Thermoplastic polyurethane as a base material for soft, high-density neural interfaces
- 1Department of Microelectronics, Delft University of Technology, Delft, The Netherlands
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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BibTeX
@misc{pak2026thermoplastic,
title = {{Thermoplastic polyurethane as a base material for soft, high-density neural interfaces}},
author = {A. Pak and A. I. Velea and T. Hosman and J. Wilson and R. Panskus and M. Seckel and P. de Anta Dardagan and R. Schmidt and D. Horvath and K. Toth and D. Meszena and A. Gollhardt and N. Bakhshaee Babaroud and B. Pahl and E. Zingkou and A. Kolianou and G. Sotiropoulou and S. Negi and F. Solzbacher and C. Kallmayer and I. Ulbert and V. Giagka},
howpublished = {bioRxiv},
year = {2026},
month = oct,
doi = {10.64898/2026.10.04.755411},
url = {https://www.biorxiv.org/content/10.64898/2026.10.04.755411v1},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - Thermoplastic polyurethane as a base material for soft, high-density neural interfaces
AU - A. Pak
AU - A. I. Velea
AU - T. Hosman
AU - J. Wilson
AU - R. Panskus
AU - M. Seckel
AU - P. de Anta Dardagan
AU - R. Schmidt
AU - D. Horvath
AU - K. Toth
AU - D. Meszena
AU - A. Gollhardt
AU - N. Bakhshaee Babaroud
AU - B. Pahl
AU - E. Zingkou
AU - A. Kolianou
AU - G. Sotiropoulou
AU - S. Negi
AU - F. Solzbacher
AU - C. Kallmayer
AU - I. Ulbert
AU - V. Giagka
PY - 2026
DA - 2026/10/04
PB - bioRxiv
DO - 10.64898/2026.10.04.755411
UR - https://www.biorxiv.org/content/10.64898/2026.10.04.755411v1
AB - 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.
ER -