**1. Introduction**

Skin is the first line of human body defense against ambiance, featuring functions such as resisting microbial invasion, maintaining body fluid and water equilibrium, and regulating body temperature [1]. Upon scalding, the first line of defense is destroyed, and wound exudates such as protein and necrosed tissue prosper at the scald site, offering adequate high-nutrient substances for microbial growth and reproduction, which enables higher wound infection rates and is highly prone to an intense inflammatory response [2]. The inflammation phase of skin tissue regeneration is a crucial phase of normal wound healing, characterized by continuous infiltration of neutrophils, macrophages, and lymphocytes [3]. A few minutes after getting hurt, neutrophils arrive at the wound site and start action for several days, and they themselves are phagocytosed by tissue macrophages. Although the primary role of neutrophils is to kill bacteria, neutrophils are also a source of proinflammatory cytokines including interleukins 1α and β (IL-1α and IL-β) and tumor necrosis factor α (TNF-α) [4]. Providing the

earliest signal to inactivate fibroblasts and keratinocytes at the wound [5], these proinflammatory cytokines play a very important role in wound healing. Moreover, in the presence of microorganisms, free radicals and reactive oxygen species released at the wound site during this phase incur serious complications including infection [6], delayed healing process, and serious wound dehydration [7], while dehydration interrupts desirable moist healing environment and further postpones wound healing. Even though considerable progress has been made in burn care and treatment nowadays, infections are still an overarching risk of increased patient deaths [8]. Therefore, a desirable dressing for trauma repair should be nontoxic, non-adherent, capable of absorbing excessive exudate, and have a number of excellent properties such as efficient microbial resistance and biocompatibility.

In recent years, biomaterial-based wound dressings have been widely used, such as chitosan (CS) [9], polymeric nanofibers [10], collagen protein [11], and sodium alginate [12], among which CS is a cationic marine natural polysaccharide obtained from chitin after deacetylation of the *N*-acetyl glucosamine groups [13]. It is extensively applied in clinical practice due to the advantages of being self-biodegradable, biocompatible, non-antigenic, water absorbable, air and moisture permeable, non-toxic, and well adherent to skin without irritation [14]. In addition, studies in the past years have demonstrated that CS has certain antimicrobial activity, and in its dilute acid solution, free amino groups can be protonated such that CS carries positive charges. Then, the positively charged amino group can directly attack the negatively charged bacterial cell membrane via electrostatic attraction to disrupt the cell membrane to achieve a good antibacterial effect, which differs from target-specific interactions of conventional antibiotics and prevents drug resistance of bacteria from occurring to some extent [15–17]. By now, some CS-based wound dressing products have been developed in dosage forms of hydrogel [18,19], film [9], and sponge [20], among which hydrogel or hydrogel film is able to provide a moist environment to the wound, effectively preventing tissue dehydration and cell death, enhancing the migration of inflammatory cells and growth factors, facilitating air exchange and angiogenesis, serving as a microbial barrier, removing excessive exudate, and accelerating wound healing, among other merits, and thus has good application prospect [21–23].

Gentamicin (GT) is an aminoglycoside antibiotic with efficient antimicrobial activity, and, therefore, widely applied in the treatment of microbial infections, in particular, burn wounds [24]. If acting directly on skin, it will be difficult for GT to penetrate skin to deeper layers. Its systemic absorption is low probably due to its cationic nature, and therefore its efficacy mainly stems from a topical effect of the superficial layer of skin [25]. Nonetheless, GT can induce renal tubular necrosis and renal tubular congestion [26] and kill intra-auricular lymphocytes [27] to trigger certain nephrotoxicity and ototoxicity and is therefore limited in clinical application to some extent. In light of the toxic side effect of GT, many researchers treat GT by embedding [10,28] or fixing [29] to control GT release so that GT can act persistently. Alternatively, GT is delivered to a target site for specific binding to maintain prolonged action between the antibiotic and the target site by local delivery [30]. Based on this practice in combination with the above excellent properties of CS and application potential of CS gel formulation in wound repair, the present work intended to prepare a CS-GT hydrogel and further investigate its potential skin scald repair-promoting effect.

CS-GT has been successfully prepared in a previous study [31]. In this study, in order to investigate its potential scald healing-promoting effect, the antimicrobial activity of CS-GT was further studied, and the cytocompatibility and hemocompatibility of CS-GT were determined by cell viability assay and hemolysis assay.

#### **2. Results and Discussion**
