Cyborgs and Hybrid Biomechatronic Devices: The Muscle-Powered Fish Robot of Robert G. Dennis (UMich) and Hugh Herr (MIT) -- Introduction The biomechatronic work of Robert Dennis and Hugh Herr - involving the development of hybrid devices containing both living tissue and synthetic components -Êadds a contemporary twist to the narrative of the cyborg. Their muscle-powered fish robot, for example, is a practical device that uses explanted frog leg muscle to actuate a swimming machine: a hybrid muscle-machine actin-myosin mobile robot. This paper will provide an overview of this work and articulate the objectives and background of this research. -- Contexts: Actin-Myosin Robotics Muscle is a robust, efficient, and lightweight material that is the exclusive actuator within the animal kingdom. Muscle activates creatures within a staggering range of scale: it powers both microscopic and gigantic organisms. Based on the requirements of the job at hand, muscle also adaptively responds and structurally modulates itself within the context of varying workloads. Furthermore, muscle is efficient and can generate a large isometric force compared to its weight: as described by the MIT Biomechatronics Group, "muscle can generate up to 4000kJ of work from just 1 Kg of glucose"[1]. For these reasons, muscle is seen as an ideal actuator. Within the field of building autonomous machines that match the power, flexibility and speed of organic biological systems, a muscle-type actuator is seen as a key material in attaining this goal. However, an effective artificial muscle has yet to be developed: nitinol actuators are fragile and inefficient, and polymer gels contract too slowly for practical applications. Biological muscle, however, exists: it can be cultured in vitro or can be taken whole from living organisms and can be used as a machine actuator. Beyond this, muscle can be tailored in vitro through genetic, chemical and electromechanical means to be robust and well-suited for robotic applications. With these concepts in mind, Robert Dennis and Hugh Herr are leading a Biomechatronics Group at MIT to developing actin-myosin machines: muscle-driven robots that feed on glucose. -- Actin-Myosin Machine: The B1 Biomechatronic Fish Funded by DARPA[2], the Biomechatronics Group at MIT set out to build a "proof of concept" fish-style biorobot, titled "B1". Two versions of the robot were made: B1a and B1b. Technically, the robot was 120 mm long, and was actuated by a single pair of whole muscle explants from frog seitendinosus muscle. A PIC16C54A microprocessor was carried on board, along with a an infrared detector, electronics and lithium batteries. The device was feed-forward controlled: a unidirectional downlink controlled the device, and no feedback was taken from the muscles or robot. Muscles were interfaced with 40 AWG stainless steel multi-strand electrode wire, and were stimulated by +/- 6 Volts in bipolar pulses at 80Hz with a width of 100 microseconds. The fish robot was placed in a small tank of liquid - amphibian ringer's solution with 2g/L glucose and broad-spectrumanibiotic/antimycotic - and surface-swam using muscle power to propel forward and turn based on signals transmitted wirelessly to the robot from a nearby computer. The two versions of the robot, B1a and B1b, were durable for 7 hours of use at about 10% duty cycle. The maximum speed was 60 mm per sec, about half a body length per second. -- Research Aims: Biological (Synthetic) Prosthetics This research aims to illustrate that muscle-powered robots are feasible, and that muscle is a practical, controllable actuator. The long-term vision for this research sees its application within the field of prosthetics: to develop prosthetic limbs that are powered by muscle and biologically integrated into the subject's body. Cells from the prosthetic user would be used to build the device: a fundamentally biological - as opposed to synthetic - prosthetic. Toward this end, the Dennis lab is also pursuing research in tissue engineering, tendon-muscle interfaces, and implantable data loggers and stimulators. In vitro engineered muscle tissue is seen as a tool for hybrid prosthetics, robotics, basic research and surgical transplantation: with about 40% of an adult human body composed of skeletal muscle, the in vitro production of functionally controllable muscle from a few cells is proposed to have a significant impact on humankind and embodiment. -- Future Vision Dennis sees hybrid prosthetic devices as a technology that will not be developed and perfected within the near future: he overtly discredits media that sensationalizes the current state of hybrid biorobotics and functional tissue engineering research, and sees this work only at an early stage of development. However, Dennis clearly does see a future that is impacted by this technology on the same level of magnitude to the Industrial Revolution: "imagine the day when clattering, inefficient, synthetic electro-mechanical contrivances seem quaint and frivolous.Ê From the first time that a proto-human grasped the first stone tool and used it to shape the environment, the use of living tissues as tools has been set in our destiny." " The ultimate vision is to integrate muscle actuators into prosthetic limbs.Ê The prosthetic devices will evolve in complexity by inclusion of greater and greater biological content, until the entire device is biologic rather than synthetic.Ê The technology will be developed to utilize cells from the prosthetic user themselves, so that eventually the re-engineered limb will be entirely compatible with the person for whom it has been engineered.Ê Tissue interfaces will also be developed, to allow innervation, blood circulation, and mechanical connection with the muscle actuators." muscle-driven robots that feed on glucose. http://www-personal.umich.edu/~bobden/biomechatronic_devices.html [1] MIT Biomechatronics Group - Project Overview http://www.ai.mit.edu/people/hherr/Project%20overview.html [2] An Actin Myosin Machine, DARPA BAA #99-31 (Hugh Herr, PI, MIT; Robert Dennis, Co-I), Pilot study, $375,000 period: 12/01/00 - 11/30/01 Robert Dennis - UMich Homepage http://www-personal.umich.edu/~bobden/index.htm MIT Biomechatronics Group - Homepage http://www.ai.mit.edu/people/hherr/biomech.html B1b Biomechatronic Fish Robot Movies http://www-personal.umich.edu/~bobden/robot_b1b-a.avi http://www-personal.umich.edu/~bobden/bob_robot_6_slow.avi http://www-personal.umich.edu/~bobden/bob_robot_7.avi Hugh Herr - MIT Homepage http://www.ai.mit.edu/people/hherr/hherr.html Robert Dennis - Vision for the Future http://www-personal.umich.edu/~bobden/bob_vision.html DARPA Defense Sciences Office - Programs http://www.darpa.mil/dso/programs.htm