Micro extruder targets booming medical applications

American Kuhne (Ashaway, RI) is leveraging its custom engineering capabilities to target fast-growing micro extrusion applications in the medical market.

The company showed the first micro extruder for the American market at MD&M West last month in Anaheim, CA.

The new Modular Micro Extruder is available in 12-, 16-, and 19-mm barrel/screw sizes and can achieve output volumes as low as 125 g/hr while still using standard size pellet shapes and granules. That's about half the best rate previously possible.

"The biggest engineering challenge in developing a micro extruder is the feeding process. You have to still use standard size pellets because you would introduce another heat history if you used micro pellets," Steven Maxson, VP extrusion systems at American Kuhne, told PlasticsToday in an interview. "We have designed a special geometry in the feed section of the machine to promote friction."

In another major change, the machine uses a servo drive system.

"If you use an AC vector drive, you have poor stability at low screw speeds. The servo drive provides very good accuracy in the full speed range of the screw."

Slow output rates are critical for production of micro catheters using medical plastics such as Pebax elastomers, nylon, polyurethane, PEEK, FEP fluoropolymers and bioresorbable plastics such as polylactic acid (PLA).  

Other target applications are tight tolerance medical tubing, co-extruded tubing, fine wire jacketing used for neuromodulation, filaments, and solid dosage forms in which drugs are encapsulated in bioresorbable plastics.

Another major target for micro extruders is the rapidly emerging market for coronary stents made from bioresorbable plastics such as PLA.

For those applications, short residence times are critical because of the heat sensitivity of bioresorbables.

"A shorter residence time protects the molecular weight of the material and ultimately the physical properties of the end product that it is use in. This is especially important for developers of medical devices, dissolving oral dosage forms and drug-eluting devices."

American Kuhne has developed a full range of equipment to go with the extruders including touchscreen control systems, spiral flow crossheads, precision cooling tanks and combination servo puller/cutter controls.

At MD&M West, American Kuhne ran a Pebax 6333 micro tubing system with a newly built 12-mm Modular Micro Extruder with servo drive and pressure control. 

Medical applications have traditionally accounted for about one-third of American Kuhne's business, but now account for slightly more than half.

The Graham Group last year acquired controlling interest in American Kuhne from The Kuhne Group of Sankt Augustin, Germany, which is owned by Peter Kuhne.