Extrusion: Beyond Simple Tubing

Medical device manufacturers have traditionally relied on their extrusion supply partners for affordable medical tubing for a variety of application areas. However, more and more, these OEMs are seeking greater capabilities and more design solutions from these same supply parterners. This article looks at how medical extrusion is impacting device development today.

Tubing, tubing, and more tubing. That’s the traditional view of what an extruder offers to medical device manufacturers. Parts, like tubing, that have a continuous profile and are to be produced in long lengths are ideal candidates for extrusion. Unfortunately, when compared to injection molding, extrusion can suffer from a limitation in the tolerances able to be achieved. Due to the manufacturing process of an extruded part, a number of factors can impact the end product and thereby influence the tolerances achieved. However, extrusion also offers an array of benefits to medical device manufacturers for emerging technologies in areas including minimally invasive surgical devices, diagnostics, neuroradiology, electrostimulation, and more.

Once the tubing is formed, it travels through the area in which the material is heat cured (photo courtesy of Sil-Pro).“As the designers of extrusion tooling continue to refine their craft, more and more complex shapes become capable for extrusion production. Specifically, the area of catheters has advanced medical procedures to new levels as surgeons enter the human body through smaller and smaller incisions. Extrusion-made probe tubes can bristle with all sorts of complex medical instruments that fit inside custom shaped cavities,” explains Paul Frechette, engineering manager at Pexco, a leader in the design and fabrication of extruded plastics products.

It is this sort of advanced capabilities that are being incorporated into more and more medical device technology. Catheters that enable doctors to access remote regions of a patient’s body without making large incisions are just one benefit. Extrusion makes it possible to deliver a host of devices to those same locations, enabling a variety of treatments to be carried out.

Claudia Aurand, global market manager with Teleflex Medical OEM—a single source provider of design, development, and production services—speaks more to this point. “The trend toward minimally invasive surgery techniques is the driving force behind smaller, more complex devices that require innovative design and manufacturing. A good example would be microcatheters, which are used for diagnostic and delicate therapeutic neuroradiology or occlusive therapies for the treatment of stroke and aneurisms. They require extrusion companies to possess a thorough understanding of catheter construction, and the deep expertise in advanced levels of precision manufacturing.”

Complex profiles, multiple lumens, and other features are becoming much more common requests for extrusion suppliers (photo courtesy of Vesta).With the continuous emergence of these minimally evasive technologies that are traveling through the canals fabricated from extrusion processes, designers are seeking more functionality and features in their catheters and other tubing products. Bill Woinowski, Vesta’s Silicone Division R&D manager—a leading medical device contract manufacturer—explains that customers are “seeking innovative extrusion solutions such as multi-durometer extrusions, increased radiopacity, higher pressure capabilities, and greater kink resistance.” He adds, “we are seeing an increase in the number of lumens and complexity of lumen configurations as our customers add functionality delivered through a single channel.”

Fortunately, along with the increased complexity designers are tasking their extrusion supply partners with, at the same time, they seem to be realizing the benefits of getting that partner on board earlier in the development process. “More of our customers are engaging us at the development stage and looking for innovative solutions to design challenges. There seems to be a movement in the medical device industry in this direction to utilize the capabilities and experience of suppliers earlier in the development process,” explains Mark Erson, QA director at Sil-Pro, a company that specializes in LEAN silicone molding and silicone extruding for a vast array of medical products.

Braided catheters offer advanced functionality and increased benefits to medical device manufacturers (photo courtesy of Teleflex Medical OEM).While not likely to surpass molding in terms of the volume of product produced for medical devices, extrusion has certainly come a long way from simply being the process used for making a basic tube. “I think that medical device companies are looking to extrusion for complex profile shapes, multiple layer tubing, and fabrication to supplement their equipment,” agrees Frechette.

As extrusion continues to move toward offering more complex solutions for sophisticated, minimally invasive medical devices, design engineers will become more familiar (and comfortable) with the array of benefits, as well as the limitations, of the process. Getting the extrusion supplier on board early in the design process is certainly an ideal scenario for achieving the best results. However, at minimum, medical device designers need to at least explore the options with a reliable partner to determine if the process is even the right option for a product, Frechette explains, “There is no shortage of examples where medical device programs have failed or struggled because the designers learned too late in the process that their parts could not be produced in extrusion, whether by shape or tolerance level. Going back through the lengthy approval process for a device with design revisions is a daunting task for any medical project manager.

Sean 

A Matter of Materials

New material offerings are critical to medical device manufacturers as they provide new opportunities in the development of cutting edge technologies. This round-up features three new materials that are impacting medical device manufacturing in the areas of adhesives/coatings, molding, and extrusion.
 

Extrusion Material Focus

By Mathew Bills and Robert LaDuca

Natural colored PebaSlix resin alongside yellow colored PEBA resins, as well as a variety of extruded catheter tubing configurations and molded componentsWith today’s medical catheters becoming increasingly smaller and more complex, it has become nearly impossible to meet new product performance requirements capable of enabling the next generation clinical applications without the development of new materials and the integration of those materials with existing manufacturing processing technologies. For example, the competing requirements for flexibility, ultrathin walls, torque response, and kink resistance are often combined with the need for lubricity—allowing the passage of other devices or motion between catheter surfaces.

The use of PTFE, FEP, or HDPE as a liner has been effective at lowering friction. These materials are often specified for catheter designs despite their limitations. For example the use of PTFE limits sterilization options, increases stiffness, has higher cost, and requires reflow processing complexities. Attempts to meet low friction requirements while avoiding the limitations of using existing material options in catheters has led to the development of hydrophilic coatings for interior lumens and the tubing’s exterior. This alternative, however, poses additional issues such as the requirement for an aqueous environment, which is not always present in many applications.

Other attempted solutions to the friction problem have been to add lubricious agents into the base resin of the tubing being produced. Several possibilities have been explored, from PTFE particles to erucamide additives. The PTFE particles may be distributed throughout the thermoplastic. However, due to the melting point difference between the fluoropolymer and the thermoplastic, the PTFE particles do not fully disperse into the thermoplastic resin, creating a less than optimal result. Adding erucamide to a base polymer will reduce the co-efficient of friction but, over a short period of time, it will leach to the surface of the tube, leaving a chalk-like contaminant substance that becomes source of particulation.

In seeking a solution to these problems, Duke Empirical has developed a class of new materials that are being introduced into the market called PebaSlix and PolySlix. These new materials are lubricious and have low friction by a proprietary patent pending process that combines certain additives with the backbone of PEBA and/or polyurethane. The additives are fully dispersed into the thermoplastic, utilizing the full benefit of the additive without changing the mechanical properties, processability, or sterilization methods. PebaSlix and PolySlix with their non-leaching, fully dispersed properties can be bonded and processed in the same manner as traditional PEBA and urethane and are available in a variety of durometers. Material biocompatibility testing is underway and master file data will soon be made available for customer’s regulatory applications. The chart shows the reduced coefficient of friction of PebaSlix compared to standard Pebax, as well as other, traditionally considered low-friction materials such as PTFE, FEP, and HDPE.

Mathew Bills is the director of extrusion technologies at Duke Extrusion, a division of Duke Empirical. Robert LaDuca is the founder and CEO of Duke Empirical.

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Adhesives/Coatings Material Focus

By Jennifer Hooker

Improved medical grade silicone formulations have been instrumental in the development of new medical electronic devices. These compounds feature easy application, convenient cure schedules, sterilization resistant properties, biocompatibility, and are environmentally friendly. They offer unmatched flexibility, temperature resistance, and cost effectiveness. Medical electronic devices are now available in smaller sizes, lighter weight, and have enhanced performance properties. Silicone systems have played a vital role in meeting the increasing challenging requirements of the medical device industry and expand future possibilities.

Optically clear MS 151Med has a low viscosity, a convenient cure schedule, and is easy to apply.One such material offering is the two component, room temperature curingMaster Bond MasterSil 151Med—a medical grade, potting and encapsulation silicone. Since flexibility is of vital importance in the design of medical devices subjected to vibration, impact, shock, and thermal cycling, this material is formulated to withstand such exposures. With a low viscosity of 1,500 cps, it is ideal for use in applications with complicated contours in very complex configurations. It is an excellent electrical insulator with a volume resistivity of 1x10¹⁵ ohm cm and can handle service over the wide temperature range of -65 to 400°F.

MasterSil 151Med cures optically clear with a refractive index of 1.43, making it well suited for use as a protective coating in optical and fiber optic applications. Cures can be accomplished at room temperature, or faster at elevated temperatures. Shrinkage upon cure is less than 0.1%. When cured, MasterSil 151Med has a Shore A hardness of 45 and an elongation at break of 160%. Even though it has such high elasticity, its tensile strength is still a favorable 880 psi at73°F. Mix ratio is 10 to 1 by weight. MasterSil 151Med fully meets USP Class VI requirements for medical applications.

Jennifer Hooker is a technical editor with Master Bond Inc. She has been reporting on new technology for over 7 years, both in the consumer and industrial markets.

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Molding Material Focus

By Scott Young, Ph.D.

Novel products for individual therapies, such as imaging for diagnostics, new antibody treatments, biomarkers, tissue engineering, nanocarriers, and gene-based and stem-cell therapies, may reach the market by 2020.¹ For many of these advanced pharmaceutical technologies, glass may not be the logical or preferred choice for containment and/or delivery. Technological advancements in therapeutics and diagnostics should be matched by innovations in containment and delivery systems.

The Daikyo Crystal Zenith polymer can be molded into containment systems suitable for a drug product’s life cycle.Glass as a primary contact material for pharmaceutical and biopharmaceuticals has hurdles to overcome with respect to suitability. The need for silicone lubricants, breakage, particles, and leachables are among the major concerns. To combat the risks associated with glass, modern polymeric materials should be considered. The manufacture and processing of polymers allows for flexibility in molding and forming throughout a drug product’s lifecycle. Qualification of such materials is dependent on intended use, and risk assessments should be considered early to support development and protection of the drug product throughout its lifecycle.

The Daikyo Crystal Zenith cyclic olefin polymer (COP) is a class of polyolefins in which the performance characteristics are enhanced. The synthesis allows for better control of the molecular structure with fewer side reactions and less need for performance additives. Precision molding can be optimized for the intended use and once the materials are qualified, forming can be adapted as needed. This class of polymer has few ingredients and offers the desired properties of transparency and break resistance. It also provides a strong moisture barrier and is easy to sterilize.

Cyclic olefin polymers are high-performance materials possessing the valuable properties necessary to manufacture, store, protect, and deliver drug products without many of the weaknesses inherent to glass. It is especially suitable for biologic applications since many of the COP’s quality attributes specifically meet the challenging needs of this market.

Scott G. Young, Ph.D. is a senior director at West Pharmaceutical Services. He is responsible for the development and commercialization of the Daikyo Crystal Zenith Platform, including syringes, vials, API containers, and novel delivery systems.

¹ Breakage and Particle Problems in Glass Vials and Syringes Spurring Industry Interest in Plastics. IPQ in the News 7, August 2011.

Motors Take on Cancer

The Project: A multi-leaf collimator device needed to offer greater levels of accuracy than any similar product on the market.
 

The Solution: Multiple devices were incorporated, including 180 motors, to shape gamma ray radiation therapy beams, controlled by one interlinked motion control system.
 

The EPOS2, brushless DC motor controllers are easy to install and implement using one of several major interfaces, plus are compact enough to keep the system’s footprint small.When it came to designing a multi-leaf collimator (MLC) device,ViewRay took on the challenge to produce an end product that would be more accurate than others on the market. ViewRay collaborated with Maxon Precision Motors for critical components, including a custom motherboard, motors, encoders, gearheads, and individual motor control modules, according to an engineering team member.

ViewRay Incorporated is a privately held medical device company developing advanced radiation therapy technology for the treatment of cancer. The ViewRay system provides continuous soft-tissue imaging during treatment, using MRI-guided radiotherapy, so that clinicians are able to see where the actual radiation dose is being delivered and adapt to changes in the patient’s anatomy.

Overall, the ViewRay system includes five sub-systems, which are seamlessly integrated to provide optimal patient care. The major subsystems are: real time MR imaging, treatment planning, dose prediction and optimization, real time soft-tissue targeting, and remote review and approval. The treatment delivery is performed in a split-magnet MRI system with rotating gantry assembly to position three shielded Cobalt-60 sources with the three multileaf collimators.

ViewRay’s MRI-guided Radiotherapy System is designed using 180 motors and controllers for accurate gamma ray delivery.The imaging in other radiotherapy technologies took place before or after treatment, not while the beam was on. This was a limitation in providing therapy because targeting could not be adjusted dynamically. Soft-tissue motion often allowed a tumor’s position to shift during treatment, causing soft tissue damage.

The ViewRay system solved this problem by using a combination of MR imaging and radiation therapy delivery technologies. With continuous soft-tissue imaging, during treatment and with the beam on, ViewRay tools can refine the target and re-optimize the dose while the patient is on the treatment table. This was the first MRI-guided Radiotherapy System produced.

According to the engineering team, “The MLC motor control system is a critical portion of the system. We knew it would also be one of the more challenging to design because of proximity to the MRI magnet, and volume constraints due to the gantry configuration.” The system uses three gamma ray sources, mounted in separate shielded heads. For ViewRay, the double-focused MLC is designed to sharpen field edges to produce penumbra comparable to conventional accelerators, so that clinicians can treat patients with greater confidence.

The team chose Maxon’s EPOS2 Module 36-2 compact digital positioning controllers for their small form factor, which allowed them to package 60 channels of motion control for each collimator. Thirty modules can fit on a single custom motherboard, and there are two motherboards per collimator. Each ViewRay system required three of these collimators, one for each of the three heads used in the system.

EPOS controllers are compact, fully digital, smart motion controllers designed for use as plug-in modules in customer-specific motherboards, and can be used for single-axis or multi-axis motion control systems. Each EPOS module implements a flexible and highly efficient power stage, and drives a brushed DC motor with digital encoder. They are especially designed to operate as a slave node in a CANopen network. They have a maximum current output capability of two amps, running from an eleven to thirty-six volt DC power supply.

This CAD drawing of one of the collimators, shows the motors extending from one of the sides.In order to interface with the controllers, the ViewRay team used the resident EPOS2 firmware, which provided simple to implement operating modes and monitoring functions required by the control system. What made things easier was that the controllers are CANopen compatible, which allowed the design team to define up to 127 device addresses on a single bus segment.

Each of the collimators contains sixty leaves that are arranged in two opposing banks of thirty. Since there are three collimators, the device uses 180 EPOS controllers as well as 180 motor/encoder/gearhead assemblies. The MLCs are mounted on the gantry system to provide collimation of the three gamma radiation sources with respect to the target. While the gantry is moving into position, each collimator leaf is positioned according to the treatment plan. To position each leaf, CANopen bus commands are directed to the associated node consisting of a motor, encoder, gearhead, and controller. The result is a precisely collimated shape that matches the treatment plan.

The 180 motors used in the system are RE16 brushed DC, 4.5 Watt motors. Each motor operates at speeds up to 11,000 rpm. Along with the motors are MEnc13 Hall-effect encoders for precise motor control and GP16A gearheads with 19:1 reduction, providing adequate torque for positioning speeds of 1.0 cm per second.

The EPOS Studio software package provided an easy-to-learn, easy-to-use development environment for proof of concept and end-product development activities, according to engineering. Due to MRI magnetic field effects, the MLC controllers had to be remote from the motors, and housed in a convection-cooled chassis.

Paul McGrath is a regional sales engineer at maxon precision motors.

Microstructure Engineering: An Alternative to Coatings

While coatings can offer an array of benefits to medical device components, in certain cases, they can also come with adverse effects that impact the overall efficacy of the product. An innovative technique—microstructure engineering—enables a surface treatment to be accomplished during the component fabrication process, providing an alternative to coatings.

Current technology to address low friction and low tack on extruded and molded medical devices is limited to coatings, lubricants, additives, or base material changes. While these options provide improved performance, they can be very expensive, add steps to the manufacturing process, flake or deteriorate during use, and/or degrade the integrity of the base material. With medical applications, these options limit the effectiveness of an otherwise innovative design and complicate testing and validation, extending time to approval.

Figure 1: A macro and micro view of silicone tubing where the microstructured surface engineering process was used.The technology of microstructured surface engineering can modify surface structure to affect a wide range of parameters to include hydro-phobicity, drag, contact angle, slip angle, fluid retention, etc. For medical device designers, this technology often provides similar or better low-friction performance while allowing the device designer to optimize the base material selection to achieve mechanical, biological, or cost targets. An example surface is shown in Figure 1. The microstructures remove the contact area from the product surface without reducing the volume and strength of the product. Lowering the contact area reduces the interference between the product and the opposing surface, allowing the surfaces to slide past each other with less drag force. Microstructure surface engineering specifically designs the pattern to create a surface applicable to a specific friction regime or surface tension.

Microstructure engineering is a relatively new science derived from the study of structures found in nature. The physical phenomena of gecko feet, lotus leaves, rose petals and many other plant and animal microstructures interacting with other surfaces has long intrigued scientists. The best attempts to mimic surface phenomena found in nature have been tried through chemistry and employed through coatings and lubricants. These attempts have fueled the explosion of polymer science over the past several decades. Incorporating micro and nano surface structures on base materials has been limited by traditional surface machining techniques. Structured micro patterns can be applied today with lasers, but this is a slow and costly process for bulk surface transformation. Surface finishing via abrasion is cost effective for bulk surface treatment, but it is only capable of random surface patterns, not designed discrete surface patterns on a bulk surface. Recent dramatic advances in bulk surface machining on the micro and nano level allow discrete engineered structures to be applied to a bulk surface in a cost-effective manner. This technology opens the door to pursuing the new science of micro surface engineering for improved product performance.

Figure 2: Graphs illustrating the differences in friction between treated and untreated tubing (click here to see larger version)Manufacture
These microstructure surfaces are formed in the base product polymer and applied during the extrusion or molding process. No additional process steps are required and die/mold life is anticipated to be equivalent to standard, non-patterned tooling. The micro pattern is engineered to achieve the desired surface characteristics and subsequently applied to the extrusion die as a negative of the shape required on the finished product, taking into account shrinkage, draw down or other processing parameters. The same engineering is employed for injection or compression molded products.

Friction Testing
As shown in Figure 2, thermoplastic tubing with microstructures outperformed conventional thermoplastic tubing by 47% when sliding against silicone rubber, and by 30% when sliding against stainless steel (both measurements made for dry sliding). Figure 2 also shows a bigger change for silicone rubber, where the sliding friction against stainless steel drops by 60% when microstructures are added to the surface. The greatest effect occurs for sliding against compliant materials, such as silicone or vinyl rubber. The compliant materials naturally conform to the area of the medical device, creating a high contact area, as compared to the behavior of stiffer materials like steel. Reducing the available contact area has a greater effect with compliant materials.

Microstructured surfaces also have lower tack or stickiness than conventional surfaces, particularly for low-durometer materials. These surfaces will not stick to themselves or other tacky surfaces, making them easier to store and deploy for use, as well as lowering the damage to these products. Coatings and fillers used to reduce tack are often washed or dissolved away before use because they change other properties of the product. Microstructured surfaces do not change the material properties of the product, and therefore do not need the removal step.

Other Characteristics
A “pop” or pinch test can be performed for the microstructured silicone or low durometer tubing. The sticking effect will not be totally eliminated; therefore, the “pop” is not silent, but is significantly muted in comparison to the conventional tubing.

Figure 3: Contact angle data on a treated surface (click here to see larger version)Figure 3 shows contact angle measurements for one microstructured surface and one conventional surface in silicone rubber tubing. The microstructured surface has increased the static contact angle by 20° and lowered the sliding contact angle by 14°. Water-based liquids flow across the microstructures more easily than the typical surface.

Conclusion
Currently available options to achieve the desired surface properties of friction, tack, surface tension, and tactile feel often limit the development of more specialized and complex medical device design. Micro surface engineering is the science of imitating surface structures found in nature, translated to specifically designed micro patterns and realized with best in class, high volume tooling to provide product designers with solutions not previously available.

Andrew Cannon, Ph.D. is the R&D manager for Hoowaki LLCand also one of the inventors of the microstructure technology. Sarah Hulseman is a product development engineer for the company.

Balloon-Forming Innovations Improve Quality and Reduce Cost

Catheter balloons are an important device for a variety of cardiovascular treatments. However, their manufacture can be a complicated process that, if completed wrong, can lead to waste and excess costs. This article highlights a number of innovative technologies that are being offered to help balloon manufacturers ensure their products are defect-free the first time.
 

Long PTA balloonMedical technology is evolving rapidly—OEMs and end users are demanding smaller, more complex, and more multi-functional products, often made from newer materials with tighter tolerances—with faster turnaround at the lowest possible cost.

The only way for medical device manufacturers to meet these demands and maintain market share (without sacrificing quality) is by staying on top of new technologies, manufacturing processes, advanced materials, quality controls, and best practices to deliver what their customers need. This requires long-term vision and commitment, as well as devoting the time, personnel, and resources to make it happen.

It’s not just technology from the manufacturer’s realm of operations, either—proactive companies bring together the best technologies and practices from other fields (optics, automation, and computer engineering, for example) to create innovative applications for their own unique set of production needs. If a company can’t find exactly what it needs, the next step should be investing in R&D to develop its own proprietary technologies.

Variety of balloons for multiple medical applicationsBalloon manufacturing is one of the most challenging, high-precision areas among medical device because there are so many critical factors that must be precisely understood, monitored, and controlled at all times to create a safe, high-quality product. Some of these factors include material chemistry and dimension, material preparation, applied force, speed of stretch and forced stretch, rate of inflation, explosive expansion, exponential pressure decay, mold venting, heat flow, chamber pressure, and rate of cooling. Even the slightest variation in any of these parameters during the balloon-forming process can result in low yields, high scrap, product failures, and unhappy customers.

A problem for many balloon manufacturers is the inconsistent behavior of the balloon extrusion from lot to lot—for example, the balloon might not form at a predetermined point or proceed in a predictable direction. These inconsistencies are often the result of lot-to-lot variations in balloon tubing properties. Correcting these annoyances requires frequent inspection and adjustments during the extrusion process, which extends balloon development times, reduces production yields, and increases costs.

Other problems can be variations in finished balloon wall thicknesses that can greatly impact burst pressure; this is becoming even more of an issue for some manufacturers as customers push for thinner walls and higher burst strength. There is also the inability to obtain higher neck-down ratios (ratio of balloon diameter to balloon neck diameter); this is a growing challenge as more customers are attaching larger-diameter balloons to smaller diameter shafts. Improper understanding of material behavior, as well as contamination of raw materials, can also lead to structural flaws known as “fish eyes” and “crow’s feet” that can cause balloon failure.

Gage R&R human inspector vs. automated inspection systemWithout the proper investment in material science and technology, balloon manufacturing involves a certain amount of guesswork that can result in low yields and create uncertainty among clients because they never feel totally secure about consistency of product. Balloon manufacturers overcome these challenges by investing in or developing the appropriate technologies and best practices to monitor and control, with high precision, every step of the balloon-forming process. This creates repeatability, which also makes validation easier. This convergence of technologies will:

• Greatly reduce balloon development time and cost
• Reduce delivery times for balloons
• Increase pre- and post-inspection yields
• Improve gross margins
• Improve overall quality and performance of balloons
• Drastically reduce rejection rates of balloon tubing extrusion runs

A Parameter Development System Essential for Success
Leading companies have a commitment to truly understand, at a deep level, the complexities and interactions that occur among the technologies, equipment, processes, materials, and manufacturing environments involved in balloon-forming. Both extrusion and balloon forming are very complex processes that involve a multitude of interacting parameters. Consistent, repeatable production of high-quality balloons that meet or exceed customer specifications is only possible through precise monitoring and control of all variables, at every stage of the balloon-forming process.

Balloon main body dimension failure

To achieve this, Interface Catheter Solutions created a proprietary parameter development system (PDS) that enables the step-by-step scientific assessment of each individual parameter. This computerized, testing device allows engineers to quickly assess the individual properties of tubing as they relate to the balloon-forming process, as well as determine optimum balloon-forming parameters. These include temperature, inflation pressure and flow, and radial expansion and axial stretch—both in terms of rate of change, uniformity, and absolute accuracy. The system can also identify small variations in mechanical properties between individual extrusion lots that may lead to flaws in the balloon wall.

Fisheye balloon visual defect

Tubing characteristics can be established on a lot-to-lot basis so balloon-forming parameters can be quickly adjusted in production. Tubing lot rejections and subsequent re-runs for unsubstantiated reasons can also be eliminated. Other advantages of the PDS are improved yields, reduced scrap, shorter machine set-up times, and faster production.

Optimized Parison Forming
Engineers can rely on the parameter development system to accurately configure the parison, which is essential for a successful balloon-forming operation. The parison defines the cone angles and the body of the balloon. The left and right sections of the tubing are necked down to make them harder than the non-necked section of tubing. The non-necked tubing is considered the parison; its length depends on the material type, desired wall thickness, and dimensional requirements, including body length, cone, and neck. The hardened sections on either side of the parison allows for stretch and blow control during the primary and secondary stretch operations. If these sections are not drawn down correctly, the force and distance required to displace the material during balloon blowing will be unpredictable and inconsistent.

Interface visual inspection customer survey responses (click the chart to view a larger version)To optimize parison forming, Interface Catheter Solutions developed a computerized parison stretcher that provides accurate, repeatable results for neck-down tubing in preparation for balloon forming. This equipment can stretch up to three parisons with the same parameters and precisely control stretch speed, temperature, distance, and timing for consistent results and optimal production yields. The stretcher is PLC-controlled and easy to program with a touch screen. Custom jaws can handle a wide range of sizes and balloon tubing materials, including nylon, polyethylene, polyurethane, and polyethylene terephthalate (PET), making it easy to load the tubing and clamp into place. The jaws extend during the tube-heating process and retract when not in use. The parisons are gripped by air-powered soft clamps located on each side of the heater jaws, which provide a secure grip during the heating and stretch cycle to obtain a well-defined transition on the parison.

High-Efficiency Water Jackets
Controlled heating is a critical phase of balloon forming. High-efficiency water jackets provide a more uniform heating and cooling environment for balloons during the balloon-forming process. They can accommodate a large range of balloon sizes and lengths. The latest models have been improved to create a more uniform thermal profile, shorter process times, and repeatable ramping capabilities. The uniform thermal profiling enhancements result in balloons that are much more consistent in wall thickness that result in higher burst pressures. The high-efficiency water jacket improvements also provide better control and cycle times, which improve balloon cost. Other advantages include quick installation and set-up, smooth thermal ramping, stable plateau, faster thermal stability, and uniform heating of circumference and length of molds. When water jackets are combined with upgraded balloon-forming equipment that provides better directional flow for water cooling and air purge control, the result is very consistent and repeatable balloon production.

Automated Visual Inspection System
Significant balloon defects can be difficult to find, categorize, and measure, especially using the manual contact measurement and inspection tools that are still considered the standard today. These tools are also inferior for determining precise critical dimensions such as interior diameter, wall thickness, and concentricity. This leads to missed gels and fisheyes and often generates inspector disagreements on defect type, which lead to high scrap, low yields, lack of control, and lack of improvement.

Automated balloon inspectionTo address these problems, Interface Catheter Solutions has developed an automated balloon inspection system that provides both visual inspection and dimensional measurement of medical balloons in a single operation, thereby increasing and improving both throughput and accuracy. Cycle time is about 30-60 seconds, depending on the size of the balloon. Using a high-speed, five-megapixel camera and telecentric measuring lens to provide high-resolution images (seven micrometers for small balloons at 40x and 28 micrometers for large balloons at 10x), this technology enables quick identification and classification of visual defects such as gel spots, fish eyes, crow’s feet/strain lines, zipper lines, and embedded foreign particulates, as well as provides highly precise, repeatable dimensional measurements, using non-contact, high-resolution camera technology. It is also equipped with filtering options for non-translucent or matt- and textured-finish balloons that improve the ability to identify defects within these finishes—another challenge for inspectors.

Conclusion
Balloon tubing must meet critical production standards to achieve important performance characteristics such as minimal wall thickness and improved burst pressures. These parameters must be within prescribed limits and must be consistently reproduced in all subsequent production runs.

Using a scientific approach to develop a balloon optimization system allows balloon catheter manufacturers to speed up cycle times, improve burst pressures, maximize quality, increase yields, limit scrap, reduce costs, improve customer satisfaction, and gain market share.

To accomplish this, balloon manufacturers must incorporate a number of advanced technologies and systems to precisely control the many variables that can impact balloon production. In fact, by providing innovative technological capabilities and options that weren’t available a few years ago, these manufacturers enable balloon engineers to expand their design capability and create new products to address unmet market needs.

David Yanes is the director of equipment technology at Interface Catheter Solutions. Eric Mabry is the VP of equipment engineering with the company. Interface Catheter Solutions is the only vertically integrated provider of outsourced solutions for balloon and catheter manufacturing. The company has been solely focused on the balloon catheter market since 1995 and continually sets industry standards through process improvements and equipment advancements in balloon catheter manufacturing.

Applying Tech: Implantable Devices

How are you influencing implantable devices?

Gabriel O. Adusei, MSc, PhD
Independent MedTech Consultant, Founder, International Association of MedTech Consultants 

Over the years, a significant number of implantable devices since their introduction into the market have seen changes from being inert to being bioactive to iterative developments to enhance their efficacy. One area with significant growth and success is the use of hydroxyapatite (HA) and amorphous calcium phosphate nanoparticles in implantology. Many modern implants (e.g., hip replacements and dental implants) are coated with hydroxyapatite. It has been suggested that this may promote osseointegration. The application of nanostructured titanium with nanocrystalline bioactive hydroxyapatite coatings has offered many biocompatibility benefits. For example, nanotubular structured titanium (Ti) substrates coated with nanoparticulate hydroxyapatite (nano-HA) offers a surface that promotes osteoblast cell adhesion and is particularly suitable for orthopedic and dental implants where deposition of osteoblasts and other proteins is important in bone formation. This enhances device-tissue integration. HA nanoparticles can be produced by a process such as sol-gel and plasma spray techniques, chemical and vapour deposition including discrete crystalline deposition (DCD) among a number other methods; however, factors such as the crystallinity, nano-particle size and shape(s) influence the surface area as well as resultant strength if they are to be as stress-bearing composites or as part of drug-release system.

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Joe Pustka
Medical Device Leak Testing Technical Support Manager, Uson

Uson has helped manufacturers to leak test nearly every type of implantable medical device used today. Initially, it was quite common for our team to tell design engineers to go back to the drawing board. The problem had been, and still sometimes is, that in totally sealed components, there is no air gap when there needs to be. Adding a free volume of air into such a sealed part will allow a gross leak to be detected. Sometimes, and especially if the overall size of the part is very small and the acceptable leak rate is comparably small, an alternate approach is to re-design processes to perform leak testing of subassemblies.

Uson’s message to any developer of an implantable device is short and to the point. It is never too early to get your supplier of test equipment involved in helping to design your process and the device itself. If you are dealing with a test equipment supplier that gives you such “advice” at premium cost—sometimes to the tune of six figures—that is money down the drain. Any reputable supplier of test equipment builds up-front consultation on application details into their pricing system.

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Andrew Kelly
Member of Technical Staff, Cactus Semiconductor Inc.

Cactus Semiconductor enables the miniaturization of implantable medical devices (IMDs) by designing customized ICs specifically for the latest battery, MEMs, wireless, and packaging technologies. This miniaturization allows for placement of IMDs near the point of therapy, instead of in the chest or abdomen, thus enabling better performance and less-invasive implant surgery.

Recent advances in battery technology have led to the availability of chip-scale batteries, which can drastically reduce the volume of IMDs. Cactus develops circuits to optimize the charging and monitoring of these unique batteries. In addition, Cactus designs ultra-low power circuits that minimize power consumption to enable use of these lower capacity batteries. One example is our fully-integrated timekeeping solution that consumes less than 200 nW.

MEMs devices are rapidly replacing traditional sensors and actuators in IMDs to enable miniaturization. These MEMs devices are often customized to specific applications so they require customized electronics to optimize power and performance.

Cactus also has wireless solutions that support simultaneous wireless communication and battery charging with a single coil. Our communication solutions employ passive back-telemetry, to minimize battery power, thus enabling the use of smaller batteries.

Finally, Cactus designs custom ICs for multi-chip die-stacks that integrate ASICs with microcontrollers and EEPROMs in a single package. The size of the entire IMD is thus optimized in ways only achievable by customization.

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Tanner Hargens, MS
Senior Biomedical Engineer, Medical Murray Inc.

Medical Murray develops and manufactures medical devices with a focus on complex catheter systems and their components. Our implantable components often intend to repair or regenerate native tissue with absorbable polymers that begin to degrade after accomplishing their initial task. Medical Murray is influencing the bioabsorbable industry through knowledgeable material selection and injection molding of the smallest and most detailed profiles on the market.

Bioabsorbable innovation at Medical Murray has been driven largely by vascular, orthopedic, and surgical applications. The absorbable polymers are initially designed by polymer scientists and engineers to meet the specific mechanical properties and degradation kinetics for each application. Each material will then have its own restrictions when processing to the desired shape. When injection molding absorbables, each material will have limits on the cavity size it is capable of properly filling and must often be processed at the lowest temperatures possible to prevent alteration of the degradation kinetics.

The Sesame nano-molder, invented by Medical Murray, is capable of producing the smallest and most detailed bioabsorbable polymer components by allowing the material to melt to sufficient flow at a lower processing temperature so the material can normalize quicker with a shorter cooling time than is otherwise available. This has also allowed minimal loss of very expensive materials through use of smaller sprues, runners, and reduced melted material in the injection unit. As an example to the understanding the materials and processing, Medical Murray has been able to design and mold the first absorbable living hinges, which allow expansion of a device into the tissue from a small delivery catheter.

The real technology companies

Those who blithely declare that Facebook versus Google or Amazon versus eBay are the big technology battlegrounds should probably avoid reading this issue because it may only blur their otherwise-clean definitions of what technology is. Wall Street, like engineers, doesn’t like blurry lines.

As an engineer, I find it easy to look at the Hot 100 Products and say definitively that these products represent the best technology had to offer in 2011. Why? Because they do! From Analog Devices’ ADA4096-2 dual op amp to Tektronix’s MDO4000 mixed-domain oscilloscope, all represent the latest thinking in integration, processing, end-user requirements, cost, features, power, and so on. The products were designed by real engineers for real engineers.

In the Hot Technologies section, our editors outline what those real engineers are now enabling with those products and looking into 2012. Contributing Editor Steve Taranovich takes a future-is-now approach to medical implants, pointing to Cactus Semiconductor Inc’s neurostimulation, pacing, defibrillation, ultrasound, and medical-monitoring technology, as well as Plessey’s EPIC(electric-potential integrated circuit), which can detect changes through clothing—and even through walls. EPIC proves once again that we have not yet reached the limits of what we can measure and detect, and that’s exciting!

Along the test theme, Test & Measurement World’s Martin Rowe describes mobile apps from Oscium and a wireless digital-multimeter app from Redfish Instruments that turn your iPad or Android device into an ultraportable, ultraflexible iTest platform.

You’ll find much more in which to immerse yourself if you’d like to get a quick update on what’s happening beyond your specific field of interest—if you’re lucky enough to be able to indulge in a specific field of interest. Margery Conner and Bill Schweber give the latest on, you guessed it, LEDs and LED drivers. You had better pay attention: 2012 will be a big year for LEDs in the United States as the federal government begins to phase out inefficient light sources.

Janine Love provides an update on low-power wireless, which will be everywhere in the coming year, and Clive Maxfield updates us on programmable logic. The GreenPak 2 from Silego is particularly exciting. I hope the company takes the time to enter it in our UBM Electronics ACE Awards, as should others from the Hot 100 Products list. Check to see whether your devices are on it and take a stab at the awards.

Finally, Rick DeMeis gives the latest in automotive innovation, Rich Pell provides an audio download, Colin Holland shows us what’s hot in microcontrollers, and Paul Rako tells us why PCBs are hotter than you’d think.

All in all, it’s an issue I’m particularly excited about, and I hope you are too. However, sitting here looking at the cover for the October issue of Test & Measurement World, I can’t help but surmise that anyone who tries to separate technology from the application of technology is in for a rough ride. The cover features a smiling Ward Ramsdell, electrical engineer and co-owner of Prototype Engineering, sitting at a bench strewn with high-end test equipment. He’s posing for a photo and looks busy testing something, but it reminds us that the components now in test systems will enable the development of the next generation of components and systems.

In the same way, those systems in data centers will allow Google, eBay, Amazon, and Facebook to develop the next generation of applications and interaction channels that will enable the communications and collaboration that will, in turn, enable the next generation of systems design. So, are Amazon, Facebook, eBay, and Google good technology companies or good applications-of-technology companies?

You could ask the same of Apple. The iPod and iPhone were and are not new technologies but good packaging of fairly standard technologies. Where do real engineers sit in this landscape? It’s a blurry line indeed. Can you help me get a clean eye diagram on this? In the meantime, enjoy the products and tools of your endeavors, and read on.

Contact me at patrick.mannion@ubm.com.

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