Needle geometry, target migration and substrate interactions in high resolution

Recent investigations considering flexible, steer-able needles for minimally invasive surgery have shown the significance of needle shape in determining the needle-tissue interactions leading to the access of targets. Digital Image Correlation has enabled internal deformation and strain caused by needle insertions to be seen in a soft tissue phantom at high resolution for the first time. Here, the impact of tip design on strains and displacements of material around the insertion axis is presented using Digital Image Correlation in a stable, plane-strain configuration. Insight into the shape of needles to minimise tissue trauma and generate interactions that would enable optimal steering conditions is provided. Needle tips with an included bevel angle up to 40° result in asymmetric displacement of the surrounding tissue phantom. Increasing the included tip angle to 60° results in more predictable displacement and strains that may enhance steering forces with little negative impact on the phantom.