Difficult-to-heal wounds, often called ulcers, or chronic wounds, refer to wounds caused by various causes that take a long time to heal, such as wounds that have not healed for more than 1 month, or have no tendency to heal. Difficult-to-heal wounds are caused by a variety of reasons, and are mostly seen in clinical situations such as diabetic foot; pressure sores and decubitus ulcers formed in some paraplegics due to impaired limb movement and long-term bed rest; including wounds and ulcers caused by vascular diseases; wounds caused by radiological factors; or wounds formed after trauma or surgical procedures.