Experimental Data-Driven Insertion Force Analyses of Hypodermic Needles in a Soft Tissue with an In-House Test Bench

Hypodermic needles are used in a wide range of medical procedures. In these procedures, an insertion force is applied to the needle to insert it through the soft tissue. In that way, when the tip of the needle encounters the surface of the tissue, several opposing forces are generated, such as stiffness, friction, and cutting forces, because of the tissue surface tension and viscoelastic properties. In addition, insertion force can influence tissue tearing and needle deflection. Thus, it is crucial to understand and analyze these forces and their effect on the tissue. We experimentally tested several commercial hypodermic needles at different diameters and bevel angles of the needle tips using an in-house test bench at different insertion velocities. In addition, chicken breasts were used as biological tissue to test the needles. As a result, the experimental cutting force increases linearly concerning the diameter of the needle and the insertion velocity. Also, the shear stress remains constant concerning insertion velocity and increases linearly with needle diameter and length. In conclusion, the results let us understand that the insertion mechanism is not trivial due to the influence of the geometry and relative velocity of the needle while penetrating the tissue and the mechanical properties of the soft tissue. All these combined parameters present challenging research to optimize medical procedures with needles.