2.3. Rat Burn Model

Seven Sprague–Dawley rats (150–200 g; 7 weeks old) were purchased from Bio-LASCO Co., Ltd. (Taipei City, Taiwan). The burning procedure was performed according to Wang et al. [33], and all animal experiments were approved by and conducted in accordance with the National Defense Medical Center Institutional Animal Care and Use Committee (IACUC-20-016). A total of 12 female rats were used in this study: five rats for the condition test and seven for the repeat experiment and data analysis. Before the burn wound was created using a 2-cm diameter brass block at 100 °C for 10 s, the rats were shaved dorsally and received anesthesia via intramuscular injection of Zoletil 50 (20 mg/kg; Virbac, Carros, France) in the calf area. Two parallel burn wounds were created on the back of each rat; the distance between the two wound edges was approximately 3 cm. The heated brass block caused second-degree burn wounds [34]; the wounds were covered with gauze and Tegaderm transparent film dressing (3M Health Care, St. Paul, MN, USA) to prevent scratching. All the rats were housed individually in cages under aseptic conditions after surgery.

After wounding on day 0, debridement was performed the next day (day 1). The two burn wounds on each rat were covered with gauze (control group) or LSFD (LSFD group), respectively. The animals were kept warm with an electrically heated blanket during the surgery, and received daily intramuscular injections of ketoprofen (2.5 mg/kg; Astar, Hsinchu, Taiwan) for analgesia and cefazolin (25 mg/kg; China Chemical & Pharmaceutical, Tapei City, Taiwan) to prevent infection after surgery. Each wound was disinfected daily with iodine solution and cleaned with sterile normal saline, cotton swabs, and gauze.