Bioprinted tissues have zero innervation, making printed organs non-functional

Every bioprinted tissue construct to date lacks nerve integration. There are no sensory neurons, no motor neurons, no autonomic innervation. So what? Without innervation, a bioprinted heart cannot respond to autonomic nervous system signals to adjust heart rate. A bioprinted bladder cannot sense fullness or coordinate contraction. A bioprinted skin graft has no sensation. So what? This means bioprinted organs, even if they achieve the correct cell composition and vasculature, cannot integrate with the patient's nervous system and therefore cannot perform the regulated, responsive functions that define a working organ. So what? A bioprinted heart that beats but cannot modulate its rate in response to exercise or stress is not a functional organ -- it's a pump that will kill the patient during their first sprint to catch a bus. Why does this persist? Nerve axon guidance requires precisely patterned molecular gradients (neurotrophins, netrins, semaphorins) over centimeters of tissue at micrometer-scale spatial resolution. No bioprinter can deposit these signaling molecules at the required resolution. Furthermore, nerve growth is slow (1-3mm per day for peripheral nerves), so even if guidance cues were perfect, innervation of an organ-scale construct would take months of post-implant remodeling with no guarantee axons follow the intended paths.