4D Printing of Advanced Scaffolds for Tissue Engineering

Abstract

Additive manufacturing, popularly known as “3D printing”, includes an array of technologies such as fused deposition modelling (FDM), selective laser sintering (SLS) and inkjet printing. Compared with conventional manufacturing technologies, 3D printing has many distinctive advantages, including the construction of 3D structures with complex shapes and functionalities. Therefore, 3D printing technologies have seen increasing popularity in many areas, such as product design and development, industrial production, consumer goods, aerospace, and education. 3D printing has already made a tremendous impact in our society. The exciting TED Talk in 2013 by Tibbits of MIT ushered in a new era in additive manufacturing: 4D printing. With 4D printing, 3D printed static objects will change their shapes over time, i.e., 4D printing uses 3D printing technologies to produce shape-morphing objects. Such objects can meet the demanding requirements in particularly applications. The concept of 4D printing has been evolving and one popular definition of 4D printing is that the shape, property and functionality of a 3D printed object can evolve with time in predefined and programmable designs. There have been numerous investigations into the application of 3D printing in biomedical engineering. So far, the greatest biomedical applications of 3D printing are in the tissue engineering field. Tissue engineering offers a new approach to treat difficult problems in human tissue repair. It involves using live cells to form implantable devices for body tissue regeneration. In scaffold-based tissue engineering, a scaffold provides a microenvironment for cells to adhere, proliferate and differentiate and a structural framework for new tissue formation. 3D printing has many advantages in scaffold fabrication, such as control of pore size, porosity, etc. Furthermore, 3D printing can make multilayered scaffolds with different layer characteristics. Most human body tissues are complex and hierarchical and their regeneration requires structurally complex scaffolds that resemble tissue structures and can provide biochemical cues such as growth factors (GFs). Incorporating GFs and even live cells in scaffolds can greatly facilitate tissue regeneration. Since 2004, we have been investigating 3D biomedical printing and have used different 3D printing techniques for developing bone tissue engineering scaffolds (e.g., S.H.Lee, W.Y.Zhou, W.L.Cheung, M.Wang, “Producing Polymeric Scaffolds for Bone Tissue Engineering Using the Selective Laser Sintering Technique”, Transactions of the Society For Biomaterials 30th Annual Meeting, Memphis, TN, USA, 2005, 348). We have also been exploring 4D printing in tissue engineering (e.g., C.Wang, Y.Zhou, M.Wang, “In situ Delivery of rhBMP-2 in Surface Porous Shape Memory Scaffolds Developed through Cryogenic 3D Plotting”, Materials Letters, Vol.189 (2017), 140-143). This talk will give an overview of our work in 3D/4D printing of scaffolds for regenerating tissues such as bone and blood vessels. It will focus on the design and 4D printing of shape-morphing and GF-delivering scaffolds for tissue engineering.