Self-powered protein robots. What happened after?

How can we use proteins to power devices at the microscale? Last year, we built self-powered protein microrobots for targeted delivery. This is what happened next.

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New micro- and nanotechnologies have been developed over the last years in the search for new minimally invasive medical procedures. Particularly, small-scale robots and devices have great potential for medical and bioengineering applications due to their small size and their ability to navigate in hard-to-reach areas of the body. However, such microrobot-enabled technologies face significant challenges: how to power the devices, how to actuate and control them, how to operate them safely in a biologically relevant scenario, etc. Last year, our team at the Max Planck Institute for Intelligent Systems (Prof. Dr. Metin Sitti, Dr. Joshua Giltinan, and myself) published a paper where we developed biodegradable self-propelled motors based on Marangoni propulsion (Pena-Francesch et al. Nat. Commun. 2019). While classical chemical motors typically require hazardous reactions, our motors were fueled by an anesthetic metabolite, and surpassed previous generations of micromotors in performance output and efficiency by several orders of magnitude. We demonstrated diverse functionalities of these motors in environmental remediation, modular powering, and drug delivery applications, taking advantage of the biodegradability and tunable properties of the motor materials.

"Shark robot" swimming in a pool of water, powered by protein-based modular motors (Pena-Francesch et al. Nat. Commun. 2019).

This particular publication allowed us to explore new research areas, and had a strong impact on our careers. Personally, I come from a mix of mechanical engineering, chemical engineering, and materials science and engineering backgrounds, with a core expertise in polymers, biomaterials, and soft materials mechanics. Most of my work has focused on fundamental research and structure-property relationships in soft materials (especially in structural proteins), which are critical in the development of new materials. However, the field of medical microrobotics presented new opportunities where materials can make a big impact, for example:

(i) Miniaturization. Traditional large-scale robots are composed of rigid components such as motors, batteries, sensors, etc. If we want to scale robot designs down to the milli-, micro-, and nanoscale, we cannot rely on traditional approaches since there is no room for such bulky components, and we need to come up with new strategies to power, actuate, and control those robots.

(ii) Multifunctionality. Since we have limited space, we will want to avoid using inactive or passive materials so we do not waste space. Instead of combining multiple components that perform a single function each, ideally we would prefer a single component that can perform different functions simultaneously.

(iii) Biocompatibility. If these robots will eventually go inside our bodies, they must be non-toxic, biocompatible, they should not trigger an immune response, and ideally they should be biodegradable (so there is no need to retrieve them once they performed their task).

Looking at these challenges, we saw many opportunities to create new solutions from a materials development perspective, and that is exactly how we approached it. I am extremely grateful to the Alexander von Humboldt Foundation and the Max Planck Society for the support during my postdoc, which gave me the freedom to explore new ideas and develop a research focus and expertise in “robotic biomaterials”. Building on what we learned in this publication, we developed new materials-based solutions to overcome challenges in medical microrobotics and soft robotics fields. For example, we developed “stealth” microrobots that can operate undetected by the immune system (Cabanach et al. Adv. Mat. 2020) and we developed protein-based self-healing materials capable of healing extreme mechanical damage within seconds (Pena-Francesch et al. Nat. Mater. 2020).

This paper was the first major publication from my postdoctoral work and it also had an impact on our careers (especially for the two junior authors!). I am starting my own research group at the University of Michigan in a few weeks, where we will be working on bioinspired functional materials for medical robotics and bioengineering. Josh obtained a position as a research scientist at the Fraunhofer Center for Experimental Software Engineering. Overall, this paper was a fun project, and we are grateful for how things have turned out. We are optimistic about the future and enthusiastic to push the limits of the microrobotics field together with the growing scientific community.

Abdon Pena-Francesch

Assistant Professor, University of Michigan

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