Programming cascade mesophase transitions of enzyme-responsive formulations via molecular engineering of dendritic amphiphiles†

The ability to program cascades of enzymatically induced transitions of polymeric assemblies across various mesophases holds promise for developing new dynamic materials with complex response mechanisms, mimicking the intricate behavior of proteins and other biological systems. In this study, we demonstrate the feasibility of controlling the rates of such sequential transitions by molecular engineering of the polymeric building blocks. To this end, we utilized a hydrogel forming PEG-based tri-block amphiphile (TBA) and micelles forming di-block amphiphiles (DBAs), composed of dendrons with enzymatically cleavable ester end-groups as their hydrophobic blocks, to create co-assembled nano-micellar formulations. We investigated their multi-step mesophase transitions, first from micelles into macroscopic hydrogels and subsequently into water-soluble polymers, in the presence of the activating enzyme porcine liver esterase (PLE). To demonstrate the ability to control the time frame of the micelle-to-hydrogel mesophase transition, we designed and synthesized three DBAs with varying dendritic architectures and degrees of hydrophobicity. These DBAs are composed of hydrophobic dendrons with two, three, and four lipophilic end-groups, designated as DBA-C6×2, DBA-C6×3, and DBA-C6×4, respectively. Our results indicated that the co-assembled micelles containing the least hydrophobic DBA-C6×2 rapidly transformed into a hydrogel within less than two hours upon exposure to PLE. In contrast, the micellar formulation with the most hydrophobic DBA-C6×4 took over two days to transition into the hydrogel mesophase. These findings underscore the potential of using molecular engineering to tailor the behavior of programable polymeric assemblies.