Multiscale Modelling of Supramolecular Assemblies of Light-Driven Molecular Motors

Abstract

Molecular “muscle” fibres built from light-driven motors promise controllable, contractile soft materials, yet the underlying molecular mechanisms causing macroscopic motion remain elusive, hindering effective design and tuning. Here, we develop a multiscale simulation workflow that connects atomistic chemistry to supramolecular mechanics across single molecules, fibres, and multi-fibre assemblies. We introduce a Martini3 coarse-grained parametrisation and a protocol for simulating the motor actuation in the condensed phase. Finally, we demonstrate several applications of our model, which both shed light on proposed mechanisms and lead to new hypotheses about how motor actuation drives collective deformation in supramolecular fibres.

Popular Abstract

Muscles are why we can move. Organisms are capable of large, but finely tuned, movements, thanks to microscopic interactions between molecules in the muscle fibres. If we could imitate these muscle contractions, we could pave the way for soft, microscopic robotics with applications in medicine and beyond. Imagine small robots navigating the bloodstream, replacing muscles in damaged tissue, or cancer drugs that are only activated at the cancer site. Human muscles are made of protein. Still, several attempts have been made to create a similar function from classical organic chemical reagents that you can find in industry. A promising direction was proposed in 2018, made from light-sensitive artificial molecular motors. Light-sensitive molecular motors are molecules that perform work when illuminated. They are a critical component of creating responsive materials or innovative drug-delivery systems. When the motors are mixed with water, they self-assemble into centimetre-long fibres. When the fibre is illuminated, and a part of the motor rotates, experiments show that the whole fibre bends, just like a biological muscle fibre. The bending is surprising to many scientists. Macroscopic movements like these are commonly caused by many small molecules bound together into a large crystal or fibre with stiff bonds. However, in the artificial molecular muscle, the molecules are held together much more loosely. The artificial muscle fibre has since been studied in several subsequent projects and used in biological applications, such as growing neurons. However, despite its use, the exact mechanism by which molecular rotation can cause macroscopic bending remains obscure. How could a movement 1000 times smaller than a human cell create visible bending?

In this thesis, we investigate the underlying mechanisms for the artificial molecular muscle using molecular dynamics simulations. Rather than studying chemical reactions under a microscope, molecular dynamics aims to simulate responses in a computer. The behaviour of individual molecules can then be viewed in isolation, just like in a movie. In contrast, classical experiments are typically limited to measuring the average properties of molecules. We describe how experiments can be simulated and document qualitative and quantitative measurements of how illumination may propagate into macroscopic movements.

Our contributions are twofold: Firstly, we propose a validated method for probing these molecular muscles using molecular dynamics via an automated pipeline. Such a framework makes it easy for scientists to vary different parts of the muscle assembly, such as the molecules used, the temperature, or other environmental variables, and test mechanisms and hypotheses in a computer before possibly laborious synthesis. Secondly, we test several established hypotheses that attempt to explain the observed behaviour in the molecular muscle. We find that the muscle likely bends due to chemical changes on the illuminated side, which trigger contraction and subsequent bending.

Our pipeline and discoveries are directly applicable to ongoing investigations into molecular muscle, where experimentalists are currently attempting to create the muscle using cheaper molecules and to make it bend faster and more forcefully. If we can reliably create cheap, fast molecular muscles via organic synthesis, these muscles could become a new industry standard for micro-robotics, medicine, and biological research, where controllable physical perturbations on the microscopic scale are needed.

• author: Akke, Mattias
• supervisor: Mikael Lund
• organization: Biophysical Chemistry
• course: KFKM05 20252
• year: 2026
• type: H1 - Master's Degree (One Year)
• subject: Chemistry
• keywords: Computational Chemistry, Organic Chemistry, Soft Materials, Molecular Motors, Molecular Dynamics, Coarse Graining
• language: English
• id: 9216455
• date added to LUP: 2026-02-03 10:11:59
• date last changed: 2026-02-03 10:11:59