A. Savva
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1
Bioelectronic neural interfaces require materials that can bridge the gap between soft, hydrated biological tissue and conventional electronic systems. Conductive hydrogels are promising candidates because they combine the mechanical softness and hydration of hydrogels with electrical functionality.
In this thesis, PEDOT:PSS-based conductive hydrogels were developed and characterised as soft material candidates for bioelectronic neural interface applications. Three formulations were investigated: PEDOT:PSS-DBSA, PEDOT:PSS-PAA, and PEDOT:PSS-PEGPACHI. PEDOT:PSS-DBSA was used as a literature-based additive-induced hydrogel formulation, while PEDOT:PSS-PAA represented a polymer-network-based approach involving redox polymerisation, post-treatment, annealing, and rehydration. PEDOT:PSS-PEGPACHI was developed in this thesis as a new formulation based on PEDOT:PSS, phytic acid, chitosan, and PEGDE. The hydrogels were evaluated through physical observation, electrochemical impedance spectroscopy, cyclic voltammetry, nanoindentation, biological compatibility assessment, and preliminary device integration. The results showed that the gelation strategy and additive system strongly influenced the final material behaviour.
PEDOT:PSS-DBSA showed the strongest electrochemical response and the most uniform local mechanical behaviour, but was fragile during handling. PEDOT:PSS-PAA was more robust and easier to handle, but showed a weaker electrochemical response and greater local variability. PEDOT:PSS-PEGPACHI showed an intermediate electrochemical response, soft hydrogel-like mechanical behaviour, and favourable preliminary biological compatibility. Based on the combined material and biological assessments, PEDOT:PSS-PEGPACHI was selected for preliminary integration into a PDMS hydrogel array device. The formulation could be patterned into hydrogel tracks and electrically accessed after gelation and hydration, demonstrating its potential for future soft bioelectronic platforms.
Overall, this thesis demonstrates that PEDOT:PSS-based conductive hydrogels are promising materials for neural interface applications and identifies PEDOT:PSS-PEGPACHI as a strong candidate for further optimisation and biological validation. ...
In this thesis, PEDOT:PSS-based conductive hydrogels were developed and characterised as soft material candidates for bioelectronic neural interface applications. Three formulations were investigated: PEDOT:PSS-DBSA, PEDOT:PSS-PAA, and PEDOT:PSS-PEGPACHI. PEDOT:PSS-DBSA was used as a literature-based additive-induced hydrogel formulation, while PEDOT:PSS-PAA represented a polymer-network-based approach involving redox polymerisation, post-treatment, annealing, and rehydration. PEDOT:PSS-PEGPACHI was developed in this thesis as a new formulation based on PEDOT:PSS, phytic acid, chitosan, and PEGDE. The hydrogels were evaluated through physical observation, electrochemical impedance spectroscopy, cyclic voltammetry, nanoindentation, biological compatibility assessment, and preliminary device integration. The results showed that the gelation strategy and additive system strongly influenced the final material behaviour.
PEDOT:PSS-DBSA showed the strongest electrochemical response and the most uniform local mechanical behaviour, but was fragile during handling. PEDOT:PSS-PAA was more robust and easier to handle, but showed a weaker electrochemical response and greater local variability. PEDOT:PSS-PEGPACHI showed an intermediate electrochemical response, soft hydrogel-like mechanical behaviour, and favourable preliminary biological compatibility. Based on the combined material and biological assessments, PEDOT:PSS-PEGPACHI was selected for preliminary integration into a PDMS hydrogel array device. The formulation could be patterned into hydrogel tracks and electrically accessed after gelation and hydration, demonstrating its potential for future soft bioelectronic platforms.
Overall, this thesis demonstrates that PEDOT:PSS-based conductive hydrogels are promising materials for neural interface applications and identifies PEDOT:PSS-PEGPACHI as a strong candidate for further optimisation and biological validation. ...
Bioelectronic neural interfaces require materials that can bridge the gap between soft, hydrated biological tissue and conventional electronic systems. Conductive hydrogels are promising candidates because they combine the mechanical softness and hydration of hydrogels with electrical functionality.
In this thesis, PEDOT:PSS-based conductive hydrogels were developed and characterised as soft material candidates for bioelectronic neural interface applications. Three formulations were investigated: PEDOT:PSS-DBSA, PEDOT:PSS-PAA, and PEDOT:PSS-PEGPACHI. PEDOT:PSS-DBSA was used as a literature-based additive-induced hydrogel formulation, while PEDOT:PSS-PAA represented a polymer-network-based approach involving redox polymerisation, post-treatment, annealing, and rehydration. PEDOT:PSS-PEGPACHI was developed in this thesis as a new formulation based on PEDOT:PSS, phytic acid, chitosan, and PEGDE. The hydrogels were evaluated through physical observation, electrochemical impedance spectroscopy, cyclic voltammetry, nanoindentation, biological compatibility assessment, and preliminary device integration. The results showed that the gelation strategy and additive system strongly influenced the final material behaviour.
PEDOT:PSS-DBSA showed the strongest electrochemical response and the most uniform local mechanical behaviour, but was fragile during handling. PEDOT:PSS-PAA was more robust and easier to handle, but showed a weaker electrochemical response and greater local variability. PEDOT:PSS-PEGPACHI showed an intermediate electrochemical response, soft hydrogel-like mechanical behaviour, and favourable preliminary biological compatibility. Based on the combined material and biological assessments, PEDOT:PSS-PEGPACHI was selected for preliminary integration into a PDMS hydrogel array device. The formulation could be patterned into hydrogel tracks and electrically accessed after gelation and hydration, demonstrating its potential for future soft bioelectronic platforms.
Overall, this thesis demonstrates that PEDOT:PSS-based conductive hydrogels are promising materials for neural interface applications and identifies PEDOT:PSS-PEGPACHI as a strong candidate for further optimisation and biological validation.
In this thesis, PEDOT:PSS-based conductive hydrogels were developed and characterised as soft material candidates for bioelectronic neural interface applications. Three formulations were investigated: PEDOT:PSS-DBSA, PEDOT:PSS-PAA, and PEDOT:PSS-PEGPACHI. PEDOT:PSS-DBSA was used as a literature-based additive-induced hydrogel formulation, while PEDOT:PSS-PAA represented a polymer-network-based approach involving redox polymerisation, post-treatment, annealing, and rehydration. PEDOT:PSS-PEGPACHI was developed in this thesis as a new formulation based on PEDOT:PSS, phytic acid, chitosan, and PEGDE. The hydrogels were evaluated through physical observation, electrochemical impedance spectroscopy, cyclic voltammetry, nanoindentation, biological compatibility assessment, and preliminary device integration. The results showed that the gelation strategy and additive system strongly influenced the final material behaviour.
PEDOT:PSS-DBSA showed the strongest electrochemical response and the most uniform local mechanical behaviour, but was fragile during handling. PEDOT:PSS-PAA was more robust and easier to handle, but showed a weaker electrochemical response and greater local variability. PEDOT:PSS-PEGPACHI showed an intermediate electrochemical response, soft hydrogel-like mechanical behaviour, and favourable preliminary biological compatibility. Based on the combined material and biological assessments, PEDOT:PSS-PEGPACHI was selected for preliminary integration into a PDMS hydrogel array device. The formulation could be patterned into hydrogel tracks and electrically accessed after gelation and hydration, demonstrating its potential for future soft bioelectronic platforms.
Overall, this thesis demonstrates that PEDOT:PSS-based conductive hydrogels are promising materials for neural interface applications and identifies PEDOT:PSS-PEGPACHI as a strong candidate for further optimisation and biological validation.
Schizophrenia is a severe and highly heritable psychiatric disorder, and rare high-risk genetic variants provide important opportunities to investigate its underlying mechanisms. One such gene harbouring these rare variants is SETD1A, with heterozygous loss-of-function mutations causing haploinsufficiency and conferring a substantially increased risk of schizophrenia, alongside a broader neurodevelopmental phenotype. This study investigated the effects of a patient-relevant SETD1A loss-of-function mutation on axonal morphology and network-level electrophysiological activity in human induced pluripotent stem cell (hiPSC)-derived neurons.
SETD1A mutant and isogenic control hiPSC lines were differentiated into neurogenin-2 (Ngn2)-induced neurons and co-cultured with astrocytes. Electrophysiological activity was assessed using high-density microelectrode arrays (HD-MEAs), while axonal phenotypes were investigated using microfluidic microtunnel devices. In parallel, the Ngn2 differentiation protocol was optimized to improve culture robustness.
SETD1A haploinsufficiency was associated with reduced spontaneous
neuronal activity and altered burst organization without alterations in temporal firing regularity, whereas no detectable difference in distal axonal occupancy was observed between SETD1A haploinsufficient and isogenic control cultures. The differentiation protocol was improved by incorporation of a replating step, resulting in improved culture homogeneity, long-term stability, and electrophysiological activity, with the strongest effects observed in later-stage network-burst organization. Furthermore, the microfluidic platform was established as a tool for studying axonal phenotypes in human neurons, although complete compartmentalization was not achieved.
Together, these findings extend the electrophysiological characterization of SETD1A haploinsufficiency using HD-MEAs and provide an initial assessment of distal axonal occupancy in a human neuronal model. More broadly, the study provides insights into neuronal phenotypes associated with SETD1A haploinsufficiency, a schizophrenia-relevant genetic model, while highlighting methodological considerations important for human neuronal disease modelling.
...
SETD1A mutant and isogenic control hiPSC lines were differentiated into neurogenin-2 (Ngn2)-induced neurons and co-cultured with astrocytes. Electrophysiological activity was assessed using high-density microelectrode arrays (HD-MEAs), while axonal phenotypes were investigated using microfluidic microtunnel devices. In parallel, the Ngn2 differentiation protocol was optimized to improve culture robustness.
SETD1A haploinsufficiency was associated with reduced spontaneous
neuronal activity and altered burst organization without alterations in temporal firing regularity, whereas no detectable difference in distal axonal occupancy was observed between SETD1A haploinsufficient and isogenic control cultures. The differentiation protocol was improved by incorporation of a replating step, resulting in improved culture homogeneity, long-term stability, and electrophysiological activity, with the strongest effects observed in later-stage network-burst organization. Furthermore, the microfluidic platform was established as a tool for studying axonal phenotypes in human neurons, although complete compartmentalization was not achieved.
Together, these findings extend the electrophysiological characterization of SETD1A haploinsufficiency using HD-MEAs and provide an initial assessment of distal axonal occupancy in a human neuronal model. More broadly, the study provides insights into neuronal phenotypes associated with SETD1A haploinsufficiency, a schizophrenia-relevant genetic model, while highlighting methodological considerations important for human neuronal disease modelling.
...
Schizophrenia is a severe and highly heritable psychiatric disorder, and rare high-risk genetic variants provide important opportunities to investigate its underlying mechanisms. One such gene harbouring these rare variants is SETD1A, with heterozygous loss-of-function mutations causing haploinsufficiency and conferring a substantially increased risk of schizophrenia, alongside a broader neurodevelopmental phenotype. This study investigated the effects of a patient-relevant SETD1A loss-of-function mutation on axonal morphology and network-level electrophysiological activity in human induced pluripotent stem cell (hiPSC)-derived neurons.
SETD1A mutant and isogenic control hiPSC lines were differentiated into neurogenin-2 (Ngn2)-induced neurons and co-cultured with astrocytes. Electrophysiological activity was assessed using high-density microelectrode arrays (HD-MEAs), while axonal phenotypes were investigated using microfluidic microtunnel devices. In parallel, the Ngn2 differentiation protocol was optimized to improve culture robustness.
SETD1A haploinsufficiency was associated with reduced spontaneous
neuronal activity and altered burst organization without alterations in temporal firing regularity, whereas no detectable difference in distal axonal occupancy was observed between SETD1A haploinsufficient and isogenic control cultures. The differentiation protocol was improved by incorporation of a replating step, resulting in improved culture homogeneity, long-term stability, and electrophysiological activity, with the strongest effects observed in later-stage network-burst organization. Furthermore, the microfluidic platform was established as a tool for studying axonal phenotypes in human neurons, although complete compartmentalization was not achieved.
Together, these findings extend the electrophysiological characterization of SETD1A haploinsufficiency using HD-MEAs and provide an initial assessment of distal axonal occupancy in a human neuronal model. More broadly, the study provides insights into neuronal phenotypes associated with SETD1A haploinsufficiency, a schizophrenia-relevant genetic model, while highlighting methodological considerations important for human neuronal disease modelling.
SETD1A mutant and isogenic control hiPSC lines were differentiated into neurogenin-2 (Ngn2)-induced neurons and co-cultured with astrocytes. Electrophysiological activity was assessed using high-density microelectrode arrays (HD-MEAs), while axonal phenotypes were investigated using microfluidic microtunnel devices. In parallel, the Ngn2 differentiation protocol was optimized to improve culture robustness.
SETD1A haploinsufficiency was associated with reduced spontaneous
neuronal activity and altered burst organization without alterations in temporal firing regularity, whereas no detectable difference in distal axonal occupancy was observed between SETD1A haploinsufficient and isogenic control cultures. The differentiation protocol was improved by incorporation of a replating step, resulting in improved culture homogeneity, long-term stability, and electrophysiological activity, with the strongest effects observed in later-stage network-burst organization. Furthermore, the microfluidic platform was established as a tool for studying axonal phenotypes in human neurons, although complete compartmentalization was not achieved.
Together, these findings extend the electrophysiological characterization of SETD1A haploinsufficiency using HD-MEAs and provide an initial assessment of distal axonal occupancy in a human neuronal model. More broadly, the study provides insights into neuronal phenotypes associated with SETD1A haploinsufficiency, a schizophrenia-relevant genetic model, while highlighting methodological considerations important for human neuronal disease modelling.
Neural microelectrode arrays (MEAs) are moving from rigid silicon toward soft and transparent substrates, so that electrical recording and optical imaging of the same cells become possible. PDMS is attractive as a substrate because it is soft, biocompatible and transparent, and PEDOT:PSS is attractive as an electrode material because its volumetric capacitance gives a low interface impedance. However, combining the two is difficult in every aspect that matters for microfabrication: surface chemistry, thermomechanical behavior, and compatibility with standard cleanroom steps. Therefore, the process has to be developed rather than adapted from an existing flow. This thesis develops a complete microfabrication process for a transparent PDMS-based MEA with PEDOT:PSS electrodes.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed. ...
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed. ...
Neural microelectrode arrays (MEAs) are moving from rigid silicon toward soft and transparent substrates, so that electrical recording and optical imaging of the same cells become possible. PDMS is attractive as a substrate because it is soft, biocompatible and transparent, and PEDOT:PSS is attractive as an electrode material because its volumetric capacitance gives a low interface impedance. However, combining the two is difficult in every aspect that matters for microfabrication: surface chemistry, thermomechanical behavior, and compatibility with standard cleanroom steps. Therefore, the process has to be developed rather than adapted from an existing flow. This thesis develops a complete microfabrication process for a transparent PDMS-based MEA with PEDOT:PSS electrodes.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed.
Master thesis
(2026)
-
J.N. Obuseh, C.M. Boutry, A. Savva, M. J. Mirzaali, T.M. Lopes Marta da Costa
Peripheral nerve injury represents a persistent clinical burden, and severe transections still depend on autograft as the gold standard treatment despite their risk of donor-site morbidity. First-generation FDA-approved synthetic conduits remain hollow tubes that struggle to drive regeneration across critical gaps compared to autograft. Recent preclinical research shows a recurrence of filling implantable lumens with hydrogels because they provide compliant matrices to scaffold regenerating nerve tissue. This work builds on that approach while challenging the single homogeneous matrices that dominate the literature. When a human allograft is freeze-dried and imaged at micron resolution, what remains is an interconnected network whose walls define porous and heterogeneous microchannels extending in one elongated direction. If the benchmark graft is itself microstructurally graded network, then directional freeze-casting combined with additive manufacturing can supply a route to template distinct morphological regions, within one synthetic scaffold.
This work pursues this through a dual-material rational design. Poly(glycerol sebacate) acrylate (PGSA, E > 6 MPa) was DLP-printed into outer shells to approximate the whole-nerve scale, and co-cast gelatin methacryloyl (GelMA, 5% and 12.5% w/v) contributed at the endo-perineurial scale. A radial boundary was established from a highly compliant core (E≈ 200 Pa) to a stiffer boundary (E≈ 3.5 kPa), and constructs were subjected to directional freezing conditions at−20,−80 and−196∘ °C to
create elongated microstructures.
Freezing temperature and polymer concentration interacted significantly for both transverse pore density (p < 0.0001) and axial directionality (p = 0.006), demonstrating that cooling behaviour cannot not be generalised across biopolymer densities alone. During templating, 5% GelMA formed wide, macro-porous channels with longer absolute axial lengths (143.7–182.4 µm, mean AR≈ 1.8-2.2), whereas 12.5% GelMA formed tightly packed, microporous channels whose narrow transverse widths (5.3 µm at−80∘C) possessed high aspect ratios (mean AR = 14.78), but reduced longitudinal directionality. However, the 12.5% gels templated in extreme cryogenic conditions produced extreme aspect ratios (mean AR = 103.57) and unfragmented polymer walls. These heterogeneous pore architectures were shown to be preserved across shared interfaces within the same processing conditions. Initial in vitro cell attachment after 7 days demonstrated the preliminary cytocompatibility of the material system’s processing methods. By demonstrating this, this work can present a scalable method towards the manufacturing of hierarchical, anatomically graded nerve scaffolds.
...
This work pursues this through a dual-material rational design. Poly(glycerol sebacate) acrylate (PGSA, E > 6 MPa) was DLP-printed into outer shells to approximate the whole-nerve scale, and co-cast gelatin methacryloyl (GelMA, 5% and 12.5% w/v) contributed at the endo-perineurial scale. A radial boundary was established from a highly compliant core (E≈ 200 Pa) to a stiffer boundary (E≈ 3.5 kPa), and constructs were subjected to directional freezing conditions at−20,−80 and−196∘ °C to
create elongated microstructures.
Freezing temperature and polymer concentration interacted significantly for both transverse pore density (p < 0.0001) and axial directionality (p = 0.006), demonstrating that cooling behaviour cannot not be generalised across biopolymer densities alone. During templating, 5% GelMA formed wide, macro-porous channels with longer absolute axial lengths (143.7–182.4 µm, mean AR≈ 1.8-2.2), whereas 12.5% GelMA formed tightly packed, microporous channels whose narrow transverse widths (5.3 µm at−80∘C) possessed high aspect ratios (mean AR = 14.78), but reduced longitudinal directionality. However, the 12.5% gels templated in extreme cryogenic conditions produced extreme aspect ratios (mean AR = 103.57) and unfragmented polymer walls. These heterogeneous pore architectures were shown to be preserved across shared interfaces within the same processing conditions. Initial in vitro cell attachment after 7 days demonstrated the preliminary cytocompatibility of the material system’s processing methods. By demonstrating this, this work can present a scalable method towards the manufacturing of hierarchical, anatomically graded nerve scaffolds.
...
Peripheral nerve injury represents a persistent clinical burden, and severe transections still depend on autograft as the gold standard treatment despite their risk of donor-site morbidity. First-generation FDA-approved synthetic conduits remain hollow tubes that struggle to drive regeneration across critical gaps compared to autograft. Recent preclinical research shows a recurrence of filling implantable lumens with hydrogels because they provide compliant matrices to scaffold regenerating nerve tissue. This work builds on that approach while challenging the single homogeneous matrices that dominate the literature. When a human allograft is freeze-dried and imaged at micron resolution, what remains is an interconnected network whose walls define porous and heterogeneous microchannels extending in one elongated direction. If the benchmark graft is itself microstructurally graded network, then directional freeze-casting combined with additive manufacturing can supply a route to template distinct morphological regions, within one synthetic scaffold.
This work pursues this through a dual-material rational design. Poly(glycerol sebacate) acrylate (PGSA, E > 6 MPa) was DLP-printed into outer shells to approximate the whole-nerve scale, and co-cast gelatin methacryloyl (GelMA, 5% and 12.5% w/v) contributed at the endo-perineurial scale. A radial boundary was established from a highly compliant core (E≈ 200 Pa) to a stiffer boundary (E≈ 3.5 kPa), and constructs were subjected to directional freezing conditions at−20,−80 and−196∘ °C to
create elongated microstructures.
Freezing temperature and polymer concentration interacted significantly for both transverse pore density (p < 0.0001) and axial directionality (p = 0.006), demonstrating that cooling behaviour cannot not be generalised across biopolymer densities alone. During templating, 5% GelMA formed wide, macro-porous channels with longer absolute axial lengths (143.7–182.4 µm, mean AR≈ 1.8-2.2), whereas 12.5% GelMA formed tightly packed, microporous channels whose narrow transverse widths (5.3 µm at−80∘C) possessed high aspect ratios (mean AR = 14.78), but reduced longitudinal directionality. However, the 12.5% gels templated in extreme cryogenic conditions produced extreme aspect ratios (mean AR = 103.57) and unfragmented polymer walls. These heterogeneous pore architectures were shown to be preserved across shared interfaces within the same processing conditions. Initial in vitro cell attachment after 7 days demonstrated the preliminary cytocompatibility of the material system’s processing methods. By demonstrating this, this work can present a scalable method towards the manufacturing of hierarchical, anatomically graded nerve scaffolds.
This work pursues this through a dual-material rational design. Poly(glycerol sebacate) acrylate (PGSA, E > 6 MPa) was DLP-printed into outer shells to approximate the whole-nerve scale, and co-cast gelatin methacryloyl (GelMA, 5% and 12.5% w/v) contributed at the endo-perineurial scale. A radial boundary was established from a highly compliant core (E≈ 200 Pa) to a stiffer boundary (E≈ 3.5 kPa), and constructs were subjected to directional freezing conditions at−20,−80 and−196∘ °C to
create elongated microstructures.
Freezing temperature and polymer concentration interacted significantly for both transverse pore density (p < 0.0001) and axial directionality (p = 0.006), demonstrating that cooling behaviour cannot not be generalised across biopolymer densities alone. During templating, 5% GelMA formed wide, macro-porous channels with longer absolute axial lengths (143.7–182.4 µm, mean AR≈ 1.8-2.2), whereas 12.5% GelMA formed tightly packed, microporous channels whose narrow transverse widths (5.3 µm at−80∘C) possessed high aspect ratios (mean AR = 14.78), but reduced longitudinal directionality. However, the 12.5% gels templated in extreme cryogenic conditions produced extreme aspect ratios (mean AR = 103.57) and unfragmented polymer walls. These heterogeneous pore architectures were shown to be preserved across shared interfaces within the same processing conditions. Initial in vitro cell attachment after 7 days demonstrated the preliminary cytocompatibility of the material system’s processing methods. By demonstrating this, this work can present a scalable method towards the manufacturing of hierarchical, anatomically graded nerve scaffolds.
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.
...
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.
...
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.
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.
This thesis investigates whether shape memory polymers (SMPs) can serve as the basis of a removable smart stylet for cochlear implant (CI) electrode array (EA) insertion. The concept targets the advanced-off-stylet (AOS) technique, which uses a passive metallic stylet to straighten a pre-curved EA during perimodiolar placement. Despite its clinical adoption, this technique carries risks of tip fold-over and friction-induced force spikes that can cause intracochlear trauma. The proposed smart stylet addresses these limitations by replacing the passive stylet with an actively controllable SMP-based alternative. Rather than a single passive release, the smart stylet supports insertion, aims to reduce uncontrolled force spikes during withdrawal and can be reactivated in vivo to correct tip fold-over without revision surgery. To evaluate this concept, the research combined theoretical design criteria, COMSOL Multiphysics finite element modelling, polymer fabrication, and experimental validation. Two finite element models were developed to establish the quantitative design boundaries within which a functional SMP stylet must operate. A transient heat transfer model was developed based on a validated uncoiled cochlear geometry [1]. Using the CEM43 thermal dose criterion [2], this model revealed a clear trade-off between activation temperature and cochlear tissue safety. Activation temperatures equal to and above 44◦C reduced the safe heating window too strongly for practical surgical use. This established a target glass transition temperature range of 38− 44◦C for any candidate SMP material. Furthermore, a beam-based mechanical model quantified the minimum counter-moment required to maintain the pre-curved electrode array in a fully straightened configuration at 2.21· 10−5Nm [3]. The basal segment contributed approximately 67% of the total resistance. Together, these models determined the safe temperature window and mechanical boundary conditions under which the smart stylet concept can operate. Additionally, they established the quantitative constraints that guide minimal viable product creation later in this research.
In practice, a poly(ethylene glycol) diacrylate (PEGDA-400) / N-hydroxyethyl acrylamide (HEAA) / Irgacure 2959 formulation was selected as the only fabrication route achievable within the practical constraints of the Else Kooi Laboratory (EKL) at TU Delft. An initial wafer-based spin-coating approach proved unsuitable for the low-viscosity resin. Therefore, fabrication was successfully transitioned to a mould-based UV-curing method. The resulting specimens demonstrated an intrinsic SME under dry conditions, with a mean shape fixity ratio of 98.7 ± 1.0% and a mean shape recovery ratio of 97.7 ± 2.2% [4]. However, the formulation showed two fundamental limitations. The estimated dry glass transition temperature of the 55:45 PEGDA-400:HEAA specimens was−9.6 ± 1.1◦C, which lies far below the clinically required activation window [5, 6]. Furthermore, the transition temperature proved highly unstable under ambient humidity due to moisture plasticization [7]. Even more so, all specimen geometries fractured or dissolved under aqueous conditions due to swelling-induced stress and hydrolytic degradation of the acrylate ester network [8]. These failures were fundamental to the material chemistry and could not be resolved by extended UV post-curing. Overall, this thesis should be seen as a foundational feasibility study. The COMSOL models provide a clear quantitative design framework for future material selection. Additionally, the laboratory work confirms both the fabrication route and the basic shape memory mechanism of PEGDA-based covalent networks within the EKL infrastructure. However, the PEGDA-400/HEAA formulation is not suitable as a final clinical material for the smart stylet design. Future progress will depend primarily on selecting a more suitable SMP chemistry. One that achieves a wet Tg in the desired 38− 44◦C range, maintains structural integrity under aqueous conditions, and provides reliable actuation behaviour within the mechanical boundaries defined by this work. ...
In practice, a poly(ethylene glycol) diacrylate (PEGDA-400) / N-hydroxyethyl acrylamide (HEAA) / Irgacure 2959 formulation was selected as the only fabrication route achievable within the practical constraints of the Else Kooi Laboratory (EKL) at TU Delft. An initial wafer-based spin-coating approach proved unsuitable for the low-viscosity resin. Therefore, fabrication was successfully transitioned to a mould-based UV-curing method. The resulting specimens demonstrated an intrinsic SME under dry conditions, with a mean shape fixity ratio of 98.7 ± 1.0% and a mean shape recovery ratio of 97.7 ± 2.2% [4]. However, the formulation showed two fundamental limitations. The estimated dry glass transition temperature of the 55:45 PEGDA-400:HEAA specimens was−9.6 ± 1.1◦C, which lies far below the clinically required activation window [5, 6]. Furthermore, the transition temperature proved highly unstable under ambient humidity due to moisture plasticization [7]. Even more so, all specimen geometries fractured or dissolved under aqueous conditions due to swelling-induced stress and hydrolytic degradation of the acrylate ester network [8]. These failures were fundamental to the material chemistry and could not be resolved by extended UV post-curing. Overall, this thesis should be seen as a foundational feasibility study. The COMSOL models provide a clear quantitative design framework for future material selection. Additionally, the laboratory work confirms both the fabrication route and the basic shape memory mechanism of PEGDA-based covalent networks within the EKL infrastructure. However, the PEGDA-400/HEAA formulation is not suitable as a final clinical material for the smart stylet design. Future progress will depend primarily on selecting a more suitable SMP chemistry. One that achieves a wet Tg in the desired 38− 44◦C range, maintains structural integrity under aqueous conditions, and provides reliable actuation behaviour within the mechanical boundaries defined by this work. ...
This thesis investigates whether shape memory polymers (SMPs) can serve as the basis of a removable smart stylet for cochlear implant (CI) electrode array (EA) insertion. The concept targets the advanced-off-stylet (AOS) technique, which uses a passive metallic stylet to straighten a pre-curved EA during perimodiolar placement. Despite its clinical adoption, this technique carries risks of tip fold-over and friction-induced force spikes that can cause intracochlear trauma. The proposed smart stylet addresses these limitations by replacing the passive stylet with an actively controllable SMP-based alternative. Rather than a single passive release, the smart stylet supports insertion, aims to reduce uncontrolled force spikes during withdrawal and can be reactivated in vivo to correct tip fold-over without revision surgery. To evaluate this concept, the research combined theoretical design criteria, COMSOL Multiphysics finite element modelling, polymer fabrication, and experimental validation. Two finite element models were developed to establish the quantitative design boundaries within which a functional SMP stylet must operate. A transient heat transfer model was developed based on a validated uncoiled cochlear geometry [1]. Using the CEM43 thermal dose criterion [2], this model revealed a clear trade-off between activation temperature and cochlear tissue safety. Activation temperatures equal to and above 44◦C reduced the safe heating window too strongly for practical surgical use. This established a target glass transition temperature range of 38− 44◦C for any candidate SMP material. Furthermore, a beam-based mechanical model quantified the minimum counter-moment required to maintain the pre-curved electrode array in a fully straightened configuration at 2.21· 10−5Nm [3]. The basal segment contributed approximately 67% of the total resistance. Together, these models determined the safe temperature window and mechanical boundary conditions under which the smart stylet concept can operate. Additionally, they established the quantitative constraints that guide minimal viable product creation later in this research.
In practice, a poly(ethylene glycol) diacrylate (PEGDA-400) / N-hydroxyethyl acrylamide (HEAA) / Irgacure 2959 formulation was selected as the only fabrication route achievable within the practical constraints of the Else Kooi Laboratory (EKL) at TU Delft. An initial wafer-based spin-coating approach proved unsuitable for the low-viscosity resin. Therefore, fabrication was successfully transitioned to a mould-based UV-curing method. The resulting specimens demonstrated an intrinsic SME under dry conditions, with a mean shape fixity ratio of 98.7 ± 1.0% and a mean shape recovery ratio of 97.7 ± 2.2% [4]. However, the formulation showed two fundamental limitations. The estimated dry glass transition temperature of the 55:45 PEGDA-400:HEAA specimens was−9.6 ± 1.1◦C, which lies far below the clinically required activation window [5, 6]. Furthermore, the transition temperature proved highly unstable under ambient humidity due to moisture plasticization [7]. Even more so, all specimen geometries fractured or dissolved under aqueous conditions due to swelling-induced stress and hydrolytic degradation of the acrylate ester network [8]. These failures were fundamental to the material chemistry and could not be resolved by extended UV post-curing. Overall, this thesis should be seen as a foundational feasibility study. The COMSOL models provide a clear quantitative design framework for future material selection. Additionally, the laboratory work confirms both the fabrication route and the basic shape memory mechanism of PEGDA-based covalent networks within the EKL infrastructure. However, the PEGDA-400/HEAA formulation is not suitable as a final clinical material for the smart stylet design. Future progress will depend primarily on selecting a more suitable SMP chemistry. One that achieves a wet Tg in the desired 38− 44◦C range, maintains structural integrity under aqueous conditions, and provides reliable actuation behaviour within the mechanical boundaries defined by this work.
In practice, a poly(ethylene glycol) diacrylate (PEGDA-400) / N-hydroxyethyl acrylamide (HEAA) / Irgacure 2959 formulation was selected as the only fabrication route achievable within the practical constraints of the Else Kooi Laboratory (EKL) at TU Delft. An initial wafer-based spin-coating approach proved unsuitable for the low-viscosity resin. Therefore, fabrication was successfully transitioned to a mould-based UV-curing method. The resulting specimens demonstrated an intrinsic SME under dry conditions, with a mean shape fixity ratio of 98.7 ± 1.0% and a mean shape recovery ratio of 97.7 ± 2.2% [4]. However, the formulation showed two fundamental limitations. The estimated dry glass transition temperature of the 55:45 PEGDA-400:HEAA specimens was−9.6 ± 1.1◦C, which lies far below the clinically required activation window [5, 6]. Furthermore, the transition temperature proved highly unstable under ambient humidity due to moisture plasticization [7]. Even more so, all specimen geometries fractured or dissolved under aqueous conditions due to swelling-induced stress and hydrolytic degradation of the acrylate ester network [8]. These failures were fundamental to the material chemistry and could not be resolved by extended UV post-curing. Overall, this thesis should be seen as a foundational feasibility study. The COMSOL models provide a clear quantitative design framework for future material selection. Additionally, the laboratory work confirms both the fabrication route and the basic shape memory mechanism of PEGDA-based covalent networks within the EKL infrastructure. However, the PEGDA-400/HEAA formulation is not suitable as a final clinical material for the smart stylet design. Future progress will depend primarily on selecting a more suitable SMP chemistry. One that achieves a wet Tg in the desired 38− 44◦C range, maintains structural integrity under aqueous conditions, and provides reliable actuation behaviour within the mechanical boundaries defined by this work.
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. ...
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.
Electric stimulation can be used to get cells to behave in all kinds of ways. Examples include getting them to move, proliferate, excrete chemicals, or stop doing any of these things. However, finding the optimal stimulation parameters is a tedious process of trial and error which is made difficult by the equipment that is currently in use. It is often bulky, expensive and only allows for a limited number of experiments to be done simultaneously. To combat this issue, this work aims to create a circuit that allows the simultaneous stimulation of as many different channels of cells as possible without causing accidental damage to the cells through harmful electrochemical reactions. To this end, a printed circuit board is designed to fit underneath a 48-well plate. It can set the waveform timing to be a square wave with variable frequency, duty cycle and amplitude with different settings for the positive and negative part of stimulation. To create this device, research is done to the state of art of the current devices used to stimulate cells. As well as the viability of stainless-steel as a cheaper alternative reference electrode material with respect to platinum and Ag/AgCl electrodes. While the stimulation part of the design works, the charge balancing circuit does not and requires more work.
...
Electric stimulation can be used to get cells to behave in all kinds of ways. Examples include getting them to move, proliferate, excrete chemicals, or stop doing any of these things. However, finding the optimal stimulation parameters is a tedious process of trial and error which is made difficult by the equipment that is currently in use. It is often bulky, expensive and only allows for a limited number of experiments to be done simultaneously. To combat this issue, this work aims to create a circuit that allows the simultaneous stimulation of as many different channels of cells as possible without causing accidental damage to the cells through harmful electrochemical reactions. To this end, a printed circuit board is designed to fit underneath a 48-well plate. It can set the waveform timing to be a square wave with variable frequency, duty cycle and amplitude with different settings for the positive and negative part of stimulation. To create this device, research is done to the state of art of the current devices used to stimulate cells. As well as the viability of stainless-steel as a cheaper alternative reference electrode material with respect to platinum and Ag/AgCl electrodes. While the stimulation part of the design works, the charge balancing circuit does not and requires more work.
Neurons are fundamental to cognitive and motor functions, relying on intricate electrical and chemical signaling. However, neurological diseases such as Parkinson’s, Alzheimer’s, and Amyotrophic Lateral Sclerosis impair neural function, posing a growing challenge due to aging populations and limited regenerative capacity of the nervous system. Advances in induced pluripotent stem cells (iPSCs) have enabled human-derived neuronal models for disease study, while neural interfaces, particularly microelectrode arrays (MEAs), facilitate electrophysiological investigation both in vivo and in vitro.
This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.
First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.
Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.
Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.
Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.
...
This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.
First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.
Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.
Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.
Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.
...
Neurons are fundamental to cognitive and motor functions, relying on intricate electrical and chemical signaling. However, neurological diseases such as Parkinson’s, Alzheimer’s, and Amyotrophic Lateral Sclerosis impair neural function, posing a growing challenge due to aging populations and limited regenerative capacity of the nervous system. Advances in induced pluripotent stem cells (iPSCs) have enabled human-derived neuronal models for disease study, while neural interfaces, particularly microelectrode arrays (MEAs), facilitate electrophysiological investigation both in vivo and in vitro.
This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.
First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.
Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.
Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.
Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.
This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.
First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.
Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.
Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.
Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.
Neurostimulation has emerged as a transformative approach for the treatment and management of a broad range of neurological disorders, including depression and epilepsy. The increase in usage of neurostimulation also necessitates high spatial resolution and depth of penetration in order to inflict minimal damage to the surrounding tissue. Optical or light-based stimulation offers unique benefits in this regard, enabling highly spatially resolved neural activation and paving the way for innovative modalities in targeted neural modulation.
In this work, an electronic platform for wireless powering and data transmission is presented,
utilising organic P–N junctions as the core technology for mediating photo-electric stimulation. These junctions are selected for their capacity to provide non-genetic neural activation with excellent spatial resolution. Power delivery to the implantable device is achieved acoustically via ultrasound, taking advantage of ultrasound’s superior tissue penetration characteristics.
Comprehensive characterisation of the organic P–N junctions was performed, culminating in
the identification of the PDCBT/ITIC architecture as the most suitable P-N junction, based on its
favourable optical absorption profile and photocurrent generation capability. In parallel, a dedicated power management and stimulation platform was developed as the initial steps in incorporating acoustic energy harvesting and efficient signal demodulation. Validation experiments confirmed reliable device performance and established a functional basis for wireless optoelectronic neurostimulation.
The results of this thesis establish a promising system-level paradigm for minimally invasive,
wirelessly powered neurostimulation using organic photo-sensitive interfaces and acoustic power links. This approach contributes a viable pathway toward the development of next-generation neural therapies with enhanced implantability. ...
In this work, an electronic platform for wireless powering and data transmission is presented,
utilising organic P–N junctions as the core technology for mediating photo-electric stimulation. These junctions are selected for their capacity to provide non-genetic neural activation with excellent spatial resolution. Power delivery to the implantable device is achieved acoustically via ultrasound, taking advantage of ultrasound’s superior tissue penetration characteristics.
Comprehensive characterisation of the organic P–N junctions was performed, culminating in
the identification of the PDCBT/ITIC architecture as the most suitable P-N junction, based on its
favourable optical absorption profile and photocurrent generation capability. In parallel, a dedicated power management and stimulation platform was developed as the initial steps in incorporating acoustic energy harvesting and efficient signal demodulation. Validation experiments confirmed reliable device performance and established a functional basis for wireless optoelectronic neurostimulation.
The results of this thesis establish a promising system-level paradigm for minimally invasive,
wirelessly powered neurostimulation using organic photo-sensitive interfaces and acoustic power links. This approach contributes a viable pathway toward the development of next-generation neural therapies with enhanced implantability. ...
Neurostimulation has emerged as a transformative approach for the treatment and management of a broad range of neurological disorders, including depression and epilepsy. The increase in usage of neurostimulation also necessitates high spatial resolution and depth of penetration in order to inflict minimal damage to the surrounding tissue. Optical or light-based stimulation offers unique benefits in this regard, enabling highly spatially resolved neural activation and paving the way for innovative modalities in targeted neural modulation.
In this work, an electronic platform for wireless powering and data transmission is presented,
utilising organic P–N junctions as the core technology for mediating photo-electric stimulation. These junctions are selected for their capacity to provide non-genetic neural activation with excellent spatial resolution. Power delivery to the implantable device is achieved acoustically via ultrasound, taking advantage of ultrasound’s superior tissue penetration characteristics.
Comprehensive characterisation of the organic P–N junctions was performed, culminating in
the identification of the PDCBT/ITIC architecture as the most suitable P-N junction, based on its
favourable optical absorption profile and photocurrent generation capability. In parallel, a dedicated power management and stimulation platform was developed as the initial steps in incorporating acoustic energy harvesting and efficient signal demodulation. Validation experiments confirmed reliable device performance and established a functional basis for wireless optoelectronic neurostimulation.
The results of this thesis establish a promising system-level paradigm for minimally invasive,
wirelessly powered neurostimulation using organic photo-sensitive interfaces and acoustic power links. This approach contributes a viable pathway toward the development of next-generation neural therapies with enhanced implantability.
In this work, an electronic platform for wireless powering and data transmission is presented,
utilising organic P–N junctions as the core technology for mediating photo-electric stimulation. These junctions are selected for their capacity to provide non-genetic neural activation with excellent spatial resolution. Power delivery to the implantable device is achieved acoustically via ultrasound, taking advantage of ultrasound’s superior tissue penetration characteristics.
Comprehensive characterisation of the organic P–N junctions was performed, culminating in
the identification of the PDCBT/ITIC architecture as the most suitable P-N junction, based on its
favourable optical absorption profile and photocurrent generation capability. In parallel, a dedicated power management and stimulation platform was developed as the initial steps in incorporating acoustic energy harvesting and efficient signal demodulation. Validation experiments confirmed reliable device performance and established a functional basis for wireless optoelectronic neurostimulation.
The results of this thesis establish a promising system-level paradigm for minimally invasive,
wirelessly powered neurostimulation using organic photo-sensitive interfaces and acoustic power links. This approach contributes a viable pathway toward the development of next-generation neural therapies with enhanced implantability.
Organic electrochemical transistors (OECTs) are a promising technology in the field of bioelectronics. They bridge electronics and biology through their ability to operate in aqueous environments. Their ability to transduce biological signals into electronic ones makes them a preferred choice for bioelectronic applications, such as biosensing and neural interfaces. While p-type materials like PEDOT:PSS have become the benchmark for the OECT performance, the development of stable, high-mobility n-type channel materials remains a major challenge. These materials are often limited by poor air stability, low electron mobility, and restricted ionic transport. In this work, a newly developed semiconducting n-type polymer with cleavable side chains is investigated. The polymer, YYBC, undergoes a post-deposition thermal treatment, which leads to a porous, more hydrophilic polymer, YYAC. This cleaved version aims to improve the performance of an n-type OECT.
The research followed three main objectives. OECT devices were first fabricated in a cleanroom environment, then a measurement setup for steady-state and transient characterization was developed, and lastly, the new n-type polymer was evaluated. For device fabrication, standard microfabrication methods were employed. For the measurement setup, programmable source-measure units, a function generator, and an oscilloscope were controlled through MATLAB for data acquisition and analysis. Lastly, the performance of the n-type polymer was assessed using electrochemical and electrical characterization. Parameters such as volumetric capacitance, transconductance, and time response were evaluated.
Results of this work show that the post-deposition side-chain removal significantly improves the polymer’s electrochemical behaviour. The findings show improved performance metrics, indicating that the new n-type polymer can be a promising material for future OECT applications. ...
The research followed three main objectives. OECT devices were first fabricated in a cleanroom environment, then a measurement setup for steady-state and transient characterization was developed, and lastly, the new n-type polymer was evaluated. For device fabrication, standard microfabrication methods were employed. For the measurement setup, programmable source-measure units, a function generator, and an oscilloscope were controlled through MATLAB for data acquisition and analysis. Lastly, the performance of the n-type polymer was assessed using electrochemical and electrical characterization. Parameters such as volumetric capacitance, transconductance, and time response were evaluated.
Results of this work show that the post-deposition side-chain removal significantly improves the polymer’s electrochemical behaviour. The findings show improved performance metrics, indicating that the new n-type polymer can be a promising material for future OECT applications. ...
Organic electrochemical transistors (OECTs) are a promising technology in the field of bioelectronics. They bridge electronics and biology through their ability to operate in aqueous environments. Their ability to transduce biological signals into electronic ones makes them a preferred choice for bioelectronic applications, such as biosensing and neural interfaces. While p-type materials like PEDOT:PSS have become the benchmark for the OECT performance, the development of stable, high-mobility n-type channel materials remains a major challenge. These materials are often limited by poor air stability, low electron mobility, and restricted ionic transport. In this work, a newly developed semiconducting n-type polymer with cleavable side chains is investigated. The polymer, YYBC, undergoes a post-deposition thermal treatment, which leads to a porous, more hydrophilic polymer, YYAC. This cleaved version aims to improve the performance of an n-type OECT.
The research followed three main objectives. OECT devices were first fabricated in a cleanroom environment, then a measurement setup for steady-state and transient characterization was developed, and lastly, the new n-type polymer was evaluated. For device fabrication, standard microfabrication methods were employed. For the measurement setup, programmable source-measure units, a function generator, and an oscilloscope were controlled through MATLAB for data acquisition and analysis. Lastly, the performance of the n-type polymer was assessed using electrochemical and electrical characterization. Parameters such as volumetric capacitance, transconductance, and time response were evaluated.
Results of this work show that the post-deposition side-chain removal significantly improves the polymer’s electrochemical behaviour. The findings show improved performance metrics, indicating that the new n-type polymer can be a promising material for future OECT applications.
The research followed three main objectives. OECT devices were first fabricated in a cleanroom environment, then a measurement setup for steady-state and transient characterization was developed, and lastly, the new n-type polymer was evaluated. For device fabrication, standard microfabrication methods were employed. For the measurement setup, programmable source-measure units, a function generator, and an oscilloscope were controlled through MATLAB for data acquisition and analysis. Lastly, the performance of the n-type polymer was assessed using electrochemical and electrical characterization. Parameters such as volumetric capacitance, transconductance, and time response were evaluated.
Results of this work show that the post-deposition side-chain removal significantly improves the polymer’s electrochemical behaviour. The findings show improved performance metrics, indicating that the new n-type polymer can be a promising material for future OECT applications.
Multi-material 4D-printing of a Magneto-responsive Hydrogel Scaffold with Tuned Stiffness
An approach to locally stimulate a hydrogel scaffold using uniaxial static magnetic fields
Master thesis
(2024)
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Elio Çinar San Segundo, M. J. Mirzaali, E.L. Fratila-Apachitei, S. Safarloo, A.A. Zadpoor, A. Savva, P. Boukany, K. Tufekci
The physical, chemical, and biological versatility and high water content of hydrogels have been taken advantage of to fabricate hydrogels that mimic the extracellular matrix (ECM) structure of native tissues and applied in the field of cell and tissue engineering to provide the cells with a 3D scaffold structure. Especially in tissue engineering, the creation of a suitable hydrogel scaffold with hard and soft interfaces that is capable of both supporting cell growth and stimulation for guided differentiation for tissue interface studies is a primary concern for advancements in tissue engineering. The ideal scaffold with hard and soft interfaces can be achieved by finetuning its biological, biochemical, structural, and mechanical properties for optimal cell proliferation and differentiation.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other. ...
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other. ...
The physical, chemical, and biological versatility and high water content of hydrogels have been taken advantage of to fabricate hydrogels that mimic the extracellular matrix (ECM) structure of native tissues and applied in the field of cell and tissue engineering to provide the cells with a 3D scaffold structure. Especially in tissue engineering, the creation of a suitable hydrogel scaffold with hard and soft interfaces that is capable of both supporting cell growth and stimulation for guided differentiation for tissue interface studies is a primary concern for advancements in tissue engineering. The ideal scaffold with hard and soft interfaces can be achieved by finetuning its biological, biochemical, structural, and mechanical properties for optimal cell proliferation and differentiation.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other.