Under Your Skin Project Report

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  • markwilsons157386

    imitations of life


  • 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.


    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.


  • 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.


  • 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 bodys 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.


  • 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.


  • 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.


  • Its 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.


  • 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.


  • 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



  • 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.


  • 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 designers

    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


    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


    1 Multi-layered patterningI 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.


  • 2 CavitiesMy 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


    3 Back and ForthThe 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 didnt 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:


    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


    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 t...