4D-Printing is based on the possibility to produce 3D objects that, subjected to the action of a stimuli (heat, strong vibrations, pH variations, chemicals), can change their shape.

In Photo-Lab we printed a double layer object with our DLP 3D Printer and resins formulated by us. Two different layers compose the object: the support and a pH-responsive hydrogel.

The pH-responsive layer absorbs water depending on the pH, while the support layer remains unaffected. In particular, at low pH (2) almost no water is absorbed but at neutral pH the layer swells. The bilayer structure thus tends to bend.

Below is shown a time lapse of the bending

The shape change can be repeated several times.