The reduction in the insertion force is due to the decrease in the friction force of the bioinspired needle with the bovine tissues, and its results are consistent with our previous results.

Shape memory alloy (SMA) materials, such as Nickel Titanium (NiTi), can generate stress and strain during phase transformation induced by thermomechanical stimulation. Therefore, they may be used to construct active actuating devices for various biomedical applications such as smart surgical tools. Since temperature rise during the operation of SMA devices may damage the surrounding tissue, it is important to thermally shield such devices. We propose to use polydopamine (PDA) as an insulating coating for NiTi-based smart needles. PDA is a biomolecule (dopamine) derived polymer that can form conformal coating on various materials including NiTi. It is hypothesized that the surface temperature of the PDA coated needle can be reduced by the low thermal conductivity of PDA and the thermal resistance of the PDA/NiTi interface. Our experiments conducted in ambient air at room temperature showed that the coating reduced the surface temperature by as much as 45%. In this paper, we will present the thermal insulating performance of the PDA coating on NiTi wires. An experimental setup where the wire is embedded inside a gel phantom/tissue has been developed to simulate needle-tissue interaction. Effects of the coating thickness (material thermal resistance) and the number of layers (interfacial thermal resistance) will be discussed. 2D finite element analyses (FEA) were performed using ABAQUS to investigate the thermal distribution around the coated NiTi wires and the tissue gel phantom. In addition, using thermal distribution, potential tissue damage was assessed.

Smart Memory Alloys have brought a range of new capabilities to existing and novel designs due to their unique properties and ability to induce stress and strain in the material due to thermomechanical loading. Shape memory alloy-based smart material has widely been used and studied for biomedical applications. This includes smart needle for percutaneous procedures, self-expanding Nitinol grafts, stents, and other permanent internal devices. The smart needle is a needle in which deflection/path of the insertion in tissues can be controlled by incorporating Nitinol wire actuators on the body of the needle. However, smart needle designs proposed in the past lack both flexibility for multidirectional angles, and they do not allow for multiple martensitic phase transformations and are thus not repeatable. Each time the Nitinol wire is actuated, the wire would have to be manually reset to its initial length. Active materials like Nitinol require a bias force or mechanism that reverts the activated form of the needle back to its original martensitic form, which in the case of active needles is a straight wire. The lack of a recovery mechanism means that subsequent austenite transformations for deflection in opposing or similar trajectories cannot be performed as the system will not fully reset itself once cooled. In our proposed design, four Nitinol wires are embedded into a needle and act independently of one another to provide multi directional needle deformations. By providing tension onto a flexible 3D printed needle shaft, they can pivot a hard needle tip into any given direction. Once the needle’s deformation is complete, the material’s natural rigidity coupled with other Nitinol wires pulling resistance will restore the initial length of the actuated wire as it cools. This allows the needle to undergo a martensitic transformation and then subsequent cooling followed by additional phase transformation in a different direction. This makes the needle’s mechanism repeatable and functional for multiple insertions.

Although needle-based surgeries are considered as minimally invasive surgeries, the damage caused by the needle insertion in soft tissues, namely brain needs to be reduced. Any minor damage, swelling or bleeding in the brain tissue can lead to a long-lasting traumatic brain injury. Our approach to this challenge is to search for a proper solution in nature such as honeybees. In our previous studies, some new bioinspired needles (passive/active) mimicking honeybee stingers have been proposed and tested by conducting needle insertion tests in tissue gel phantoms. The main feature of the bioinspired needles is specially-design barbs on the needle structures. It was discovered that the insertion forces of the bioinspired needles are decreased by as much as 35%, which means that there is a decrease in tissue gel phantom damages. It was also observed that the needle path deflection in the tissue was greatly affected by the reduction in needle bending stiffness and the insertion force. The reduction in the bending stiffness would require lower forces of Nitinol actuators to navigate our smart/active needle inside the tissues. This work specifically aims to investigate the mechanics of the bioinspired needles in bovine brain tissues. The needle insertion tests in real tissues are designed and performed. The insertion mechanics of the bioinspired needles in bovine brain is studied and presented.