**2. Wounds and wound types**

A wound is generally described as a tissue disruption from the normal anatomic structure leading to a subsequent loss of function [9]. The classical way to define a wound is to say that it is a disruption in the anatomic and cellular continuity of a tissue. Wounds tend to rupture the skin's epithelial integrity and may occur with or without microbial infection [10]. Wound may take place on many occasions during an individual's lifetime due to chemical, physical, and microbial factors influencing it. The physiological response by an individual to an injury is termed as wound healing, which involves integrated sbiochemical and cellular events leading to the regaining of functional and structural integrity at the injury site [11]. Healing of a wound starts right from the time of injury and carries on throughout the wound repair with the duration and extent varying according to the wound. Wound healing involves the action of many cells, soluble mediators and growth factors, and cell-extracellular matrix interactions. The coordinated action of all these events leads to the healing of wound *via* the process of hemostasis, inflammation, and epithelization, followed by fibroplasia and angiogenesis, finally resulting in wound contraction and remodeling [10, 12].

Humans possess an *in situ* property of wound healing, that is, self-regeneration, which depends on a person's age, gender, living habits, environment, microbial

*Nanotechnological Interventions and Mechanistic Insights into Wound-Healing Events DOI: http://dx.doi.org/10.5772/intechopen.106481*

infection, and types of wounds [13]. This leads to various criteria for wound classification: etiology, level of microbial infection, and morphology. Firstly, based on etiology, the wounds could be classified into abrasions, burns, cuts, lacerations, and stab wounds. Based on microbial infections, wounds have been categorized mainly into three groups: aseptic, contaminated, and septic wounds. There is one more characterization: closed and open wounds. Wounds are termed as closed when the skin shows no damage, but the underlying layer is injured while in open wounds the skin injury leads to exposure of the underlying tissue [14]. Finally, the duration of healing is a prime factor in wound management that leads to other criteria of wound categorization: acute and chronic wounds, which are discussed here in detail.

#### **2.1 Acute wounds**

A wound that follows an orderly and timely process of healing is termed as acute wound. These wounds tend to repair themselves following the normal stages of healing and results in timely restoration of anatomical and functional trait. They are generally caused by traumatic injury or surgery with healing time ranging from a week to a maximum of a month [10].

#### **2.2 Chronic wounds**

The wounds that fail to follow the normal procedure of the healing process thus leading to impairment in timely repair are called chronic wounds, which include diabetic and pressure wounds as well as venous and arterial ulcers. Generally, one or more than one stages of the wound-healing cascade are prolonged due to various factors leading to incomplete and disrupted healing [10]. Ulcers tend to remain in the chronic inflammation stage in pathological conditions and are characterized by an abundant infiltration of neutrophils and reactive oxygen species that release enzymes such as collagenase and elastase, leading to the destruction of cells, connective tissue, and growth factors [15]. These nonhealing wounds have a perpetual inflammation state, and they frequently relapse due to disrupted and dis-coordinated healing events [10, 16].

Millions of people globally suffer from chronic wounds affect, accounting for massive healthcare costs with estimates suggesting an annual burden of about \$30 billion in the USA alone [17]. Bacterial infection is the most frequent complication of chronic wounds, hence the search for effective treatment options that evade infections has been a continuous process over centuries with antibiotic-resistant strains emerging as a major concern [18]. The imbalances in various signaling networks coordinating cellular interactions lead to nonhealing, chronic wounds characterized by prolonged inflammation, decreased angiogenesis, impaired cellular function, and bacterial infection [19–21]. The rate of chronic wound healing differs from acute wounds and shows dependence on the patient's immunological status [22]. Despite extensive efforts to develop therapeutic strategies for the effective treatment of chronic wounds, so far, limited clinical success has been achieved [23].
