Wound Repair at a Glance
- Acute and chronic wounds are different but overlap.
- In acute wounds, there is an orderly progression from injury to coagulation, inflammation, proliferation, cell migration, and tissue modeling.
- In the initial phases, a wide range of growth factors, including platelet-derived growth factor and transforming growth factor-β1, play an important role. In the proliferation/migration and modeling phases, tissue matrix metalloproteinases (MMPs), integrins, basic fibroblast growth factor, and endothelial growth factor are critical. MMP-1, MMP-9, and MMP-10 are essential for remodeling.
- Moist wounds heal faster, and a variety of wound dressings are now available to fit this requirement. They include transparent films, hydrocolloids, foams, alginates, gels, and collagen-based products.
- Chronic wounds are different from acute wounds in that the one-way relationship between the different phases is lost. Chronic wounds are the complex result of ischemia, pressure, and infection; healing is highly dependent on these factors.
- Wound healing of skin grafts is also different, as it is completely dependent on revascularization, be it true neovascularization or inosculation.
The terms “wound healing”, “wound repair”, or “tissue repair” are often used interchangeably, but actually “healing” and “repair” point to different sets of events and outcomes. First of all, before any distinction is made, one must recognize the rather obvious fact that “healing” and “repair” are not confined to the skin, but can encompass any organ system. Technically, wound healing is a term that should be used only in the context of true regeneration, when the original architecture and structure of an organ or anatomic part is completely restored to the way it was before injury. More primitive animals, such as small amphibians and reptiles, are still capable of this type of regeneration. However, as animals became larger and more complex during evolution, true regeneration was no longer possible. The human fetus is still largely capable of regeneration (especially in the early stages) but, in adults and with the possible exception of the liver (probably a compensatory enlargement and not regeneration), true regeneration does not take place. Rather, man and other higher vertebrates heal by a process of repair (wound repair or tissue repair), whereby the eventual outcome is not true anatomic restoration but a functional compromise. Still, because of well established terms and the published literature, even within our discussion here, we may at times use “healing” and “repair” interchangeably; we will be more specific when truly referring to the process of tissue regeneration.
There are probably evolutionary reasons for why repair occurs in higher vertebrates compared to true healing or regeneration. Teleologically and from an evolutionary standpoint, the process of repair for higher animals needed to be rapid, economical from an energy standpoint, and allow for the immediate survival of the organism. However, by necessity, repair leads to a rapid solution to injury and thus to scarring. Another important consideration is that most of the mechanisms of wound repair that have evolved are aimed at addressing acute tissue ...