ADVANCED MATERIALS & PROCESSES | MARCH 2026 39 FEATURE Adona’s first-in-human trial successfully demonstrated atraumatic in vivo actuation of their shunt even months after implantation. Importantly, the Adona team envisioned methods whereby bidirectional actuation could be achieved remotely using ex vivo induction heating coils. By nesting two actuators preset to either a small or large size, and by tuning them to respond to different radio frequencies (RF) for heat induction, each of the actuators operate independently to drive the shunt diameter to any desired size by applying the RF signal external to the patient’s chest (Fig. 4). It remains unknown if any of the previously mentioned investigational devices will achieve regulatory approval and commercial success. Regardless, they serve to inspire the next generation of medical-device designers to explore shape memory for innovative Nitinol implants. Early concepts such as removal of implants days/ months/years after implantation by shape memory shrinking them back to catheter size or articulated robotic arms for remote surgery that have since been abandoned in favor of mechanical pull-wire mechanisms may now be worth revisiting in the modern era[7,8]. Arguably, the most impactful opportunity for shape memory innovation is in the field of pediatric devices where the patient’s size (and hence target therapeutic size of the implant) changes substantially throughout their lifetime. Are these size modifications achievable through unique shape memory actuator designs that eliminate traumatic surgeries currently performed to remove obsolete devices and replace them with upsized implants as the child matures to adulthood? CHALLENGES AND OPPORTUNITIES Several challenges (i.e., opportunities for innovation) lie ahead for designers wishing to use shape memory for implantable devices: • Can binary Nitinol, with its established biocompatibility and regulatory pathway, provide the necessary actuation movements and/or forces using times and temperatures below which would traumatize human tissue? • If ternary or quaternary alloys are pursued to overcome temperature limitations (e.g., NiTiCu with its very narrow temperature hysteresis) what are the biocompatibility and consequent regulatory challenges for those alloys that haven’t historically been proven in vivo? • Manufacturing techniques must be developed to selectively tailor regions of a device to be shape memory while retaining regions of superelasticity elsewhere in the same implant such as that developed by the V-Wave Medical team. • What methods of heat delivery (e.g., warm saline, induction heating, joule heating) will be available to safely deliver the power required to trigger in-vivo actuation? Self-expandable superelastic devices have evolved from the humble beginnings of simple wireform stents into the complex laser-cut metal/polymer/tissue composite heart valves that are commonplace today. Having been involved in the emerging field of shape memory implants and given the recent advancements in bioelectronics as well as power supply miniaturization, this author is optimistic that the industry is at a similar entry point of exponential growth for in vivo actuatable shape memory devices that are beyond current imagination. ~SMST Note: The V-Wave Magical and the V-Wave Ventura are registered trademarks of Johnson & Johnson. For more information: Scott Robertson, vice president, Resonetics, 26 Whipple St., Nashua, NH 03060; scottrobertson@resonetics. com; www.resonetics.com. References 1. A.R. Moritz and F.C. Henriques, Jr., The Relative Importance of Time and Surface Fig. 4 — Adona Medical’s nested actuator design enables bidirectional actuation within a single device. Two shape memory implants with a preset cylindrical shape and conical shape are thermally isolated from one another, nested, and joined such that they achieve a stable neutral position between a cylindrical and conical shape. When the outer ring (the cylindrical shape) is heated (e.g., by joule heating through an electrical circuit) the composite structure widens to its dilated position, and vice versa when the inner ring (the conical shape) is heated. Adapted from Alexander et al.[6]
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