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MINIR: Minimally Invasive Neurosurgical Intracranial Robot

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Main Participants

J. P. Desai, S. K. Gupta, R. Gullapalli, M. Simard, M. Ho, and A. Ananthanarayanan


This work is supported by the National Institutes of Health (NIH).


Shape memory alloy actuator, Neurosurgery, Meso-scale robot, MRI-compatible robotics


oneBrain tumors are among the most feared complications of cancer and they occur in 20-40% of adult cancer patients. Despite numerous advances in treatment, the prognosis for these patients is poor with a median survival of 4-8 months. The primary reasons for poor survival rate are the lack of good continuous imaging modality for intraoperative intracranial procedures and the inability to remove the complete tumor tissue due to its placement in the brain and the corresponding space constraints to reach it. To overcome the above limitations, we envision developing a Minimally Invasive Neurosurgical Intracranial Robot (MINIR), which would be operated in an intraoperative MRI environment. We envision MINIR to be under the direct control of a human operator, with targeting information obtained exclusively from frequently updated MRI. MINIR will be fully MRI compatible, so that the physician can use frequently updated MRI to accurately perform tumor resection.


The objectives of this project are:

1) Development of suitable actuation strategy for operation within the MRI: The goal of this aspect of the project is to develop an MRI compatible actuation strategy that will enable the physician to operate the robot within the MRI while performing the procedure.

2) Development of a compact meso-scale robot for tumor removal: The goal of this aspect of the project is to develop a meso-scale robot (less than 12 mm in diameter and about 10 cm long) that can be introduced by the physician into the brain through a predetermined surgical corridor. The workspace of the robot should be such that it is able to electrocauterize the tumor roughly 5 cm in diameter.

3) Development of a scalable manufacturing process for prototyping the robot: The goal of this aspect of the project is to develop a cost-effective manufacturing process for fabricating the meso-scale robot. The manufacturing process that is used should enable processing of materials which are 1) MRI compatible to allow for continuous control during the surgery and 2) Bio-compatible to ensure that it does not cause any damage to brain tissue cells during surgery. The manufacturing process should be scalable to enable the disposability of the robot after each surgical operation.

Overview of Approach

twoMRI-Compatible actuator: Actuators such as electromagnetic motors are not feasible for use in MRI in this application since they are fabricated from ferromagnetic materials and permanent magnet parts. Several other actuation methods such as electroactive polymers, electrostatic actuators, piezoelectrics, electrorheological fluids, Lorentz force actuators, cable/rod transmission, pneumatics, and hydraulics are also eliminated due either special requirements in the MRI environment or the space limitation in the robot. Shape memory alloy (SMA) has been proven to be MRI compatible and due to its unique microstructure and molecular characteristics, it possesses many unique properties. If SMA encounters any external load during phase transformation, it can generate extremely large forces. This phenomenon thus provides a unique mechanism for actuation. In neurosurgical application, since electrocauterization of the tumor (through the electrocautery probes located on the robot end-effector) will enable removal of tissue, it may not be necessary for the robot to exert a large force to move the tissue. However, it is advantageous to be able to generate the required force at the end-effector through SMA actuation of the distal links to move the tumor, if necessary, during electrocautery.

Highly dexterous meso-scale robot: Like any human current neurosurgeon, MINIR will be operated under frequently-updated MRI and resect tumor by positioning an instrument that liquefies tissue and washes out the debris. Consequently, the goal of this part is to develop a prototype of MINIR with demonstrated degrees of freedom, MRI compatible actuation technology, and MRI compatible robot body. In current design of MINIR, we put all joints on the outside surface of the robot and kept it hollow in the center. Thus, all the wiring and tubes will be kept inside the robot body. This design makes the robot more compact, safer and easier to shield. We used two antagonistic SMA wires as actuators for each joint, so that each joint can be moved back and forth and operated independently. This design greatly increases the motion range and controllability of the robot.

Robot Fabrication: MINIR is a multiple degree of freedom structure which is made of articulating joint assemblies. The current design of MINIR is made of 9 revolute joints which allow for significant out of plane motion of the robot. We prototype the design illustrated above using injection molding. We use a process known as in-mold assembly using insert molding to manufacture MINIR. This process involves the use of cylindrical metallic parts made of Brass as mold inserts.

The metallic inserts serve as shut off surfaces between the mold cavities which form the different parts of the revolute joint. This shut off surface ensures that the molten plastic that is injected into the mold cavities don’t fuse the two cavities together during the filling phase. Subsequently after cooling, the in-mold assembled revolute joint is ejected from the mold cavity. Using this approach we have developed a mold design which can be used to fabricate the 9 degree of freedom MINIR.

fourRelevant publications

Mingyen Ho and Jaydev P. Desai, “Characterization of SMA actuator for application in robotic neurosurgery,” in Int. Conf. of the IEEE Engineering in Medicine and Biology, 2009, pp. 6856–6859.

Nicholas Pappafotis, Wojciech Bejgerowski, Rao Gullapalli, Marc Simard, Satyandra K. Gupta, and Jaydev P. Desai, “Towards design and fabrication of a miniature MRI-compatible robot for applications in neurosurgery,” in Int. Design Eng. Technical Conf. & Computers and Information in Eng. Conf., 2008.


Prof. Jaydev P. Desai
Director—Robotics, Automation, and Medical Systems Laboratory
Department of Mechanical Engineering
0160 Glenn L. Martin Hall
University of Maryland College Park, MD-20742
Phone: 301-405-4427
Email: jaydev (at)
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