The Wound Healing Process: Know It All

Do you recall that first fall from your bicycle as a child? Or was it an accident that left you a scar to remember for life? Well, wounds are an unpredictable part and parcel of everyday life. While some wounds are nothing to worry about like the usual knee and elbow scrapes you’re used to by now, the others that are deep and often end up leaving a scar needs optimal care to avoid any further complications. Here’s everything you need to know about wound healing!

What Are Wounds?

Wounds are injuries that cause the skin or other tissues of the body to break and may include cuts, scrapes, scratches, and punctured skin. They are often the result of an accident, however, even surgeries can result in wounds. While minor wounds aren’t serious and will heal on their own, infected wounds can turn out to be dangerous if left untreated and it is important to get medical attention immediately if necessary.¹

Types Of Wounds

Wounds are usually categorized into different types based on varying factors. They are categorized into closed and open wounds with respect to their exposure to the external environment. Wounds are also commonly categorized into acute, and chronic wounds, based on the time taken for them to heal.

1. Closed Wound: 

In a closed wound, the skin’s surface is usually intact. However, the underlying tissues could be damaged.¹ 

2. Open Wound:

In an open wound, the skin could be cracked or split, exposing the underlying tissues to the external environment.¹

3. Acute Wound¹:

Wounds that heal without causing any complications within a predicted time are known to be acute in nature.

4. Chronic Wound¹:

Wounds that take a long time to heal while also causing some complications are defined as chronic wounds. The healing of such wounds could be impacted by various factors like the presence of a biofilm, the size and depth of the injured site, and its location. 

Depending on the type of wound, it may take anywhere between days to even years to heal completely. 

What Is Wound Healing?

The term ‘wound healing’ refers to the recovery of injured skin. This process begins immediately following an injury to the epidermis and may even take years to heal completely. In an adult, the process of wound healing takes 4 phases, more about which is explained in the sections below.²

Wound Healing Types

Wound healing can also be further classified into 2 types: primary and secondary healing.²

a) Primary Healing: 

It is used to define the healing of non-infected and well-approximated wounds without any complications like a surgical wound.

b) Secondary Healing:

If the primary wound healing phase is disrupted due to an infection or immune dysfunction, then the secondary healing stage takes over. During this phase, the formation of granulation tissues and the growth of epithelial cells over these newly formed tissues take place. Such wounds are generally more susceptible to poor healing as well as infections.

Stages Of Wound Healing In Adults

For optimal healing of wounds, the process of wound healing in adults involves 4 phases that are continuous and overlapping. They include: Haemostasis, inflammation, proliferation, and remodeling.²

The 4 Stages Of Wound Healing

1. Hemostasis Phase: 

• This wound healing phase involves the closure of the wound via clotting. 
• It begins as soon as there is an external bleeding from a wound. 
• It causes the blood vessels to constrict so that the bleeding is restricted.
• Within seconds of the blood vessels in the epithelial wall rupturing, the platelets accumulate and stick to the sub-endothelial surface.
• In about 60 seconds after the above step, the fibrin (an insoluble protein that forms during blood clots) strands start adhering.
• As the formation of the fibrin mesh takes place, the blood transforms from its liquid form to a gel-like consistency via the release of prothrombin (a plasma protein found in blood) and with the help of procoagulants (agents that promote blood clotting).
• The formed clot (also known as thrombus) helps in keeping the platelets as well as the blood cells restricted to the wounded area.
• While the clot or thrombus is usually significant for aiding wound healing, it can become a cause of concern if it detaches from the wall of the endothelial blood vessel and enters the circulatory system, thereby increasing the risk of causing a stroke or heart attack.

2. Inflammatory Phase:

• This wound healing phase usually follows an injury that causes localized swelling with the injured blood vessels leaking transudate (made up of salt, protein, and water).
• It helps in preventing the onset of an infection, while also controlling the bleeding.
• The accumulation of fluids as a result of inflammation promotes healing and also repairs the cells so that they move to the wounded area.
• The damaged cells along with the pathogens and bacteria, if any, are removed from the wounded site during this phase.
• The common symptoms of pain, redness, swelling and heat associated with this phase are a result of the action of white blood cells, nutrients, growth factors, and enzymes involved.
• While the inflammatory phase forms a natural and integral part of the wound healing process, it can turn out to be problematic only if prolonged.

3. Proliferative Phase:

• The proliferative phase includes steps leading to the formation of new tissues comprising the collagen (a structural protein found in connective tissues) and extracellular matrix (a network made up of proteins and molecules that provide structural support to cells and tissues).
• It helps in the contraction of a wound as the formation of new tissues takes place.
• Following this, the construction of a new network of blood vessels takes place for the granulated tissue to be healthy and receive ample nutrients and oxygen.
• Contraction of the wound takes place with the help of myofibroblasts that grip the edges of the wound and pull them together.
• Lastly, the epithelial cells help in resurfacing the injury. The process of epithelialization (repair of wounded skin by epithelial cells) takes place faster when the wound is kept hydrated and moist.
• Normally, the application of occlusive or semi-occlusive dressings within 48 hours of an injury helps in optimizing epithelialization while also maintaining appropriate humidity required by the tissue.

4. Remodeling (Maturation Phase):

• This phase mainly involves the remodeling of type III collagen to type I, and leads to the complete closure of the wound.
• The cells used for wound repair but are no longer needed will be discarded via apoptosis (programmed cell death).
• The collagen is disorganized and then remodeled into an organized structure, therefore providing additional tensile strength to the healing tissues.
• It is the enzymes secreted by fibroblasts that helps in remodeling type III collagen to type II.
• The process of remodeling usually begins within 21 days following an injury, but may continue for a year or even more.
• Despite cross-linking, the wounded areas that are healed will be weaker than the uninjured skin, with only about 80% tensile strength as compared to the wounded skin.

Let us now have a look at what happens if the process of wound healing is disrupted in any way. 

Disrupted Wound Healing

Any disruption in the phases described above will lead to excessive wound healing or formation of chronic wounds.

Excessive Wound Healing:

While the exact pathway of excessive wound healing is not yet fully understood, it is defined as an abnormal kind of healing characterized by localized inflammation. It can be triggered by excessive collagen synthesis or exaggerated cell membrane accumulation resulting in keloid /hypertrophic scars.²

Chronic Wound Formation: 

As already discussed in the previous sections, wounds that do not heal 4 weeks after injury are referred to as chronic wounds.² Factors that can increase one’s risk of developing chronic wounds include: Immune resistance, age, smoking, medications, radiation and chemotherapy. Chronic wounds are further classified into: pressure injuries and diabetic ulcers.

Types Of Chronic Wounds

Wounds that do not heal completely even after 30 days are termed as chronic wounds. The 2 types of chronic wounds are:

1. Pressure injuries: Such injuries are also known by the terms pressure sores, decubitus ulcers and bedsores. Individuals who have been on bed rest for a long time are more prone to such wounds due to recurrent pressure on the immobilized part of the body.
2. Diabetic ulcers: Diabetes is known to cause changes to the circulation and nerves, and are known to occur in the feet.
   It is important to understand the type of tissues in the wounded site prior to opting for an appropriate treatment and management approach. Let us find out how we can differentiate between tissue types on a wounded site.

Recognizing Tissue Types

The type of tissues involved in a wound can be identified via its color, consistency, and texture. While tissues that have lost their structure along with other physical characteristics due to a wound are known as nonviable tissues, the tissues that retain their biological activities after a wound are termed as viable tissues.³

Tissue Types & Characteristics

Here are some different types of tissues and their characteristics that can help in identifying them.⁴

• Epithelial Tissue: When the epidermal layer of your skin regenerates over a wounded area, it leads to the formation of epithelial tissue (also known as epithelialization). This tissue is observed to be light pink in color with a subtle shine to it.
• Granulation Tissue: The formation of the granulation tissue is one of the most prominent signs of healing. While healthy granulation tissue is pink or red in color and unevenly textured, unhealthy granulation is darker in appearance, bleeds fast, and is often the sign of an underlying infection.
• Slough: This is one of the types of nonviable tissue that is sticky, stringy, or thick in consistency. The color of slough tissues may vary between yellow, brown, green, or gray.
• Eschar: Such tissues are dead and often a result of a fungal infection, burn, spotted fever, or gangrenous ulcer. They have a leather-like or spongy appearance.

Healing Of Chronic Wounds⁵

Once you’ve managed a chronic wound with steps like basic cleaning, debridement (removal of dead cells), and appropriate dressing, it will soon pass the inflammation phase and move towards proliferation and remodeling stages as discussed in the above section.

While proliferation helps in the closure of the wound with connective tissues, you must take extra care in ensuring that your injury is managed well on a daily basis as there is a possibility for it to go back to being inflamed. Nonetheless, once the chronic wound goes through proliferation successfully, it may take years to complete the remodeling phase, depending on the size and intensity of the wound.

To ensure optimal healing of wounds, there are many treatment options available like: compression stockings (promotes blood circulation), skin grafts (transplant of skin from other body parts), negative pressure wound therapy (air-tight dressing), and antibiotics. All of these support the wound healing process and help the injury close faster.

To Conclude 

The process of wound healing is quite complex and fragile at the same time. Any disturbance in the stages of healing may lead to the formation of chronic or excessive wounds. Appropriate wound care and management via keeping the injury moist and clean can help in speeding up the wound healing process.