Under Your Skin Project Report
Post on 13-Apr-2017
markwilsons157386imitations of lifeunderyourskin 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.projectstatementcontact | firstname.lastname@example.org | markthielenTU/eThe 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.introductionMedical 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.medicalsimulationCapillaries 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 laryrefillAfter 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.existingproductsInspiration 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.designinfluenceThe 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.anatomyIts 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 lariesIn 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.sensoryobservationIt 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.microfluidicsUsing 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.conceptTangoPlus 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.tangoplusUsing 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 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 iconeAfter 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 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.3dprints2 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 through.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 iconemouldingI 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 inalproductThe 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.futurestepsThank 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
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