Min Wang1
University of Hong Kong1
Additive manufacturing, commonly called “3D printing”, is being applied in the tissue engineering field since two decades ago and has now gathered momentum in producing novel tissue engineering products. Tibbits of MIT in 2013 ushered in a new era in additive manufacturing: 4D printing, with which 3D printed objects can change their shapes, properties and/or functions under appropriate stimulus/stimuli such as temperature, pH, humidity, light, electricity, magnetic field, acoustics, or a combination of these stimuli. Such dynamic objects can meet the demanding requirements in particular applications. There have been numerous investigations into the application of 3D printing in biomedical engineering (J.Lai, C.Wang, M.Wang, “3D Printing in Biomedical Engineering: Processes, Materials and Applications”, <i>Applied Physics Review</i>, <b>8 </b>(2021), 021322). So far, the greatest biomedical application of 3D printing is in the tissue engineering field. 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, and it can use patients’ own medical imaging data to produce personalized products for individuals. Furthermore, 3D printing can easily make complex, multilayered scaffolds with different layer characteristics. Suitable 3D printing technologies can also incorporate in scaffolds biochemical cues such as growth factors (GFs). The application of 3D printing in tissue fabrication has led to bioprinting, which uses solvent-free, aqueous systems to print materials embedded with live cells into 3D structures. 4D biomedical printing has now focused on shape-morphing or function-change structures under external stimulus/stimuli. While 4D biomedical printing is emerging, it faces various challenges in its development. Since 2005, we have been investigating 3D printing (and later, 4D printing) and their applications in tissue engineering (W.Y.Zhou, <i>et al</i>., “Selective Laser Sintering of Porous Scaffolds from Poly(L-Lactide) Microspheres and its Nanocomposite with Carbonated Hydroxyapatite Nanospheres”, <i>20<sup>th</sup> European Conference on Biomaterials</i>, Nantes, France, 2006). Selective laser sintering was assessed for making novel scaffolds for regenerating bone (B.Duan, <i>et al.</i>, “Three-dimensional Nanocomposite Scaffolds Fabricated via Selective Laser Sintering for Bone Tissue Engineering”, <i>Acta Biomaterialia</i>, <b>6</b> (2010), 4495-4505). Cryogenic printing was developed for producing GF-encapsulated scaffolds (C.Wang, <i>et al.</i>, “Cryogenic 3D Printing for Producing Hierarchical Porous and rhBMP-2-loaded Ca-P/PLLA Nanocomposite Scaffolds for Bone Tissue Engineering”, <i>Biofabrication</i>, <b>9</b> (2017), 025031). Graded scaffolds were 3D printed for osteochondral tissue engineering (C.Wang, <i>et al.</i>, “Cryogenic 3D Printing of Heterogeneous Scaffolds with Gradient Mechanical Strengths and Spatial Delivery of Osteogenic Peptide/TGF-β1 for Osteochondral Tissue Regeneration”, <i>Biofabrication</i>, <b>12</b> (2020), 025030). 4D printing was explored for obtaining shape-morphing scaffolds (C.Wang, <i>et al.</i>, “Advanced Reconfigurable Scaffolds Fabricated by 4D Printing for Treating Critical-size Bone Defects of Irregular Shapes”,<i> Biofabrication</i>, <b>12</b> (2020), 045025). New materials/mechanisms were investigated for 4D printing (J.Lai, <i>et al.</i>, “4D Printing of Highly Printable and Shape-morphing Hydrogels Composed of Alginate and Methylcellulose”, <i>Materials & Design</i>, <b>205 </b>(2021), 109699). We have also conceptualized 5D printing and apply it in tissue engineering. This talk will present some of our 3D/4D/5D printing work for tissue engineering.