Batch manufacturing technology based on micro-electro-discharge machining and application to cardiovascular stents.

摘要

The use of bulk metals in micro-electro-mechanical systems (MEMS) can significantly broaden the possible applications of this technology. The investigation proposed in this report focuses on the development of batch-compatible bulk-metal micromachining based on micro-electro-discharge machining (muEDM) and its application to cardiovascular stents. In particular, this work explores batch muEDM using electrode arrays to achieve high parallelism and throughput in the machining. Constraints in the fabrication and use of high-aspect-ratio LIGA-fabricated electrode arrays as well as the limits imposed by the pulse discharge circuits on machining rates are studied. To increase the spatial and temporal multiplicity of discharge pulses, arrays of electrodes with lithographically fabricated interconnect and block-wise independent pulse control RC circuits are used, resulting in >100x improvement in throughput compared to the use of single electrodes. A modified electrode-circuit scheme that exploits the parasitic capacitance of the interconnect offers similarly high machining rates of 1.3 mum/s as well as smooth surfaces with tighter tolerance of 5 mum and is more amenable to integration.; The batch mode muEDM concept is applied to the design and manufacturing of new cardiovascular stents. To form a tubular stent, a planar microstructure with overall dimensions of 7x2.6 mm2, which is cut from 50 mum thick stainless steel foil by muEDM, is plastically expanded to a cylindrical shape with diameter up to 3.5 mm by inflation of an angioplasty balloon. This planar approach potentially permits other planar microfabrication technologies based on lithographical processes to be exploited, offering opportunities to introduce additional functionality to the devices. The planar approach is extended to the development of stents serving as antennas (stentennas) for implementing the wireless monitoring of microsensors integrated with the stents. The stents are designed to form helical structures after the deployment. Wireless monitoring of a silicon-micromachined capacitive pressure sensor is successfully demonstrated by showing frequency shifts of the resonant impedance in a separate transmitting coil that is telemetrically coupled to the LC tank, i.e., a combination of the stentenna and the pressure sensor. With this capability, wireless flow sensing is explored by designing a dual-inductor stentenna integrated with two capacitive pressure sensors. A device with an emulated blockage shows flow response of 152--569 KHz per mL/min. The planar approach is also extended to the development of an intraluminal ring-shaped cuff for electromagnetic (EM) flow sensing in the presence of a magnetic field. Flow measurement with sensitivity of 50--70 ppm per cm/s is demonstrated using the EM cuff with flow of saline up to 180 cm/s and magnetic field of 0.25 T.