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diabetic wounds.

2.2.1. Optical cross-linking method

Photo cross-linking method represented a pivotal approach in chemical cross-
linking method. It utilized photosensitizers, such as riboflavin and methacrylic

anhydride, to initiate free radical reactions under specific wavelength light source

irradiation. This process leaded to the formation of covalent bonds or dynamic

coordination bonds, ultimately constructing a 3D network structure within the

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hydrogel. Besides, photo cross-linking method exhibited a rapid gel characteristic,
with gel times capable of reaching the sub-second range under optimal conditions,

which was highly consistent with the immediate molding requirements of 3D printing

technology, especially suitable for the scene of rapid wound closure in diabetic wound

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repair. Zengjie Fan et al. fabricated a 3D printed dual-network hydrogel containing
ceria-based MOF nanoenzymes with a cerium-crosslinked sodium alginate (SA) and a

polyacrylamide network. During the printing process, 365nm ultraviolet light is used to

promote the polymerization of acrylamide. After printing, the sample was further cured

under ultraviolet light for 10 minutes to achieve rapid cross-linking. Owing to the anti-
inflammatory and hypoglycemic effected of the cerium metal-organic framework

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nanoenzyme hydrogel, wounds of 1 cm in size in diabetic rats were completely healed
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within 21 days. Changyou Gao et al. addressed ROS excess and pro-inflammatory
versus anti-inflammatory cell/factor imbalance by preparing a wound dressing

consisting of DoxH-loaded ROS-responsive polyurethane membrane and 3D printed

hydrogel strips using photoinitiator LAP to promote skin regeneration in diabetic

wounds. This multifunctional MD-CH dressing obviously enhanced the healing rate of

chronic wounds, exhibiting well epithelialization, angiogenesis, and collagen

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deposition. Xiaoying Wang et al. developed a highly self-supporting CS based
hydrogel ink (CMAL) using the photoinitiator irgacure 2959 for in-situ 3D printing of

diabetic wound dressings. The ink was a reversible physical cross-linked structure

through multiple electrostatic interactions and H bond network between carboxymethyl

CS (CMA) and clay nanoparticles (LAP). Meanwhile, after the autoclaving process,

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