ABSTRACT
<p><b>OBJECTIVE</b>To investigate the effect of chitosan on the capsule inside the expanded flap.</p><p><b>METHODS</b>The expanders were implanted in animals with the treatment of chitosan(experimental group, n = 15) or without (control group, n = 15). After taking out the expanders, the flap contraction rate was calculated. The samples were observed through HE, Masson dyeing and CD34 immunohistochemical study. The thickness of capsule inside the expanded flap was measured under microscope. The samples were also studied under electron microscope.</p><p><b>RESULTS</b>The thickness of capsule was 516.000 +/- 128.491 microm in the experimental group, and 833.000 +/- 227.379 microm in the control group (P < 0.05). The number of microvessels was 8.200 +/- 2.150 per visual in experimental group, and 7.900 +/- 1.729 per visual in control group (P > 0.05). Under the electron microscope, the rough endoplasmic reticulum (RER) in the capsule in experimental group decreased and enlarged with degranulation. The mitochondria emerged or disappeared. The number of ribosome was reduced. In the control group, the RER enlarged without degranulation, the mitochondria was intact. The number of ribosome was not reduced.</p><p><b>CONCLUSIONS</b>The chitosan can effectively reduce the contraction of expanded flap through collagen secretion of fibroblast, delaying the differentiation from fibroblast to fiber cell, inhibiting thansform from fibroblast to myofibroblast. It has no effect on the microvascular generation and expansion, so the flap blood supply will not be affected with thicker capsule.</p>