The size-effect, fabrication methods and biomedical applications of heparin-based and heparin-inspired hydrogels are reviewed.

Pathogenic bacterial infection has been becoming a global threat toward people's health, especially the massive usage of antibiotics due to the lack of antibacterial agents with less side effects. Developing new nanoagents to fight pathogenic bacteria has provided enormous new possibilities in the treatment of bacterial infections, such as graphene-based two-dimensional (2D) antibacterial nanoagents with different bacterial inhibition capabilities; however, mussel-inspired design of near-infrared (NIR)-responsive and biocompatible Ag-graphene nanoagents possessing efficient and versatile bacterial disinfection activities have rarely been reported. In this study, we developed a new kind of antibacterial nanoagent, dopamine-conjugated polysaccharide sulfate-anchored and -protected Ag-graphene (Ag@G-sodium alginate sulfate ((SAS)) nanocomposite, to combat bacterial infection and contamination in different application fields. Ag@G-SAS exhibited robust antibacterial activity toward both Escherichia coli and Staphylococcus aureus; notably, the nanoagent can significantly inhibit S. aureus infection on wounded pig skin without or with NIR laser. Besides wound disinfection, the 2D Ag@G-SAS can also serve as a good layer-by-layer (LbL) building block for the construction of self-sterilizing coatings on biomedical devices. All of the results verified that the LbL-assembled Ag@G-SAS coating exhibited favorable bactericidal activity, extraordinary blood compatibilities, and good promotion ability for cell proliferation. Owing to the shielding effects of heparin-like polysaccharide sulfates, the Ag@G-SAS nanoagent showed limited cytotoxicity toward mammalian cells. Combining all of the advantages mentioned above, it is believed that the proposed Ag@G-SAS nanoagent and its LbL-assembled coatings may have versatile application potentials to avoid bacterial contaminations in different fields, such as wounded skin, disinfection of biomedical implants and devices, and food packaging sterilization.

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Free radical polymerization is a mature method and can be used for preparing multifunctional hydrogels by simply changing the commercial monomers, but the harsh and timeconsuming initiation conditions restrict its injectable ability, which further limits its application in the biomedical field. Though some catalysts can be used to accelerate the polymerization, their application is restrained by the biotoxicity. Hence, finding a biocompatible catalyzer for in situ free radical polymerization of hydrogels has a great prospect in biomedical application but is still challenging. In this study, we discovered that silver ions could catalyze free radical polymerization under ambient by transforming hydrone into hydroxyl radicals in the presence of ammonium persulfate, and the in situ-formed hydrogels prepared by this way showed great histocompatibility, hemocompatibility, cytocompatibility, and immunocompatibility. Benefitting from its convenience and biocompatibility, the in situ polymerization of polyacrylamide-based hydrogels for tissue adhesion, wound dressing, and conductive materials on the skin could be realized by simply blending diverse ingredients. Furthermore, this discovery may be a step toward the in situ-polymerized hydrogels for biomedical applications.

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