Multi-scale multi-physics model of brain interstitial water flux by transcranial Direct Current Stimulation

Area of Science:

• Neuroscience
• Biophysics
• Computational Biology

Background:

• Transcranial direct current stimulation (tDCS) induces electric fields in the brain.
• These fields may be amplified at the blood-brain barrier (BBB), potentially driving fluid flow via electroosmosis.
• Enhanced interstitial fluid flow could impact brain homeostasis and waste removal.

Purpose of the Study:

• To model the effects of tDCS on interstitial fluid flow across the BBB.
• To quantify the potential for tDCS to enhance brain fluid exchange.
• To develop a multi-scale modeling pipeline coupling electrical and fluid dynamics.

Main Methods:

• Developed a multi-scale modeling pipeline (mm to nm) integrating electric current and fluid flow.
• Coupled electrical fields with fluid flow across BBB layers using electroosmotic principles.
• Parametrized models using prior experimental data on BBB fluid transport.

Main Results:

• Predicted significant electric field amplification across BBB capillary walls and tight junctions.
• Calculated peak water fluxes across the BBB driven by tDCS-induced electroosmosis.
• Estimated interstitial water exchange rates comparable to endogenous flow, with localized 'jets'.

Conclusions:

• tDCS can significantly enhance brain interstitial fluid exchange.
• The developed multi-scale model allows prediction of tDCS effects on fluid flow for various stimulation parameters.
• Further research is needed to validate the 'brain flushing' implications of tDCS.