They used the muscle cells to sheathe the outside of a bladder-shaped polymer scaffold, and the lining cells to cover the inside.
British Dictionary definitions for sheathe
sheathe
/ʃiːð/
verb (transitive)
1.
to insert (a knife, sword, etc) into a sheath
2.
(esp of cats) to retract (the claws)
3.
to surface with or encase in a sheath or sheathing
Word Origin and History for sheathe
v.
c.1400, "to furnish (a sword, etc.) with a sheath," from sheath; meaning "to put (a sword, etc.) in a sheath" is attested from early 15c. Related: Sheathed; sheathing.