Advancements and Challenges in Medical Extrusion Technology

Advancements and Challenges in Medical Extrusion Technology

Biodegradable Polymers in medical devices along with PVC replacements are two new material advancements in the plastics extrusion industry.  These along with Multi-layer Microextrusion reflect the current call in the industry and our society for safe, eco-friendly products and processes that meet the demand for intelligent design and keep up with rapidly changing technology.

Biodegradable and BioabsorbablePolymers

Biodegradable Polymers are polymers that are created from natural resources. For many years biodegradable polymers have been used for food packaging, clothing and electronic packaging. Now, special Bioabsorbable polymers are being used in Medical tubing for invasive medical device applications designed to release medication and eventually be completely absorbedby the body with no ill effects. Other devices, such ascoronary stents are developed from bioabsorbable polymersand are implanted to perform a task and then benignly breakdown over time.

The biodegradable polymers such as polylactic acid (PLA) are heat sensitive and will degrade with elevated temperatures. Processing PLA is very similar to processing polyesters in the sense of needing high extruder torque. Therefore, attention is paid to the proper motor sizing and/or screw speed setup to avoid utilizing elevated barrel settings.Also a low shear screw design is needed to minimize melt temperature.In addition, these polymers are also very sensitive to moisture and require stringent drying before processing.

PVC Replacement – TPE

Further developments in the trend for soft PVC replacements can be seen with the thermoplastic elastomer (TPE) family of resins. These resins not only fulfill safety concernsand have a similar aesthetic appearance, but maintain equivalent physical properties and ease of processing.

As an added bonus, TPE compounds can run on existing PVC lines with minimal equipment changes. Production tests at American Kuhne prove that the TPE resins are extremely forgiving, with very stable processing conditions at high extruder output levels. This means that tight tolerance levels can be achieved at very high production line speeds. Recently a demonstration was performedwith an 83 Shore A TPE compound on a high speed extrusion line running a 2.67mm OD x 0.508mm wall tube up to 243 m/min with very stable processing conditions. 

Multi-Layer Microextrusion

The need for device manufacturer’s to improve physical properties while simultaneously reducing the product’s outer dimensions to aide minimally invasive surgery has led to an increased requirement for microbore, multi-layer coextruded tubes.For instance, a multi-layer balloon tube may have improved physical properties such as increased burst strength as compared to a similarly sized single-layer balloon tube.  Furthermore, a multi-layer tube with a thinner overall wall thickness as compared to the single-layer tube of the same nominal diameter can provide additional medical device benefits.

Complex, high dimensional, multi-layermicrobore tube structures create an opportunity as well as a challenge for extrusion systemmanufacturers. The ultra-low volumes needed for each layerleads toa requirement for multi-layer Microextrusion Systems.Conventionalsize medical extruders such as a 25mm machinecannot be used because of the long residence time in the barrel and screw channels will degrade the extrudate.Care must be taken to properly dry the resins prior to extrusion and large area filters are used to capture gels during the extrusion process.








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