Origami-Inspired Smart Implants for New-Age Neurology

Intracranial aneurysms are balloon-like disfigurations along the brain blood vessels. If not treated such aneurysms can rupture and cause brain hemorrhage. Many different implants are available in the market for intracranial aneurysm treatment. Though the available implants fabricated from wire braiding and laser cutting are successful, specific gaps must be filled to allow for low treatment complications. One such gap is that all the available implants have simple geometries and do not allow any personalization. Such individualization of implants is essential to provide safer treatments to patients with complex aneurysms. Second, all available implants have passive operation and currently, there are no “smart aneurysm implants” that could potentially monitor the treatment over time. Such a smart implant could detect if the intended blood flow reduction is not achieved after its placement and could potentially alert to early intervention. Smart implants require integrated antennas for data and energy transfer as well as sensors for the measurement of blood flow.<br/>Magnetoelectric (ME) antennas consisting of magnetostrictive and piezoelectric layers have shown that they can be scaled down by orders of magnitude in size compared to conventional electromagnetic antennas [1]. This is because the ME antennas operate at their acoustic resonance rather than at their electromagnetic resonance. Such compact miniaturized ME antennas on the implant surface provide an optimal way to transmit the data wirelessly for a smart implant operation. However, there are certain difficulties to integrating such antennas into conventional implants as their fabrication technology of wire braiding and laser cutting does not allow monolithic integration of ME composites. Second, the conventional implant design does not allow such sensitive components to survive the harsh crimping process, which is pre-requirement for a minimally invasive treatment.<br/>On the other hand, the origami-based design approach provides an attractive alternative for implant design. It consists of a 2D pattern with regions of rigid panels and flexible hinges. The folding pattern for origami can be generated from a flat 2D sheet and converted into a complex 3D shape on folding. Such structures have great potential as medical implants as they provide two major advantages (1) they allow the folding of large implants into a compact area to be loaded into a catheter and (2) certain regions in the origami pattern are almost stress-free during folding, making them ideal sites for loading sensitive elements such as sensors and antennas. The main challenge lies in fabricating these microscale devices without compromising the quality and performance.<br/>Recent developments in microsystem technology offer a method to fabricate freestanding nitinol (NiTi) shape memory thin films. The fabricated implants are flexible, biocompatible, and have high design freedom, e.g., allowing films with multiple thicknesses [2]. Thus, providing a solution for origami-based implant fabrication. The wafer-based approach allows the monolithic integration of functional layers for biosensing and smart implant functioning. Thus, allowing for the incorporation of ME antennas on the NiTi implant surface.<br/>The current work focuses on fabricating an ME antenna on top of a NiTi substrate using microsystem technologies, as a first step in realizing origami-based smart implants. In this work, we discuss the various challenges and possible solutions for integrating an ME antenna on top of a NiTi substrate. Furthermore, we consider the choice of magnetostrictive and piezoelectric materials that are essential for the required antenna operation at a frequency that is permissible for human use. We intend to demonstrate the potential of an origami-based design approach for fabricating brain implants.<br/><br/>[1] Nan, T. <i>et al.</i> <i>Nat. Commun.</i> 8, 1–7 (2017).<br/>[2] Velvaluri, P. <i>et al.</i> <i>Sci. Rep.</i> 11, 1–10 (2021).