Fig. 4
From: Emerging 3D bioprinting applications in plastic surgery
Various types of Smart Printing Materials that Respond to Chemical Stimulation. A Schematic diagram of pH-responsive 4D bioprinting products [158]. After pH stimulation, the function of the hydrogel is transformed. B Schematic diagram of ion-responsive 4D bioprinting products. Ca.2+ triggers shape transformation of PVDT-PAA-PBS(PVDT-PAA is synthesized by 2-vinyl-4,6-diamino-1,3,5-triazine, acrylic acid, and polyethylene glycol diacrylate; PBS is phosphate buffered saline) hydrogels into box-like, pyramid-like, and spring-like shapes [161]. C Schematic diagram of 4D printed products based on bio-orthogonal crosslinking design [162]. D Schematic diagram of a biologically responsive 4D bioprinting products [163]. CS-PEG (an enzymatically formed chondroitin sulfate and poly (ethylene glycol) based hybrid hydrogel system) hydrogel formation mediated by transglutaminase XIII factor. Reprinted with permission from Ref. [158, 161,162,163]