The effect of personalised 3D printed metamaterial insoles in combination with a prefabricated offloading device for the reduction of plantar pressure in healthy individuals

This is a within-subjects repeated measures cross-over study design evaluating the influence that a personalised 3D printed 'metamaterial' insole may have on changing plantar pressures in conjunction with an ankle-high offloading device. In current practice, treatment for forefoot diabetes-related foot ulceration frequently includes the use of a prefabricated ankle-high offloading device. This study evaluates whether the efficacy of this treatment is changed through use of functionally graded 3D printed insoles that have materials stiffness personalised according plantar pressure. This study 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 an ankle-high offloading device worn on the right foot. 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. Prior engineering work has benchmarked the stiffness of the metamaterial to that of materials that are commonly used in insole and footwear manufacture. Intervention Arm 1: will use algorithm parameters that will define a relatively soft flat insole, that has compressive mechanical properties similar to Plastazote and Poron. Intervention Arm 2: will use algorithm parameters that will define a relatively hard flat insole, that has compressive mechanical properties similar to low- to medium-density Ethylene-Vinyl Acetate (EVA) Intervention Arm 3: will use algorithm parameters that will define a flat insole with hardness between that of Arm 1 and 2. It will have compressive mechanical properties similar to Plastazote, Poron, and low-density EVA. Intervention Arm 4: will use an insole contoured to the shape of the participants plantar foot, and apply the same stiffness algorithm as used for Intervention Arm 3 to set the stiffness of the insole. It will have compressive mechanical properties similar to Plastazote, Poron, and low-density EVA 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 a prefabricated ankle-high offloading device 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 not be controlled, but will be calculated from the time it takes the person to walk the predefined distance. Three trials will be completed for each study arm. There will be an washout and rest period between study arms of at least 3 minutes. When trialing the interventions, the participant will wear the offloading device with trial insole on the right foot, and their own shoe on the contralateral foot. 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 will be designed, manufactured, and fit by a podiatrist at a university research facility.