Shape-Memory-Based Smart Materials for Endovascular and Cochlear Navigation

Smart materials offer opportunities for navigating arteries or other body passages to deliver biomedical devices for sensing, diagnosis, and treatment. Shape-memory alloys can be programmed to useful geometries such as a bend or a coil in a wire to steer through a desired vessel or cavity. In this work, heat activation of the programmed shape into the austenite phase of Nitinol is achieved by passing current through the wire to generate resistive heating. Two primary applications of smart shape-memory alloy wires will be presented: (1) endovascular navigation and (2) guided insertion of electrode arrays and their placement for cochlear implantation.<br/> <br/>At present, neurosurgeons and cardiothoracic surgeons utilize guidewires that typically are inserted in the groin and guided to the treatment site by feel, advancing or retracting by twisting or angling the wire manually. To facilitate navigation, shape-memory alloys, such as Nitinol, can be trained to bend at the tip or in a specific section of the wire in order to steer or select a branch of an artery. One of the challenges of this smart endovascular navigation is location of the guidewire, particularly as the diameters of the wire are reduced to reach narrow capillaries. While current practice is to use repeated x-ray fluoroscopy, we present results of successfully locating small-diameter wires (50–250 µm) using ultrasound and differential imaging techniques. Successful navigation and localization have been demonstrated in gelatin phantoms and a manikin forearm.<br/> <br/>We also present programming of shape-memory alloys into coil shapes, with the long-term goal of enhanced insertion depth of the electrode array and its placement in cochlear implantation. While the human cochlea has a snail shape that spirals 2.5 turns (900°) as the chamber elevates from base to apex, insertion of the electrodes for cochlear implants typically is limited to 1–1.5 turns (&lt;540°), as the physician will stop at the first sign of resistance in order to avoid injury or trauma. This shallower insertion results in a frequency mismatch between the clinically mapped frequencies on electrodes and corresponding cochlear frequencies, particularly affecting low-frequency processing and perception. An additional challenge can occur due to poor lateral placement of the electrode array relative to the cochlea’s ganglion cells as well as insertion depth, and these shape-memory alloys offer an opportunity to enable lateral control for better placement in addition to deeper insertion, which may result in enhanced spectral and temporal transmission to central auditory pathway. Results will be presented for training and relaxation of the programmed coil shapes as well as engineering the coils for sectional activation to achieve deeper insertion.