Thermoplastic polyurethanes (TPUs) offer several features that suit them for a range of
medical devices
that require durability and flexibility. Common applications include catheters, tubing, implantable devices, and prosthetic components. They can also be used for housings, seals, films, and other components.
To help medical device design engineers understand and specify TPUs, we asked Jennifer Green, senior global technical business development manager at Lubrizol, to detail TPUs, their performance, application parameters, and best practices for material selection. Green specializes in innovative material solutions for medical devices and healthcare applications and offers a deep understanding of polymer science. With 15 years of industry experience, she is passionate about advancing biocompatible materials like thermoplastic polyurethanes (TPUs) and medical-grade silicones. She collaborates closely with medical device developers to enhance patient outcomes, focusing on sustainability, material performance, and regulatory compliance.
For engineers who may not work with thermoplastic polyurethanes every day, how would you describe TPU? How does it differ from other materials? What makes it so conducive to use in medical device design?
Green:
TPU is a versatile polymer known for combining flexibility with strength. It is best thought of as a material platform as its performance can be adjusted to meet very different device needs, from soft, flexible tubing to durable molded components. At the molecular level, it’s a segmented copolymer, so you have hard segments contributing strength and soft segments contributing elasticity. By changing that chemistry and the balance between the two, you can tune everything from mechanical performance and chemical resistance to surface behavior and processability.
That tunability is a big advantage: within the same material family, you can adjust hardness, tensile strength, elastic recovery, surface energy, solvent resistance, and melt behavior to line up with a device’s functional needs, sterilization method, and manufacturing process.
That’s why TPU shows up in so many applications that need both flexibility and durability, such as thin-wall catheters and tubing, films, membranes, strain reliefs, and precision injection-molded parts. You also see moderate softening at body temperature, which can be useful; the device maintains pushability during placement, then becomes more compliant and conformable in vivo.
When we compare TPU with other polymers, we usually look at four things: mechanical behavior, processing, in-body performance, and overall device trade-offs. Consider the following:
Against
silicone elastomers
, TPU generally offers better tear and abrasion resistance, thermoplastic processing with tighter dimensional control, and easier assembly through thermal or solvent bonding. Silicone has proven performance when you need very high elastic recovery, extreme temperature stability, long-term implant durability, or exceptional chemical inertness.
Against
polyamide elastomers
, TPU often brings greater flexibility and stronger abrasion performance, especially in dynamic or high-cycle applications. It’s also available in very soft grades for more atraumatic designs, especially for interventional catheter components. That said, while some TPU grades can match polyamide stiffness at room temperature, they usually soften in vivo because of heat and moisture. That hydrothermal drop in flexural modulus can affect push and torque response compared with polyamide elastomers, which tend to hold stiffness more consistently in the body. You see that most clearly in unsupported or unbraided shafts, where bulk polymer properties matter most.
Against
plasticized PVC
, TPU achieves softness from its polymer architecture rather than from plasticizers. That usually means more stable mechanical performance over time, along with better tear resistance, elastic recovery, and fatigue durability. PVC is widely used due to good cost-effective performance, but its chemistry and use of plasticizers can raise added regulatory and life-cycle considerations as regulations and healthcare sustainability requirements evolve.
Against
polyolefins
, TPU tends to deliver better elastic recovery, toughness, and fatigue resistance, especially in thin sections. That makes it a strong option for parts that see cyclic loading, tight bend radii, or extended use without cracking, whitening, or taking a permanent set. Polyolefins remain attractive on cost and chemical resistance, particularly in less mechanically demanding applications, but when durability and repeated flexing matter, TPU often gives you a broader performance envelope.
At the end of the day, material selection decisions made early in development need to account for body-contact type and duration, mechanical demands, processing and joining methods, sterilization, chemical exposure, and regulatory requirements. When those inputs are clear, TPU gives you a versatile platform for dialing in performance through chemistry and formulation.
What aspects of TPU’s molecular structure most influence how it behaves in medical applications? What factors are medical device manufacturers concerned about? How can TPU be altered to solve these problems?
Green:
Usually, one of the first places engineers start is hardness and modulus because those are key design variables. TPU can range from very soft to fairly rigid, and even small changes can affect stiffness, elongation, elastic recovery, and kink resistance. This is especially true in thin-wall tubing and catheter shafts.
So, the question often starts with, ‘What does the device need to feel like, or how stiff does it need to be?’ Once that’s defined, the chemistry gets refined around stability, sterilization, and processing.
What really drives TPU performance in a medical device is its segmented molecular structure. You have hard segments that provide strength and soft segments that provide flexibility, and by changing the chemistry and balance between those segments, you can tune things like mechanical performance, chemical stability, processing, and in-body behavior.
For the hard-segment chemistry, the key distinction is typically aromatic versus aliphatic. Aromatic TPUs are often chosen for higher stiffness, strength, and chemical resistance, and they tend to retain stiffness better in vivo at the same nominal hardness. The trade-off is that they are more prone to yellowing when exposed to UV or ionizing radiation, which makes them less suitable for applications that require optical clarity, strong aesthetics, or radiation‑based sterilization.
Aliphatic TPUs are often better when clarity and color stability are more important. They tend to soften more in vivo, which influences material selection depending on the balance between desired post‑placement compliance and stiffness retention. From a processing standpoint, aliphatic TPUs are generally more forgiving, particularly when working with higher filler loadings such as radiopaque additives, and they typically offer a wider extrusion window.
The soft segment is just as important because it drives flexibility and biostability:
Polyester TPUs
usually offer strong mechanical properties, along with good abrasion and chemical resistance, but they are sensitive to hydrolysis through moisture exposure, so they’re often a better fit for shorter-term or non-invasive applications.
Polyether TPUs
are common in tubing and catheter applications because they offer flexibility and good hydrolytic stability. Oxidative stability becomes more important in long-term blood-contacting uses and is typically durometer and application-dependent.
Polycarbonate TPUs
offer strong resistance to both hydrolytic and oxidative degradation. Therefore, they are typically used when long-term biostability, strength, and chemical resistance are top priorities, especially in blood-contacting implantable devices.
Beyond common chemistries, specialty formulations can be designed for applications where additional performance is needed, such as enhanced permeability control, tailored surface properties, improved chemical or oxidative resistance, or extended long-term biostability.
This is where TPU is differentiated because it offers significant flexibility to tune performance through chemistry.
How does the intended duration of a device’s use—whether once or days, weeks or years—change the way engineers should think about selecting a TPU material?
Green:
One of the biggest factors in material selection is how long the device is intended to be used because that changes what “long-term performance” actually means.
In medical devices, there’s an important distinction between short-term and long-term use. Short-term devices are generally used for 30 days or less, consistent with ISO 10993 and FDA guidance. Implanted devices may need to function for months or even years.
For short-term devices, material selection is usually more flexible. The focus is on clinical performance, manufacturing efficiency, cost, and sometimes sustainability. Because many polymers are compatible with short-term body contact, engineers often have more freedom to choose the material and property set that best fits the device and process.
In long-term implanted applications, the requirements get tighter. The material has to retain its mechanical and performance properties over time while it’s exposed to the physiological environment. In those applications, long-term biostability, resistance to degradation, and compatibility with tissues and bodily fluids become critical.
The environment inside the body must be considered carefully when selecting materials. For example, blood contact exposes materials to both biological and chemical interactions which can affect material performance over time. When the material is placed in the bloodstream, native blood proteins can stick to its surface and influence how blood clots and the device's surface characteristics. In addition, immune cells carried in the bloodstream can create localized oxidative conditions that can attack and degrade the material over time. Therefore, multiple factors must be considered together, including how the material interacts with blood (hemocompatibility) and how the material resists immune system attack (oxidative stability).
GI and gastric applications bring a different set of challenges. In these environments, materials may be exposed to low pH, enzymes, and continuous mechanical stress from digestion and motility. Depending on the TPU chemistry, gastric conditions can accelerate hydrolytic or chemical degradation. Therefore, it’s important to select materials that resist acidic environments and maintain mechanical properties over time.
Reusable devices add additional considerations related to repeated sterilization and cleaning cycles. Repeated cleaning can create cumulative thermal, chemical, and oxidative stress, so those effects should be considered early in material selection and validation planning to ensure material performance is maintained across the anticipated life of the device.
When evaluating the suitability of TPU for a specific device component, what mechanical and functional characteristics must engineers carefully consider?
Green:
Many medical device components are designed to bend, flex, compress, or move relative to tissue and fluids. Material selection must consider mechanical performance properties like tensile strength and elongation as well as fatigue and hysteresis properties over many cycles of motion in the clinical environment.
When considering mechanical requirements, it’s important to note that both part design and material influence the final performance. For catheter and tubing applications, factors like wall thickness, material modulus (stiffness), overall design, including lumen size and configuration, all influence flow, device size, handling, and resistance to kinking. Reducing wall thickness can help improve flow and enable device miniaturization. However, it may also reduce kink resistance and column strength. These challenges are typically addressed by tuning material properties, selecting formulations with higher stiffness or better elastic recovery, and, in some cases, using multilayer or composite constructions.
When a device interacts with the body, whether through blood contact or long-term implantation, what environmental stressors should engineers also consider?
Green:
During clinical use, the physiological environment becomes an important factor. TPU softens in contact with heat and moisture of the body, which should be considered during design. Depending on the application, this change can be either advantageous or limiting. Increased flexibility may enhance atraumatic performance and patient comfort, while in other cases it may reduce pushability and torque control.
Surface behavior is just as important. Friction, surface finish, and wear affect insertion force, flow behavior, and device motion relative to tissue or blood. And if you add coatings, surface treatments, or other functional layers, those features also need to be evaluated after processing, sterilization, and time over shelf life to ensure consistent performance throughout the device’s intended use time frame.
What do engineers need to understand about how TPU behaves during medical device sterilization, and how should sterilization considerations influence material selection?
Green:
The most common sterilization methods for polymeric devices are ethylene oxide (EtO), gamma irradiation, e-beam irradiation, and vaporized hydrogen peroxide (VHP), and each can have a different impact on the material:
EtO is widely used because it operates at relatively low temperatures and is gentle on many polymers. However, residuals must be carefully managed through proper aeration and compliance with established safety and environmental requirements.
Irradiation methods (gamma and e-beam) are also common as they are fast and provide deep penetration. However, they can be harsh on some polymers due to the high-energy interactions they can cause such as chain scission or crosslinking. As a result, some aromatic TPUs may yellow or exhibit slight property changes following irradiation.
VHP is increasingly more common, especially for reprocessed devices and low-temperature applications, but its oxidative nature requires careful consideration of a material’s chemical and oxidative resistance.
Autoclave or high-pressure steam sterilization is not recommended for TPU-based devices because the combination of heat, pressure, and moisture can initiate hydrolytic degradation, resulting in material chemical and physical degradation.
As sterilization technologies keep evolving, TPU’s broad chemistry and formulation flexibility can be a real advantage because it gives engineers more room to tailor performance as requirements and performance needs change.
LUBRIZOL
Beyond sterilization, what compliance, supply chain, and cost factors should engineers consider when selecting TPU materials for medical devices?
Green:
Material selection usually begins with technical performance, but regulatory expectations and supplier capabilities matter just as much.
And while medical-grade TPUs are typically supported by biocompatibility data aligned with standards like ISO 10993 and USP <88>, manufacturers still need to make sure that documentation fits the device’s intended use, duration of contact, and regulatory pathway.
Predicate devices using similar materials can also be helpful, especially on established regulatory paths. A history of use can help reduce uncertainty, support risk assessments, and help shape test strategies. It doesn’t replace application-specific validation, but it can strengthen the overall regulatory rationale.
Supply chain reliability is another major consideration, particularly for higher-risk or long-life-cycle devices. Manufacturers need suppliers with strong quality systems, controlled specifications, and formal change-notification processes, because even small formulation or process changes can trigger revalidation, added testing, or regulatory review.
That’s why supplier partnership matters too. OEMs often need technical expertise, formulation insight, and regulatory support throughout development and commercialization.
Additionally, cost really should be viewed more broadly than resin price alone. A cost-effective material without supply stability, change control, or technical support can create higher downstream costs through redesign, revalidation, or production disruption. A material supported with appropriate stewardship and long-term support may cost more up front, but it can lower risk and lower the total cost of ownership.
What processing considerations should engineers keep in mind when designing parts that will be extruded or molded from TPU?
Green:
Moisture control is essential when processing TPU because the material is hygroscopic and must be thoroughly dried before extrusion or molding. If it isn’t properly dried, voids, surface defects, dimensional variation, reduced molecular weight, and inconsistent mechanical properties are the likely result. This is why the saying goes, “If you don’t dry it, don’t try it.”
Processing also has a major impact on performance. The same TPU formulation can behave differently depending on how it’s shaped, cooled, and joined. Since most medical TPU components are made by extrusion or injection molding, process design and material selection are closely linked.
During extrusion, factors like drawdown, cooling rate, and line speed can change the thickness of the wall, the stability of the inner diameter, the finish on the surface, and how the material shrinks. TPU shows elastic recovery and thermal contraction during cooling, which must be considered, especially in thin-wall tubing. Engineers usually manage these factors through careful control of thermal and cooling profiles, post-extrusion relaxation or annealing, and targeting final (not in-process) dimensions.
TPU can also be used in solvent processes for very thin films, conformal coatings, or complex geometries that are difficult to achieve with extrusion or molding alone. Those approaches require tight control of solvent choice and polymer viscosity.
Joining and bonding strategies also need to be considered early. TPU can be joined with heat welding, RF welding, solvent bonding, and reflow, which is often used in catheter construction to fuse layers or transitions between different durometer segments.
What practical framework can engineers use to evaluate and choose a TPU material for a new medical device application?
Green:
A structured framework helps keep TPU selection tied to device requirements rather than individual material attributes.
Define the use case and risk profile.
Start by clarifying the type of biological contact, duration of use, temperature range, fluid and chemical exposure, and expected mechanical demands. It’s also important to know whether the device is single-use or reusable, blood-contacting or implanted because those factors define the main performance and durability risks.
Establish sterilization expectations early
. Identify the primary sterilization method, any acceptable alternatives, and how much post-sterilization change can be tolerated in areas like mechanical performance and appearance. That assessment needs to be based on the full formulation and not just the base polymer.
Translate use conditions into targets
. Application requirements need to become quantifiable goals (e.g., stiffness, kink resistance, tensile or tear strength, compression behavior, surface friction, optical clarity, or radiopacity) based on how the component is expected to function.
Select chemistry strategically.
Hard-segment chemistry, soft-segment chemistry, and hardness should be chosen around the main risks already identified, whether that’s oxidative stability, hydrolytic resistance, or retention of modulus in vivo, rather than around one property alone.
Evaluate construction and architecture.
Consider whether a single material is enough, or whether the device needs a composite structure or other additives or treatments to meet functional, mechanical, and durability targets.
Confirm processing and joining compatibility.
The selected material must support the intended manufacturing route, including extrusion or molding, achievable tolerances, moisture control, shrink behavior, and joining methods such as welding or reflow.
Assess regulatory and supply chain readiness.
That means looking at predicate devices with similar materials, supplier quality systems, notification-of-change policies, and the ability to support long-term production and regulatory needs.
Validate the full formulation as a system.
Additives, pigments, fillers, coatings, and surface treatments all need to be evaluated together, with testing that includes sterilization effects and aging, rather than being assessed one at a time.
From a risk standpoint, the best path is usually early screening followed by device-relevant bench testing, with
in vivo
studies where the application and regulatory pathway require them, before the design and supply chain are locked.
And in practice, the strongest programs treat material selection as a collaborative process. TPU performance reflects the interaction of chemistry, formulation, processing, and use conditions, so working with an experienced supplier can help reduce late-stage risk and support long-term device performance and compliance.
