Experimental model for strain-induced mechanical neurostimulation on human progenitor neurons

Aim: Although non-invasive, such as focused ultrasound stimulation, and invasive, such as neural interface implantations, neurological interventions on the brain are increasing in the clinics nowadays, there is no detailed experimental model of these mechanical effects on neurons. In this study, we built an experimental model to mimic mechanical strain stress on neurons and compared the experimental model's effectiveness with the existing literature. Methods: In this study, we designed unidirectional, bidirectional, and omnidirectional strain setups integrated with a high-speed camera. Neural membrane potentials and intracellular calcium levels were calculated with a custom algorithm based on the calcium signal collected with Fluo-4 from RenCell human progenitor neurons, which was strained up to 20%. During this analysis, confounding effects of motion, strain, and background were removed with a custom-made algorithm. Results: In these experiments, human progenitor neurons subjected to instantaneous omnidirectional strain stress application above 15% generate action potential responses. While the action potential generation behavior is related to fast intracellular calcium influx, slow internal calcium increase due to strain application is not associated with action potential propagation. Conclusion: In this study, we have produced an experimental model for reproducible omnidirectional strain stress application and determined the threshold strain-stress values of action potential propagation behavior in human progenitor neurons. These results from this experimental model can be combined with theoretical models, such as the Hodgkin & Huxley model, and can be an effective simulation tool for future clinical applications.