Material, technology developments drive growth in medical-tubing industry

Small, high-tech applications appear to be realizing some of the biggest growth in the medical-tubing industry. There?s a growing demand for minimally invasive devices such as multilumen and neurological catheters that require very thin walls and innovative design. The medical-tubing market overall is expanding, but it is in these specialized areas where some machinery processors are seeing a notable shift.

According to a report titled ?Plastics for Medical Devices? from Businesses Communications Co. (Norwalk, CT), disposable medical devices (a high percentage of which is tubing) represent 60% of the total volume of plastics used for medical devices. The total volume in 2003 was 2.3 billion lb and is projected to grow at an annual rate of 4.3%, reaching almost 2.9 billion lb by 2008.

Lumen Limits

The quest for minimally invasive procedures is the main driver for innovations in multilumen tubing, according to Simon Dominey, business manager of Killion, Specialty Systems group of Davis-Standard.

?The more lumens, the better. It began with three-lumen tubing, which is now commonplace; the same goes for five-lumen. Now seven-lumen tubing is the rarity.

?For instance, in a single procedure, you may need a guidewire to guide the tubing, a cutting device, a gripping device, an irrigation device to flush the area, an illuminator, and a removal or suction system to name a few,? says Dominey. ?When there?s an impetus to develop technology?like improving minimally invasive procedures?you see a surge of activity. In the last few years we?ve personally seen an influx of tubing startups. About 15 years ago there were a lot of startups that were eventually gobbled up by bigger manufacturers. Now we?re seeing them crop up again due to material advances and the need for less-invasive technology.?

In addition to the hunt for improvement in multilumen technology, there is an ongoing search for innovative methods to incorporate biological agents in the tubing, especially for items that will remain in the body, such as drug-eluting stents.

Small but Mighty

Smaller machines for low-volume runs and frequent material changes are ideal for research and development, and are currently in high demand, according to Joseph Scuralli, president of Wayne Machine & Die Co. (Totowa, NJ). He attributes the heightened activity that Wayne Machine?s seen in the last two years not only to emerging startups but also to material and technological advances that necessitate a need for companies to upgrade their machinery.

?There was a shakeout in the industry 10 years ago that flooded the market with used machinery that can no longer keep up with the changing demands of the industry,? he says.

Wayne has just introduced a new tabletop medical tubing extrusion system (1?4 to 1 1?4 inches) geared primarily toward these R&D applications. The line uses a crosshead die that facilitates quick adjustments for manufacturing multilumen tubing or tubing with integral wires. ?This line is designed to work quickly for ?boutique? runs. For instance, a company doing R&D work will run 200 ft of tubing with a material that?s 10% barium loaded, then 200 ft that?s 11% barium loaded, and so on,? says Scuralli. ?Between each of these runs, they need to break down the machine to be sure that the material isn?t contaminated. The tabletop design allows them to do this easily.?

He points out that the line is more heavy duty than others because it?s designed with a double-reduction helical gearbox that increases durability and easily transfers torque from the motor to the screw. ?This allows stable output and longer life. The motor stays cooler than in a worm gearbox and is more efficient.?

Dominey agrees with Scuralli regarding the value of focusing on smaller-run applications. ?Many machinery manufacturers and resin producers don?t want to deal with the small-run applications because there?s obviously more revenue in the larger commodity runs, but we think there?s value in also dealing with the specialist,? says Dominey. The company touts a microloop water-filtration and disinfection system to safeguard against contamination, which is always a concern for medical-tubing manufacturers. Primary filtration occurs through a prefilter, with secondary filtration for removal of pyrogens, microorganisms, and other contaminants. Dominey says that this system is very popular with small producers because it is affordable, even for customers running just one extrusion system.

The company has also launched an upgraded version of its vacuum-sizing technology to allow for even more precise sizing. ?This precision allows for more demanding ID and OD wall dimensions, and enables sizing of sticky materials such as flex PVC and urethane,? says Dominey. As multilumen manufacturing becomes more complex, the vacuum-sizing technology eliminates the need for using internal air supplies to maintain outer-wall consistency from lumen to lumen.

Not to be outdone, American Kuhne (Norwich, CT) recently launched a new line of ULTRA extruders for the medical market. The machines range from 3?4 to 1 3?4 inches and are tailored to medical applications with stainless steel construction and sophisticated controls. In July 2005, Kuhne introduced its AKcell control designed specifically for medical tubing manufactures. ?We?ve pared down the graphics because the medical manufacturers don?t need sexy graphics, and instead we?ve included more recipe storage and a cost-effective integration of an ID/OD gauging system,? says David Citron, director of sales and marketing.

The company has noticed that many producers who used to outsource their tubing production are now being outfitted with an extrusion system to bring their production in-house. ?People who?ve been buying tubing seem to be more eager to manufacture the tubing themselves. The first-time producer requires a higher level of hand-holding but they don?t take the machine until we?re running their product to specifications, which usually happens from start to finish in 12 to 14 weeks,? says Citron.

Material World

The primary materials used for medical tubing are: PVC and TPEs; olefins (PP and PE); urethanes; nylon (polyamide); FEP and PTFE (fluoropolymers); and silicone.

Silicone tubing is used for applications including peristaltic pump systems, surgical drains, catheter systems, and as an intravenous drug-delivery vehicle. Tubing supplier Specialty Silicone Fabricators (Paso Robles, CA) recently developed close-tolerance silicone tubing that can spiral or twist to a desired pitch, which improves kink resistance, flexibility, and electrical noise reduction, says Paul Mazelin, director of marketing. SSF is capable of building and customizing its equipment, in addition to the standard extrusion machinery. ?We have equipment that?s off-the-shelf, but we?ll use our in-house engineering capabilities to modify and optimize our equipment for a process,? says Mazelin.

Silicone is processed differently than thermoplastics?it must be fed from strips and kept cool during the extrusion process to prevent premature curing. Wayne Machine introduced a medical-grade silicone extruder (3?8 to 3 1?2 inches) with an improved feed system and its own drive system that is electronically linked to the extruder screw drive. ?This development allows the operator to advance, match, or retard the surface feet speed of the feed roll as compared to the screw surface feet, to allow optimal feed rates,? says Scuralli.

A new line of silicone extruders from American Kuhne will also address the strip-feeding problem. Citron says that new features include a wider feed opening; a power hinge feed opening that allows fast and easy access for cleanout, which is a priority for medical silicone processors; and off-the-shelf feed roll gear reduce for a lower initial cost.

FEP and PEEK

Tubing supplier Zeus Inc. (Orangeburg, SC) deals primarily with the fifth material area?fluoropolymers. The company produces tubing for a wide variety of industries but medical represents the largest segment. According to Karl Graffte, Zeus?s director of marketing, fluoropolymers fit the bill for minimally invasive medical procedures because of their lubricity, biocompatibility, and chemical-resistance properties. ?The properties of these materials give design engineers the latitude they require in developing and commercializing next-generation devices,? says Graffte.

Some drawbacks of working with a material like FEP are its highly corrosive nature and the high heat at which it?s processed (over 500°F). Zeus?s extrusion machinery can handle temperatures of up to 800°F and nickel-based alloys are used in the machinery?s flow paths to combat corrosion. Zeus will soon be branching out and launching a new line of PEEK heat-shrinkable tubing. PEEK is becoming more desirable to manufacturers because it is a more specialized replacement for PE. ?It?s much more specialized and allows for designs that just aren?t doable with PE,? says Dominey of Killion. Like FEP, PEEK requires high processing temperatures (700-800°F).Because of PEEK and FEP?s growing popularity, producers are upgrading their equipment to handle the materials. Citron of American Kuhne says that many nylon producers are moving toward PEEK and FEP to differentiate themselves in the market. ?In order to make the move, they need to buy new machinery that?s equipped to handle those materials,? he says.