Modelling, Materials and Methods Investigating Needle Insertion in Biomechanics

This project aimed to investigate the forces that both needle and tissue experienced during a needle insertion, and how they altered the needles trajectory. An investigation into the current literature showed that existing skin tissue surrogates did not perform similarly to real skin tissue in vivo during needle insertions. A new surrogate is required to aid with validation for computational models of needle insertions, while avoiding the ethical issues raised from testing real tissue. This study developed an improved skin tissue surrogate for use in photoelastic testing which focused on replicating the fracture mechanism observed during a needle insertion through human skin tissue. It is demonstrated that konjac glucomannan gel fractures in the same way as human skin tissue. Experimental assessments determined that at a concentration of 1.5% gel powder to water konjac jelly had a stiffness which closely matched the stiffness of human skin tissue in vivo. In order to use the surrogate in photoelastic analysis it must be clear and exhibit temporary birefringence, and it is shown that with careful preparation konjac satisfies these criteria. The strain optic coefficient for the gel is determined, which links the optical response to the strain and stress experienced by the surrogate. A variety of needle insertion experiments were conducted which assess how varying the insertion speed, needle length, and needle gauge affect the overall response. The results prove that konjac jelly accurately replicates needle insertion response through soft tissue better than existing surrogates. With use of the GFP2500 poleidoscope, a novel digital polariscope, full field and directional information from a needle insertion is obtained. The results identify never-before-seen locations of principal strain magnitude near the puncture surface. For the first time the forces directional response was reported, and show how a bending moment acts on the needle; resulting in deflection