markwilsons157386

imitations of life

underyourskin

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.comcoach | markthielenTU/e

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

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

Capillaries are the smallest blood vessels in

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.

capil laryrefill

After exploring existing products that simulate

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

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

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

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.

capil laries

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

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.

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

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

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

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.

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.

si l icone

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

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.

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.

si l iconemoulding

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.

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.

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.

f inalproduct

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

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