional advantages. Multilayer tubing offers a modern, effective, and practical solution for various medical applications. This tubing provides a design solution for medical systems which require the use of inert materials for drug delivery applications or bondable outer tubing layers.
A major benefit of multi-layer extrusion is to manufacture tubing with as many as four different materials within a single tube. One result is that multilayer solutions can transform key material properties to create distinctly different materials.
Typical applications for multi-layer extruded tubing include drug delivery, insulin delivery, angiography, and pain therapy. Micro multi-layer extrusions also are a rapidly growing application. The trend to minimally invasive surgery demands increasingly complicated catheters to treat patients with care. Also in diagnostics, miniature tubes are increasing in use due to sample quantities and in small sizes previously unavailable. Internal diameters for these products range down to 0.3 mm with external diameters of 0.6 mm.
Co-extrusion of wires
Within the medical device industry, many products have traditionally required hand stringing wires, cables, and coils through multilumen tubing. That is an expensive practice. To address this, tubing extruders have developed the processing capability to co-extrude a wide variety of metal wires and glass fibers within the plastics tubing walls. Metals that can be contained in the tubing include copper, stainless steel, nitinol, platinum alloys, nickel, and silver plated wires. Polymers available for the tubing exteriors include polyurethane, silicone, polypropylene, polyethylene, nylon, and high-performance resins such as FEP, PEEK, PPSU, PEI and PTFE Moldflon.
The co-extrusion of wires eliminates the need to hand string wires, cables, and coils through multi-lumen tubing. Co-extrusion of wires within tubing walls cuts fabrication costs, reduces scrap rates, and improves the ability to meet tight tolerances. Co-extruded tubing can accept wires that are embedded or wires that are loose enough to resist kinks. Typical applications are lead systems, cardiovascular catheters and PTFE liners.
Wire coating
Co-extrusion also encompasses wire coating in which wires, cables, and coils are extruded in-line within a thin polymeric layer, rather than the traditional coating process.
Wires with a polymer layer thickness between 0.05mm to 0.1mm and up to 1mm are readily accommodated. In some cases, technology has extended that capability to 0.02-mm thick. With these extreme capabilities, the extruded layer protects the wire against corrosion and can influence friction (higher or lower) and assist with electric insulation. An extruded wire coating also provides a consistent wall thickness, while allowing for a more continuous process with greatly reduced variation.
Potential applications include neurovascular, lead systems, neuromodulation and cardiovascular.
