Real-time assessment of cell concentration and viability onboard a syringe using dielectric impedance spectroscopy for extrusion bioprinting

Bioprinting produces personalized, cell-laden constructs for tissue regeneration through the additive layering of bio-ink, an injectable hydrogel infused with cells. Currently, bioprinted constructs are assessed for quality by measuring cellular properties post-production using destructive techniques, necessitating the creation of multiple constructs and increasing the production costs of bioprinting. To reduce this burden, cell properties in bio-ink can be monitored in real-time during printing. We incorporated dielectric impedance spectroscopy (DIS) onto a syringe for real-time measurement of primary chondrocytes suspended in phosphate buffered saline (PBS) using impedance (|Z|) and phase angle (theta) from 0.1 to 25 000 kHz. Cell concentration and viability ranged from 0.1 x 106 cells ml-1 to 125 x 106 cells ml-1 and from 0%to 94%, respectively. Samples with constant or with changing cell concentration were exposed to various flow conditions from 0.5 to 4 ml min-1. The background PBS signal was subtracted from the sample, allowing for comparisons across devices and providing insight into the dielectric properties of the cells, and was labeled as |Zcells| and theta cells. |Zcells| shared a linear correlation with cell concentration and viability. Flow rate had minimal effect on our results, and |Zcells| responded on the order of seconds as cell concentration was altered over time. Notably, sensitivity to cell concentration and viability were dependent on frequency and were highest for |Zcells| when theta cells was minimized. Cell concentration and viability showed an additive effect on |Zcells| that was modeled across multiple frequencies, and deconvolution of these signals could result in real-time predictions of cell properties in the future. Overall, DIS was found to be a suitable technique for real-time sensing of cell concentration and viability during bioprinting.