1Department of Burn and Plastic Surgery, Provincial Hospital Affiliated to Shandong University, Jinan 250021, Shandong Province, China 2Department of Burn, Weihai Municipal Hospital, Weihai 264200, Shandong Province, China
3Department of Pathology, Shandong Medical College, Jinan 250002, Shandong Province, China
4Department of Pathology, Provincial Hospital Affiliated to Shandong University, Jinan 250021, Shandong Province, China

Yongqiang Feng☆, M.D., Attending physician, Department of Burn and Plastic Surgery, Provincial Hospital Affiliated to Shandong University, Jinan 250021, Shandong Province, China

Yongqiang Feng and Xia Li contributed equally to this paper.

Corresponding author: Yibing Wang, Doctor, Professor, Chief physician, Department of Burn and Plastic Surgery, Provincial Hospital Affiliated to Shandong University, Jinan 250021, Shandong Province, China
sdfrank@126.com

Supported by: the Natural Science Foundation of Shandong Province, No. Y2002C29*

Abstract
Burn wound healing involves a complex sequence of processes. Recent studies have revealed that skin reinnervation may have an impact on physiological wound repair. Few studies have addressed the process of reinnervation and morphological changes in regenerated nerve fibers. The regeneration of neurites during full-thickness burn wound healing was determined by immunofluorescent staining using an anti-neurofilament protein monoclonal antibody, and three-dimensional morphology was observed under a laser scanning confocal microscope. Morphology and the volume fraction of collagen and nerve fibers were measured. Skin reinnervation increased during wound healing, peaked during the proliferative scar stage, and then decreased to lower levels during the maturation period. The results from the skin nerve fibers correlated with those from collagen using semi-quantitative analysis. Disintegration and fragmentation were observed frequently in samples from the proliferative stage, and seldom occurred during the maturation stage. There was a remodeling process of regenerated nerve fibers during wound healing, which comprised changed innervation density and topical morphology. The mechanism of remodeling for nerve fibers requires further investigation.
Key Words: burns; scar; wound healing; collagen; nerve fibers; reinnervation; tissue remodeling; neural regeneration
 

INTRODUCTION
  
The nervous system of the skin is involved in skin wound healing. It is reported that cutaneous nerves can basically return to normal 3 weeks after full-thickness damage in rat skin[1]. Navarro et al [2] reported that by 14 days post-crush and 35 days post-section of the sciatic nerve, the first regenerated axons appeared in large nerve trunks, quickly extending to the epidermis and sweat glands. The innervation of collagen-chitosan tissue-engineered skin, was first detected 60 days after transplantation and was more abundant 90 and 120 days after the graft had been applied[3]. The reinnervation of nerve-damaged skin occurred via collateral sprouting from neighboring healthy skin and axonal regeneration from deeper tissues. The former occurred within 2 weeks. The innervation density finally normalized 30–75 days post injury[4].
Numerous studies previously confirmed regeneration of skin nerves during scar tissue formation[5-7]. This study observed the number of nerve fibers in scars during the proliferative and maturation stages and found that the number of nerve fibers in hyperplastic scars continued to increase. In scars at the maturation stage, the number of nerve fibers gradually decreased to normal[6]. Few reports have been concerned with skin nerve remodeling during burn wound healing. In this study, regenerated skin nerve fibers were observed utilizing fluorescence microscopy and a laser scanning confocal microscope with neurofilament protein as a nerve marker, and the dynamic variation of skin nerves during wound healing was studied.