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. 2023 Jan 3;27:1. doi: 10.1186/s40824-022-00338-7

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© The Author(s) 2022

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 4 — 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, 161–163]