Evaluation of heart tissue viability under redox-magnetohydrodynamics conditions: Toward fine-tuning flow in biological microfluidics applications

A microfluidic system containing a chamber for heart tissue biopsies, perfused with Krebs-Henseleit buffer containing glucose and antibiotic (KHGB) using peristaltic pumps and continuously stimulated, was used to evaluate tissue viability under redox-magnetohydrodynamics (redox-MHD) conditions. Redox-MHD possesses unique capabilities to control fluid flow using ionic current from oxidation and reduction processes at electrodes in a magnetic field, making it attractive to fine-tune fluid flow around tissues for "tissue-on-a-chip" applications. The manuscript describes a parallel setup to study two tissue samples simultaneously, and 6-min static incubation with Triton X100. Tissue viability was subsequently determined by assaying perfusate for lactate dehydrogenase (LDH) activity, where LDH serves as an injury marker. Incubation with KHGB containing 5mM hexaammineruthenium(III) (ruhex) redox species with and without a pair of NdFeB magnets (~0.39T, placed parallel to the chamber) exhibited no additional tissue insult. MHD fluid flow, viewed by tracking microbeads with microscopy, occurred only when the magnet was present and stimulating electrodes were activated. Pulsating MHD flow with a frequency similar to the stimulating waveform was superimposed over thermal convection (from a hotplate) for Triton-KHGB, but fluid speed was up to twice as fast for ruhex-Triton-KHGB. A large transient ionic current, achieved when switching on the stimulating electrodes, generates MHD perturbations visible over varying peristaltic flow. The well-controlled flow methodology of redox-MHD is applicable to any tissue type, being useful in various drug uptake and toxicity studies, and can be combined equally with on- or off-device analysis modalities.