The terms upper-case and lower-case to designate the size of letters stem from printer’s slang from the days of typesetting. Since they used small letters most of the time, so they were kept in a case that was lower, and therefore more easily...
bio-ink n. organic or cellular fluid used in printer-like devices to construct solid, layered matrices that can be used medically or surgically. (source: Double-Tongued Dictionary)