Nitinol living hinges

Background: Nitinol has numerous properties that recommend it as a material for biomedical applications, including its superelasticity, biocompatibility, kink resistance, torquability, and fatigue resistance in strain-controlled environments. By exploiting these properties, passive devices such as stents, catheter tubes, guide wires, and stone baskets enable less invasive interventions and better surgical outcomes than would be possible with more rigid stainless steel tools. Incorporating nitinol in active robotic devices is an ongoing research interest, marked by the development of a variety of robotic systems and mechanisms that leverage nitinol’s unique properties to facilitate minimally invasive surgical interventions. Core to these efforts have been the development of new fabrication and processing techniques for machining the material while retaining its superelastic structure.

Project: In this project, I developed a hybrid manufacturing process that combines abrasive jet and laser micromachining to enable the creation of living hinges in nitinol that retain the superelastic properties of the bulk material. The former selectively etches through the thickness of a workpiece and the latter defines the part’s final geometry. Because the majority of the material removal is done with the room-temperature mechanical etching procedure, thermal damage to the part is minimized. Processing parameters to achieve desired geometries are described, a bending stiffness model for the living hinges is provided, and validation experiments are presented. Lastly, to demonstrate the usefulness of these components to millimeter-sized robotic systems and medical devices, I show their integration in two prototype devices: an endoscopic camera wrist and a simple laser beam steering system.

Overview video: This video shows detail of the fabrication process, stiffness testing, and the prototype devices: