Insoles for diabetics have traditionally been handmade by makers of orthopedic shoes. In the future, these specialist shoemakers will be able to produce insoles more cost effectively using new software and 3D printers.

3D structures made of TPU for insoles. These structures were designed using CAD, and their properties were simulated and compared with experiments. (©Photo Fraunhofer IWM)

If your shoe feels too tight, you may shift your weight to take the pressure off the sore area. But for people with diabetes, nerve endings in the foot often become atrophied, and those affected cannot feel the soreness. This can lead to pressure points and wounds that don't heal properly. Some relief is promised by insoles that are very soft in the area of the injury, and that are custom-made by orthopedic shoemakers in a variety of materials. It will soon be possible to digitize the manufacture of insoles.

Fraunhofer Institutes for Mechanics of Materials IWM and for Environmental, Safety, and Energy Technology UMSICHT in Germany are collaborating with industry partners to digitize the process through the LAUF (for laserassisted construction of customized footwear) project. “Digital foot mapping is already common practice. As part of this project, we have now also completely digitized the insole production process,” said IWM scientist Dr. Tobias Ziegler. “Using newly developed software, the orthopedic shoemaker can design an insole for an individual patient and can print out the result on a 3D printer.”

This has a number of immediate advantages. The mechanical properties of each insole become readily apparent, which is something health insurance companies want. Also, insoles can be produced at greatly reduced cost. In about two years, the software might be available to orthopedic technicians through a member company of the project.

IWM scientists have meanwhile been optimizing the three-dimensional structures that are required when the thermoplastic polyurethane (TPU) material is used for insoles. How soft or rigid the insoles are depends not just on the material itself, but also on how it is shaped. “First we think about structures — straight rods, crooked arms, or triangles, for instance — then we produce a computer model of them, key in the data for a particular material, and simulate how rigid the result is under pressure,” Ziegler explained. “Where does an insole need to be soft or more rigid? By altering the structure type, we can precisely determine the rigidity of the insole.”

The IWM team uses application-oriented load simulations to resolve which structures are needed where to achieve the desired properties. They test the material's load-bearing strength and its expected lifespan. “We simulate the entire production process, too, in order to identify where there is potential for optimization,” Ziegler said. He also uses this approach in relation to other materials and structures for 3D printing.

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NASA Tech Briefs Magazine

This article first appeared in the April, 2017 issue of NASA Tech Briefs Magazine.

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