When Bioinspiration Doesn't Help: Mechanical Behavior of Bio-inspired Curved Needles During Curvilinear Insertion

This study investigates the effectiveness of bio-inspired barbed geometries applied to curved needles for percutaneous procedures. The geometries of insect stingers, such as honeybees and mosquitoes, have been applied to straight needles to reduce insertion forces, tissue deformation, and tissue damage during linear insertion. However, whether these benefits extend to curved needles undergoing curvilinear base manipulation remains unclear. In this study, mosquito-inspired barb geometry was adapted onto bevel-tip curved needles with bent angles of 7.5°, 15°, 22.5°, and 30°. The effect on transverse and axial insertion forces, bending moments, and needle-tip trajectories was evaluated. The regular and bio-inspired curved needles were fabricated using high-resolution 3D printing and tested in tissue-mimicking gel under curvilinear insertion. Force and moment data were recorded at the needle base, and the needle tip paths were quantified using radius of curvature analysis from video tracking. No statistically significant reductions were found in insertion forces or bending moments under curvilinear insertion. These findings suggest that, for curved needles following predefined trajectories under the tested conditions, the measured forces did not change significantly with the addition of barbed surface features under curvilinear insertion. This suggests that the tested surface modification does not substantially alter the overall mechanical response under these conditions. This work highlights that friction-reducing surface features effective in linear insertion may not directly translate to curvilinear insertion, and that optimization strategies for curved needle applications may benefit from prioritizing geometric and trajectory-based design considerations.