Trelleborg Healthcare and Medical is a global supplier of medical device components and services. Dan holds a BS in Mechanical Engineering from California Polytechnic State University, San Luis Obispo, and has been in silicone manufacturing for the healthcare and medical industry since 1998. He and the Trelleborg team help medical device designers realize their product concepts through engineered manufacturing solutions and design for manufacturability support. Dan and the global Trelleborg Healthcare and Medical Team invite you to contact them early in your design phase to act as an extension of your engineering team, offering design, materials, process development, and manufacturing support to reduce overall costs and time to market.
What is the smallest tube that can be manufactured and what dimensional tolerance can be achieved?
Trelleborg is continuously advancing its silicone extrusion capabilities to achieve ever smaller extrusions to meet the demand for less-invasive devices. Currently, silicone tubes can be extruded reliably with a 0.007 inch inner diameter (ID) and 0.015 inch outer diameter (OD) to a tolerance of ±0.001 inch. Achieving a silicone wall thickness below 0.004 inch is challenging and depends on the diameter and durometer of the silicone used.
Durometer plays an important role in the ability to produce small silicone tubing. Lower durometer silicones have a greater tendency for gels, and as the tube wall gets thinner, potential gels occupy a larger percentage of the wall and create a greater risk of failure to the tube performance. While extrudable durometers of roughly 20 to 80, Shore-A, are available, the ideal range of hardness for extrudability is 50–70 durometer, Shore-A.
Material and processing expertise is critical to enabling devices to become smaller. Trelleborg partners with customers early during the concept to help with device innovations.
What materials can be extruded? Can materials be coextruded?
A variety of plastics can be extruded. However, according to Markets and Markets Research , in terms of volume, silicone is the largest and fastest-growing material within the global medical tubing segment. This is primarily due to its biocompatibility. Other characteristics, such as its suitability for multilumen and kink-resistant designs, enable silicone to be used for numerous long-term implantable devices. Some companies extrude Liquid Silicone Rubber (LSR). However, the vast majority of silicone extrusions use High Consistency Rubber (HCR). The clay-like strength of HCR in its uncatalyzed state works well in a variety of highly precise extrusion processes.
Extrudable silicones are available in a range of durometers and have long been used in healthcare and life science applications, conforming to long-term implantable device standards, including USP Class VI pharmaceutical processing equipment and ISO 10993.
Multiple silicones can also be coextruded to allow for designs, such as barium-filled stripes for radiopacity or pigments for color-coding purposes, or to strategically place different durometers within the extrusion cross-section. Trelleborg’s engineering team has decades of experience in polymers and silicone extrusion, and we regularly provide material selection guidance to our customers before design freeze.
What options are there for improving the performance of an extruded component?
Choosing the materials with the best mechanical properties for the application is essential.
Performance of the extruded component can then be enhanced with advanced extrusion processes and by incorporating reinforcement. Post-cure, or post-bake, processes, for example, increase mechanical performance and help reduce silicone leachables and extractables. Controlled bends can be added to silicone during the forming process, enabling extrusions to better conform to anatomical features.
Processes like Trelleborg’s GeoTrans™, which is capable of producing multiple cross-sections along the length of an extrusion, can reduce the number of individual components and assembly processes, while incorporating smoother transitions. Wires and monofilaments can also be integrated into an extrusion process to improve resistance to burst under pressure, kinking from tight bends, and abrasion from rubbing during cycles.
Selecting the right combination of extrusion and post-extrusion processes, like choosing the appropriate materials, is critical to ensuring optimum performance of components and devices. At Trelleborg, we act as an extension of our customers’ project teams, lending our expertise in technologies like extrusion, to help them determine the best options for their devices.
What are the benefits of horizontal versus vertical silicone extrusion?
Horizontal and vertical extrusion process each have their drawbacks and advantages. Trelleborg employs these and other extrusion processes to best meet customer needs and achieve an optimized balance of cost and quality.
Horizontal extrusion processes are typically easier to set up and can often produce faster extrusion rates because the heat tunnel is longer. For silicone, one drawback is that the extrudate sits on a conveyor belt while curing and can take an impression from the belt before hardening. Also, if the cross-section includes a thin wall, gravity can cause a round OD to become oval before it catalyzes and hardens. Similarly, complex cross-sections with multiple lumen and precise tolerances can also be distorted by gravity in a horizontal process.
Vertical extrusion processes are typically more difficult to set up and have limited height for the length of the heat tunnel. Because the extrudate is pulled vertically through the heat tunnel, gravity does not collapse or distort the cross-section. Therefore, roundness and precision are improved.
For more complex extrusions, such as very small, reinforced, or sheet-like designs, Trelleborg may employ an innovative custom process that is neither a traditional horizontal nor vertical extrusion process. For all extrusion processes, equipment accuracy and process control must align with the product’s requirements. These can often outpace the capabilities of standard equipment offerings. To keep pace with the medical device industry’s ever-evolving performance requirements, Trelleborg’s engineering team builds and customizes process equipment as needed.
What secondary extrusion processes are available?
A variety of value-added processes can be performed post-extrusion. Working with an extrusion provider that offers all necessary secondary processes in-house reduces additional costs, which might be incurred if using multiple suppliers, such as supplier management, handling, inspection, and freight.
Post-cure is one of the most common secondary processes for silicone. This is necessary for older peroxide catalyzing silicone systems to remove the catalyst and byproducts. For newer platinum catalyst silicones, it can improve biocompatibility by maximizing material properties to improve mechanical performance and reduce leachables and extractables.
Another standard secondary process is cutting to length, which can include lengths shorter than the outer diameter of the cross-section. Drilling and punching of holes in catheters to remove fluids and deliver drugs are also typical. Printing continuously or on cut lengths with a pad printer is employed to add length marks for placement or logos for branding. Special packaging, such as coiling of longer lengths, bulk winding on spools, and bundling shorter cut tubes in straight lengths, is often used to support the efficiency of downstream assembly processes.
At Trelleborg, we offer all of these secondary processes and are continuously identifying and developing new value-adding ones to further support our customers’ success and reduce their overall costs.
What advancements/changes are happening in extrusion and how will the industry change in the next 5 years?
As medical device manufacturers continuously seek to make procedures and devices less invasive and more effective, devices and components, including extruded components, are shrinking in size and becoming more complex.
Reduced device size is driving the need for tighter tolerance control and improved accuracy. This, in turn, is driving innovations in extrusion equipment to increase process resolution and control, and in metrology to more accurately measure in-line and cross-sectional samples. Trelleborg continuously upgrades and builds new extruders, extrusion heads, and supporting equipment to improve process control and regularly designs and evaluates new inspection methods for improved verification accuracy.
Also as medical devices become smarter, integrating sensing and feedback features, conductors, and delicate sensors will be included in extrusion and related secondary processes. Innovations, such as continuously twisted tubing; micro-tubing; extrusions with changing cross-sections; and spiral and braid reinforcement for kink-, burst-, and abrasion- resistance are being employed as solutions.
To move new device designs to market faster, a comprehensive understanding of the available materials and extrusion and secondary processes is needed. At Trelleborg, we partner with customers to provide the polymer and silicone processing expertise needed to overcome their design and manufacturing challenges, ensuring their innovations get to market more rapidly.