**6. Wound**

By functioning as a physical/chemical barrier [9], skin the largest organ of body protects the internal organs and is responsible for protecting against infections and dehydration from environmental aggressions [58]. However, it is the human body's most often damaged organ. Skin (acuteand chronic) wound defence from pathogens when it is injured (diabetes mellitus, chronic venous, arterial insufficiency, immunological and other infections) is a very difficult problem for the recovery of the injured skin. Wound is described by the Wound Healing Society as the disturbance of normal anatomical structure and functions [59]. The prevalence and severity of wounds prompted researchers to focus on wound healing management studies, as well as the demand for wound dressings. Accidents, burns, surgical operations, and violent impact all cause breaks or lacerations in the skin's membrane layers, causing damage to underlying tissues or disruption of cellular integrity, resulting in wounds [60]. Physical, mechanical, thermal, biochemical, surgical, or metabolism-related problems can all result in wounds [61–64]. If left untreated, the wound can develop sepsis, necessitating amputation or even death [60].

Wounds are graded based on (a) the time and nature of the wound healing process, (b) the depth of the wound injury, and (c) the appearance of the wounds [12]. Acute and chronic wounds are the two types of wounds that are often encountered. An acute wound is a skin injury that happens unexpectedly rather than over time, and heals in 1–12 weeks, depending on the type of the wound. It should be noted that for optimal health and cost, the healing of an acute wound (which may occur in a variety of ways) is preferable for recovery [65]. Chronic wounds can be caused by a variety of factors, including venous insufficiency, arterial perfusion, diabetes, and so on. Chronic wounds do not heal in the expected time frame because they are more vulnerable to infections and are more difficult to treat [9, 66].

Chronic wounds are divided into four categories based on their aetiology: (a) decubitus ulcers (bedsores), (b) diabetic ulcers, (c) venous ulcers (leg ulcers), and (d) arterial insufficiency ulcers [67]. Wounds are also divided as (i) superficial wounds (injury of surface of epidermis only), (ii) partial-thickness wounds (injury on both epidermis and deep into dermis like blood vessels, sweat ducts etc.), and (iii) full-thickness wounds (injury on underlying the subcutaneous fatty layers along with the layers of epidermis and dermis), (iv) on the other hand, wounds may be categorised as necrotic, sloughy, granulating, epithelializing, contaminated,

**Figure 2.** *Classification of wounds [12].*

or malodorous depending on their appearance (**Figure 2**). Complex wounds, which are either acute or chronic wounds that are difficult to heal are another new type of wounds [68–70]. Burn injuries are a form of serious wound that is frequently painful and physically damaging, accompanied by pain and inflammation. Burn wounds may often result in prolonged sensory difficulties, serious illness, and mortality as a result of long hospitalisation and recovery [71, 72]. Medical Treatment forburn wounds is still difficult, and several studies are being conducted to develop better therapeutic aids. For successful care, current industrial wound dressing products and engineered skin replacements are being pushed towards a functionalized wound dressing strategy [72].

## **7. Wound dressing classification**

Traditional, biomaterial-based, interactive, and bioactive dressings are the four types of wound dressings [73]. Traditional dressings, also called as passive wound dressings, are utilised to shield wounds from the environmental contact while also preventing bleeding [73, 74]. Traditional dressings include gauze and gauze-cotton composites, both of which have a high absorptive quality. These can, however, cause bleeding, having poor vapour permeability, and damage the freshly formed epithelium when removed. Exudates leaking from these dressings may also cause bacterial infections. Allografts, tissue derivatives, and xenografts are three types of biomaterial-based wound dressings [73]. Allografts can be defined as skin fragments collected from donors that may be fresh or freeze-dried, and their usages was restricted due to an immune response that causes the body to reject them. There's also the possibility of infection and disease transmission [75, 76]. They are costly and have a short shelf life. Tissue derivatives are made from collagen, but their use is restricted due to the possibility of infection over a long time. Artificial dressings, also called immersive wound dressings, are made up of gels, foams, films, sprays, composites, and other materials [73, 74]. Biopolymers and synthetic polymers are used to prepare them. Alginate, chitosan, gelatine, and other biopolymers are commonly used. Wound dressings may also be categorised as bioactive wound dressings, with alginates, collagens, hydro-fibres, and hydrocolloids being examples. Wound healing is aided by the addition of growth factors and antimicrobials agents. A lot of biopolymers are now being frequently used to make the wound healing materials for different type of wounds [1, 73].
