These pliers were printed in one piece and function due to their microstructure. Material properties do influence the performance of the device, but the microstructure makes the object a pair of pliers. Hence the term metamaterial. The microstructure governs the (different) rigidity of the various parts. The handles and beak are relatively stiff, the hinge can flex much more easily. Thus, movement of the handles controls the beak.
For more information on metamaterials see https://hpi.de/baudisch/projects/metamaterial-mechanisms.html.
This 3D printed object was reproduced for 3D printing education.