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Supramolecular machineries with life-like mechanical functions

Periodic Reporting for period 2 - MechanoTubes (Supramolecular machineries with life-like mechanical functions)

Reporting period: 2020-04-01 to 2021-09-30

Artificial molecular machines have the potential to become a core part of nanotechnology. However, a wide gap in length scales remains unaccounted for, between the operation of these molecules in solution, where their individual mechanical action is randomly dispersed in the Brownian storm, and on the other hand their action at the macroscopic level, e.g. in polymer networks and crystals. Bridging this gap, requires chemo-mechanical transduction strategies that will allow dynamic molecules to perform a range of unprecedented tasks, e.g. by generating strong directional forces at the nanoscale and in fluid environment. Showing the way for synthetic systems, biological machinery has emerged from the pool of dynamic biomolecules operating in fluid environment. The key strategy that nature uses to overcome the Brownian storm and perform useful mechanical work is to connect the dynamics of individual biomolecular building blocks with the self-assembly processes. Such molecular machineries operating at the level of the self-assembly processes are known as polymerisation and depolymerisation motors. Developing synthetic mechanically active molecular systems that operate on the same principles constitutes the next major challenge in the field of artificial molecular machines.
In this project, we address conceptual aspects of these challenges. The key strategy is to use molecular self-organization as means of generate mechanical force. To do so we draw inspiration from the operational principles of cellular microtubules. By incorporating photo-switches into the design of the molecular monomers we enable the controlled growth and disassembly of the tubes by using light as the energy input. The specific strategy to gain new knowledge and reach these goals consist of: (i) Synthesizing stiff supramolecular tubes made of molecules that grow actively under continuous illumination, and disassemble as soon as illumination stops; (ii) Measuring, and harvesting the forces generated by the tubes to manipulate individual nanoparticles with a sense of directionality; and (iii) Encapsulating the tubes into water droplets and vesicles, to yield shape-shifting, and eventually rudimentary splitting models for cells.
This project will lay the foundations for machineries that are capable of manipulating matter at length scales that are also those at which the cytoskeleton operates.
1. Interfacing and crosslinking self-assembled tubes
In order to transfer mechanical forces exerted by biological polymerization motors effectively these need to be connected/interfaced with the upon which they act. Also, for more substantial mechanical effects action of more supramolecular machines is amplified by their crosslinking. At mid-term, our published scientific output primarily concerns this aspect of the work, with significant contribution in developing strategies that allow crosslinking and and interfacing of supramolecular tubular structures. This research has also consequences for material science as it gives new insights into the behavior of crosslinking and interacting supramolecular polymers.
2. Light-fuelled self-assembly into tubular architectures
The work performed by supramolecular polymers, such as microtubules and actin filaments, supports the life of the cell, and essentially involves fuel-driven self-assembly pathways. Developing fuel-driven supramolecular polymerization processes is therefore crucial to the realization of mechanically active molecular systems. We demonstrated supramolecular tubules with non-equilibrium steady states that are fuelled by light. This dynamic supramolecular system features rapid cycles of self-assembly and disassembly, at rates that appear fast enough to perform mechanical tasks in fluids effectively.
3. Mechanical properties of hydrogel networks made of supramolecular tubes
Growing supramolecular fiber can exert mechanical force as long as it is sufficiently stiff to avoid its bending and breaking. Therefore, we looked into mechanical properties of the fibers we designed. The stiff tubular fibers that we designed exhibit analogous properties to collagen and fibrin networks. We have discovered that under mechanical stress our artificial hydrogel networks exhibit enthalpic strain stiffening before they plastically deform to ensure their survival.
We have demonstrated a strategy to synthesize cross-linked networks made of stiff tubular fibers where all the interactions between monomers as well as fibers are of supramolecular character. While being fully tunable and reformable these networks exhibit sufficient kinetic stability. Further, we have developed a new strategy of fuelling self-assembly by photo-acid. And lastly, we have discovered unprecedented mechanical behavior in synthetic stiff supramolecular networks including enthalpic strain stiffening and plastic remodeling. Building on these findings we are developing approaches to measure and harness mechanical forces produced during the self-assembly and disassembly of these fibers and networks. These forces will push and pull nanoscale objects such as nanoparticles and deform static soft matter (vesicles, emulsion droplets).