The skin acts as a natural barrier of the human body preventing microbial invasion and playing an important role in maintaining the stability of the internal environment. If the skin is damaged in a large area, it will cause local or systemic problems such as excessive loss of water and protein, imbalance of the immune system, and even endanger life in serious cases. The effective means of wound treatment is to cover the wound with medical dressings to provide an environment conducive to wound healing, waiting for wound epithelization or transition to the reconstruction of permanent skin barrier. However, there are usually a large number of denatured and necrotic tissues as well as effusion of plasma-like components in wounds, pathogens such as Staphylococcus aureus and Escherichia coli easily multiply in wounds, which can cause wound infection, and make it difficult to be healed. In some cases for patients with extensive skin trauma, pathogenic bacteria may enter the body causing serious infections like sepsis, meningitis or bacteremia, with life-threatening potential [1]. Therefore, to construct an ideal wound dressing with excellent antibacterial function and reduce serious infection caused by wound pathogens, has become a crucial research direction in the field of trauma treatment.
In order to prevent wound infection, much effort has been made to add antibacterial substances to wound dressings. Due to the wide application of various antibacterial drugs, the bacterium has developed new drug-resistant bacterial strains. More and more researches have been made to develop new antibacterial materials against the drug-resistant bacterial strains. The noble metal antibacterial agent such as silver nanoparticle is widely favored due to their lack of drug resistance[1, 2]. Previous studies have shown that silver nanoparticles can inhibit most positive and negative bacteria, such as: Staphylococcus aureus, Escherichia coli[3], Pseudomonas aeruginosa[4], Proteus and Acinetobacter baumannii[5], etc. Silver nanoparticles show great prospects in biomedical applications due to their unique potential to combine the inherent antibacterial effect with multiple other functionalities[1, 6]. For example, silver nanoparticles were explored to detect and diagnose malignant tumors [7, 8], control and trigger drug delivery system[9]. When combined with other antibacterial agents, silver nanoparticles show a good synergistic antibacterial effect and enhanced performance[1, 10]. Although it has many advantages, there are still some problems needed to be solved when transferring silver nanoparticles to biological media, for silver nanoparticles tend to aggregate to minimize their surface energy in the process of preparation[11], leading to reduce the antibacterial efficiency. In this regard, a practical method is to anchor them on support matrix, which can not only improve the stability, but also enhance their antibacterial properties [12, 13]. Such a suitable material is graphene oxide (GO), which is usually a single or multi-layer graphite oxide exfoliated from graphite. Upon exfoliation, graphene oxide is endowed with many oxygen-based moieties, namely epoxy and hydroxyl groups on the sheet's basal plane and carbonyl, carboxyl, hydroxyl, lactone, and phenol structures towards the sheet edge[14], which enable graphene oxide to be easily dispersible in water and other organic solvents. Graphite oxide with a transverse size of micrometer can be used as an effective template for anchoring silver nanoparticles, and the functional groups on the base and edge of GO can act as nucleation sites of silver ions, so silver nanoparticles can be stably dispersed among GO sheets avoiding the agglomeration in the synthesis process[15, 16]. Additionally, it has been proved that GO exhibit antibacterial activity against many bacterial species[17, 18]. Hence, the introduction of silver nanoparticles onto GO can not only solve the problem of aggregation and stability of silver nanoparticles, but also combine the bactericidal effect of GO and silver nanoparticles.
In recent years, many studies have demonstrated that graphene oxide-silver (GO-Ag) composites prepared by loading silver nanoparticles on graphene oxide have better antibacterial properties than silver nanoparticles. The experimental results of Zhu et al.[19] showed that the minimum inhibitory concentration of silver nanoparticles against Escherichia coli is 6.4µg/ml, while the minimum inhibitory concentration of GO-Ag nanocomposites against Escherichia coli is 3.2µg/ml, indicating that GO-Ag nanocomposites have superior antibacterial activity. Liu et al.[20] also showed that when the concentration of GO-Ag particles was 80µg/ml, its bacteriostatic rate against Escherichia coli could reach 99%, while the bacteriostatic rate of silver nanoparticles at the same concentration was 86%, and the bacteriostatic rate of GO at the same concentration was only 10%. Similar studies have found that GO-Ag nanocomposites have better antibacterial activity[15, 21–23]. Therefore, GO-Ag can be used as an outstanding nano-antibacterial filler to improve the antibacterial property of medical dressings.
Among various medical dressings materials, chitosan based biological dressings have been one of the most widely studied and applied. Chitosan is a natural cationic polysaccharide generated by the deacetylation of chitin which is abundant in nature, and mostly comes from bacteria, fungi and the shells of shrimp and crab[24]. Chitosan can increase the network structure of wound tissue, increase collagen synthesis and enhance wound tensile strength. Chitosan has great advantages in air permeability which can activate macrophages and promote wound healing[25]. Chitosan also has good biocompatibility and biodegradability, antibacterial, anti-inflammatory, anti-acid, anti-ulcer, anticoagulant properties[25–27]. Modified chitosan hydrogel was able to stable the bleeding wound under wet state and possessed potential to be a hemostatic sealant[25]. Moreover, chitosan can be used to make various forms of wound dressings such as membranes, coatings, hydrogels, fibers, powders, and nanoparticles. It has broad application prospects in medical dressings and artificial skin[28].
Taking into account the properties of the above discussed materials, the present study is combining the advantages of GO-Ag particles and chitosan to prepare graphene oxide-silver/graphene oxide/chitosan (GO-Ag/GO/CS) composite antibacterial dressing. The physicochemical and antibacterial properties of GO-Ag/GO/CS composites were investigated, with the expectation that graphene oxide contained in the dressing can adsorb bacterial substances at the wound owing to its excellent adsorption performance and high affinity for bacterial substances[29, 30], and graphene oxide-silver contained in the dressing can inhibit bacterial substances adsorbed at the wound without drug resistance. The expected GO-Ag/GO/CS composite may have a good prospect to be used as antibacterial medical dressing for skin tissue engineering.