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Zolfagharian, et al
light processing, and Carbon’s digital light synthesis contact to area off toe. Figure 1 shows an image where
[35]
(DLS) . These methods are based on a similar technique, ground reaction forces generated on the foot are derived by
[32]
in which a light source (laser, light-emitting projector or foot movement using an experimental gait analysis.
diodes) is applied to a liquid resin layer by layer, thereby To build an individual shoe sole for a person,
consolidating it. Besides resin-based technology, shoe plantar pressure needs to be lower which is possible
manufacturers also employ powder-based technologies, using different lattice structures and a single 3D printing
such as Multi Jet Fusion (MJF) from HP and Selective material. As midsole is subjected to low velocity impact
Laser Sintering (SLS) . The MJF and SLS are more test, visco-hyper-elastic materials are most suitable as
[33]
frequently utilized in the manufacture of insoles, as they offer high elasticity and show positive results on
opposed to resin-based technologies used in midsoles. dynamics humans’ body.
In this study, we present three different lattice The effects of sole designs on the plantar pressure
patterns designed with same wall thickness and amount and the ground reaction force over a period of time have
[36]
of a DLS 3D printing-based material. The midsoles been studied . The results revealed the reaction force
were positioned according to the foot sole to create a value changes by changing the stiffness and damping
specific design taking into consideration the visco-hyper- structure. It was also observed that both elastic and viscos
elastic material effects as per individual specifications. properties of sole give torque to ankle and knee joints and
The type of lattice depends on the required demands make the body propulsion. The aim of midsole design is
of the individual applications. These patterns were also to reduce plantar pressure generated on different areas of
compared in different loading scenarios under different foot and give more relaxation to the person’s body while
input loads simulating the type of activities to judge the they do activities in footwear.
efficiency of viscoelastic lattice design in distributing the Therefore, in the present work, the shoe sole was
stress. The results of the conducted simulations showed designed by considering different activities of person,
that the physical properties of customized 3D-printed such as walking, running and jumping, and for this trend,
midsoles are affected by the pattern type with the same viscoelastic material was selected and subjected to low-
amount of material and properties. The contribution of velocity impact test that results in a graph of load over
our study is as follows: time. This load versus time graph gives the idea about
a) The 3D-printed grade TPU material properties were how shoe midsole is helpful to reduce the plantar pressure
validated in ABAQUS finite element analysis (FEA) in people based on their specific activity. The novelty of
platform. the present study compared to other currently commercial
b) A specific design for the customized 3D printing was models is the investigation of functional customization
introduced along with flexible patterns, considering that does more than just geometry consideration with
the viscoelasticity property of material. the incorporation of viscoelastic material properties into
c) A procedure was presented to design and 3D print performance evaluation for specific user demand.
a customized midsole in terms of specific individual A detailed workflow of design and simulation
features, such as body weight and type of activity, proposed in this study is illustrated in Figure 2. The
using merely one type of material at minimum cost
and material use.
The rest of this paper is organized as follows:
Section 2 is dedicated to the detailed methodology of
3D-printed customized midsole design and the materials
characterizations; Section 3 provides the description
of the FEA and simulation results and discussion; and
Section 4 summarizes the study.

2. Methodology

2.1. Custom midsole design workflow
The pressure distribution is practically consistent in
ordinary people. Originally, the body mass appeared on the
heel area than that on the middle foot as it transitioned to
the forefoot and then was received by that of the toe region
in the end . In ordinary humans, the maximum pressure
[34]
is located on the second metatarsal. The variation of the Figure 1. Reaction force generated on feet (from ref. licensed
[35]
plantar pressure in normal individuals is from region of heel under Creative Commons Attribution 4.0 License).
International Journal of Bioprinting (2021)–Volume 7, Issue 4 171