Dr. Max Ortiz Catalan is Research Director at Integrum AB, a medical device company based in Molndal, Sweden. Wisse Hettinga recently interviewed him about his work in the field of prosthetic design and biomedical systems.
As an electrical engineer, your first focus is to create new technology or to bring a new schematic design come to life. Dr. Max Ortiz Catalan is taking this concept much further. His research and work is enabling people to really start a new life!
People without an upper limb often find it difficult to manage tasks due to the limitations of prostheses. Dr. Catalan’s research at Chalmers University of Technology and Sahlgrenska University Hospital in Gothenburg, Sweden, focuses on the use of osseointegrated implants and a direct electronic connection between the nervous system and a prosthetic hand. People can control the prosthesis just like you control your hand, and they are able to sense forces as well. The results are impressive. The first patient received his implant three years ago and is successfully using it today. And more patients will be treated this year. I recently interviewed Dr. Catalan about his work. I trust this interview will inspire seasoned and novice engineers alike.—Wisse Hettinga
HETTINGA: What led you to this field of research?
CATALAN: I was always interested in working on robotics and the medical field. After my bachelor’s in electronics, my first job was in the manufacturing industry, but I soon realized that I was more interested in research and the development of technology. So I left that job to go back to school and do a master’s in Complex Adaptive System. I also took some additional courses in biomedical engineering and then continued working in this field where I did my doctoral work.
HETTINGA: I was surprised you did not mention the word “robot” once in your TEDx presentation (“Bionic Limbs Integrated to Bone, Nerves, and Muscles”)? Was that coincidence or on purpose?
CATALAN: That was coincidence, you can call a prosthesis a “robotic device” or “robotic prosthesis.” When you talk about a “robot,” you often see it as an independent entity. In this case, the robotic arm is fully controlled by the human so it makes more sense to talk about bionics or biomechatronics.
HETTINGA: What will be the next field of research for you?
CATALAN: The next step for us is the restoration of the sense of touch and proprioception via direct nerve stimulation, or “neurostimulation.” We have developed an embedded control system for running all the signal processing and machine learning algorithms, but it also contains a neurostimulation unit that we use to elicit sensations in the patient that are perceived as arising from the missing limb. The patients will start using this system in their daily life this year.
HETTINGA: You are connecting the controls of the prosthesis with nerves. How do you connect a wire to a nerve?
CATALAN: There are a variety of neural interfaces (or electrodes) which can be used to connect with the nerves. The most invasive and selective neural interfaces suffer from long-term instability. In our case we decided to go for a cuff electrode, which is considered as a extra-neural interface since it does not penetrate the blood-nerve barrier and is well tolerated by the body for long periods of time, while also remaining functional.
HETTINGA: Can you explain how the nerve signals are transferred into processable electric signals?
CATALAN: Electricity travels within the body in the form of ions and the variations in electric potentials, or motor action potentials for control purposes. They are transduced into electrons by the electrodes so the signals can be finally amplified by analog electronics and then decoded on the digital side to reproduce motor volition by the prosthesis.
HETTINGA: What is the signal strength?
CATALAN: Nerve signals (ENG) are in the order of microvolts and muscle signals (EMG) in the order of millivolts.
HETTINGA: What technologies are you using to cancel out signal noise?
CATALAN: We use low-noise precision amplifiers and active filtering for the initial signal conditioning, then we can use adaptive filters implemented in software if necessary.
HETTINGA: How do you protect the signals being disturbed by external sources or EM signals?
CATALAN: Since we are using implanted electrodes, we use the body as a shielding, as well as the titanium implant and the electronics housing. This shielding becomes part of the amplifier’s reference so it is rejected as common noise.
HETTINGA: How are the signals transferred from the nerves to the prosthesis?
CATALAN: The signals from nerves and muscles are transferred via the osseointegrated implant to reach the prosthesis where they are amplified and processed. In a similar ways, signals coming from sensors in the prosthesis are sent into the body to stimulate the neural pathways that used to be connected to the biological sensors in the missing hand. Osseointegration is the key difference between our work and previous approaches.
HETTINGA: What sensors technologies are you using in the prosthetic hand?
CATALAN: At this point it is rather straightforward with strain gauges and FSRs (Force Sensitive Resistor), but on research prostheses, motors are normally instrumented as well so we can infer joint angles.
This interview appears in Circuit Cellar 307 February.
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