Micromechanisms for Laser Phonosurgery: A Review of Actuators and Compliants Parts

Phonosurgery has to do with a surgical procedure, performed with an aim to enhance the voice. Common anomalies of the vocal fold includes a wide variety of pathologies such as nodules, polyps, cysts, and cancer. The method most commonly used of phonosurgery is done using a laser beam. The laser beam source is located approximately fourty centimeters away from the vocal cords. With this long distance, a small accuracy error would strongly impact the quality of the intervention. Recent advances in the area of micromechanisms used in medicine have increased the potential for an early detection and a better treatment against vocal folds diseases Using microdevices, micromechanisms can be designed to guide the laser beam nearest to the vocal fold, for an accurate treatment and for minimizing the risk of detriment of the delicate vocal fold structures. Micromechanisms are designed in accordance with the constraints of the microworld and with the requirements of the task. These include the limited space, biocompatibility and severe accuracy (micrometric or submicrometric). To build micromechanisms, there are often tasks of microassembly and micromanipulation of the small components that compose them. However at the sizes of the components (micrometric), new phenomena, identified as scale effects, appear. They include the adhesion forces composed of Van Der Walls forces, the capillary force and the electrostatic force. In order to account all these scale effects, the constraints of the microworld and te required accuracy, smart materials combined with compliant structures are often used as principal components of micromechanisms. [1]. In this review, we describe and discuss the most used smart material used for actuation in micromechanisms: thermomechanical actuators (shape memory alloy, thermal dilatation of solids, thermal expansion of gas), magnetomechanical actuators (Magnetostriction, magnetic fluids, shape memory alloy magnetic), electromechanical actuators (piezoelectric, electroactive polymers, fluid electric, electrostatic), fluid mechanical actuators, and also those that use multiple principles at the same instant. Their advantages and drawbacks will be discussed with particular regard to biocompatibility. This review also present compliant parts that can be used in combination with the smart materials to make micromechanisms. Compliant mechanisms are commonly made of flexure hinges. This review gives a brief presentation of different flexure hinges for microscale applications. A flexure hinge is a thin member that provides a rotation between two adjacent rigid members. Flexure hinges can be made in a monolithic way making them very interesting for micromechanisms ; less expensive manufacturing methods for complex geometries can be achieved, little or no assembly required (so easy to manufacture), the monolithic nature eliminates the backlash and does of the hysteresis a variable predictable, practically no maintenance needed and it is availble for used in microscale. Also compliant parts for applications in two dimensions are axposed. Flexure parts in two dimentions are supposed to be compliant only around one axis called sensitive axis.