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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
Research engineers at Saarland University and medical researchers at the Saarland University Medical Center are developing smart implants that can both monitor and promote healing in fractured bones. When installed at the fracture site, these implants, which are constructed using shape memory alloys, can stiffen or relax in a continuously controlled manner that optimizes bone healing. As part of an EU-funded project, the researchers are miniaturizing the technology for use in thin intramedullary nails (IMNs), which provide internal support and stability during the healing process. The team will be demonstrating this medical technology at Hannover Messe from 31 March to 4 April.
If you break one of your body’s long bones, such as your shin bone (tibia), chances are that the surgeon will use a stabilizing rod, known as an intramedullary nail, to support the bone as it heals. The long ‘nail’ or rod is carefully inserted into the bone via the marrow-filled central medullary cavity, stabilizing the bone and enabling it to heal. Compared to the placement of an orthopaedic plate, which is attached to the bone from the outside, the process of inserting an INM is generally less invasive as the fracture site does not need to be opened up in an operation. Typically, all that is required is a small incision at the end of the affected bone. ‘The tissue and blood circulation around the fracture site are not compromised, which is beneficial for healing. Our patients can immediately put their weight on the leg after surgery, which facilitates mobility and leads to fewer post-operative complications,’ explains fracture healing expert Bergita Ganse, Professor of Innovative Implant Development at Saarland University.
Together with a team of engineers led by Professors Paul Motzki and Stefan Seelecke at the Center for Mechatronics and Automation Technology (ZeMA), trauma surgeon Ganse is working on imparting new properties to these intramedullary nails. By permanently transmitting measurement data from the fracture gap, this new type of IMN enables medical practitioners to monitor from the outset whether the bone is healing properly. Up until now, physicians could only ever get the occasional snapshot from x-ray images of the fracture site. Another feature of this new technology is the ability of the INM to stiffen or relax at the fracture site. If the patient wants to walk, they have the full stability provided by the stiff intramedullary nail; if they are resting, however, they can cause it to soften via an app on their phone. ‘Our goal is to create an intramedullary nail that actively promotes healing. We are developing an INM that will stimulate the growth of new bone tissue by micro-massaging the fracture gap,’ says Bergita Ganse.
This is something that the research team has already managed to achieve with orthopaedic fixation plates. The plates are able to measure the forces acting at the fracture gap and can flex independently of one another, thereby optimizing the applied load and improving the healing process. The team have been developing these smart implants for more than five years as part of an €8 million project funded by the Werner Siemens Foundation.
The researchers are now miniaturizing the technology so that it can also be used in intramedullary nails. ‘The results and the experience we gained from the fixation plates are now being incorporated into the new implants,’ explains Paul Motzki, Professor of Smart Material Systems for Innovative Production at Saarland University and Managing Director at ZeMA. The current project is being funded by the EU under the Horizon Europe programme as part of the €21 million research project SmILE (Smart Implants for Life Enrichment), in which 25 partner institutions from twelve European countries are conducting research into how older people can be protected from musculoskeletal disorders.
The engineering team led by Paul Motzki and Stefan Seelecke had to come up with a number of innovative ideas to fit the technology inside the intramedullary nail, which is only a few millimetres wide. Paul Motzki explains one of the challenges: ‘We have to ensure that the mechanism that causes the implant to stiffen precisely at the site of the break does not result in any thickening at that point, as this could seriously damage the already fragile fracture site.’ The solution to this problem resulted in the development of a patented movement mechanism. Two miniature actuators working in opposite directions are configured so that one of them pulls a rod with a conical head into the opening of a soft, elastically compliant sleeve. Once in position, the cone-shaped head is held securely in position and is later withdrawn from the sleeve by the second actuator. When the conical head is inserted into the interior of the elastomeric sleeve, the IMN stiffens at this point but does not expand in size. When the rod is later retracted from the sleeve, the IMN becomes softer again.
The actuators in this case are bundles of ultrathin wires made from the shape memory alloy nickel-titanium. ‘We use these wire bundles as drives that are able to deliver a directed force within a restricted space, which in this case allows us to manipulate the rod within the intramedullary cavity. These actuators are able to exert remarkably large forces for their size. In fact, nickel-titanium wire has the highest energy density of all known drive mechanisms,’ explains Professor Motzki. The wire can be made to contract by applying short pulses of electric current; switching off the current causes the wire to return to its original length.
The reason for this behaviour lies in the crystal structure of the alloy. ‘Nickel-titanium has two crystal lattice structures that can transform into each other,’ explains Paul Motzki. One of the lattices is shorter than the other. If electric current flows through the wire, the material heats up, causing it to adopt the crystal structure with the shorter lattice and thus shortening the wire. When the current is switched off, the wire cools down, the material switches to the other lattice structure and the wire returns to its original length. The researchers use bundles of these ultrathin wires as artificial muscles that they use to control small mechanical components. ‘The advantage of using bundles of ultrathin wires is that a bundle has a large total surface area and can therefore dissipate heat more rapidly, allowing us to contract the wires at high frequency,’ says Paul Motzki. After years of researching shape memory alloys, the Saarbrücken team knows how to customize these wire bundles for different technical applications by carefully configuring them in terms of wire thickness and the number of wires used.
The sensor technology needed to control the motion of the rod as it is drawn into or retracted from the intramedullary cavity is supplied by the actuators themselves. ‘When the wires change shape, so too does their electrical resistance. We can assign precise resistance values to even the smallest of deformations, and we use this data to train a neural network. The resulting AI is now so good that it can generate positional information efficiently and accurately even in the face of disruptive influences,’ says Motzki. ‘Our approach allows us to extract all the sensory data needed to control the motion of the wire bundle,’ explains Susanne-Marie Kirsch, a doctoral research student in the Saarbrücken group. And because this technology is self-sensing, the researchers have a means of monitoring the fracture healing process. Even the smallest change in the fracture gap produces a change in the resistance of the wires, which enables medical staff to see whether new bone tissue is growing at the fracture site.
The clinical aspects of the research project are managed by a research team led by Bergita Ganse. Her team is specialized in extracting biomechanical information from the measurement data. They conduct gait analyses, perform computer simulations and use artificial intelligence systems to gain the necessary medical insights. By monitoring the increasing stiffness at the fracture site and using blood flow measurements, the medical team can assess healing progress. They are also interested in understanding what factors promote bone healing. The goal is to get the actuators used in the IMNs to perform precisely coordinated movements that promote bone tissue growth. ‘We have to construct the implant in such a way that it can perform the micro-movements and pressure changes needed to support healing,’ explains Professor Ganse.
‘The aim is to have everything controlled by an app on the patient’s phone so that, after having received medical instruction, they can adjust the mechanism themselves,’ says Paul Motzki. The electrical pulses that control the movement of the actuators will be supplied by a battery in the body that can be charged by wireless induction.
The Saarbrücken engineers want to miniaturize their technology even further so that it can be used in much smaller bones. ‘Our technology is scalable. The next goal is to develop smart implants for use in maxillofacial surgery, for example in the treatment of fractured jaws,’ explains Paul Motzki.
Paul Motzki and Stefan Seelecke’s team will be showcasing their technology and demonstrating prototypes of these smart medical implants at this year’s Hannover Messe, Hall 2, Saarland Stand B10.
Background
The research team led by Stefan Seelecke and Paul Motzki uses shape memory technology for a wide range of applications, from innovative cooling and heating systems to robot grippers, valves and pumps. At the Hannover Messe, the Saarbrücken-based experts for smart material systems will be demonstrating smart miniature drives, energy-efficient robot gripper systems and a novel, elastocaloric cooling and heating system. The technology is under continuous development by PhD students who are conducting research as part of their doctoral dissertation projects. The research work is funded through a number of large-scale research projects and the results have been communicated extensively in high-impact scientific journals, with numerous papers receiving international recognition.
To facilitate the transfer of their applications-driven research to commercial and industrial applications, the researchers established the company ‘mateligent GmbH’, which will also be exhibiting at the Saarland Innovation Stand at this year’s Hannover Messe, Hall 2, Saarland Stand B10.
ZeMA – Center for Mechatronics and Automation Technology in Saarbrücken is a research hub for collaborative projects involving researchers from Saarland University, Saarland University of Applied Sciences (htw saar) and industrial partners. ZeMA focuses on industrially relevant development work aimed at transferring ideas and technology from academic research to the industrial sector.
Prof. Dr.-Ing. Paul Motzki, Chair of Smart Material Systems for Innovative Production,
Tel.: +49 681 85787-13; Email: paul.motzki@uni-saarland.de
Prof. Dr. med. Bergita Ganse, Werner Siemens Foundation Endowed Professorship in Innovative Implant Development, Tel.: +49 6841 16-31570, Email: Bergita.Ganse@uks.eu
https://zema.de/projekt/smart-implants-2-0/
https://www.horizon-smile.eu/
https://www.uni-saarland.de/en/chair/ganse.html
https://www.wernersiemens-stiftung.ch/en/projects/smart-implants/
The shape memory tech developed for fixation plates (right) is now being adapted for use in intramed ...
Credit: Oliver Dietze
Saarland University
Paul Motzki, Professor of Smart Material Systems for Innovative Production at Saarland University an ...
Credit: Oliver Dietze
Saarland University
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