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participate in Schiff's base reaction, while retaining some phenolic hydroxyl groups to

continue to exert the ability to eliminate ROS. This multiple cross-linking strategy has

increased the gel-forming speed of the bio-ink by 375%, its stiffness by 161%,
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mechanical elasticity by 231%, and its biodegradability by 208%. Yue Wang et al.
prepared 3D printed grid-like hydrogels loaded with ferroamine (DFO) by using Schiff

base bonds formed by -CHO provided by oxidized mannan oligosaccharides (OMOS)

and -NH2 in hyaluronic acrylamide (HA-AM) as crosslinking cores. This hydrogel not

only exhibited antioxidant effect, but also effectively regulated inflammatory response.

Additionally, the incorporation of DFO significantly promoted wound angiogenesis,

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providing a novel strategy for healing chronic diabetic wounds. Yan Li et al. utilized
the aldehyde group of oxidized sodium alginate (OSA) to undergo Schift base reaction

with the amino group of gelatin to prepare bioinks containing SA, OSA, gelatin and

CaCO3 microspheres, thereby enhancing their printability. Based on this, they

constructed porous 3D printing hydrogel scaffolds. This scaffold features a stable

structure (pore area 4.43 ± 0.14 μm², wire diameter 184 ± 25 μm), providing a potential

solution for improving wound healing in diabetes. While dynamic hydrogels were
valuable for tissue repair, improving their ability to adapt to complex chronic wounds

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without adding active substances remains a major challenge. Yuanjin Zhao et al.
created a 3D printed hydrogel scaffold using aldehyde modified glucan (DEX-BA) and

MoS₂ nanosheets. This hydrogel scaffold formed a dynamic Schiff base bond with -

NH2 on the surface of wound tissue proteins through -CHO provided by DEX-BA,

achieving a firm adhesion to the wound surface and thereby promoting the healing of

chronic diabetic wounds. Direct 3D printing of scaffolds into chronic diabetic wounds

was found to accelerate healing, promote wound closure, mitigate oxidative stress, and

eradicate bacterial infections. This study provided a multifunctional strategy for in-situ

3D printed hydrogel scaffolds, which was of great value for the healing of chronic

diabetic wounds and other related tissue engineering applications.

2.2.3. Click chemical cross-linking reaction

Click chemical cross-linking method was another common method to prepare 3D

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