Abstract: Methods, devices and systems for in situ formation of an implant within a post-surgical cavity. A balloon is provided within the cavity and a gelling initiator such as a cross-linking agent is introduced into the balloon. A polymer susceptible to solidifying in the presence of the gelling initiator is then introduced into the balloon. The introduced polymer is allowed solidify through contact with the introduced gelling initiator to form the implant while the balloon isolates the solidifying implant from the cavity. The balloon is then ruptured and extracted from the cavity such that the formed implant remains within and directly contacts an interior surface of the cavity.