NLMD65 series: aliphatic polycarbonate TPU for long-term implantation

Three backbones, three failure modes

Almost every medical TPU decision reduces to a choice between three soft-segment chemistries, because the soft segment decides how the polymer dies.

• Polyester — excellent mechanical strength, oil and abrasion resistance, but the ester bond hydrolyses. It is the wrong choice for steam sterilisation or long wet contact.
• Polyether — good hydrolysis resistance and flexibility, but polyether soft segments are vulnerable to oxidative attack, which is the dominant degradation route in a long-implant blood-contact device.
• Polycarbonate — no ester linkage to hydrolyse and a soft segment substantially more resistant to oxidation than polyether. This is the backbone for devices that stay in place.

Why aliphatic hard segments matter here

Conventional TPU hard segments are built on aromatic diisocyanate. Under long-term exposure to body fluid, oxidation and sterilisation, aromatic structures are the ones that generate degradable species and, in the worst case, potentially carcinogenic aromatic amine residues.

An aliphatic hard segment removes that route. The trade-off is real — aliphatic systems are more expensive and harder to process than aromatic ones — but for a device that must sit in the vasculature for months, it is the difference between a material with a defined degradation pathway and one with an undefined one.

What the NLMD65 series is

The NLMD65 series is an aliphatic polycarbonate TPU built for long-term implantation: vascular catheters, implantable components and balloon substrates. Three hardness points are standard — NLMD6575A at 75A, NLMD6585A at 85A and NLMD6595A at 95A — and each is available with a barium sulphate radiopacity option.

Because the aliphatic polycarbonate platform is the same across the three, a device family can move between durometers without changing its chemical basis, which keeps the biological evaluation and the change-control file on familiar ground.

Performance in a blood-contact environment

• Oxidative stability — retains physical and chemical properties under long-term exposure to body fluid and to sterilisation.
• Hydrolytic stability — no ester linkage, so no bulk hydrolysis over a multi-year implant life.
• Biocompatibility — implant-grade testing, with 52-week intramuscular data on the 95A point showing an irritation index of 0.0 against a negative control.
• Customisation — hardness, colour and radiopacity specified per device, rather than picked from a fixed catalogue.

Processing and sterilisation

The series extrudes and injection moulds on standard TPU equipment. It tolerates the sterilisation routes used for implantable devices — the specific method should be agreed before qualification, because irradiation and ethylene oxide loading both interact with the stabiliser package, and the effect on a 75A shaft is not the same as on a 95A hub.

For tubing, the practical limits are draw-down ratio and die swell at the soft end; for balloons, they are wall-thickness uniformity at the blow ratio the device needs. Both are better resolved with trial material than with a datasheet.

Selection note

Aliphatic polycarbonate is the default for long-term implant, not the universal answer. Short-contact devices, guidewire jackets that need maximum stiffness, and single-use moulded components are usually better served by an aromatic polyether or polyester grade at lower cost.

For devices combining a soft tip with a rigid proximal section, the 75A / 85A / 95A ladder covers most shaft and hub combinations from one chemistry. Confirm the exact grade against the current TDS and the device's own biological evaluation.