Direct Electrical Stimulation Approaches for Bone Repair and Regeneration

Abstract

Electrical stimulation (ES) has been an effective tool for enhancing bone healing in pre-clinical and clinical studies. It has been shown that ES could regulate a wide range of cellular activities; however, the mechanism of ES-induced bone formation has not yet been fully elucidated. Moreover, it was also previously hypothesised that the faradic by-products generated during ES may also influence the cellular responses, which has not been evaluated by end-to-end experiment before. Hence, this study has addressed this hypothesis by using direct ES system with L-shaped platinum (Pt) electrodes. The electrolyte potential relative to the cathode and current density during constant DC ES were visualised by computational modelling. The electrically stimulated media (ES media) were also characterised, which revealed the increases in H2O2 and dissolved Pt concentration without significant change in pH. Two experimental approaches were implemented on hBM-MSCs in order to evaluate their responses and the role of faradic by-products. The first approach was to deliver pulsed DC ES with minimal presence of faradic by-products to the cells. However, no significant correlation between the cellular responses and pulsed DC ES was observed. The second approach was to compare cellular responses to constant DC ES and ES media. The results showed the increased ERK1/2 phosphorylation, osteopontin (SPP1) expression, and cell proliferation after ES, in which the faradic by-products have partially enhanced the latter two. Further experiments with murine pre-osteoblasts and macrophages have shown that constant DC ES could also promote SPP1 and BMP2 expression from both cell types and reduce M1 macrophage marker. Meanwhile, faradic by-products have partially enhanced SPP1 expression from macrophages, but not pre-osteoblasts. In contrast to MSCs, the density of both murine cells was significantly reduced in the vicinity of the electrodes, which corresponds with the high current density distribution from computational modelling. This study has shown that direct ES could regulate cellular activities from various cell types and confirmed the involvement of faradic by-products, although the latter was found to be minimal. These findings could be a part of the mechanism behind the electrically induced osteogenesis.

Date of Award	3 Jan 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Julie Gough (Supervisor) & Sarah Cartmell (Supervisor)