Resonant magnetoelastic microstructures for wireless actuation of liquid flow on 3D surfaces and use in glaucoma drainage implants

Magnetoelastic resonators made from metal alloy foils are widely used for miniature wireless anti-theft tags and have also been explored for use in various sensing applications. Through annealing within three-dimensional (3D) molds, these foils can be formed into curved structures. Consequently, magnetoelastic materials present an opportunity for the development of a new class of wireless, actuators that have small form factors and low surface profiles and that can conform to curved surfaces. This paper describes passive, wireless, resonant magnetoelastic actuators intended for the generation of fluid flow on the surfaces of implantable Ahmed glaucoma drainage devices. The actuators are remotely excited to resonance using a magnetic field generated by external coils. The fluid flow is intended to limit cellular adhesion to the surface of the implant, as this adhesion can ultimately lead to implant encapsulation and failure. The actuators are micromachined from planar 29-mu m-thick foils of Metglas 2826MB (Fe40Ni38Mo4B18), an amorphous magnetoelastic alloy, using photochemical machining. Measuring 10.3 x 5.6 mm(2), the planar structures are annealed in 3D molds to conform to the surface of the drainage device, which has an aspherical curvature. Six actuator designs are described, with varying shapes and resonant mode shapes. The resonant frequencies for the different designs vary from 520 Hz to 4.7 kHz. Flow velocities of up to 266 mu m s(-1) are recorded at a wireless activation range of 25-30 mm, with peak actuator vibration amplitudes of 1.5 mu m. Integrated actuators such as those described here have the potential to greatly enhance the effectiveness of glaucoma drainage devices at lowering eye pressure and may also be useful in other areas of medicine.