ISBN 9783843957984

978-3-8439-5798-4, Reihe Mikrosystemtechnik

Ali Sharbatian
Redefining and Refining Biocompatibility in the Context of Neural Implants

211 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2026), Softcover, B5

Zusammenfassung / Abstract

This work re-examines how biocompatibility is defined and measured for chronically implanted neural devices. Established standards, in particular capsule-thickness criteria, evaluate a dynamic tissue process through a single static endpoint. As an alternative readout, this work proposes the molecular weight of hyaluronic acid (HA), a principal component of the brain extracellular matrix, as a barometer of tissue state: high-molecular-weight HA is associated with homeostasis through CD44, whereas low-molecular-weight fragments act as damage-associated molecular patterns through TLR2 and TLR4.

A weighted gene co-expression network analysis of public transcriptomic datasets from brain and spinal cord injury identifies a conserved, HA-centred programme of extracellular matrix remodelling with injury-specific temporal dynamics. These molecular findings are translated into device engineering along two lines. Non-wettable, microstructured probe surfaces with re-entrant geometries were fabricated by two-photon lithography and retained air-liquid interfaces in 65 percent of cavities after 24 hours of immersion in deionised water. Finite element analysis of probe-tissue mechanics shows that smaller-diameter probes reduce the tissue volume above the 5 percent strain threshold within the critical 60 micrometre peri-electrode zone, and challenges the use of that threshold as a standalone damage metric. A concluding integrative study combines neural cell culture on the engineered surfaces with micromotion simulation of the same geometries.