The features of the microbot include: Self-propelled movement, controlled movement through magnetic fields, and real-time hydrogel production to catch cells with high degree of biocompatibility.
Postdoctoral scientists behind this study, Sarvesh Kumar Srivastava and Fatemeh Ajalloueian, who are both part of Professor Anja Boisen’s research center IDUN, have termed it as TRAP technology: Thread-like Radical-polymerization via Autonomously Propelled (TRAP) Bots. The top illustration depicts a TRAP Bot where rapid formation of polymer has created a tail and propels it forward.
The TRAP Bot
TRAP Bot with bubble formation
The TRAP Bot itself is a micro device (height: 220 µm, inner diameter: 190 µm) with a sealed bottom to create a cavity inside. This allows loading of reaction mixture together with a monomeric cap to seal the assembly. When the microbot is exposed to an aqueous environment, diacrylate monomers react with the radical agents loaded inside, and generate a tail of hydrogel (i.e. polymerized PEGDA).
Cell-catching tail
The reaction inside the TRAP Bot is actually a rapid formation of polymer. Within a few microseconds, the polymer or hydrogel expands and shoots out of the micro cavity like a long tail. The tail has a mesh-like structure, which can catch cells or other micro particles, and it provides an ideal 3D environment for cells, where they are completely wrapped in the hydrogel polymer.
Authors explain that the traditional way of growing cells in a petri dish is less than ideal in terms of mimicking the natural environment of cells. And even though different polymer materials, which are inherently 3D-like due to their mesh-like structure, have been tested as surfaces for culturing cells, they only provide a 3D environment for the part of the cell that touches the surface, i.e. the remaining of the cell is still in a 2D environment.
Image of TRAP Bot and its hydrogel mesh-like tail
This is where TRAP bots become interesting. They can capture the cells and carry them from one place to another (via external magnetic fields). The inherent biocompatibility of TRAP bots allow cells to stay viable, thereby, opening potential applications in cellular therapy.
Controlled movement
The TRAP Bots move autonomously due to the chemical reaction that takes place during the polymer formation. When the polymer tail shoots out from the reaction micro chamber, it propels the microbot forward (much like a lift-off). Further, motion can be sustained for abiotic applications via incorporation of low concentration of peroxides, which can react with a thin layer of platinum embedded inside the TRAP bots.
TRAP Bot - polymer initiation has just started.
Furthermore, the TRAP Bots have a thin layer of Ni-metal on the inside, which makes it possible to move the microbot with magnetic fields. I.e. it can be controlled externally and directed towards the site of requirement.
Cells thrive in the TRAP Bot tail
To be able to use the TRAP Bots for biological and health technology related research, it is essential to use biocompatible materials. The study includes an exhaustive 7-days test, which showed that cells are alive and well after 7 days in the hydrogel.
Of course, further clinical testing is needed for using the TRAP Bots in medical research, but so far the first steps look promising.
Living cells trapped in the wake of a TRAP Bot
Future perspectives
The TRAP Bots open up a range of new opportunities the authors explain. For example in single cell manipulation, where the TRAP Bot can be directed towards a specific place in the body and collect a specific single cell. Another avenue of interest is in nanomedicine, where the TRAP Bot could be used to deliver drugs on a cellular level. As the 3D hydrogel structure mimics the natural environment for cells, it could also prove useful for enhancing bioproduction via anchorage-dependent cell lines, for example, in a setup where various cells produce a certain product that can be removed or harvested instantly with a magnet.
Links:
The full article was published in Advanced Materials, Vol 31, No. 30, July 2019.
Science News by Novo Nordisk Fonden has also published a popular science article about the study.
Optical images by Sarvesh Kumar Srivastava.
Illustrations by Nanna Elmstedt Bild.
Front cover: Advanced Materials Vol 31, No. 30, July 2019
