A needle may be fired into tissue by a needle firing mechanism, which may include a fork for holding the needle and a firing rod coupled with the fork. A spring urges the fork to a distal, fired position. A screw gear is coupled with the rod. A sled is positioned at the proximal end of the rod. A catch is configured to engage the sled when the sled is moved to a proximal position. The screw gear is operable to convert rotational motion from a motor and gear set into linear motion to move the rod proximally to engage the sled with the catch, thereby cocking the needle firing mechanism. The motor may also be used to translate the screw gear distally relative to the rod after the sled has engaged with the catch. A trigger is used to fire the cocked needle firing mechanism.