An adaptive finite element model for steerable needles.
2020
Penetration of a flexible and steerable needle into a soft target material is a complex problem to be modelled, involving several
mechanical challenges. In the present paper, an adaptive finite element algorithm is developed to simulate the penetration of a
steerable needle in brain-like gelatine material, where the penetration path is not predetermined. The geometry of the needle
tip induces asymmetric tractions along the tool–substrate frictional interfaces, generating a bending action on the needle
in addition to combined normal and shear loading in the region where fracture takes place during penetration. The fracture
process is described by a cohesive zone model, and the direction of crack propagation is determined by the distribution of
strain energy density in the tissue surrounding the tip. Simulation results of deep needle penetration for a programmable
bevel-tip needle design, where steering can be controlled by changing the offset between interlocked needle segments, are
mainly discussed in terms of penetration force versus displacement along with a detailed description of the needle tip trajectories. It is shown that such results are strongly dependent on the relative stiffness of needle and tissue and on the tip offset.
The simulated relationship between programmable bevel offset and needle curvature is found to be approximately linear,
confirming empirical results derived experimentally in a previous work. The proposed model enables a detailed analysis of
the tool–tissue interactions during needle penetration, providing a reliable means to optimise the design of surgical catheters
and aid pre-operative planning.
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