A porcine model of full-thickness burn, excision and skin autografting

Abstract

Acute burn wounds often require early excision and adequate coverage to prevent further hypothermia, protein and fluid losses, and the risk of infection. Meshed autologous skin grafts are generally regarded as the standard treatment for extensive full-thickness burns. Graft take and rate of wound healing, however, depend on several endogenous factors. This paper describes a standardized reproducible porcine model of burn and skin grafting which can be used to study the effects of topical treatments on graft take and re-epithelialization. Procedures provide a protocol for successful porcine burn wound experiments with special focus on pre-operative care, anesthesia, burn allocation, excision and grafting, postoperative treatment, dressing application, and specimen collection. Selected outcome measurements include percent area of wound closure by planimetry, wound assessment using a clinical assessment scale, and histological scoring. The use of this standardized model provides burn researchers with a valuable tool for the comparison of different topical drug treatments and dressing materials in a setting that closely mimics clinical reality.

Fig. 1

Custom-made aluminum burn application device. Application pressure is measured by a 50 ml syringe attached to the aluminum bar via the heat insulation unit. This device was designed to reach a pressure of 0.4 kg/cm² when the piston is pushed into the barrel of the syringe from the “20 ml” mark down to the “10 ml” mark with one hand, while the other hand keeps the unit in place without exerting additional pressure.

Fig. 2

(A) Skeletal muscle from wound ground 24 h after burn and (B) skeletal muscle from wound ground without preceding burn. Muscle fasciculi cut longitudinally. After burn injury, the structure with wider endomysium, containing loose collagenous connective tissue (stained blue), changes to a more compact structure, however, no coagulation or necrosis of the muscle fibres is noted. Masson’s trichrome, 400× magnification. Bar represents 20 μm. (C) Dermal and subdermal tissue 24 h after burn and (D) healthy dermal and subdermal tissue. Loss of viable tissue represented by color change from green (healthy connective tissue) to red (coagulated tissue). A general compression of tissue thickness is observed. Masson’s trichrome, 25× magnification. Bar represents 600 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

Fig. 3

Multi-layer dressing to ensure maximum protection against outside contamination and avoid cross-contamination of wound fields when different test substances are used on adjacent wound fields.

Fig. 4

Digital photographs of a wound series showing wound closure during the course of the study. (A) Postoperative (PO) day 0. (B) PO day 5. (C) PO day 9. (D) PO day 14.

Fig. 5

Planimetric wound measurements. (A) Entire burn size traced and measured by planimetry using computer software. (B) Autograft mesh interstices are manually and individually traced. The total wound size is measured by planimetry. (C) Wounds show a contraction of approximately 25% of the initial wound size throughout a typical experimental course. (D) Open wound size in % of original wound size at days 9 and 14 post autograft coverage. Data presented as means ± standard error of the mean, n = 8.

Fig. 6

Clinical assessment scores for graft adherence, graft dislocation, hypergranulation, and fibrin deposition in a series of control wound fields at postoperative days 2, 5, 9 and 14. Clinical scores were made according to Table 1. Data presented as means ± standard error of the mean, n = 11.

Fig. 7

Cross section of wound center at postoperative day 14. Hematoxylin and Eosin staining. (A) Dermal tissue with three measurement markings (I = 2370 μm, II = 2735 μm, III = 2254 μm, 25× magnification). (B) Epidermal tissue with four measurement markings (I = 124 μm, II = 44 μm, III = 36 μm, IV = 76 μm. 200× magnification).

Fig. 8

Mean levels for (A) hemoglobin, (B) white blood cells, and (C) platelets. No pathologically elevated values were detected. Data presented as means ± standard error of the mean, n = 6.