Less Invasive Procedures Mean Extrusions Get Thinner, Narrower

Frank Vinluan

TE Connectivity can make extrusions in a wide range of shapes and sizes to meet the needs of medical device companies. 

For some patients who have aortic valve stenosis, or the narrowing of the heart’s aortic valve, open chest surgery is deemed too risky. Transcatheter aortic valve replacement (TAVR) gives these patients an alternative: a way to implant a replacement valve without the risks of cutting through the ribcage, stopping the patient’s heart, and surgically replacing the old and failing valve. In TAVR, a catheter inserted into an artery is steered to the heart. A replacement valve passed through the narrow tubing is positioned to replace the diseased valve, and then inflated with a balloon catheter.

Medical devices are getting smaller and smaller as device makers come up with new ways to reach even deeper into the human anatomy. But the shrinking size of medical technology means that the medical tubing that delivers devices to their destination must likewise reduce in size, while also maintaining the required stiffness and the strength to navigate through a patient’s body. These changing requirements mean that extrusion suppliers must adjust accordingly.  

Tilak Shah, CEO of Polyzen in Apex, NC, says that the demand he sees in catheters and medical tubing comes from medical device companies seeking to offer devices that do the same procedures, but in a smaller space. (See Polyzen at the BIOMEDevice San Jose Expo, booth #320.) This demand is fed by the growing adoption of minimally invasive surgical techniques, particularly in cardiovascular procedures, such as TAVR. Neuroendovascular procedures are also pushing extrusion suppliers to make microcatheters in smaller sizes, and with thinner walls.

“It’s all driven by the space—how much space do you have in a minimally invasive surgery and where you need to reach,” Shah says.

In TAVR procedures, medical tubing must be steerable so that the surgeon can guide the catheter to the heart. It also needs to be pushable, requiring that the tubing retains more rigidity at the proximal end. Inside of the tubing, the inner walls must be sufficiently smooth and lubricious to ensure that the replacement valve can pass unobstructed. Each area of the body requires a different type of catheter with different performance requirements, says Ken Koen, portfolio manager for extrusions and tubing at Switzerland-based TE Connectivity. (See TE Connectivity at the BIOMEDevice San Jose Expo, booth #321.) But regardless of the application, Koen says that device makers are seeking the same basic requirements for medical tubing. “Thinner, stronger, flexible is what they’re after,” he says.

As medical extrusions get thinner and narrower, extrusion suppliers are challenged to make sure that devices can smoothly move through the tubing. Koen says extrusions are moving away from hydrophilic coatings in favor of lubricious additives that are incorporated into the polymer itself. Improving the lubricity of the tubing is important, particularly for devices that are steerable with wires, because surgeons want assurances that they will be able to easily push the device through the tubing, and that the tubing will be easily pushed through a blood vessel or some other part of the patient’s body.  

Multiple lumens in TE Connectivity's extrusions can accommodate the miniaturized components of medical devices used in minimally invasive surgeries.

Devices have become smaller and smarter, and extrusions have likewise become more sophisticated. The geometry on the inside of the tube has evolved to accommodate the devices and electronics that move through them. Koen sees device makers increasingly seeking multiple lumens—different channels on the inside of the tube—to handle different wires for optics or sensors. In some cases, the lumens have a square shape to match the shape of the devices passing through them, such as an LED light, a camera, or a transducer.

“Devices are getting smarter, they’re sort of pushing the envelope on really where they’re going in the anatomy,” Koen says. He notes that medical device companies say, “Basically, we want the same device with the same kind of equipment on the product, but we want to make it much smaller.”

As devices fit into tighter spaces, Koen says that TE Connectivity has had to press the makers of extrusion machines for equipment that gives tighter control to make narrower tubing with thinner walls. Laser gauges measure tube diameter to ensure that the tubing is just the right size.

Materials selection is an important step in making sure that the tubing meets the desired performance characteristics and biocompatibility requirements. As medical tubing walls get thinner, tubing suppliers can take different approaches to retain tubing strength. Reinforcement can come from multiple layers of materials that pair a softer material and a harder material, Shah says. Extrusions can also incorporate a braided or coiled layer of reinforcement material that gives the tubing the appropriate stiffness. “It enables the devices to go into these really tight vascular turns and bends,” Koen says. “It just gives the wall reinforced strength.”

Polyzen provides only custom extrusions. Shah says the custom nature of the work means that Polyzen prefers to get involved with device manufacturers early on in their development process. Knowing details about the device and the materials that will be used to assemble it helps guide Polyzen’s own material selection. The company can also help the device maker make adjustments, if necessary. “We help with our experience to steer them or guide them on alternative ways of reaching some of the functional requirements they have,” Shah says.

TE Connectivity has some stock components but Koen says the growing complexity of devices means that custom-designed catheters are often more appropriate. In most cases, TE Connectivity works on development with the customer as early as possible so that the company can provide input and recommendations on a medical device maker’s design.

“Devices continue to be innovative, which pushes the envelope for everyone to be innovative,” Koen says.

Frank Vinluan is a contributor to MD+DI Contact him at [email protected]

[Images courtesy of TE CONNECTIVITY]