Fig. 1 – Tubing that is free of the plasticizer DEHP is frequently called for in medical devices.

Determining what tubing to use in a medical device involves considerable research. Designers must investigate ingredients, performance, documentation requirements, sterility, and other qualifying aspects that cannot be disregarded.

Fig. 2 – Spiral reinforcement gives tubing more pressure and vacuum resistance.

Regulations are an unavoidable part of the medical device arena and for good reason. The industry involves substances and products that affect our bodies. In the US, the Food and Drug Administration (FDA) verifies that medical devices are safe to use and do what their manufacturers say they will.

Many medical devices include plastic tubing for fluid or gas transfer. When it comes to that tubing, the FDA’s oversight can involve everything from the individual ingredients that make up a plastic or rubber compound, to manufacturing processes, to the tubing’s reaction with things with which it may come in contact.

The following tips focus on topics including lot traceability, regulatory organization approvals, flexibility, pressure and vacuum requirements, and temperature capabilities. The information is designed to help avoid specification errors and, in turn, ensure the safety of medical devices and, most importantly, the wellbeing of patients.

  1. Know what company is manufacturing the tubing. This may seem obvious, but there are many resellers of tubing, some of whom position themselves as manufacturers when they are, in fact, private label distributors. The situation is not necessarily a negative, but you should be aware of the controls in place that ensure a high quality product. Ask about the manufacturer’s production practices, quality policies, and safeguards. Documented work instructions and/or good manufacturing practices should be followed, and quality control procedures must be in place to ensure consistent tubing. Although your particular device may not require tubing that’s manufactured in a clean room, it should still be made with precision and uniformity. If you have doubts about the manufacturer, consider a visit to the facility. It is wise to have a backup supplier as well.

  2. Make sure the tubing is made from raw materials that have full lot traceability all the way back to the resin ingredient manufacturers. Some extrusion companies make their own compounds, while others purchase them ready to process into tubing. In either case, full traceability for each ingredient in a formulation should be available to you.

  3. Determine what regulatory documentation is needed for the tubing in your device. Examples are USP (United States Pharmacopeia) Class VI or UL (Underwriters Laboratories) listings, as well as Material Safety Data Sheets. Your tubing supplier should be able to tell you what documentation they can provide with their product, but don’t assume they will have all the documentation you need for regulatory concerns. In some cases, it may be necessary to have your own testing performed by an independent laboratory.

  4. Make certain you have an agreement stating that any time a material ingredient or manufacturing equipment change is scheduled to take place, you are notified in advance. A risk assessment may need to be performed to determine how the proposed change may or may not affect your device. The important thing is that you are made aware of the change and have the opportunity to determine if it will impact your product.

  5. Check for ingredient approvals and incompatibilities. You may need to know whether the tubing under consideration is manufactured with FDA, NSF (National Sanitation Foundation), or other association-compliant ingredients. Check the supplier’s tubing specifications for this information. Also be aware of incompatible or unacceptable ingredients like Di(2-ethylhexyl) phthalate, better known as DEHP. It’s a chemical agent added to resin to increase workability during processing and to impart flexibility in the finished product. DEHP and other plasticizers such as BBP, DBP, DnHP, and DIDP can leach from, or come out of, the tubing and contaminate the gas or fluid flow. These chemicals are included on lists of carcinogens from both the federal government and the state of California, and their use in medical devices has caused concern. In fact, products containing these chemicals over a certain concentration must display a warning label. Some tubing materials, polyurethane for example, do not contain plasticizers. (See Figure 1)

  6. Learn whether the tubing will impart a taste or odor to the flow. If your device’s application involves foods, beverages, or oral medications, any taste or odor transferred to those products is likely undesirable. Candidate tubing should be tested to see how the material might affect the stream, the end product, and the patient.

  7. Determine whether you need transparent, translucent, or opaque tubing. If the fluid within the tubing must be viewed to check for consistency, progression, or to note measurements, you’ll need tubing that’s transparent (clear) or translucent (allowing light to show through but not a detailed view). Depending on the application and the fluid involved, it may actually be undesirable to see the flow within the tubing. Certain tubing materials are available in transparent, translucent, or opaque styles while others, due to their nature, are available in only one type. Tubing construction can also greatly affect its viewing ability. Tubing made with reinforcement such as wire, braid, or spirals may have restricted sight.

  8. Take note of pressure and vacuum capabilities. In a medical device application where the tubing acts as a waste fluid drain, these capabilities are likely to be of minimal concern. But when the tubing usage involves suction, you must use tubing that will not collapse. This type often uses reinforcement (commonly braid, wire, or like-material spirals) to help support the tubing walls and lessen the risk of failure. Pressure uses may also require reinforced tubing depending on the amount of force involved. (See Figure 2)

  9. Make sure the proposed tubing is flexible enough for your device. If the tubing needs to bend around other components, it will have to do so without kinking and cutting off the flow of gas or liquid. Certain tubing materials, silicone for example, are highly flexible, while others are better suited to applications where the tubing remains on a straight path or one with only a slight curve. If the application involves repetitious movement—a pump or robotics— the tubing must be able to withstand repeated compression and/or flexing. Resiliency and elasticity can come into play here as well. Resilient tubing will spring back to shape after being bent or compressed, while elastic tubing will return to its shape quickly after being stretched or expanded.

  10. Closely related to a tube’s flexibility performance is its hardness. The harder the tubing, the more it will be prone to kinking at tight bends if unsupported by reinforcement or external means such as a clip or guide to direct the tubing. Softer tubing will be more flexible and although not kink-free, it will handle turns, twists, and bends more easily. Tubing hardness is measured as its durometer, and different scales, namely Shore A, Shore D, and Rockwell R, are commonly used for plastic and rubber materials. The lower the scale number, the softer and more flexible the material will be. For instance, a typical latex tubing hardness rating is Shore A35. Polyurethane tubing is not as soft and can measure between Shore A70 and A95. Harder materials like nylon and polyethylene are normally measured on the Shore D scale, and others (polypropylene, for example) use the Rockwell R scale. Learn how different hardnesses of tubing will operate in your particular application.

  11. Be aware of all temperatures involved. This means not only the temperature of the fluid or gas going through the tubing but of the environment in which it will operate. Is the room where the device will be located kept cool or refrigerated? Is it heated? There may be no adjustments available for regulating the temperature, so the device and its tubing may need to withstand a range of fluctuating temperatures. Keep in mind that the higher the temperature, the less pressure the tubing can handle. Humidity levels should also be considered.

  12. Learn which sterilization methods the tubing can withstand, e.g., autoclaving, low-pressure steam, gamma irradiation, ethylene oxide. Sterilization costs vary greatly, so choosing tubing that can be sterilized by one of the lower cost methods may help minimize the overall cost of your medical device. If sterilization for reuse is involved, consider whether the labor and equipment involved with cleaning is worth the expense. In some cases it may be more economical—and safer for the patient—to simply replace the tubing.

Fig. 3 – Because of its extreme flexibility and resiliency, silicone tubing is often used as a pump component.

This article was written by John Stover, Director of Product Management & Regulatory Compliance, NewAge Industries, Inc., Southampton, PA. For more information, Click .