Ideal material-structure interface for personalised prosthetic socket via additive manufacturing
This project aims to develop a robust and personalised prosthetic socket for children that is comfortable, suitable for exercise and play, and adaptable to limb growth.
Residual limbs of children grow non-uniformly and experience volumetric changes throughout a day, because of this, frequent replacements are expected. A socket’s lifespan is further reduced due to the necessary high rigidity of the used materials; support, via a secure fit, takes precedence over comfort, therefore little room is given to accommodate growth cycles.
This project aims to increase the lifespan of children’s prosthetic sockets by incorporating auxetic structures into a novel design, whilst utilising the potentials of digital manufacturing methods. As children’s limbs typically grow longer faster than in circumference, a combination of auxetic structures were selected where each was fit for purpose. A bow tie structure was used to support areas along the longitudinal axis, whereas a 3D star honeycomb structure was used for a base component at the distal end. Both low and high frequency limb volume changes may be compensated for, subject to user trials, by maintaining contact between adjacent components and the user throughout a day. Auxetic structures, therefore, may provide a prosthetic wearer with increased comfort and safety in comparison to conventional alternatives. In this application, the natural channels of the structures also increase air circulation to the skin, which may reduce perspiration by the wearer.
Modularity of the novel design also allows for heterogenous materials to be used throughout, which allowed the researchers to create a stiffness gradient. A low stiffness rubber-like polymer was selected for the liner component, as it is in contact with the skin, whereas a high stiffness nylon, pre-impregnated with short carbon fibres, was chosen for the socket shell. One benefit of additive manufacturing is the reduced restriction on combinations of geometries and materials, therefore, the researchers will be exploring alternative materials without the requirement to modify component forms.
Dr Simin Li - Senior Lecturer in Mechanics of Biomaterials
“Transforming the way we manufacture prosthetic sockets is only possible if we can disrupt the entire manufacturing workflow.”