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Hematin has been used as an alternative enzyme catalyst to horseradish peroxidase (HRP) due to its iron-containing activity center. Although hematin and it derivatives have been widely used for polymerization of phenol/analine compounds, it has some drawbacks such as the limited solubility and reaction only at high pH condition. Herein, we report a nanosized biomimetic catalyst, hematin-decorated polyamidoamine dendrimer (G3.0-He) that can effectively catalyze the in situ hydrogelation of phenol-conjugated polymers under neutral pH condition. We demonstrate that G3.0-He particles are smaller than 100 nm and have excellent enzyme-mimetic functions. Interestingly, the nanosized catalyst is not inactivated at high H 2 O 2 concentration. Compared to pure hematin, G3.0-He has significantly higher dispersion in acidic and neutral media, and preserves the percentage of survival of fibroblasts over 90%. Notably, G3.0-He possesses an exquisite HRP-mimicking activity in gelation of gelatin derivative with phenolic hydroxyl (tyamine) moieties under mild physiological conditions. The in vitro study demonstrated that Gel-Tyr hydrogel by G3.0-He catalyzed reaction had excellent cytocompatibility and an excellent scaffold for adhesion to fibroblast cells. Therefore, the designed minimalistic G3.0-He catalyst could serve as an effective catalytic alternative for HRP enzyme in the preparation of biomedical hydrogels., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The purpose of this research is to investigate the effect of different oxidation degrees and volume ratios of components on the physical properties and biocompatibility of an in situ cross-linking chitosan-hyaluronic acid-based hydrogel for skin wound healing applications. Carboxymethyl groups (-CH 2 COOH) were introduced to the polymer chain of chitosan, producing N,O - Carboxymethyl Chitosan (NOCC). Hyaluronic acid was oxidized to obtain aldehyde hyaluronic acid (AHA) with three oxidation degrees (AHA40, AHA50 and AHA60). The gelation was induced by forming Schiff base linkage between aldehyde groups of AHA and amino groups of NOCC. Then, the polysaccharide derivatives were combined at three NOCC:AHA volume ratios (3:7, 5:5 and 7:3) to form composite hydrogels without using any additional cross-linker. FT-IR analysis, surface morphology observation and wettability test, in vitro degradation test and rheological analysis were carried out to characterize the hydrogels. Additionally, in vitro cytotoxicity and in vivo wound healing evaluations were also conducted to study the biocompatibility of the composite. Our findings showed that when increasing the volume of NOCC, the homogeneity and hydrophobicity of the resulting hydrogels were also improved and their pore walls became thicker, leading to slower degradation rate. On the other hand, when raising the oxidation degree of AHA, the hydrophilicity of the gels decreased and less time was required to form the gel matrix. Besides, the obtained in vitro and in vivo results indicated that lower oxidation degree of AHA supports cell proliferation, cell attachment and wound healing process better. It is also concluded that NOCC-AHA40 5:5 hydrogel is most suitable for skin wound healing applications since it possesses superior morphology with high uniformity, favorable pore size and suitable density along with appropriate wettability. The NOCC-AHA gel matrix is expected to be used as a delivery system for other factors and employed as an effective bio-glue in further tissue engineering applications., (Copyright © 2019 Elsevier B.V. All rights reserved.)