## 4 Discussion  
The repeated failure of prostheses can be challenging to manage, often necessitating re-fabrication, which underscores the importance of evaluating key parameters such as stress, pressure, and slip. Advancements in computational biomechanics, particularly FEA, have significantly enhanced the ability to predict biomechanical responses within stump-socket assemblies with high accuracy. Interface pressure is a critical biomechanical property of trans-tibial prostheses, as prolonged exposure to high pressures can lead to complications such as ulcers, inflammation, or vascular occlusions [48]. Both finite element and clinical measurements in this study revealed that pressure distribution was consistent across the residual limb, in line with prior findings [49,50]. The Standard Deviation (SD) of pressures from FE analysis and experimental analysis, measured at nine points on the stump (proximal and distal regions of each side and one at the stump end), were found to be 8.53 kPa and 4.46 kPa, with mean pressures of 44.6 kPa and 22.11 kPa under FBW and HBW conditions, respectively. A higher variation in the average interface pressures obtained from the FE simulation compared to the experimental measurements was observed at the stump end during FBW loading. This discrepancy can be attributed to the mechanical properties assigned to the FE model, where all materials were assumed to be homogeneous. In reality, the materials are not entirely homogeneous due to the presence of different tissues, such as skin, muscles, tendons, and others. Additionally, sensor sensitivity, placement variability, and minor dynamic factors during experiments could contribute to measurement differences. These factors highlight the inherent challenges in aligning FE simulations with real-world experimental conditions. [PERSON] et al. [51] work on elastomeric liners also indicated slightly higher interface pressures compared to experimental results, suggesting material differences might play a role in pressure mitigation. Currently, there are no established standard threshold values for pressure tolerance in the soft tissues of amputees, as these values depend on the condition of the individual's limb tissues and the type of amputation. However, a previous study quantified the pain-inducing pressure thresholds on the patellar tendon and lateral side to be up to 120 kPa and 50 kPa, respectively [52]. Shear stress and frictional slip are critical parameters in determining the efficiency of lower limb prosthesis and socket fitting. High magnitudes of shear stress can cause tension and fatigue in the soft tissues of the residual limb during the loading and unloading phases. This study observed a small range of shear stress at the stump-liner interface, varying from 2 to 11 kPa. The maximum shear stress was detected near the fibula head region, attributed to the pointed shape of the fibula head on the stump's lateral side. Similarly, a small magnitude of frictional slip was observed, with a maximum slip of 0.68 mm and an overall average of 0.48 mm. The low frictional slip values in this model are due to the bony nature of the residual limb and tissue rectification. For TSB-type socket fittings, minimizing frictional slip is recommended. The extent of slip is primarily influenced by the rectification of soft tissues and their material properties. Greater rectification and stiffness in the soft tissues reduce the amount of slip. [PERSON] et al. [31] found that TSB sockets significantly reduced frictional slip compared to other designs, which aligns with the findings of minimal slip in this FE model. It is noteworthy that slip occurs only during transitions between loading and non-loading states. This study also emphasizes the advantages and broader opportunities of additive manufacturing in prosthetic socket fabrication. Among the materials used in fused deposition modeling (FDM) printers, PLA is the most commonly utilized.