Trypan blue dye exclusion first was proposed as a means of measuring mammalian cell damages over a century ago in 1917 (1). Despite extensive documentation of its limitations (2), it remains the “gold standard” method of measuring cell viability in common use today. But can this method truly measure viability? And how do we define cell viability, for that matter? Those fundamental questions are linked to whether we refer to cells as “alive” or “dead” in the context of bioprocessing…