Pointing the way towards safer implants
Implants can enhance quality of life, but it’s essential to first ensure that they are safe and will function effectively in the body. We spoke to Dr. Anna Igual Munoz and Dr Stefano Mischler about their work with Prof. Dr Brigitte Jolles-Haeberli in investigating electrochemical reactions at the interface between biomaterials and the surrounding biological environment, such as body fluids and tissue.
A high level of resistance to corrosion is highly desirable in an implant material, as the release of metal ions can cause adverse tissue reactions and eventually lead to the body rejecting the implant. As Senior Scientist in the SCI STI SM Group at EPFL in Lausanne, Dr Stefano Mischler is investigating how metals like titanium react with synovial fluid, the liquid which effectively lubricates our joints. “We carry out electrochemical measurements and look at the reactions that take place on the metal,” he outlines. While previously most researchers used simulated body fluids to investigate electrochemical reactions in the body, Dr Mischler and his colleagues, in particular Yueyue Bao, PhD student, are using synovial fluids collected directly from patients during implant surgeries done by Prof. Jolles-Haeberli. “We have brought our lab very close to the surgery room. Once the synovial fluid is recovered when it falls into the operative field during the procedure, it’s rapidly transferred to us and we can directly do the measurements,” explains Dr. Anna Igual Munoz, Scientific Consultant to the SCI STI SM Group.
Electrochemical measurements
This approach could lead to deeper insights into the reactions which occur at the interface between biomedical materials and surrounding fluids, and ultimately help scientists develop improved and patienttailored implants. The metal is exposed to the synovial fluid, and then electrochemical measurements are taken, from which researchers aim to build a fuller picture.
“With our knowledge of corrosion and electrochemistry, we can interpret the results and obtain information about not only the corrosion rate, but also the behaviour of the liquid,” says Dr Mischler. Researchers are using several electrochemical and surface analysis techniques including Auger Electron Spectroscopy (AES), to determine surface changes of the metal after being in contact with the body fluid. “AES is a very effective technique, it’s surface sensitive and it has a high lateral resolution,” continues Dr Mischler.
“With AES we look at the topography of
the material but we also have chemical information from the outermost surface, the first atomic monolayers.” A technique called infrared spectroscopy is also being used in the project, which provides information about the different functional groups which are present and enables researchers to discriminate between them.
proteins on the surface,” he explains. “The higher the oxygen concentration, the higher the corrosion rate of the metal. But the higher the protein concentration, the more adsorption and lower oxygen. A good patient has low oxygen, and a lot of proteins.”
This type of patient is less likely to react aggressively to the implant and reject it. While
The higher the oxygen concentration, the higher the corrosion rate of the metal. But the higher the protein concentration, the more adsorption and lower oxygen. A good patient has low oxygen, and a lot of proteins.
The evidence gathered so far suggests that the key parameters in terms of determining the corrosion rate of implants are the interplay between oxygen content and the amount of organic components (i.e. proteins) in the body fluid. “Titanium is passive and its corrosion rate is affected by the reduction of oxygen. Electrochemical measurements suggest that oxygen content varies between patients,” outlines Dr Mischler. Another important consideration is the amount of proteins or organic molecules in the synovial fluid, says Dr Mischler. “This affects the adsorption of
quality of life, enabling them to keep doing the things they enjoy,” points out Dr. Igual Munoz. “We have an aging population, and many of these people want to stay active for longer.”
Biocompatibility
The ideal scenario is to give each patient the right implant for them individually, improving biocompatibility so that the implant is accepted by the body. The project’s research will make an important contribution in this respect, with Dr Mischler and Prof. JollesHaeberli aiming to help more accurately predict how an individual patient will react to an implant material. “This is a really longterm oriented project, and we can follow the release of the material following surgery over the course of years. We have a predictive tool, and are also interested in blood analysis,” he outlines. The project’s work could also help researchers anticipate the sensitivity of patients to the wear of a joint, as well as point the way towards improved testing methods to assess the long-term performance of implant materials.
“Some companies are using hip joint simulators to test implants in vitro These machines are used to test the materials in mechanically demanding circumstances over extended periods” continues Dr Mischler. A lot of attention has historically been focused on assessing the impact of weight and the biomechanics of patients on the material, while by contrast the chemistry of the synovial fluid has been relatively neglected. However, it has since been shown that the interactions of the metal with the synovial liquid are in fact highly important. “This importance is now more widely recognised, and people are thinking about how they can improve their simulator tests and make them much more predictive,” says Dr Mischler. This research could also inform work to develop
In-SItu InvEStIgAtIon of IntErfAcIAl rEActIonS
In-situ investigation of interfacial reactions of metal surfaces in contact with human synovial fluids
Project objectives
To design and validate an optimal experiment protocol to determine the electrochemical behavior of biomedical implant alloys in human synovial fluids and to understand their reaction behavior as a function of the clinical state of the patients. This will be achieved through a collaboration between surgeons and corrosion scientists.
Project funding
This project is funded by the Swiss National Science Foundation (SNSF). https://data.snf.ch/grants/grant/184851
Project Partners
• Tribology and Interface Chemistry (TIC) group of the Materials Institute of EPFL
and manufacture more effective implants which are less likely to be rejected. “There are some surface structures that are more prone to the adsorption of proteins, which is a favourable mechanism. We can promote this with certain materials,” says Dr Mischler.
“There is interest in developing in vivo surfaces tailored to patients.”
There are several further strands to this research, with Dr Mischler and Dr. Igual Munoz working to gain deeper insights into the behaviour of metal implants in the body.
Part of this work involves looking at the wear and friction on the system. “We can use in vitro tests to investigate the effectiveness of the synovial fluid as a lubricant, and the sensitivity of the ball part of an implant to wear and corrosion,” explains Dr Mischler. These are important considerations for companies seeking to develop improved implants, and the project’s research helps lay the foundations for further development.
“This research shows feasibility. In future we can maybe look towards more focused studies and collaborations with companies,” outlines Dr Mischler.
• The Swiss BioMotion Lab (SBML) at the Department of Musculoskeletal Medicine of the Centre Hospitalier Universitaire Vaudois (CHUV) contact Details
Project Coordinator, Prof Anna Igual Munoz EPFL SCI STI SM MXC 341 (Bâtiment MXC) Station 12, CH-1015 Lausanne t: +41 21 693 68 83 E: anna.igualmunoz@epfl.ch W: https://data.snf.ch/grants/grant/184851
titanium implants work pretty effectively in general, some patients experience adverse reactions, which will affect durability. “In cases where patients react unfavourably, implants don’t last more than 10-15 years on average. This may be fine for an older individual, but not for a younger person,” says Dr. Igual Munoz. A major challenge now is to increase the durability of these implant materials, making them suitable for all patients, particularly with demand set to increase further as life expectancy rises.
“Implants are intended to improve a patients’
Anna Igual Munoz is a Senior Scientist in the Tribology and Interface Chemistry Laboratory at EPFL in Lausanne. She gained her PhD from the University of Valencia and has held research positions at institutions in Europe and America.
Stefano Mischler is head of the Tribology and Interface Chemistry Unit at EPFL. He has published more than 100 articles in academic journals and is a member of several societies, including the Swiss Society for Materials Technology.
Brigitte Jolles-Haeberli is a Senior Consultant Orthopaedic Surgeon, specialising in knee and hip surgery, and an Associate Professor in the Faculty of Biology and Medicine at the University of Lausanne.
Yueyue Bao is a PhD student at the EPFL in Lausanne, who has recently successfully defended her thesis on in vivo investigation of the electrochemical behaviour of Ti and CoCrMo alloys in human synovial fluids.
