From Biomimetic Multicompartments towards Artificial Cells. Design of Smart Polymeric Materials with Responsive Properties to Mimic Cellular Functionalities

Polymeric stimuli-responsive multicompartment vesicles can be designed to self-regulate their activity in a bioinspired manner, which mimics cellular signaling pathways. In this thesis, the modularity of our system is highlighted, giving a truly flexible multipurpose tool that can be readily adapted for multiple functions. A multicompartment architecture based on synthetic vesicles with sizes in the micrometer range (giant unilamellar vesicles, GUVs) is loaded with nanosized synthetic subcompartments and their functionality through a stimulus present in their environment is introduced. To achieve the environmental responsiveness, the loaded subcompartments are reduction-sensitive thus possessing a triggered activity resulting in a morphological change. The multicompartments are formed by one-pot self-assembly of a mixture of amphiphilic block copolymers poly(2–methyl-2-oxazoline)5–block–poly(dimethylsiloxane)58–block–poly(2–methyl-2-oxazoline)5 (PMOXA5-b-PDMS58-b-PMOXA5) and PDMS65-b-heparin in the presence of specific molecules (enzymes, reporter compounds) and previously formed stimuli-responsive subcompartments, which contains the enzyme substrates or ion channels. By simultaneous co-encapsulation of desired molecules, and respective partners entrapped inside subcompartments, molecular tandems with a spatial segregation inside GUVs is realized. PDMS65-b-heparin served to equip the surface of the multicompartment with a biological receptor-like moiety that will further support possible bio-interactions.
A sequential setup provides the multicompartments’ activity: production of desired molecules by in situ triggered enzymatic reactions or selective flow of ions in/out via ion channel recruitment in the GUVs’ membrane for biosensing purposes. An external signaling molecule added to the environment of the multicompartments diffuses across the GUVs’ membrane, inducing the disassembly of the reduction-sensitive nanoparticles and the release of the entrapped cargo. Depending on their chemical nature (enzyme substrates or biopores), these molecules initiate either an enzymatic reaction or a selective ion flow through the polymer membrane. In a more complex system, the biopore recruitment was induced to trigger the formation of an actin cytoskeleton (monomeric actin polymerized into filamentous actin) within the polymeric GUV, when selected ions could enter the vesicle’s lumen. On the contrary, when the subcompartments are non-responsive or the external stimulus is not present, the multicompartments preserve their architecture and remain in a “silent mode” for several months. The combination of a primary signal (presence of stimulus in the environment of multicompartments) with a secondary one (induced ion flow to/from the environment) represents an important advance in multicompartment assembly, responsiveness, and triggered signal transduction. Our multicompartments have remarkable stability and activity because they preserve their integrity and respond “on demand” to signaling molecules to release the desired molecules. Triggered activity and change in the architecture of synthetic multicompartment vesicles, in auto-controlled sequences, are expected to open new directions for potential applications of these multifunctional systems in the domains such as medicine, catalysis and biosensing. The development of this bioinspired multicompartment with unprecedented mode of action and careful in situ characterization was achieved by combining expertise from materials science, chemistry and nanotechnology.