Design, mechanical evaluation, and wear trial of 3D printed insole for plantar off-loading in older adults with diabetes

Abstract

Background: Up to 15 % of people with diabetes are at risk of developing a foot ulcer. Diabetic insoles are crucial for preventing foot ulcers by redistributing plantar pressure and increasing contact area. This study investigated the effects of novel insoles made with three-dimensional (3D) printed auxetic structure in older adults with diabetes. Research question: What are the effects of insoles on plantar off-loading, pressure distribution and mechanical properties in older adults with diabetes, as evaluated using a novel 3D printed auxetic-structured insole and compared to conventional insoles? Methods: Twenty-three elderly patients with diabetes were recruited as research subjects to evaluate the plantar off-loading effect of the insole prototype while walking. A total of seven 3D printed reentrant structures with varying internal angles and beam sizes were fabricated and evaluated. The differences in foot contact area and plantar pressure distribution were compared with conventional insoles. The mechanical properties of the heel pad material, especially its force absorption and compression properties were also evaluated. Results: The mean peak pressure (MPP) has been reduced by using diabetic insoles during walking. Compared to the commercial diabetic insole, the 3D printed insole shows a reduction of MPP up to 30.7 % which is also able to maintain the most evenly distributed plantar pressure by a 19.7 % increase of contact area with the midfoot. Significance: The capability of 3D printing on making insoles with 3D geometries that fit the human plantar surface was confirmed. The proposed 3D printed insole reliably alleviates peak plantar pressure based on laboratory findings and future long-term follow-up studies are necessary to confirm these benefits in daily life activities. The output of the study could also extend to the development of customized insole orthosis to prevent the development of diabetic foot ulcers.