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Mechanical Engineering
SMASH Lab
Smart Materials and Shock Lab

Shape Memory Alloy / Focused Ultrasound

Using focused ultrasound and the shape memory effect to make the expansion of stents more controllable.

It's been demonstrated that focused ultrasound can generate sufficient localized energy to trigger the shape memory effect in Nitinol under simple ex vivo conditions, causing a deformed wire to return to its original shape. We are conducting research with the aim to extend those findings to demonstrate the feasibility of expanding a Nitinol stent in deep tissue using focused ultrasound under near physiological conditions.

Shape memory alloys

Shape memory alloys (SMAs) exhibit a remarkable ability to revert to their original configuration following plastic deformation. This distinctive behavior, known as the shape memory effect (SME), manifests in two primary forms: thermal SME, often termed pseudoplasticity, and mechanical SME, also called pseudoelasticity. The former effect is often harnessed for generating force or displacement, while the latter finds suitability in applications demanding significant strain. Generally, the SME arises from a crystallographic, diffusionless phase transition between austenite and martensite. When exposed to sufficient thermal energy from external sources, such as electric currents, thermal conduction from the surroundings, or focused ultrasound as examined in our investigation, a physical transformation from martensite to austenite is initiated. Upon reaching the austenite finish temperature, the transformation concludes, resulting in a fully austenitic microstructure. This alteration in microstructure prompts the SMA to revert to its pre-defined shape, established through thermomechanical conditioning in previous procedures. Upon cooling, the microstructure reverts to martensite, however, its shape remains unchanged. Nitinol, owing to its remarkable shape memory effect, finds diverse applications across biomedical, automotive, aerospace, and robotics domains. While Nitinol has been successfully employed in self- expanding stents within the human body, its actuation within the body remains challenging, primarily due to the difficulty in heating SMA materials without causing damage to surrounding tissue.

Ultrasound

Ultrasound traditionally serves as a diagnostic tool for visualizing soft tissues deep within the body using high-frequency sound waves. By increasing the power several orders of magnitude and focusing the sound waves akin to a magnifying glass with light, ultrasound can induce localized tissue heating for therapeutic purposes. This non-invasive heating can affect areas as small as a grain of rice. Therapeutic focused ultrasound (FUS) has been used in a wide range of medical applications, including enhancing blood flow, facilitating local drug delivery using thermosensitive liposomes, ablating diseased tissues, augmenting the efficacy of radiation- and chemo-therapies, eliciting immunotherapeutic responses, ablating cancerous or other tumors, dissolving blood clots, and treating diseased nerves. The spectrum of FUS clinical applications spans all stages of research, development, and commercialization, underscoring its versatility and potential impact in healthcare settings.