Microfluidic Flow Simulations and Characterization of Conductive Hydrogels in a Gradient Generator
M.T. Bergman (TU Delft - Mechanical Engineering)
A. Savva – Mentor (TU Delft - Electrical Engineering, Mathematics and Computer Science)
L. Abelmann – Graduation committee member (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
Neurological conditions affect more than one in three people worldwide, yet effective treatments remain limited due to gaps in understanding of neuronal behaviour. More physiologically relevant in vitro models are therefore needed. Hydrogels are promising scaffolds for neural tissue engineering due to their soft mechanical properties and high water content, which closely mimic the native neural environment. Incorporating PEDOT:PSS into hydrogels introduces electrical conductivity while maintaining cytocompatibility. Since neurons in the body are exposed to gradients of electrical, mechanical and chemical cues, introducing a spatial conductivity gradient into conductive hydrogels may provide a more physiologically relevant platform for studying neuronal behaviour.
This thesis presents the design, fabrication and characterization of a microfluidic gradient generator for producing conductive hydrogel gradients. Computational fluid dynamics simulations were used to evaluate four gradient generator designs, comparing concentration uniformity and mixing behaviour for hydrogel precursors containing PEDOT:PSS. A symmetric outlet configuration with increased channel length and decreased channel width was selected as the optimal design and validated with FITC – Dextran experiments. These experiments showed agreement with the simulation results.
Three hydrogel systems, hyaluronic acid methacrylate (HAMA), gelatine methacryloid(GelMA) and alginate, were evaluated experimentally. An important finding was that crosslinking is essential for gradient stability. UV – crosslinked HAMA successfully immobilized PEDOT:PSS for at least one month, whereas uncrosslinked alginate showed redistribution of PEDOT:PSS within two days. Alginate experiments provided the clearest optical evidence of gradient formation, demonstrating a gradual increase in PEDOT:PSS concentration across the chamber length. EIS measurements were performed to find the conductivity at known concentrations of PEDOT:PSS. These showed that the majority of the alginate gradient has similar conductivity. However, direct electrical characterization remains as future work.
These results provide proof of concept that the microfluidic platform can generate concentration gradients of PEDOT:PSS in hydrogels. However, these resulted in a constant conductivity instead of a gradient. The main obstacles were related to hydrogel preparation, rather than fundamental limitations of the platform design. Direct electrical characterization remains as the next step to confirm whether the observed concentration gradient translates into a conductive gradient.