A new model for studying deep partial-thickness burns in rats

Abstract

Burn injuries are one of the most devastating injuries in the world. A uniform burn wound is essential for burn research. The objective of this study was to describe a new model for inducing deep partial-thickness burns in rats. Burn wounds were performed on the dorsal part of Sprague-Dawley rats using a constructed heating device in our laboratory. Digital images of each animal were captured every day for macroscopic evaluation and for assessment of the wound contraction rate. Six animals were sacrificed on days 1, 3, 7, 11, 14, and 21 after onset of burn and their skin tissues were harvested for histological analysis. Uniform deep partial-thickness burns could be achieved in Sprague-Dawley rats under the condition of a contact temperature of 70°C, with the weight of heating devices of 300 g, and a duration of 10 s. Macroscopic evaluation recorded the general appearance of the deep partial-thickness burns. Evaluation of the wound contraction rate showed that the deep partial-thickness wound area was reduced by 90.39% of the original wound area by day 21 after burn. Microscopic evaluation by hematoxylin-eosin staining revealed the histological changes during the wound healing process. This is a standardized and reproducible model for inducing deep partial-thickness burns in Sprague-Dawley rats.

Keywords: Animal model; deep partial-thickness burn; macroscopic evaluation; microscopic evaluation.

Figure 1

Burn wound creation apparatus. A. A single-channel WD 1000 power unit; B. A soldering pencil; C. An aluminum head with a diameter of 20 mm; D. An insulated ring; E. Type K thermometer.

Figure 2

Microscopic assessment of burn depth at different temperatures on day 3 post-burn. Manifestation: ×20 E: epidermis D: dermis SG: sweat gland HF: Hair follicles AT: Adipose tissue M: muscle. A. 60°C burn, showing superficial burn, where the epidermis was affected (became thinner) and the dermis was normal; B. 65°C burn, showing superficial partial-thickness burn, where all epidermal layers could not be observed and the hair follicles still existed; C. 70°C burn, showing deep partial-thickness burn, where all epidermis were destroyed, and the dermis was occupied by adipose tissue.

Figure 3

Macroscopic changes of deep partial-thickness burn wound over time in Sprague-Dawley rats. Immediately after burn, he wound was round in shape and white in color, edema was obvious. From day 1 to day 3, edema gradually disappeared and the wound was covered by a firm crust. From day 7 to day 14, the crust on the wound gradually turned drier and smaller and finally fell off from the wound, and then a second discreet crust was formed. By day 21 after burn, the discreet crust was still present but much less. The wound area was very small but complete epithelialization had not been achieved.

Figure 4

Wound contraction rates of rats with deep partial-thickness burns over time. n = 6. Data are expressed as means ± S.D. *P < 0.05 versus day 3; #P < 0.05 versus day 7; ψP < 0.05 versus day 11.

Figure 5

Microscopic images of deep partial-thickness burn wound in Sprague-Dawley rats over time after burn. ×4 (A-F); ×10 (G-L). (A, G) Injured tissue on day 1 after burn, showing thinner epidermis and normal structure of dermis; (B, H) Injured tissue on day 3 after burn, showing complete destruction of epidermis and significant adipose tissue substitution in the dermis; (C, I) Injured tissue on day 7 after burn, showing tight attachment of eschar, moderate adipose tissue substitution and increasing number of inflammatory cells; (D, J) Injured tissue on day 11 after burn, showing moderate epidermal migration, mild adipose tissue substitution and mild fibrosis; (E, K) Injured tissue on day 14 after burn, showing falling of crust and moderate fibrosis; (F, L) Injured tissue on day 21 after burn, showing well-developed granulation tissue and incomplete tissue epithelialization.