# A Tunable Self-Offloading Module for Plantar Pressure Regulation in Diabetic Patients
## 4 Experimental Studies
### Pressure Redistribution  
The pressure-sustaining capability up to 778 kPa of the proposed device was validated along with its tunability to change this limit to as low as 38 kPa. In order to use this module for PP redistribution among diabetic patients, there would be a need for an array of such modules distributed in the shoes. To be able to validate the proof of the device's functionality, a simplified version of foot loading (as shown in Figure 1a) was approximated experimentally. The experimental setup is shown in Figure 4a, where the foot was replaced by a soft-rigid combined surface linked to a custom-made load applicator, while the shoe base by fixed rigid surfaces. The proposed module was placed between two wooden blocks, which were fixed. The FlexiForce A301 sensor from Tekscan was fixed, respectively, on the head of the module and on the surface of the wooden blocks (in line along the Y axis) and marked S1, S2, and S3 (respectively, from left to right). The module was set to a threshold limit of 350 kPa by adjusting the spacing \(d\) to about 2.45 mm. The load applicator was positioned on the head of the module; the load applicator end comprised soft and rigid materials, as shown in Figure 4a. With a completely rigid interface in the middle and softer on the sides, a higher load distribution profile at the center can be created (similar to Figure 1a). The soft silicone Elastosil R 101 from Wacker was used as a soft interface; a thickness of 1.7 mm was used (0.2 mm stepped out from the rigid part), as it was convenient for the compression range for the different spacings used and the desired pressure at the loading end. A manually added load was applied and increased using a custom-made load applicator; the obtained pressure measured by the three sensors S1, S2, and S3 over time is shown in Figure 1b. During the initial phase of the loading, the soft surfaces on the sides (Figure 1a) deformed, and so, until they reached the same Z-level (as for the rigid part), the applied load was distributed among these two soft ends (left and right of the rigid part). Once this limit was reached for these soft ends (-95 s), further loading would start appearing on the centrally placed module. This continued to cause the placed module to be under higher pressure compared to the surfaces on the left and right. Once the threshold pressure limit was reached on the module end (-231 s), the excess pressure was redistributed. The module was configured to withstand a pressure of up to 350 kPa; therefore, once this value was reached, an additional 40 kPa was applied to allow the excess pressure's redistribution. The opening of the module happened around 360 kPa, while the total pressure (combined from \begin{table}
\begin{tabular}{c c} \hline \hline \(i\) **(for \(a_{i}\))** & **Value** \\ \hline
1 & 0.33 \\
2 & 4.35 \\
3 & 43.48 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Identified parameters for the calibration of the module. S1, S2, and S3) before opening was ~720 kPa. Following the pressure redistribution, the total final pressure obtained was ~740 kPa. The noise level of the sensors signal acquired was ~20 kPa; therefore, overall, the total pressure measured before opening and after redistribution was the almost same, which is consistent with what it was supposed to be under the static loading condition. The proposed device, therefore, allows pressure distribution among the neighboring exposed area once the defined threshold limit is reached. Another interesting side of the pressure redistribution noticed in Figure 1b for S2 consisted of the achieved pressure after offloading, which was about 210 kPa, which means more than a 35% reduction following offloading. International guidelines recommend [37] achieving at least a 30% reduction in peak plantar pressure to reduce the risk of foot ulcers among diabetic people. Therefore, the obtained result also validated the device's capability to address the need in the prescribed limit.