CUSTOMISATION OF COSMETIC COVERS FOR ARTIFICIAL LIMBS

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This proposal combines academic expertise in digital manufacturing and heterogeneous foams (University of Strathclyde, Department of Design, Manufacture and Engineering Management) with prosthetics practitioners (University of Strathclyde, National Centre for Prosthetics and Orthotics) and non-academic partners, manufacturers (Blatchford Ltd.) and service users (PACE Rehabilitation, an SME), to investigate the feasibility of revolutionising the functionality and appearance of prosthetic cosmoses. Currently, flexible polyurethane foam cosmoses are a widely used component of prostheses for limbs. In a very labour intensive process, cosmoses may be machined from slab stock to a semi finished form and then shaped further to match patient requirements. An ordinary covering stocking is often added to enhance the cosmetic appearance of the prosthesis. Amputees cover their metal orthopaedic limb (i.e. artificial leg, arm, etc) with a two-fold function cosmesis: it protects the expensive equipment and, in theory, it provides a better aesthetic appearance to the patient's orthopaedic prosthesis. The reality is that cosmetic covers underperform the artificial limb, attract dirt, are non-water proof or fire resistant, impede the normal functioning of joint(s) and have a poor visual finishing which hinders the patient's psychological recovery and acceptance of their new condition and appearance.Although widely used, the foam cosmesis neither deforms like human limbs nor withstands repeated flexure, and its appearance is far from resembling human skin. These problems have their root in the standardized nature of the foam used; with a homogeneous and uniform pore size throughout the material, the stiffness will also be constant and consequently it will bend in an 'unnatural' way. Ultimately the highly stressed areas will fail, and the foam will tear at the joints (especially on the knee). The mechanical properties of foams are determined by their cellular structure; so small cells with thicker walls create stronger, stiffer materials than large open pours. Traditional manufacturing methods have fabricated cosmoses from blocks of homogeneous foam resulting in objects that have uniform mechanical properties. However it is also well known that variation in cellular structure can produce impressive combinations of strength and flexibility. To date, no manufacturing process for mass production has existed capable of dynamically varying the cellular structure of foamed material. Consequently, a controlled variation of features in the cosmesis to suit patient's movements and needs is not available. This proposal seeks to enable the mass customization of functionally graded foams, so they can be fitted to orthopaedic limbs and replicate the movement of the existing (healthy) limb. Using recently reported advanced manufacturing techniques never used before in this field, (e.g. computational modelling and simulation of foamed materials' behaviour, rapid prototyping technologies, ultrasonic irradiation, etc), as well as cutting-edge technology in scanning and measurement of materials properties, we aim to provide end-users (both practitioner prosthetists and patients) with a method of influencing shape, appearance, function and behaviour of foam cosmoses for orthopaedic applications.This proposal envisages a 2 year work program during which the commercial partners will help with patient satisfaction interviews, will input directly into the specification of requirements, and assist with the assessment of results. Our intention with the outcomes of this project is to pave the way for our partners to apply the results and implement them in the production process, allowing them to take the work forward and exploit the benefits that the project's output will provide to the relevant industry, rehabilitation services, carers (i.e. orthotists), the National Health Service and, most importantly, the patient.