Myoplant – Implants for bionic hand prosthesis

The focus of the project “Myoplant” is developing a bionic (i.e. simulating the human model) hand prosthesis. The complexity of the the hand prosthesis movement increases with the demand on its operation and the information interface for the prosthesis regulation. Ideally prostheses should operate intuitively i.e. without major training for the wearer. The prosthesis in the project “Myoplant” will be based on a myogen-regulated intelligent implant i.e. via muscle signals. The Fraunhofer IBMT is developing biological-technological interfaces (including processes and technology) for manufacturing and evaluating microimplants. In addition, the communication with the implant and the telemetric energy supply are being developed.

The hand is the most important part of the human locomotor system. It has 22 degrees of freedom and is capable of reaching a grip strength of 500 N for a weight of only 400g and a volume of 50 cm³. The number of sensors is 17 000 including those for position, movement, strength, pressure, acceleration, temperature, and pain. Therefore, the loss of an extremity is always a dramatic incident for the person concerned. To compensate, aside from functional aspects, cosmetic ones have to be considered.

To participate in everyday life as inconspicuously as possible, it is particularly important for the prosthesis wearer that the artificial limb is modeled as realistically as possible. However, the functionality of the prosthesis is also essential for its acceptance. Aside from purely motor aspects (the restoration of different grips), increasingly high expectations are put on the sensors. For example, if wearers hold a hot cup of coffee in their hand, grip strength, surface character, weight, and temperature are important. This requires the integration of actuators and sensors in the prosthesis and also the generation of interfaces between biological and technical systems.

Initial situation

The status quo in myoelectric hand prosthesis is the sequential regulation of individual prosthesis movements. Upward and downward movements of the wrist, for example, can only be performed using the same signal after the hand is opened or closed. The change between the two motion modes occurs by co-contractions or a switch. The muscle activity for regulation is registered by surface electrodes. Sensory feedback is currently not available.

Project goals

The goal of this project is to develop a bionic hand prosthesis based on myogenically regulated intelligent implants to significantly improve the prosthesis’s functionality and its wearing comfort. On the one hand, this will be achieved by providing the artificial limbs with complex motion procedures and on the other hand by multifunctional intuitive regulation.

This system will register, process, and transmit signals that will steer the hand prosthesis. The implant will be supplied wirelessly with energy and the communication will occur via transcutaneous interfaces. The necessary key components provide the best possible functionality for the preparation of intelligent implants considering intermediate term solutions.

The complete system will consist of the following components:

  • Implantable flexible microelectrodes for invasive registration of myogenic activity
  • Signal preparation and signal processing
  • Telemetric modules for wireless signal transmission
  • Inductive energy transmission
  • Pattern recognition and classification of the signals
  • Signal processing and recognition of the desired hand movement
  • Prosthesis regulation
  • The actual hand prosthesis
  • Surface electrodes for sensory feedback

For the development and implementation of bionic hand prostheses, the project partners will take over the following tasks in Myoplant:

  • Otto Bock HealthCare GmbH
    Pattern recognition and signal processing, supply of arm prosthesis, adaptation of prosthesis to telemetric interface, integration of sensors in the prosthesis, energy supply of the prosthesis, system integration, system evaluation, sensory feedback.
  • Werner-Wicker-Clinic
    Medical evaluation of the subsystems and complete system, development of implantation methods, implantation in animal models.
  • German Primate Center
    Preparation, care, and analysis of experiments in animal models.
  • Technical University Hamburg-Harburg
    Development and programming of highly integrated implant electronics.
  • Fraunhofer-Institute for Biomedical Engineering
    Microsystem technical interface for the divertion of myogenic signals in animal models, capsling, implant telemetric interface, wireless implant energy supply, surface electrodes for skin stimulation.

 

Funding: 16SV3697
Funding period: 08/2008 – 06/2011


The myoplant complete system has been implemented over several weeks in an animal model. The complete transmission path has been evaluated. At the Primate Center, the microelectrodes were epimyisally implanted on a Rhesus monkey’s triceps, biceps, and deltaideus. The implant module was positioned in the shoulder region. Energy was supplied without an energy buffer with an outside inductive link.

The myogenic signals that were registered in 4 channels are processed by the implant electronics. They are transmitted via an interface to an extracorporal base station. There a channel separation and data analysis takes place. Following a signal classification, these processed data will generate highly selective commands for the bionic hand prosthesis.