Research Area: Biomechatronic Devices Robert G. Dennis, Ph.D., Hugh Herr, Ph.D.

The Biomechatronics Group at MIT has recently been funded by DARPA to develop muscle-based actuators for robotic and prosthetic applications.  Our objective is to develop practical hybrid devices, containing both living tissue and synthetic components.  As a proof of concept, we have designed and built a muscle-powered fish robot (see movie link below).

Design specifications for Robot B1:
    Actuators: single pair of whole muscle explants from frog semitendinosus muscle.

    General Construction:
        Length Over All (LOA): 120 mm
        Rigid body length: 70 mm
        Fin Length: 50 mm
        Floatation: closed-cell styrofoam
        Frame: machined acetyl (Delrin) with nylon threaded fasteners
        Propulsion: cast silocone RTV elastomer, hinged, single degree-of-freedom

    Electronics (on board):
        Embedded microprocessor:  PIC16C54A (SSOP package), operated at 3 VDC and 40 kHz clock.
        Stimulation output buffer:  Logic Level HEXFETs, International Rectifier IRF7105;capacitive pulse discharge.
        Communication: Paired IR emitter/detector.
        Encapsulation: Electronic grade epoxee, 6 coats of Dow silicone elastomer #734 dispersed with toluene.

    Fuel sources: (electronic and metabolic)
        Muscles immersed in glucose bearing Ringer's solution
        Electronics powered by 2 lithium batteries, 45 mAh capacity, total system voltage = 6 Volts

    Tissue Interfaces:
        40 AWG stainless steel multi-strand electrode wire (TFE coated).
        5-0 braided silk suture to attach tendons to the robotic platform.

    Control Interface:  Infra-red unidirectional command downlink.
        User preset for autocycle or manual control of train duration and dwell.

    Stimulation Parameters:
        Fixed parameters:
            Amplitude: +/- 6 Volts, bipolar pulses.
            Frequency: 80 Hz.
            Pulse Width: 100 micro seconds.
        Remotely controlled parameters:
            Train Duration:  remotely controlled, 8-bit resolution, 0 ms to 2550 ms, in 10 ms increments.
            Dwell Time (between stimulus trains):  remotely controlled, 8-bit resolution, 0 ms to 2550 ms, in 10 ms increments.
            Actuator selection:  automatically alternated between muscles for each stimulus train input signal.

    Operating conditions:
        Temperature:  Room temperature, ~20 ^oC, not controlled.
        Fluid:  Amphibian Ringer's solution supplemented with 2 g/L glucose and broad-spectrum antibiotic/antimycotic.
        Test bath was aerated with non-filtered room air.

NOTE: (if the movie loads into a Netscape window)
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Click on the image to the left to see a video of our Biomechatronic fish (serial number B1b).

What did we learn from this robot?
    Using very simple control and interface design, muscles can act as a practical, controllable actuator.
    Electrical isolation of loop electrodes is adequate for multiple actuator operation in a conductive medium.
    Electrode stiffness and interface to the muscle tissue is a critical design issue.
    Muscle mechanical interface to the robotic frame is critical: tissue fiber alignment, adjustment to physiologic length...

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