As a company that develops medical products that typically comprise micro-electromechanical systems (MEMS), our greatest engineering challenge is rooted in the sheer physical size of our devices. For example, our flagship product is a robotically steerable interventional guidewire with a diameter of 0.014 in. (0.36mm)—the IntelliWire. Equivalent to just two strands of human hair thick, the core of this device houses an array of electrical and mechanical components, which collectively make up a proprietary multi degree-of-freedom motor and its supporting systems. Each of these components must be precisely manufactured and assembled to tolerances of much less than the size of a dust mite in order to ensure optimal operation and functionality. As a result, our most stringent constraints are derived from the capabilities of cutting-edge microtechnology production.
|The electrical and mechanical components in the IntelliWire guidewire must be manufactured to tolerances smaller than the size of a dust mite.|
Of late, we have observed a steady paradigm shift in microtechnology. In the early years, practical MEMS devices were largely confined to thin-film technologies, and were fabricated using silicon chip processing capabilities. Whilst this bottom-up approach is highly scalable, repeatable and cost-effective, many problems cannot be solved via thin-film technologies alone. In the case of actuators and motors, thin-film devices tend to produce high actuation speeds, but with low stresses and strains. In a practical sense, this translates into actuators that produce only minuscule forces, which are often orders of magnitude lower than required for the application at hand. With this, there is a clear and demonstrable need for top-down, bulk technologies to complement their thin-film counterparts. Here, the term top-down refers to more traditional forms of device manufacture (such as piecewise machining and assembly), and it is this need that is driving more companies to develop and manufacture top-down MEMS devices.
For a long time, there has been a wide gap between the manufacturing envelopes of bottom-up and top-down methods, but this is slowly changing too. Device designers now have the option of using complex parts as long as 1 mm that are grown via a bottom-up method. These parts can be produced with remarkable vertical and horizontal resolution, are highly repeatable and are cost-effective for large-scale production. However, there are still many devices that cannot be produced via even these advanced bottom-up methods, giving rise to a continued reliance on top-down manufacturing approaches. Striking the right balance between top-down and bottom-up production is typically the greatest challenge that micro-device designers face.
Geoff Rogers is one of the directors of IntelliMedical Technologies, an Australian startup company that specializes in the development of microscale medical devices. They are currently developing a steerable 0.014-in. guidewire based on proprietary technologies, as well as other devices for use interventional cardiology, neuroradiology, and other minimally invasive procedures.