www.markwilsondesign.co.nz/under-your-skin

1. markwilson
s157386
imitations of life
underyourskin

2. Using our own microanatomy as
inspiration, Under Your Skin attempts to
artificially recreate capillary refill. It explores
manufacture methods and processes that
allow for an anatomically accurate simulation
of this physiological phenomenom.
projectstatement
contact | markwilsonnz33@gmail.com
coach | markthielen
TU/e

3. The aim of this project is to create a product
that could be used in medical training
scenarios. It looks at product systems
and services surrounding existing medical
simulation products and attempts to find
ways to design or redesign aspects to
ultimately improve the effectiveness of
medical simulation training.
introduction

4. Medical simulation is used as a method of
education for training health professionals
in their various medical fields. Its main
purpose is to reduce the number of
accidents that could occur in patient
diagnosis, surgery, prescription, or
general practice.
It is important that products used in
medical simulation succeed in creating
an experience that is as realistic as
possible. The more life-like and realistic
the experience is, the more effective and
valuable the training becomes.
Currently, there are very few products that
convincingly simulate capillary refill. They
lack realism, consequentially hindering
the sense of realism simulation products
aim to achieve.
medicalsimulation

5. Capillariesarethesmallestbloodvesselsin
our body. When our skin in pressed, blood
is squeezed from these vessels and, due
to circulation, this blood is restored. This
phenomenon is called capillary refill. It is
seen as a change of colour in the surface
of your skin – generally from yellow/white
to red/purple. Our body’s circulation can
be easily affected by our physiological or
pathological. By observing the capillary
refill time (CRT) health professionals
are able to make quick assessments of
this condition using no equipment. For
example, a person who has lower blood
pressure will have a higher CRT once their
skin is pressed.
This type of test is commonly conducted
during neonatal examinations. A small
amount of pressure is applied to the
sternum, forehead, or ankle for five
seconds, and the CRT is observed. The
test conductor is then able to quickly
assess the general health of the baby.
capillaryrefill

6. Afterexploringexistingproductsthatsimulate
capillary refill, it was quickly apparent that
the lack of realism needed to be addressed.
The products adopted various techniques
such as RGB LEDs to simulate a change in
skin colour. Fake hard-plastic bodies with
glowing chests left a lot to the imagination,
detracting from what is supposed to be a
realistic experience.
existingproducts

7. Inspiration for this project was taken from our
own bodies. Through examining the systems and
mechanisms within skin, and by observing it from
a sensory perspective, we are able to build an
understanding and knowledgebase to design with.
Using this knowledge, we will be able to produce
the most life-like simulation products.
designinfluence

8. The skin is the largest organ of your
body. Its primary functions include
providing protection against invasions of
microorganisms and regulation of body
temperature. Skin itself is fundamentally
comprised of three layers: the epidermis,
the dermis, and the subcutis. The
epidermis is the outer most layer of skin,
providing a waterproof barrier and the
colour of our skin tone. The average
thickness of this layer ranges between
0.05mm over our eyelids, to 1.5mm on
the soles of our feet and palms on our
hands. The dermis contains various
tissues and structures such as connective
tissue, hair follicles, sweat glands, and
capillaries. The thickness of this layer
ranges between 0.3mm at our eyelids, to
3.0mm on our backs. The deepest layer of
skin is called the subcutis or hypodermis.
It is comprised of connective tissue and
fat cells.
anatomy

9. It’s the blood vessels and capillaries in your
dermis that are squeezed and emptied
when pressure it applied to your skin.
The lack of blood creates a yellow/white
spot where pressure was, which quickly
refills depending on your various factors.
The upper normal limit for refill time in
newborns is 2 seconds. A prolonged refill
time can indicate various health issues
such as shock or dehydration. The longer
the time taken for capillaries to be refilled,
the more serious the state of health can
be assumed.
capillaries

10. In order for products that simulate skin
to achieve ‘suspense of disbelief,’ they
must replicate qualities of real human
skin. These qualities can be defined and
categorised as ‘sensory relationships’ we
have with our skin. There are only two
senses used in observing capillary refill
time: sight and touch. By observing skin
visually, we recognise it by its colour and
surface texture including small details
such as wrinkles, hairs, or pores. We
can detect what part of the body areas
of skin is by observing its shape and
contours, which is determined by what
lies underneath it (bones, organs, etc.).
By observing the tactility of skin through
touch, we can feel what lies beneath it
and we can estimate how thick it might
be. We can detect the temperature, and
the softness and elasticity as it reacts to
our touch. Its colour changes when we
apply and release pressure. All of these
factors and qualities make skin both
dynamic and static, making it very difficult
to simulate.
sensoryobservation

11. It are these intrinsic qualities of skin that can be implemented
to induce ‘suspense of disbelief.’ They are key to providing
an effective empirical experience through a mirror of reality.

12. Microfluidics defined as the study of
flows that are simple or complex, mono
or multiphasic, which are circulating in
artificial microsystems. I briefly explored
microfluidic mechanics in an attempt
to discover methods or systems I could
design with.
I learnt about a method using a silicone
called polydimethylsiloxane. This type of
material could be treated with plasma to
make it hydrophilic or hydrophobic. This
means that artificial capillary action such
as self-filling capillaries could be created
using microfluidic mechanics. However,
although it was possible to create idyllic
micro-channels, fabrication methods
required relatively advanced machines. I
instead decided to move on to exploring
fluidic behaviours for myself by observing
trial-and-error iterations with manageable
fabrication techniques.
microfluidics

13. Using my new understanding of the
sensory and mechanical properties of
skin, I began to think about how I could
create artificial capillary systems and
mechanisms. I explored materials and
their aesthetic and tactile properties, and
thought of ways I could create products
that closely mimicked our own anatomy.
I first looked at comparisons between
human skin and artificial materials by
using the Shore scale. This is a scale
determined using a Shore durometer - a
small instrument designed to measure
the hardness of polymers, elastomers,
and rubbers. Human skin has a Shore
hardness of about 0 – 15 on the Shore A
Scale. I was able to then identify materials
with similar Shore hardnesses that could
be used as a starting point for my project.
Two materials interested me. These were
TangoPlus and silicone. Because these
materials are used and manufactured in
two very different ways, I needed to make
two clear directions in order to explore
both.
concept

14. TangoPlus is used in high-resolution 3D
printers such as the Connex2. It is a rubber-
like material that can be fused with varying
amounts of Vero (another material) to print
a combine material of any Shore hardness
value between Scale A 26 and Scale D 86.
The closest Shore hardness value to skin
is that of pure TangoPlus, which has an A
Shore hardness of around 26 – 28. Pure
TangoPlus has great elasticity, flexibility, and
strength, enabling it to be stretched to just
over two times its length before tearing. It
is printed clear, but can be coloured using
pigments or dyes.
tangoplus

15. Using 3D printing as a method to
create capillaries has advantages and
disadvantages. Developments in 3D
printing technology has allowed for higher
resolution - and therefore higher detailed
- prints. I wanted to see how small I could
create channels to use as capillaries.
Some printers today can print as small
as 16microns. The elasticity and freedom
with form appealed to me, as I would
be able to rapidly prototype channels
to explore fluidic behaviour across
varying compositions, scales, and Shore
hardness values.
However, I knew 3D printing has its
limitations. When printing, a support
material is used to fill the channels in
order to lay the TangoPlus down onto
something before it is cured. This support
material needs to then be removed after
printing. This can sometimes be difficult,
depending on the complexity and size of
the channels. Limitations of 3D printing is
very much dependent on the designer’s
level of skill with computer-aided design
software. It is also very expensive.

16. Silicone is a rubber-like material that can
come in a large variety of Shore hardness
values from Shore A 00 and upwards. It
is relatively easy to work with due to its
flexibility, strength, and ability to be cast
and moulded. Silicones can also be easily
coloured using pigments and dyes. These
factors make it an ideal material to imitate
human skin.
Moulding silicone is a relatively easy
manufacturing method. It cures as a thick
liquid around any object or mould, picking
up even the smallest surface textures.
The level of detail that can be achieved
with silicone moulding appealed to me. I
wanted to see how small I could mould
channels.
Moulding silicone has a lot of limitations,
too. The composition of the channels
would be limited by the manufacturing
technique. Silicone is also expensive.
silicone

17. After numerous sketch-explorations of
composition, channel size, and layering,
I designed three small models that I
would 3D print. Each print would be used
to demonstrate different properties of
TangoPlus that I wanted to intentionally
exploit.
1 Multi-layered patterning
I designed this print to test the behaviour
of fluid within 1mm channels when
pressed. By having two layers of tight-knit
patterns, I was able to demonstrate how
fluid could be pushed around within the
channels. On one of the layers I included
multiple entrances to the pattern to see
if a change in pressure would affect the
behaviour of the fluid. The additional
entrances increased the distribution of
the fluid when pushing it through the
channels. They also made the removal
of the support material from within the
structure easier.
3dprints

19. 2 Cavities
My second sample model is designed with
two cavities that could be filled with fluid.
These cavities are joined using three small
channels. The aim of this design was to
see if a thin layer of TangoPlus’ would be
soft enough to push fluid through to the
second cavity, and whether it had enough
tensile strength to pull any fluid back
through when the structure was sealed
off. This proved semi-successful. A 2mm
layer of TangoPlus was soft enough to
easily push fluid through 1mm channels.
However, when sealed, the material was
not strong enough to pull the fluid back
through.
3 Back and Forth
The third sample model was designed
to see how fluid behaved in varying sizes
of channels. I wanted to see how thin I
could get the channels. This model took
the longest to remove all the support
material as it was difficult to reach the
support material trapped at the centre of
the model.

21. I began exploring with silicone by testing
different brands, mix types, and Shore
hardness values. I quickly found that
silicone quality was important. A lot of
the cheaper products were 10:1 mixes.
Even at a relatively low Shore A hardness
of 20, these silicones were not ideal to
use as artificial skin. Although they were
quite strong, they often cured far too hard
and didn’t possess softness similar to
skin. They also often ‘sweated,’ leaking
moisture and oils.
The best and most realistic silicones were
from the 1:1 Smooth-On range. Smooth-
On Dragon Skin and Smooth-On EcoFlex
20 provided the most realistic artificial
skin samples. Dragon Skin was strong
enough to withstand a considerable
amount of force and was therefore highly
elastic. EcoFlex 20 was soft and could be
compressed easily. It felt most like skin
tissue and would therefore be perfect for
simulating human skin.
siliconemoulding

22. I briefly experimented with layering these
two silicones. A thin layer of Dragon Skin
on top of a thicker layer of EcoFlex 20
acted in a very similar way to our own
skin – the epidermis and the dermis. This
led me to the next stage of my process:
moulding.
Silicone can pick up extraordinary detail
whilst retaining the form in which it cures.
I experimented with moulding silicone
around varying thicknesses and different
types of strings, suspending them in
a shallow dish. I quickly found nylon
thread to be easiest to work with due
to its consistent surface. It left perfectly
smooth and consistent channels inside
the silicone, and were easy to remove
without damaging the structure.

24. From here, I developed a method to
suspend rows of nylon thread evenly
across a thin sample patch of clear
silicone. This thread was 0.25mm thin.
Once the silicone cured and the nylon
thread was removed, I was able to fill the
channels with red dye. I could observe
the behaviour of the fluid within these
channels when the silicone was pressed
in different ways. Interestingly, the fluid
was visibly displaced beneath applied
pressure, and instantly refilled once it was
removed. I could recognise potential to
include mechanical or intelligent systems
to control the refill time of these channels.

28. Although the refill time of these channels
cannot yet be controlled, the realistic tactile
and visual qualities of this type of patch are
highly effective. This is believed to be the first
time a product that simulates the change
of colour in skin using moulded micro-
channels when pressure is applied has been
produced.
finalproduct

31. The next step to this project would be to
finalise these silicone patches. Although
systems to control the time it takes for
fluid to refill the channels once they have
been pressed would be essential for a
product that simulates capillary refill, it
is as equally important that the silicone
patch achieves the ‘suspense of disbelief’
through its skin-like qualities.
The control of refill time has the potential
to be achieved using mechanical and
intelligent actuators. This could involve a
pressure sensor beneath the patch, and
an adjustable fader that could control
a small machine to restrict the flow of
fluid through a small tube connected to
the channels. However, because of the
incredibly small scale of the channels, this
might be has the potential to be difficult
to achieve.
futuresteps

32. Thank you to everyone who helped me
with this project, especially my coach, Mark
Thielen, whose passion and enthusiasm was
highly contagious and actually made me
want work until late into my Friday evenings
after our meetings.
acknowledgements