No standard defines what 'functional' means for a bioprinted organ, so no one can prove one works

When a lab claims they have bioprinted a 'functional' liver construct, they typically mean it secretes albumin or metabolizes a drug in a dish. When a transplant surgeon hears 'functional,' they mean it can filter blood, produce bile, synthesize clotting factors, metabolize drugs, store glycogen, and regenerate after injury -- all simultaneously, for decades. So what? There is no agreed-upon minimum performance benchmark for any bioprinted organ. Every lab defines 'success' differently, making cross-study comparison meaningless. So what? Funders, regulators, and clinicians cannot evaluate progress in the field because a 'functional bioprinted kidney' in one paper means 'some cells expressed aquaporin-2' and in another means 'it filtered urea for 48 hours.' So what? Without standardized functional benchmarks, clinical translation stalls because no one can demonstrate that a bioprinted organ meets the threshold required to sustain a patient's life. Why does this persist? Native organ function is the integrated output of dozens of cell types, vascular perfusion, innervation, and mechanical properties operating across length scales from nanometers to centimeters. Reducing this to a checklist of minimum viable metrics requires consensus between bioengineers, transplant surgeons, regulators, and physiologists -- communities that rarely collaborate and have different incentive structures.