## 3 Results
### Electrophysiological Phenotype of the Hybrid Model
Figure 2: Image of hiPSC-derived cortical neurons cultured on (control) polystyrene (**A**,**B**) and the MEA (**C**) showing eight endpoints measured in parallel as controls (**D**); (**A**) after 7 days of differentiation, cells were (immuno)histochemically stained for neuronal marker MAP2 (red), indicating a successful induction of a neuronal lineage (Magnification 10\(\times\)); (**B**) after 16 days (i.e., 7 days of differentiation and maintained for an additional 9 days in culture; DIV16), cells were (immuno) histochemically stained with markers for more mature neurons, including synaptophysin (red) and Beta tubulin III (green), and with nuclear marker DAPI (blue), indicating that the neurons matured and started to develop a network (Magnification 20\(\times\)); (**C**) bright field image of hiPSC-derived cortical neurons that were cultured for 16 days on a MEA, representing the stage as used for assembly with the biopsy (Magnification 20\(\times\)). All scale bars = 50 \(\mu\)m; (**D**) electrophysiological characterization of the control hiPSC-derived neuronal culture, measured at DIV16 (=before the assembly with the biopsy) and in parallel during the week of experiment (DIV0 to DIV6 neuronal cell + biopsy co-culture equivalent to DIV16 to DIV22 neuronal cell culture). Error bars represent mean with standard error of the mean (SEM) of three 2 min recordings per condition. To gain insight into the reproducibility of the model, a biopsy from another epilepsy patient was submitted to the same procedures. In this second case, the recorded electrical activity was similar to that of the first case, with the exception of ISI, which showed an inconsistent and less pronounced increase over days in culture (Supplementary Figure S2). Figure 3: Samples of electrophysiological activity in the hybrid model recorded by a 120-electrode MEA device one hour after assembly (DIV0). (**A**) Temporo-spatial distribution of neuronal activity (array wide raster plot) of a 2 min recording. Network burst activity (blue) suggests an epileptiform phenotype; (**B**) example of a single-channel full trace with detection threshold (7 RMS), and (**C**) the corresponding detected network bursts (black lines represent the blue lines in A and show the actual network bursting events). Red dots in (**C**) indicate detected single spikes. Figure 4: Electrophysiological recordings of the hybrid model one hour after assembly (DIV0) (**A**); at DIV3 (**B**) and at DIV6 (**C**). The left of each panel shows an array-wide rasterplot (120 electrodes on the Y-axis vs. time in seconds (s) on the X-axis), from which some epileptiform phenotypes were extracted (orange rectangles). The right of each panel represents a single-channel trace from the corresponding timeframe at a higher temporal resolution, showing voltage activity. This suggests that burst activity of 25\(-\)30 s can be detected for up to 3 days after resection of the biopsy and diminishes to bursts of 5 s by culture day 6; (**D**) Electrophysiological characterization (fire rate, burst rate and durations, isolated spikes, network bursts and durations, as well as ISI and cv of ISI) of the hybrid model, with biPSC neuronal derived cultures (DIV16) measured before and after biopsy assembly for 6 days (hiPSC + Biopsy, orange). Error bars represent mean with SEM of three 2 min recordings per condition. Figure 5: Electrophysiological characterization. (**A**) Fire rate, bursts and burst durations, isolated spikes, network bursts and durations, as well as ISI and cv of ISI of the hybrid model (hiPSC + Biopsy, orange),  
with hiPSC neuronal derived cultures (DIV16 = DIVO on graph) measured before and after biopsy assembly for 6 days and compared with the control hiPSC neuronal-derived cultures (DIV16) (hiPSC, blue) during the same 6-day period. Error bars represent mean with SEM of three 2 min recordings per condition.