Magnetic shape memory actuators for energy-passive medical implants

• Applicant: Dr.-Ing. Holger Neubert
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics ; Production Automation and Assembly Technology
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 251112451

It is the aim of the project to develop magnetic field controlled actuators based on magnetic shape memory alloys for applications in energy-passive medical implants. Technology demonstrators of the actuators to be developed will be built, tested and investigated. Three work packages are defined.Initially, a generalization of the Tellinen hysteresis model will be used to model phenomenologically the three-dimensional hysteresis between strain, stress and flux density of magnetic shape memory actuator elements. The objective is to develop numerically robust and sufficiently precise one-dimensional models of magnetic shape memory elements for the simulation of dynamic system by multiphysics network models. The development of the models is focused on the typical operation modes of magnetic shape memory actuators and the Ni-Mn-Ga alloys which are currently available. Furthermore, model extensions will be studied which allow to consider future materials, other operational modes and additional influence parameters like temperature or cycle times as well. It is planned to implement the models into the Dymola and SimulationX environments using the Modelica language. In the second work package, the models are used to design and investigate field controlled actuators for medical implant applications. The operating principle is an arrangement where the magnetic shape memory elements are located inside of large air gaps. This allows to place the magnetic excitation sources outside of the body whereas the implant with the actuator is inside. Controlled by the outer magnetic field, the implants drive mechanical loads inside of the body without any energy sources inside of it. Field sources with coils and permanent magnets have to be designed which provide the required field strength. Achievable performance parameters (force, stress, mechanical power and power density, power loss) are to be evaluated and the designs to be optimized by applying the models developed in the first work package. The third work package intends to investigate the developed magnetic shape actuators in two demonstrators of different potential applications. The first demonstrator is a miniaturized, fully implantable actuator for a surgical distraction application, the second is an actuator for an implantable drug infusion pump which can be used for pain therapy. Energy-passive magnetic shape memory actuators have a simple structure with only a few elements which make them capable to be miniaturized, reliable and robust. In contrast, implanted electromagnetic or thermal actuators always need an energy storage element and a control electronics. Therefore, miniaturized field controlled magnetic shape memory actuators open an application field which is closed for other actuator principles, e.g. in foot and hand or dental, oral and maxillo-facial surgery. In co-operation with clinicians, it is planned to develop and investigate the application potential of these actuators.

• DFG Programme: Research Grants