Biomechanical evaluation of multi-bevel angled flexible needle insertion to improve deflection and decrease insertion force

Beveled-tip flexible needles facilitate steering during minimally invasive procedures by producing a transverse force that induces deflection, enabling steering around critical anatomical organs. An optimal bevel tip configuration of a flexible needle efficiently divides the insertion force into axial and transverse components, enhancing steerability while simultaneously reducing tissue penetration resistance. A dual-bevel needle design featuring a 30° primary bevel and a 15° secondary bevel offers the advantage of high deflection with low insertion force and a minimal penetration force. Excessively high penetration force can lead to buckling, while a very low penetration force risks harming vital organs unnoticed. This new type of multi-bevel-angle needle has moderate penetration force with less insertion force and provides greater deflection. A comprehensive modeling approach combines Mooney-Rivlin hyperelastic material properties (to represent tissue behavior) with Euler-Bernoulli beam theory (to predict needle deflection). Experimental validation was conducted using agar-based tissue phantoms characterized by C 10 = 46.72 kPa, C 01 = − 35.12 kPa, and a Young’s modulus of 69.6 kPa. Results demonstrate that the (30 + 15)° dual-bevel needle achieved a deflection of 16.00 mm at an insertion depth of 130 mm, exceeding the performance of the single-bevel 15-degree needle (14.31 mm) and the single-bevel 30-degree needle (13.38 mm) by 12% and 19.5%, respectively, while maintaining a low insertion force of 2.34 N. The proposed analytical model demonstrates strong agreement with experimental data, achieving correlation coefficients above 0.95 for depths greater than 65 mm. A polynomial trajectory fitting accurately reconstructs full needle paths with an R 2 value near 1.0 and RMSE below 0.15 mm. The multi-bevel-angle strategy with a computational platform improves the targeting accuracy for clinical applications.