More Complexity, Tighter Tolerances

The pressure’s on. OEMs expect their extrusion vendors to help them out like never before, and they’re not shy about asking. As the market continues to evolve (especially with minimally invasive procedures and smaller medical devices), extrusion customers are demanding greater precision and tighter tolerances. Extruders report that an increasing number of designs involve complex extrusions such as multi-lumen, co-extrusion and braid/coil reinforcement integrated into single extrusion products, usually designed for specific medical applications. Customers also want cleaner extrusion processes with more process controls that reduce contamination (thereby eliminating cleaning steps and saving time), reduce waste and scrap, improve quality and consistency and lower overall manufacturing costs. Medical device manufacturers also are incorporating a wider range of materials into their products that provide expanded performance characteristics.

“Clients are showing more interest in products made from thermoplastics like PEEK (polyetheretherketone) and Ultem (amorphous thermoplastic polyetherimide resin) that have extremely thin walls, very small tubes and tighter tolerances, along with demonstration and validation of process control,” said Ken Larson, national sales manager for Jaffrey, N.H.-based Medefab, a manufacturer of plastic disposable products for the medical industry. “We regularly get requests for .001-.002 inch walls, less than .010 inch interior diameter (ID) and tolerances in the .0005 inch range. This often requires more sophisticated process control and operator precision.”

The trend toward minimally invasive surgery techniques is a powerful driver for smaller, more innovative manufacturing and design, according to Jerry Kiely, general manager for the OEM product development and extrusion/catheter facility of Teleflex Medical in Limerick, Ireland. Teleflex Medical OEM provides custom extrusion, catheters and medical devices.

“Our clients demand smaller extrusion and catheters to deliver medication and medical devices into the body,” Kiely said. “We can extrude tubing as small as 0.004 inch ID +/- 0.0005 inch—a fraction of the size of human hair. Catheter sizes range from as small as 1 Fr all the way to 35 Fr.”

Medical device manufacturers and their vendors continue to explore an expanded range of materials, including blended materials specifically engineered to have certain extrusion qualities, such as viscosity, chemical behavior and flow rate. Blended products also include tubing reinforced with metallic or nonmetallic braid or coil extruded into the wall of the tubing.

“Clients are even challenging the inherent properties of the material,” said Frank East, marketing manager for Specialty Silicone Fabricators, a Paso Robles, Calif.-based extruder of silicone and polyurethane. “For example, silicone is an elastomeric and conformal material but some designers want it to behave as if it were rigid material.”

Clients also expect more guidance from their extrusion partners about process validation—particularly the areas of liability as well as governmental and regulatory agency requirements that call for tighter tolerances and more documentation.

“We validate our own quality system as well as offer custom validation activities,” said East. “This includes the speeds they run, how long they post-cure, other secondary operations and governmental and regulatory body requirements. We often need to work through the challenges of the design, tolerances and acceptance criteria that may be beyond the capability of the material or design function.”

Because of these multiple demands, device companies seek out product development and outsourcing partners that can deliver fully vertically integrated “concept to completion” services, which shortens the supply chain, speeds decision-making and saves time and investment. By working together they better understand the product’s application and end-user needs so critical issues are identified early in the product development process.

“You can’t just be an extruder anymore,” said Greg Forrest, general manager of Teleflex Medical OEM’s extrusion/catheter facilities in Jaffrey, N.H., and Plymouth, Minn. “It is critical to provide design, engineering, material selection, prototyping, testing and validation, manufacturing, assembly, packaging and labeling. Due to the complex web of international regulatory environment, there is also growing demand for regulatory services.”

OEMs also expect higher minimums on custom runs—another big challenge.

Extruders add value wherever they can—for example, Qosina, an Edgewood, N.Y.-based supplier of stock OEM components for medical and pharmaceutical industries, has started cutting set lengths of tubing as it comes off the extrusion line for an increasing number of clients.

“Customers are concerned about possibly having a rounded coil set in their assembly from coiled tubing,” said Maria Stazzone, senior product marketing manager for Qosina. “To eliminate this risk we provide cut-to-length orders, which also make assembly easier and faster for our clients.”

Complex Tubing Designs
Extruders continue to see an increasing number of multi-lumen requests for complex and difficult shapes. For example, East indicated he has received proposals for products with up to 128 lumens.
Raumedic, a Leesburg, Va.-based producer of medical-grade extrusion and fabricator of medical tubing, subassemblies and systems, reports an increase in microbore tubing and precision tubing.

“An example would be a microbore multilumen with two holes of greater than 1.5 mm and tight tolerances in a small microtube, in an engineered plastic such as FEP (fluorinated ethylene propylene),” said Richard DiIorio, Raumedic’s technical sales manager for the northeastern U.S. “Companies are trying to set themselves apart from their competition by offering more innovative, complex and precise parts.”

This level of complexity often requires fully automated systems.

“For example, we have a two-shot molded coupling with three different parts (one of which is a two-shot part) and three different materials, molded and assembled in a fully automated process,” continued DiIorio. “This process includes part parameters checked by camera controls. We are also working with sensors and electronics within some devices, such as very small optics or sensors that can detect pressure, temperature or even radiation levels. Combining these more complex capabilities with our foundation of extrusion and molding allows us to help customers open up project paths for more complex system products.”

Like other companies in the industry, Teleflex Medical OEM continues to invest in new equipment and technologies to stay competitive and add value. For example, the company now uses ultrasound technologies instead of lasers to control tubing dimensions. The company continues to scour trade shows looking for new extrusion equipment, extrusion controls and secondary processing tools that can improve their processes.

“Sometimes we also make suggestions to the manufacturers about what they can do to support advanced extrusion capabilities,” said Forrest.

However, without top talent, the latest technologies will only get you so far; it is critical to have a deep operational understanding of a material’s physical and chemical characteristics and how to precisely control these properties during processing and manufacturing. This saves time and money in prototyping, leading to fewer iterations and less wasted material.

“Clients want a partner that knows the ins and outs of materials and their best applications and will provide material recommendations, including alternative suggestions,” said Kiely. “For example, EFEP (perfluoronated ethylene-propylene copolymer) is a material we researched to see how it could be best utilized by our customers. This led us to develop an etchless EFEP co-extrusion that offers outstanding transparency and can lower production costs by eliminating typical etching processes.”

The EFEP is co-extruded with polyamide- or polyether block amide (PEBA)-type materials in a one-step process, resulting in tubing with high clarity. EFEP works where conventional fluoropolymers cannot be used. It can be co-extruded as an outer layer or tube liner or laminated over coil- or braid-reinforced assemblies. EFEP combines the advantages of fluoropolymers (lubricity, chemical resistance and biocompatibility) with the advantages of traditional materials such as polyamide or PEBA (flexibility, ease of bonding and overmolding). Tubing stiffness also can be tailored to specific applications by varying the durometer of the co-extruded materials.

Complex Extrusion Engineering
Extrusion can range from ultra-small (1 Fr) for delivering medications to the body to large-diameter tubes as big as 35 Fr (typically used for delivering medical devices into the body, such as heart valves). Specialized coatings and liners for catheters sometimes are used to customize the performance characteristics, such as lubricity. Resins also can be formulated to include antimicrobial agents (usually silver); the key is finding the right “carrier” to distribute the antimicrobial agent homogenously throughout the resin matrix without altering its physical or thermal properties.

East indicated that Specialty Silicone Fabricators receives many requests for kink-resistant tubing, antimicrobial tubing, unique multi-lumen tubing and ribbon. Because tubing provides the pathway by which fluids can be both introduced or evacuated, it must have the best possible mechanical characteristics for proper function—especially flexibility, strength and lubricity.

Companies are trying to set themselves apart from the competition by offering more innovative, complex and precise parts. Photo courtesy of Raumedic.

“With kink resistance there is a design function where you can be assured that the fluid path won’t be restricted or ‘pinched off’ when the tubing is manipulated or bent as a part of its function or in the case of implants limiting patient mobility,” said East. “Our kink-resistant tubing meets all of these design characteristics, including resistance to flow-restricting conditions. The tubing is designed with embedded filaments that wind in a continuous helical pattern along its length.”

Specialty Silicone Fabricators uses a technology called Geo-Trans that allows the operator to transform the cross-section of a continuous silicone extrusion, thereby providing the client more creativity in designing new applications. The process employs computer-aided sequencing that allows extrusion tooling, including the die and mandrel, to be manipulated such that cross-sectional geometries can be changed in fractions of a second within a short section of tubing, resulting in single-lumen and multi-lumen tubing with various wall thicknesses.

“Being able to do variable durometer extrusions in line right off the extruder has the potential to eliminate many labor-intensive operations currently used to get varying stiffness along the length of a catheter,” said Andre Noronha, director of extrusion for Interface Catheter Solutions, a manufacturer of medical balloons, balloon tubing and multi-lumen based in Laguna Niguel, Calif. “The labor cost savings would be significant, perhaps as much as 70 percent.”

Interface Catheter Solutions also uses an automated balloon visual inspection system to reduce inspection time and improve inspection consistency.

“In one customer interaction we calculated that the cost of the Auto-I 360 Balloon Visual Inspection System would be recovered in 4.5 months based on the inspection time savings,” said Mark Geiger, vice president of sales and marketing for Interface Catheter Solutions.

A critical element in some of Interface’s extrusions (especially small, tri-layer extrusions) is a uniform middle layer of adhesive that holds the outer and inner layers together. Without uniformity, the layers can delaminate and cause problems with the finished catheter.

“To maintain this uniform ‘tie-layer’ we invested in an expensive imaging system that captures high-resolution pictures of the cross-section of these micro-extruded tubes that we supply with every order,” said Geiger. “This technology gives us the ability to stop a run if the tie-layer isn’t circumferentially present and reset parameters.”

Yet another industry innovation is extruded sheeting.

For example, Specialty Silicone Fabricators now has the capability to extrude sheeting up to eight inches across—an economical alternative to standard calendered sheeting. “Extruded sheeting is similar to calendered sheeting with two exceptions,” said East. “The first is that it comes in a continuous length as opposed to sheets; the second is that it is less expensive to produce. A sheet of calendered sheeting is nearly four times as expensive as an extruded sheet.”

Specialty fluoropolymer resins are being used more frequently by medical device manufacturers to take advantage of their good dielectric properties, lubricity, biocompatibility and ability to meet the tight specs and performance demands of their devices. For example, the lubricious nature of fluoropolymer-lined catheters makes it easier to smoothly deliver devices into the body.

Teleflex Medical OEM has engineered an encapsulated tungsten layer that is an effective alternative to marker bands for providing radiopacity.

“The encapsulated layer improves flexibility to navigate tight vessels and torturous anatomy,” said Kiely. “It also allows us to product a very soft tip on the device, which eases navigation within the body.” Teleflex also offers large-diameter shafts that use a continuous coil technology in order to increase the stability, kink resistance and “pushability” of the product. The traditional approach involves the production of coiled shafts to set lengths such as six feet—a time- and operator-intensive process. Continuous coiling allows the run of an entire custom shaft project at one time, before the shaft is cut to length, saving time and production costs. The company also has developed a patented process that can compress or extend the space between the coils (known as “pitch”) during the extrusion/manufacturing process.

“This unique process allows outstanding customization of pushability and flexibility characteristics literally anywhere along the shaft,” remarked Forrest.

Any variation in tubing extrusion parameters can diminish the mechanical properties of the finished product. For example, Interface Catheter Solutions has seen fluctuations as high as 300 percent in both tensile and elongation values for tubing produced from the same batch of resin by different extrusion vendors—a reflection of varying extrusion process controls and operator skills. Therefore, extruders must work diligently to maximize efficiencies and improve internal processes to deliver the precise, consistent tolerances customers want. State-of-the-art equipment is important; however, the combination of deep material knowledge, internal quality requirements and manufacturing process expertise is what really makes the difference.

One of the way companies respond to meet these quality demands is by manufacturing extrusions solely in clean rooms with extrusion processes designed to significantly improve consistency.

“We had to do it for ourselves as a balloon contract manufacturer because defects seen on tubing will be transposed onto the balloons,” said Interface’s Geiger. “We were rejecting 60 percent of the extrusion we were purchasing outside, so we brought it all in-house and spent three years perfecting the process. Our extrusion has also been certified by a third-party laboratory to be pyrogen-free.”

Advanced Materials
Customer requests vary dramatically when it comes to type of material, durometer and color. They generally know what materials they want but adjustments often are required after initial runs. Proactive extruders always are looking for new materials that will meet increasingly specialized needs, such as polymers or blends that are gamma-stable and can withstand all sterilization methods while still performing as well as existing extrusion/catheters materials.

Customer requests vary dramatically when it comes to type of material, durometer and color. Photo courtesy of Raumedic.

Some vendors provide custom compounding to create materials and configurations for clients who want to optimize the performance of their products, or are targeting specialty applications.

“During the development stage we compound multiple versions of a material (sometimes as many as 15 variations), then test each variation,” said Kiely. “Since we provide in-house custom compounding, short-run extrusion and testing, we can shorten this phase of product development and lower overall production costs. For example, we can compound a material in a small batch, do a short run, test it, and do another variation the very next day.”

A growing concern for some medical device manufacturers is DEHP (Di[2-ethylhexyl]phthalate), a polyvinyl chloride (PVC) softener that is considered a health hazard and is banned in Europe.

“The leaching of the DEHP from the PVC material is driving interest in alternative, more biocompatible plasticizers such as DOP (dioctyl phthalate) and TOTM (trioctyl trimellitate),” said Stazzone. “Also, depending upon the application, customers sometimes request other alternatives such as silicone and C-flex.”

Raumedic recently added the material Moldflon to its material offering—a thermoplastic-processed polytetrafluoroethylene (PTFE) that’s fairly new to the market.

“This is very innovative material technology because PTFE was never able to be processed in a normal thermoplastic extruder,” said DiIorio. “Before Moldflon, PTFE had to be processed through a very difficult and expensive procedure. Now, because there is no need for a ram extruder, the processing of the PTFE material will make it more adaptable to some projects where it was previously not even considered. In the past there were limitations in PTFE use because of the processing difficulties and the number of suppliers in the market. Now, however, Moldflon will help companies build projects upon the strengths of PTFE while looking ahead to a new way of processing it.”

Challenges Ahead
Extrusion these days is all about speed, responsiveness and adding value (but then again, what process isn’t?)—not just filling orders but developing partnerships where extruders become key partners who supply meaningful advice about designs and validation. Customers expect a quick turnaround of samples and prototypes—meeting these expectations especially can be difficult, depending on the specific product requirements and the variety of specialization and customization.

As the market continues to evolve (especially with minimally invasive procedures and smaller medical devices), extrusion customers demand greater precision and tighter tolerances. Photo courtesy of Teleflex Medical.

“The development runs required with each customer’s specification can be extensive when it comes to very difficult extrusions,” said Geiger. “There is a great deal of back and forth with the customer and, in many cases, the customer does not always understand the trade-offs associated to meet the specification and the performance characteristics of the part or device. This requires deep in-house expertise to help customers navigate through the iterations to arrive at the desired outcome.”

Ultimately, it always is a challenge for the extruder to meet the aggressive timelines, increasing complexity of tube design, and the longer and more costly tooling and development period that usually results.

“It still comes down to balancing the quality, cost and lead time of a project,” said DiIorio. “This is the truly difficult challenge as the complexity of the part increases. For example, for difficult multi-lumen tubing, you may want to call on the best tool maker you can find to ensure a quality tool, quality process and precise end product. However, using this toolmaker may add cost or lead time.

Understanding the needs of the customer, while balancing the variables of the project, take experience to master. This is where investing in technology and knowledge to deliver quality makes a huge difference, as well as engaging the client in the earliest possible stages of the project, in delivering the best possible extrusion solutions and expanding future possibilities.”

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Mark Crawford is a full-time freelance business and marketing/communications writer based in Madison, Wis. His clients range from startups to global manufacturing leaders. He also writes a variety of feature articles for regional and national publications and is the author of five books. Contact him at [email protected].