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Abstract

As medical technologies advance, surgical procedures are moving toward minimally invasive techniques. Procedures such as biopsies and vaccinations rely on needle insertion into soft tissues, where precision is vital for patient safety and procedural success. This thesis utilizes an energetic approach to model the puncture mechanics of hollow, flat-end needles in soft solids. The proposed models take material properties, needle geometry, and interfacial properties as inputs to predict fracture patterns and steady-state penetration forces. The work is divided into two primary modelling phases: a frictionless baseline and a friction-mediated refinement. By incorporating interfacial friction and adhesion, the refined model reduces the prediction error for critical rupture force (Fc) by 67%, demonstrating that interfacial interactions are a dominant factor in hollow needle mechanics. Additionally, experimental investigations into puncture instability revealed that hollow and larger needles are more prone to conical crack formation compared to solid or smaller needles. These findings provide a theoretical and empirical foundation for optimizing needle design and improving trajectory control in robotic-assisted surgeries, ultimately reducing the risk of collateral tissue damage.