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3D Printing Custom Shoe Sole
The need is to have a perfect shoe which will not only across the sole, changing wall thickness of infill walls and
provide comfort, but also maintain the functionality in changing infill density and height of each voxel. Hence,
diverse daily activities . It can also be inferred from the midsole designed could not only be customized to the
[11]
the open literature that shoe sole plays a critical role individual’s foot, but also is customized to the types of
in rehabilitation of lower limb while it improves activity, such as walking, running, or jumping. The same
[12]
walking function and reduces foot lesions. Patients level of performance will be hard to do or impossible with
[13]
often complain of foot pain and fatigue after prolonged machining and conventional subtractive manufacturing.
walking, followed by pain in the knee and ankle that Recent studies were conducted on different lattice
generally deteriorates the quality of life . The effects of structures by changing its unit cell size and shape to check
[14]
custom-made sole on the life quality of individuals both the behavior of their mechanical property, deformation
physically and mentally are proven . Due to difference in behavior, and compressive property [27-29] . Different lattice
[15]
foot structures of people, customizable midsole has come structures with closed and open unit cells of same size
into picture, which provides more comfort as compared were investigated in these studies and found that lattice
to prefabricated counterparts. One solution is 3D printing structure with a closed unit cell has higher stiffness
of custom shoe midsole, where 3D scanning techniques compared to the open lattice. A comparison analysis of
helps in getting the exact shape and size of the foot which lattice structures made from different unit cells by additive
act as input to design. Custom soles are more suitable for manufacturing were conducted . The compression tests
[30]
plantar structure of patient and can further be improved were performed on four different topologies such as
[16]
if traditional support structure is optimized; therefore, Diamond, Grid, X shape, and Vintiles to investigate the
further damage reduction at a lower cost, material waste, mechanical property of all four topologies. It has been
and fabrication time [17,18] . found that the Grid lattice delivered the highest stiffness
In the past years, there has been considerable compared to others which can be helpful to use in heel
amount of research in footwear industry to provide part of the insole as it requires stiffer material. Diamond
best comfort shoes for different walks of people from shape lattice structure has shown the most uniform stress
various fields, such as the sports or health sector; many distribution property which can be helpful for reducing
researchers continue to deliver crucial information based the plantar pressure.
on the experimental and theoretical works . The stiffness Shoe firms have been moving away from leather to
[19]
reported as a crucial factor accounts for 70% of the comfort shoes that are almost entirely polymeric. Thermoplastic
for diabetic users . High plantar pressure generated on urethane (TPU) is a soft material that is highly resistant
[20]
foot can be impacted by changing the stiffness of the to wear and abrasion, and is already used widely in many
shoe sole material [21,22] . A study has shown the efficacy industries, including footwear. The visco-hyper-elastic
of customized sole in reducing the peak of load by property of TPU is preferred due to their elasticity property
40% at metatarsal region . Custom-made insoles have and resistance they offer when subjected to compression.
[23]
proven to provide considerably better stress distribution The TPU also meets the requirements for medical devices
and much less maximum stress (around 40%) compared with regard to cytotoxicity and skin sensitization in
to flat insoles, which is very important in fabrication accordance with the DIN EN ISO 10993-5 and 10993-10
and selection of comfortable insoles . Furthermore, standards. The major advantage of soft-filament materials
[24]
the effect of custom-made 3D-printed foot orthoses in is the flexibility that makes them deformed under a load
the treatment of pain result in the foot of workers due and its ability to revert back to their original state when
to prolonged standing has been studied . Analysis of the load is removed. This property makes it possible
[25]
the participants’ test results revealed that after wearing to fabricate durable 3D objects with high deformation
customized 3D printing orthoses, feeling of discomfort, stability. In addition to its softness and flexibility, TPU is
pain, and heavy legs were reduced significantly. also known for its functional properties of being durable
Increase of thickness makes the stress distribution and being able to withstand ambient temperatures up to
more uniform and decreases the maximum stress value 80°C. TPU is therefore practical for both consumer and
up to 10%. However, simply increasing the thickness industrial use.
does not necessarily lead to less maximum stress after The fast print speeds and compatibility with springy
a certain thickness of the insole that is where more and flexible materials such as TPU, silicone, and elastic
[26]
sophisticated lattice design from 3D printing could play polyurethane, common for athletic shoes, have made resin-
a significant role. 3D printing has been recently focused based 3D printing technology a sustainable manufacturing
as the most flexible technology in making midsoles due option. At present, vat photopolymerization is the most
to its unit features in designing and developing variable popular category of 3D printing methods for footwear
density and stiffness products with changing the infill manufacturing . This category includes resin-based
[31]
pattern in two and three dimensions, changing the infill technologies, such as stereolithography and digital
170 International Journal of Bioprinting (2021)–Volume 7, Issue 4