The extrusion process is challenged by advancing medical technology requirements.

As an accelerating array of new medical technologies is introduced, the demands on medical extrusion technology continue to require ever greater performance in ever smaller and smaller applications.

These intensified requirements of more performance in less space, along with rising costs of and shifts in materials used, have increased the demands on extruders for a continually increasing level of product and process innovation in all types of tubing and all other related medical applications.

Moreover, the new medical technologies require much tighter tolerances, more and more sophisticated co-extrusions, as well as newer generations of multilumen and multilayer tubing. The extrusion industry is responding with improvements in both products and manufacturing processes.

Ever-tighter tolerances are the norm

Tighter tolerances are a key requirement for the new medical extrusions. The president at one of our customer OEMs notes that the tolerance requirements are getting ever tighter. "What used to work as a 6 French catheter is 5 French today; and people want it to be a 3 French tomorrow," he says. "It has to have all the same properties, carry all the same amounts of fluid through it, or other accessory components have to fit with it, even though it's only half the size."

In the past, customers were satisfied with tolerances of a thousandth of an inch. More recently, it was half a thousandth. Now, they need to get even tighter than that.

[FIGURE 1 OMITTED]

For example, in terms of percentage of wall, the previous tolerance goal was 90%, but today, we don't blink at 95%. In fact, we have customers that are running 99% to 99.5% tolerances on their walls. (See figure 2 for how to calculate tighter wall tolerances, and figure 3 for calculating the draw down ratio to determine the tube diameter size).

[FIGURE 2 OMITTED]

Figure 3

The draw down ratio (DDR) provides a guideline for the
selection of the appropriate die and pin for tube/wire
extrusions. DDR is defined as the ratio of the cross-sectional
area of the die aperture or extrudate at the extrusion
die-face, to the cross-sectional area of the finished
wire insulation or tube.

With a draw ratio balance of approximately 1, the outside
and inside surfaces of a tube are drawn by the same
amount. Illustration 1:

DDR = [D.sub.D.sup.2] - [D.sub.T.sup.2]/[D.sub.CW.sup.2]
- [D.sub.BW.sup.2]

Draw ratio balance (DRB)

For quality extrudate, the inside surface of a tube of melted
resin should draw the same amount as the outside
surface. In this state, the draw is said to be balanced.
Illustration 2 shows how to calculate the draw ratio balance
using the same symbols as defined in illustration 1.
Illustration 2:

DDB = [D.sub.D]/[D.sub.CW]/[D.sub.T]/[D.sub.BW] = 1

The draw-down ratio/draw ratio balance

[D.sub.D] = diameter of the die aperture or opening

[D.sub.T] = outside diameter of the die

[d.sub.CW] = diameter of coated wire or cable, outer diameter of tubing

[d.sub.BW] = diameter of base wire or core, inner diameter of tubing

Draw-down ratio = cross-sectional area of aperture,
cross-sectional area of insulation or tubing.

New devices require multilayer and multilumen tubing

The increased sophistication of the latest medical devices now requires extruders to produce tubing with multiple layers and multiple lumens. The new specifications may call for anywhere up to eight lumens, some with wire inside, some with braids, and some with different lining materials.

And there seems to be no end in sight for the complexities that users demand. Right now, the sky's the limit on multilayer needs. For example, sheet manufacturing requirements may go up to 10 layers.

As a percentage of the business, one of our customers says that about 50% of the requests are multilumen, compared with 25% a year ago.

Coextrusion to the rescue

As wall thicknesses decrease due to the new smaller size requirements of tubing and other medical extrusions, it becomes difficult to retain all the desired properties using a single material, and increasingly the solution has been coextrusion. By combining two materials, with each material containing specific benefits, it's now possible to create a thin-wall tube that will maintain the feel of a thicker-wall tube.

Demand for tubing with varying stiffness

There's also a growing demand for tubing with stiffness that varies with length, making tooling more complex. For these requirements, the extruder is basically being oscillated--going from one durometer to the other, and back. Within a single tube, there are actually two or three durometers, which are changing along the length of the tube so it can be guided through the patient's body with a harder durometer, and have it go around other areas in the body with the soft durometer.

That's just the beginning, our medical extrusion customers are telling us. For example, some tubing OEMs are manufacturing braided catheters that require changing the braid, as well as the hardness of the material along the braid. In an even more complex process, the manufacturer is required to change the braid, the hardness and the inner or outer diameter--all at the same time. This becomes more and more complicated for the process engineers to accomplish.

More business as an outsourced service provider

As in many other industries, medical equipment manufacturers are outsourcing some operations to reduce costs. Instead of developing in-house expertise in everything, companies are asking manufacturers to perform more and more secondary operations

One medical OEM tells me that, instead of just extruding PEEK and silicon, they will also include an internal or external striping, as well as cut-to-length, along with corporate markers. They'll also laser mark, where required.

In another example, instead of just providing a single tube, an OEM would deliver tubing that's been necked, bonded together, bonded to a fitting, label the tubing, put markers on it and form it.

Coating materials

The benefits of bioactive coatings, to add lubricity, to prevent blood clotting or to resist the formation of biofilms, for example, are becoming much better known. While OEMs don't generally apply these coatings to their products, they are aware of these benefits, and are often advising and recommending such coatings to their customers.

For instance, one of our OEM customers says that some of his manufacturing customers are asking for complex processes, like coextruding a product with one material on the outside and another on the inside--and with the inside portion with something that's going to make it lubricious, or with an anticoagulant. Or vice versa, they want a material on the inside that gives them, say, a certain degree of burst strength, or a certain amount of flexibility. And for the outside material, they want to know if there's some anticoagulant that can be applied.

Raw materials price increase impact planning

Constantly rising raw materials prices are impacting the planning process of extruders and molders, as well as tooling manufacturers. One performance plastics customer of ours tells me that their overall materials prices have gone up about 20% in the past year, with a similar rise possible this year. But while 15% to 20% increases have been the norm, prices have not gone up across the board, with some materials up 35% and others just a little.

With advanced machining and design engineering practices greatly improved in the last several years, closer tolerances and thinner walls are a necessity for certain applications. From single layer to co-extrusion and even to triple layer (applications with three different materials in one tube), the future is more layers that are thinner and meet the most stringent medical tube applications.

Furthermore, price changes are often sudden, making planning doubly difficult. One of our customers says he sometimes gets a month's notice, sometimes a week.

Distributors often use other ways, too, of boosting overall carrying costs. For example, one of our customers says, some distributors have significantly upped the minimum order size, for example from 50 lbs., 100 lbs. or 300 lbs, to 1,300 lbs. at a time. You can sell more material that costs them less because they're not putting anything extra into bagging and handling. The price stays the same, but this customer has to buy the much larger quantity, which will then sit for six months or a year until he needs it. This can become a problem with certain silicones and polymers that have a limited shelf life.

Extruders and molders aren't the only ones feeling the pinch of increased raw material prices. Tooling manufacturers, too, are seeing increases in both prices and lead times for their raw materials, e.g., high-quality steel and other alloys. That stymies the business, because customers don't want to wait up to a year for a tool. Part of the long lead time is because of a greater domestic demand--we're seeing a 50% increase ourselves over last year. But, we believe most of this is probably due to an increasing demand for shipping overseas, especially Asia.

Accelerating changes in materials

While medical polymers tend to change slowly, there are some interesting new developments. Resin manufacturers are beginning to embrace the medical device market more than previously, and are making available materials that they previously did not.

Also of significance is an increasing demand for bio-absorbing materials, as well as some increase in the use of materials that promote bone regeneration, and proprietary compounds and mixtures for orthopedic applications that promote bone growth and then will absorb as that growth occurs.

Phthalates and other plasticizers

In recent years, there has been increasing concern about the possible dangers of phthalate plasticizers such as the additive DEHP used in PVC tubing. Users are looking at alternatives in a wide range of engineered polymers. While many longtime users of PVC seem content to stay with what they have, one of our customers says, others, particularly those planning new products for sale in Japan or Europe and more recently in the USA, have begun to request DEHP-free materials. One of them, for example, sells its Tygon MPF lines as a replacement for PVC, and polymers such as EVA, polyolefins, polyesters and polybutadiene have been investigated.

For some manufacturers, of course, phthalates are not a concern because either they don't use PVC very much or their products are used more in medical offices than in surgical units.

The bottom line is that all of these changes taken together have seriously ramped up the challenges for and the pressure on the manufacturing of medical products. As part of this challenge, the extrusion industry has no choice but to respond with greater innovation, creativity and even advancing products that meet the rapidly increasing technical demands of this competitive marketplace.