Magnetically propelled MOFBOTs perform microrobotic drug delivery (w/video)
(Nanowerk Spotlight) Metal-organic frameworks (MOFs) are porous materials that consist of regular arrays of metal atoms surrounded by organic 'linker' molecules to form unique cage-like structures. Due to this hollow structure, MOFs have an extraordinarily large internal surface area.
This high surface-to-volume ratio makes them ideal materials for storing gases or other payloads such as biomolecules of various sizes. One potential application of MOFs is as microcarriers for biomedical payloads.
"While initial efforts have been made to produce mobile MOF-based small-scale machines, the locomotion features of most of these systems lack the level of sophistication of current state-of-the-art micro- and nanoswimmers," Dr. Josep Puigmartí-Luis from ETH Zurich, tells Nanowerk. "For example, the controlled directionality of chemically propelled MOF crystals has yet to be addressed."
By applying concepts developed in micro- and nanorobotics, Puigmartí-Luis and an international team of collaborators demonstrate the controlled motion and delivery of cargo payloads embedded in MOFs. They report their findings in Advanced Materials ("MOFBOTS: Metal–Organic-Framework-Based Biomedical Microrobots").
The researchers' helical MOF-based micromachine, propelled by artificial bacterial flagella (ABF), can swim and follow complex trajectories in three dimensions under the control of weak rotational magnetic fields.
"We focused our research on ZIF-8 MOFs due to their excellent biocompatibility and degradation characteristics in relatively mild acidic conditions," explains Puigmartí-Luis. "We also show that our highly integrated multifunctional micromachine can successfully release drugs to a designated location, where the pH values are around 6, which corresponds to the similar acidic conditions found in tumor microenvironments."
a–f) Schematic illustration of the component steps involved in the manufacture of ZIF-8@ABF microrobots. g) A SEM image of multiple ZIF-8@ABFs. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
To fabricate their MOFBOTs, the researchers 3D-printed helical frameworks and coated them with nickel and then titanium to make them magnetic and biocompatible. After functionalization with PDA, a coating of ZIF-8 MOF crystals was grown on the ABF surface. The thickness and compactness of the ZIF-8 coatings can be tailored by the variation of reactants concentration and reaction time.
"To illustrate the potential of our integrated micromachine, we have shown that these swimmers are tumor-responsive and can act as selectively automated and targeted drug delivery platforms," Puigmartí-Luis points out. "We have also demonstrated that the motion of our MOFBOTS can be precisely controlled and that they can follow complex trajectories within microfluidic channels to deliver drugs in a regioselective manner."
This video shows a MOFBOT writing the letters "mof".
The team is already working on the fabrication of fully degradable MOFBOTs for biomedical applications.
"In the future, we plan to design new MOFBOTs that will be loaded with real drugs, and ideally, we will investigate them in vivo," Puigmartí-Luis concludes. "A big challenge will be to chemically define the MOF that will enable the loading of specific drugs and at the same time avoids the interaction with undesired healthy tissues."