English

• Current clinical strategies for diabetes patients with chronic wound or foot ulcer are still limited and unsatisfactory due to the complex pathological mechanism stemmed from hyperglycemia environment. Specifically, compared with normal wound, diabetic wound exhibited a more unfavorable microenvironment for healing and regeneration, often characterized by persistent oxidative stress, chronic inflammation, impaired angiogenesis and other pathological features that are not conducive to wound healing [1–3]. Previous studies have shown that wound healing process generally involves a cascade of physiological activities including hemostasis, inflammation, proliferation and remodeling [4,5]. Draw back to the whole regeneration process, moderate maintenance of reactive oxygen species (ROS) plays a particularly critical role in each stage [6,7]. Therefore, strategy focusing on modulating the inflammatory environment induced by excessive ROS regeneration is proposed and thus widely investigated. In fact, numerous studies have confirmed the efficacy of natural antioxidants (such as mercaptan compounds, non-mercaptan compounds (e.g., polyphenols and anthocyanins), vitamins and various enzymes (e.g., catalase, glutathione reductase, glutathione peroxidase) on accelerating chronic wound healing [8–11]. Moreover, combined with inherent moisture property and tunable mechanical properties, hydrogels loaded with such natural compounds have also been widely exploited for application in diabetic wound healing [12–14]. Besides that, hydrogel-based wound dressings further functionalized with antibacterial nanoparticles or foods-derived materials were reported either to provide a more favorable environment to accelerate the healing process [15–17]. However, due to the complicated synthesis and the underlying allergic or toxic risks derived from raw materials, few hydrogel-based wound dressings have been successfully translated into clinical application. Therefore, the facile construction of hydrogel with high biosafety and modulation on the whole wound healing process is of great clinical significance.

  Metallic materials with biomimetic enzyme-like properties such as peroxidase-like (POD), glucose oxidase-like (GOD) have attracted much attention in the field of tissue engineering due to its persistent and effective catalysis potential on endogenous metabolites [18–20]. Ferrocene is a well-known organometallic compound that has attracted considerable interest as a candidate for antibacterial, anticancer, antifungal and antiparasitic application. According to the relevant studies, ferrocene and its derivatives with chemical and electrochemical redox reversibility have biomimetic POD-like properties, and are thus often used as redox-responsive building units, where the metal center acts as a redox-responsive center for charge-transfer active species that can undergo a reversible oxidation reaction to form Fc⁺ persistently [21–23]. However, due to its low solubility under physiological conditions, ferrocene is generally exploited as polymer derivatives through copolymerization with monomers like poly(ethylene glycol) to be used in various biomedical applications [24]. In fact, many co-polymer derivatives with ferrocene as the main chain or side chain have been developed as advanced functional materials with intriguing physiochemical properties like shape memory, anticancer treatment, oxidation-responsive [25,26]. For example, Xu et al. constructed a ε-polylysine-g-ferrocene (EPL-g-Fc) biodegradable copolymer and successfully demonstrated its remarkable efficacy in regulating the oxidative microenvironment and alleviating inflammatory responses [27].

  Spermidine, a natural polyamine widely distributed in mammalian cells, has been shown to have a wide range of biological functions, such as anti-inflammatory properties, antioxidant function, and improved mitochondrial metabolic function [28,29]. To date, spermidine may regulate cellular functions by mediating various cellular signaling pathways such as autophagy, mTOR or AMPK signaling pathway through integrating polyamine metabolism [30,31]. It has been reported that chronic injury-related diseases may benefit from the supplementation of spermidine. Spermidine with abundant active primary amine groups thus is feasible to be polymerized with carboxyl acid monomers to construct co-polymer for wound dressings. Indeed, spermidine, as a chemical cross-linker, has been reported to integrated into hydrogel framework for accelerating diabetic wound healing by modulating inflammatory microenvironment. For example, in the study of Wang et al., spermidine and terephthalaldehyde were introduced as crosslinker to construct a chitosan methacryloyl/GelMA hydrogel for accelerating wound healing. Through modulating the metabolic reprogramming and promoting the repolarization of macrophage from M1 to M2 phenotype, this wound dressing exhibited remarkable enhancement on wound enclosure while still preserve low implant-induced foreign body reaction in wound bed [32]. Taken together, it thus holds great potential to exploit bioactive polymer with spermidine as a major monomer in the backbone to be applied in diabetic wound management.

  Therefore, stemmed from the pleiotropic physicochemical properties of ferrocene and spermidine, this essay reported a ferrocene-spermidine co-polymer (FcS) for the first time through facile amidation reaction. Molecular dynamics simulation revealed its self-assembly through hydrogen bonds and van der Waals forces instead of conventional hydrophobic interaction. The self-assembled FcS nanoparticles were demonstrated to exhibit great antioxidant property on cells to facilitate their migration and angiogenesis. The integration with photocuring hydrogel, gelatin methacrylate (GelMA), to construct FcS nanoparticles loaded wound dressing (GelMA@FcS) further confirmed the potential on promoting diabetic wound enclosure through enhancement of re-epithelization and collagen deposition. Together with its great biocompatibility and biosafety, GelMA@FcS is expected to be translated into a wound dressing for clinical diabetic wounds management.

  The synthesis of FcS was achieved through the amidation reaction of 1,1′-ferrocenedicarboxylic acid and spermidine as outlined in supplementary information (Scheme S1 in Supporting information). Fourier Transform infrared spectroscopy (Fig. S1 in Supporting information), ultraviolet-visible spectroscopy (UV–vis) spectra (Fig. S2 in Supporting information) and nuclear magnetic resonance hydrogen spectroscopy (¹H NMR) spectroscopy (Fig. S3 in Supporting information) was employed to verify the successful synthesis of FcS. In the Fourier transform infrared spectrometer (FT-IR) results, the absorbance peak at 3330 and 1475 nm, derived from the N—H and CO—NH vibrations could be observed in the spectrum of FcS, preliminarily demonstrating the polymer has been successfully synthesized. Subsequently, there is no obvious change was observed in the results of UV–vis spectra, indicating no formation of extra unsaturated bond. Further, the chemical shift of 8.29 and 8.11 ppm, derived from amide H, also demonstrates the successful preparation of FcS. The FcS formed nanoparticles through self-assembly, exhibited an average diameter of 158.7 nm (polydispersity index (PDI): 0.119) with negatively charge surface (zeta potential = −10.39 mV) (Fig. 1a). The transmission electron microscopy (TEM) images revealed that the morphology of FcS nanoparticles was not traditional spherical shape (Fig. 1b). Fig. 1c showed the photo-polymerization of the GelMA@FcS hydrogel. To gain further insight into the underlying supramolecular self-assembly mechanism, molecular dynamics (MD) simulations were conducted to investigate the self-assembly process of FcS in aqueous solution. As illustrated in Figs. 1e and f, a dynamic self-assembly process could be distinctively observed from 0 ps to 8000 ps. In specific, at the initial self-assembly process (0–2000 ps), partial aggregates of FcS presented in aqueous environment could be observed. Subsequently, with the increase of time, more FcS co-polymers further stacked and interacted with each other to contribute to the final steady self-assembly. During this process, the van der Waals forces between the synthesis products of ferrocene and spermine exhibited a continuous increase, while the van der Waals forces between the FcS and water molecules demonstrated a consistent decrease, indicating the self-assembly process of FcS is drive by the van der Waals forces instead of hydrophobic interaction that generally presented in the conventional self-assembly of polymers. Concluding from the simulation by GROMACS, van der Waals forces play an important role in the self-assembly of nanoparticles.

  Figure 1

  

  Figure 1.  Preparation and characterization of GelMA@FcS hydrogel. (a) Tyndall effect, DLS and zeta potential results of FcS nanoparticles. (b) TEM image of FcS nanoparticles. Scale bar: 200 nm. (c) The gelation process of the GelMA@FcS hydrogel. (d) Morphology of GelMA@FcS hydrogel with different concentrations of FcS investigated by SEM. Scale bar: 100 µm. (e) Snapshots of FcS self-assembly process at various time depicted by GROMACS. (f) The van der Waals force between FcS and water molecules analyzed by GROMACS. (g) Compressive stress–strain characterization and (h) corresponding compressive modulus of the GelMA@FcS hydrogels. (i) Swelling ration of GelMA@FcS hydrogel with different concentrations of FcS. All data are shown as mean ± SD (n = 3). **P < 0.01. ns, not significant.

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  However, considering the chronic and persistent inflammation environment in diabetic wound bed with high demanding on long-term management, FcS nanoparticles were further incorporated into the photocurable GelMA hydrogel to better satisfy the clinical needs and the potential clinical translation. The morphology of the hydrogels loaded with different concentrations of FcS nanoparticles was illustrated in Fig. 1d by scanning electron microscope (SEM). It should be noted the pore diameter slightly decreased with the enhancement of FcS nanoparticle contents, indicating the further non-covalent interaction between GelMA and FcS nanoparticles. Therefore, the mechanical properties of GelMA@FcS hydrogels with different concentrations of FcS nanoparticles were studied. As demonstrated in Figs. 1g and h, the stress compression experiment corroborates the results of SEM, indicating that GelMA@FcS has a smaller pore size than GelMA, suggesting that FcS nanoparticles participate in the gelation process of GelMA. A smaller pore size literally indicated that the hydrogel is more tightly integrated and therefore more rigid. Subsequently, to ensure the hygroscopicity of GelMA@FcS and its anchoring on the wound bed, we tested its swelling rate, as shown in Fig. 1i. Incorporating FcS nanoparticles result in a slight decrease in the swelling rate, indicating that FcS nanoparticles participate in the gelation process of GelMA, occupying the space of GelMA and reducing the volume of liquid absorbed by swelling.

  The hemocompatibility of GelMA@FcS was identified as the most critical factor to be evaluated considering the direct contact with defect wound bed. Subsequently, the effect of GelMA@FcS on hemolysis was detected. As illustrated in Fig. 2a, the supernatant of GelMA@FcS with varying concentrations and the negative control group exhibited a near-colorless appearance, whereas a distinct red color was evident in the positive control group. Moreover, no notable discrepancy was discerned in the hemolysis ratio between the negative and GelMA@FcS-treated groups, verifying that GelMA@FcS can serve as an efficacious tissue engineering scaffold with excellent hemocompatibility. The cytotoxicity of GelMA@FcS was further evaluated using the MTT assay. As illustrated in Fig. 2b, GelMA@FcS does not exhibit any significant toxicity towards human umbilical vein endothelial cells (HUVECs), as evidenced by the comparable cell viability observed in the control group when incubated with GelMA@FcS concentrations ranging from 5 µg/mL to 100 µg/mL. Furthermore, the results of live/dead staining corroborate this conclusion. Calcein AM is susceptible to hydrolysis by esterase, which results in the binding of the dye to calcium ions, thereby emitting green fluorescence in live cells. In contrast, propidium iodide (PI) is capable of binding to DNA, leading to the display of red fluorescence in cells that have undergone apoptosis. As illustrated in Fig. 2c, the intensity of green fluorescence in the GelMA@FcS-treated group was found to be comparable to that of the untreated cells, thereby confirming the low cytotoxicity of GelMA@FcS.

  Figure 2

  

  Figure 2.  Hemocompatibility and cytotoxicity of GelMA@FcS hydrogel. (a) Hemolysis ration of GelMA and GelMA@FcS hydrogel with different concentrations of FcS. (b) Cell viability of FcS with different concentrations toward HUVEC. (c) Representative images of calcein AM/PI staining cells after treating with FcS (5 µg/mL), extracts of GelMA and GelMA@FcShydrogel (equivalence of 5 and 10 µg/mL FcS) respectively. Scale bar: 100 µm. All data are shown as mean ± SD (n = 3). ***P < 0.001.

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  The overloading of ROS represents a critical factor in the inflammatory process associated with the wound bed. A number of tissue engineering scaffolds with exceptional antioxidant properties have been demonstrated to facilitate wound healing by regulating redox balance. It is notable that ferrocene can be readily oxidated to ferrocenium, and that the reversible reduction process has been demonstrated to be feasible in biological systems, where it is widely employed as a radical scavenger and antioxidant. An antioxidant capacity evaluation was conducted using a 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging assay. As illustrated in Fig. 3a, notable discrepancies in the DPPH radical scavenging ratio are evident in the GelMA@FcS-treated groups. Furthermore, the DPPH radical scavenging ratio exhibited a slight increase with enhancement of FcS concentration, accompanied by a change in solution color from violet to brown. The redox capability of Fe²⁺ in ferrocene allows for the catalysis of H₂O₂ to O₂ and H₂O in neutral conditions. As shown in Fig. 3b, under the catalysis of GelMA@FcS hydrogel or FcS nanoparticles, the H₂O₂ level was significantly reduced, indicating this catalysis capability was derived from FcS nanoparticles. To further examine the antioxidant potential of GelMA@FcS, ROS scavenging assay was conducted using 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) probe. As illustrated in Figs. 3c, d and f, the intensity of green fluorescence diminished following with the addition of GelMA@FcS extracts to the cells, whereas no obvious alteration in the fluorescence signal was observed in GelMA-treated or untreated cells, confirming the antioxidative role of ferrocene in this formulation. Flow cytometry also verified the ROS scavenging ability of GelMA@FcS. We also investigated the ability of GelMA@FcS to catalyze hydrogen peroxide to produce O₂ in endothelial cells. The fluorescence signal (red) of the oxygen probe [Ru(dpp)₃]Cl₂ was largely quenched in endothelial cells treated with GelMA@FcS, indicating significant intracellular O₂ production (Fig. 3e). In conclusion, the results of the ROS scavenging assay demonstrate that GelMA@FcS exhibits remarkable antioxidant capabilities in scavenging ROS within cytoplasm, thereby holding the potential to accelerate the wound healing process in vivo. Inflammatory microenvironment derived from hypoglycemia in diabetic wound sites is another critical parameter to interfere the healing process. Therefore, the efficacy of GelMA@FcS on mediating the polarization of macrophages was investigated. Reverse transcription-polymerase chain reaction (RT-PCR) results showed that GelMA@FcS hydrogel inhibited the inflammatory phenotype (M1 phenotype) of RAW 264.7 by down-regulating expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNF-α), and consequently reduced the release of pro-inflammatory factors including interleukin-6 (IL-6), and TNF-α (Fig. S4 in Supporting information).

  Figure 3

  

  Figure 3.  Antioxidative property of GelMA@FcS hydrogel. (a) DPPH radical scavenging ration of FcS. (b) The H₂O₂ clear capability of GelMA@FcS hydrogel. (c) Quantitative analysis of ROS level in HUVEC treated with GelMA, FcS (5 µg/mL) or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). (d) Representative images of HUVEC stained with DCFH-DA after treatment of GelMA, FcS (5 µg/mL), or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Scale bar: 100 µm. (e) Oxygen level of HUVEC stained with Ru(dpp)₃Cl₂ after treatment of GelMA, FcS (5 µg/mL), or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Scale bar: 100 µm. (f) The ROS clear capability of GelMA@FcS hydrogel. **P < 0.01, ***P < 0.001.

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  Spermidine, a naturally occurring polyamine that is widely distributed in mammalian cells, plays a critical role in a number of physiological processes, including apoptosis, autophagy and the maintenance of chromatin stability. Previous studies revealed spermidine may have a potential role in regulating proliferation and angiogenic functions. Cell migration represents a vital process in the context of wound healing. Therefore, scratch assay was conducted to assess the migratory capacity of the cells. As illustrated in Fig. 4a, both the FcS and the extract of GelMA@FcS hydrogels demonstrated notable scratch contraction as the FcS and GelMA@FcS (5 and 10 µg/mL) treatments displayed a more pronounced migratory effect, with wound contraction reaching 70.7%, 69.7%, and 81%, respectively. While in GelMA hydrogel and control groups, wound contraction of cells only reached to 48.6% and 39.5%, respectively. These findings suggest that GelMA@FcS hydrogels may offer a promising approach for enhancing wound healing (Fig. 4c). It has been demonstrated that the supplementation of spermidine can enhance the angiogenic capacity of senescent endothelial cells. To evaluate the angiogenic capacity of GelMA@FcS, tube formation assay was performed. As illustrated in Fig. 4b, both FcS and the extract of GelMA@FcS-treated cells exhibited a notable increase in the total length and nodes of newborn microtubes, indicating that GelMA@FcS possesses the capacity to enhance angiogenesis during the wound healing process (Figs. 4d and e).

  Figure 4

  

  Figure 4.  In vitro migration and angiogenesis induced by GelMA@FcS hydrogel. (a) Representative photos of HUVECs migration at 0, 12, 24 and 48 h-post incubated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS), Scale bar: 100 µm. (b) Representative photos of tube formation after HUVECs were treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS) for 8 h, Scale bar: 100 µm. (c) Quantitative analysis on cell migration induced by GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Quantitative analysis on (d) number of nodes and (e) total lengths in the experiment of tube formation. All data are shown as mean ± SD (n = 3). P < 0.05, **P < 0.01, ***P < 0.001 vs. control group.

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  A diabetic wound is defined as a chronic wound with biochemical disorders, including hyperglycaemia, dyslipidemia and insulin resistance. It is generally regarded as the main complication resulting in an increasing risk of amputation and death. The aberrant wound healing process observed in diabetic patients renders the suppression of inflammation and infection particularly challenging. The animal experiments were approved by the Sun Yat-sen University Ethics Committee (Approval No: SYSU-IACUC-2024–000360). The capacity of GelMA@FcS on promoting wound healing process was investigated on diabetic wound rat models constructed by intraperitoneal injection with streptozotocin (STZ). As illustrated in Fig. 5a, the area of the wound beds demonstrated minimal variation on day 1, suggesting a relatively slow healing rate during the initial phase of the wound healing. At the initial state of the wound establishment, the wound may undergo the acute inflammation stage following with the swollen of wound sites. Moreover, given that the models are established on diabetic rats, hyperglycemia environment at wound site would extravagate the inflammation status further sustainedly. Therefore, negative values were detected in all groups excluding GelMA with 10 µg/mL FcS nanoparticles on day 1. Subsequently, the area of the wound bed was enclosed by approximately 60% in the GelMA@FcS -treated group, while the control and GelMA groups exhibited a reduction of only 30% on day 5. The wound beds in the GelMA@FcS (10 µg/mL) treated group exhibited complete closure by day 13, whereas an obvious wound bed persisted in the control and GelMA groups. These findings suggested that FcS-loaded GelMA may facilitate wound healing in vivo (Figs. 5b and c). Given the satisfactory capacity for wound healing, tissue samples from Sprague Dawley mice on days 3, 7 and 13 were collected for hematoxylin-eosin staining (H&E) and Masson staining in order to investigate the process of wound healing (Figs. 6a and b). On day 3, the GelMA@FcS group showed more collagen deposition than the control group. On day 7, the GelMA@FcS-treated group exhibited superior regeneration compared to the control and GelMA groups, as evidenced by the increased blue staining area observed in the GelMA@FcS group in Masson's trichrome staining. On day 13, the wound bed in the GelMA@FcS -treated group exhibited greater collagen deposition and re-epithelization than the control or GelMA group, indicating a higher degree of tissue repair. Statistical analysis showed the GelMA@FcS treated group had significantly higher collagen deposition rates on 7 and 13 days than the other groups (Fig. 6c). Re-epithelialization is an important indicator of wound healing process. The results showed that the re-epithelialization ratio of wounds treated with GelMA@FcS hydrogel showed a significant increase in thickness on day 7 (P < 0.01). On day 13, the re-epithelialization ratio from GelMA@FcS (10 µg/mL) group was enhanced to ~90%, indicating that GelMA@FcS hydrogel effectively promoted wound healing in vivo by scavenging ROS and facilitating the progression from the inflammatory and proliferative phase to the remodeling phase (Fig. 6d).

  Figure 5

  

  Figure 5.  Wound healing ratio promoted by GelMA@FcS hydrogel on diabetic wound model. (a) Representative photos of mice wounds treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS) on days 0, 1, 3, 5, 7, 10, 13. (b) Wound repair routes induced by GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). (c) Wound repair rate of mice treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS), all data are shown as mean ± SD (n = 5).

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  Figure 6

  

  Figure 6.  Chronological wound repair process promoted by GelMA@FcS hydrogel on diabetic wound model. Skin slices from different treatment groups on days 3, 7, and 13 stained by (a) H&E and (b) Masson. Scale bar: 300 µm. (c) Quantification of the collagen deposition rate. (d) Quantification of epidermal thickness. (e) Immunohistochemical analysis on VEGF and CD31 expression in skin tissues. Positive area was stained as brown and the nuclei was stained as purple. Scale bar: 100 µm. All the results are shown as mean ± SD (n = 5). P < 0.05, **P < 0.01, ***P < 0.001 vs. control group.

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  Furthermore, an immunohistochemical analysis of CD31 and vascular endothelial growth factor (VEGF) expression was conducted on day 13 (Fig. 6e). Neovascularisation is a pivotal process in skin wound healing, in which CD31 and VEGF play a pivotal role. The immunohistochemical results demonstrated that the GelMA@FcS group exhibited elevated CD31 and VEGF expression levels in comparison with the other groups, thus indicating that the GelMA@FcS hydrogel can effectively promote angiogenesis during wound healing.

  The findings revealed that GelMA@FcS hydrogels displayed remarkable regenerative capacity in facilitating wound healing. To further investigate the potential biosafety of the GelMA@FcS hydrogel, the main organs of the Sprague Dawley rats from the different groups, including hearts, livers, spleens, lungs, and kidneys, were collected and stained with H&E. As illustrated in Fig. S5 (Supporting information), no discernible histological alterations were observed in these organs in compare with the control group, thereby indicating low toxicity associated with the GelMA@FcS hydrogel. In conclusion, the GelMA@FcS hydrogel demonstrated excellent wound healing properties without significant physiological toxicity.

  Overall, in this study, FcS was successfully synthesized for the very first time. Molecular dynamics simulation by groningen machine for chemical simulations (GROMACS) revealed its self-assembly through hydrogen bonds and van der Waals forces instead of conventional hydrophobic interaction. The results also highlighted the integration of spermidine with abundant amine groups into the backbone of FcS polymer may significantly decrease the hydrophobicity of ferrocene derived from the two cyclopentadienyl rings in the structure through its hydrogen bonding with water molecules, thereby potentially enhancing the bioavailability of FcS in vivo. The further integration with photocuring hydrogel, GelMA, to construct FcS nanoparticles loaded wound dressing (GelMA@FcS) exhibited great antioxidant properties and biocompatibility towards HUVECs, and thus may effectively promote cell proliferation and angiogenesis in vitro. Subsequently, in vivo studies on diabetic wound models also have revealed that this multifunctional hydrogel can accelerate wound healing in diabetic mice through enhancement of re-epithelization and collagen deposition. Together with its great biocompatibility and biosafety, GelMA@FcS is expected to be developed into a wound dressing for clinical diabetic wounds management.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Lina Xie: Writing – review & editing, Writing – original draft, Visualization, Validation, Project administration, Methodology, Conceptualization. Xiaohe Zhang: Writing – original draft, Validation, Project administration, Methodology, Formal analysis, Data curation. Xiaobo Wang: Writing – review & editing, Validation, Resources, Investigation, Funding acquisition. Zhen Zhang: Validation, Project administration, Investigation, Formal analysis, Data curation. Tianqi Nie: Writing – review & editing, Visualization, Validation, Funding acquisition, Formal analysis. Jun Wu: Writing – review & editing, Validation, Supervision, Funding acquisition, Formal analysis, Conceptualization. Xiaojun Xu: Writing – review & editing, Validation, Supervision, Resources, Funding acquisition, Conceptualization.

  Acknowledgments

  This project was supported by National Natural Science Foundation of China (Nos. 52173150 and U22A20315), the Guangzhou Science and Technology Program City-University Joint Funding Project (No. 2024A03J0604), the Science and Technology Program of Guangzhou (No. 2024A03J0431), the start-up funding for the Seventh Affiliated Hospital of Sun Yat-sen University (Shenzhen) (No. ZSQYRSFPD0053), Guangdong Basic and Applied Basic Research Foundation (No. 2023A1515111126). We sincerely acknowledge the funding and generous support from these foundations.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.110848.

  
  
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  Figure 1  Preparation and characterization of GelMA@FcS hydrogel. (a) Tyndall effect, DLS and zeta potential results of FcS nanoparticles. (b) TEM image of FcS nanoparticles. Scale bar: 200 nm. (c) The gelation process of the GelMA@FcS hydrogel. (d) Morphology of GelMA@FcS hydrogel with different concentrations of FcS investigated by SEM. Scale bar: 100 µm. (e) Snapshots of FcS self-assembly process at various time depicted by GROMACS. (f) The van der Waals force between FcS and water molecules analyzed by GROMACS. (g) Compressive stress–strain characterization and (h) corresponding compressive modulus of the GelMA@FcS hydrogels. (i) Swelling ration of GelMA@FcS hydrogel with different concentrations of FcS. All data are shown as mean ± SD (n = 3). **P < 0.01. ns, not significant.

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  Figure 2  Hemocompatibility and cytotoxicity of GelMA@FcS hydrogel. (a) Hemolysis ration of GelMA and GelMA@FcS hydrogel with different concentrations of FcS. (b) Cell viability of FcS with different concentrations toward HUVEC. (c) Representative images of calcein AM/PI staining cells after treating with FcS (5 µg/mL), extracts of GelMA and GelMA@FcShydrogel (equivalence of 5 and 10 µg/mL FcS) respectively. Scale bar: 100 µm. All data are shown as mean ± SD (n = 3). ***P < 0.001.

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  Figure 3  Antioxidative property of GelMA@FcS hydrogel. (a) DPPH radical scavenging ration of FcS. (b) The H₂O₂ clear capability of GelMA@FcS hydrogel. (c) Quantitative analysis of ROS level in HUVEC treated with GelMA, FcS (5 µg/mL) or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). (d) Representative images of HUVEC stained with DCFH-DA after treatment of GelMA, FcS (5 µg/mL), or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Scale bar: 100 µm. (e) Oxygen level of HUVEC stained with Ru(dpp)₃Cl₂ after treatment of GelMA, FcS (5 µg/mL), or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Scale bar: 100 µm. (f) The ROS clear capability of GelMA@FcS hydrogel. **P < 0.01, ***P < 0.001.

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  Figure 4  In vitro migration and angiogenesis induced by GelMA@FcS hydrogel. (a) Representative photos of HUVECs migration at 0, 12, 24 and 48 h-post incubated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS), Scale bar: 100 µm. (b) Representative photos of tube formation after HUVECs were treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS) for 8 h, Scale bar: 100 µm. (c) Quantitative analysis on cell migration induced by GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). Quantitative analysis on (d) number of nodes and (e) total lengths in the experiment of tube formation. All data are shown as mean ± SD (n = 3). P < 0.05, **P < 0.01, ***P < 0.001 vs. control group.

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  Figure 5  Wound healing ratio promoted by GelMA@FcS hydrogel on diabetic wound model. (a) Representative photos of mice wounds treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS) on days 0, 1, 3, 5, 7, 10, 13. (b) Wound repair routes induced by GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS). (c) Wound repair rate of mice treated with GelMA, 5 µg/mL FcS or GelMA@FcS hydrogel (equivalence of 5 and 10 µg/mL FcS), all data are shown as mean ± SD (n = 5).

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  Figure 6  Chronological wound repair process promoted by GelMA@FcS hydrogel on diabetic wound model. Skin slices from different treatment groups on days 3, 7, and 13 stained by (a) H&E and (b) Masson. Scale bar: 300 µm. (c) Quantification of the collagen deposition rate. (d) Quantification of epidermal thickness. (e) Immunohistochemical analysis on VEGF and CD31 expression in skin tissues. Positive area was stained as brown and the nuclei was stained as purple. Scale bar: 100 µm. All the results are shown as mean ± SD (n = 5). P < 0.05, **P < 0.01, ***P < 0.001 vs. control group.

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