ISPO UK ASM 2023 - Poster Exhibition

Sustainable Manufacturing of Orthotic and Prosthetic Devices

 

Presenter:  Urvashi Gunputh. Researcher in Additive Manufacturing, University of Derby, UK

E-mail:  u.gunputh@derby.ac.uk

Other authors:  Gavin Williams, Paul Wood

 

The ambiguity in prosthetic socket traditional design and manufacture in the UK and US has led to misfit and increased waiting time for amputees to obtain their correctly adjusted socket. Whenever an amputee’s stump shape changes, a new cast and mould is hand-made a using a traditional craft manufacturing process which involves material and time wastage and very often incorrect. Although high strength composite materials are used which produces a strong and lightweight socket, the base material is resin and hence toxic to manufacture and carries a high carbon footprint. Polyamide 11, PA11, is a 100 % biobased nylon which is known to have good all-round mechanical properties and is biocompatible. PA11 can be 3D printed using selective laser sintering to high dimensional accuracy.

The aim of this work is to manufacture prosthetic sockets for major lower limb amputee patients using a digitalised manufacturing process and a biobased nylon feed stock PA11. For the prosthetic sockets testing, a sample stump cast obtained from the NHS was 3D scanned and the prosthetic socket designed, and 3D printed using PA11. The stress and distortion of the 3D￾printed socket was simulated under static loading (100Kg Loading). The tensile properties of the PA11 input to the simulation were obtained from mechanical testing of 3D printed material coupons. Similarly, a simulation of the traditionally made socket using composite material Ramie Stockinette fibre reinforced resin was performed.

The maximum stress in the simulated PA11 socket was 1.3 MPa which was well below the allowable design stress of 25.5 MPa for this material. Although the deformation of the PA11 socket remained elastic it was slightly more pronounced than in the traditionally made fibre reinforced socket which was stiffer. This was expected because the design of the socket made from PA11 was not optimised for use with this material. Nonetheless, 3D-printed PA11 under static load was theoretically shown to be a viable solution displaying similar characteristics to the composite resin socket. This will help develop design specifications for socket manufacturing.

This work started with the orthosis design and manufacturing using PA11. In collaboration with the University Hospital of Derby and Burton NHS Trust, patients’ need, and orthosis’ manufacturing requirements were identified. Starting with fundamental research on the material and manufacturing process, the reuse of PA11 powder was investigated which adds to ASTM F3456-22 (Paper submitted to Additive Manufacturing Journal(IF:11.6)) and standard tensile testing was done on PA11 coupons as-built, exposed to UV and humidity.  The ultimate tensile strength of as-built PA11 was 54.1 MPa in the horizontal direction with a modulus of 1437 MPa. UV increased the ductility of PA11.

Using the UKRI Healthy Ageing Catalyst Awards 2022 (£62K) and UKRI Healthy Ageing Accelerator Funds 2023 (£125K), human factor is being investigated with a user-trial. Current work is testing the 3d printed orthosis on stroke patients while developing the commercialisation pathway targeting a B2B spinout.