Design and 3D printing of adjustable modulus porous structures for customized diabetic foot insoles

Designs with adjustable gradient modulus have become necessary for applications with special demands such as diabetic insole, in which the contact stress between the foot and insole is a critical factor for ulcers development. However, since the adjustment of elastic modulus on certain regions of insole can hardly be achieved via materials selection, a porous structural unit with varying porosity becomes a feasible way. Therefore, porous structural units associated with adjustable effective modulus and porosity can be employed to construct such insoles by 3D printing manufacturing technology. This paper presents a study on the porous structural units in terms of the geometrical parameters, porosity, and their correlations with the effective modulus. To achieve this goal, finite element analyses were carried out on porous structural units, and mechanical tests were carried out on the 3D printed samples for validation purposes. In this case, the mathematical relationships between the effective modulus and the key geometrical parameters were derived and subsequently employed in the construction of an insole model. This study provides a generalized foundation of porous structural design and adjustable gradient modulus in application of diabetic insole, which can be equally applied to other designs with similar demands.