Thermoplastic polyurethane as a base material for soft, high-density neural interfaces

Pak, A.; Velea, A. I.; Hosman, T.; Wilson, J.; Panskus, R.; Seckel, M.; de Anta Dardagan, P.; Schmidt, R.; Horvath, D.; Toth, K.; Meszena, D.; Gollhardt, A.; Bakhshaee Babaroud, N.; Pahl, B.; Zingkou, E.; Kolianou, A.; Sotiropoulou, G.; Negi, S.; Solzbacher, F.; Kallmayer, C.; Ulbert, I.; Giagka, V.

doi:10.64898/2026.10.04.755411

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bioRxiv · 10.64898/2026.10.04.755411

Thermoplastic polyurethane as a base material for soft, high-density neural interfaces

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Abstract

Polymers used as substrate and encapsulation for implantable devices are typically deposited layer-by-layer, leaving polymer-polymer interfaces that adhere poorly and become a critical failure point. Thermoplastic polyurethane (TPU) elastomers combine four properties not found together in any other candidate: decades of clinical use in long-term implants and availability in medical grade, a stiffness well below that of polyimide and parylene C, compatibility with microfabrication, and thermoplastic self-fusion, which removes the polymer-polymer interface entirely. This work introduces TPU as a base material for soft, high-density neural interfaces and demonstrates one route to realizing them. Gold is patterned on a sacrificial copper sheet by maskless lithography and transferred into TPU by vacuum lamination, giving conformally coated tracks down to 15 um at 30 um pitch within a single, merged polymer body. An additional electroplating step produces a nanostructured pinecone gold surface that increases the electrochemically active area of the electrodes, approximately doubling the charge injection capacity. Daisy-chain silicon chips were also embedded within the soft polymer body. The films transmit up to 88% at 470 nm, a wavelength commonly used for optogenetics. TPU showed no cytotoxicity towards differentiated SH-SY5Y cells and only a mild tissue response after 9.5 months of subcutaneous implantation in rats.

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Pak, A., Velea, A. I., Hosman, T., Wilson, J., Panskus, R., Seckel, M., de Anta Dardagan, P., Schmidt, R., Horvath, D., Toth, K., Meszena, D., Gollhardt, A., Bakhshaee Babaroud, N., Pahl, B., Zingkou, E., Kolianou, A., Sotiropoulou, G., Negi, S., Solzbacher, F., Kallmayer, C., Ulbert, I., Giagka, V.. 2026-10-13. Thermoplastic polyurethane as a base material for soft, high-density neural interfaces. https://doi.org/10.64898/2026.10.04.755411

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