4D Additive-Subtractive Manufacturing of Shape Memory Ceramics

Sophisticated Structural Ceramics Shaped from 3D Printed Hydrogel Preceramic Skeleton

Shaping ceramic materials into sophisticated architecture with 3D hierarchical structure is desirable in multiapplication yet remains challenge due to their brittle and stiff nature. Herein, a new method to achieve ceramic architectures with unsupported and large-spanning structure by shaping vat photopolymerization 3D printed hydrogel preceramic skeleton with unique flexible and deformable character is proposed. Specifically, the present photopolymerizable hydrogel preceramic achieves one stone, two birds: the photosensitive polymer matrix coupled with ceramic nanoparticles for the first shaping by vat photopolymerization 3D printing and the secondary plasticity of the 3D printed ceramic body through flexible shape deformation of hydrogel networks. Inorganic binder aluminum dihydrogen phosphate serves as hydrogel dispersion medium to achieve ultralow shrinkage photopolymerization ceramic. Compared with conventional polymer-derived photocuring ceramics, the linear shrinkage of lamina structure is solely 2%, and which of cubic ceramic structure is just 13.3%. More importantly, one 3D printed preceramic is conducted to reshape repeatedly myriad constructions, realizing reusability of intrinsic brittle ceramic, improving manufacturing fault tolerance rate. Finally, a variety of paradigms for ceramic structure applications are proposed toward stereo circuit, biomedicine, and catalytic applications, breaking the limitation of intrinsic brittleness of ceramic in high-precision manufacturing of complex ceramic devices.

Multimaterial 3D and 4D Bioprinting of Heterogenous Constructs for Tissue Engineering

Additive manufacturing (AM), which is based on the principle of layer-by-layer shaping and stacking of discrete materials, has shown significant benefits in the fabrication of complicated implants for tissue engineering (TE). However, many native tissues exhibit anisotropic heterogenous constructs with diverse components and functions. Consequently, the replication of complicated biomimetic constructs using conventional AM processes based on a single material is challenging. Multimaterial 3D and 4D bioprinting (with time as the fourth dimension) has emerged as a promising solution for constructing multifunctional implants with heterogenous constructs that can mimic the host microenvironment better than single-material alternatives. Notably, 4D-printed multimaterial implants with biomimetic heterogenous architectures can provide a time-dependent programmable dynamic microenvironment that can promote cell activity and tissue regeneration in response to external stimuli. This paper first presents the typical design strategies of biomimetic heterogenous constructs in TE applications. Subsequently, the latest processes in the multimaterial 3D and 4D bioprinting of heterogenous tissue constructs are discussed, along with their advantages and challenges. In particular, the potential of multimaterial 4D bioprinting of smart multifunctional tissue constructs is highlighted. Furthermore, this review provides insights into how multimaterial 3D and 4D bioprinting can facilitate the realization of next-generation TE applications.

4D printing for biomedical applications

While three-dimensional (3D) printing excels at fabricating static constructs, it fails to emulate the dynamic behavior of native tissues or the temporal programmability desired for medical devices. Four-dimensional (4D) printing is an advanced additive manufacturing technology capable of fabricating constructs that can undergo pre-programmed changes in shape, property, or functionality when exposed to specific stimuli. In this Perspective, we summarize the advances in materials chemistry, 3D printing strategies, and post-printing methodologies that collectively facilitate the realization of temporal dynamics within 4D-printed soft materials (hydrogels, shape-memory polymers, liquid crystalline elastomers), ceramics, and metals. We also discuss and present insights about the diverse biomedical applications of 4D printing, including tissue engineering and regenerative medicine, drug delivery, in vitro models, and medical devices. Finally, we discuss the current challenges and emphasize the importance of an application-driven design approach to enable the clinical translation and widespread adoption of 4D printing.