Flexible Microelectrode Arrays

Developing chronic neural interfaces has been one primary objective of the field of neuroprosthetic. However, currently available interfaces result in severe foreign body responses (FBR) and their performance degrade over time. With respect to the mechanical properties, the mechanical mismatch of the soft brain tissue and the rigid neural implant was one the first properties of the probe which researcher focused on to improve. The key finding of such endeavour was that flexible probes decrease the strain and result in increased neuronal viability, and in short, they are better. So, the logic might follow that the more flexible the electrode, the more reliable the chronic interface will be. But no!

In order to answer that question they evaluated the FBR of four microelectrodes with differing flexibility, compare the FBR of the four types of probes at 4 and 8 weeks post-implantation. And the results suggests that mechanical compliance (i.e., flexibility) of neural probes can mediate the degrees of FBR, but its impact diminishes after a hypothetical threshold. Hence, mechanical mismatch is not the only aspect that should be improved and it has limited impact on improving the lifetime of neural implants.

To make his talk interactive and actively engage the audience in the talk, Lennard used kahoot.it to ask questions from the audience once a while and have them discuss the reason for choosing a specific answer. There was also an interesting discussion after the talk. Lennard put forward some interesting questions such as how much did the audience believe in the findings of the paper, and how much does the finding contribute to today’s research. And also how was the hypothesis of the paper data-driven, in a sense that they tested an initial hypothesis (e.g., one electrode works better than the other) and it fails, then they decided to explain about the reason underlying the results.

Francisco studied electronics and specialized in power electronics. Since his parents are physicians, he developed an early interest in healthcare, particularly related to nervous system. However, he preferred an engineering approach, and that directed him towards pursuing his studies in the field of neuroengineering. Currently he is a second-year master student at Technical University of Munich, in master program of neuroengineering.

Cardiac muscle cells or cardiomyocytes are the muscle cells that make up the heart tissue. These cells communicate with each via action potentials, and their coordinated activity generates the heart's pumping. After a heart attack, there are cases of tissue death, generating tissue configurations in which a few cells must excite a larger amount of them. With only a few cells to propagate the action potential, the current they provide may be insufficient, causing a delay in the propagation or even blocking the transmission. That is to say, the geometry of this network has an influence in the propagation of the electrical signal.

During his internship, Francisco investigated the effect of network geometry on signal propagation in cardiomyocytes, by creating a geometrically non-uniform culturing platform. The channels these cells grow on present abrupt expansion of width, to simulate the electrical mismatches generated by dead tissue. To test the effect of network geometry on signal propagation delay, he evaluated the action potential propagation in both directions (wide to narrow, and narrow to wide directions) and measured the signal propagation time at each point along the network using optical fluorescent techniques. He observed differences in the two cases: when the signal enters a wider from a narrower strand, the signal propagation exhibits a delay in the interface. However, in the other direction (entering a narrower from a wider network) this delay is not present, as there is enough current to depolarize the rest of the strand. Due to lack of time, it is yet to be calculated a correlation between the width mismatch and the delay in more cases.