4D Printing Shape-Morphing Hybrid Biomaterials for Advanced Bioengineering Applications

Four-dimensional (4D) printing is an innovative additive manufacturing technology used to fabricate structures that can evolve over time when exposed to a predefined external stimulus. 4D printed objects are no longer static object but programmable active structures that accomplish their functions thanks to a change over time in their physical/chemical properties, that usually displays macroscopically as a shape-shifting, in response to an environmental stimulus. 4D printing is characterized by several entangled features (e.g., involved material(s), structure geometry, and applied stimulus entity), that need to be carefully coupled to get a favorable fabrication and a functioning structure. Overall, the integration of micro-/nanofabrication methods of bio-material with nanomaterials represents a promising approach for the development of advanced materials. The ability to construct complex and multifunctional triggerable structure capable of being activated allows to control biomedical device activity reducing the need for invasive interventions. Such advancements provide new tools to biomedical engineers and clinicians to design dynamically actuated implantable devices. In this context, the aim of this review is to demonstrate the potential of 4D printing as an enabling manufacturing technology to program the environmentally triggered physical evolution of structures and devices of biomedical interest.