Full length articleElectrofabrication of functional materials: Chloramine-based antimicrobial film for infectious wound treatment
Graphical abstract
Introduction
Conventional methods to fabricate polymeric materials were developed in the last century and enlisted the remarkable advances in industrial organic chemistry. Often, the methods developed to create structure and confer function to polymers relied on processing steps and/or reactive reagents that subsequently were found to pose threats to worker safety, public health and the environment. There is a growing interest in employing electrical signals to programmably fabricate functional materials and devices [1], [2], [3], [4], [5], [6], [7], [8]. Electrical signals can be imposed with exquisite spatiotemporal control and provide exciting opportunities to create structure and confer function [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Here, we report the use of electrical inputs to program the fabrication of an antimicrobial chitosan film for a demanding medical application of chronic wound treatment.
With an aging population and increasing rates of diseases linked to ulcers and other skin wounds, such as diabetes, obesity and heart disease, the prevalence and incidence of chronic wounds are increasing [20]. Chronic wounds are defined as acute wounds that fail to heal in a normal physiological process. Bacterial infections are considered to be a major local factor resulting in chronic wounds, in which bacterial toxins stimulate inflammatory cells to secrete pro-inflammatory cytokines to induce exudate formation, delay wound healing, and facilitate improper collagen deposition [14], [20], [21]. Microbiological investigations have shown that Staphylococcus aureus (S. aureus) plays a major role in delaying the healing of nearly 25–30% of chronic wounds [22]. In fact, the contamination of chronic wounds with Methicillin-resistant Staphylococcus aureus (MRSA) represents an increasing worldwide problem. If MRSA infection progresses towards a systemic infection, options for antibiotic therapy become very limited [23].
Topical wound treatment using dressings with antimicrobial bioactivities is highly recommended to accelerate wound healing [24], [25], [26], [27], [28], [29]. Films are capable of providing a moist environment and enhancing the autolytic debridement of necrotic tissues at the wound site [30], [31]. Moreover, they can deliver antimicrobial agents locally which require smaller amounts of the antimicrobial and thus reduce the risk of systemic toxicity and the development of resistance [32]. Chitosan is a beta-1,4-linked polymer of glucosamine (2-amino-2-deoxy-beta-d-glucose) with a small amount of N-acetylglucosamine. Chitosan is often considered an appropriate material for wound dressings because it is reported to offer hemostatic, wound-healing, antimicrobial, nontoxic, biocompatible, and biodegradable properties [33], [34], [35], [36], [37], [38]. Typically, fabrication of desirable chitosan dressings involves both assembling chitosan into macro-scaled structures (i.e., matrix, fiber or film), as well as enhancing antimicrobial function. Chitosan-based macro-scaled structures are often obtained via chemical or photo cross-linking [39], [40], [41], macromolecular blending [42] solvent induced sol-gel processing [43], [44], [45], [46], or electrospinning [47]. A variety of chemical modification approaches have been considered to enhance chitosan’s antimicrobial functionality [48], [49], [50], [51], [52]. In this study, we focus on chloramine functionality which is increasingly considered as broad spectrum disinfectant active against a range of microorganisms such as bacteria, fungi and viruses, etc. [53], [54], [55], [56], [57]. A chloramine compound is defined as a compound containing one or more NCl covalent bonds that are usually formed by chlorination of amine, amide or imide functional groups using halogenating agents (e.g., hypochlorous acid, sodium hypochloride or dichlorisocyanurate sodium) [57], [58], [59], [60]. A chloramine has biocidal properties owing to the oxidation state chlorine atoms in chloramines. Chitosan, as an amino-polysaccharide, thus has the potential to be chlorinated and endowed with antibacterial property [52], [61], [62], [63].
In the present work, we report a two-step approach for enlisting electrode-imposed electrical signals for the facile fabrication of a chlorinated chitosan antimicrobial film. This approach is illustrated in Scheme 1A. In the first step, cathodic electrodeposition is used to organize chitosan (Chit) chains into a macroscopic film at the electrode surface. Mechanistically, the cathodic reduction reaction of hydrogen peroxide creates a localized region of high pH that induces chitosan chains to undergo pH-dependent self-assembly through reversible noncovalent interactions [64], [65], [66], [67], [68]. The second step is the anodic chlorination of the deposited chitosan to obtain chlorinated chitosan film (Chit-Cl). Chlorination is achieved by biasing the underlying electrode to an anodic voltage capable of oxidizing chloride ions for the in-situ generation of the reactive mediator HClO. As illustrated in Scheme 1A, we hypothesize that HClO chlorinates chitosan’s nitrogen groups to form NCl bonds [52]. This anodic chlorination step also likely includes a partial oxidation of chitosan leading to the formation of aldehyde and related derivatives, as shown in the dotted box in Scheme 1A [15], [69], [70], [71], [72]. As illustrated, this electrofabricated modified chitosan film can be peeled from electrode to obtain a free-standing chloramine film.
Here, we specifically report that electrical inputs control both the physical interactions required for macroscale structure formation by cathodic electrodeposition and the chemical reactions required for functionalization by anodic chlorination. We demonstrate that the chlorinated chitosan films confer antimicrobial activities in vitro and also promote wound healing in vivo using a MRSA infected wound model. Presumably, the antimicrobial mechanism involves the release of active chlorine from the Chit-Cl film as shown in Scheme 1B. We envision that electrofabrication provides a simple, rapid and controllable approach for the programmable preparation of antimicrobial chitosan films for wound management. More broadly, this study demonstrates the potential of electrochemistry to create novel structure and functions for achieving high performance polymeric materials.
Section snippets
Materials
Chitosan from crab shells (75–85% deacetylation and medium molecular weight) was purchased from Sigma-Aldrich. Hydrochloric acid, hydrogen peroxide, acetic acid, sodium thiosulfate, potassium iodide, glutaraldehyde, ethanol, paraformaldehyde, sodium phosphate dibasic, potassium phosphate monobasic, and sodium chloride were all purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. Starch was purchased from Sinopharm Chemical Reagent Co., Ltd. Luria-Bertani broth and agar was purchased from
Characterization of Chit and Chit-Cl films
In this study, we program the fabrication of a chloramine chitosan film using a cathodic electrodeposition of chitosan and a subsequent anodic chlorination of the deposited material. The Chit-Cl1.70C film was generated with a total charge transferred during the anodic chlorination step of 1.70 C and this condition was used as a representative for chlorinated film characterization. The visual observations of the films in Fig. 1a show that chlorination converts the transparent chitosan film into
Conclusions
In this study, we report a rapid and controllable electrochemistry approach to construct functional biomaterials for wound treatment. This method involves a cathodic electrodeposition of pristine chitosan film and a subsequent anodic chlorination of this deposited material. We provide physical and chemical evidence for the occurrence of film chlorination. Chlorination can occur on the amino groups as well as on the amide groups in chitosan molecules. This electrofabrication approach is
Acknowledgements
The support from the National Natural Science Foundation of China(51621002, 51573047), the 111 project (B14018), the Fundamental Research Funds for the Central Universities (222201717002) and the United States National Science Foundation (CBET-1435957) and Defense Threat Reduction Agency (HDTRA1-13-0037).
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2022, CarbonCitation Excerpt :The presence of organic chlorine on graphene has already been detected by exposing the graphene to chlorine gas in graphene-based gas sensors. However, it has been suggested in the literature that the appearance of two new peaks at 198.78 eV (Cl 2p3/2 chloride) and (200.38 eV Cl 2p3/2 chloride) is due to chlorine that is covalently bound to the amine nitrogen of the pyrene (-N-Cl) (Fig. 6e) [65–67]. Further evidence of chlorination can be observed in N 1s spectra.