The ins and outs of microextruded medical tubing


Natvar microextruded medical tubing

[Image courtesy of Natvar]

Microextruded medical tubing could enable increasingly smaller surgical and home care products, according to Tekni-Plex’s Natvar. 

Surgical and home care products including catheters are becoming increasingly complex and smaller in size. Neurovascular interventional therapies and surgical procedures also require tight tolerances for those small sizes. Until now, options for these components were limited to glass and fluoropolymer, both of which come at a high cost.

Tubing experts, however, have been working to create new sources of technology that will meet the tolerance requirements and improve the cost of the devices. Natvar, a Tekni-Plex company, in May launched its microextrusion capability, which uses thermoplastics and other highly-engineered materials.

The company believes it is addressing many challenges medtech OEMs face when developing and manufacturing minimally invasive surgical products and miniaturizing devices.

“This product line will open up developments of devices that require specialized extrusions in areas of neurosurgery and arterial reconstruction,” said Bob Donohue, general manager of Natvar.

The repeatability and consistency in the process lead to repeatability and consistency in the procedures and outcomes, according to Donohue. The logical next step would be to incorporate this technology into multipolymer extrusions where the durometer of the product can be changed in one single microextrusion. This would again lead to further microextrusion developments with enhanced clinical applications.

Closed loop and optical measurements

Natvar uses a proprietary extrusion process that employs a closed-loop extrusion process. A closed-loop feedback system adjusts screw speed to maintain a constant die pressure, thereby minimizing variations in the extruder output. For example, feedback loops based on the tube OD readings are taken by a laser micrometer. If the OD readings move to the high end of the allowable range, the system automatically adjusts the extrusion process. It then continues to monitor and make further adjustments as required independently.

Donohue noted that stability and repeatability are of utmost importance to the process, and said Natvar’s biggest challenge was in developing the measuring technique.

“With products this small, calibration between Natvar and its partners is critical.”

Natvar chose to use high-end optical measuring equipment to obtain an acceptable gage repeatability and reproducibility (Gage R&R) between organizations. Gage R&R is a statistical tool that measures the amount of variation in the measurement system arising from the measurement device and the people taking the measurement.

The system is measured in CPK values. The CPK value indicates how close a process is running to its specification limits, relative to the natural variability of the process. The higher the index, the less likely it is that any item will be outside the specs. As a frame of reference, a CPK of 1.33 or better is what medical device companies typically require. Donohue said Natvar can run tubing or profiles at CPK values above 2.0

Enabling lower-cost materials

Material options have limited microextrusion’s ability to be used in all but the most expensive products. As mentioned before, glass and fluoropolymers are available, but at a high cost. Adding versatility to the process enables developers to choose from less expensive options including nylon, polyurethane, and polyvinyl chloride.

The development comes at the request of Natvar’s clients, said Donohue. “We have received several requests to replace glass extrusion to drive cost out,” he said.

Donohue is confident that applications that currently use glass or other highly-engineered materials can switch to lower-cost alternatives like nylon and still hold the same tight tolerances.

“Natvar is positioning itself to serve applications where cost is addressed while quality and functionally are maintained.”

Tubing diameters

Natvar can microextrude monolayer, coextruded. multi-lumen tubing or profiles in a variety of thermoplastic (PVC, urethanes, TPEs) materials.

“Typically, with these type of extrusions, manufacturers struggle to hold and maintain consistent ID and OD dimensions,” Donohue said. However, with the closed loop technology, Donohue said Natvar is able to hold tolerances at levels of +/- .0002 in. depending on overall product size. In addition, Natvar has successfully produced ID sizes as low as .001 in. with French size for catheters in the 3 to 4 French range.

Donohue stressed that “holding the tolerance is critical in microextrusion.” With Natvar’s new microextrusion system, designers and developers have options in material selection to improve cost profiles.

Other considerations

When looking to take advantage of tubing that offers the latest technological advances, it is important for most OEMs to take speed-to-market and global supply chain attributes into consideration.

With many multinational companies marketing medical device products that require advanced tubing solutions, OEMs should strive to understand the supplier’s manufacturing footprint. An inability to receive seamless supply across the globe can negatively impact OEMs commercialization and pipeline goals.

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