This work was supported by La Direction G&#233;n&#233;rale de L&#39;Armement, l&#8217;Agence de l&#8217;Innovation de D&#233;fense and &#201;cole Polytechnique. We thank our colleague Mr Yann Plantier from &#201;cole Polytechnique who provided insight and expertise that greatly assisted the production of the video file. The authors thank Mr Benoit Peuteman and Ms Charlotte Auriau from INSERM Lavoisier (SEIVIL) US 33, H&#244;pital Paul Brousse, Villejuif for their animal well-being and care expertise provided during the course of this project.

All experiments were approved by the French Department of Higher Education and Research (Study Number: 122162017111616517670v2 and DAP180012). All mice were single-housed upon arrival in plastic cages and were allowed a 7-day acclimatization period prior to the study. The animal room was maintained at a 12/12 h light/dark cycle (lights on at 07:00). Food and tap water were provided ad libitum. BALB/c and SKH1-Hrhr mice were fed traditional wheat/soy-based diet. Sawdust bedding was provided along with nesting material.
1. Equipment preparation
<ol>
	<li>Prepare a burning device for the procedure and set it to 80 &#176;C using the temperature controller (Figure 1A). Verify the temperature of the brass template (Figure 1B,C) using the infrared thermal imaging camera.</li>
	<li>Ensure that the digital manometer is operating correctly.</li>
	<li>Cover the stage with a surgical drape and adjust the height of the table (Figure 1A).</li>
</ol>
2. Pre-operative and intra-operative animal care
<ol>
	<li>Acquire BALB/c and SKH1-Hrhr mice, 6-8 weeks of age.</li>
	<li>Add paracetamol suspension at 3 mg/mL to drinking water and supply 12 hours before and up to 72 hours after the procedure.</li>
	<li>Using a 1 mL syringe and a 26 G needle, administer buprenorphine subcutaneously at 0.05 &#181;g/g 30 min before the procedure and every 6 hours for the first 72 hours after the procedure.</li>
	<li>Using a 1 mL syringe and a 26 G needle, administer lidocaine to the dorsum of the mouse and 2-3 mm distal to the area of the burn wound. Inject lidocaine at 0.05 &#181;g/g subcutaneously 15 min before the induction of the burn wound.</li>
	<li>Anesthetize mice using an intraperitoneal injection of xylazine at 10 mg/kg and ketamine 100 mg/kg. Use a 1 mL syringe and a 26 G needle to administer the injection.</li>
	<li>Critical step: Place the anaesthetized mouse on a heated pad and keep the mouse warm to prevent hypothermia for the first 30 minutes after the induction of anesthesia and for at least 15 minutes after the recovery from anesthesia. In addition to the heated pad, other modalities including heat lamps, circulating warm liquids or air, and pre-warmed heat reservoirs may be used to regulate the body temperature.</li>
	<li>Apply lubrication gel on the eyes of the mouse to prevent dehydration of the cornea.</li>
	<li>Use the toe pinch withdrawal reflex to assess the depth of anesthesia.</li>
	<li>Using a 1 mL syringe and a 26 G needle administer 200 &#181;L of Lactated Ringer&#8217;s Solution supplemented with 5% dextrose. Administer fluid replacement subcutaneously immediately after the induction of anesthesia and 6 hours after the procedure to prevent dehydration.</li>
</ol>
3. Full thickness burn wound induction
<ol>
	<li>Shave the anaesthetized mouse with the hair clippers.</li>
	<li>Apply depilating cream on the dorsum surface of the mouse for 1 minute. Wipe off the cream using some sterile gauze and clean the area with a piece of damp gauze. Blot the skin with some gauze until dry.</li>
	<li>Place the mouse on the stage covered with a surgical drape and move the stage upward closer to the preheated brass template.</li>
	<li>Apply the circular brass template on the back of the mouse (80 &#176;C for 20 s) using constant pressure of 0.15 N (Figure 2).</li>
	<li>Critical step: Immediately after the burn induction, place the anaesthetized animal on the heated pad to prevent hypothermia and keep the mouse warm during and after the procedure. Once recovered from anesthesia, return the mouse back to the cage.</li>
	<li>Critical step: Provide a mashed diet on the cage floor for the first 72 hours after the surgical procedure. Mice are sometimes reluctant to reach up to a sipper tube to drink water after a burn wound injury.</li>
</ol>
4. Harvesting of the donor graft
<ol>
	<li>Make a longitudinal incision with a scalpel in the upper part of the tail of the donor mouse and gently remove the skin using surgical forceps.</li>
	<li>Place the tail skin into a sterile Petri dish filled with 10 mL of sterile 0.9% saline solution. Use a ruler to measure out individual grafts and cut the tail skin into pieces, each measuring 15 mm, using a scalpel.</li>
	<li>Once prepared, keep the skin grafts in 0.9% saline solution at 4 &#176;C for up to 2 hours.</li>
</ol>
5. Surgical excision and skin grafting
<ol>
	<li>Twenty-four hours after the burn induction, prepare the mouse for anesthesia by inhalation of isoflurane. Place the mouse into the induction chamber and induce anesthesia using 5% isoflurane in 100% oxygen at a flow rate of 4 L/min. To maintain anesthesia during surgery, use 2% isoflurane at 2 L/min.</li>
	<li>Place a surgical drape on the mouse and cut out a window to expose the surgical field. Using the aseptic technique, swab the wound first with povidone-iodine and then with 70% alcohol.</li>
	<li>Gently pick up the burned tissue with a pair of surgical tweezers and excise all necrotic and nonviable tissue with sterile surgical scissors and tweezers. Remove the panniculus carnosus layer of the hypodermis to create a stable recipient bed.</li>
	<li>Place the skin graft on the freshly prepared wound bed. Gently pull the surrounding skin toward the skin graft using surgical tweezers. Apply some surgical adhesive to attach the graft to the wound bed and gently press to align the skin edges. Critical step: The size of the wound bed must be slight larger than the size of the skin graft to ensure successful engraftment.</li>
	<li>Allow the mouse to recover from anesthesia. Critical step: Place the mouse on a heated pad. Keep the mouse warm during and after the procedure to prevent hypothermia.</li>
	<li>Apply inert paraffin gauze dressing and adhesive secondary dressing over the grafted wound.</li>
	<li>Place the mouse into an individual cage. Critical step: Provide some mashed diet on the cage floor for the first 72 hours after the surgical procedure and monitor daily.</li>
	<li>Provide toys and enrich the environment.</li>
</ol>
6. Digital imaging and post-mortem wound collection
<ol>
	<li>Photograph wounds with a digital camera by placing a ruler next to the wound (Figure 3).</li>
	<li>At the end point of the experiment, euthanize animals by exposure to carbon dioxide and cervical dislocation. Critical step: Excessive pulling action of the skin during the cervical dislocation may damage the graft.</li>
	<li>At post-mortem, surgically excise the dorsal burn wounds to the fascia using scissors. Bisect wounds. Fix half in 10% buffered formalin and process for histology and immunohistochemistry. Fast freeze the other half in liquid nitrogen for RNA extraction and protein quantitation and keep at -80 &#176;C.</li>
</ol>
7. Skin histology, immunohistochemistry and collagen visualization
<ol>
	<li>Embed samples of skin into paraffin, cut to 4 &#181;m sections and place onto positively charged slides.</li>
	<li>Use slides stained with hematoxylin and eosin to evaluate the rate of re-epithelialization (% of the original wound). The area of the wound that is covered with neo-epidermis may be expressed as a percentage of the entire wound (Figure 4). Use a digital microscope application and ImageJ software to perform the microscopic analysis of the sections.</li>
	<li>Use histological sections (4 &#181;m thickness) prepared from formalin-fixed and paraffin-embedded tissue and subject them to immunohistochemistry.</li>
	<li>To assess collagen I and fibronectin expression in wounds, apply primary antibodies and incubate for 1 h. Detection may be performed by species-specific horseradish peroxidase (HRP) or alkaline phosphatase (AP)-conjugated secondary antibodies.</li>
	<li>React sections with either: (i) HRP,3,3&#39;-diaminobenzidine (DAB) or (ii) AP, Bond Polymer Refine Red (Table of Materials), which yields a bright red color (Figure 5). Scan the sections using an instrument and analyze with the digital microscope application and ImageJ.</li>
	<li>To enable histological assessment of collagen deposition, perform trichrome staining on histological sections using a commercial kit.</li>
	<li>For collagen fiber visualization, use multiphoton microscopy and second harmonic generation technique (Figure 5). Use a multiphoton microscope for tissue imaging as previously described20. Use a Ti:Sapphire laser with a center wavelength at 810 nm as the laser source for generating second harmonic and two-photon excited fluorescence signals (TPEF).</li>
	<li>Use a laser beam equipped with a 25x/0.95 W objective to collect and excite second harmonic generation (SHG) and TPEF. Detect signals as described previously21 by NDD PMT detectors. Use software for laser scanning control and image acquisition.</li>
</ol>

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The authors declare that they have no competing financial interests.

According to the thickness classification of burn injury23, full thickness burns are characterized by evident involvement of the whole thickness of the skin and certain portion of the subcutaneous tissue. This type of wound can heal only by contraction or with skin grafting2. An inherent limitation of the method described in this article is that only full thickness grafts, as opposed to the split thickness grafts, which are often used in the clinical setting, were harvested from the tail of a mouse. This was due to the technical difficulty, as the mouse skin is too thin to obtain split thickness grafts. It must be pointed out that full thickness grafts require a well vascularized wound bed, whereas split thickness skin grafts are able to survive at donor sites with less vascularity24. Previous studies showed that a burn wound induced on the back of the mouse was associated with a robust formation of new vasculature5. This suggests that a well vascularized area, such as the dorsum of the mouse, could be considered as the anatomical landmark for the induction of burn wounds.
Burn wound depth is an important factor to consider. The depth of the burn wound must be consistent between individual mice. The reproducibility of the burn wound depth depends on the temperature of the brass template, pressure and duration of the heat exposure. The burn wound depth must be verified histologically. It is important to keep in mind that excessive pressure or prolonged exposure of the skin to the preheated brass template may injure the underlying tissue. The tissue surrounding the vertebral column, including the components of the central and peripheral nervous system, are sensitive to heat, and if damaged may result in hind leg paralysis.
Although no postoperative mortality was directly associated with the surgical procedure, a small number of hairless SKH1-Hrhr mice, which are especially sensitive to cold, developed hypothermia and failed to recover after the general anaesthesia. Therefore, supplementary heat must be provided during all aesthetic events and constant surveillance is required while the mouse is anaesthetized.
The method described in this study was not associated with the surgical site infection. However, aseptic technique must be used to prevent the transfer of microorganisms into the surgical wound during the perioperative period. Inoculation of the wound with bioluminescent or fluorescent microorganisms may be incorporated into the procedure. This technique may be useful in studying infectious organisms and their pathogenesis25. For example, exogenous addition or injection of bioluminescent bacteria, may permit the monitoring of the microbial burden using the in vivo whole animal imaging25. Given that mouse hair is known to interfere with the in vivo whole animal fluorescence and bioluminescence imaging, hairless SKH1-Hrhr mice are ideal hosts for the studies involving fluorescent or bioluminescent reporters.
Wound tissue samples may be collected at different time points and processed for histological and immunohistochemical analysis. Protein and RNA may be isolated from the skin biopsy and molecular biology techniques may be used to assess the expression of key molecules involved in wound healing.
In the present study, we described an experimental model of burn wound healing and allogeneic skin engraftment. This procedure can be modified and serve as a model for preclinical studies.

Surgical debridement and skin grafting are common clinical practices used in the management of chronic wounds1, burn wounds2, and acute wounds such as traumatic wounds3. Skin grafting refers to the surgical procedure, which involves the removal of healthy skin from one part of the body and transferring it to another. Donor grafts replace the lost tissue and provide a structural scaffold for cellular migration and growth. Following integration into the recipient site, skin grafts replace the lost skin barrier by providing protection from microbial invasion, harmful effects of the external environment and excessive loss of moisture4. Successful skin graft integration depends on several factors. These include adequate immune responses in the presence of microbial infections and timely resolution of inflammation, robust angiogenesis at the wound site and establishment of vascular anastomoses between the recipient bed and the donor graft5. As the graft begins to degrade, resident dermal cells must be replaced by cells capable of producing new extracellular matrix. At the same time, the epidermal keratinocytes must crawl over the newly produced matrix to form the neo-epidermis and re-epithelialize the wound. It is, therefore, evident that efficient migration of cells from the recipient bed into the donor graft is another determining factor that influences successful graft incorporation. Given the vast number of factors involved in wound healing6, which may be impossible to control in the human trials due to ethical limitations, models of pre-clinical experimental skin grafting are necessary. Development of pre-clinical models of burn wound healing and associated skin grafting will be important for understanding of complex mechanisms involved in cutaneous tissue repair and essential for the testing of new therapeutic agents. The in vitro models of wound healing are unable to accurately mimic the complexity of the cutaneous tissue. The in vivo animal models are an indispensable investigative tool in understanding the mechanisms involved in tissue repair.
Several methods of skin grafting technique were developed in rodents to mimic surgical excision and burn wound reconstruction7,8,9. However, most of the previously described procedures failed to induce a thermal burn injury prior to skin grafting. Instead of the burn wound, a full thickness excisional wound was induced, which was then reconstructed with a full thickness skin allograft7. Various anatomical landmarks such as the ear, tail and back have been used for harvesting of the donor skin in rodents7,8. Different graft fixation and stabilization techniques were reported, including a &#8220;no suture technique&#8221;9, sutures7 and surgical glue10,11,12.
The purpose of this study was to develop a murine model of a full thickness burn wound that would recapitulate the current gold standard approach in burn treatment, which involves nonviable tissue excision and skin grafting. A thermal burn was induced on the dorsum surface of a mouse using a preheated brass template. Burn eschar was excised and replaced with a full thickness graft harvested from the tail of a donor mouse. There are three key advantages to this experimental model. First, more than one burn wound may be induced on the back of the recipient mouse, and four donor skin grafts may be harvested from a single tail of the donor mouse. This means that several experimental and control treatments may potentially be compared using the same recipient and donor animals. Depending on the desired route of administration, the control treatment may include local or systemic administration of the vehicle or placebo control (e.g., topical application of ointment, subcutaneous, intraperitoneal or intravenous injection of solution). Second, timing of the treatment and the endpoint of the experiment may be controlled. Third, this model depends on the reconstruction of wounds using full thickness grafts harvested from the tail, which are known to have a higher probability for successful incorporation into the donor site compared to the skin harvested from the back13. This may be due to the lower number of epidermal Langerhans cells, which play a key role in cutaneous immunobiology, and are associated with the skin graft rejection14.
The proposed model of wound healing and graft integration may well be applied to transgenic and knockout mice. The use of genetically modified mice will assist in elucidating the roles that certain genes may play during wound repair. Exogenous application of topical wound preparations or subcutaneous administration of therapeutic antibodies at the site of the injury may also be considered.
Due to technical difficulties, split thickness skin grafts consisting of the epidermis and part of the dermis are difficult to obtain in mice. Full thickness skin grafts consisting of the epidermis and full thickness dermis are known to require a well-vascularized wound bed for successful integration. The inability to harvest split thickness skin grafts in mice may be regarded as a limitation of this model. The fixation of the skin graft to the recipient wound bed was achieved via the application of the surgical adhesive glue, which is associated with less trauma and rapid degradation compared to other means of tissue fixation15. Previous studies have shown that suturing is associated with stronger tissue fixation than the surgical glue at 24 h after the surgical procedure15, which may be considered as a disadvantage of the procedure. However, at later timepoints, the biomechanical strength of wounds treated with a surgical adhesive becomes comparable to sutures15 and better than staple fixation16. Following tissue fixation with the surgical glue, wounds must be covered with a wound dressing. Although wounds on the dorsal surface of the mouse are difficult for the animal to reach, the wound dressing, on the other hand, is easy for the animal to manipulate and remove. Frequent wound dressing changes may be warranted.
Anesthesia-induced hypothermia in small rodents is a well-documented phenomenon17. Hypothermia is a side effect of this procedure, which causes complications, and potentially compromises both animal health and data quality. Therefore, this method warrants the implementation of temperature management strategies, especially if hairless SKH1-Hrhr are used.
The most significant limitation of using mice to mimic human wound closure is the difference between the skin anatomy and physiology. Mouse wounds heal mostly via contraction, whereas human wounds heal through granulation tissue formation and re-epithelialization18. To account for this discrepancy, the current model may be modified and used in combination with a splinting ring tightly adhered around the wound to prevent skin contraction19. Given some advantages and disadvantages of this in vivo protocol, this model could serve as a tool to study certain processes involved in wound healing that are impossible to study in vitro.

<table><tbody><tr><td>1 ml syringue</td><td>Terumo</td><td>SS + 01T1</td><td></td></tr><tr><td>26 G needle</td><td>Terumo Agani</td><td>NN-2613R</td><td>1/2&#039;&#039; - 0,45 X 12mm</td></tr><tr><td>96X21 mm Petri Dish</td><td>Dutscher</td><td>193199</td><td></td></tr><tr><td>Animal Weighing scale</td><td>Kern</td><td>EMB 5.2K5</td><td></td></tr><tr><td>BALB/c mouse</td><td>Janvier labs</td><td>BALB/cAnNRj</td><td>6-weeks old</td></tr><tr><td>Biopsy foam pads 30.2X25.4X2mm</td><td>Simport</td><td>M476-1</td><td></td></tr><tr><td>Bond polymer Refine Red</td><td>Leica Biosystems</td><td>DS9390</td><td></td></tr><tr><td>Brass block</td><td>BVG</td><td>custom-designed</td><td>Circular 10 mm in diameter</td></tr><tr><td>Buprenorphine (BUPRECARE)</td><td>Axience</td><td>FR/V/6328396 3/2011</td><td>administered subcutaneously at a dose of 0.05 &amp;mu;g/ g</td></tr><tr><td>Burning apparatus Kausistar 400</td><td>Tra&amp;ccedil;aMatrix</td><td>34010</td><td></td></tr><tr><td>CaseViewer</td><td>3DHISTECH Ltd.</td><td></td><td>3Dhistech, Budapest, Hungary</td></tr><tr><td>Collagen I antibody</td><td>Abcam</td><td>ab34710</td><td>Recommanded concentration 1:50; 1:200</td></tr><tr><td>D-(+)- glucose (Dextrose)</td><td>Sigma Aldrich</td><td>G-8769-100 ml</td><td></td></tr><tr><td>DAB</td><td>Leica Biosystems</td><td>AR9432</td><td></td></tr><tr><td>Digital camera</td><td>NIKON</td><td>D3400</td><td>objective: SIGMA 18-250mm F3.5-6.3 DC MACRO C45</td></tr><tr><td>Depilating cream</td><td>Veet</td><td></td><td></td></tr><tr><td>Disposable scalpels</td><td>Swann Morton</td><td>6601</td><td></td></tr><tr><td>DPBS</td><td>PAN biotech</td><td>P04-36300</td><td></td></tr><tr><td>Ethanol absolute</td><td>VWR chemicals</td><td>20821.310</td><td></td></tr><tr><td>Fibronectin antibody</td><td>Abcam</td><td>ab23750</td><td>Recommanded dilution 1:1000</td></tr><tr><td>Filter 0.22um</td><td>Sartorius</td><td>16532</td><td></td></tr><tr><td>Fine Scissors</td><td>F.S.T.</td><td>14094-11</td><td></td></tr><tr><td>Forceps Dumont</td><td>F.S.T.</td><td>11295-10</td><td></td></tr><tr><td>Hair clippers</td><td>AESCULAP</td><td>B00VAQ4KUY (ISIS)</td><td></td></tr><tr><td>Heating pad</td><td>Petelevage</td><td>120070</td><td></td></tr><tr><td>Isofluorane</td><td>Piramal healthcare</td><td>FR/V/03248850/2011</td><td></td></tr><tr><td>Ketamine</td><td>Imalgene</td><td>FR/V/0167433 4/1992</td><td>surgical anesthetic, administered intraperitoneally at a dose of 100mg/kg</td></tr><tr><td>Lactated Ringers solution</td><td>Flee-Flex</td><td>1506443</td><td></td></tr><tr><td>Lamina multilabel slide scanner</td><td>Perkin Elmer</td><td></td><td></td></tr><tr><td>LAS software</td><td>Leica</td><td></td><td>version 2.7.3</td></tr><tr><td>Leica Bond III</td><td>Leica Biosystem</td><td>1757</td><td></td></tr><tr><td>Leukosilk dressing</td><td>BSN medical</td><td>72669-01</td><td></td></tr><tr><td>Lidocaine</td><td>Aguettant</td><td>N01BB02</td><td>local analgesic, administered subcutaneously at a dose of 0.05 &amp;mu;g/ g</td></tr><tr><td>Manometer</td><td>Kern</td><td>HDB-5K5</td><td></td></tr><tr><td>Masson Trichrome Staining kit</td><td>Sigma-Aldrich</td><td>HT15-1KT</td><td></td></tr><tr><td>Micromesh Biopsy cassettes</td><td>Simport</td><td>M507</td><td></td></tr><tr><td>Multiphoton inverted stand Leica SP5 microscope</td><td>Leica microsystems</td><td>DM500</td><td>Scanner 8000Hz NDD PMT detectors</td></tr><tr><td>Non adhering dressing Adaptic</td><td>Systagenix</td><td>A6222</td><td>12.7cm X 22.9 cm</td></tr><tr><td>Ocrygel</td><td>Tvm France</td><td>###</td><td></td></tr><tr><td>Paracetamol 300mg</td><td>Dolliprane</td><td>Liquiz</td><td></td></tr><tr><td>Paraformaldheyde 4%</td><td>VWR chemicals</td><td>1169945</td><td></td></tr><tr><td>Povidone-iodine</td><td>MEDA pharma</td><td>D08AG02</td><td>diluted to 1:2</td></tr><tr><td>SKH1-Hrhr mouse</td><td>Charles river</td><td>686SKH1-HR</td><td>6-weeks old</td></tr><tr><td>Slides</td><td>Thermoscientific</td><td>AGAA000080</td><td></td></tr><tr><td>Surgical adhesive</td><td>BSN medical</td><td>9927</td><td></td></tr><tr><td>Sterile Gauze</td><td>Hartmann</td><td>418545/9</td><td>10 X 10 cm</td></tr><tr><td>Sterile water</td><td>Versylene Fresenius</td><td>B230521</td><td></td></tr><tr><td>Surgical drape</td><td>Hartmann</td><td>2775161</td><td></td></tr><tr><td>Ti:Sapphire ChameleonUltra</td><td>Coherent</td><td>DS 16-02-16 F</td><td>690-1040 nm</td></tr><tr><td>Thermal imaging Camera</td><td>Testo</td><td>Testo 868</td><td></td></tr><tr><td>Xylazine (Rompum 2%)</td><td>Bayer</td><td>FR/V/ 8146715 2/1980</td><td>surgical anesthetic, administered intraperitoneally at a dose of 10 mg/kg</td></tr></tbody></table>

a murine model of a burn wound reconstructed with an allogeneic skin graft

Trivial superficial wounds heal without complications by primary intention. Deep wounds, such as full thickness burns, heal by secondary intention and require surgical debridement and skin grafting. Successful integration of the donor graft into a recipient wound bed depends on timely recruitment of immune cells, robust angiogenic response and new extracellular matrix formation. The development of novel therapeutic agents, which target some key processes involved in wound healing, are hindered by the lack of reliable preclinical models with optimized objective assessment of wound closure. Here, we describe an inexpensive and reproducible model of experimental full thickness burn wound reconstructed with an allogeneic skin graft. The wound is induced on the dorsum surface of anaesthetized inbred wild type mice from the BALB/C and SKH1-Hrhr backgrounds. The burn is produced using a brass template measuring 10 mm in diameter, which is preheated to 80 &#176;C and delivered at a constant pressure for 20 s. Burn eschar is excised 24 hours after the injury and replaced with a full thickness graft harvested from the tail of a genetically similar donor mouse. No specialized equipment is required for the procedure and surgical techniques are straightforward to follow. The method may be effortlessly implemented and reproduced in most research settings. Certain limitations are associated with the model. Due to technical difficulties, the harvest of thinner split thickness skin grafts is not possible. The surgical method we describe here allows for the reconstruction of burn wounds using full thickness skin grafts. It may be used to carry out preclinical therapeutic testing.

The results demonstrate that the protocol developed is a straightforward method, which permits the induction of a full thickness burn wound in mice. Burns are induced using a preheated brass template (Figure 1A-C). The burned area appears as a circular wound with a white eschar and a hyperemic zone. The size of the burn wound is slightly larger at 24 hours after the burn injury as a result of the well-described phenomenon known as the burn injury progression, which is possibly due to acute inflammation22. After excision, burn wounds are reconstructed using allogeneic skin graft (Figure 3). On day 7 after the burn injury, wounds become vascularized5, which is an indication of successful engraftment. Epidermal keratinocytes migrate from the adjacent recipient skin in the effort to close the wound and bridge the gap between the two edges of the wounds. Microscopic analysis of H and E stained section of wounds revealed that the length of the neo-epidermis becomes significantly longer on day 7 after burn injury compared to day 3 after burn injury (Figure 4B). Prior to performing a large study, it is highly recommended that researchers complete a pilot study, which enables the exploration of a novel intervention, assessment of feasibility, identification of modifications to the method to ensure reproducibility. Statistically significant effects are difficult to detect in smaller samples, whereas increasing the sample size is one way to boost the statistical power of a test. For example, to detect a statistically significant difference (p &#60; 0.05) in the rate of wound re-epithelialization (Figure 4) between groups, the sample size should be between six and eight mice per group. All experiments should be repeated at least twice. As matrix producing cells, such as fibroblasts, migrate from the recipient tissue into the graft, key components of the extracellular matrix, including collagen I and fibronectin become highly expressed in the newly formed matrix (Figure 5).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61339/61339fig01.jpg" /> 
Figure 1: Burning device setup.&#160;(A) Placement and set-up of the burning device. The burning device is connected to the temperature controller and is attached to the digital monometer to enable the monitoring of pressure. The burning device is suspended above an adjustable stage &#8211; flat surface onto which mice are placed for the induction of burn. (B-C) A close up image of the brass template used to induce wound burns. (C) The diameter of the brass template is 1 cm. <a href="https://www.jove.com/files/ftp_upload/61339/61339fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61339/61339fig02.jpg" /> 
Figure 2: Schematic illustration of the different steps required to reproduce the experimental model described in this article.&#160;There are three main steps to the procedure: (i) induction of the burn wound using a preheated brass template; (ii) surgical excision of the non-viable necrotic tissue at 24 hours after the burn injury; (iii) surgical wound reconstruction using a full thickness allogeneic skin graft harvested from a donor mouse. <a href="https://www.jove.com/files/ftp_upload/61339/61339fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61339/61339fig03.jpg" /> 
Figure 3: The macroscopic view of reconstructed mouse burn wounds.&#160;Representative digital images of burn wounds reconstructed with allogeneic skin grafts on days 0, 1, 3 and 7 after burn injury. The ruler on images is in millimeters. <a href="https://www.jove.com/files/ftp_upload/61339/61339fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61339/61339fig04.jpg" /> 
Figure 4: Microscopic appearance of wounds at 3 and 7 days after burn injury.&#160;H&#38;E-stained sections of wounds 3 and 7 days after burn injury. The length of neo-epidermis (dotted line) is significantly increased in (A) day 3 wounds compared to (B) day 7 wounds. In (A) and (B), the scale bar is 100 &#181;m. (C) Graphical representation of the percentage of wound re-epithelialization. This was evaluated by measuring the length of neo-epidermis at day 3 and 7 post-burn injury and expressed as a percentage of the whole wound length. Results represent mean &#177; S.E.M. (n = 6 mice in day 3 group; n = 6 mice in day 7 group, *p &#60; 0.05; Student&#8217;s t-test). <a href="https://www.jove.com/files/ftp_upload/61339/61339fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61339/61339fig05.jpg" /> 
Figure 5: Assessment of the extracellular matrix and collagen I visualization.&#160;Representative images of immunohistochemistry analysis on day 7 mouse wounds stained for (A) collagen and (B) fibronectin. Note intense red staining in elongated spindle-shaped collagen I-positive cells. Note brown staining in fibronectin-positive cells in the dermis of day 7 wounds. Scale bar = 50 &#181;m in all images. In (A) and (B), e denotes epidermis and d denotes dermis. (C) Visualization of collagen fibers and histological assessment of collagen deposition. (D) Representative TPEF/SHG collagen image of day 7 mouse wounds. Simultaneous TPEF/SHG acquisition using circular polarization and SHG signals were selectively processed to obtain a binary distribution of SHG after applying a threshold. TPEF images (green) and SHG images (white) were pseudo-colored and overlaid. Scale bar = 50 &#181;m. <a href="https://www.jove.com/files/ftp_upload/61339/61339fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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A Murine Model of a Burn Wound Reconstructed with an Allogeneic Skin Graft

The aim of this study was to develop a murine model of burn wound healing. A thermal burn was induced on the dorsal skin of mice using a preheated brass template. Burned tissue was debrided and overlaid with a skin graft harvested from the tail of a genetically similar donor mouse.

Trivial superficial wounds heal without complications by primary intention. Deep wounds, such as full thickness burns, heal by secondary intention and ...

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9.8K Views.  Sorbonne Université, CNRS. The aim of this study was to develop a murine model of burn wound healing. A thermal burn was induced on the dorsal skin of mice using a preheated brass template. Burned tissue was debrided and overlaid with a skin graft harvested from the tail of a genetically similar donor mouse.

Video: A Murine Model of a Burn Wound Reconstructed with an Allogeneic Skin Graft

The Three-Dimensional Human Skin Reconstruct Model: a Tool to Study Normal  Skin and Melanoma Progression

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells behave differently when they are grown within a 3D extra-cellular matrix and also interact with other cells (1-5). Mouse models have been broadly utilized to study tissue morphogenesis in vivo. However mouse and human skin have significant differences in cellular architecture and physiology, which makes it difficult to extrapolate mouse studies to humans. Since melanocytes in mouse skin are mostly localized in hair follicles, they have distinct biological properties from those of humans, which locate primarily at the basal layer of the epidermis. The recent development of 3D human skin reconstruct models has enabled the field to investigate cell-matrix and cell-cell interactions between different cell types. The reconstructs consist of a "dermis" with fibroblasts embedded in a collagen I matrix, an "epidermis", which is comprised of stratified, differentiated keratinocytes and a functional basement membrane, which separates epidermis from dermis. Collagen provides scaffolding, nutrient delivery, and potential for cell-to-cell interaction. The 3D skin models incorporating melanocytic cells recapitulate natural features of melanocyte homeostasis and melanoma progression in human skin. As in vivo, melanocytes in reconstructed skin are localized at the basement membrane interspersed with basal layer keratinocytes. Melanoma cells exhibit the same characteristics reflecting the original tumor stage (RGP, VGP and metastatic melanoma cells) in vivo. Recently, dermal stem cells have been identified in the human dermis (6). These multi-potent stem cells can migrate to the epidermis and differentiate to melanocytes.

In this report, we describe the three-dimensional skin reconstruct model which mimics human skin in architecture and composition. Melanocyte physiology, melanoma progression and the fate of dermal stem cells have been investigated using the skin reconstruct model. The model is also useful as a preclinical tool for drug assessment.

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells ...

Bioengineering

Murine Skin Transplantation

As one of the most stringent and least technically challenging models, skin transplantation is a standard method to assay host T cell responses to MHC-disparate donor antigens. The aim of this video-article is to provide the viewer with a step-by-step visual demonstration of skin transplantation using the mouse model. The protocol is divided into 5 main components: 1) harvesting donor skin; 2) preparing recipient for transplant; 3) skin transplant; 4) bandage removal and monitoring graft rejection; 5) helpful hints. Once proficient, the procedure itself should take &lt;10 min to perform.

Allogeneic skin transplantation is a standard model to assay host T cell responses to MHC-disparate donor antigens. This video-article provides a visual tutorial of each step involved in performing a BALB/c--&gt;C57BL/6 skin transplant.

As one of the most stringent and least technically challenging models, skin transplantation is a standard method to assay host T cell responses to ...

Murine Model of Wound Healing

Wound healing and repair are the most complex biological processes that occur in human life. After injury, multiple biological pathways become activated. Impaired wound healing, which occurs in diabetic patients for example, can lead to severe unfavorable outcomes such as amputation. There is, therefore, an increasing impetus to develop novel agents that promote wound repair. The testing of these has been limited to large animal models such as swine, which are often impractical. Mice represent the ideal preclinical model, as they are economical and amenable to genetic manipulation, which allows for mechanistic investigation. However, wound healing in a mouse is fundamentally different to that of humans as it primarily occurs via contraction. Our murine model overcomes this by incorporating a splint around the wound. By splinting the wound, the repair process is then dependent on epithelialization, cellular proliferation and angiogenesis, which closely mirror the biological processes of human wound healing. Whilst requiring consistency and care, this murine model does not involve complicated surgical techniques and allows for the robust testing of promising agents that may, for example, promote angiogenesis or inhibit inflammation. Furthermore, each mouse acts as its own control as two wounds are prepared, enabling the application of both the test compound and the vehicle control on the same animal. In conclusion, we demonstrate a practical, easy-to-learn, and robust model of wound healing, which is comparable to that of humans.

A murine model of cutaneous wound healing that can be used to assess therapeutic compounds in physiological and pathophysiological settings.

Wound healing and repair are the most complex biological processes that occur in human life. After injury, multiple biological pathways become activated. ...

Medicine

Murine Excisional Wound Healing Model and Histological Morphometric Wound Analysis

The murine excisional wound model has been used extensively to study each of the sequentially overlapping phases of wound healing: inflammation, proliferation and remodeling. Murine wounds have a histologically well-defined and easily recognizable wound bed over which these different phases of the healing process are measurable. Within the field, it is common to use an arbitrarily defined &#8220;middle&#8221; of the wound for histological analyses. However, wounds are a three-dimensional entity and often not histologically symmetrical, supporting the need for a well-defined and robust method of quantification to detect morphometric defects with a small effect size. In this protocol, we describe the procedure for creating bilateral, full-thickness excisional wounds in mice as well as a detailed instruction on how to measure morphometric parameters using an image processing program on select serial sections. The two-dimension measurements of wound length, epidermal length, epidermal area, and wound area are used in combination with the known distance between sections to extrapolate the three-dimension epidermal area covering the wound, overall wound area, epidermal volume and wound volume. Although this detailed histological analysis is more time and resource consuming than conventional analyses, its rigor increases the likelihood of detecting novel phenotypes in an inherently complex wound healing process.

This protocol describes how to generate bilateral, full-thickness excisional wounds in mice and how to subsequently monitor, harvest, and prepare the wounds for morphometric analysis. Included is an in-depth description of how to use serial histological sections to define, precisely quantify and detect morphometric defects.

The murine excisional wound model has been used extensively to study each of the sequentially overlapping phases of wound healing: inflammation, ...

Developmental Biology

Murine Full-thickness Skin Transplantation

Murine full-thickness skin transplantation is a well-established in vivo model to study alloimmune response and graft rejection. Despite its limited application to humans, skin transplantation in mice has been widely employed for transplantation research. The procedure is easy to learn and perform, and it does not require delicate microsurgical techniques nor extensive training. Moreover, graft rejection in this model occurs in a very reproducible immunological reaction and is easily monitored by direct inspection and palpation. In addition, secondary skin transplantation with donor-matched or third-party skin grafts can be performed on more complex transplant models as an alternative and uncomplicated method to assess donor-specific tolerance. The complications are low and are in general limited to anesthesia overdose or respiratory distress after the procedure. Graft failure, on the other hand, occurs commonly as a result of poor preparation of the graft, incorrect positioning in the graft bed, or inappropriate placement of the bandage. In this article, we present a protocol for full-thickness skin transplantation in mice and describe the important steps necessary for a successful procedure.

Murine full-thickness skin transplantation is a well-established model to study rejection in an alloimmune setting. Here, we provide a tutorial of each step involved in performing a BALB/c--&#62;C57BL/6 full-thickness skin transplant.

Murine full-thickness skin transplantation is a well-established in vivo model to study alloimmune response and graft rejection. Despite its limited ...

Immunology and Infection

Assessment of Acute Wound Healing using the Dorsal Subcutaneous Polyvinyl Alcohol Sponge Implantation and Excisional Tail Skin Wound Models.

Wound healing is a complex process that requires the orderly progression of inflammation, granulation tissue formation, fibrosis, and resolution. Murine models provide valuable mechanistic insight into these processes; however, no single model fully addresses all aspects of the wound healing response. Instead, it is ideal to use multiple models to address the different aspects of wound healing. Here, two different methods that address diverse aspects of the wound healing response are described. In the first model, polyvinyl alcohol sponges are subcutaneously implanted along the mouse dorsum. Following sponge retrieval, cells can be isolated by mechanical disruption, and fluids can be extracted by centrifugation, thus allowing for a detailed characterization of cellular and cytokine responses in the acute wound environment. A limitation of this model is the inability to assess the rate of wound closure. For this, a tail skin excision model is utilized. In this model, a 10 mm x 3 mm rectangular piece of tail skin is excised along the dorsal surface, near the base of the tail. This model can be easily photographed for planimetric analysis to determine healing rates and can be excised for histological analysis. Both described methods can be utilized in genetically altered mouse strains, or in conjunction with models of comorbid conditions, such as diabetes, aging, or secondary infection, in order to elucidate wound healing mechanisms.

Here, two murine wound healing models are described, one designed to assess cellular and cytokine wound healing responses and the other to quantify the rate of wound closure. These methods can be used with complex disease models such as diabetes to determine mechanisms of various aspects of poor wound healing.

Wound healing is a complex process that requires the orderly progression of inflammation, granulation tissue formation, fibrosis, and resolution. Murine ...

Severe Burn Injury in a Swine Model for Clinical Dressing Assessment

Wound healing is a dynamic repair process and is the most complex biological process in human life. In response to burn injury, alterations in biological pathways impair the inflammation response, resulting in delayed wound healing. Impaired wound healing frequently occurs in patients with diabetes leading to unfavorable outcomes such as amputation. Hence, dressings having beneficial effect in promoting burn wound repair are needed. However, studies on burn wound treatment are limited due to lack of proper animal models. Our previous study demonstrated wound-healing performance in rat and swine models using a minimally invasive surgical technique. This study aimed to demonstrate a swine model of severe burn injury that eliminates wound contraction and more closely approximates the human processes of re-epithelialization and new tissue formation. This protocol provides a detailed procedure for creating consistent burn wounds and examining the wound-healing performance under the treatment of an experimental dressing in a swine model. Six burn wounds were created symmetrically on the dorsum, which were covered with a clinical dressing composed of four layers: an inner contact layer of experimental materials, an inner intermediate layer of waterproof film, an outer intermediate layer of gauze, and an outer layer of adhesive plaster. Upon the completion of experiments, wound closure, wound area, and Vancouver Scar Scale score were examined. The samples of skin resected from each animal post-sacrifice were histologically prepared and stained using hematoxylin and eosin staining. Antibacterial activity of each dressing in the context of wound healing was also examined. The application of the clinical dressing to the wounds in swine model mimics the biological processes of human wound healing with respect to the processes of epithelialization, cellular proliferation, and angiogenesis. Therefore, this swine model provides an easy-to-learn, cost-effective, and robust method to assess the effect of clinical dressings in severe burn injury.

To closely mimic the mode of burn injuries requires the interplay between clinical observation and studies in animal models. In this study, a swine model of severe burn injury was established to assess an experimental dressing in physiological and pathophysiological settings.

Wound healing is a dynamic repair process and is the most complex biological process in human life. In response to burn injury, alterations in biological ...

Xenograft Skin Model to Manipulate Human Immune Responses In Vivo

The human skin xenograft model, in which human donor skin is transplanted onto an immunodeficient mouse host, is an important option for translational research in skin immunology. Murine and human skin differ substantially in anatomy and immune cell composition. Therefore, traditional mouse models have limitations for dermatological research and drug discovery. However, successful xenotransplants are technically challenging and require optimal specimen and mouse graft site preparation for graft and host survival. The present protocol provides an optimized technique for transplanting human skin onto mice and discusses necessary considerations for downstream experimental aims. This report describes the appropriate preparation of a human donor skin sample, assembly of a surgical setup, mouse and surgical site preparation, skin transplantation, and post-surgical monitoring. Adherence to these methods allows for maintenance of xenografts for over 6 weeks post-surgery. The techniques outlined below allow maximum grafting efficiency due to the development of engineering controls, sterile technique, and pre- and post-surgical conditioning. Appropriate performance of the xenograft model results in long-lived human skin graft samples for experimental characterization of human skin and preclinical testing of compounds in vivo.

Xenograft Skin Model to Manipulate Human Immune Responses In Vivo

The present protocol describes how to graft human skin onto non-obese diabetic (NOD)-scid interleukin-2 gamma chain receptor (NSG) mice. A detailed description of the preparation of human skin for transplant, preparation of mice for transplant, transplantation of split-thickness human skin, and post-transplantation recovery procedure are included in the report.

The human skin xenograft model, in which human donor skin is transplanted onto an immunodeficient mouse host, is an important option for translational ...

Yucatan Minipig Burn Wound Model for Analysis of Multi-Depth Burns

A Swine Burn Model for Investigating the Healing Process in Multiple Depth Burn Wounds

Burn wound healing is a complex and long process. Despite extensive experience, plastic surgeons and specialized teams in burn centers still face significant challenges. Among these challenges, the extent of the burned soft tissue can evolve in the early phase, creating a delicate balance between conservative treatments and necrosing tissue removal. Thermal burns are the most common type, and burn depth varies depending on multiple parameters, such as temperature and exposure time. Burn depth also varies in time, and the secondary aggravation of the &#34;shadow zone&#34; remains a poorly understood phenomenon. In response to these challenges, several innovative treatments have been studied, and more are in the early development phase. Nanoparticles in modern wound dressings and artificial skin are examples of these modern therapies still under evaluation. Taken together, both burn diagnosis and burn treatments need substantial advancements, and research teams need a reliable and relevant model to test new tools and therapies. Among animal models, swine are the most relevant because of their strong similarities in skin structure with humans. More specifically, Yucatan minipigs show interesting features such as melanin pigmentation and slow growth, allowing for studying high phototypes and long-term healing. This article aims to describe a reliable and reproducible protocol to study multi-depth burn wounds in Yucatan minipigs, enabling long-term follow-up and providing a relevant model for diagnosis and therapeutic studies.

Author Spotlight: A Multi-Depth Porcine Model for Comprehensive Study of Burn Injuries and Healing Processes

This protocol describes a reproducible multi-depth burn wound model in a Yucatan minipigs.

Burn wound healing is a complex and long process. Despite extensive experience, plastic surgeons and specialized teams in burn centers still face ...

Consistent Burn Injury Model in Mice for Evaluating Therapeutic Dressings

Chessboard-like Burn Wound Healing Model of Mice Based on Digital Heating Device

Severe burn injuries are among the most traumatic and physically debilitating conditions, impacting nearly every organ system and resulting in considerable morbidity and mortality. Given their complexity and the involvement of multiple organs, various animal models have been created to replicate different facets of burn injury. Methods used to produce burned surfaces vary among experimental animal models. This study describes a simple, cost-effective, and user-friendly mouse burn model for creating consistent full-thickness burns using a digital heating device. The tip of this device was applied to the dorsum of mice for 10 s at 97 &#176;C to establish a chessboard-like burn and examine wound healing under the treatment of an experimental dressing. Skin samples were collected for histological analysis, including Hematoxylin and Eosin (H&amp;E) staining and Masson's staining. Wound healing was assessed through analysis of the wound area and microscopic examination of inflammatory infiltration, re-epithelialization, and granulation tissue formation. The mouse burn injury model can serve as a fundamental tool in studying the pathophysiology of thermal injuries and evaluating therapeutic interventions.

A streamlined protocol is presented for establishing a burn wound healing model in mice using a digital heating device. The chessboard-like experimental sites created on the skin facilitate further functional analysis for the wound healing assay.

A Murine Model of a Burn Wound Reconstructed with an Allogeneic Skin Graft

Summary

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Chapters in this video

The Three-Dimensional Human Skin Reconstruct Model: a Tool to Study Normal Skin and Melanoma Progression

Murine Skin Transplantation

Murine Model of Wound Healing

Murine Excisional Wound Healing Model and Histological Morphometric Wound Analysis

Murine Full-thickness Skin Transplantation

Assessment of Acute Wound Healing using the Dorsal Subcutaneous Polyvinyl Alcohol Sponge Implantation and Excisional Tail Skin Wound Models.

Severe Burn Injury in a Swine Model for Clinical Dressing Assessment

Xenograft Skin Model to Manipulate Human Immune Responses In Vivo

A Swine Burn Model for Investigating the Healing Process in Multiple Depth Burn Wounds

Chessboard-like Burn Wound Healing Model of Mice Based on Digital Heating Device