Classification of Wounds and Different Phases of Wound Healing Process

The primary function of the skin is to serve as a protective barrier against the environment. When this integrity of the skin gets lost after trauma either by accident or by any intent procedure, wound healing plays an important role to maintain the same.

Wound healing is the physiological process which mainly includes the three successive steps i.e,

  • Haemostasis
  • Inflammatory phase
  • Proliferative phase
  • Remodelling phase

These phases are overlapping to each other. First phase includes achieving haemostasis followed by aggregation of the platelets and damaged parenchymal cells at the site of injury. They release the growth factors and other chemical mediators for healing to attract and activate inflammatory cells and fibroblasts. Consequently, vasodilation and increased permeability of local capillaries promote the neutrophils to move at the site for the phagocytosis of the bacteria and debris. In proliferative phase the process of re-epithelization begins and formation the granulation tissue is been stimulated as result of releasing vascular endothelial growth factors (VEGF) and other growth factor from activated macrophages. Last phase includes the remodelling of collagen matrix by fibroblast to increase the tissue strength followed by wound contraction.

Phases of Wound Healing Process

Figure: Natural wound healing phases; (where, E: epidermis, D: dermis, H: hypodermis)

There are mainly two types of wounds: Acute wounds and chronic wounds.

Chronic wounds get stuck into a particular phase and cannot pass through all the phases of wound healing. Therefore, it can take more than 6 weeks and can persist up to 3 months since the time of injury. It majorly involves the destruction of all the layers of skin from epidermis, dermis and subcutaneous fat tissue layer. The affected age group can be from children, young population and old ages, irrespective of gender. Sometimes, chronic wounds typically result as complications of other disease processes i.e., foot ulcers from diabetes, pressure ulcers resulting from spinal cord injuries, etc. Apart from this, the other reasons for non-healing/ chronic wounds can be presence of biofilm at the site, hypoxia of wound bed, increased level of inflammatory mediators such as matrix metalloproteinase (MMPs), Poor nutrition or wound infections.

Acute wounds takes around 3-6 weeks to heal as it involves basically superficial layer of skin and mainly is associated with surgical incisions, thermal wounds, abrasions, and lacerations etc. Acute wounds basically progress through all the phases of wound healing that is haemostasis, inflammation, proliferative phase and remodelling phase, so they heal comparatively faster than chronic wounds.

Terminologies of different types of wounds

1. Open wound

An open wound is an injury involving an external or internal break in body tissue, usually involving the skin.

2. Abrasion

An abrasion occurs when your skin rubs or scrapes against a rough or hard surface. There’s usually not a lot of bleeding, but the wound needs to be scrubbed and cleaned to avoid infection.

3. Laceration

A laceration is a deep cut or tearing of your skin. In the case of deep lacerations, bleeding can be rapid and extensive.

4. Puncture

A puncture is a small hole caused by a long, sharp object, such as a nail or needle.

5. Avulsion

An avulsion is a partial or complete tearing away of skin and the tissue beneath.

6. Pressure ulcers

Injury to skin and underlying tissue resulting from prolonged pressure on the skin.

7. Venous ulcers

Venous ulcers are wounds that are thought to occur due to improper functioning of venous valves, usually of the legs.

8. Arterial ulcers

Arterial ulcers, also referred to as ischemic ulcers, are caused by poor perfusion (delivery of nutrient-rich blood) to the lower extremities. The overlying skin and tissues are then deprived of oxygen, killing these tissues and causing the area to form an open wound.

9. Diabetic foot ulcers

A diabetic foot ulcer is an open sore or wound that occurs in patients with diabetes and is commonly located on the bottom of the foot.

Characteristics of an Ideal Wound dressings

Dressings are designed to be in contact with the wound site in order to accelerate the wound healing process and protect it from the environment. Depending on the type of wound suitable dressing should be used. An ideal wound dressing should have below characteristics.

Desired physical characteristics

  • Ability to provide or maintain moist environment
  • Permeability to allow gas exchange between environment and wound tissue
  • Absorb the exudate from the wound bed
  • Property to provide protection to the skin from bacteria and other infectious agents
  • Tendency to regulate the tissue temperature to improve the blood flow at the wound site
  • Adaptable according to wound shape
  • Ease of application and ease of removal

Desired chemical characteristics

  • Adequate degradation rate
  • Biocompatible, non- allergic
  • Free from toxicity of the polymers or its derivatives
  • Anti-microbial activity and ability to prevent biofilm formation

Desired biological characteristics

  • Ability to enhance the epidermal migration
  • Ability to promote angiogenesis and connective tissue synthesis
  • Ability to provide debridement action to enhance leukocytes migration and support the accumulation of enzyme