Provided are rapidly cross-linkable silicone compositions, systems, kits, and methods for filling implanted medical devices in situ, the implanted medical devices, including for example, body implants and tissue expanders, the compositions including a platinum divinyl disiloxane complex; a low viscosity vinyl terminated polydimethylsiloxane; a low viscosity hydride terminated polydimethylsiloxane; and a silicone cross-linker, where the rapidly cross-linkable silicone composition has a viscosity of ≤150 cPs for ≥1 min. post-preparation and ≤300 cPs≤5 min. post-preparation, at ambient temperature.