Recently, great efforts are being invested to develop new materials for healing the damaged skin rapidly and relieving suffering (Rowan et al. 2015). Wound dressings had been developed from a simple plain textile strip to engineered composite materials such as gauzes, membranes, sponges, gels, hydrocolloids and hydrogels (Pinho and Soares 2018). As an ideal dressing material, it should be readily operated and painlessly removed, absorbing fluids and exudes effectively, haemostaticity, maintaining a moist wound environment, showing higher gas permeation and preventing microbial infection (Cheng et al. 2019; Chen et al. 2018; Capanema et al. 2018). Non-toxicity, favorable biocompatibility, high elasticity and also adequate mechanical strength are the other desired properties of an ideal wound dressing (Naseri et al. 2015).
Properties such as biodegradability, biocompatibility, similarity to macromolecules recognized by the human body and promoting cell growth make some natural polymers suitable for widely using in biomedical applications (Gonzalez et al. 2014). In the last decade, natural polymers, like polysaccharides and derivatives (chitin, chitosan, alginates, heparin and cellulose), proteoglycans and proteins (collagen, gelatin, fibrin, keratin), have been developed as wound dressings (Mogoşanu and Grumezescu 2014; Ganesan 2017; Ye et al. 2018; Jayakumar et al. 2011; Clark 2018; Ge et al. 2018; Li et al. 2016; Deepachitra et al. 2014; Singaravelu et al. 2015).
Chitosan, a positively charged polysaccharide obtained by partial N-deacetylation of chitin, is known to possess unique properties including antibacterial activity, wound healing, hemostasis, and is widely used in Celox and Hemcon (Chen et al. 2018; Pourshahrestani et al. 2017). However, the fact that chitosan shows poor solubility in neutral water limits its applications in biomedicine, and the chemical modification of chitosan requires toxic organic substances. Carboxymethyl chitosan (CMCS), one of the chitosan derivatives with high solubility under physiological conditions, inherited the basic merits from chitosan that make it to be a potential candidate for wound dressings. Wang et al. reported that CMCS coated carboxymethylated cotton showed better hemostatic capacity than the cotton fabric (Wang et al. 2020). However, the water-soluble polymers are too weak to be used by itself for wound dressing or scaffolding application, many attempts have been made to increase the structural strength of CMCS. CMCS films were crosslinked by microwave technique to prolong their dimensional integrity for possible use in wound care applications (Zhang et al. 2019). CMCS-based hydrogel reinforced with modified cellulose nanocrystal for deep partial thickness burn wound healing was developed by Huang et al. (2018). The hydrogels exhibit high self-healing efficiency, injectability, good mechanical strength, and a high equilibrium swelling ratio of 350% while maintaining integrity. Furthermore, natural polymers such as gelatin have been combined with CMCS by radiation crosslinking, which was efficient to stabilize the hydrogel structure and prolong the degradation time. The CMCS/gelatin hydrogel could induce granulation tissue formation and accelerate the wound healing (Huang et al. 2013).
Because their biocompatible and biodegradable, cellulose and its derivatives have been also developed for wound dressing materials (Harkins et al. 2014; Cheng et al. 2018; Capanema et al. 2018; Fawal et al. 2018). Moreover, cellulose with stiffness molecular chain could be used effectively to strengthen the materials (Harkins et al. 2014; He et al. 2018). Thus, we attempted to introduce cellulose as a backbone into CMCS matrix, and fabricate novel cellulose/CMCS composite hydrogels for use as wound dressing material. In the present work, cellulose and CMCS were dissolved in LiOH/urea aqueous solution to construct macroporous hydrogels by using epichlorohydrin as cross-linker. The structure and morphology of cellulose/CMCS composite hydrogels were characterized by Fourier transform infrared (FT-IR) spectroscope, wide-angle X-ray diffraction (WXRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The swelling behavior and the mechanical properties of the composite hydrogels were investigated and discussed. In addition, the hydrogels were evaluated for use as wound dressing material.