The wound healing process is a complex series of events that begins at the moment of injury and can continue for months to years. The process is generally divided into four precisely orchestrated, overlapping phases:
In the hemostasis phase, the body’s clotting mechanisms work to stop the wound from bleeding. Hemostatis begins immediately after the wound occurs, and is typically achieved within minutes. However, this phase also involves the activation of various wound-healing substances that contribute to healing well after hemostasis itself is completed.
The inflammatory phase is also triggered by the initial injury, and is fully underway within several hours after the wound occurs. In this phase, the blood vessels supplying the wound tissue become leaky, allowing various inflammatory cells to migrate into the wound site. These inflammatory cells cleanse the wound by engulfing and destroying bacteria and cellular debris. During this phase, the wound typically becomes red, warm, swollen and painful. In normally-healing wounds, the inflammatory phase peaks between one to three days after the injury and can last four to six days. In chronic wounds, however, this phase often persists, interfering with healing.
The proliferative phase is when new tissue grows to fill in and cover the wound site. It typically begins about two days after the injury and lasts three to four weeks in a normally-healing wound. In a chronic wound, however, the healing process becomes “stuck” in this phase. Bringing the proliferative phase to completion is a central focus of the Winthrop Wound Healing Center.
The tissue that grows to fill in the wound during this phase is known collectively as granulation tissue. One key element of this tissue is a matrix of collagen (connective tissue). This collagen matrix provides a supportive framework for other important tissues to grow, including new capillaries (tiny blood vessels) that transport nutrients, healing factors and immune cells to the wound site and carry waste products away. Encouraging the growth of these capillaries (a process known as angiogenesis) plays an important role in our wound-healing protocols at the Winthrop Wound Center.
Other key elements of the proliferative phase are wound contraction (a drawing together of the wound edges), and epithelialization—the growth of a protective skin membrane (epithelium) over the wound. When the wound is completely covered with a new epithelial layer, we say that the wound has “closed.” Chronic wounds may sometimes require a skin graft to complete this step.
The remodeling phase, sometimes referred to as the “scar maturation” phase, is the final phase of the healing process. It begins after a wound has successfully closed, and can last up to two years. While a wound is commonly considered to have “healed” once the proliferative phase is completed, the scar tissue covering the wound continues to be replaced by newer, more organized collagen cells during this remodeling phase, producing a stronger network of skin across the wound surface.