The influence of tip shape on bending force during needle insertion.

Area of Science:

• Medical Devices
• Biomechanical Engineering
• Surgical Instrumentation

Background:

• Needle steering is crucial for minimally invasive procedures, requiring precise control over instrument-tissue interactions.
• Understanding the forces involved during needle insertion is essential for developing effective steering models.
• Existing models often assume constant tip load orientation, which may not reflect reality.

Purpose of the Study:

• To investigate the effect of needle tip shape on insertion forces and steering capabilities.
• To analyze how different tip geometries influence axial and bending forces during tissue indentation.
• To determine if tip load orientation is constant or varies with insertion depth and tip design.

Main Methods:

• Six different 10 mm diameter needle tips (beveled, conical, with/without pre-bend/pre-curve) were tested.
• A six-degree-of-freedom force/torque sensor measured loads during indentation in tissue simulants.
• Force-displacement slopes (axial and radial forces) were analyzed in relation to insertion depth.

Main Results:

• The ratio of radial to axial forces varied, indicating a non-constant tip load orientation.
• Tip load orientation shifted towards radial with increased axial load, more pronounced in straight tips.
• Higher force-displacement slopes were observed for increased tip angles and beveled tips compared to conical tips.
• Bent or curved tips resulted in increased bending force and decreased variability in tip load vector orientation.

Conclusions:

• Needle tip geometry significantly influences insertion mechanics and steering potential.
• The assumption of constant tip load orientation in current models is challenged by these findings.
• Pre-bent or pre-curved needle tips offer improved steering control by modulating force dynamics and load orientation.