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Chronic non-healing wounds are wounds that have the failure to progress through a timely sequence of repair or one that proceeds through the wound healing process without restoring anatomic and functional results. Although there is no clear consensus in the duration of a wound that defines chronicity, a range of 4 weeks to 3 months is used to define non-healing wounds. Chronic wounds are classified into four major categories which include pressure ulcers, diabetic foot ulcers, venous ulcers, and arterial insufficiency ulcers.

In general, unstable wounds share similar characteristics: high level of proteases, elevated inflammatory markers, low growth factor activity, and reduced cellular proliferation. Common factors that affect wound healing and contribute to the pathogenesis of chronic wounds are an infection, ischemia, metabolic conditions, immunosuppression, and radiation. The wound healing process occurs in three stages: the inflammatory stage, proliferative stage, and lastly, the maturation and remodeling stage.