Surgical Microbots

Introduction

A study by Watson B, et al (2010), conducted at Monash University, Australia, developed a micro-motor using piezoelectric material to create a drive system for in vivo surgery. It is hoped that complex surgical procedures used to treat cerebral complications, such as seen with a stroke, will be more effective by using a small swimming robot (a micro-robot), that can get to small vascular components that are near-to-impossible with standard operating tools (see video below). The motivation behind engineering such state-of-the-art robotic technology comes from complicated invasive procedures such as neurosurgical and cardiovascular surgery (also termed minimal access surgery) where the likelihood of error and strain is increased and could result in prolonged pain, delayed recovery time, or in extreme cases death or serious injury to the patient.

The idea of developing microbots with the functional capacity of conducting intricate in vivo surgery is set to revolutionize medicine if put into practice on a larger scale. Piezoelectric motors have been tested as micro-motor robots, though research into ultrasonic resonant motors has yet to be tweaked to meet performance requirements. The basic architecture to a piezoelectric resonance motor involves a resonant stator mode that generates circular motions at a tip of a stator. The stator is made of piezoelectric material that banks an array of electrodes to generate an electrical impulse. A basic prototype introduced by Watson et al (2010) is made of helical grooves and a magnet that works to balance the axial, torsional, and electro-magnetic resonance.

The basic structure can be broken down into five distinct parts: a power supply, a piezoelectric element, a stator, a rotor, and the flagellum. The stator axial moves back and forth and the stator torsional force vibration mode moves in a spiral fashion. Both the stator and torsional vibration mode work as one unit and forces a stator-tip motion to occur. The spiral-circular motion of the stator tip forces the rotor to move the flagellum (see detailed animation below). The micro-robots, if designed to carry micro-needles, micro-pumps, and force could then help perform intricate surgical tasks that would otherwise pose a rise to surrounding tissue if using larger surgical tools.

Working Example

A group of researchers at the Institute of Robotics and Intelligent Systems part of the Swiss Federal Institute of Technology-Zürich (ETHZ) are currently developing micro-robots for invasive eye surgery. The micro-robots are being designed to move magnetically through vitreous humour of the eye. The use of an external magnetic controller is known to manoeuvre the micro-robots and guide them to a specific target point. This is an exciting approach for modern-day medical technology and could also pave the way for drug delivery systems. The following video is News release that demonstrates how micro-robots have been applied in eye surgery.

The micro-robotic device is controlled by an external magnetic field. Though an exciting technique, a great deal of precision is required to control the movement and to guide the micro-robot to the target site – a rather complex challenge for future development of this technique. However, if perfected, this novel technique could see medical procedures such as drug delivery to the eye and the re-construction of retinal tissue achieved with increased level of precision and accuracy. Conditions such as macular degeneration will favor in this instance because treatment of this disease requires delivery of drugs to a retinal vein which is quite specific and carries high risks.

Advantages

One of the main advantages to the application of micro-robots in surgery is the reduction in the possibility of injury following an invasive surgical procedure. There is also the advantage of greater accuracy achieved, particularly as the micro-robot is controlled externally. Use of micro-robots that involve needle insertion also helps reduce workspace limitations though this is controlled by a macro robot device positioned at a particular location in the operating space.

Disadvantages

One of the biggest questions regarding surgical micro-robotics is power supply. It is fundamental that a power supply is sufficient enough to control performance of micro-robots during an operation period. A lack of energy supply during an operation will be a dangerous risk to the patient. There also needs to be further research on geometric limitations to micro-robots and focus on how sensitive human tissue actually is to a robot system when considering exposure to radiation. Battery capacity also needs to be taken into consideration when understanding operational period and the ability of a battery to deliver a particular electrical current at a precise voltage.

Future Direction

• Possible human limitations that could restrict use of micro-robotics in surgery.
• Ways to improve the safety of micro-robot application in surgical procedures.
• How will use of micro-robotics impact healthcare costs and patient recovery.
• The application of micro-robots to achieve effective drug delivery.

Research

• Siciliano, B., Khatib, O. (2008). Springer Handbook of Robotics. Germany, Berlin: Springer Science and Business Media.
• Gulrez, T., Hassanien, A.E. (2012). Advances in Robotics and Virtual Reality. Germany, Berlin: Springer Science and Business Media.
• Rosen, J., Hannaford, B., Satava, R.M. (2011). Surgical Robotics: Systems Applications and Visions. UK, London: Springer Science and Business Media, LLC.
• Watson, B., Friend, J., Yeo, L. Modelling and testing of a piezolelectric ultrasonic micro-motor suitable for in vivo micro-robotic applications. Journal of Micromechanics and Microengineering. 2010. 20: 115018.
• Edd, J., Payen, S., Rubinsky, B., et al. Biomimetic Propulsion for a Swimming Surgical Micro-Robot. Published in IEEE/RSJ Intelligent Robotics and Systems Conference, Las Vegas, USA, October, 2003.