Alginate bioink properties influence real-time impedance monitoring of cells during extrusion bioprinting.

Abstract

Bioprinting processes have greatly advanced in recent years through improvements in print accuracy and bioink optimization. Despite these advances, optimizing cell distribution and viability still relies on guess-and-check methods and destructive post-printing testing. The ability to monitor cells during printing would improve print quality and inform complex bioprinting processes, such as the generation of cellular gradients or controlled bioink transitions. Real-time monitoring using dielectric impedance spectroscopy (DIS) alleviates this burden by correlating impedance<i>|Z|</i>to cell properties. However, the influence of bioink properties on these measurements is unknown. Using an in-line impedance sensor, we assessed the effects of alginate bioink concentration, pH, and crosslinking on impedance over 1-25 000 kHz and determined how these properties influenced the detection of primary chondrocytes. In each scenario, impedance was highest in samples with low alginate concentration, low sample pH, or crosslinker. In nearly all samples, the addition of cells resulted in an increase in impedance compared to acellular samples, and this difference in impedance was used to quantify cell presence, termed |<i>Z</i>_cells|. Higher alginate concentrations at 1 w/v% and 3 w/v% showed greater |<i>Z</i>_cells|, indicating reliable cell detection. Although |<i>Z</i>_cells| varied greatly with alginate or phosphate-buffered saline pH, similar measurements were found in pH resembling cell media. Optimal frequency ranges for monitoring acellular and cellular samples were from 10-100 kHz and 1000-25 000 kHz. Furthermore, cells were detected in real-time as acellular and cellular alginate bioinks were transitioned during bioprinting. This transition in cell concentration was spatially mapped to deposited bioink, providing a visual display of bioink transition using impedance. In summary, DIS detected cells suspended in alginate bioink and showed potential for real-time mapping of cell deposition.