Designing Self-floating Anisotropic Macroporous Hydrogel by Step Emulsification and Buoyancy-assisted Microfluidics

• Anisotropic macroporous hydrogels with tailored topology and geometry are produced. • The macroporous hydrogels maintain self-floating in different salt concentrations. • The macroporous hydrogels can serve as pressure-responsive micro-swimmers. • Air-liquid interface culture of cells is achieved with the self-floating hydrogels. Macroporous hydrogel with self-floating properties shows promising applications in gastric drug delivery, water purification and air–liquid interface cell culture. Microfluidic bubble templating is an emerging routine to produce macroporous hydrogel. However, current methods are in lack of the control over the anisotropy and porosity. Here, we describe new developments for the buoyancy-assisted microfluidic fabrication of anisotropic hydrogel products by templating from bubbles formed using step emulsification. The step emulsification method generates bubbles with exceptional precision which enables convenient tailoring the internal porosity of the hydrogel particles. Further design over the device structure and the buoyancy during the drop formation produces irregular hydrogel products such as macroporous fibers and core/shell beads. The anisotropic hydrogel beads provide pressure-responsive swimming behaviors and controllable release of the carried cargos. They are proved to be competent as carriers for culture of bronchial epithelial cells on air–liquid interfaces.