Of Prosthetic Limbs - Case Study Example

MATERIALS ENGINEERING Student’s Name Code + Course Name Professor’s Name University Name City, State Date Summary Prosthetic limbs are used by amputees to restore the normal use of their body parts. These prosthetics have to be so designed such that they would fit just right with the amputee’s joint(s). The artificial limbs must allow the amputee to walk normally, or hold things normally in case it is a hand prosthetic. Typically, a prosthetic leg consists of several parts including its internal structure, specially designed fitting socket, prosthetic socks for cushioning the joint where contact with the rest of the body is made and the belts and knee cuffs used to attach to the body. In some minor cases, a practical-looking skin may be attached to the prosthetic leg. Whereas the normal limbs can function in any environment and naturally heal when bruised, the same is not the case with prosthetic ones. Careful choice of materials must be exacted when designing and manufacturing the prosthetic legs. Such materials include acrylics and other suitable hydrocarbons. This is the basis upon which the gist of this report is based, thus: Polar expedition leg should be made from carbon fibre by the 3D printing manufacturing process. Day leg should be made from high density polyethylene by the injection moulding process. Introduction This report is a study of prosthetic limbs. It will look at below the knee (BK) prosthesis for use on a polar expedition; and for realistic looking (BK) prosthesis for everyday use. The report will establish the service requirements in terms of load, strength, appearance, etc., as well as environmental conditions. The report will also assess the environmental impact of the materials selected. It was divided into two tasks: Task 1 This task required that suitable materials be selected, and suitable manufacturing techniques highlighted for the BK prosthetics. The design is to ensure that the leg is an endurance walking leg for a polar expedition. In order to achieve the same, the service requirements had to be identified in terms of the load and the impact strength as well as the environmental conditions which could affect its use. Task 2 This task analysed the service limitations and the possible impact on the environment that the chosen materials will have on the finished product. Report and Analysis Material Grading Criteria Several factors are considered when selecting the material to be used to manufacture the prosthetic legs. Regardless of where the artificial limb is to be used, the strength of the material must be able to withstand the weight of the user without fracturing it. Its aesthetics must also be put into consideration. With regards to this report, the material grading criteria considered the following factors: a) Compressive strength b) Fatigue resistance c) Rigidity d) Corrosion resistance e) Density/weight f) Comfort g) Chemical non-reactivity to the skin/body h) Working temperature i) Colour j) Durability Several materials were subjected to analysis based on the above factors. The materials included carbon fibre, polyamide (PA) nylon, polyethylene (HDPE), titanium, 6082 aluminium, acrylic nitrile butadiene (ABS), polypropylene (PP), glass filled polyamide (PAGF) nylon, polyurethane (PU), MULYI polymer 3D print and stainless steel. The properties of the various types of materials were graded based on their performance when the prosthetic leg manufactured from it is used in a polar expedition and on a normal day. The grading criterion was as below: Excellent 3 Good 1 Okay 1 Not suitable 0 The materials were graded and weighed thus: 1. Material: Carbon fibre Requirement Polar Day Compressive strength 3 2 Fatigue resistance 3 3 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 3 3 Comfort 2 2 Non-reactive to skin/body 3 3 Working temperature 2 1 Colour 1 2 Durability 3 3 2. Material: Polyamide (PA) nylon Requirement Polar Day Compressive strength 2 1 Fatigue resistance 3 2 Rigidity 2 3 Corrosion resistance 3 2 Density / weight 2 2 Comfort 3 3 Non-reactive to skin/body 3 3 Working temperature 3 3 Colour 3 3 Durability 3 3 3. Material: Polyethylene (HDPE) Requirement Polar Day Compressive strength 1 0 Fatigue resistance 2 0 Rigidity 2 2 Corrosion resistance 3 3 Density / weight 2 1 Comfort 2 1 Non-reactive to skin/body 2 1 Working temperature 2 0 Colour 3 3 Durability 3 3 4. Material: Titanium Requirement Polar Day Compressive strength 3 3 Fatigue resistance 3 3 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 3 3 Comfort 3 3 Non-reactive to skin/body 2 2 Working temperature 3 2 Colour 2 3 Durability 3 3 5. Material: 6082 aluminium Requirement Polar Day Compressive strength 3 3 Fatigue resistance 3 3 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 3 3 Comfort 3 3 Non-reactive to skin/body 3 3 Working temperature 2 2 Colour 2 3 Durability 3 3 6. Material: Acrylic nitrile butadiene (ABS) Requirement Polar Day Compressive strength 2 3 Fatigue resistance 2 3 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 3 2 Comfort 3 2 Non-reactive to skin/body 3 3 Working temperature 3 3 Colour 3 3 Durability 2 3 7. Material: Poly propylene (PP) Requirement Polar Day Compressive strength 2 3 Fatigue resistance 2 2 Rigidity 3 2 Corrosion resistance 3 3 Density / weight 2 2 Comfort 3 2 Non-reactive to skin/body 3 3 Working temperature 3 3 Colour 2 3 Durability 3 3 8. Material: Glass filled polyamide(PAGF)nylon Requirement Polar Day Compressive strength 3 3 Fatigue resistance 3 2 Rigidity 2 2 Corrosion resistance 3 3 Density / weight 3 2 Comfort 2 1 Non-reactive to skin/body 2 3 Working temperature 3 3 Colour 3 2 Durability 3 3 9. Material: Polyurethane (PU) Requirement Polar Day Compressive strength 2 3 Fatigue resistance 2 2 Rigidity 2 0 Corrosion resistance 2 3 Density / weight 1 1 Comfort 1 2 Non-reactive to skin/body 3 3 Working temperature 3 2 Colour 3 2 Durability 2 3 10. Material: MULYI polymer 3D print Requirement Polar Day Compressive strength 3 3 Fatigue resistance 3 2 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 2 1 Comfort 2 2 Non-reactive to skin/body 3 3 Working temperature 3 3 Colour 3 3 Durability 2 3 11. Material: Stainless steel Requirement Polar Day Compressive strength 3 3 Fatigue resistance 2 3 Rigidity 3 3 Corrosion resistance 3 3 Density / weight 3 2 Comfort 3 1 Non-reactive to skin/body 3 3 Working temperature 3 3 Colour 3 2 Durability 3 3 Materials such as fibre and nylon glass are bonded using reinforcement textiles. These textiles vary in strength, durability, brittleness and malleability. The goal of prosthetic manufacture is to reduce the weight and increase the strength of the material. This is the reason carbon fibre scores very highly in the material selection criteria. With regards to weight, titanium is ultralight and this makes it very desirable in the fabrication of prosthetic limbs. It is also very strong, stable chemically and thus it is candidate for a great leap in the arena of smart prosthetics (Bpf.co.uk, 2017). Task 1 There have been significant developments in prosthetic limbs. The development of materials such as carbon fibre have made such limbs stronger and lighter, and thereby increasing the flexibility with which the wearer can manipulate it during movement. Other materials have allowed the prosthetic limbs to appear more realistic than artificial. This is advantageous to the transhumeral and transradial amputees since they are likely to have the prosthetic limbs exposed. Apart from the new materials, the use of electronics is gaining momentum in the manufacture of prosthetic limbs. In particular, myoelectric limbs are presently more common and popular than the limbs operated by cables. This is because they control the limbs by converting the movement of muscles to electric signals. These ‘smart’ limbs allow those amputated to have more control over their prosthetic limbs. The delicate and intricate design has been made possible by the use of computer software like the Computer Aided design and Computer Aided Manufacturing in the design and the manufacture if such prosthetics (Seymour, 2002). The conventional artificial limbs are attached to the stump of the amputated person using cuffs and belts. Alternatively, suction can be used. The prosthetic is designed to fit just perfectly onto the stump. This means that every artificial limb must be uniquely and custom designed for every amputee. This is necessary to eliminate wear and tear at the joint on the stump. To create a custom socket, a plaster cast of the stump is taken and a mould is made from it. Modern methods of doing the operation include using laser guidance in measuring the dimensions of the stump and then fed into a computer to permit a detailed analysis and design of the socket. To obtain and endurance walking prosthetic leg, especially in a polar expedition, the artificial limbs must be padded. This padding refers to a cut system that encloses the edge of the stump. This is basically to increase the comfort to the amputee. The material used to do so is silicone because of its unique properties that it has. It especially protects the stump from friction with the socket. Similarly, polyurethanes can do the same function. Fibrous materials that are also gaining momentum in the prosthetic industry are Kevlar. It is very tough and flexible. Also, it is durable. This is the reason the straps around the stump are made from it. Aesthetically, many amputees prefer t have the artificial limbs covered in such a manner that it looks just like the rest of other body parts. The material used for this purpose is silicone. This is because it can be so designed to match the colour and hue of the flesh to a great degree. In fact, it can be painted or coloured to match any colour or tone of the flesh. The result of doing so is a life-like feeling to the amputee. Another material which can be used in place of silicone is foam. However, when using foam, it must first be made slightly above the size of the amputee and then shaped down to fit the shape and the size of the amputee. The reason for using such filler materials is to hide the prosthetic materials and give the user lively natural feel and look on that artificial limb. This is especially necessary for polar expedition where it is necessary to cover the prosthetic materials to protect them from extreme temperature conditions in those places. It is also to protect the materials from being covered in ice which can induce inactivity of the limb. On the other hand, athletes would not need to cover their artificial limbs using such materials as silicone or foam. This is to cut down on any extra potentially unwanted weight to the limb (Gallagher et al., 2011). One of the major challenges facing the joint at the socket and stump is the large amounts of rubbing between the two surfaces. The amputee can experience a lot of pain and subsequent tearing of tissues. The following steps outline how artificial limbs are manufactured: 1. Measuring the stump on the amputee using a suitable measuring aid like laser guidance. 2. Measuring the body of the amputee to gauge the size required to make the prosthetic limb. 3. Generating a model of the stump. 4. To test the fit of the artificial limb, a thermoplastic sheet is formed around the model of the stump. 5. Forming a permanent socket. 6. Creating of the plastic parts of the limb. Various techniques can be used such as injection moulding or vacuum forming. 7. The metal parts of the artificial limbs are then created using die casting technique. 8. Assembling the whole limb. Service Requirements The material used to make prosthetic limbs for polar expedition must have the following in-service requirements: a) Tensile strength – 0.20 - .040 N/mm2 b) Notched impact strength – no break kJ/m2 c) Thermal coefficient of expansion – 100 – 220 d) Maximum day temperature - 65 e) Density – 0.944 – 0.965 g/cm3 Extreme hot environmental conditions with temperatures exceeding 650C may affect the functionality of the material used to make the limb. In cases of myoelectric limbs, the electrical system can be affected and damaged. Therefore, it is necessary to use the artificial limbs within the set temperature limit. In addition, the material is waterproof, has high resistance to chemicals and possesses good toughness even at low temperatures like. Task 2 Service Limitations and Possible Impact on the Environment The greatest perceived barriers to individuals who have lost their limbs are in the structural/physical environment. Considering the limb is to be used in polar expeditions, the prosthetic limbs are subject to sensitivity to climate change. For instance, perspiration has an effect on the comfort of the amputee. On the other hand, snow – synonymous with polar regions – or even mere wetness, have great impact on the movement of the person wearing the limb, and thus the subsequent inability to participate in polar expeditions. Participation restriction, differences in the impacts and barriers on the environment and the limitations on activity are some of the service limitations facing prosthetic limbs. In addition, physical environment barrier is a challenge to amputees with below the knee prosthetic limbs. To enhance better polar expedition, the ability to gain easy access and sufficient mobility are essential facilitating factors (Your guide to Medicare's durable medical equipment, prosthetics, orthotics, and supplies (DMEPOS) competitive bidding program, n.d.). The manufacturing processes for the materials used to make the prosthetic limbs do not have any negative impact on the environment. These processes include injection moulding and vacuum forming. The limbs also do not affect the amputee medically. That is, they do not transmit any diseases to the wearer. Regarding the social environment, the amputee may feel isolated and lonely because of the prosthetics. Conclusion For the polar prosthesis, carbon fibre and titanium are the best materials because they can withstand low temperatures and have excellent durability. They are also tough and light. For the realistic leg, high density polyethylene is the best material because it is chemically stable, lightweight, durable and has good colouration. In both cases, manufacture will be by vacuum forming and injection moulding respectively. This is because these manufacturing processes are ideal in producing high accuracy components. Discussion The effect from the environment from manufacturing in these processes is nil. Recycling and reprocessing at the end of life is done by melting them in the crematorium or furnace and then sent back to medical manufacturers. The materials can also be used by other industries such as airplane manufacturers. Innovations and advancement in technology have seen the prosthetics industry develop such materials as pre-pregs and the LISA leg. The intention is to give the amputees greater mobility, comfort and confidence. In fact, the lightweight materials such as titanium have enabled amputees to take part in sports such as athletics and polar expedition exercises. The manufacturing of such prosthetics can be complex undertaking. This is why complex manufacturing processes such as 3D printing and additive manufacturing have been employed in the production of such prosthetics. These processes need to be very accurate so that the manufactured limb may look like a normal one. To help in doing so, computer programs are incorporated. These programs include CAD and CAM. They are used in designing and manufacturing the prosthetic component. The choice of the material for the manufacture of the prosthetic leg must be aesthetically pleasing to the wearer. This would boost his/her confidence. Silicone and form are the materials used to cover up the prosthetic materials and painted according to the hue of the skin in order to make the artificial limb blend with the rest of other body parts. References Bpf.co.uk. (2017). Polyethylene (High Density) HDPE. [online] Available at: http://www.bpf.co.uk/plastipedia/polymers/HDPE.aspx [Accessed 10 May 2017]. Gallagher, P., O'Donovan, M., Doyle, A. and Desmond, D. (2011). Environmental barriers, activity limitations and participation restrictions experienced by people with major limb amputation. Prosthetics and Orthotics International, 35(3), pp.278-284. Seymour, R. (2002). Prosthetics and orthotics. 1st ed. Philadelphia: Lippincott Williams & Wilkins. Your guide to Medicare's durable medical equipment, prosthetics, orthotics, and supplies (DMEPOS) competitive bidding program. (n.d.). 1st ed. Read More