**3.3 Pig**

*Animal Models in Medicine and Biology*

mouse to humans.

**3.2 Rat**

strategies.

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

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

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

**46**

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 burn models than nearly every other animal model.

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 comprehensive understanding of the mechanisms of burn healing.

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

#### *Animal Models in Medicine and Biology*

application of a nitric oxide-releasing agent accelerated wound reepithelialization and angiogenesis in this model. As there are similarities in skin anatomy and physiology between pig and human, therefore, this treatment can be considered as alternative burn care in patients. However, future studies should discover other approaches to deliver nitric oxide to burn wounds and improve long-term outcomes.

Besides those advantages to capture most pig burn model can be quite challenging to implement due to its risk of infection and high expense of housing with the greatest care.

#### **3.4 Rabbit**

Severe burn injuries are known to induce analogous hypermetabolic and pathological systemic alterations in rabbits and humans [49]. Hence, due to their remarkable similarity in metabolic characteristics, rabbit was considered as a promising animal model for burn research. Rabbit is also a cost-effective choice as burn animal model compared to the use of pig.

Rabbit model provides facilities to conduct the systemic effects of burn injury such as dynamic changes in whole-body amino acid and substrate metabolism [49]. It has also been revealed that rabbits present a high level of resting energy expenditure after a thermal injury that indicates the same evidence in burn patients [49]. Moreover, rabbit model has proven to demonstrate the involvement of leucine as an important amino acid in muscle anabolism that shows the similar kinetics and pattern of change post-thermal injury in human patients [50]. Recently, Friedrich et al. have demonstrated a quantifiable deep partial-thickness burn model in the rabbit ear using a dry-heated brass rod for 10 and 20 seconds at 90°C, resulting in a measurable burn progression and minimization of burn healing by contraction [51]. This animal model could be an important new tool to guide the treatment strategies of burn hypertrophic scarring.

#### **3.5 Dog**

Instead of several animal models that have been developed in early research, dog can be performed as a mature model for burn-blast combined injury studies. Hu et al. have established the Beagle dogs in the development of a stabilized, controllable, and repeatable animal model that can mimic the actual site of the burn-blast combined injury using explosion and napalm burns [52]. The hemodynamic changes in the early shock stage of burn were successfully investigated in this model, and it also can be used as a good research platform on the mechanisms of fluid resuscitation during burn-blast combined injury shock. Another dog burn-blast combined injury model was established including blast injury caused by explosion immediately followed by seawater immersion that is known to induce the hemodynamic changes and metabolic acidosis [53]. This model supports the investigation of the early symptoms and unique pathophysiology of the blastburn combined injury that will be valuable in defining the suitable management of such patients. However, the use of dog burn animal model for examining the comprehensive of wound healing process needs to be more considered due to the ethical regulations, limited standardized reagents, and its looser skin over the body/ trunk which results in a wound that heals primarily by contraction. Rapid contraction is a common feature of animals with loose skin, while in the tight-skinned species (human, porcine), the wound closure occurs principally as the result of reepithelialization.

**49**

**Table 1.**

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

gies through animal testing [54].

Mouse • Shares several physiological and pathological

and transgenic feasibility

Rat • Similar to mouse but possesses a larger body size and is less easily stressed by human

Pig • Possesses great anatomical and physiological similarities with human

Rabbit • Shares remarkable similarity in metabolic

and pathological alterations of burn with

• Can mimic the actual site of the burn-blast combined injury so it can be used as a good research platform on the mechanisms of fluid resuscitation during burn-blast combined injury shock as well as its early symptoms and unique pathophysiology

*Comparison of the advantages and disadvantages of burn animal model.*

organ systems) • Superior immune system

• Low morbidity • Cost-effective • Easy handling

contact

human

• Lower cost than pig

Dog • Similar environment to human

features with human (e.g., the skin, cardiovascular, musculoskeletal, other internal

• Provides various mouse-specific reagents

**4. Clinical advantages of animal models in burn research**

In clinical purposes, animal research models should be determined by maximizing their translational relevance to humans. Besides that each animal model has the unique strengths and limitations (summarized in **Table 1**), its most important value is the capability to represent the nature of disease and accurately evaluate the outcomes. There are several reasons the treatment strategies are considerably tested on animal models: (1) animals offer a degree of environmental and genetic manipulations that are rarely feasible in humans as well as unique insights into the pathophysiology and etiology of disease that frequently reveal novel targets for directed treatments; (2) if preliminary testing on animals shows their not clinically useful results, it may not be essential to test on humans; and (3) the authorities concerned with public protection have to ensure the toxicity and safety of the treatment strate-

Progress has been made in the area of assessment and measurement, either the comprehensive evaluation of burn pathological mechanisms or novel therapeutic approaches, by involving the animal models of burn. As we have discussed before, there are numerous animal models of burn established to disclose these issues. The ultimate goal of these animal studies is to examine a safe and effective test condition

**Species Advantages Disadvantages References**

• Rapid healing along with wound contrac[29–31, 35, 37]

[16, 43]

[49]

[52, 53]

• Different chemokines and chemokine receptors system • Looser skin with dense hair structure

• Similar to mouse

• Risks of infection and morbidity • High expense of housing and care

• Risks of infection and morbidity

• Ethical regulations • Limited standardized

reagents • Cost hurdles • Looser skin over the body/trunk

tion issue

*Animal Models in Medicine and Biology*

model compared to the use of pig.

of burn hypertrophic scarring.

**3.5 Dog**

outcomes.

greatest care.

**3.4 Rabbit**

application of a nitric oxide-releasing agent accelerated wound reepithelialization and angiogenesis in this model. As there are similarities in skin anatomy and physiology between pig and human, therefore, this treatment can be considered as alternative burn care in patients. However, future studies should discover other approaches to deliver nitric oxide to burn wounds and improve long-term

Besides those advantages to capture most pig burn model can be quite challenging to implement due to its risk of infection and high expense of housing with the

Severe burn injuries are known to induce analogous hypermetabolic and pathological systemic alterations in rabbits and humans [49]. Hence, due to their remarkable similarity in metabolic characteristics, rabbit was considered as a promising animal model for burn research. Rabbit is also a cost-effective choice as burn animal

Rabbit model provides facilities to conduct the systemic effects of burn injury such as dynamic changes in whole-body amino acid and substrate metabolism [49]. It has also been revealed that rabbits present a high level of resting energy expenditure after a thermal injury that indicates the same evidence in burn patients [49]. Moreover, rabbit model has proven to demonstrate the involvement of leucine as an important amino acid in muscle anabolism that shows the similar kinetics and pattern of change post-thermal injury in human patients [50]. Recently, Friedrich et al. have demonstrated a quantifiable deep partial-thickness burn model in the rabbit ear using a dry-heated brass rod for 10 and 20 seconds at 90°C, resulting in a measurable burn progression and minimization of burn healing by contraction [51]. This animal model could be an important new tool to guide the treatment strategies

Instead of several animal models that have been developed in early research, dog can be performed as a mature model for burn-blast combined injury studies. Hu et al. have established the Beagle dogs in the development of a stabilized, controllable, and repeatable animal model that can mimic the actual site of the burn-blast combined injury using explosion and napalm burns [52]. The hemodynamic changes in the early shock stage of burn were successfully investigated in this model, and it also can be used as a good research platform on the mechanisms of fluid resuscitation during burn-blast combined injury shock. Another dog burn-blast combined injury model was established including blast injury caused by explosion immediately followed by seawater immersion that is known to induce the hemodynamic changes and metabolic acidosis [53]. This model supports the investigation of the early symptoms and unique pathophysiology of the blastburn combined injury that will be valuable in defining the suitable management of such patients. However, the use of dog burn animal model for examining the comprehensive of wound healing process needs to be more considered due to the ethical regulations, limited standardized reagents, and its looser skin over the body/ trunk which results in a wound that heals primarily by contraction. Rapid contraction is a common feature of animals with loose skin, while in the tight-skinned species (human, porcine), the wound closure occurs principally as the result of

**48**

reepithelialization.
