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International Journal of Bioprinting Review of 4D-printed smart medical implants

Figure 6. 4D printing cell-seeding scaffolds. (A) The fabrication procedure of a 4D platform with a time-dependent topographic transformation [126] .
Copyright 2020, Wiley-VCH. (B) The preparation of 4D scaffold with tubular structure and 3D cell organization [125] . Copyright 2020, Wiley-VCH. (C) Self-
folded cell-seeding microstructures designed with different layouts and patterns have great potential for different tissue-engineering applications [109] .
Copyright 2020, IOP Publishing.

septal defect (VSD) [140] and atrial septal defect (ASD) firstly for further reduction of the insertion profile of
(Figure 8C) [112] . the stent. Ciprofloxacin was added into the ink, which
was released in vitro over time and endowed the stent
5.3.3. Tracheal stents with antimicrobial activity to prevent implant-related
Trachea is an important air conduit connecting the larynx infections. This shows that 4D-printed implants are
to the carina with the function of ventilation, secretion feature-rich after design and function well for tracheal
removal, and keeping the airway unobstructed [141] . It defects. Shape-morphing hydrogels are also utilized for
is fragile and can be damaged by many disorders [142] . tracheal reconstruction. Kim et al. presented a bi-layered
Trachea stents are an effective treatment for maintaining Sil-MA hydrogel based on digital light processing (DLP).
airway patency [143] . Due to its natural tubular structure, The 4D deformation depended on the anisotropic volume
4D printing can be a potential approach to make trachea- change of the bi-layered hydrogel in an aqueous solution.
like stents for the treatment of tracheal injury and airway Then curved trachea mimetic tissue was made equipped
stenosis. SMP-based custom-made endotracheal stents are with two types of cells, and performed well in tracheal
presented in several studies [144-148] . Maity et al. described a injury of rabbits (Figure 9A) .
[76]
personalized tracheal stent based on photopolymerizable
inks containing polypropylene glycol/polycaprolactone 5.3.4. Other organs
triblocks using a DLP-based 3D printer [144] . The stent In addition to these typical applications mentioned above,
demonstrated great shape memory behavior for safer 4D printing has also demonstrated application value in
implantation. In situ welding strategy was also developed bionic artificial muscle [31,149] , brain model [150,151] , neuronal

Volume 9 Issue 5 (2023) 327 https://doi.org/10.18063/ijb.764