Session: 02-02-01: Design, Modeling and Systems

Paper Number: 113297

113297 - Voxel Printing of a Multi-Material 3D Printed Prosthetic Socket Based on FEM Simulations 

There are more than 1 million annual limb amputations around the world. Prostheses allow amputees to continue with their day-to-day life, enhancing them to walk, run, and continue with several sorts of life activities. It is crucial to have a good assessment, design, elaboration and anatomical adaptation of those external devices on the human body. This study aims to obtain results from Finite Element Model (FEM) simulations about the stresses and contact pressures acting on the residual limb of a transfemoral amputee wearing a prosthesis in different load conditions, namely the donning phase, a stabilization phase and a phase with applied human gait loads.

The collection of the reaction forces and moments on the knee joint concerning the human gait was obtained using the open-source software OpenSim. Extracted data were processed in Matlab to be used in the FEM simulations. Geometries of both the stump and the femur have been reconstructed from medical images obtained by Magnetic Resonance Imaging (MRI); as regards the socket, this has been derived from the digital model of the residual limb.

Gradually increasing complexity simulations were performed in Ansys software: two different materials for the limb (linear elastic and hyper-elastic), as well as frictional and non-frictional contacts and different ways to displace the socket in the donning phase were introduced. Furthermore, two phases were established after the donning phase, namely the stabilization phase, where no external forces or displacements are applied and which acts as a transition to the third phase, where forces and moments are applied at the knee joint level. Computed stresses on the residual limb, contact pressures between the limb and the socket, the reaction force at the fixed end and the displacement of the socket were considered.

For the linear elastic material, results for the different displacement cases show that donning phase stresses are way lower if the socket is allowed to deform by only displacing the distal end. The stabilization phase counteracts this effect showing that the deformation of the socket is mainly responsible for the stresses on the limb in this case. However, the reaction force on the fixed end of the limb, stresses in general and the contact pressure are too high to be considered realistic results. In comparison, the gait forces and moments are very low, leading to little influence on the already high existing stresses in the stabilization phase. For the hyper-elastic material, only the donning phase with friction was investigated, due to convergence problems. Results in terms of contact pressure are in the same magnitude as experimental data found in the literature, which confirms the assumption of a more realistic material. On the other hand, the reaction force is very low and the highest shear stresses appear around the femur because of a high deformation gradient due to the bonded contact between the rigid femur and a very soft limb material.

Further methods and ideas are given to fix convergence and improve the reliability of the results on a qualitative and quantitative basis. Moreover, to reach even more realistic results further investigation into the connection between the socket and the knee joint is necessary.

Presenting Author: Marco Rossoni Politecnico di Milano

Presenting Author Biography: Assistant professor at Politecnico di Milano.

Authors:

Riccardo Pigazzi Politecnico di Milano
Michele Bertolini Politecnico di Milano
Marco Rossoni Politecnico di Milano
Giorgio Colombo Politecnico di Milano