A vessel sealing instrument includes a housing having a shaft extending from a distal end thereof, the distal end including an end effector assembly having a pair of opposing jaw members operably coupled thereto. One or both of the jaw members is moveable between open and closed positions for clamping tissue with a closure pressure. One or both of the jaw members connects to a generator that provides energy thereto in accordance with a sealing algorithm upon activation thereof. An anti-backdrive mechanism is coupled to the end effector assembly and includes a drive shaft coupled at one end to a solenoid and another end that engages one of the jaw members upon extension thereof to provide additional closure pressure between the jaw members. The drive shaft is extendible by the solenoid to extend the drive shaft in response to tissue expansion during sealing based on the sealing algorithm.