Researchers are hopeful that new advances in tissue engineering and regenerative medicine could one day make a replacement liver from a patient’s own cells, or animal muscle tissue that could be cut into steaks without ever being inside a cow. Bioengineers can already make 2D structures out of many kinds of tissue, but one of the major roadblocks to making the jump to 3D is keeping the cells within large structures from suffocating; organs have complicated 3D blood vessel networks that are still impossible to recreate in the laboratory.