Introduction: Human Schwann cells (hSC) receive signals from axons to coordinate normal myelination and most of these signals are molecular factors. There is evidence, however, that non-molecular factors in the form of patterned electrical impulses (PEI) play an important role in myelination. PEI have been investigated in co-cultures where both neurons and myelinating cells were present. This co-culturing prevents an uncoupling of the direct effect of PEI on myelinating cells from the indirect effect mediated by neurons. To uncouple these effects, we developed an in vitro model where an electroconductive carbon fiber (CF) acts as an artificial axon.

Materials and Methods: The CF provides the biophysical characteristics of an axon but does not contribute any molecular signaling. In our suspended-wire-model, the CF is suspended in a liquid media supported by a 3D printed polymeric scaffold, with PEI generated by using an Arduino 101 microcontroller. Characteristics of the pattern were defined via software. The PEI apparatus was created using an Arduino 101 microcontroller board which is based on the 32 bit, 32 MHz Intel Curie module. The embedded software which generates the PEI, was written using the Arduino IDE code. Validation of the output was conducted using a 1 GS/s 50 MHz 4-channel Rigol DS1054Z Digital Oscilloscope.

Results: Human Schwann cells were cultured on our model and two sets for voltage and frequency were tested (32 mV and 75 mV; 5 Hz and 10 Hz). When PEI was delivered in vitro, hSC started to adhere to the CF and expand their membrane on the surface of the fiber. The cells continue to wrap around the CF in the presence of PEI, thus reproducing the early steps of the myelination process. Helium-ion scanning microscopy and high definition confocal laser microscopy showed evidence of a complete wrapping of the CF by human Schwann cells in the presence of PEI together with the presence of cytoplasmic channels which spiral around the CF.

Conclusions: Developing an apparatus to successfully deliver PEI to cells in culture makes it feasible to investigate the response of hSC to PEI in vitro. In this study, we demonstrated the adherence and enstheathment of hSC to CF in the presence of PEI. Our results showed that hSC can sustain the administration of PEI up to 3 hours (the maximum duration tested so far).