Effects of continuous stretching on cell proliferation and collagen synthesis in human burn scars

Hypertrophic and contracted scars are common complications of deep and partial thickness burns, and the usual way to prevent them is to stretch the burn are actively as well as passively. However, little has been written about the effects of stretching on burn scar tissue at a cellular and molecular level. The stretching usually results in an increased area of skin, and a central question is whether this is caused by stimulation of cell proliferation or decreased cell density, which could lead to impaired quality of the skin. In the present study a new in vitro model was developed and used to study the effects of stretching on the proliferative activity as well as on the synthesis of collagen in human burn scars. Proliferation was measured quantitatively by thymidine incorporation and spatially by immunohistochemistry. The net proliferation in the burn scar was decreased after one day, and significantly decreased after six days of continuous stretching (p = 0.02). However, immunohistochemistry showed increased proliferation in the basal layer of the epidermis while the proliferative activity in the dermal cells was inhibited. Collagen synthesis was decreased after six days of stretching whereas no effect was shown after one day. These findings indicate that static stretching of a human burn scar results in inhibition of proliferation in dermal cells leading to a low cell density in the dermis which, combined with increased collagen synthesis, could lead to reduced biomechanical strength.