Strength and Clinical evaluation of Self-reinforced Polymer Composite Prosthetic Sockets

The prosthetic socket is essential to the prosthesis because it is specifically created to fit comfortably on the amputee’s residual limb. The advanced prostheses costs maximum of $100k, which means that many of the 35-40 million amputees living in less-resourced nations cannot afford them due to the high cost and shortage of prosthetists. This problem is expected to become even more significant as natural disasters caused by global warming, diabetes and conflicts resulting from wars increase the number of people who need prosthetic devices. Therefore, this thesis aims to develop frugal manufacturing methods to create affordable prosthetic sockets for lower-limb amputees.

The study begins with using a 3D scanner and shape analysis toolbox to characterize the correction procedures performed on the residuum cast. Over one-hundred digital scans of the residuum limb casts were obtained during field trials at a non-profit rehabilitation service provider in India. The clinical implications of this research are: (a) the comparison data can serve as training resources for junior prosthetists, (b) it helps prosthetists to identify specific regions that need rectification and assess socket fit.

The substitute low-cost socket material and manufacturing technology were developed to fabricate prosthetic sockets using commingled yarn based self-reinforced polymer(srP) composites. The matrix and reinforcement in the single polymer composite are made from the same type of polymer, such as Polylactic acid(SPLA) and Polyethylene terephthalate(SPET) fibres. In contrast, the dual polymer composite has carbon fibre and glass fibre reinforcement with a PET matrix(DCF and DGF). For effective utilisation of srP, a purpose-built reusable vacuum bag and Infrared curing oven were commissioned to produce flat laminates and prosthetic sockets. Considering material cost, socket weight, and strength of the range of socket materials, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) decision criteria demonstrated that SPLA socket ranks high than SPET, DGF, and DCF. The performance index of SPC and DPC sockets has been proven to be much higher than that of the currently used expensive laminated composite fabricated using resin infusion and additively manufactured sockets. An ISO socket testing campaign revealed that the single polymer composite made from PET-fibre reinforcement complies with the socket strength requirement of 4426 N and is cheaper to produce. Therefore, the final study elucidates the performance of newly developed prosthetic sockets made from the PET single polymer composite in field trials in India. The unilateral and bilateral amputee’s gait performances were recorded with the help of a wearable device during the six-minute walking tests with the newly developed PET and traditional sockets. It has been shown that the amputees using the PET-based sockets showed that they can engage in daily activities without interruptions, reaffirming the functional efficacy of newly developed PET sockets. In addition, the cost per kilogramme of the woven PET fabric used in the socket manufacturing process was only 13 USD, proving that it is an economical and capable material alternative for prosthesis production.

The thesis outcome represents significant progress towards achieving affordable and personalised prostheses catering to amputees’ needs in less-resourced nations. This thesis also provides a foundation to fabricate functional prosthetic components, such as pylon foot pieces, with upcyclable and bio-degradable single polymer composites.