No bioprinted tissue >1cm thick survives because vasculature can't be printed at capillary scale

Researchers attempting to bioprint therapeutically relevant tissues (kidney, liver, cardiac patches) hit a hard wall: cells more than 200 micrometers from a blood vessel die within hours from hypoxia and waste buildup. So what? This means any construct thicker than ~1cm that lacks a perfusable microvascular network becomes a necrotic core surrounded by a thin shell of living cells. So what? It renders every large-organ bioprinting effort (heart, kidney, liver) non-viable for transplant because the interior tissue dies before the host vasculature can grow in. So what? The 100,000+ patients on organ transplant waitlists get no relief from bioprinting despite two decades of promises. Why does this persist? Extrusion bioprinters resolve features at ~200-500 micrometers when loaded with cells, but human capillaries are 5-10 micrometers in diameter. The physics of pushing cell-laden hydrogel through nozzles small enough to mimic capillaries would generate shear forces that kill the cells. Sacrificial ink and coaxial printing can create channels down to ~100 micrometers, but that is still 10-20x too large to replicate the capillary beds where gas exchange actually happens. No current printing modality bridges this resolution gap while maintaining cell viability.