Realization of muscle‐like actuation for a liquid crystal elastomer (LCE) requires mesogen alignment, which is typically achieved/fixed chemically during the synthesis. Post‐synthesis regulation of the alignment in a convenient and repeatable manner is highly desirable yet challenging. Here, a dual‐phase LCE network is designed and synthesized with a crystalline melting transition above a liquid crystalline transition. The crystalline phase can serve as an “alignment frame” to fix any mechanical deformation via a shape memory mechanism, leading to corresponding mesogen alignment in the liquid crystalline phase. The alignment can be erased by melting, which can be the starting point for reprogramming. This strategy that relies on a physical shape memory transition for mesogen alignment permits repeated reprogramming in a timescale of seconds, in stark contrast to typical methods. It further leads to unusual versatility in designing 3D printed LCE with unlimited programmable actuation modes.

Encoding molecular ordering during liquid crystalline network (LCN) formation endows preprogrammed but fixed shape morphing in response to external stimuli. The incorporation of dynamic covalent bonds enables shape reprogramming but also permanently alters the network structures. Here, an entropic approach that can program complex shapes via directed solvent evaporation from an isotropic LCN organogel is discoursed. Different shapes can be erased and reprogrammed from the same LCN on demand depending on the modes of deformation of the organogel during solvent evaporation. The ability to decouple network synthesis and molecular alignment relaxes the requirements to LCN chemistry and alignment methods, allowing for the realization of a variety of origami/kirigami structures and 4D shape morphing of LCNs printed from the digital light processing technique with unattainable spatial and temporal controls.

Dynamic regulation of substrate micro‐structures is an effective strategy to control stem cell fate in tissue engineering. Translating this into in vivo tissue repair in a clinical setting remains challenging, which requires precise temporal control of multi‐scale structural features. Using 4D printing technique, a multi‐responsive bilayer morphing membrane consisting of a shape memory polymer (SMP) layer and a hydrogel layer, is fabricated. The SMP layer is featured with responsive surface micro‐structures, which can switch the phase between proliferation and differentiation precisely, thus promoting the bone formation. The hydrogel layer endows the membrane with the ability to digitally regulate its 3D geometry, matching the specific macroscopic bone shape in clinical scenario. The authors’ in vivo experiments show that the 4D shape‐shifting membrane exhibits over 30% improvement in new bone formation in comparison to a reference membrane with static micro‐structure. More importantly, the 4D membrane can conformally wrap a bone defect model in a non‐invasive way and this strategy can be extended to repairs involving complex tissue defects.