A needle-based medical device and a method for constructing it are disclosed. The medical device includes a needle blocking object movable from a non-blocking position offset from the longitudinal axis of the needle to a blocking position a needle shield housing, the needle shield housing including: a lumen for accommodating at least part of the needle such that the needle shield housing an opening for accommodating at least part of the needle blocking object and a biasing member for applying a biasing force on the needle blocking object, the biasing force including a first component substantially perpendicular to the longitudinal axis of the needle and a second component substantially parallel to the longitudinal axis of the needle. The needle blocking object moves by exertion of the biasing force to the blocking position, preventing the needle from emerging from the needle shield housing, in response to a triggering proximal movement of the needle.
