Originally Published MDDI November 2003Extrusion

William Leventon

November 1, 2003

14 Min Read
Extrusion Changes to Meet New Challenges

Like the tubing used to make medical devices, extrusion change comes in many forms. In the last year, extrusion materials, manufacturing processes, and services have all been adapting to powerful change-driving forces such as economic conditions, ever-more-demanding customers, and alterations in the competitive landscape.

For medical device firms, these changes can yield feature-rich tubing with improved properties at lower costs. In some cases, however, they may also produce higher prices, lower quality, and new manufacturing complications.

New Material Options

In the medical device industry, material changes can add delay and difficulty to the product development process. Nevertheless, many device firms are taking advantage of new material options. For drug-delivery applications, some OEMs are replacing metal stents with bioresorbable polymer products, reports Hans Kramer, research and development manager at Innercool Therapies Inc., a San Diego–based medical device firm. Kramer has designed structurally sound bioresorbable polymer stents with up to 30% drug content. “That's huge,” he says, noting that drug-coated metal stents can't carry comparable drug amounts.

In addition, Kramer points out that drug coatings can come off metal stents as they're moved to the target site. That's not the case with bioresorbable drug-delivery stents. In fact, designers can set the exact rate that a polymer stent will release its drug load. Designers can also set the rate at which a bioresorbable stent will degrade in the body. “It's amazing how precisely you can engineer those two parameters,” Kramer notes.

Rather than using new materials, some extruders are blending commonly used plastics that are compatible with each other. According to Kramer, some companies blend materials to get around intellectual property restrictions, which are common in the heavily patented medical device industry.

In many cases, though, blending is done to change tubing properties. Some companies blend different resins to get an “in-between” hardness or modulus, according to Tilak Shah, president of Polyzen Inc. (Cary, NC). Others are blending barium sulfate or tungsten compounds into their material mix to add radiopacity to the extruded products, Shah says.

Precision Extrusion Inc. (Glens Falls, NY) is blending varieties of nylon together to make tubes for balloon angioplasty products. These blends increase the tear resistance and burst strength of the products, says Mike Badera, president of the company. In addition, Precision Extrusion is blending nylons and polyurethanes to make thin-wall catheter shafts that offer a relatively large inside diameter for a given outside diameter. Despite the thin walls, shafts made of these blends provide adequate kink resistance and burst strength, Badera says. 

Blends that include new liquid-crystal polymers (LCPs) can also reduce tubing wall thickness. Compatible with a variety of homopolymers, LCPs “vastly improve a structure's tensile properties in whatever direction you lay down the fiber,” Kramer says. With this fiber reinforcing, he adds, “I can make a catheter shaft with a wall half as thick [as an unreinforced tube] but with the same tensile properties.”

Another property-enhancing option is the use of plastics with some sort of additive. These include nanocomposites, which contain small amounts of nanometer-size clay particles. According to Shah, nanocomposites can improve the stiffness of extruded products, but they also require secondary processes that add cost and complication to the manufacturing process.

Other additives can improve surface characteristics such as lubriciousness or anticlotting capability. But when surface enhancement is all that's required, why use an additive (which will be present throughout a plastic device) instead of a coating? “It's an easier way to get the enhancement everywhere you want it,” Badera explains. “When you look at the process of applying a coating, it's easy to get it on an outside surface, but not so easy to get it on an inside surface.”

On the downside, some additives can cause problems as well as solve them. Because of health and environmental concerns, many firms device are shying away from polyvinyl chloride (PVC) formulated with DEHP, a plastic-softening phthalate. In some cases, companies decide to switch to a different plasticizer, says Mark Colton, senior process development engineer at Saint-Gobain Performance Plastics. In other cases, PVC is replaced by another plastic, such as silicone, polyolefin, or styrenic block copolymer.

But in all these cases, the replacement will be less capable than the PVC-DEHP combination, Colton notes. “In a certain application, you'll find a material that will work,” he says. “It won't have all the properties [of PVC-DEHP], but it'll have the properties the application needs.”
According to Colton, the task of replacing DEHP can be complicated by a number of factors. For one thing, some who object to the popular plasticizer have concerns about all substances in the phthalate family. Then there's the issue of cost. PVC and DEHP are the cheapest polymer and plasticizer, respectively, Colton notes, so replacing either or both of them will increase material costs. Thus, once a replacement is chosen and extrusion begins, “the battle is to keep costs in line,” he says.

A Multilayer Solution

In some cases, Saint-Gobain gets around the PVC-DEHP problem with multilayer tubing, which is becoming a bigger part of the company's product mix. To allay concerns about the controversial polymer-plasticizer combination, the company will extrude tubing with a PVC outer jacket and an inner barrier layer made of some other polymer. The result: “By weight, such tubing is predominantly PVC, but the fluid path is non-PVC,” Colton explains.

But this solution doesn't satisfy some customers, who worry that the DEHP in the jacket will eventually permeate the inner layer and work its way into the fluid path. Over short periods of time, Colton believes that the non-PVC liner will probably be an adequate barrier. “But in a long-term situation, DEHP may still come through,” he says, adding that the two-layer solution would probably be best for tubing meant to be used only once.

MedSource Technologies Inc. (Minneapolis) is extruding multilayer tubes for other reasons. To meet the demands of high-performance catheter applications, the company is extruding composite constructions made up of two or more material layers that perform different functions. According to Bill Ellerkamp, MedSource's vice president of market development, a composite construction might include a lubricious PTFE or FEP inner layer that eases passage of a stent or other device through the tube. Since lubricious materials have poor engineering characteristics, MedSource might add a nylon layer that provides torsional stability. And in some cases, a third material layer may also be added to provide the tube with some other key property.

Composite constructions can be made using coextrusion and fuse-down techniques, Ellerkamp notes. In addition, other processes can be employed in special situations. In some cases, for example, a fluoropolymer liner is subjected to plasma-ion or sodium naphthalene treatment to produce adhesion to a nylon outer layer added in a second extrusion process.

Unfortunately for customers, the creation of composite constructions can be “a relatively expensive process,” Ellerkamp notes. In fact, he estimates that it can cost 10–20 times as much as the extrusion of a simple commodity-type tubing product.

Another extrusion technique produces different properties along the length of a tube. Variable stiffness extrusion requires two extruders, each containing a different material. During extrusion, the output of the extruders is changed in order to produce optimum properties in different tube segments, Kramer explains.

For example, he says, consider a catheter shaft to be extruded out of nylon 12 and Peebax. In the first part of the variable-stiffness process, the extruders put out 90% nylon 12 and 10% Peebax, creating a stiff proximal end for greater pushability. Then servo-driven gear pumps change the extruder output to produce a stiff-to-soft transitional section in the middle of the catheter. Finally, after another output change, the extruders create a soft distal catheter end made of 80% Peebax and 20% nylon 12. This flexible distal end will ease catheter movement through the patient's cardiovascular system.

As an alternative, Kramer notes, a manufacturer could extrude each of the three sections separately and then fuse them together. But such a process would produce a catheter with abrupt property transitions at the fusion points. In addition, this multistep process would be more costly and labor intensive than the one-step variable-extrusion technique.

Getting Smaller and Thinner

Other innovative techniques help suppliers meet customer demands for ever smaller and thinner extruded tubing. These demands have reached the point that manufacturers such as Advanced Polymers Inc. (Salem, NH) can no longer extrude tubes with walls thin enough to satisfy device firms. So the company has turned to secondary processes to thin the walls of tubes that have already been extruded, according to Mark Saab, Advanced Polymers' president.

For example, Advanced Polymers has developed a proprietary process consisting of a series of stretches that gradually thins tubing walls to the required dimensions. Though effective, the process is “incredibly expensive compared to just extruding tubing and putting it on a spool or cutting it to length,” Saab notes.

To make smaller tubing, some extruders simply run their machines faster, drawing the tubes rapidly out of the same dies they use for larger tubing. While this technique does shrink the tubing, it also leaves high residual stresses in the finished product. “There's so much stress in that tube that as soon as you heat it up, it'll change its shape,” shrinking in length and expanding in diameter, Saab says. The result: “You'll have a different size tube than the one you thought you had.”

According to Saab, a key to extruding small tubing that retains its shape is to use small tooling. Another important step is to “relax” small tubes in secondary processes like annealing. These processes “take out the stresses you've put in by stretching [tubes] too much or too far,” he explains.

Along the production line itself, sophisticated gauging equipment is helping extruders meet stringent dimensional requirements. Recently, for example, Teel Plastics Inc. (Baraboo, WI) has been adding gauging instruments to its extrusion lines. The company uses laser gauging for OD measurements and ultrasonic gauges to measure tube wall thickness. These instruments have reduced extrusion scrap and eliminated human error from the measurement process, according to Joe Datka, a process engineer at Teel Plastics.

During extrusion operations, the laser gauges take measurements at a rate of 200 per second, while ultrasonic instruments take about 10 measurements per second. Using these measurement data, a computerized control system adjusts line operations every second and a half to keep part dimensions within specified ranges.

Sliding Down the Cost Curve

Obviously, special equipment and processes can drive up extrusion costs. According to MedSource's Ellerkamp, many makers of cardiology products can bear high manufacturing costs at the time of a new product launch. But when a device matures, cost pressures from buyers will tend to drive down the price, so the OEM won't be able to pay the contract extruder as much to manufacture the product. OEMs usually make this clear to their suppliers at the beginning of the process, Ellerkamp notes. “They'll say, ‘I might be able to pay you $10 today [to make the product], but you have to show me how you're going to be at $2 in three years' time.'”

MedSource meets these cost-cutting demands in a number of ways. For one thing, the company can boost yields with improved extrusion head designs, process controls, and curing systems. The firm can also cut production costs by getting tolerance concessions from customers. According to Ellerkamp, this is possible because OEMs often “overspecify the tolerance” of a new device to be sure that it will reliably perform all of its functions. But over time, as users become more familiar with the device and the associated procedures, it may become clear to them that the original tolerance requirements were stricter than necessary.

In cases like this, Ellerkamp notes, “We might say to a customer: ‘Let's reevaluate the tolerance. If you can add a thousandth to the ID tolerance, I can reduce your costs by 15% because my yield will go way up.'”

MedSource may also suggest less-expensive materials with properties similar but inferior to those of the original materials. “You're offering a compromise in the performance of a product to reach [a customer's] cost objective,” Ellerkamp explains.

After it's made, today's supersmall, superthin tubing presents extruders with new challenges in product packaging. “In the old days, people wanted tubing on a spool or roll so they could take off whatever length they needed,” Saab says. But now, “they don't want it on a roll because they'll destroy most of the product just trying to get it off the spool and cut it to length.”

Instead, Saab's customers want their tubing delivered in a form as close as possible to the form in which it will be used. “If they need pieces that are 1.2 inches long, they want those parts to come in at 1.2 inches long,” he says. “And they want them bagged 50 pieces per bag if that's their lot size. So all they have to do is pull [the tubing] off the stockroom shelf and put it out on the floor.”

Today, some device firms want to carry less inventory in their stockrooms. So companies like Precision Extrusion are asked to hold some ready-to-ship tubing, Badera notes. Customers also want his company to have raw material ready for extrusion on short notice to meet their changing needs. While adding to the extruders' costs, these changes allow OEMs to reduce inventory expenses without running the risk of not having products when needed.

Another change affecting extruders is the sharp increase in the price of natural gas, which is used in the resin manufacturing process. At Teel, this has resulted in material price increases of about 10–30% in the last year, according to Kevin Copsey, the firm's director of sales and marketing.

But material costs don't matter that much to U.S. makers of high-tech catheters, Badera maintains. The reason: “Materials might [account for] 25 or 30% of the cost of the tube I'm making,” he says. “But that tube might [account for] only 2% of the finished cost of goods. So if you have tubing that costs $2 in a $500 catheter, the fact that the price of the material changes 25% is almost irrelevant.”

He adds, however, that material price changes are much more relevant when products are extruded for foreign markets, where pricing for finished goods is much lower than in the United States. “A product that sells for $50 in the United States might sell for $35 in Italy and only $10 in India,” he says. “So if it's got $8 worth of material and tubing in it, it's hard to sell.” 

A slow economy can also make some tubing products hard to sell. At Precision Extrusion, demand for high-tech catheter tubing has been down a bit during the economic slump. According to Badera, high-end tubing is used in some elective procedures, which are less common during tough economic times, when people tend to see doctors less often than they do when the economy is strong.

Commodity Competition

On the other hand, the economic slowdown hasn't affected orders for Precision Extrusion's commodity-type medical tubing. But there's another threat to U.S.-based extruders of commodity tubing: offshore competition.

At Minnesota Extrusion Inc. (Maple Grove, MN), Brian Packard is feeling the pressure from overseas extrusion operations. Packard, the company's president, says he has a hard time competing with foreign outfits such as a Somalia-based extruder that worked with one of his customers. “I couldn't even buy plastic as cheaply as the people from Somalia could buy the material, extrude it, do some secondary processing, and ship it,” he reports.

According to Packard, there are a couple of ways for offshore manufacturers and U.S. device firms to find each other. Some foreign outfits are partnering with U.S. distributors that offer their services to American firms. In addition, there are companies that specialize in matching American OEMs with offshore manufacturing partners.

Packard tries to distinguish his company from foreign competitors by offering product development help. But after taking that help, many OEMs give the extrusion work to offshore manufacturers—despite an understanding at the outset that Packard's firm will make the product once it's designed. “I'd say about 75% of the time, once we develop a product for them, they take it overseas to get it [made] cheaper,” he says.

Nevertheless, he adds, for difficult jobs involving new and/or critical components, OEMs “prefer to go to someone close by, so they can keep their finger on” the project. U.S.-based extruders can also offer American customers faster turnaround times and easier communications than offshore outfits, he notes.

Then there's the quality of foreign-made tubing, which is still “questionable,” according to Ellerkamp. That's not a deal breaker for some OEMs, who have told MedSource that the cost of offshore extrusion is so low that it beats U.S. extrusion even when the “good rate” is only 60%.

But output of that caliber wouldn't satisfy most of MedSource's customers, Ellerkamp says: “They want 100% quality coming through their doors, regardless of price.” 


Recent changes in extrusion materials, processes, and services can bring a variety of benefits to medical device OEMs. These include tubing with tighter tolerances, better properties, and new capabilities, as well as more-efficient and less-expensive contract services. But device firms should also be aware of the pitfalls in the new extrusion landscape. Among these are high costs for special services, increased production complexity, and quality questions about the output of low-priced offshore extruders. 

Copyright ©2003 Medical Device & Diagnostic Industry

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