Evaluating the electrical stimulation of bone cells based on an induced transmembrane potential model and intracellular calcium levels.

Abstract

Electrical stimulation holds promise for enhancing bone healing; however, it has not yet seen widespread clinical adoption. A significant obstacle is the limited understanding of the biological mechanisms involved and the electric field parameters required to trigger them. It has been observed that the intracellular calcium ion concentration increases upon electrical stimulation, possibly via the activation of voltage-gated calcium channels. In this work, we introduced a digital twin framework to rationally choose stimulation parameters. We aimed to induce a transmembrane potential sufficient to activate the voltage-gated calcium channels. We focused on kilohertz-frequency stimulation, which offers advantages for clinical translation, and applied electrical stimuli using a well-established direct-contact stimulation chamber. By combining this with live-cell calcium imaging, we observed the immediate stimulation effect. We found that a stimulation at 1  kHz or 100  kHz, adjusted to induce a transmembrane potential of about 10  mV, did not alter the intracellular calcium concentration. In contrast, direct current stimulation at 5  V consistently increased intracellular calcium concentrations. However, our results indicate that this effect is not caused by the electric field itself but by electrochemical by-products leading to local changes in the pH value. We further confirmed that chemical stimulation could reproduce the effect. The presented workflow enables researchers to distinguish between purely electrical and mixed electrochemical stimulation. It is easily transferable and contributes to a more precise understanding of the effects of electrical stimulation.