PDMS-based platforms for in vitro neural cultures and axon guidance
Y. a PENG (TU Delft - Mechanical Engineering)
A. Savva – Mentor (TU Delft - Bio-Electronics)
Paola Fanzio – Graduation committee member (TU Delft - Micro and Nano Engineering)
C. M. Boutry – Graduation committee member (TU Delft - Electronic Components, Technology and Materials)
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Abstract
Microfluidic
platforms that physically guide axons enable controlled studies of neuronal
connectivity, injury, and regeneration in vitro. This thesis investigates two
fabrication routes for Polydimethylsiloxane (PDMS)-based axon-guidance
structures: direct ink writing of printable PDMS inks and cleanroom microfabrication
using photolithography and DRIE, with the goal of achieving high-aspect-ratio
and high-density features suitable for neuronal applications. Printable PDMS
inks were formulated by blending shear-thinning SE1700 with Sylgard 184 at varying
ratios and characterized by shear viscosity and oscillatory rheology at 25 °C.
SE1700-containing blends exhibited pronounced shear thinning and gel-like
behavior (G′ > G″) in the linear viscoelastic regime. DIW printability was
assessed via dual-layer tests and filament-width analysis under different nozzle
sizes, speeds, and displacements. The 8:2 ink provided the best balance between
extrusion and shape retention; however, multilayer pores still showed sagging
or merging depending on overhang span and dose, and dimensional errors on
printed microchannels ranged from 32 to 157 µm depending on geometry. Additionally,
microfabrication produced high-aspect-ratio features on silicon using positive
and negative routes. PDMS–PDMS double casting from positive molds revealed
failure modes—lateral collapse and longitudinal tearing, in dense, narrow
structures during demolding. Direct PDMS casting from negative silicon molds
improved geometric fidelity and avoided tearing; measured aspect ratio is close
to the wafer values and spontaneous collapse was not observed after demolding. Overall,
DIW enables fast, mold-free prototyping but is limited in resolution and
multilayer fidelity; microfabrication delivers micron-precision HAR arrays but
entails higher process complexity and demolding risks for dense features. The
results outline practical design and process for building PDMS platforms that
can be further integrated with MEAs for functional neural studies.