#14: Why do implants rust?
A biologist, a mechanical engineer and an orthopedist meet - what at first sounds like the beginning of a joke among researchers is actually a very successful trio at our university! Because Prof. Thorsten Halle from the Faculty of Mechanical Engineering, the biologist Prof. Jessica Bertrand and the orthopedist Prof. Christoph Lohmann are jointly researching new materials for implants. In the new episode of the podcast "Know when you want", Lisa Baaske talks to Prof. Halle and Prof. Bertrand about how the collaboration came about, what the advantages are, but perhaps also problems, and why it is important to improve implants.
Prof. Dr.-Ing. Thorsten Halle is head of the Chair of Metallic Materials at the Institute of Materials and Joint Technology at the University of Magdeburg, and Prof. Dr. Jessica Bertrand heads the research laboratory at the Orthopedic University Hospital. Together with Prof. Dr. Christoph Lohmann, director of the Orthopaedic University Hospital, they want to form a working group to find out how endoprostheses act in the body, in particular the abrasion particles that are produced every day when these implants are placed in the human organism. The extraordinary research project is embedded in the doctoral program MEMoRIAL, a graduate school funded by the European Social Fund ESF. MEMoRIAL, which stands for "Medical Engineering and Engineering Materials". In this program, international doctoral students are supported in two research-intensive engineering scientific programs of the university: medical engineering and materials science. Starting in the winter semester, there will also be a new master's program, "Biomechanical Engineering," in which students can opt for the Endorprosthetics discipline.
Prof. Jessica Bertrand and Prof. Thorsten Halle research new materials for implants (Photo: Hannah Theile / Uni Magdeburg)
*the audio file is only available in German
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Intro voice: "Wissen, wann du wilst." The podcast about research at the University of Magdeburg.
Lisa Baaske: A biologist, a mechanical engineer and an orthopedist meet. What at first sounds like the start of a joke among researchers is actually a very successful threesome at our university. Professor Thorsten Halle from the Faculty of Mechanical Engineering, biologist Professor Jessica Bertrand and orthopedic surgeon Professor Christoph Lohmann are conducting joint research on new materials for implants. This is, admittedly, quite unusual, but perhaps that's why it's so successful. My name is Lisa Baaske, I work at the university's press office, and today's guest is one duo of the actual trio, namely Professor Halle and Professor Bertrand. We'll talk about how the collaboration came about, what the advantages are, but perhaps also the problems, and why it's important to improve implants. Welcome to both of you.
Prof. Thorsten Halle: Hello!
Prof. Jessica Bertrand: Hello!
Lisa Baaske: As I have already announced, you are collaborating in a working group that is actually not so common. You are working on implants. What exactly are you researching?
Prof. Jessica Bertrand: We mainly deal with endoprostheses, which, when inserted into the body, generate abrasion and then lead to inflammation. There are different materials. Ceramics are often used, but polyethylene is also used. Our focus is on the metallic components of these implants.
Prof. Thorsten Halle: So what we essentially want to do: We want to understand, what are the mechanisms behind this? Why is this abrasion harmful in the broadest sense? How can we avoid it? Or if we can't avoid it, how can we reduce it? We want to understand what exactly happens. I always say jokingly: we want to keep the electrodes. Mrs. Bertrand doesn't want them. That's our task, to see how we can moderate, adjust, understand these mechanisms and ultimately make the interaction between material and biological tissue the focus of our research.
Lisa Baaske: Okay, so the common denominator is, the electrons are not wanted, sort of?
Prof. Thorsten Halle: We want to keep them
Lisa Baaske: Right! (laughs)
Prof. Thorsten Halle: … and Mrs. Bertrand does not want to have them.
Lisa Baaske: But no common denominator. (laughs) But it's about electrodes. Okay. How did this unusual collaboration come about?
Prof. Jessica Bertrand: This was actually initiated by Professor Lohmann. During his operations, he repeatedly noticed that patients with metallic implants often had large osteolyses, i.e. bone loss, and wanted to investigate this in more detail. When I then came to Magdeburg from Münster, he commissioned me a little further to research this and then also initiated the cooperation with Professor Halle. Then we invited Dr. Döring from the IMF and hired him, who was able to work on this topic more closely with us from an engineering perspective. Moreover, he is a bit of an interface between us.
Prof. Thorsten Halle: Exactly, Dr. Döring from the IFQ, i.e. from production technology, is ultimately the interface and we continued the entire project in a graduate school funded by the European Structural Funds. MEMoRIAL was the name of the school, and there was an intersection that specifically trains doctoral students between engineering sciences and the medical sciences/biologists. One of the doctoral students, Ms. Herbster, who will soon be finishing her doctorate, was with us, and we are specifically continuing the topics we defined there in our trilateral cooperation.
Lisa Baaske: Yes, in fact, I wanted to come back to this Research Training Group later. But now that you mention it-- It's about conducting interdisciplinary research with each other: Medical technology and materials technology?
Prof. Thorsten Halle: Yes, medical technology or engineering in the broadest sense. That's how you could define it.
Lisa Baaske: Exactly. And what exactly are you doing in this research training group?
Prof. Thorsten Halle: In this research training group, we have more or less two large modules, submodules, where the engineers work together with the biologists and the physicians, especially in the field of imaging, i.e. CT, MRI. These are also the natural scientists, very, very strongly involved and also very successful. And a second pillar, which is aimed more at the material sciences, as a borderline discipline to the biologists, to the physicians, in order to research and understand interactions in or on the body and to adjust them in a targeted manner.
Lisa Baaske: Sounds very exciting and also very important, in any case. You've been researching implants for a very long time now. It's obviously something that occupies you a lot in your everyday life. What interests you personally about implants? I can imagine that you, as a materials scientist, and you, as a biologist, have a different view of it.
Prof. Jessica Bertrand: Generally speaking, it's like this... at some point everyone gets it, at some point everyone needs some kind of implant. So whether it's a dental implant, which is perhaps the smallest and most common, but also a knee or hip, many people get them at some point in their lives. And in our opinion, or in my opinion, it should be the case that everyone gets the implant that is best for them, that fits their body biologically, because some people have metal allergies, for example, we know this from ear studs or so. But it should also be as durable as possible, so that once the implant has been fitted, it can be kept for as long as possible and no revision is necessary. That's what we're concerned about, or at least that's what I'm concerned about.
Prof. Thorsten Halle: Exactly. So, that we want to try to improve the longevity, the resilience of such implants, from both sides of the scientific field. Prof. Bertrand is more concerned with biology and orthopedics, and we are more concerned with materials. And from my point of view, there is still a lot of wasted potential. This means that there is still room for microstructural optimization. You can optimize the compositions, you can optimize the process chain, you can adapt manufacturing mechanisms or manufacturing processes so that the longevity of the implants can really be significantly increased, from our point of view. And from my personal point of view, this is a previously untapped potential, and we are trying to leverage it.
Lisa Baaske: When you mentioned allergies, I actually have a nickel allergy. So maybe I should pay a little bit of attention to that if it's necessary at some point with me.
Prof. Jessica Bertrand: Opinions differ as to whether what really happens on the skin also takes place in the body. But nickel, that has been recognized as a general problem and has been largely taken out of the implant materials from the alloys.
Lisa Baaske: Okay, that sounds good, so I know what to expect later. Professor, you imagine that once you've survived the operation, you'll keep an artificial hip joint like that forever and that it will remain a part of you forever. In reality, however, prostheses have to be replaced. Why is that? And how long does a prosthesis usually last?
Prof. Jessica Bertrand: The fact is that an artificial joint only lasts 15 to 20 years in the best case. It also depends a bit on where it is implanted. So whether it's the shoulder, hip, knee, thumb, joint or ankle, it really doesn't last as long as the hip and knee. In addition, people who receive implants are getting younger and younger. There are different factors that contribute to that. And to make matters worse, people are getting older. This means that if you now assume that a patient receives their first knee implant at the age of 50 or perhaps even at 40. If you then add 15 years, there is still a little bit of life left, fortunately for the patient. For the implant, however, it is bad, because 15-20 years you are then at well, let's say 65/70 and then you have another 20 years. That means it has to be revised at least once. And you can imagine, with every revision a little bit of the bone is taken away and you need a bigger and bigger implant, so the possibility to revise is not infinite.
Lisa Baaske: I see, so the goal is to actually develop an implant that doesn't have to be replaced after 15 to 20 years, so that it doesn't have to be operated on again and again?
Prof. Jessica Bertrand: Exactly. It should be as durable as possible and the intensity of use also changes over time. So if you imagine that a 50-year-old gets such an implant inserted. He might still have the ambition to play soccer or go skiing. An acquaintance of mine has an artificial hip and wants to run a marathon with it. The question is whether that's the best approach. laughs Because it's a bit like driving a car: if you drive a lot, the tire wears out faster, and that's basically the same with implants. So you have to create a sensible use or simply adapt the materials to the usage requirements of the patients, and that's where our modified implant materials or improved implant materials would come into play again.
Lisa Baaske: In your research - which is kind of obvious when you're a materials expert like Professor Halle - you focus a lot on the materials used in endoprostheses, i.e., on the materials the implants are made of. Why?
Prof. Thorsten Halle: Ultimately, there are a wide variety of material classes that are also used for a wide variety of reasons. There are mechanical reasons, there are biocompatibility reasons and, as Ms. Bertrand has already said, there are essentially ceramics, plastics and, of course, metallic materials. Of course, the focus of our research cooperation is on metallic materials, which is simply due to my area of expertise. And in the case of metallic materials, titanium and titanium alloys are used very frequently, as you may have heard, and steels are used. A large area of research, especially in our group, is cobalt-chromium or cobalt-chromium alloys, which are used there. These are the most common materials used in the field of endoprostheses, apart from the dental field, where there are other materials. Why are they made of metals? Why is our focus on metallic materials? Ultimately, they need a certain strength. This means that such a joint has to survive a marathon, and not just one, but ideally many of them. It should therefore last as long as possible, and there are certainly forces acting on such an implant. So if you imagine: An artificial hip joint or a knee joint, that the patient steps out of place, stumbles or something similar, then we can assume, as we know from the movement sciences, that up to ten times the body weight acts on such an implant. And then there is definitely a risk that it will break or something similar. And that shouldn't happen, because that would be more than bad for the patient and you don't want to have increased abrasion. You don't want particles of the cement to come out and loosen the implant. So there is definitely a risk that it will be mechanically overloaded. And that's why metallic materials are often used, especially for such implants, and not plastics, which have advantages over metallic materials in one or another biocompatibility direction, but often cannot withstand the mechanical load.
Lisa Baaske: That all sounds very complex and you have to think of many things, obviously. In about 5% of patients, an implant has to be replaced after only ten years, i.e. if it doesn't work well, but they could have it for more than 20 years. One of the most common causes is corrosion, i.e. rusting. Why do implants rust in the body?
Prof. Thorsten Halle: Yes, ultimately, as you just said, this is a very complex mechanism, because corrosion is always a problem of the underlying system. That means that the whole thing also plays a very, very strong role here: Patients, individual properties and the like. Well, you all know that body fluids ultimately contain salts, i.e. chloride ions, and metals don't normally like that very much. Then there is also the fact that we have micro-movements, i.e. we have micro-movements between the ball and the shaft, if we imagine such a simple implant model, we have micro-movements that lead to corrosion occurring here. We have a hypoxic environment, which means that relatively little oxygen binds. This again changes the corrosion system. We have a poor formation of passivation properties. Let's stay in the area of steels. Then it is the case that these steels are corrosion-protected or corrosion-inhibiting in that they form a passive layer that is not visible to the human eye. However, this only works if there is sufficient oxygen. And I had just said, in hypoxic environments it is not there and that complicates the whole system. And corrosion is indeed one of the bigger problems that we have to try to solve in the long-term use of metals in the body.
Lisa Baaske: That sounds a bit scary when you think about it: Something is rusting in my body. What exactly is the effect on the body when an implant rusts inside it? Do you have an example, Prof. Bertrand?
Prof. Jessica Bertrand: So as we said at the very beginning, Professor Halle wants to keep the ions and I don't really want to have them. However, if such an ion becomes detached from this implant due to, in quotation marks, rusting, it naturally depends on the material. In the case of titanium-aluminum-vanadium alloys, titanium, aluminum and vanadium can be dissolved out. Titanium is not as well tolerated. You might know that from the deodorant sprays where titanium was taken out. Aluminum and vanadium is also not tolerated as well. Cobalt, on the other hand, from these cobalt-chromium steels is actually needed as a trace element for the body. There is cobalamin, which binds cobalt, which is why it is called cobalamin. Chromium, on the other hand, is not tolerated well at all. These heavy metal ions, in the end, lead to the fact that they, for example... Because of their hydrate shell, they fit through calcium channels, can block these and then lead to oxidative stress in the cells. So stress, I think, can be noted, nobody likes it. The cell doesn't like it either. But they can also block nerve pathways, thus having a neurotoxic effect and leading, for example, to a chef who has an implant that is corroding, no longer being able to taste. This is bad, of course, but if you remove this implant, this cook can then taste again. So some factors are reversible, others are not. So it comes to an enlargement of the heart, it comes to kidney damage in the long run. That's why you should avoid it. But some of these effects from heavy metal poisoning, from rusting implants are also reversible if you replace the implant.
Lisa Baaske: And how can you tell? So if I imagine I have an implant, I have some kind of a problem, and then how can the doctor tell that there are problems with my implant?
Prof. Jessica Bertrand: You can of course measure the heavy metal ions in the blood, in the serum, and you would then also see on the X-ray that the implant has loosened. So if it's really so severe that you have systemic effects, like neuronal disturbances, then you would also see that the implant is no longer fixed. But you would probably also have pain at the corresponding joint.
Lisa Baaske: So, the things that are supposed to help you make your life easier can sometimes make it harder. But that's what you're working on, so that this doesn't happen so often anymore. You are focusing primarily on combating corrosion. Not many working groups do that. Have you told us before, why not?
Prof. Jessica Bertrand: The corrosion of implants that actually hasn't been known to be a problem for that long. There was a phase where metal-on-metal implants were really implanted because they thought that was a good idea, to have hard metal rubbing on metal. That you would have less abrasion and patients would have fewer problems. Exactly the opposite was the effect that patients actually ended up with much more problems; massive wear, massive loosening, and these implants had to be replaced relatively early. This means that, on the one hand, this problem has not been known for very long and the competence does not exist at many locations. This means that here in Magdeburg we really have the unique opportunity to bring together the expertise that is already available from the materials sciences with the expertise of Professor Lohmann, who has really been dealing with endoprosthesis wear and aseptic loosening and so on for years, and with me, who can then really understand these biological effects. In other words, this is actually the ideal constellation to investigate this.
Lisa Baaske: In fact, interdisciplinary is the decisive keyword for you. As has already been mentioned very often, you come from very different disciplines that would probably otherwise have nothing to do with each other. But how can one imagine a collaboration when a mechanical engineer, a biologist and, yes, actually an orthopedist meet?
Prof. Jessica Bertrand: In fact, Professor Lohmann can observe different types of damage in his patients in the operating room. There are very different types of damage, for example septic loosening. This means that the implant has been attacked by bacteria, for example. And here we would look together with the physicians or also with the microbiologists, which bacteria are there. How can you dissolve them well with antibiotic therapy and what therapy options are there? Or are there antibacterial implant materials, for example? But there are also biomechanical problems. That is, either the implant was not installed optimally or the implant itself is damaged because of the load. These are again things that we look at with the materials scientists and also do simulations here, such as how shoulder implants are impacted into the patient. That can also be simulated, and that is something that we are investigating on an interdisciplinary basis. However, one of our biggest topics is of course corrosion, which we observe again and again in different joints. Not only on the hip, for example, but also on joints that are less stressed, such as the shoulder. And here we are also trying to solve the problems on the materials side by modifying the implant materials. But Professor Halle can certainly say more about that.
Prof. Thorsten Halle: Yes, the cooperation is strongly driven by the access to quite complex cases of damage that are found in Professor Lohmann's patients. And if we then suspect such a cause on the material side, for example, then we take a closer look at it, for example, we take plug connections between the cone and the ball head or those with the head of such an implant. Corrosion mechanisms occur very frequently there, and one of the reasons for this is that there is traditionally a very, very narrow gap. So that means you have oxygen depletion, you have these micromovements that I talked about earlier, and that's then the trigger for the corrosion. And our question, our goal is to somehow systematize the whole thing, to understand the underlying mechanics, in order to prevent such cases of damage by adapting the material, for example by adapting the geometric conditions. So we also do tests, experiments, we have in the experimental orthopedics, we have a so-called hip joint simulator. This is where our modified prostheses are ultimately tested. And all of this is done with the patient in mind, understanding the mechanisms, eliminating the causes, increasing the service life. So it works quite well. So we are really driven by real patient cases, in our group.
Lisa Baaske: Okay, to break it down: Professor Lohmann has surgery and has to remove an implant and sees: Okay, this was probably caused by corrosion. And then passes it on to you, so to speak. Do you then also receive the implant that was removed and take a look at it?
Prof. Thorsten Halle: Exactly, that's how it is. So, that means we really look at the implant to see, for example, how has the surface changed? Are there any traces there? We can then use analytics, material analytics, to look at this very closely and draw conclusions about the mechanisms, which are always a feature of the underlying system, and that's why we always have to work closely with biologists to understand what interactions there are with the surrounding tissue.
Prof. Jessica Bertrand: Of course, we ask the patient beforehand whether it is okay for him or her that we examine this implant.
Lisa Baaske: Yes, for science, so to speak, exactly. Okay, and then they meet every few months and talk about it?
Prof. Jessica Bertrand: We actually have regular meetings, every two months, where we present our results to each other and then discuss the results in an interdisciplinary way, so to speak, and explain to each other what we actually see.
Prof. Thorsten Halle: Yes, in the last five or six years, since we've been doing this, I've learned a lot about biological mechanisms, what happens in and on a surface like that. And perhaps Ms. Bertrand has learned a thing or two about the materials.
Prof. Jessica Bertrand: Yes, I now know grain boundaries, I now know mechanical measured values.
Prof. Thorsten Halle: And I know the difference between an osteoclast and an osteoplast. Not every materials scientist knows that.
Lisa Baaske: Actually, I don't know that either. What is the difference?
Prof. Thorsten Halle: One is bone-degrading cells and the other is bone-building cells.
Prof. Jessica Bertrand: There is this nice saying: the Klast steals and the Plast builds.
Lisa Baaske: Interesting. (laughs) Exactly, that would have been the next question in principle: What have you learned from each other now? So, many new, interesting scientific terms. And I've now learned that bone resorbing cells obviously exist. Very interesting. Okay, what do you see as the greatest advantage of your working group?
Prof. Thorsten Halle: A great advantage is indeed that we have a deep insight into the respective other disciplines due to the close cooperation. This means that when we have identified issues, it is very often the case that we first look beyond our own specialist areas to deal with the technical terms and the use of language, which is quite different in medicine and biology than it is in the engineering sciences. And that took a while, we have to admit, until we were no longer talking past each other, but were really talking to each other. Then, a few things had to be done with regard to the use of language, how one ultimately deals with a living system... That is the engineer, and I was not used to that either, that one gets another variable, namely the living system, the patient, and who certainly also has repercussions for the technical system. And that has been quite a challenge, but I think we have mastered it relatively well in the last five years and, as I said, we are now talking to each other and not at each other.
Prof. Jessica Bertrand: The important thing is that we can learn a great deal. The degrees of freedom that are tolerated in the automotive industry, for example, far exceed in implant production. In other words, the standards that exist or the characteristic values that are specified. This is so widespread in the case of implants that people in production engineering really do say that we would never tolerate this. And I think this is where we can learn a great deal. And also to improve the materials within this standard in such a way that the longevity of these implants is increased for the patient and simply the service life is extended. So yes, I think we can learn a great deal from each other.
Lisa Baaske: Okay, so a lot of learning from each other. That sounds very nice in any case. Above all, somehow changing things together. That's what it's all about. Yes, and that brings us to the end and a classic question: What does the future look like for you? What do you still want to achieve together? What is planned now for the future?
Prof. Thorsten Halle: What we are constantly developing and continuing, of course, is our scientific work. In other words, we are always striving to continue projects there, to drive our topic forward, because we not only believe, but also know, that it is absolutely relevant, also for patients and for the life sciences, and from my point of view, we as engineers can contribute significantly to improving this. And our working groups are set up in such a way that they work closely together. This means that we have joint doctoral students, we have joint student assistants, and we have joint research topics that we are of course constantly advancing. Also, we now have introduced a new master's program, "Biomechanical Engineering," in which there is, among other things, a specialization that deals precisely with this issue: Which implant materials are suitable for which applications from the point of view of engineers, but also from the point of view of physicians and biologists, in order to be able to train young people who will then be in a position to improve what is available now.
Prof. Jessica Bertrand: Furthermore, we want to continue to train students in addition to the master's program, so we also want to be able to offer another perspective. In other words, we want to be able to offer a graduate school in the future, where other departments will also be involved. For example, there is also cooperation with tribology, which means we want to try to understand how the joint lubrication in a hip implant works and whether something can be improved. But there are also interactions with other working groups that deal with exoskeletons, with mathematical modeling, and this is something that we simply want to expand across the entire campus, because there are many, many working groups that are active in similar areas. And we want to bring them together in a larger group, perhaps also in this graduate school or in a larger cluster, so that we can collaborate even better on an interdisciplinary basis.
Lisa Baaske: Very nice. So, whoever still wants to do research with you, so to speak, and also wants to improve implants, should enroll in your new program in the winter semester. Otherwise, many thanks for being here. It was super exciting and very interesting. But now, in conclusion, a bit of self-promotion should be allowed. If you want to learn more about the exciting research on prostheses, you should come to the Long Night of Science on campus on June 11. Professor Halle will be giving a lecture on the subject. And, of course, there will also be a whole host of other exciting programs and activities. But if you don't want to wait until June 11, you can also read about it in our research magazine, which also contains an exciting article on the research project we just talked about. Until then, thank you for listening. Stay healthy and feel free to tune in again soon.
Intro voice: "Wissen, wann du wilst." The podcast about research at the University of Magdeburg.