This work was supported by NIH grant 1R21EB021590-01A1 to Arun Gosain and Ellen Kuhl.

This protocol involves animal experiments. The protocol was approved by the IRB of Ann and Robert H. Lurie Children&#39;s Hospital of Chicago Research Center Animal Care and Use Committee to guarantee humane treatment of animals. The results for two expansion studies using this protocol have been published elsewhere 16,31.
Execution of this protocol requires a team with complementary expertise. The first part of the protocol describes ...

<ol>
	<li>Gosain, A. K., Zochowski, C. G., Cortes, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Refinements+of+tissue+expansion+for+pediatric+forehead+reconstruction:+a+13-year+experience.">Refinements of tissue expansion for pediatric forehead reconstruction: a 13-year experience.</a> Plast Reconstr Surg. 124, 1559-1570 (2009).</li><li>Neumann, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+expansion+of+an+area+of+skin+by+progressive+distention+of+a+subcutaneous+balloon:+Use+of+the+Method+for+Securing+Skin+for+Subtotal+Reconstruction+of+the+Ear.">The expansion of an area of skin by progressive distention of a subcutaneous balloon: Use of the Method for Securing Skin for Subtotal Reconstruction of the Ear.</a> Plast Reconstr Surg. 19, 124-130 (1957).</li><li>De Filippo, R. E., Atala, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stretch+and+growth:+the+molecular+and+physiologic+influences+of+tissue+expansion.">Stretch and growth: the molecular and physiologic influences of tissue expansion.</a> Plast Reconstr Surg. 109, 2450-2462 (2002).</li><li>Buganza Tepole, A., Joseph Ploch, C., Wong, J., Gosain, A. K., Kuhl, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growing+skin:+A+computational+model+for+skin+expansion+in+reconstructive+surgery.">Growing skin: A computational model for skin expansion in reconstructive surgery.</a> J Mech Phys Solids. 59, 2177-2190 (2011).</li><li>LoGiudice, J., Gosain, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pediatric+Tissue+Expansion:+Indications+and+Complications.">Pediatric Tissue Expansion: Indications and Complications.</a> J Craniofac Surg. 14, 866-866 (2003).</li><li>Rivera, R., LoGiudice, J., Gosain, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+expansion+in+pediatric+patients.">Tissue expansion in pediatric patients.</a> Clin Plast Surg. 32, 35-44 (2005).</li><li>Marcus, J., Horan, D. B., Robinson, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+expansion:+Past,+present,+and+future.">Tissue expansion: Past, present, and future.</a> J Am Acad Dermatol. 23, 813-825 (1990).</li><li>Patel, P. A., Elhadi, H. M., Kitzmiller, W. J., Billmire, D. A., Yakuboff, K. 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F., Huber, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+different-shaped+tissue+expanders+on+transluminal+pressure,+oxygen+tension,+histopathologic+changes,+and+skin+expansion+in+pigs.">Effects of different-shaped tissue expanders on transluminal pressure, oxygen tension, histopathologic changes, and skin expansion in pigs.</a> Plast Reconstr Surg. 76, 731-736 (1985).</li><li>van Rappard, J. H., Molenaar, J., van Doorn, K., Sonneveld, G. J., Borghouts, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-area+increase+in+tissue+expansion.">Surface-area increase in tissue expansion.</a> Plast Reconstr Surg. 82, 833-839 (1988).</li><li>Pusic, A. L., Cordeiro, P. 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Here we presented a protocol to characterize the deformations induced during a tissue expansion procedure in a porcine model using multi-view stereo (MVS) and isogeometric kinematics (IGA kinematics). During tissue expansion, skin undergoes large deformations going from a smooth and relatively flat surface to a dome-like 3D shape. Skin, like other biological membranes 34, responds to stretch by producing new material, increasing in area that can be then used for reconstructive purposes <sup class=...

Tissue expansion is a common technique in plastic and reconstructive surgery that grows skin in vivo for the correction of large cutaneous defects 1. Neumann, in 1957, was the first surgeon to document this procedure. He implanted a balloon below the skin of a patient and inflated it gradually over a period of several weeks to grow new tissue and resurface an ear 2. Skin, like most biological tissues, adapts to applied forces and deformations in order to reach mechanical homeostasis. When stretched beyond the physiological regime, skin grows 3,4. One of the central advantages of tissue expansion is the production of skin with proper vascularization and the same hair bearing, mechanical properties, color, and texture as the surrounding tissue 5.
After its introduction six decades ago, skin expansion has been widely adopted by plastic and reconstructive surgeons and is presently used to correct burns, large congenital defects, and for breast reconstruction after mastectomy 6,7. Yet, despite its widespread use, skin expansion procedures can lead to complications 8. This is partly due to the lack of sufficient quantitative evidence needed to understand the fundamental mechanobiology of the procedure and to guide the surgeon during preoperative planning 9,10. Key parameters in this technique are the filling rate, filling volume per inflation, the selection of the shape and size of the expander, and the placement of the device 11,12. Current preoperative planning relies largely on the physician&#39;s experience, resulting in a wide variety of arbitrary protocols that often differ greatly 13,14,15.
To address the current knowledge gaps, we present an experimental protocol to quantify expansion-induced deformation in a porcine animal model of tissue expansion. The protocol relies on the use of multi-view stereo (MVS) to reconstruct three-dimensional (3D) geometries out of sequences of two-dimensional (2D) images with unknown camera positions. Employing splines, representation of smooth surfaces leads to the calculation of the corresponding deformation maps by means of an isogeometric (IGA) description. The analysis of the geometry is based on the theoretical framework of continuum mechanics of membranes having an explicit parameterization 16.
Characterizing physiologically relevant deformations of living materials over long periods of time still remains a challenging problem. Common strategies for imaging of biological tissues include stereoscopic digital image correlation, commercial motion capture systems with reflective markers, and biplane video fluoroscopy 17,18,19. However, these techniques require a restrictive experimental setup, are generally expensive, and have been primarily used for ex vivo or acute in vivo settings. Skin has the advantage of being a thin structure. Even though it consists of several layers, the dermis is largely responsible for the mechanical properties of the tissue and thus the surface deformation is of primary importance 20; reasonable kinematical assumptions can be made regarding the out of plane deformation 21,22. Moreover, skin is already exposed to the outside environment, making it possible to use conventional imaging tools to capture its geometry. Here we propose the use of MVS as an affordable and flexible approach to monitor in vivo deformations of skin over several weeks without interfering majorly with a tissue expansion protocol. MVS is a technique that extracts 3D representations of objects or scenes from a collection of 2D images with unknown camera angles 23. Only in the last three years, several commercial codes have appeared (see list of materials for examples). The high accuracy of the model reconstruction with MVS, with errors as low as 2% 24, makes this approach suitable for the kinematic characterization of skin in vivo over long periods of time.
To obtain the corresponding deformation maps of skin during tissue expansion, points between any two geometric configurations are matched. Conventionally, researchers in computational biomechanics have used finite element meshes and inverse analysis to retrieve the deformation map 25,26. The IGA approach employed here uses spline basis functions which offer several advantages for the analysis of thin membranes 27,28. Namely, the availability of high degree polynomials facilitates representations of smooth geometries even with very coarse meshes 29,30. Additionally, it is possible to fit the same underlying parameterization to all the surface patches, which circumvents the need for an inverse problem to account for non-matching discretizations.
The method described here opens new avenues to study skin mechanics in relevant in vivo settings over long periods of time. In addition, we are hopeful that our methodology is an enabling step towards the ultimate goal of developing computational tools for personalized treatment planning in the clinical setting.

<table border="0" cellpadding="0" cellspacing="0" width="817">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Yucatan miniature swine</td>
			<td style="width:263px;">Sinclair Bioresources, Windham, ME</td>
			<td style="width:141px;">N/A</td>
			<td style="width:197px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Antibiotics</td>
			<td>Santa Cruz Animal Health, Paso Robles, CA</td>
			<td style="width:141px;">sc-362931Rx</td>
			<td>Ceftiofur, dosage 5mg/kg intramuscular</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Chlorhexidine-based surgical soap</td>
			<td style="width:263px;">Cardinal Health, Dublin, OH</td>
			<td>AS-4CHGL(4-32)</td>
			<td>4% chlorhexidine gluconate surgical hand scrub</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Tattoo transfer medium&#160;</td>
			<td style="width:263px;">Hildbrandt Tattoo Supply, Point Roberts, WA</td>
			<td>TRANSF</td>
			<td>Stencil thermal tattoo transfer paper</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lidocaine with epinephrine</td>
			<td style="width:263px;">ACE Surgical Supply Co, Brockton, MA</td>
			<td style="width:141px;">001-1423</td>
			<td>Lidocaine Hcl 1% (Xylocaine) - Epinephrine 1:100,000, 20ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Buprenorphine</td>
			<td style="width:263px;">ZooPharm, Windsor, CO</td>
			<td style="width:141px;"></td>
			<td>1 mg/ml sustained release, dosage 0.01 mg/kg intramuscular</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Digital camera</td>
			<td style="width:263px;">Sony</td>
			<td style="width:141px;">Alpha33&#160;</td>
			<td>Standard digital camera with 18-35mm lens, 3.5-5.6 aperture. Used in automatic mode, no flash</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tape measure</td>
			<td style="width:263px;">Medline, Mundelein, Illinois</td>
			<td style="width:141px;">NON171330</td>
			<td>Retractable tape measure, cloth, plastic case, 72inches</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tissue expanders</td>
			<td style="width:263px;">PMT, Chanhassen, MN</td>
			<td style="width:141px;">03610-06-02</td>
			<td>4cm x 6cm, rectangular, 120cc, 3610 series 2 stage tissue expander with standard port</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ReCap360</td>
			<td style="width:263px;">Autodesk</td>
			<td style="width:141px;">N/A</td>
			<td>MVS Software, Web application: recap360.autodesk.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Blender</td>
			<td style="width:263px;">Blender Foundation</td>
			<td style="width:141px;">N/A</td>
			<td>Computer Graphics Software, open source: blender.org</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">SISL</td>
			<td style="width:263px;">SINTEF</td>
			<td style="width:141px;">N/A</td>
			<td>C++ spline libraries, open source: https://www.sintef.no/projectweb/geometry-toolkits/sisl/</td>
		</tr>
	</tbody>
</table>

quantification of strain in a porcine model of skin expansion using multi-view stereo and isogeometric kinematics

Tissue expansion is a popular technique in plastic and reconstructive surgery that grows skin in vivo for correction of large defects such as burns and giant congenital nevi. Despite its widespread use, planning and executing an expansion protocol is challenging due to the difficulty in measuring the deformation imposed at each inflation step and over the length of the procedure. Quantifying the deformation fields is crucial, as the distribution of stretch over time determines the rate and amount of skin grown at the end of the treatment. In this manuscript, we present a method to study tissue expansion in order to gain quantitative knowledge of the deformations induced during an expansion process. This experimental protocol incorporates multi-view stereo and isogeometric kinematic analysis in a porcine model of tissue expansion. Multi-view stereo allows three-dimensional geometric reconstruction from uncalibrated sequences of images. The isogeometric kinematic analysis uses splines to describe the regional deformations between smooth surfaces with few mesh points. Our protocol has the potential to bridge the gap between basic scientific inquiry regarding the mechanics of skin expansion and the clinical setting. Eventually, we expect that the knowledge gained with our methodology will enable treatment planning using computational simulations of skin deformation in a personalized manner.

This methodology has been successfully employed to study the deformation induced by different expander geometries: rectangle, sphere and crescent expanders 31,32. The results corresponding to the sphere and crescent expanders are discussed next. Figure 2 illustrates the three steps of MVS model reconstruction. The starting point is a collection of photographs from a static scene. The animal with the tattooed grids...

Watch this Scientific Journal Video about Quantification of Strain in a Porcine Model of Skin Expansion Using Multi-View Stereo and Isogeometric Kinematics at JoVE.com

Quantification of Strain in a Porcine Model of Skin Expansion Using Multi-View Stereo and Isogeometric Kinematics

This protocol uses multi-view stereo to generate three-dimensional (3D) models out of uncalibrated sequences of photographs, making it affordable and adjustable to a surgical setting. Strain maps between the 3D models are quantified with spline-based isogeometric kinematics, which facilitate representation of smooth surfaces over coarse meshes sharing the same parameterization.

Tissue expansion is a popular technique in plastic and reconstructive surgery that grows skin in vivo for correction of large defects such as burns and ...

The overall goal of this experiment is to quantify strain maps of skin during tissue expansion using isogeometric analysis and multi-view stereo. This method can help answer key questions in the field of reconstructive surgery with tissue expansion such as determining regional deformations induced by different expander shapes, sizes and inflation rates. The main advantage of this technique is that it uses computational analysis and flexible 3D imaging techniques.Thus, it can be used in the operating room without altering the routine procedure. The implications of this technique extend towards therapy because it can be easily translated to the clinical setting to monitor skin deformation maps of human patients undergoing tissue expansion. To begin, prepare and anesthetize Yucatan mini pig for the surgery by shaving its dorsal skin with a razor.Remove any remaining hair with tape and wipe the skin thoroughly with an isopropyl alcohol to clean it up from contaminants. Next, identify the dorsal midline on the animal's body, and using a pen, mark the dorsal limits of four grids so that they are positioned approximately two centimeters away from the dorsal midline. After marking on the skin the location of the first anterior grid, leave a three centimeter gap and mark the position of the posterior grid.Finally, confirm that the marked anterior and posterior grid locations are symmetric with respect to the dorsal midline and positioned at the same supracaudal distance. Once the locations of the grid are marked, prepare a paper template of a 10 centimeter by 10 centimeter grid. To do this, heavily outline the grid by coloring the lines repetitively with a ballpoint pen and then trim the template.Next, thoroughly moisten the desired skin area with isopropyl rubbing alcohol to facilitate the transfer of the grid tracing, and allow the excess alcohol to air dry, which will prevent the ink from leaking. Align the edges of the prepared grid template to the marking on the skin, and apply the grid to the skin with the ink side facing down, then gently press the grid template against the skin to ensure a complete transfer of the ink. After several seconds, slowly remove the grid from the skin and make sure the grid tracing was properly transferred.Prior to tattooing, cover the grid tracing with petroleum jelly to decrease smearing of the ink, and using a tattooing device, cover the lines of the grid with tattoo ink. Once the first grid is tattooed, transfer to the animal's skin the tracing for the second grid, ensuring that both grids are positioned three centimeters apart from each other. After tattooing the second grid, confirm that both grids are located two centimeters lateral to the dorsal midline.Once four grids are tattooed, confirm that they are positioned two centimeters away from the dorsal midline and spread apart in three centimeters one more time. To begin the surgery, mark on the skin of the anesthetized pig an incision site, located at the midpoint between two grids, then mark the desired location of the expander so that it is positioned in the upper part of the tattooed grid. Incise the skin with a surgical blade, and using scissors, create a tight subcutaneous tunnel connecting the initial incision with an area where the expander is going to be placed, then bluntly dissect out the pocket within the marked expander placement site.Next, wash the created tunnel with an antibiotic solution to prevent infection and insert the expander to its subcutaneous pocket. Once the expander is in place, mark the sites of two incisions adjacent to the dorsal midline that will be used for an expander port placement, and make the cuts with the scalpel. Afterward, insert a hemostat through the caudal incision and dissect another subcutaneous tunnel connecting it with the incision previously used for expander placement, then seize the expander's tubing and pull it out through the caudal port incision.Use the second incision to dissect a pocket for an inflation port placement, and insert the port in the pocket. Create with hemostat another subcutaneous tunnel connecting the two port placement incisions, then seize the port's tubing with the hemostat and pull it out through the same incision where the expander tubing is placed. After trimming both of the tubes, connect them through a metal adapter.Secure the connection on both sides of the adapter by suturing around the tubing. Pull the tube through the initially made incision so that the tubing system is placed subcutaneously, then introduce a 21 gauge needle attached to a 50 milliliter syringe filled with liquid through the skin to the expander port and remove the air from the expander by pulling the plunger. Once all air is removed, inject to the expander port approximately 10 milliliters of the liquid to confirm that it fills properly.Finally, close all three incisions by applying surgical sutures, then proceed by marking the incision site between the two grids on the opposite side of the pig's body to place the second expander diagonally in respect to the first expander placement site. After anesthetizing the animal, attach plastic flexible tape measures between the grids using surgical tape, then place the animal on one side to photo document the grid. It is critical to take the photographs from many different angles, making sure that the images are focused and contain primarily the object of interest rather than the background.This will ensure accurate 3D geometry reconstruction, which is crucial to the analysis. Begin by positioning the camera above the animal but leaning to the caudal side to capture a shot approximately parallel to the ground where the tattooed grids are fully visible and fill the frame, then move in a circular pattern around the animal in an arch from the caudal to the rostral direction, taking photographs along the way and always capturing all of the tattooed grids in frame, with the grids filling the frame. Next, position the camera towards the ventral side to capture a shot angle that is approximately parallel to the ground, and take photographs in an arch from the ventral to dorsal region.After photographing both sides of the animal, perform the inflation step according to the protocol in use. First, cleanse the skin of the animal around the port with isopropyl alcohol. Next, load a syringe with 0.9%injectable saline and attach it to a 25 gauge butterfly needle.Next, attach the needle to the port, then inject the saline into the expander. After the injection, photo document the grids again, as before. To make the digital reconstruction, use commercially available software.In this demonstration, MVS is used. Begin by selecting photo to 3D on the top left corner. Next, click add photos, browse to the location of the images and manually select the 30 photographs corresponding to a single model, then name the model and click create.It can take several minutes for the model to be created. Next, click dashboard on the right to go back to see representative images of the geometric models. To save a model for analysis, select it at the bottom right corner, click downloads and select obj.Use opensource software to process the geometric model. Import the file generated from the MVS software, then on the bottom of the 3D view, click on viewport shading and select texture. Look for a tab on the right of the 3D view with the submenu containing shading.From shading, select shadeless, then right click on a geometry to select it, and on the bottom of a 3D view, choose edit mode to visualize the triangular mesh. Now, one by one, select the nodes of the grid by right clicking and highlighting the point. The coordinates for the point will appear on the tab on the right hand side of the 3D view.Select and copy those coordinates, then paste them into a text file. Proceed to do this for all the points of the grid to save all 121 coordinates, then follow the instructions in the text protocol to ultimately quantify the deformation from this data. This methodology has been successfully employed to study the deformation induced by different expander geometries.The variations in regional strains induced by sphere and crescent expanders were focused on. Both devices were filled to the same volume at every time point. From the reconstructed spline surfaces, deformations were calculated using a reference and a deformed grid.Day zero was considered the reference. Comparing the end of every inflation step to the reference configuration results and the contour plots, the progression of the area change, theta, and the stretching in the two orthogonal directions, lambda, was then analyzed. Ultimately, the spacial variation of the contour plots revealed that skin was stretched more at the center of the expander than at the periphery.Interestingly, even though both expanders were filled to the same volume, filling the sphere shaped expander induced larger deformations compared to the filling of the crescent shaped expander. After watching this video, you should have a good understanding as to how to quantify deformation maps of skin using multi-view stereo and isogeometric analysis. While attempting this procedure, it's important to photo document every step of the process with tape measures so the geometries can be scaled during analysis.Following this procedure, other methods, like tissue biopsies, subsequent histochemical analysis, and genome sequencing can all be performed to answer additional questions about the underlying cellular responses to skin stretching.

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Research

JoVE Journal

Bioengineering

11.5K visualizações.  Purdue University. The overall goal of this experiment is to quantify strain maps of skin during tissue expansion using isogeometric analysis and multi-view stereo. This method can help answer key questions in the field of reconstructive surgery with tissue expansion such as determining regional deformations induced by different expander shapes, sizes and inflation rates. The main advantage of this technique is that it uses computational analysis and flexible 3D imaging techniques.Thus, it can be used in...