Design of an actively actuated prosthetic socket

Purpose - A prosthetic socket worn by an amputee must serve a wide variety of functions, from stationary support to the transfer of forces necessary to move. Because a subject's residual limb changes volume throughout the day, it is desirable that the socket adapt to accommodate volume changes to maintain fit and comfort. The purpose of this paper is to provide steps towards designing a transtibial nylon prothestic socket, fabricated by selective laser sintering (SLS), that automatically adapts to volumetric changes of a residual limb. Design/methodology/approach - An adaptive socket design that has both rigid and compliant regions is proposed to be manufactured by SLS and actuated by inflation. To assess the feasibility of this approach, thin membrane test specimens of various thicknesses and materials were created to understand the relationship between inflation pressure and deflection for SLS manufactured plastics. Finite element analysis (FEA) was assessed as a predictive design tool and verified with the experimental inflation/deflection results. Findings - The initial flat test specimens could only achieve deflection of 2.13 mm at 145 kPa (nylon 12) and 3.38 mm at 340 kPa (nylon 11). A curved specimen is created that met performance goals with 7.67 mm maximum deflection at 714 kPa. FEA for the flat specimens is an accurate predictor of performance, but the results of analyzing the curved specimens are an order of magnitude different from the experimental data. Research limitations/implications - The success of the physical curved specimens is encouraging for future research, but the FEA will need to be further developed before socket performance can be predicted with confidence. Originality/value - A socket that does not fit the subject well will cause movement problems, rehabilitation difficulties, and potentially long-term health issues. This research shows great potential for developing a socket that provides greater comfort and fit.