Mapping Cell Viability Quantitatively and Independently from Cell Density in 3D Gels Noninvasively.

Objective In biomanufacturing there is a need for quantitative methods to map cell viability and density inside 3D bioreactors to assess health and proliferation over time. Recently, noninvasive MRI readouts of cell density have been achieved. However, the ratio of live to dead cells was not varied. Herein we present an approach for measuring the viability of cells embedded in a hydrogel independently from cell density to map cell number and health. Methods Independent quantification of cell viability and density was achieved by calibrating the 1H magnetization transfer- (MT) and diffusion-weighted NMR signals to samples of known cell density and viability using a multivariate approach. Maps of cell viability and density were generated by weighting NMR images by these parameters post-calibration. Results Using this method, the limits of detection (LODs) of total cell density and viable cell density were found to be 3.88x10^8 cells mL^-1 Hz^-1/2 and 2.36x10^9 viable cells mL^-1 Hz^-1/2 respectively. Conclusion This mapping technique provides a noninvasive means of visualizing cell viability and number density within optically opaque bioreactors. Significance We anticipate that such nondestructive readouts will provide valuable feedback for monitoring and controlling cell populations in bioreactors.