The effect of personalised 3D printed metamaterial insoles on plantar pressures in healthy adults.

Current Australian and international guidelines recommend the use of medical-grade footwear and personalised insoles to prevent diabetes-related foot ulceration in individuals at risk, particularly those with foot deformities or pre-ulcerative lesions. This study will evaluate whether functionally graded 3D printed insoles that have material stiffness personalised according plantar pressure measurements are as effective as the current standard of care in reducing plantar pressures. It will also examine if the design algorithms and input pressures used to manufacture these insoles effect their ability to reduce plantar pressures when used with medical grade footwear. This study therefore includes several arms and intends to evaluate the effect of data-driven insole design algorithms. As a cross-over study, each participant will experience each intervention and control arm. Participants will be invited to attend two appointments. Each appointment is anticipated to take approximately 60 minutes. At an initial appointment, following screening for inclusion/exclusion criteria, plantar pressures will be measured barefoot and when wearing the issued medical grade trial footwear. This plantar pressure data will be used to design insoles using automated algorithms. Specifically, the plantar pressure will be used to define the stiffness of the metamaterial across the insole. This study has four intervention arms and three control arms for each intervention arm, different algorithm parameters will be used to define the stiffness of the metamaterial insole. Intervention arm 1 will be a 3D printed metamaterial insole comprising metamaterials of uniform stiffness that approximates low density EVA foam (the current standard of care). Intervention arms 2-4 will be a 3D printed metamaterial insoles comprising metamaterials with graded stiffness that ranges from low density EVA foam (at hardest) through to Poron a material commonly used as a component of insoles designed to reduce plantar pressures in clinical practice (at softest). The stiffness of the insole will be set based upon the peak plantar pressure at the corresponding part of the foot. Between these thresholds, the stiffness will be interpolated. For intervention arm 2, the design algorithm parameters will define a broad transition zone., whereby at sites of the foot with low pressures (less than 50 kPa), the insole will have properties approximating low density EVA, and at sites of high pressures (greater than 200kPa), the insole will have properties approximating Poron. For intervention arm 3, The design algorithm parameters will define a moderate transition zone, whereby at sites of the foot with low pressures (less than 100 kPa), the insole will have properties approximating low density EVA, and at sites of high pressures (greater than 200kPa), the insole will have properties approximating Poron. For intervention arm 4, the design algorithm parameters will define a narrow transition zone., whereby at sites of the foot with low pressures (less than 150 kPa), the insole will have properties approximating low density EVA, and at sites of high pressures (greater than 200kPa), the insole will have properties approximating Poron. Prior engineering work has benchmarked the stiffness of the metamaterial to that of materials that are commonly used in insole and footwear manufacture (EVA foam and Poron). Following the initial appointment, each of the interventions and control insoles will be designed and fabricated for the individual. The second appointment is anticipated to occur 2-4 weeks following the initial appointment. At the second appointment, each of the intervention and control insoles will be fit to the standardised medical grade footwear in a randomised order. The participant will be blinded to the difference between the different insole conditions. Primary outcome measures (plantar pressure in device during gait) will be recorded after a brief period of acclimatisation.(at least 2 minutes). The participant will walk straight for approximately 10m at a self-selected speed while data is recorded to provide at least 12 steps of data for the foot. Walking speed during the trial will be self-selected for the first trial and measured, to ensure each subsequent trial is within ten percent of this speed. Trials outside of this will be discarded and repeated to ensure walking speed is kept consistent during testing of each condition. Three trials will be completed for each study arm. There will be a washout and rest period between study arms of at least 3 minutes. As an immediate effects study design, insoles will not be worn for an extended period nor taken by the participants, and no assessment of adherence will be performed. Should any intervention be discontinued prior to data collection (e.g. due to discomfort reported by participant), this will be reported. Each intervention insole will be designed, manufactured, and fit by a podiatrist at a university research facility.