Abstract
Understanding the diffusion of nanoparticles through permeable membranes in cell mimics paves the way for the construction of more sophisticated synthetic protocells with control over the exchange of nanoparticles or biomacromolecules between different compartments. Nanoparticles postloading by swollen pH switchable polymersomes is investigated and nanoparticles locations at or within polymersome membrane and polymersome lumen are precisely determined. Validation of transmembrane diffusion properties is performed based on nanoparticles of different origin—gold, glycopolymer protein mimics, and the enzymes myoglobin and esterase—with dimensions between 5 and 15 nm. This process is compared with the in situ loading of nanoparticles during polymersome formation and analyzed by advanced multiple‐detector asymmetrical flow field‐flow fractionation (AF4). These experiments are supported by complementary i) release studies of protein mimics from polymersomes, ii) stability and cyclic pH switches test for in polymersome encapsulated myoglobin, and iii) cryogenic transmission electron microscopy studies on nanoparticles loaded polymersomes. Different locations (e.g., membrane and/or lumen) are identified for the uptake of each protein. The protein locations are extracted from the increasing scaling parameters and the decreasing apparent density of enzyme‐containing polymersomes as determined by AF4. Postloading demonstrates to be a valuable tool for the implementation of cell‐like functions in polymersomes.
Highlights
Cells are considered the fundamental building blocks of life
The most distinct proof for cargo encapsulation is to directly visualize its location in the polymersome.[52,53,54]. For this reason gold nanoparticles (AuNPs) of either 5 or 10 nm in diameter were chosen as a cargo, because they offer an excellent contrast for cryo-TEM measurements
In contrast to the hollow fiber filtration (HFF)-purified samples used in the other experiments, for the AF4 study no purification step was performed to the complexation solution of polymersome and enzyme, free enzyme and loaded polymersomes are coexisting in the sample solution
Summary
Cells are considered the fundamental building blocks of life. substantial efforts have been—and still are— directed toward artificial construction of rudimental cells, protocells, or the socalled cell mimics.[1,2,3,4,5,6,7,8,9] Very often these approaches are focused, for example, on mimicking spatially separated biological pathways[8,9,10,11,12] or on stimulating the even more dynamic processes of fusion in synthetic protocell communities.[13,14] There is a significant progress in the development of different types of vesicles (e.g., liposomes, polymersomes, hollow capsules, proteinosomes) and their multicompartments to establish cell-like functions. It is observed that polymersomes can encapsulate hydrophilic molecules in their lumen, whereas hydrophobic cargo can be loaded into the membrane.[17,18] This simple model works sufficiently well for the use of small molecules like drugs and dyes, but lacks any deeper consideration of the interactions for larger, nanometersized cargo with the inner and outer surfaces of the polymersomes as well as within the polymersome membrane In this context, our photocross-linked polymersomes with reversibly pH switchable membrane permeability through photocrosslinked membrane of polymersome (Figure 1) (for details of polymersome composition, see the Supporting Information) offer the chance to study the postloading of nanometer sized cargo in addition to the frequently used in situ loading. The uptake efficiency of enzymes for the fabrication of reversibly switchable enzymatic nanoreactors was evaluated, comparing postloading and in situ loading approach
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