Maturation chamber

A maturation chamber is a device used by the Borg Collective to accelerate the development of adolescent humanoids until they are ready to service the Collective as drones. Among those who were placed in such chambers are Annika Hansen (Seven of Nine), Icheb, Maryl and the young boy Seven of Nine met in Unimatrix Zero. 

Children assimilated by the Borg are placed in maturation chambers where they will spend the following seventeen cycles. 

Maturation chambers were first encountered in 2365 when Commander William Riker and Lieutenant Worf beamed aboard the damaged Borg cube to investigate after its initial attack upon the USS Enterprise (NCC-1701-D). Riker referred to the chambers as a "nursery". This "nursery" consisted of several drawers in the wall, each containing an infant in an early stage of assimilation. The Borg infants did not exhibit either the extensive implants or the body armor of mature drones, nor was it known at the time if Borg infants required food sources other than the electricity consumed by adults. 

After assimilating The Doctor's mobile emitter and sampling DNA from Ensign Mulcahey in 2375, Seven of Nine's nanoprobes created a modified maturation chamber in one of USS Voyager's science labs. The growth rate of the drone inside, known as One, was 25 times faster than normal. The chamber was protected by a force field.