The medical area has long required specialized materials be utilized to treat patients, and the processes of drug delivery and fluid handling are no exception. Hospitals across the globe make use of large volumes of tubing and medical bags every day for the transmission of blood, medications, and other fluids, and these devices require specific properties to be considered safe and effective. (See Figure 1)
Because of the nature of the polymers used to create these devices, however, it can be challenging to create tubing and medical devices with the properties and functionality desired for optimal use. While it might be beneficial to have a soft, lubricious inside of a tube for optimal flow rate and a hard, matte finish on the outside to protect the tube from damage, these opposing properties are customized on a continuum, and the tweaking of one property inversely affects another.
Thanks to processing breakthroughs and rheology modification of thermoplastic polyurethane (TPU), one of the most resilient polymers used in the manufacture of medical bags and tubing, tubing and films used for medical device manufacturing can now be created in multilayer construction. This allows for various layers of properties being extruded into a single piece of material, with no coatings required. The ability to design different functionality into one construction has been present in other industries before, such as food packaging, but it is new for the medical market and has not been accomplished before now with TPU.
This article will explore the properties of TPU that make it a compelling material and the new possibilities created through multilayer constructions for drug delivery and fluid handling. Designers and engineers will also be provided with the information and expertise they should seek out to incorporate the new functionality offered by multilayer TPU extrusion into manufacturing and design.
Multilayer TPU Films and Tubes: What are the Benefits?
Available in hundreds of formulations to meet a wide range of application needs, TPU is a polymer recognized for its versatility. Pellets of TPU can be processed and extruded as sheets of cast film, as a bag-like blown film, as tubing via profile extrusion, or coated onto various products. TPU polymers can be manipulated to demonstrate a variety of properties, making it an ideal material for medical device manufacturing and many other uses. Customizable properties of TPU include:
- Solvency or chemical-resistance,
- Softness or rigidity,
- Low-friction or tackiness,
- Clear or dark coloring,
- Matte or shiny finish,
- Hydrophobic or hygroscopic properties, and
- Breathability or barrier properties.
TPU also is a robust material, demonstrating high tear strength, durability even when soft, resistance to oil and grease, superior clarity, and abrasion resistance. TPU also is safe, as there are no plasticizers used in TPU production. It does not exude any harmful byproducts, and there are TPU formulations certified as biocompatible.
Now that TPU can be extruded into a multilayer construction, designers and engineers involved in the creation of medical devices no longer have to decide between desired properties, choosing one over the other — they can have both. For example, a TPU film no longer must be soft or rigid; it can be both. Different TPU compounds mere micrometers thick can now be combined and extruded as a single substrate, delivering advanced functionality. When we consider the needs of medical devices such as tubes and fluid storage bags, it is clear that there is an advantage to this sort of construction. (See Figure 2) These devices require:
- Base materials that will not contribute to leaching of harmful substances into fluids;
- Durability to stand up to the rigors and fast pace of the medical environment;
- Barriers to oxygen, moisture, or contaminants entering or leaving fluids; and
- A U.S. Pharmacopoeia (USP) Class 6 material with a clear history of biocompatibility and the capability to meet tight regulations regarding blood and fluid contact.
To meet all of these requirements in the past, films and tube had to be coated multiple times as no one polymer exhibited all of these qualities, adding thickness and cost. With a multilayer construction, however, all of these properties can reside in the uncoated film or tube. For example, an outer layer can contribute to a bag or tube’s durability, a middle layer can yield barrier properties to resist moisture or oxygen infiltration, and an inner layer rated as a USP Class 6 material can meet fluid contact requirements. The same or better functionality that would reside in a heavily coated or single-layer film is now more easily attainable.
When testing has been done on multilayer constructions composed of various TPU compounds to add the durability, barrier and biocompatibility properties desired, the tri-layer constructions have been shown to outperform laboratory control materials in every category. Specifically, multilayer films and tubes demonstrated superior:
Tensile strength – for burst, tear, and cut resistance. This allows for fluid storage bag resilience, whether in centrifuges or applications where there is abrasion risk;
Heat-sealing properties – to ensure the longevity of fluid storage bags, and that contents can be reliably stored without contamination;
Moisture vapor transmission rate – to maintain the appropriate consistency and protection of fluids; and
Oxygen transmission rate – to maintain the integrity of transmitted fluids that are sensitive to oxygen content.
How to Make the Most of Multilayer Technology
As long as the necessary processing equipment, such as multi-barreled extruders, is in place, and the TPU polymers are appropriately formulated, there is virtually no limit to the number of layers or properties that can be instilled in a multilayer construction. To make the most of this technology, however, it is crucial to start with finding the right supplier partner.
Not every thermoplastic is processed in the same manner, and the number of companies that have the capabilities, knowledge, and experience to effectively process TPU, let alone to do so in a multilayer fashion, is limited. An effective partner will have knowledge of rheology, the properties of TPU polymers, and the processing quirks of the material for which you must account if manufacturing with it. Having a large, diverse portfolio of polymers to choose from is also a plus, as it allows more flexibility to add the exact functionality you need in a medical device. Finally, and most importantly, look for a supplier that exhibits a willingness to educate and assist with design, polymer modification, processing procedures, and solution development. A partner should help you to comprehend how multilayer constructions can benefit you, teach you how you can work with TPU effectively, and not simply try to sell you a product.
Multilayer TPU constructions offer substantial promise to make medical devices more resilient, safe, and customizable. This technology also means they can be manufactured cost-effectively and can be made thinner than ever, without sacrificing functionality. As you design, develop, or otherwise work with polymer-based medical devices, consider a multilayer TPU construction as a means to meet your requirements.
This article was written by Ralf Hüther, Global Business Manager for Lubrizol LifeScience Polymers Division in Wickliffe, OH. For more information, Click Here