BACKGROUND:Among all types of injuries, burns are one of the most prone to inducing scars. However, there is an absence of appropriate animal models for research. This study aimed to establish an easy and reliable animal model for major burn-induced scarring and evaluate its characteristics systematically. METHODS:Rats were subjected to deep second-degree burns covering approximately 30 % of the total body surface area (TBSA) using hot liquid (94℃-98℃). Wounds were meticulously dressed, and the dressing was changed every 1-3 days. Multivariate analysis was performed to explore the critical factors for modelling. Macroscopic features and their temporal evolution were observed from day 0 to day 300 after modelling. Skin ultrasound was used to assess physicochemical properties. Haematoxylin-eosin (HE) staining, Masson staining, and immunohistochemistry staining were performed to evaluate general histological characteristics and the dynamic distribution of specific cells. Western blotting and picrosirius red staining were performed to quantify the content and ratio of collagen Ⅰ and collagen Ⅲ. RESULTS:Scar formation around 40 days post-burn, higher rat weight, and wound dressing change frequency were associated with a high success rate of modelling. Macroscopically, scars exhibited distinctive pinkish pigmentation, increased firmness, absence of new hair growth, and long-term contraction. Ultrasound imaging and histopathological staining revealed an increase in the thickness of the epidermis and dermis. Compared with normal skin, diminished dermal density and water content, and elevated transepidermal water loss rate, haemoglobin content, and elastic retraction rate were revealed in scars. Microscopically, scars manifested marked thickening of the epidermis and dermis, diminished skin appendages, and abundant collagen fibre bundles. Activated fibroblasts and microvessels were significantly increased in scars compared with those in normal skin; moreover, collagen Ⅰ and collagen Ⅲ content and collagen Ⅰ to collagen Ⅲ ratio were increased. CONCLUSION:The burn scar model in rats we constructed and continuously observed for 300 days replicates the intricate biological characteristics of scars post-burn, with simple and reliable methodology and a high success rate of more than 70 %.

BACKGROUND:Hypertrophic scars present a serious concern after surgeries and trauma, particularly with the highest risk following burn injury. The current modeling methods usually involve relatively complicated surgical operations and special equipment, and have unstable reproducibility and reliability. This study aimed to establish a simple and reliable model of post-burn hypertrophic scarring in the rat tail. METHODS:Wet gauze saturated with hot water (94-98 °C) was applied to the dorsal side of the rat tail for varying durations to induce burn injury. Wounds were left exposed until completely healed, and the optimal duration for scalding treatment was determined based on gross examination. Thereafter, the optimal scalding duration was used again to evaluate scar formation over time, which was tracked through hematoxylin-eosin (HE) and Masson staining, immunohistochemistry of scar-related proteins and number/distribution of vascular endothelial cells, and picrosirius red staining to measure the quantities and proportion of type I and III collagen. RESULTS:The scalding duration which led to optimal post-burn scarring was 15 s, with an overall success rate of 87.5 %. Complete healing of the wound occurred after roughly 30 days, leading to the formation of scars grossly red in appearance, tough to the touch and raised compared to the surrounding skin. Microscopically, the epidermis and dermis of the scar were significantly thicker than normal rat tail skin, and the dermis of scar contained a large number of disorganized bundles of fine filamentous collagen. We also observed a significant increase in the number of TGF-β1-positive cells and capillaries in the dermis (p < 0.05). Picrosirius red staining showed that compared to type III collagen, the expression of type I collagen was more dominant in scar tissue, and was more finely distributed than in normal rat tail skin. CONCLUSION:We successfully established a model for post-burn hypertrophic scarring, utilizing reliable and simple techniques and materials, which could simulate the biological characteristics of post-burn scarring. Our innovative model has the potential to facilitate the study of post-burn wound healing and scar formation.

Objective:To explore the effect of neurolysis and tendon transplantation in functional reconstruction of the upper limb with severe thermal crush injury.Methods:A retrospective case series study was conducted to analyze the clinical data of 12 patients with thermal crush injuries of the upper limb admitted to Changhai Hospital of Naval Medical University from January 2014 to December 2018. There were 9 males and 3 females, aged 22-54 years (mean, 38 years). The percentage of total body surface area (TBSA) burn ranged from 3% to 8% [(4.9±1.4)%], and wound depth was III degree. According to the damage condition of nerve/tendon and whether there was any dysfunction of the affected limb after wound healing, 12 patients received 2 to 4 times of neurolysis and tendon transplant-related surgeries, with an average surgery of 2.7 times. Among them, a total of 18 times of neurolysis were performed, including 7 times of radial neurolysis, 6 times of median nerve neurolysis and 5 times of ulnar neurolysis, and 14 times of tendon transplantation were done, including 6 times of anastomosis of superficial flexor tendon and long thumb extensor tendon, 5 times of tendon repair transplantation and 3 times of anastomosis of lateral wrist extensor tendon and long thumb extensor tendon. The time interval of each operation was 3-6 months [(4.5±1.0) months]. The Changhai pain ruler, disability of arm-shoulder-hand table (DASH) and joint activity assessment table were assessed before the first operation, 3 months and 6 months after the last operation.Results:All the patients were followed up for 6-12 months (mean, 9.2 months). The score of Changhai pain ruler in the affected limb improved from 3 (2, 3)points before surgery to 1 (0.5, 1)points 3 months after surgery and 1 (0, 1)points 6 months after surgery ( P<0.01). The score of DASH improved from (69.9±2.7) points before surgery to (35.1±1.7) points 3 months after surgery and (33.8±2.0) points 6 months after surgery ( P<0.01). The range of motion score was improved from (1.3±0.5) points before surgery to (2.4±0.5) points 3 months after surgery and (2.8±0.4) points 6 months after surgery ( P<0.01). Conclusion:Neurolysis and tendon transplantation in the treatment of severe thermal crush injuries of the upper limb can alleviate pain in the affected limbs, improve upper limb dysfunction, increase mobility of the palm and upper limb joints, and enhance the quality of life of the patients.

Human amniotic epithelial cells (hAECs) are nontumorigenic, highly abundant, and low immunogenic and possess multipotent differentiation ability, which make them become ideal alternative stem cell source for regenerative medicine. Previous studies have demonstrated the therapeutic potential of hAECs in many tissue repairs. However, the therapeutic effect of hAECs on diabetic wound healing is still unknown. In this study, we injected hAECs intradermally around the full-thickness excisional skin wounds of db/db mice and found that hAECs significantly accelerated diabetic wound healing and granulation tissue formation. To explore the underlying mechanisms, we measured inflammation and neovascularization in diabetic wounds. hAECs could modulate macrophage phenotype toward M2 macrophage, promote switch from proinflammatory status to prohealing status of wounds, and increase capillary density in diabetic wounds. Furthermore, we found that the hAEC-conditioned medium promoted macrophage polarization toward M2 phenotype and facilitated migration, proliferation, and tube formation of endothelial cells through in vitro experiments. Taken together, we first reported that hAECs could promote diabetic wound healing, at least partially, through paracrine effects to regulate inflammation and promote neovascularization.