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 the surgical procedure on the animal model, requiring personnel with the appropriate medical training. The subsequent analysis, particularly sections 4 and 5, involve basic computer programming skills in C++ and Python, and use of a command line shell.
1. Surgical Procedure for Expander Placement
NOTE: Personnel involved in the operation must be scrubbed and gowned in a sterile fashion. Sterile towels and drapes are applied around the surgical field to maintain sterility. All instruments, sutures, and tissue expanders are received in sterile packaging and handled only by sterile personnel. Sterility of the operative site must not be violated until the procedure is complete.
<ol>
	<li>Acclimate one-month-old male Yucatan mini pigs to standard housing for one week, and feed ad libitum.</li>
	<li>On the day of surgery, anesthetize the animal using ketamine/acepromazine for induction (4 - 6 mg/kg), then isoflurane for maintenance. Evaluate depth of anesthesia by monitoring the palpebral reflex. Also, monitor vital signs (heart rate, body temperature, respiratory rate, and/or response to pinch by tissue forceps). Apply ophthalmic ointment to the eyes to protect against corneal abrasions.</li>
	<li>Administer pre-procedural antibiotics and clean the dorsal skin with chlorhexidine-based surgical soap. Transfer four 10 x 10 cm2 grids, two on each side of the animal, with 1 cm line markings to the pig skin using tattoo transfer medium. The grids correspond to the following four regions: left rostral, right rostral, left caudal, and right caudal. Use a template with a midline reference to ensure symmetric placement of the grid patterns.
	<ol>
		<li>Create the grids on paper by tracing the grid outlines heavily with a ballpoint pen. Wash the area on the animal where the grid is to be placed with isopropyl rubbing alcohol.</li>
		<li>Apply the grid (pen-ink side down) directly onto the skin. The alcohol serves to leech some of the ink off of the paper, transferring the grid to the animal&#39;s skin.</li>
	</ol>
	</li>
	<li>Inject local anesthetic (1% lidocaine with 1:100,000 epinephrine) subcutaneously at the site of each planned incision.</li>
	<li>Make an incision on either side of the animal in the midpoint between the two grids. 
	NOTE: The incisions are placed on the left and right side of the animal between the 2 grids on that side. There is a left sided incision and a right sided incision</li>
	<li>Use a hemostat to develop a subcutaneous tunnel beneath the grid of interest. After developing a tunnel, insert the expander beneath the grid. 
	NOTE: Tunnels are placed under any grid that will have a tissue expander.</li>
	<li>Place the port for expander inflation remotely through a subcutaneous tunnel developed in a similar fashion along the dorsal midline of the animal. Repair wounds by suturing.</li>
	<li>Postoperatively, treat the animal with prophylactic antibiotics (Ceftiofur 5 mg/kg IM once) as well as analgesics (Buprenorphine 0.05 - 0.1 mg/kg) via intramuscular injection every 12 h for 4 doses, with additional doses available for evidence of animal distress.</li>
	<li>Observe animals continuously for 2 h postoperatively, including routine measurement of vital signs until they have resumed ambulation and are able to maintain normothermia. House the animal in a separate cage and monitor until it is able to walk independently on all 4 legs before transferring it back to its normal housing area and leaving it unattended.</li>
	<li>Following the immediate post anesthesia recovery period, check animals daily to evaluate wound healing. Remove the sutures 14 days postoperatively. These incisions do not require dressings. Leave the incisions to heal for 3 - 4 weeks before beginning expansion</li>
</ol>
2. Inflation Protocol
NOTE: The timing of the inflations and amount of solution used in each expander depends on the specific question being studied. To characterize the effect of different expander geometries, a suitable protocol is to perform five inflation steps at 0, 2, 7, 10, and 15 days to achieve filling volumes of 50, 75, 105, 165, and 225 cc respectively.
<ol>
	<li>Before each inflation step, sedate the animal administering ketamine (4 - 6 mg/kg) and dexmedetomidine at 20 - 80 &#181;g/kg. 
	NOTE: Dexmedetomidine is an alpha-adrenergic agonist that can be reversed with atipamezole (1:1 volume:volume) to facilitate faster recovery; however, this level of sedation may not be adequate for the animal to tolerate expansion without undue risk of harm to the animal or handlers. If this is the case, administer general anesthesia by delivering isoflurane via mask ventilation following ketamine/acepromazine induction.</li>
	<li>Attach two plastic flexible tape measures to the skin of the animal using surgical tape. Place the tape measures between the grids on the left and right sides.</li>
	<li>Place the animal on one side and acquire 30 photographs of the scene from as many different angles as possible. 
	NOTE: The objective is to capture the geometry of the two grids visible when the animal is laying down on one side.
	<ol>
		<li>First, position the camera above the animal and leaning towards the caudal side, to capture a shot where the tattooed grids are fully visible and fill the frame.</li>
		<li>Move in a circular pattern around the animal in an arch from the caudal to the rostral direction, taking photographs along the way, ensuring that, for every photograph, the tattooed grids that are visible appear entirely in the frame.
		<ol>
			<li>At the same time, try to maximize the space that the grids occupy in the frame. An ideal shot would capture the back of the animal with the tattooed grids and only small regions of background.</li>
		</ol>
		</li>
		<li>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 the dorsal region. 
		NOTE: The amount of photographs is not a fixed value. For a good reconstruction, every point on the tattooed grid should be in at least 3 photographs; 30 photographs in total is an adequate amount for successful geometry reconstruction.</li>
	</ol>
	</li>
	<li>Place the animal on the opposite side and take 30 photographs of the two remaining grids following the same steps outlined above.</li>
	<li>Perform the inflation step by finding the remote filling port and injecting the required amount of saline solution corresponding to the expansion protocol of interest. Use sterile 0.9% injectable saline.
	<ol>
		<li>Locate the ports and prep over the skin of the animal with isopropyl alcohol wipes. Access the port with a sterile 25-gauge butterfly needle attached to a syringe filled with sterile injectable saline. 
		NOTE: As described above, the ports are tunneled subcutaneously to a position on the anterior midline dorsum during expander placement.</li>
		<li>Inject the desired amount of saline solution. Please refer to the note at the beginning of this section for the inflation volumes injected at each step of the expansion process.</li>
	</ol>
	</li>
	<li>Repeat the photo acquisition steps after inflation.</li>
	<li>Once the inflation protocol is complete, euthanize the animals.
	<ol>
		<li>Administer general anesthesia by delivering isoflurane via mask ventilation following ketamine/acepromazine induction. Evaluate depth of anesthesia by monitoring the palpebral reflex. Also, monitor vital signs (heart rate, body temperature, respiratory rate, and/or response to pinch with tissue forceps).</li>
		<li>Euthanize the animal by intravenous overdose of pentobarbital 90 - 100 mg/kg. Following pentobarbital overdose for euthanasia, confirm death by the absence of detectable heartbeat using a pulse oximeter and pulse palpation as well as the absence of spontaneous respirations.</li>
	</ol>
	</li>
</ol>
3. Multi-view Stereo Reconstruction
<ol>
	<li>Use commercially available software to upload the image files and reconstruct the geometric models.
	<ol>
		<li>Launch the MVS software on the browser and log in.</li>
		<li>Select Photo to 3D on the top left corner.</li>
		<li>Click add photos, browse to the location of the images and manually select the 30 photographs corresponding to a single model.</li>
		<li>Name the model and click create</li>
		<li>Wait for the model to be created. This can take several minutes. Click dashboard on the right to go back to the original landing page of the software. 
		NOTE: The dashboard shows representative images of the geometric models that have been created by the user.</li>
		<li>Place the cursor on the model that has just been created. Place the cursor on the bottom right corner of the model image. Click downloads and select obj.</li>
	</ol>
	</li>
</ol>
4. Spline Surface Fit
<ol>
	<li>Use open source software to process the geometric models.</li>
	<li>Click File-&#62;Import-&#62;obj to import the file generated from the MVS software. 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 submenus: Transform, Grease Pencil, View, 3D Pencil, etc. Click on Shading and select Shadeless.</li>
	<li>Right click on the geometry to select it. On the bottom of the 3D View select Edit Mode to visualize the triangular mesh.</li>
	<li>Select one by one the nodes on the 1 cm markings of the tape measure.
	<ol>
		<li>To select a point, right click on it, and highlight the point. Coordinates for the point appear on the tab on the right-hand side of the 3D View. Select and copy the coordinates of the selected point to a text file.</li>
		<li>Repeat this operation for all the points on the 1 cm markings of the tape measure.</li>
		<li>Do this for both tape measures. Examples of coordinate text files are provided: tape1.txt, tape2.txt. 
		NOTE: If there are no nodes of the mesh on the point of interest, subdivide the mesh until there is a node on the point of interest. To subdivide the mesh select the three vertices of a triangle by pressing Shift key and right-clicking on the vertices. Then click on the button Subdivide on the tab appearing on the left-hand side of the 3D View. This operation adds three more nodes inside the selected triangle.</li>
	</ol>
	</li>
	<li>Select the 11 x 11 points of the grid and save the coordinates of the 121 points to a text file in the pattern shown in Figure 1.
	<ol>
		<li>Analogously to what was done for the tape measures, to select a point of the grid, right click on it, the point will be highlighted. Coordinates for the point will appear on the tab on the right-hand side of the 3D View. Select and copy the coordinates of the selected point to a text file 
		NOTE: The numbering of the grid points is always caudal to rostral and from the dorsal midline towards the ventral region. This ordering guarantees that the parameter space is consistent for any two patches. As an example, the file gridReference.txt which contains the coordinates of 121 points of a skin patch is provided.</li>
	</ol>
	</li>
	<li>Download, compile and install C++ spline libraries. The file splineLibraryInstallation.txt contains the link to the source code of the spline libraries and instructions for installation.</li>
	<li>Compile the source code generateCurve.cpp to generate the executable generateCurve 
	NOTE: The program generateCurve only needs to be compiled once. To compile this C++ source code and generate an executable follow the instructions at the top of the source code file generateCurve.cpp.</li>
	<li>Use the program generateCurve to fit splines to the tape measures and to the grid points. To run the executable in a Bash shell, type 
	directory$ ./generateCurve
	<ol>
		<li>Upon running the program, it will ask the user to type in the path to the file containing the coordinates of the tape measure. Then the program will ask for a name for the output file. Add the termination .g2 to the filename. 
		NOTE: The termination .g2 stands for go tools, and is associated to the spline libraries. Two examples of spline files corresponding to the tape measures are available with this protocol (tape1.g2, tape2.g2).</li>
	</ol>
	</li>
	<li>Use the Python script scalePoints.py to scale the grid points. Run the program in a Bash shell prompt with three arguments: the filename of the grid points and the file names of the splines corresponding to the tape measures 
	directory$ python scalePoints.py gridReference.txt tape1.g2 tape2.g2 
	NOTE: The script scalePoints.py imports the scripts B_spline.py and NURBS_Curve.py, therefore all three scripts must be in the same folder.</li>
	<li>Compile the source code generateSurface.cpp to generate the executable generateSurface. 
	NOTE: This step only needs to be done once. More detailed instructions are available at the beginning of the source code file generateSurface.cpp.</li>
	<li>Use the program generateSurface to fit a spline surface to the grid points. Run the executable generateSurface on the Bash shell 
	directory$ ./generateSurface
	<ol>
		<li>Running the program in a shell will ask for the filename containing the scaled points. Then it will ask for the name of the output file. Add the termination .g2 to the output filename. 
		NOTE: The termination .g2 is suggested by the spline libraries and stands for go tools. The files gridReference.g2 and gridDeformed.g2 are provided as examples.</li>
	</ol>
	</li>
</ol>
5. Quantification of Expansion-induced Deformation
<ol>
	<li>Start Python in the Bash shell prompt 
	directory$ python 
	NOTE: Python initializes the interpreter, which is an interface similar to the shell that will show a new command line environment &#62;&#62;&#62;</li>
	<li>Import the script expansionIGA.py which contains a function called evaluateMembraneIGA 
	&#62;&#62;&#62; from expansionIGA import evaluateMembraneIGA</li>
	<li>Call the function evaluateMembraneIGA to calculate the deformation maps. 
	NOTE: This function takes as arguments: 
	Filename of the reference surface 
	Filename of the deformed surface 
	Resolution of the evaluation (how many points are evaluated in each direction) 
	Minimum value of area stretch used to scale the contour plot 
	Maximum value of area stretch used to scale the contour plot 
	Minimum value of stretch in longitudinal direction used to scale the contours 
	Maximum value of stretch in longitudinal direction used to scale the contours 
	Minimum value of stretch in transverse direction used to scale the contours 
	Maximum value of stretch in transverse direction used to scale the contours 
	Spacing between grid lines in the contour plot 
	Output filename
	<ol>
		<li>For example, run 
		&#62;&#62;&#62; evaluateMembraneIGA(&#39;gridReference.g2&#39;, &#39;gridDeformed.g2&#39;, 250, 3, 0.5, 2, 0.5, 2, 0.5, 25, &#39;deformation&#39;) 
		NOTE: This command will generate and save six output files. Note that the last argument in the example above is the output filename deformation, thus, the files that will be generated are: 
		deformation_theta.png: contour plot of the area stretch 
		deformation_theta.txt: table of values corresponding to the contour plot of area stretch 
		deformation_G1.png: contour plot of the stretch along the longitudinal axis of the animal 
		deformation_G1.txt: table of values corresponding to the contour plot of stretches along the longitudinal axis of the animal 
		deformation_G2.png: contour plot of the stretch component in the transverse axis of the animal 
		deformation_G2.txt: table of values corresponding to the contour plot of the component of the stretch in the transverse axis of the animal 
		NOTE: Do not confuse the termination of the spline files, .g2, with the vector G2. The spline files have ending .g2 following the naming conventions of the spline library. On the other hand, the vectors G1 and G2 denote the longitudinal and transverse directions with respect to the animal. 
		NOTE: The contour files are generated with distinct features at the four corners to facilitate interpretation of the parameter space: Black pixel: most caudal, most dorsal point; Red pixel corner: most rostral, most dorsal point; Green pixel corner: most caudal, most ventral point; Blue pixel corner: most rostral, most ventral point.</li>
	</ol>
	</li>
</ol>

<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. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+expander+complications+in+the+pediatric+burn+patient:+a+10-year+follow-up.">Tissue expander complications in the pediatric burn patient: a 10-year follow-up.</a> Ann Plast Surg. 72, 150-154 (2014).</li><li>Pietramaggiori, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensile+Forces+Stimulate+Vascular+Remodeling+and+Epidermal+Cell+Proliferation+in+Living+Skin.">Tensile Forces Stimulate Vascular Remodeling and Epidermal Cell Proliferation in Living Skin.</a> Ann Surg. 246, 896-902 (2007).</li><li>Khalatbari, B., Bakhshaeekia, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ten-year+experience+in+face+and+neck+unit+reconstruction+using+tissue+expanders.">Ten-year experience in face and neck unit reconstruction using tissue expanders.</a> Burns. 39, 522-527 (2013).</li><li>Brobmann, F. 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. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+accelerated+approach+to+tissue+expansion+for+breast+reconstruction:+experience+with+intraoperative+and+rapid+postoperative+expansion+in+370+reconstructions.">An accelerated approach to tissue expansion for breast reconstruction: experience with intraoperative and rapid postoperative expansion in 370 reconstructions.</a> Plast Reconstr Surg. 111, 1871-1875 (2003).</li><li>Schneider, M. S., Wyatt, D. B., Konvolinka, C. W., Hassanein, K. M., Hiebert, 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=Comparison+of+Rapid+Versus+Slow+Tissue+Expansion+on+Skin-Flap+Viability.">Comparison of Rapid Versus Slow Tissue Expansion on Skin-Flap Viability.</a> Plast Reconstr Surg. 92, 1126-1132 (1993).</li><li>Schmidt, S. C., Logan, S. E., Hayden, J. M., Ahn, S. T., Mustoe, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+versus+conventional+tissue+expansion:+experimental+verification+of+a+new+technique.">Continuous versus conventional tissue expansion: experimental verification of a new technique.</a> Plast Reconstr Surg. 87, 10-15 (1991).</li><li>Buganza Tepole, A., Gart, M., Purnell, C. A., 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=Multi-view+stereo+analysis+reveals+anisotropy+of+prestrain,+deformation,+and+growth+in+living+skin.">Multi-view stereo analysis reveals anisotropy of prestrain, deformation, and growth in living skin.</a> Biomech Model Mechanobiol. 14, 1007-1019 (2015).</li><li>Tonge, T. K., Atlan, L. S., Voo, L. M., Nguyen, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Full-field+bulge+test+for+planar+anisotropic+tissues:+Part+I-Experimental+methods+applied+to+human+skin+tissue.">Full-field bulge test for planar anisotropic tissues: Part I-Experimental methods applied to human skin tissue.</a> Acta Biomater. 9, 5913-5925 (2013).</li><li>Park, S. I., Hodgins, 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=Capturing+and+animating+skin+deformation+in+human+motion.">Capturing and animating skin deformation in human motion.</a> ACM Trans Graph. 25, 881-881 (2006).</li><li>Rausch, M. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+dynamic+strains+of+the+ovine+anterior+mitral+valve+leaflet.">In vivo dynamic strains of the ovine anterior mitral valve leaflet.</a> J Biomech. 44, 1149-1157 (2011).</li><li>Leyva-Mendivil, M. F., Page, A., Bressloff, N. W., Limbert, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mechanistic+insight+into+the+mechanical+role+of+the+stratum+corneum+during+stretching+and+compression+of+the+skin.">A mechanistic insight into the mechanical role of the stratum corneum during stretching and compression of the skin.</a> J Mech Behav Biomed Mater. 49, 197-219 (2015).</li><li>Buganza Tepole, A., Kabaria, H., Bletzinger, K. -. U., 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=Isogeometric+Kirchhoff-Love+shell+formulations+for+biological+membranes.">Isogeometric Kirchhoff-Love shell formulations for biological membranes.</a> Comput Methods Appl Mech Eng. 293, 328-347 (2015).</li><li>Prot, V., Skallerud, B., Holzapfel, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transversely+isotropic+membrane+shells+with+application+to+mitral+valve+mechanics.+Constitutive+modelling+and+finite+element+implementation.">Transversely isotropic membrane shells with application to mitral valve mechanics. Constitutive modelling and finite element implementation.</a> Int J Num Meth Eng. 71, 987-1008 (2007).</li><li>Seitz, S. M., Curless, B., Diebel, J., Scharstein, D., Szeliski, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparison+and+evaluation+of+multi-view+stereo+reconstruction+algorithms.">A comparison and evaluation of multi-view stereo reconstruction algorithms.</a> Proc IEEE CVPR. 1, 519-528 (2006).</li><li>Furukawa, Y., Ponce, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dense+3D+motion+capture+for+human+faces.">Dense 3D motion capture for human faces.</a> 2009 IEEE CVPR. , (2009).</li><li>Jor, J. W. Y., Nash, M. P., Nielsen, P. M. F., Hunter, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+material+parameters+of+a+structurally+based+constitutive+relation+for+skin+mechanics.">Estimating material parameters of a structurally based constitutive relation for skin mechanics.</a> Biomech Model Mechanobiol. 10, 767-778 (2010).</li><li>Weickenmeier, J., Jabareen, M., Mazza, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suction+based+mechanical+characterization+of+superficial+facial+soft+tissues.">Suction based mechanical characterization of superficial facial soft tissues.</a> J Biomech. 48, 4279-4286 (2015).</li><li>Hughes, T. J. R., Cottrell, J. A., Bazilevs, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isogeometric+analysis:+CAD,+finite+elements,+NURBS,+exact+geometry+and+mesh+refinement.">Isogeometric analysis: CAD, finite elements, NURBS, exact geometry and mesh refinement.</a> Comput Methods Appl Mech Eng. 194, 4135-4195 (2005).</li><li>Echter, R., Oesterle, B., Bischoff, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hierarchic+family+of+isogeometric+shell+finite+elements.">A hierarchic family of isogeometric shell finite elements.</a> Comput Methods Appl Mech Eng. 254, 170-180 (2013).</li><li>Benson, D. J., Hartmann, S., Bazilevs, Y., Hsu, M. C., Hughes, T. J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blended+isogeometric+shells.">Blended isogeometric shells.</a> Comput Methods Appl Mech Eng. 255, 133-146 (2013).</li><li>Chen, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Explicit+finite+deformation+analysis+of+isogeometric+membranes.">Explicit finite deformation analysis of isogeometric membranes.</a> Comput Methods Appl Mech Eng. 277, 104-130 (2014).</li><li>Buganza Tepole, A., Gart, M., Purnell, C. A., 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=The+Incompatibility+of+Living+Systems:+Characterizing+Growth-Induced+Incompatibilities+in+Expanded+Skin.">The Incompatibility of Living Systems: Characterizing Growth-Induced Incompatibilities in Expanded Skin.</a> Ann Biomed Eng. 44, 1734-1752 (2016).</li><li>Buganza Tepole, A., Gart, M., 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=Characterization+of+living+skin+using+multi-view+stereo+and+isogeometric+analysis.">Characterization of living skin using multi-view stereo and isogeometric analysis.</a> Acta Biomater. 10, 4822-4831 (2014).</li><li>Rose, E. H., Ksander, G. A., Vistnes, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+tension+lines+in+the+domestic+pig.">Skin tension lines in the domestic pig.</a> Plast Reconstr Surg. 57, 729-732 (1976).</li><li>Rausch, M. 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=On+the+mechanics+of+growing+thin+biological+membranes.">On the mechanics of growing thin biological membranes.</a> J Mech Phys Solids. 63, 128-140 (2014).</li><li>Argenta, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+tissue+expansion+in+reconstructive+surgery.">Controlled tissue expansion in reconstructive surgery.</a> Br J Plast Surg. 37, 520-529 (1984).</li><li>Hudson, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maximising+the+use+of+tissue+expanded+flaps.">Maximising the use of tissue expanded flaps.</a> Br J Plast Surg. 56, 784-790 (2003).</li><li>Bartell, T. H., Mustoe, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+human+tissue+expansion.">Animal models of human tissue expansion.</a> Plast Reconstr Surg. 83, 681-686 (1989).</li><li>Belkoff, S. M., et al. <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+subcutaneous+expansion+on+the+mechanical+properties+of+porcine+skin.">Effects of subcutaneous expansion on the mechanical properties of porcine skin.</a> J Surg Res. 58, 117-123 (1995).</li><li>Ni Annaidh, A., Bruy&#232;re, K., Destrade, M., Gilchrist, M. D., Ott&#233;nio, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Automated+estimation+of+collagen+fibre+dispersion+in+the+dermis+and+its+contribution+to+the+anisotropic+behaviour+of+skin.">Automated estimation of collagen fibre dispersion in the dermis and its contribution to the anisotropic behaviour of skin.</a> Ann Biomed Eng. 5, 139-148 (2012).</li><li>Kiendl, J., Bletzinger, K. U., Linhard, J., W&#252;chner, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isogeometric+shell+analysis+with+Kirchhoff-Love+elements.">Isogeometric shell analysis with Kirchhoff-Love elements.</a> Comput Methods Appl Mech Eng. 198, 3902-3914 (2009).</li></ol>

SThe authors have nothing to disclose.

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

quantification-strain-porcine-model-skin-expansion-using-multi-view

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

11.5K Views.  Purdue University. 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.

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

Monitoring the Wall Mechanics During Stent Deployment in a Vessel

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the arterial wall lead to tissue injury, which initiates restenosis2-7. This hypothesis needs further investigations including better quantifications of non-uniform strain distribution on the artery following stent implantation. A non-contact surface strain measurement method for the stented artery is presented in this work. ARAMIS stereo optical surface strain measurement system uses two optical high speed cameras to capture the motion of each reference point, and resolve three dimensional strains over the deforming surface8,9. As a mesh stent is deployed into a latex vessel with a random contrasting pattern sprayed or drawn on its outer surface, the surface strain is recorded at every instant of the deformation. The calculated strain distributions can then be used to understand the local lesion response, validate the computational models, and formulate hypotheses for further in vivo study.

Stent-induced arterial strain distributions are characterized using an optical surface strain measurement system. This visualization technique is used to gain insights into the impact of stent implantation on the host vessel.

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the ...

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue remodeling. Based on this interest, several analytical techniques have been developed to measure local tissue strains within tendon explants during loading. However, in several cases, the accuracy and sensitivity of these techniques have not been reported, and none of the algorithms are publicly available. This has made it difficult for the more widespread measurement of local tissue strains in tendon explants. Therefore, the objective of this paper was to create a validated analysis tool for measuring local tissue strains in tendon explants that is readily available and easy to use. Specifically, a publicly available augmented-Lagrangian digital image correlation (ALDIC) algorithm was adapted for measuring 2D strains by tracking the displacements of cell nuclei within mouse Achilles tendons under uniaxial tension. Additionally, the accuracy of the calculated strains was validated by analyzing digitally transformed images, as well as by comparing the strains with values determined from an independent technique (i.e., photobleached lines). Finally, a technique was incorporated into the algorithm to reconstruct the reference image using the calculated displacement field, which can be used to assess the accuracy of the algorithm in the absence of known strain values or a secondary measurement technique. The algorithm is capable of measuring strains up to 0.1 with an accuracy of 0.00015. The technique for comparing a reconstructed reference image with the actual reference image successfully identified samples that had erroneous data and indicated that, in samples with good data, approximately 85% of the displacement field was accurate. Finally, the strains measured in mouse Achilles tendons were consistent with the prior literature. Therefore, this algorithm is a highly useful and adaptable tool for accurately measuring local tissue strains in tendons.

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

This paper describes an open-source digital image correlation algorithm for measuring local 2D tissue strains within tendon explants. The accuracy of the technique has been validated using multiple techniques, and it is available for public use.

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue ...

Engineering

Controlled Strain of 3D Hydrogels under Live Microscopy Imaging

External forces are an important factor in tissue formation, development, and maintenance. The effects of these forces are often studied using specialized in vitro stretching methods. Various available systems use 2D substrate-based stretchers, while the accessibility of 3D techniques to strain soft hydrogels, is more restricted. Here, we describe a method that allows external stretching of soft hydrogels from their circumference, using an elastic silicone strip as the sample carrier. The stretching system utilized in this protocol is constructed from 3D-printed parts and low-cost electronics, making it simple and easy to replicate in other labs. The experimental process begins with polymerizing thick (&#62;100 &#956;m) soft fibrin hydrogels (Elastic Modulus of ~100 Pa) in a cut-out at the center of a silicone strip. Silicone-gel constructs are then attached to the printed-stretching device and placed on the confocal microscope stage. Under live microscopy the stretching device is activated, and the gels are imaged at various stretch magnitudes. Image processing is then used to quantify the resulting gel deformations, demonstrating relatively homogenous strains and fiber alignment throughout the gel&#8217;s 3D thickness (Z-axis). Advantages of this method include the ability to strain extremely soft hydrogels in 3D while executing in situ microscopy, and the freedom to manipulate the geometry and size of the sample according to the user&#8217;s needs. Additionally, with proper adaptation, this method can be used to stretch other types of hydrogels (e.g., collagen, polyacrylamide or polyethylene glycol) and can allow for analysis of cells and tissue response to external forces under more biomimetic 3D conditions.

The presented method involves uniaxial stretching of 3D soft hydrogels embedded in silicone rubber while allowing live confocal microscopy. Characterization of the external and internal hydrogel strains as well as fiber alignment are demonstrated. The device and protocol developed can assess the response of cells to various strain regimes.

External forces are an important factor in tissue formation, development, and maintenance. The effects of these forces are often studied using specialized ...

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, multiple ligaments, and approximately 20 muscles. Unfortunately, shoulder pathologies (e.g., rotator cuff tears, joint dislocations, arthritis) are common, resulting in substantial pain, disability, and decreased quality of life. The specific etiology for many of these pathologic conditions is not fully understood, but it is generally accepted that shoulder pathology is often associated with altered joint motion. Unfortunately, measuring shoulder motion with the necessary level of accuracy to investigate motion-based hypotheses is not trivial. However, radiographic-based motion measurement techniques have provided the advancement necessary to investigate motion-based hypotheses and provide a mechanistic understanding of shoulder function. Thus, the purpose of this article is to describe the approaches for measuring shoulder motion using a custom biplanar videoradiography system. The specific objectives of this article are to describe the protocols to acquire biplanar videoradiographic images of the shoulder complex, acquire CT scans, develop 3D bone models, locate anatomical landmarks, track the position and orientation of the humerus, scapula, and torso from the biplanar radiographic images, and calculate the kinematic outcome measures. In addition, the article will describe special considerations unique to the shoulder when measuring joint kinematics using this approach.

Biplane videoradiography can quantify shoulder kinematics with a high degree of accuracy. The protocol described herein was specifically designed to track the scapula, humerus, and the ribs during planar humeral elevation, and outlines the procedures for data collection, processing, and analysis. Unique considerations for data collection are also described.

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, ...

Biomechanical Analysis of Peripheral Nerves Using DLT-Calibrated Stereo-Imaging

Direct Linear Transformation for the Measurement of In-Situ Peripheral Nerve Strain During Stretching

Peripheral nerves undergo physiological and non-physiological stretch during development, normal joint movement, injury, and more recently while undergoing surgical repair. Understanding the biomechanical response of peripheral nerves to stretch is critical to the understanding of their response to different loading conditions and thus, to optimizing treatment strategies and surgical interventions. This protocol describes in detail the calibration process of the stereo-imaging camera system via direct linear transformation and the tracking of the three-dimensional in-situ tissue displacement of peripheral nerves during stretch, obtained from three-dimensional coordinates of the video files captured by the calibrated stereo-imaging camera system.
From the obtained three-dimensional coordinates, the nerve length, change in the nerve length, and percent strain with respect to time can be calculated for a stretched peripheral nerve. Using a stereo-imaging camera system provides a non-invasive method for capturing three-dimensional displacements of peripheral nerves when stretched. Direct linear transformation enables three-dimensional reconstructions of peripheral nerve length during stretch to measure strain. Currently, no methodology exists to study the in-situ strain of stretched peripheral nerves using a stereo-imaging camera system calibrated via direct linear transformation. Capturing the in-situ strain of peripheral nerves when stretched can not only aid clinicians in understanding underlying injury mechanisms of nerve damage when overstretched but also help optimize treatment strategies that rely on stretch-induced interventions. The methodology described in the paper has the potential to enhance our understanding of peripheral nerve biomechanics in response to stretch to improve patient outcomes in the field of nerve injury management and rehabilitation.

Stereo-Imaging System DLT Calibration to Capture 3D In Situ Displacements of Stretched Peripheral Nerves

This protocol implements a stereo-imaging camera system calibrated using direct linear transformation to capture three-dimensional in-situ displacements of stretched peripheral nerves. By capturing these displacements, strain induced at varying degrees of stretch can be determined informing the stretch injury thresholds that can advance the science of stretch-dependent nerve repair.

Peripheral nerves undergo physiological and non-physiological stretch during development, normal joint movement, injury, and more recently while ...

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function relationships at the joint level remain challenging to quantify due to difficulties in accurately measuring dynamic joint motion. The soft tissue artifact errors inherent in optical skin marker motion capture are exacerbated by the depth of the hip joint within the body and the large mass of soft tissue surrounding the joint. Thus, the complex relationship between bone shape and hip joint kinematics is more difficult to study accurately than in other joints. Herein, a protocol incorporating computed tomography (CT) arthrography, three-dimensional (3D) reconstruction of volumetric images, dual fluoroscopy, and optical motion capture to accurately measure the dynamic motion of the hip joint is presented. The technical and clinical studies that have applied dual fluoroscopy to study form-function relationships of the hip using this protocol are summarized, and the specific steps and future considerations for data acquisition, processing, and analysis are described.

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Dual fluoroscopy accurately captures in vivo dynamic motion of human joints, which can be visualized relative to reconstructed anatomy (e.g., arthrokinematics). Herein, a detailed protocol to quantify hip arthrokinematics during weight-bearing activities of daily living is presented, including the integration of dual fluoroscopy with traditional skin marker motion capture.

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function ...

Medicine

Using Digital Image Correlation to Characterize Local Strains on Vascular Tissue Specimens

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and product development. Stress-strain relationships are typically obtained from mechanical testing data to enable comparative assessment among samples and in some cases identification of constitutive mechanical properties. However, errors may be introduced through the use of average strain measures, as significant heterogeneity in the strain field may result from geometrical non-uniformity of the sample and stress concentrations induced by mounting/gripping of soft tissues within the test system. When strain field heterogeneity is significant, accurate assessment of the sample mechanical response requires measurement of local strains. This study demonstrates a novel biomechanical testing protocol for calculating local surface strains using a mechanical testing device coupled with a high resolution camera and a digital image correlation technique. A series of sample surface images are acquired and then analyzed to quantify the local surface strain of a vascular tissue specimen subjected to ramped uniaxial loading. This approach can improve accuracy in experimental vascular biomechanics and has potential for broader use among other native soft tissues, engineered soft tissues, and soft hydrogel/polymeric materials. In the video, we demonstrate how to set up the system components and perform a complete experiment on native vascular tissue.

We describe the use of digital image correlation to characterize the local surface strain field on vascular tissue samples subjected to uniaxial tensile testing. These measurements facilitate precise quantification of the sample mechanical response and the generation of constitutive stress-strain relations.

Characterization of the mechanical behavior of biological and engineered soft tissues is a central component of fundamental biomedical research and ...

Biology

Ascending Aortic Banding for Studying Pressure-Overload Induced Heart Failure

A Minimally Invasive Model of Aortic Stenosis in Swine

Large animal models of heart failure play an essential role in the development of new therapeutic interventions due to their size and physiological similarities to humans. Efforts have been dedicated to creating a model of pressure-overload induced heart failure, and ascending aortic banding while still supra-coronary and not a perfect mimic of aortic stenosis in humans, closely resembling the human condition.
The purpose of this study is to demonstrate a minimally invasive approach to induce left ventricular pressure overload by placing an aortic band, precisely calibrated with percutaneously introduced high-fidelity pressure sensors. This method represents a refinement of the surgical procedure (3Rs), resulting in homogenous trans-stenotic gradients and reduced intragroup variability. Additionally, it enables swift and uneventful animal recovery, leading to minimal mortality rates. Throughout the study, animals were followed for up to 2 months after surgery, employing transthoracic echocardiography and pressure-volume loop analysis. However, longer follow-up periods can be achieved if desired. This large animal model proves valuable for testing new drugs, particularly those targeting hypertrophy and the structural and functional alterations associated with left ventricular pressure overload.

Author Spotlight: Development of a Minimally Invasive Large-Animal Model for Reliable and Reproducible Cardiovascular Research 

This protocol describes a minimally invasive surgical procedure for ascending aortic banding in swine.

Large animal models of heart failure play an essential role in the development of new therapeutic interventions due to their size and physiological ...

3D Visualization of Bone Remodeling Under Tensile Load in Suture Expansion Mice

A 3-D Visualization Technique for Bone Remodeling in a Suture Expansion Mouse Model

Craniofacial sutures play a crucial role beyond being fibrous joints connecting craniofacial bones; they also serve as the primary niche for calvarial and facial bone growth, housing mesenchymal stem cells and osteoprogenitors. As most craniofacial bones develop through intramembranous ossification, the sutures' marginal regions act as initiation points. Due to this significance, these sutures have become intriguing targets in orthopedic therapies like spring-assisted cranial vault expansion, rapid maxillary expansion, and maxillary protraction. Under orthopedic tracing force, suture stem cells are rapidly activated, becoming a dynamic source for bone remodeling during expansion. Despite their importance, the physiological changes during bone remodeling periods remain poorly understood. Traditional sectioning methods, primarily in the sagittal direction, do not capture the comprehensive changes occurring throughout the entire suture. This study established a standard mouse model for sagittal suture expansion. To fully visualize bone remodeling changes post-suture expansion, the PEGASOS tissue clearing method was combined with whole-mount EdU staining and calcium chelating double labeling. This allowed the visualization of highly proliferating cells and new bone formation across the entire calvarial bones following expansion. This protocol offers a standardized suture expansion mouse model and a 3-D visualization method, shedding light on the mechanobiological changes in sutures and bone remodeling under tensile force loading.

Author Spotlight: PEGASOS Tissue Clearing Technique to Visualize Bone Remodeling 

This protocol presents a standardized suture expansion mouse model and a 3-D visualization method to study the mechanobiological changes of the suture and bone remodeling under tensile force loading.

Craniofacial sutures play a crucial role beyond being fibrous joints connecting craniofacial bones; they also serve as the primary niche for calvarial and ...

Quantitative Strain Mapping of an Abdominal Aortic Aneurysm

Source: Hannah L. Cebull1, Arvin H. Soepriatna1, John J. Boyle2 and <a href="https://jove.unicartagenaproxy.elogim.com/author/Craig+J._Goergen">Craig J. Goergen</a>1 
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana
2Mechanical Engineering &#38; Materials Science, Washington University in St. Louis, St Louis, Missouri
The mechanical behavior of soft tissues, such as blood vessels, skin, tendons, and other organs, are strongly influenced by their composition of elastin and collagen, which provide elasticity and strength. The fiber orientation of these proteins depends on the type of soft tissue and can range from a single preferred direction to intricate meshed networks, which can become altered in diseased tissue. Therefore, soft tissues often behave anisotropically on the cellular and organ level, creating a need for three-dimensional characterization. Developing a method for reliably estimating strain fields within complex biological tissues or structures is important to mechanically characterize and understande disease. Strain represents how soft tissue relatively deforms over time, and it can be described mathematically through various estimations.
Acquiring image data over time allows deformation and strain to be estimated. However, all medical imaging modalities contain some amount of noise, which increases the difficulty of accurately estimating in vivo strain. The technique described here successfully overcomes these issues by using a direct deformation estimation (DDE) method to calculate spatially varying 3D strain fields from volumetric image data.
Current strain estimation methods include digital image correlation (DIC) and digital volume correlation. Unfortunately, DIC can only accurately estimate strain from a 2D plane, severely limiting the application of this method. While useful, 2D methods such as DIC have difficulty quantifying strain in regions that undergo 3D deformation. This is because out-of-plane motion creates deformation errors. Digital volume correlation is a more applicable method that divides the initial volume data into regions and finds the most similar region of the deformed volume, thereby reducing out-of-plane error. However, this method proves to be sensitive to noise and requires assumptions about the mechanical properties of the material.
The technique demonstrated here eliminates these issues by using a DDE method, thus making it very useful in the analysis of medical imaging data. Furthermore, it is robust to high or localized strain. Here we describe the acquisition of gated, volumetric 4D ultrasound data, its conversion into an analyzable format, and the use of a custom Matlab code to estimate 3D deformation and corresponding Green-Lagrange strains, a parameter that better describes large deformations. The Green-Lagrange strain tensor is implemented in many 3D strain estimation methods because it allows for F to be calculated from a Least Squares Fit (LSF) of the displacements. The equation below represents the Green-Lagrange strain tensor, E, where F and I represent the deformation gradient and second order identity tensor, respectively.
<img alt="Equation 1" src="/files/ftp_upload/10480/10480eq1v2.jpg" /> (1)

4-D Ultrasound &amp; Quantitative Strain Mapping in Abdominal Aortic Aneurysm

Source: Hannah L. Cebull1, Arvin H. Soepriatna1, John J. Boyle2 and Craig J. Goergen1 
1Weldon School of Biomedical Engineering, Purdue University, West ...

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

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