## 4 Discussion  
The behavior of the SPA has been widely assessed using FEM analysis to optimize its design. The performance of SPA strongly depends on the design parameters and material used [26]. Considering that food-grade silicone has the same properties as commercial silicone, including the ability to provide effective pressure transfer as well as being non-hazardous, this study aimed to anticipate the influence of the material selection of three silicone elastomeric rubbers composed of commercial and food-grade silicone. The findings showed that A10 Shore silicone has the highest deformation compared to A15 Shore and Sylgard 184. These outcomes are in agreement with the properties of A10 Shore which has a lower Shore hardness than A15 Shore and Sylgard 184 [39]. [PERSON] et al. [40] stated that very large deformation is exerted on the inflatable actuators and, to avoid high pressure, elastomers with a low Shore hardness are preferred. Silicone is an isotropic material with unique mechanical properties, such as Young's modulus, Poisson's ratio, and shear modulus, which can lead to dissimilar deformation during inflation. A10 Shore has the lowest Young's modulus compared to A15 Shore and Sylgard 184. A10 Shore is softer than other elastomers, requiring lower pressure levels to achieve the desired deformation of the soft actuators. In a study on the characterization of pneumatic muscle actuators, [PERSON] et al. [41] discovered that materials with a low Young's modulus create greater deformation and force when stimulated. The amount of compressed gas that must be introduced into the chamber to reach the required pressure is specified by the elastomeric material's deformation [42]. This study analyzed the reliability between the simulated and experimental conditions using a relative measure. The mean difference between the two conditions in this study was illustrated and analyzed using a Bland-Altman approach. The Bland-Altman plotting was used to compare a new measurement instrument or procedure to an approved method. In a study by [PERSON] et al. [43], the authors applied a Bland-Altman and correlation analysis to assess the two methods of blood pressure measurement. The mean difference between the two conditions in this study was illustrated and analyzed using a Bland-Altman plot method. Based on the Bland-Altman plot, the deformation points in both the simulation and experimental were within the intervals and limits of agreement (LoA). The findings showed  
Figure 9: The Bland-Altman plot of the SPA unit deformation for simulation and experiment. an acceptable agreement when testing the method of deformation between the simulation and experimental conditions. There was no apparent proportional partiality, implying that the differences between the two methods of testing occurred at random over the pressure range. A study by [PERSON] et al. [44] on the validation of a 3D finite element (FE) coupled model of the foot and sports shoe reported most of the points were scattered between \(\pm\)1.96 SD to indicate the two approaches are in good agreement. The high ICC values for the deformation parameters indicated that the SPA unit was dependable. No clear agreement has been reported on the applicable standard values for accepted reliability using ICC. A study by [PERSON] considered ICC \(\geq\) 0.75 as excellent, 0.75-0.40 as good to moderate, and <0.40 as poor [45]. Overall, the SPA chamber fabricated using food-grade silicone was able to apply interface pressure on the skin for a pressure range of 0-120 mmHg. The pressure range corresponds to the literature's interface pressure for compression therapy [46]. The outcomes showed that the model accurately captured the physical system in this pressure range. Although the results show that the SPA chamber can generate high skin interface pressure, determining the optimal pressure is still crucial in treating venous disease. Therefore, an appropriate approach to measure the interface pressure for a desired treatment should be proposed.