Application of Chitin and Chitosan in Wound Dressings

School of Materials Science and Engineering, Beijing Institute of Technology Institute of Field Transfusion, Academy of Military Medical Sciences

Skin is a vital human organ responsible for thermoregulation, infection prevention, body‑fluid retention, immune response and sensory perception. Traumatic injuries, abrasions, skin ulcers, burns and other insults may cause extensive skin damage. Skin lesions are prone to bacterial infection, excessive fluid loss and various secondary complications. Wound dressings are commonly applied to protect wounds against infection and dehydration, maintain a therapeutically favourable moist microenvironment, improve therapeutic outcomes and accelerate wound healing.

General requirements for wound dressings are summarized as follows [2‑7]: (1) Possess softness comparable to human skin and retain adequate shape‑retention and mechanical strength even under moist conditions. (2) Maintain a moist wound bed, exhibit satisfactory exudate‑absorbing capacity and appropriate gas permeability. (3) Be non‑toxic, induce no adverse biological responses or irritation to human tissues, prevent bacterial ingress to avoid secondary infection, block particulate matter and toxic contaminants, and be pyrogen‑free. (4) Preferably possess haemostatic and analgesic effects, promote granulation‑tissue formation and skin regeneration, accelerate healing and reduce scar formation. (5) Feature good storage stability, preferably be biodegradable, and produce environmentally‑benign waste upon disposal.

Chitin is a natural polymer extracted from the exoskeletons of crustaceans such as shrimp and crabs as well as the cell walls of fungi and algae. It ranks as the second‑most abundant bio‑derived resource in nature, next only to cellulose. Chitosan is the deacetylated derivative of chitin and the only naturally‑occurring alkaline polysaccharide. Generally, chitin is termed chitosan when more than 50 % of its N‑acetyl groups are removed.

In recent years, chitin and chitosan have attracted growing research interest in the field of biomaterials. Investigations have covered wound dressings, absorbable surgical sutures, sustained‑release drug carriers, enzyme immobilization, haemostatic and anticoagulant agents, anti‑obesity drugs, anti‑cancer agents and ophthalmic materials; some products have already been commercialized. Owing to their unique and excellent physiological activities, research on chitin‑ and chitosan‑based wound dressings has become a hotspot in biomaterial studies.

Chitin and chitosan exhibit desirable properties including analgesia, haemostasis, wound‑healing promotion, scar reduction, antibacterial activity, favourable biocompatibility and biodegradability, making them ideal raw materials for wound‑dressing fabrication.

1. Analgesic Effects of Chitin and Chitosan

Chitin and chitosan exert prominent soothing effects on wound‑related pain. Allen et al. reported that chitosan delivers a cooling, comfortable emollient effect upon contact with wounds. Okamoto et al. explored the analgesic mechanisms against inflammatory pain induced by dilute acetic‑acid solution. Chitosan relieves pain by capturing protons released by acetic acid at inflamed sites, whereas chitin achieves analgesia mainly through bradykinin adsorption.

2. Wound‑Healing‑Promoting and Scar‑Reducing Effects of Chitin and Chitosan

Multiple studies have investigated the mechanisms by which chitin and chitosan facilitate wound healing. Wound healing proceeds through three overlapping phases: inflammation, granulation‑tissue formation and extracellular‑matrix remodelling. Chitin and chitosan promote leukokinin release and macrophage migration. Usami et al. demonstrated chemotactic attraction of canine neutrophils toward chitin and chitosan; both substances trigger chemotactic migration of canine polymorphonuclear neutrophils (PMNs) in vitro. It is proposed that enhanced PMN migration is mediated via complement‑system activation and generation of the chemokine C5a. High local concentrations of wound‑derived chemokines recruit PMNs, which exert phagocytic and bactericidal functions at inflamed sites.

Mori et al. showed in vitro that chitin and chitosan stimulate fibroblasts to secrete interleukin‑8 (IL‑8). IL‑8 induces angiogenesis and exerts chemotactic effects on endothelial and epidermal cells, thereby stimulating fibroblast and endothelial‑cell migration and proliferation. Moreover, chitin and chitosan up‑regulate multiple mediators that promote angiogenesis and cell migration, including prostaglandin E₂, IL‑1, leukotriene B₄ (LTB₄), fibroblast‑growth‑factor‑like substances (in canine models) and IL‑1β (in human systems). Angiogenesis supplies oxygen and vitamin C required for proline and lysine hydroxylation within fibroblast cytoplasm, favouring collagen biosynthesis. Immunohistochemical evidence reveals that chitin‑ or chitosan‑treated wounds exhibit accelerated type‑III‑collagen secretion, facilitating granulation‑tissue and epithelial‑tissue formation.

Severe scarring frequently arises from an imbalance between type‑I and type‑III collagen. Animal experiments in dogs and rats indicate that chitosan application suppresses excessive scar formation. Chitin and chitosan down‑regulate type‑I‑collagen synthesis at wound sites to mitigate scarring. They also promote granulation‑tissue and epithelial regeneration and reduce wound contraction, further limiting scar development.

3. Anti‑inflammatory Properties of Chitin and Chitosan

Positively‑charged synthetic biomaterials often provoke severe inflammatory responses owing to strong, irreversible bacterial adhesion. Although primary amino groups along chitosan chains readily protonate into −NH₃⁺ in acidic environments, chitosan seldom induces marked inflammation. Zeta‑potential measurements of chitosan films with varying degrees of deacetylation (Table 1) show moderately positive surface potentials due to chitosan’s weak alkalinity, indicating minimal irritancy toward surrounding tissues.

4. Haemostatic Effects of Chitosan

Chitosan accelerates blood coagulation and thrombus formation. Haemostasis assays performed by Bhaskara et al. confirmed that chitosan promotes clotting by aggregating erythrocytes from human and animal blood. The proposed mechanism involves electrostatic attraction between positively‑charged chitosan chains and negatively‑charged teichoic acid on cell membranes. Erythrocyte agglutination induced by chitosan adhesion drives clot formation and achieves haemostasis.

5. Antimicrobial Activities of Chitin and Chitosan

Chitin, chitosan and their derivatives display broad‑spectrum inhibitory activity against bacteria, yeasts and fungi. Significant growth suppression is observed against common skin commensals such as Staphylococcus epidermidis and Escherichia coli, Candida tropicalis, as well as burn‑associated pathogens including Pseudomonas aeruginosa and Staphylococcus aureus. The precise antimicrobial mechanisms remain incompletely elucidated. One widely‑accepted hypothesis holds that electrostatic interactions between cationic chitosan and anionic microbial‑membrane components trigger leakage of bacterial proteins and intracellular constituents, leading to microbial death. At lower pH values, chitosan carries more positive charges at the C‑2 position than chitin, conferring superior antibacterial performance. Cuero et al. suggested that abundant hydroxyl and amino groups enable chitosan to act as a chelating agent that sequesters trace‑metal ions, inhibiting toxin production and microbial proliferation. Additional proposed pathways include stimulation of host‑tissue defence responses, enzyme‑inhibiting hydrogen‑bonding interactions, and intracellular penetration of low‑molecular‑weight chitosan to suppress microbial growth by blocking DNA‑to‑RNA transcription.

6. Biodegradability of Chitin and Chitosan

Chitin and chitosan can be degraded by chitinase and lysozyme. Neutrophils infiltrating wound sites secrete lysozyme, chitotriosidase, nitric oxide (NO) and other mediators, and phagocytose chitin‑ and chitosan‑derived fragments to drive degradation; NO release is more profoundly influenced by N‑acetylglucosamine units than glucosamine units. Accordingly, chitin and low‑deacetylation‑degree chitosan undergo more pronounced enzymatic degradation, whereas highly‑deacetylated chitosan degrades relatively slowly. This finding is supported by in‑vitro and in‑vivo degradation studies performed by Tomihata et al. Wound dressings fabricated from chitin or chitosan can be gradually resorbed by host tissues. This eliminates bleeding and pain during dressing removal and prevents residual debris that would retard wound healing.

Thanks to their outstanding wound‑care‑relevant performance and natural origin that aligns with the pursuit of natural biomaterials, chitin and chitosan possess prominent advantages for wound‑dressing manufacture. Chitin, chitosan and their derivatives can be processed into diverse dressing forms: powders, films, non‑woven fabrics, adhesive tapes, bandages, solutions, hydrogels, xerogels, absorbent papers, lotions and creams. Research on chitin‑ and chitosan‑based wound dressings constitutes a major research hotspot, with an increasing number of relevant publications. Further advances in this field will enable natural polymers chitin and chitosan to deliver greater benefits for human health.