A needle protection assembly (6) comprising: a needle cannula (7) having a proximal end (25) and a distal end (27) with a puncture tip (31)； a needle cone (11) having a proximal end (33) and a distal end (35) and a conduit (37) between the ends, in which an inner part of the distal end (35) of the needle cone supports the proximal end (25) of the needle cannula (7)； a mobile protection element (15) between a first position in which the puncture tip (31) of the needle cannula (7) is exposed and a second position in which the puncture tip (31) of the cannula ( 7) Needle is protected by the protection element (15)； an actuation element (9) that pushes the protection element (15) towards the second position, in which the protection element (15) and the needle cone (11) include an interference coupling between them to maintain the protection element (15) in the first position against a pushing force of the actuating element (9)； and characterized by an activation material (57) adapted to deform after a fluid medium flows through the needle cannula (7), thereby causing the activation material (57) to deform and release the coupling by interference between the protection element (15) and the needle cone (11) and allowing the actuation element (9) to push the protection element (15) to the second position.Un conjunto (6) de protección de aguja que comprende: una cánula (7) de aguja que tiene un extremo (25) proximal y un extremo (27) distal con una punta (31) de punción； un cono (11) de aguja que tiene un extremo (33) proximal y un extremo (35) distal y un conducto (37) entre los extremos, en el que una parte interior del extremo (35) distal del cono de aguja soporta el extremo (25) proximal de la cánula (7) de aguja； un elemento (15) de protección móvil entre una primera posición en la que la punta (31) de punción de la cánula (7) de aguja está expuesta y una segunda posición en la que la punta (31) de punción de la cánula (7) de aguja está protegida por el elemento (15) d
