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.

A device that can provide articulation to surgical tool tips is needed in natural orifice transluminal endoscopy surgery (NOTES). In this paper, we propose a compliant articulation structure that uses superelastic NiTiNOL to achieve a large deflection angle and force in a compact size. Six geometric parameters are used to define this structure, and constraints based on the fabrication process are imposed. Using finite element analysis, a family of designs is evaluated in terms of the free deflection angle and blocked force. The same family of designs is evaluated for both NiTiNOL and stainless steel. It can be seen that significant benefits are observed when using NiTiNOL compared to 316 stainless steel; a maximum free deflection angle of 64.8° and maximum blocked force of 24.7 N are predicted. The designs are refined to avoid stress concentrations, and design guidelines are recommended. The meso-scale articulation structure is fabricated using both a Coherent Avia Q-switched, 355 nm laser and a Myachi Unitek 200 W single mode pulsed fiber laser with active water cooling. Select fabricated structures are then tested to validate the finite element models.

Despite great strides in materials science and control, an automated surgical tool is still in the fiction pages due to the lack of a surgical tool employing a self-sensing actuator. In an attempt to fill this void, we present magnetoelectric materials as a solution for designing surgical tools. This paper discusses our ongoing work to model the dynamics of the magnetoelectric material for use in a control loop. The surgical tool is a two-segment magnetoelectric cantilever in which one of the two magnetoelectric segments is attached to a fixed support called the base. A floating segment called the cutting tip is attached to the base using a flexible hinge. The two-segment tool is placed in a remote magnetic field to generate the cutting force in the magnetoelectric tip. Displacement in the tip generates a proportional electrical response from the piezoelectric layer and serves as the self-sensing signal. The self-sensing signal from the two segments is used for operating the tool in closed loop operation. The dynamic characterization of the magnetoelectric cantilever in bending is derived from constitutive equations for the magnetoelectric material. The strain terms in the constitutive equation is expressed using generalized coordinates in the shape function for the cantilever in bending mode. The equivalent stiffness of the magnetoelectric cantilever is derived using variational principles for calculating the tip displacement in the cantilever.