This document discusses research into developing a method of expanding skin grafts taken from burn victims to cover larger areas. The researcher is experimenting with using a translucent membrane and light detection to monitor skin thinning during the expansion process. Tests were conducted using Dragon Skin silicone and various molds, but induced stress caused clouding that made the material unsuitable. Future work will explore alternative materials or determining if consistent clouding still allows the membrane to be useful for light detection during expansion.

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Engineering Autologous Skin Using an Orbicular Skin Tissue
Expander
Julianne Spencer
Department of Industrial and Systems Engineering
North Carolina State University, Raleigh, NC 27695-7906, USA
Abstract
The most common treatment for burns of the skin, the largest organ in the body, is skin grafting. Skin
grafting is described as replacing burned areas of skin with healthy skin harvested from other areas of the
same body [6]. However, when a high percentage of the body is burned, there may not be enough skin to
salvage in order to conduct this surgery [5]. This research presents an approach in which one harvests skin
from a trauma subject and then “expands” it by method of mechanical deformation with the goal of
attaining permanent tensile plastic deformation in the skin, increasing surface area,while growing and
regenerating skin cells. The way in which the skin is stretched must be done strategically due to its
fragility. In a new approach described in this paper, shining light underneath the tissue expander allows
detection of areas in which the skin is getting thinner, thus allowing measures to be taken to prevent
premature tearing. This method is made possible by using translucent and transparent membrane in which
the skin lays against while light is shown from underneath. A two-part epoxy called Dragon Skin was
chosen to be used in the experimentation and creation of this membrane because it fit the necessary
criteria of being translucent, elastic, and FDA approved. After discovering the correct thickness and
diameter through three main trial methods of creation, the use of Dragon Skin as a translucent membrane
was rendered inconclusive due to a cloud that formed within the material upon tensile stress. While this
particular type of silicon membrane was not ideal for this method of use, other materials such as
BioPlexus, an easy to cut, premade material, are being considered for future use [4]. At maximum
capacity, relatively small amounts of skin harvested from healthy places on the body can be quickly
expanded to larger usable areas. The research within this branch of regenerative medicine has the ability
to ease the suffering experienced in severe cases of burned skin. Burn victims experience significantly
less pain and the results are more aesthetically pleasing, allowing them to live more normal and
productive lives.

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Table of Contents
Abstract……………………………………………………………………………………………………..1
1. Introduction………………………………………………………………………………….………...3
2. Methods and Materials………………………………………………………………………….…… 3
2.1 Implied Use…………...…………………………………………………………………….4
2.2 Preliminary Experimentation: Glass PetriDish……………………………………….…...5
2.3 Following Experiments: Custom Mold and Plastic Petri Dish……………………………..5
2.4 Membrane View……………………………………………………………………………6
3. Procedures………………………………………………………………………………….…………… 6
3.1 Preliminary Experimentation: Glass PetriDish Results…………….………..…….………6
3.2 Secondary Experimentation: Custom Mold Results…………………………….……….… 6
3.3 Third Experimentation: Plastic PetriDish Results………………………………………….7
3.4 Membrane View Results……………………………………………………………………7
4. Discussion…………………………………………………………………………………….…… 9
5. References………………………………………………………………………………….……… 10

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1. Introduction
Within the field of regenerative medicine, a new type of research has emerged in the treatment of
seriously burned human victims. This research utilizes mechanical properties and methods of efficiency in
order to increase the surface areas of skin removed by using a dermatome. Skin grafts that once required
the removal of large areas of skin from unharmed areas of the body will now be able to be done using
significantly smaller areas,decreasing physical suffering of patients and making previously difficult
surgeries possible.
In tissue engineering, skin stretching utilizes an epidermal biopsy that is secured in a biological reactor
where externaltensile forces are applied to expand the biopsy while nutrients are added to maintain a
healthy growing specimen [5]. One of the current methods used in cases where there is not enough skin
from the same body to cover burned areas is called a Meshed Skin Graft. This method is not ideal because
it uses small pieces of skin with tiny slits and allows new skin to grow in between. This method causes an
aesthetically displeasing diamond-shaped pattern of permanent scars on the skin’s surface [6].
At North Carolina State University, the process of skin expansion is being researched by the Edward P.
Fitts Department of Industrial & Systems Engineering. Through collaboration with Wake Forest
University, University of North Carolina, and the North Carolina State School of Veterinary Medicine,
Industrial and Systems Engineering is moving towards the goal of creating a systematic process for future
medical skin expansion treatments. This new method, titled “orbicular tissue expansion” (patent pending),
employs fluid pressure to unvaryingly expand tissue secured in a bioreactor. This method differs from
previous research because of the way in which it is stretched. Instead of skin being stretched laterally, this
method mimics the behavior of a balloon via a controlled induced strain. The method also mimics the
notion of skin’s elasticity and ability to stretch during pregnancy. Trial outcomes using this method with
swine tissue have shown great promise with a 39% increase in surface area in a 7-day time frame.
However,there is much room for improvement due to certain factors. One of these factors lies in the
difficulty of monitoring the varying thickness of different areas of the skin. Due to the delicate condition
of the skin during the stretching process,premature tearing often occurs.
To counteract this, an optical light transmission-based in-situ monitoring method will be implemented to
detect tear formation and propagation in the tissue prior to rupture. The first step in accomplishing this
goal is to ensure the accurate detection of light through the materials used to hold the skin. Specifically, a
previously red silicon membrane in which light was unable to pass through needed to be replaced with a
translucent membrane. This paper reports the results of a preliminary study in developing a translucent
membrane material using Dragon Skin, the exploration of molding methods, troubleshooting
complications with the developed membrane, and a discussion of the findings.
2. Methods and Materials
In order to accurately observe light being shown through the skin to detect tears,the membrane on which
the skin sits must be as tensile as the skin itself as well as perfectly and evenly translucent. To achieve
this type of criteria, we experimented with a two-part epoxy called Dragon Skin by Smooth-On
Incorporated that is typically used for theatrical makeup[1].

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2.1 Implied Use
The intended use is to evaluate pictures during the expansion process to identify thinning areas of the skin
based on the grey values of pixels. This will allow for the system to detect a tear before it happens. Using
image j software, pictures are converted to grey scale. Once the conversion is complete, a range of pixels
are selected based upon their color. These pixels are changed to red (Figure 1). Below there are two
graphs of a line drawn diagonally through the picture. Figure 2 shows the grey value of each pixel that
falls under that line relative to its position. Figure 3 represents a 3D surface plot of the line graph. Figures
2 and 3 help to visualize where the light is strongest in the picture.
Figure 1
Figure 2
Figure 3

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2.2 Preliminary Experimentation: Glass Petri Dish
Membranes were made with equal parts and placed in glass petri dishes to dry 1.1-1.5 hours, depending
on their thickness. The edge was touched to sense the texture of the membrane to establish drying time. A
standard glass petri dish was first selected for use as a mold due to its appropriate size.
The following process was used in all three membrane creation methods:
1. Use syringes to measures equal parts A and B
2. Place measured portions in dishes
3. Thoroughly mix together parts with a mixing tool
4. Spread contents evenly over top of dish
5. Leave on level surface to dry for approximately 1.25 hours(depending on the individual
thickness)
2.3 Following Experiments:Custom Mold and Plastic Petri Dish
The next approach to standardizing the size and thickness of the membrane was to create an actualmold
with ideal measurements and materials. This mold was created in SolidWorks 2014 x16 Edition(Figure 4)
and was then printed in PLA on a CubePro in NCSU’s Additive Manufacturing lab(Figure 5). For exact
procedure, reference section 2.2. After the mold was manufactured, the surface of the mold was smoothed
with fine sandpaper to remove ridges.
Following the same methods described in section 2.2, a plastic petri dish was used as the mold.
Figure 4 Figure 5

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2.4 Membrane View
Using a Hirox KH 7700 Digital Microscope, views were interpreted of the membrane stretched and
unstretched under lighting conditions of bright field (BF) and dark field (DF).
3. Results
3.1 Preliminary Experimentation: Glass Petri Dish Results
6 areas for future improvement:
1. Thickness consistency
2. Air bubbles (Figure 7)
3. Clarity
4. Replicability
5. Removing from mold
a. The edge of the membrane often became disfigured when removed prematurely (Figure 6).
3.2 Secondary Experimentation: Custom Mold Results
This attempt was also unsuccessful because of the method used in creating the mold. The CubePro lays
material down in strips that left texture on the surface of the mold. This did not allow for the smooth
finish that was desired (Figure 8). Using fine sandpaper in an attempt to fix this texture still did not
produce an optimally level surface mold.
Figure 6 Figure 7
Figure 8

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3.3 Third Experimentation: Plastic Petri Dish Results
Molding the Dragon Skin in a plastic petri dish proved to be successfulin terms of size, shape, consistent
thickness, and ease of removal from mold. However,upon induced stress to the membrane, clouding
within the material occurred (Figure 9, 10). Due to the nature of the membrane’s intended use, these
results motivated a deeper look into what was causing this clouding. Predictions included:
1. Nonhomogeneous mixing of parts
2. Microscopic air bubbles
3. Unclean working conditions causing impurities
4. Material forming cloud chemically at a molecular level for unknown reason
3.4 Membrane View Results
Views included:
Figure 11 (No Strain 150x(BF)) Figure 12 (Strain 150x(BF))
Figure 9 (without stress) Figure 10 (with stress)

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Figure 13 (No Strain 1050x(BF) ) Figure 14 (Strain 1050x(BF))
Figure 15 (No Strain 1050x (DF))
Predictions after viewed on microscope:
1. Internal voids that are opened and shown upon induced stress(Figure 14)
2. Microscopic craters all over the surface of the membrane due to improper drying techniques
(Figure 11, 12)
3. Nonhomogeneous mixing of parts (Figure 15)
Research on clouding yielded indeterminate results.

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4. Discussion
While the use of Dragon Skin as a translucent membrane initially seemed promising due to its ability to
be developed with the proper size and shape, lateral stretch induced clouding occurred within the
membrane, rendering it likely to be unusable for this purpose. After looking into what could be causing
this clouding by viewing it through a digital microscope, indeterminate results were yielded. There is
ongoing research on moving forward to determine cost effectiveness within two major different routes of
proceeding: 1.) Move on from using Dragon Skin as an option and look into other alternatives such as a
medical grade silicone sheeting called BioPlexus [4]. 2.) Look into how consistent the clouding within the
membrane is when it is placed in the orbicular tissue expander. If the clouding occurs evenly and relative
to if the membrane was perfectly transparent, it will still be a viable option for use. Within these two
different options for future action, there is much promise for future research to find an ideal transparent
membrane. The research proposed overall by all participating institutions has potential to help a large
number of patients in need of a skin transplant. It will also add to the scientific knowledge about skin
stretching and skin expansion from an engineering and biological perspective.

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4. References
[1]"Dragon Skin® 10, 20, 30 Silicone Product Information | Smooth-On." Dragon Skin® 10, 20, 30
Silicone Product Information. N.p., n.d. Web. 30 Jan. 2015.
[2]J.S. Arneja, A.K. Gosain, Giant Congenital Melanocytic Nevi, Plast. Reconstr. Surg. 120 (2007)
26E-40E.
[3]L. ARGENTA, M. WATANABE, W. GRABB, The use of Tissue Expansion in Head and Neck
Reconstruction, Ann. Plast. Surg. 11 (1983) 31-37.]
[4]"Medical Grade Silicone Sheeting." BioPlexus. N.p., n.d. Web. 30 Jan. 2015.
[5]"Printing Skin Cells on Burn Wounds." - Wake Forest School of Medicine. N.p., n.d. Web. 29 Jan.
2015.
[6]"Regions Hospital - St. Paul, Minnesota - Burn Center - Skin Grafting." Regions Hospital. N.p., n.d.
Web. 30 Jan. 2015.