Prosthetic limbs: reality meets science fiction

The expert: Max Ortiz Catalan. A researcher at Chalmers University of Technology and Sahlgrenska University Hospital in Sweden, Dr. Max Ortiz Catalan is specializes in techniques for attaching prosthetic limbs and treatment of phantom pain, which afflicts many amputees. He developed the first bionic arm connected to the bones, nerves, and muscles, which has enabled patients to return to a relatively normal social and professional life.

How has osseointegration changed the field of prosthetic limbs?Max Ortiz Catalan: Osseointegration is a concept that was developed in Sweden in the 1960s by Professor Brånemark. It’s defined as direct contact between bone tissue and a biomaterial, in this case titanium. From the 1950s, scientists had started to notice that the human body tolerates this metal very well. Bone cells can grow with titanium and almost assimilate it. It’s therefore possible to insert titanium implants into a bone and use them to attach the prosthetic limb. This option is much more comfortable for the amputee than the traditional socket prostheses, which can be painful and can limit freedom of movement. I was lucky to work with Professor Brånemark on this technology, which provided access for me to insert a direct neural interface as a communication channel. In January 2013 we implanted a prosthetic right arm that the patient controls by thought. Today this man leads a relatively normal life and has even been able to return to his work as a truck driver.
Further reading: Home-made prosthetics

This man is the first person to use a thought-controlled prosthetic arm connected by osseointegration. It has enabled him to return to his work as a truck driver. © Ortiz-Catalan et al., Sci. Trans. Med., 2014
What are the biggest challenges right now?
My colleagues and I all dream of creating prosthetic limbs that are just as efficient as human limbs. But if we consider the arm, it is incredibly sophisticated, and very difficult to imitate. Right now, our main goal is to restore functionality and offer a better quality of life to users. Osseointegration has enabled us to overcome the crucial obstacle of connecting the artificial limb and the body. The next step is to have access to all the information that the brain sends to the nerves and muscles, because right now, there are only a few communication channels available to us. The current neural interfaces let us control about 20 per cent of the abilities of an artificial limb. With our prosthetic arm, for example, we control three degrees of freedom, while the hand alone has 27. We need the ability to create many more communication channels to capture and restore more signals. Perfecting the neural interface is also essential for recreating a sense of touch. This is something we’re starting to do and one of the other major research areas in our field.
OsseointegrationOsseointegration was developed in the 1960s by Professor Per-Ingvar Brånemark in Göteborg, Sweden. Initially this procedure, which creates a physical connection between a bone and an artificial implant, met with great scepticism from the medical community. But today it’s used for dental implants as well as for anchoring prosthetic upper and lower limbs. The amputee receives an implant made of titanium, a metal that is especially well tolerated by bone cells. After six months, once the implant is firmly assimilated to the bone, it’s possible to connect the prosthesis. This kind of prosthetic limb is much more mobile and less painful to wear than a socket prosthesis. As Dr. Max Ortiz Catalan explained, osseointegration is a ground-breaking technique with great possibilities for creating thought-controlled prosthetic limbs.

What are the most promising technologies today?
We hear a lot about artificial skin. It works in the lab, but in real life it’s a different matter. There is always the problem of how much information can be transmitted from the external interface; 3D printing will play an important role in the coming years. It will enable us to repair or further develop a prosthesis, but I have to stress that we need good control of this technique to produce something functional and durable.In my view, the most promising technology for our work is optogenetics. This engineering technique is used to identify neural networks and stimulate the cells using a blue light. The light activates a protein (channelrhodospine) in these neural cells. Applied to a neural interface, optogenetics would enable us to control a single nerve in charge of a specific function. This would help us be very selective in order to reproduce the degrees of freedom and functionality of a limb more precisely. Neuroscientists see enormous potential in optogenetics. But we’re working on cells and it will take time before we can apply this technology to humans.

Three patients suffering from plexus brachial injuries (where the neural connections between the brain and the limb are broken) agreed to replace their inert limbs with thought-controlled bionic prostheses. This bold technique, which is called bionic reconstruction, was performed by a research team at the Vienna Medical School in Austria. © The Lancet
Will healthy people one day choose to have bionic limb transplants, to go beyond their physical limits?We hear a lot about this kind of development now. But I guarantee you that we are a long way away from Luke Skywalker’s bionic arm! For example, there are nerves that activate an emotional touch. Holding someone’s hand sends sensations to the brain that we are very far from replicating with neural interfaces. Maybe one day we will have excellent prosthetic limbs that are good enough to replace a healthy limb. But I don’t think I’ll see it in my lifetime. I think in the near future, about five years from now, we’ll have high-performing prosthetic limbs for certain tasks that will offer a better quality of life to the people who use them.To go further
A bank of artificial bones printed in 3D
The bionic ankle helping a woman dance again
The self-adjusting prostheses that give amputees a new lease of life at minimal cost
Capsulight: the healing power of light
Artificial touch
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