In article number 1900435 by Bin Li and co-workers, various complex helical structures and cell-laden hydrogel microfibers are fabricated using microfluidics-based technology. Human umbilical vein endothelial cells (HUVECs) can grow in the inner wall of hollow microfibers and form lumen similar to natural blood vessels. Helical cell tubes can also be prepared to mimic helical blood vessels. Such cell-laden microfibers hold great potential in blood-vessel-on-a-chip applications.