The successful development of ActiDrops has enabled the achievement of most of the research goals, ensuring the delivery of key milestones and generating significant scientific impact.
A diverse library of chemical reaction cycles (CRCs) has been established, leading to the formation of active modules with a wide range of residence times (Chen et al., JACS, 2023). These reactions have been carefully optimized to minimize the formation of undesired by-products (Chen et al., Chem Sci, 2023). CRCs typically involve the activation of a carboxylate using fuel, producing a transient anhydride that subsequently hydrolyzes. The reduction in negative charge upon activation promotes self-assembly.
These CRCs have been successfully integrated into various self-assembling systems, resulting in the formation of active oil droplets (Schwarz et al., Chem Sci, 2021) and complex coacervates (Donau et al., Nat Commun, 2020), both of which have been studied extensively.
Active oil droplets were developed using long aliphatic precursors that phase-separate from water. Since these droplets are water-excluded, both activation and deactivation occur in the surrounding aqueous environment. Remarkably, these droplets exhibit accelerated ripening, growing significantly faster than classical models would predict. The growth rate can be tuned by adjusting the residence time of the active module (Tena-Solsona et al., ChemSystemsChem, 2021). Additionally, unexpected behaviors such as parasitic and self-emulative dynamics were observed (Schwarz et al., Chem Sci, 2021).
In contrast, active complex coacervates were formed by combining a cationic peptide—generated upon fuel addition—with an anionic polymer, such as RNA. These coacervates, which can consist of up to 95% water, display distinct spatial organization: activation occurs in the external medium, while deactivation takes place within the droplets via hydrolysis. They assemble spontaneously and disassemble in the absence of fuel. Notably, they exhibit life-like behaviors such as fusion, vacuole formation, and transient enrichment of functional RNA (Donau et al., Nat Commun, 2020). These systems have laid a strong foundation for the rational design of fuel-driven, self-assembled compartments (Donau et al., Angew Chem, 2022; Späth et al., Angew Chem, 2022).
The fuel-dependent nature of these compartments has revealed behaviors that challenge classical thermodynamic paradigms. For instance, accelerated ripening in active oil droplets occurs at rates several orders of magnitude higher than predicted by Ostwald ripening (Tena-Solsona et al., ChemSystemsChem, 2020). In addition, liquid spherical shells have been shown to emerge as non-equilibrium steady states (Bergmann et al., Nat Commun, 2023), emphasizing the unique potential of energy-driven assembly processes.
Among the most recent discoveries is the spontaneous emergence of spatio-temporal oscillations in the number, size, and position of droplets within synthetic cells. In these systems, coacervate-based droplets sediment and fuse, followed by controlled shrinkage via a size-regulation mechanism that leads to the expulsion of internal material. This behavior marks a significant step toward the development of life-like, dynamic materials (Sastre et al., Nat Commun, 2025).
Building upon these findings, we expanded our approach to include the formation of active vesicles, which serve as valuable models for synthetic cells. A key characteristic of these vesicles is that their formation and disassembly are regulated by the presence or absence of fuel (Zambrano et al., JACS, 2024; Zozulia et al., Angew Chem, 2024). This dynamic control has generated considerable interest in the synthetic biology field.
We have also achieved significant progress in the area of vesicle self-division. Fatty acid-based vesicles respond to chemical fuel by undergoing membrane budding and division, without requiring complex molecular machinery. (Zambrano et al., JACS, 2024). A complementary manuscript on cell division has recently been accepted in Chem.
