Degradable 4D-printed hydration-driven actuators from a single family of amphiphilic star-shaped copolymers

Actuators are largely used in biomedical applications in the presence of sensitive live cells or biomolecules, which makes actuators triggered by water uptake highly appealing. Dual-material printing and hydration driven expansion is a method of choice to produce such actuators, but mostly rely of non-degradable polymers or on the combination of polymers of different nature that may lead to interface incompatibilities. To overcome this challenge, we report here on two photocrosslinkable resins based on a single family of degradable hydrophilic or hydrophobic star-shaped poly(ethylene glycol)-poly(lactide) copolymers. The two materials are first printed individually and characterized to ensure that their properties enable the printing of dual material objects by stereolithographic digital-light processing. Dual-materials actuators are then printed by sequential switching of the hydrophobic and hydrophilic resin baths. Objects of simple and complex shapes are easily obtained and exhibit rapid actuation (<60 s) upon hydration. The swelling-induced shape changes are accurately reproduced by numerical modeling of the printed geometries using the obtained material swelling properties. This set of results offers new perspectives to develop 4D-printed temporary medical devices.