The most common SMP is the one-way double SMP under thermal excitation, where thermal excitation specifically refers to the assignment of a temporary shape to the material in a thermal environment and triggers the return of a permanent shape under thermal stimulation. One-way indicates that the deformation of the temporary shape to the permanent shape is one-way irreversible and cannot be reversed spontaneously. Double indicates that the SMP can only remember one temporary shape during the deformation process. However, the single stimulus-response model of the thermal response dual SMP and its sensitivity to temperature change conditions have greatly limited its application, and this shortcoming has largely affected the continued development of SMP. To meet the adaptation needs of SMP in various fields, conventional solutions focus on the design of SMP material modification, such as enriching the SMP response deformation mode by adding functional fillers. Recently, with the emergence of 4D printing, it provides a new idea for the design and manufacturing of efficient, intelligently deformed, and multifunctionally integrated prototypes. [10][11][12] And SMPs have become one of the most widely used material types in 4D printing research due to their superior material properties and printability. [13] And they show great potential for applications in biomedicine, intelligent robotics, aerospace and other fields. [14][15][16][17] Therefore, this review provides an overview of the 3D printing processes commonly used in 4D printing SMP and the shape deformation patterns of SMP, an analysis of novel 4D deformation patterns realized with the unique molding principles of 3D printing, and 4D printing strategies for integrated structure-material-function manufacturing, as shown in Figure 1, providing a research basis for next-generation biomedical implants, smart devices, and origami structures.

Carbon quantum dots (CQDs), having outstanding biocompatibility, attractive catalytic performance, excellent optical properties, and valuable environment friendliness, are emerging as a new paradigm to design luminescent devices and show great potential in application fields such as biomedical sensors, optical and photonic devices. Furthermore, CQDs are known as one of the most promising carbon-based nanomaterials in the 21st century. Therefore, they have attracted a lot of attention since they were first discovered in 2004. In this review, we explain the accepted photoluminescence mechanism of CQDs, including fluorescence and phosphorescence. There are two main types of synthesis strategies: top-down approach and bottom-up approach. At the same time, the main application fields, including ion detection, anti-counterfeiting, biological imaging, food safety, sensors, lubrication additives, are reviewed. Finally, the existing bottlenecks, pending problems and prospects for the future of CQDs are discussed.

Electron transport layer (ETL), one of the important layers for high-performing perovskite solar cells (PSCs), also has great potential in bioengineering applications. It could be used for biological sensors, biological imaging, and biomedical treatments with high resolution or efficiency. Seldom research focused on the development of biological material for ETL and their application in biological uses. This review will introduce commercial and biological materials used in ETL to help readers understand the working mechanism of ETL. And the ways to prepare ETL at low temperatures will also be introduced to improve the performance of ETL. Then this review summarizes the latest research on material doping, material modification, and bilayer ETL structures to improve the electronic transmission capacity of ETLs. Finally, the application of ETLs in bioengineering will be also shown to demonstrate that ETLs and their used material have a high potential for biological applications.

Carbon-nanotube (CNT) is a promising material owing to its compelling mechanical, thermal and electrical properties and has been applied in a broad variety of fields such as composite, fiber, film and microelectronic. Although the introductions of CNT have brought huge improvement for many applications, these properties of macrostructures prepared by CNTs still cannot meet those of individual CNT. Disordered alignment of CNTs in the matrix results in degradation of performance and hinders further application. Nowadays, quantities of methods are being researched to realize alignments of CNTs. In this paper, we introduce the application of CNTs and review some typical pathways for vertical and horizontal alignment, including chemical vapor disposition, vertical self-assembly, external force, film assisted, electric field, magnetic field and printing. Besides that, advantages and disadvantages of specific methods are also discussed. We believe that these efforts will contribute to further understanding the nature of aligned CNT and generating more effective ideas to the relevant workers.