Polymer skeleton keeps synthetic cell in shape

If you want to build a functional, true-to-life synthetic cell, a cytoskeleton is an indispensable component. Considerable work has already been done in this area, including approaches based on DNA, but Sebastian Novosedlik, Jan van Hest, and colleagues at Eindhoven University of Technology took a different tack. ‘We approached it more from the polymer angle,’ explains professor of bio-organic chemistry Jan van Hest. In collaboration with the company SyMO-Chem and the Max Planck Institute Erlangen, they succeeded in building a polymer skeleton that exhibits several natural functions.

Surprised

‘Our cell system consists of amylose polymers and polymer membranes, and to keep the whole thing consistent, we looked at polymer-like fibres,’ Van Hest continues. ‘Our initial approach was to use small molecular systems that self-assemble and then bundle together into larger filaments. That was immediately very successful.’ When the microfibres formed came into contact with positively charged polymers, a well-defined network emerged. Compared with DNA-based cytoskeletons, the use of polymer fibres offers greater control and more opportunities for functionalising the system, according to Van Hest.

‘For the basis of our synthetic cell, we use amylose coacervates — a type of liquid droplet containing a mixture of polymers with opposing charges, which gives rise to phase separation. Despite their density being comparable to that of a real cell, they are sufficiently different to possess distinct properties.’ The team was therefore most surprised by the fact that they were able to mimic the mechanical properties of a living cell so effectively.

High-throughput system

With the help of the confocal microscopes of Jochen Guck (MPI Erlangen), they were able to compare the properties of the synthetic and living cells in a high-throughput system. Van Hest: ‘The mechanical properties are essential for interactions between cells, so we were keen to elucidate those in our system as well. But with our standard techniques, you can only examine one cell at a time.’

They therefore enlisted the group of Jochen Guck, who are able to examine living cells at high speed. ‘They had not yet worked with synthetic cells, however, so it was a new experience for them too. But as a result, we were able to establish that, for instance, the Young’s modulus corresponds nicely — you get a clear picture of the cells’ behaviour. The fact that we were able to replicate the properties of the cytoskeleton so faithfully is truly quite remarkable.’

Two types

Incorporating the skeleton into the ‘cell’ required careful attention. ‘Depending on the modifications made to the fibres, you can see that they either coat the entire interior of the cell or stabilise the membrane,’ says Van Hest. ‘Once we understood that, we were able to deliberately develop two types of cytoskeleton. Sebastian had a good instinct for that and went about it very efficiently.’

Van Hest and colleagues work with coacervates as their basis, but other systems are possible. ‘We wanted to know whether the behaviour of our cytoskeleton is specific to coacervates or whether it can be applied elsewhere as well.’ To that end, they incorporated the polymer skeleton into, amongst other things, a large liposome, and there too the fibres formed a network. ‘The principle of cytoskeleton formation can therefore be used in other cell types as well — it is a robust and versatile system.’

Dynamic

Despite all its advantages, the Eindhoven cytoskeleton still has one drawback, Van Hest acknowledges. ‘In reality, a cytoskeleton continuously adapts to its changing environment, including during cell deformation and division. Our system cannot do that — it is not dynamic. Once it is fixed, it can no longer change.’ They therefore have a clear next step in mind. ‘We want to make the transition to a dynamic system whilst preserving these mechanical properties. That would take you into territory where you have a cell capable of truly adaptive interactions — it would then be even more “alive” than anything developed so far.’

Novosedlik, S. et al. (2025) Nat. Chem. DOI: 10.1038/s41557-024-01697-5