**3. Animal models in burn wound studies**

The use of animals as experimental models in various biological researches for transposition into human physiology was initially provoked by Bernard in 1865 [17]. Over time, the notable similarities of anatomy and physiology between humans and animals have further encouraged many researchers to investigate a large range of mechanisms and therapies in the animal models before translating their findings to humans. In burn studies, there are some common techniques for producing wound burns in the animal model including hot water, hot metal tools, electricity, and heated paraffin [18–20]. In these methods, the back of the animal is shaved, and a heated material is executed to the skin to induce the desired burn surface area. The specific parameters such as raised temperatures and duration of exposure are required in each different burn models [21–23]. Furthermore, the integral planning for the burn animal model experiment is also crucial to be estimated. The most significant difference in the skin histology between human and animal is the density of hair. The rapidity of reepithelialization and the morphology of hair follicle are extremely influenced by the hair cycle; it would affect the planimetry area of wound and the microscope data of observable skin biopsy [24–26]. For instance, the hair cycle of rodents is short (approximately around 23–28 days). In order to avoid their hair cycle effects for the evaluation of the wound, rodents with a similar birth date should be used. Because different animals possess different hair cycles, the specific time consideration of each animal model is necessary to be highlighted. In addition, the hair might reduce the heat transfer, and some serious infections source could be hiding in the hair; thus the animal hair needs to be thoroughly depilated. Shaving by hair clipper and then applying with hair removal cream can remove the hair entirely. However, the hair removal cream might induce contact dermatitis so its administration time should be carefully controlled. Last but not least, appropriate post-operation care is needed to be considered too in order to elevate the survival rate of animal. The rational use of antibiotics can prevent wound infections, and the proper administration of analgesics can improve the appetite and self-harm of the animal [27, 28]. Moreover, large areas of burns can also cause severe loss of body fluids; therefore, intensive monitoring and handling for the dehydration of animals are necessary.

The right choice of method of burn induction and its maintenance in animal models are important as this impacts the burn outcome and determines how the wounds are treated. There is diversity among the species in the structure and anatomy of the skin along with their pros and cons as an experimental burn injury model. In this section, several animal models of burn in literature will be evaluated.

### **3.1 Mouse**

As a research model, mouse contains the major layers of the human skin (e.g., epidermis, dermis) and provides the main insights of the signaling pathways associated in the healing process due to the variety of mouse-specific reagents and transgenic feasibility in mouse. Mouse also shares several physiological and pathological features with human, including cardiovascular, musculoskeletal, and other internal organ systems [29]. Additionally, the morbidity of mouse in research is relatively low owing to an extensively reduced healing time and superior immune system [30, 31].

In burn, mouse animal models are usually used to understand the burn wound healing process and have a reproducible model. Recently, Lateef et al. demonstrated a highly reproducible partial-thickness injury in mouse that mimics the key aspects

of the inflammatory and hypertrophic scarring responses observed in humans [32]. Further, Calum et al. have established a 6% third-degree burn injury mouse model with a hot air blower [33]. This model resembles the clinical situation and provides an opportunity to examine or develop new strategies such as new antibiotics and immune therapy for handling burn wound. Moreover, a 25% third-degree burn injury was demonstrated by exposure to boiling water for examining the efficacy of new formula-based traditional medicine [34]. Although burn mouse model has its specific advantages, evidently this model fails to completely mimic the wound healing process of humans. Mouse wound healing occurs mainly through wound contraction and the presence of enriched progenitor cells from their dense skin's hair, which facilitates rapid skin healing and keratinization [30, 35]. In order to alleviate the wound contraction issue, the splinting strategy (performing mechanical fixation of the skin by using devices or splints) has been developed [36]. This method could maintain the wound volume to remain relatively constant, so it allows the histomorphometric or biomolecular quantification of the cellular response under well-controlled, experimental conditions. Another issue is the differences of chemokines and chemokine receptor system between human and mouse including chemokines IL-8, neutrophil-activating peptide-2, inducible T cell chemoattractant, and monocyte chemoattractant, which is critical for wound repair as they contribute to the inflammatory events and reparative processes [31, 37]. Because management strategies for burn injuries are advancing, it becomes essential to consider the potential limitations when assessing the translational accuracy from mouse to humans.

#### **3.2 Rat**

Rat is one of the most widely used animal models in burn studies and mainly shares similar features with mouse burn model. Both of them have the cheapest cost in terms of housing, maintenance, and reproduction. Compared with the mouse, rat possesses a larger body size and also is easier to handle as well as less easily stressed by human contact. Despite their popularity, the rapid wound healing mechanics in rats are opposed to the wound healing process seen in humans. This limitation is because rodents (rat, mouse) own a subcutaneous panniculus carnosus muscle that facilitates skin healing by both wound contraction and collagen formation [30, 38]. However, this rapid wound contraction enables the researchers to quickly study the comprehensive mechanics of wound healing to develop advanced treatment strategies.

Motamed et al. have demonstrated third-degree burn rat animal model to investigate the efficacy of amniotic membrane combined with adipose-derived stem cell treatment. The burn wound was fabricated using a hot bar (boiled in water) suppression on the dorsal site for 30 seconds [39]. In our previous study, we have developed a similar model using the implementation of 190°C brass block onto the rats' backs parallel to the midline for 20 seconds [40]. This model was used to evaluate the medical dressing's treatment on severe burn wound as well as its inflammatory responses and healing mechanisms. Recently, a rat model of polytrauma (the combination of severe burns, bone fracture, and blunt force trauma) was established to investigate the abnormal immune response leading to inadequate healing and resolution [41]. This model is proposed to create a useful model of battlefield injuries or severe traumatic injuries in a civilian population for evaluating the interventional strategies to enhance wound healing outcomes. Nevertheless, while the rat burn model is relatively simple, it loses significance when it purposes to learning the complex post-burn etiology of hypermetabolism. In the early postburn phase with high total body surface area in humans, hyperglycemia will occur

**47**

*Animal Models of Burn Wound Management DOI: http://dx.doi.org/10.5772/intechopen.89188*

**3.3 Pig**

the hypermetabolism observed in human burns.

burn models than nearly every other animal model.

sive understanding of the mechanisms of burn healing.

and initiate an overall increase of glucose and lactate [42]. As the burn wound of greater than 60% of total body surface area in rats results in reduced survivability and is not maintainable for the experimentation [14], therefore, it needs to be considered to have a burn injury model with high total body surface area to recapture

It is well known that the pig's skin characteristics such as structure, function, and cellular components most closely resemble that of humans. The epidermis and dermis of the pig are thick just like the case in humans, and their epidermis ranges from 30 to 140 μm and from 50 to 120 μm, respectively [16, 43]. Physiologically, the pig's skin responds as the human skin does to various growth factors and cytokines and displays the reepithelialization rather than contraction during the wound healing process, similar to that observed in humans. In addition, they also share important similarities such as epidermal enzyme forms, epidermal tissue turnover time, the keratinous proteins, and the composition of the lipid film of the skin surface [16]. Based on those aforementioned great anatomical and physiological similarities between pig and human, pig then has been extensively used as the experimental

Severe burn injuries cause hypertrophic scarring that generates the painful permanent hard, red, and raised scars. With great similar skin characteristics to human, pig appears to produce scarring most identical to human hypertrophic scarring. Cuttle et al. have demonstrated a pig model of hypertrophic scarring after burns using a glass bottle containing water at 92°C to the skin of a large white pig for 14 seconds to create the partial-thickness burn wound [44]. This model of hypertrophic scarring after deep dermal partial-thickness burn injury can be used to further understand the pathophysiology of burn wound healing and scar formation as well as for the testing of various agents which could potentially improve the outcome of the burn wound. Another report demonstrated the reproducible burn hypertrophic scar model using the Bama miniature pig by applying a homemade heating device for 35 seconds followed by debridement surgery [45]. This model has displayed a similar macroscopic, histologic, and biologic criteria of burn wound compared to the human hypertrophic scars. As some burn characteristics in human can be practically well mimicked, hence, the examination of various treatment strategies for severe burn injuries can be specifically applied to gain a comprehen-

Several studies developed the severe burn pig model in order to evaluate the advanced strategy for the reconstruction of burn injuries. Our laboratory has demonstrated a severe pig burn model using a minimally invasive surgical technique with an easy-to-learn, cost-effective, and reproducible method [46]. This model provides crucial tools for the evaluation of any clinical dressings and uncovers the pathophysiology of burn wound healing. Recently, full-thickness burn wounds in pig model were utilized to evaluate the effect of fractional CO2 laser therapy on objectively measured scar outcomes including scar area, pigmentation, erythema, roughness, histology, and biomechanics [47]. This model offers a powerful platform to examine the efficacy of laser therapy as a function of many treatment parameters such as the timing of therapy initiation, energy, and laser density. The use of pig as a large animal model provides the standardized location of burn injury and the therapy investigation in greater depth of wound via noninvasive and invasive analyses. Further, Singer et al. established a partial-thickness burn in pig model to investigate the efficacy of topical nitric oxide application to the burn wound [48]. They found that topical

and initiate an overall increase of glucose and lactate [42]. As the burn wound of greater than 60% of total body surface area in rats results in reduced survivability and is not maintainable for the experimentation [14], therefore, it needs to be considered to have a burn injury model with high total body surface area to recapture the hypermetabolism observed in human burns.
