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Skin wounds have become an important issue that affects human health and burdens global medical care. Hydrogel materials similar to the natural extracellular matrix (ECM) are one of the best candidates for ideal wound dressings and the most feasible choices for printing inks. Distinct from hydrogels made by traditional technologies, which lack bionic and mechanical properties, 3D printing can promptly and accurately create hydrogels with complex bioactive structures and the potential to promote tissue regeneration and wound healing. Herein, a comprehensive review of multi‐functional 3D printing‐based hydrogel dressings for wound healing is presented. The review first summarizes the 3D printing techniques for wound hydrogel dressings, including photo‐curing, extrusion, inkjet, and laser‐assisted 3D printing. Then, the properties and design approaches of a series of bioinks composed of natural, synthetic, and composite polymers for 3D printing wound hydrogel dressings are described. Thereafter, the application of multi‐functional 3D printing‐based hydrogel dressings in a variety of wound environments is discussed in depth, including hemostasis, anti‐inflammation, antibacterial, skin appendage regeneration, intelligent monitoring, and machine learning‐assisted therapy. Finally, the challenges and prospects of 3D printing‐based hydrogel dressings for wound healing are presented. This review comprehensively describes the development of customizable multi‐functional 3D printing‐based hydrogel dressings in the field of wound healing, objectively evaluates the advantages and disadvantages from various perspectives, and proposes the core development concept, which is obviously distinct from previous work and will provide valuable information for the research and clinical transformation of 3D printing‐based hydrogel dressings for wound healing.

Wound management is a major global challenge and a big financial burden to the healthcare system due to the rapid growth of chronic diseases including the diabetes, obesity, and aging population. Modern solutions to wound management include hydrogels that dissolve on demand, and the development of such hydrogels is of keen research interest. The formation and subsequent on-demand dissolution of hydrogels is of keen interest to scientists and clinicians. These hydrogels have excellent properties such as tissue adhesion, swelling, and water absorption. In addition, these hydrogels have a distinctive capacity to form in situ and dissolve on-demand via physical or chemical reactions. Some of these hydrogels have been successfully used as a dressing to reduce bleeding in hepatic and aortal models, and the hydrogels remove easily afterwards. However, there is an extremely wide array of different ways to synthesize these hydrogels. Therefore, we summarize here the recent advances of hydrogels that dissolve on demand, covering both chemical cross-linking cases and physical cross-linking cases. We believe that continuous exploration of dissolution strategies will uncover new mechanisms of dissolution and extend the range of applications for hydrogel dressings.

Main-sequence turnoff (MSTO) stars are good tracers of Galactic populations since their ages can be reliably estimated from atmospheric parameters. Based on the GALAH survey, we use the Yale rotation evolution code to determine the ages of 2926 MSTO stars with a mean age uncertainty of ∼10% considering the variation of C and O abundances. The ages of CO-poor stars are systematically affected by ∼10% due to the C and O abundances, globally shifting to ∼0.5 Gyr older compared to the results using solar metal mixture. Of the stars with [Fe/H] ∼ 0.3–0.5 or [O/Fe] ≤ −0.25, many have fractional age differences of ≥20%, and even reach up to 36%. The age–metallicity relation appears to possibly indicate the existence of two distinct sequences: a young sequence of stars with ages mostly <7 Gyr, and a relatively older sequence of stars with ages mostly >7 Gyr, overlapping at 5 Gyr ≤ age ≤ 7 Gyr. Moreover, the trends of abundances-to-age ratios show two corresponding sequences, especially in the [O/Fe]–age plane. We also find that [Y/Mg] is a good chemical clock in disk populations. The young sequence and the old sequence cannot be separated based on chemistry or kinematics; therefore, stellar age is an important parameter to distinguish these two sequences in our sample.

Main sequence turn-off (MSTO) stars are good tracers of Galactic populations since their ages can be reliably estimated from atmospheric parameters. Based on the GALAH survey, we use the Yale Rotation Evolution Code to determine ages of 2926 MSTO stars with mean age uncertainty \\(\\)10\\% considering the variation of C and O abundances. Ages of CO-poor stars are systematically affected by \\(\\)10\\% due to the C and O abundances, globally shifting to \\(\\)0.5 Gyr older compared to the results using solar metal-mixture. Of the stars with [Fe/H] \\(\\)0.3-0.5 or [O/Fe]~\\(\\)~-0.25, many have fractional age differences~\\(\\)~20\\%, and even reach up to 36\\%. The age-metallicity relation appears to possibly exist two distinct sequences: a young sequence of stars with age mostly \\(<\\) 7 Gyr, and a relatively older sequence of stars with age mostly \\(>\\) 7 Gyr, overlapping at 5 Gyr \\(\\)~age~\\(\\) 7 Gyr. Moreover, the trends of abundances to age ratios show two corresponding sequences, especially in [O/Fe]-age plane. We also find that [Y/Mg] is a good chemical clock in disk populations. The young sequence and the old sequence can not be separated based on chemistry or kinematics, therefore stellar age is an important parameter to distinguish these two sequences in our sample.