Investigation of the damping properties of 3D-printed liners with controlled perforation

This study focuses on thermoplastic polyurethane (TPU) liners with controlled internal perforation intended for use in the “residual limb–liner–socket” system of lower-limb prostheses. The influence of material stiffness, hole geometry, and degree of perforation on vibration damping efficiency under impact–dynamic loading is investigated. The aim of the work is the experimental determination and optimization of the damping characteristics of TPU liners by varying material stiffness, hole shape, and perforation percentage using the free-decay vibration method. Tasks: to analyze the functional role of the liner as a damping element in the prosthetic system; to fabricate a series of 3D-printed TPU specimens with different stiffness levels, hole geometries, and perforation degrees; to implement an impact-based method for measuring free damped vibrations for each specimen; to determine the damping ratio and vibration attenuation percentage; to process experimental data in order to identify optimal combinations of material and geometric parameters; and to establish the relationships between material stiffness, perforation level, hole pattern, and the damping properties of liners. Results: a method for evaluating the damping characteristics of 3D-printed TPU liners with controlled internal structures was implemented and experimentally validated. A nonlinear dependence of vibration damping efficiency on the degree of perforation was identified, along with a systematic decrease in damping as TPU stiffness increased. It was shown that hexagonal hole geometry provides a more uniform deformation distribution and slightly higher damping efficiency compared to rhombic and triangular patterns. The obtained relationships enable targeted design of damping liners with an optimal balance between stiffness and vibration attenuation capacity. These findings support the solution of the following practical challenges: reduction of impact loads by decreasing peak dynamic forces transmitted from the prosthetic socket to the soft tissues of the residual limb; pressure redistribution through the formation of more uniform contact stresses at the skin–liner interface; improved user comfort by reducing vibration, pain, and skin irritation during walking; individual optimization through personalized selection of liner geometry and material based on body parameters, activity level, and tissue condition; and engineering design of structurally optimized components for biomedical applications. Conclusions: the study experimentally confirms the feasibility of controlling the damping properties of TPU liners by adjusting material stiffness, degree of perforation, and hole geometry. An optimal perforation range was identified for each TPU stiffness level, as well as the advantages of hexagonal perforation in terms of deformation uniformity and vibration damping efficiency.