4D-printed adaptive hydrogel tissue expanders for ear and breast reconstruction

Tissue expanders are widely used for organ and tissue reconstruction surgery. Hydrogel tissue expanders that swell in a biofluid are promising for minimally invasive operations. Nevertheless, clinical applications of existing hydrogel tissue expanders exhibit simple geometries, rapid swelling and insufficient mechanical performances. Here we develop a negatively charged polyelectrolyte hydrogel ink for light-based printing and prolonged yet large expansive profiles for surface organ and tissue reconstruction. This 4D-printed hydrogel tissue expander can be moulded in architecturally sophisticated constructs that adapt to the environment and show favourable mechanics without the need of external triggers for expansion. The ionization degree of the polyelectrolyte hydrogels is tunable by pH value in the surrounding medium and allows a volume equilibrium-swelling up to 10-30 times. In a rabbit model, we use the tissue expander for reconstruction of human-size ears and breasts, highlighting their multifold advantages over existing clinically adopted methods and thus future translation potentials.