Novel bio-functional architectures of polymersomes

Cell, as a source of inspiration, is a key functional unit of living organism. Its interior consists of different structures composed of soft matter that are highly selective and functions with different roles. Compartmentalization is one of the main features of eukaryotic cells, giving organelles to achieve some essential functions, such as protein synthesis, replication and energy production within close proximity. With the purpose to mimic cellular compartments, lots of model systems based on lipids (liposomes) or polymers (polymersomes) have been developed. Polymersomes (also known as polymer vesicles) are spherical nanostructured entities with a hollow aqueous compartment enclosed by a bilayer membrane of synthetic amphiphilic block copolymers. Compared to the traditionally used liposomes, they have several properties which make them especially suited for lots of applications in biomedicine and biotechnology. Amongst others, their superior stability and excellent chemical diversity allowing their properties of its membranes to be tuned (e.g. selective permeability). Here, the thesis covers two parts of research work and the focus of the study is to use polymersomes system with specific functionality to build novel architectures for mimicking the complexity of living cells.DOCTOR OF PHILOSOPHY (MSE

Polymersomes-based high-performance reverse osmosis membrane for desalination

Polymersomes-based reverse osmosis (RO) membrane (PBM) for desalination was reported for the first time. An amphiphilic tri-block copolymer, PMOXA6-PDMS35-PMOXA6 (ABA), was self-assembled to form polymersomes with spherical nanostructure. The polymersomes were then immobilized into a polyamide network via an interfacial polymerization reaction on top of polysulfone membrane substrate. Under a moderate salinity condition, the PBM presented almost doubled water permeability and higher salt rejection than the control membrane without polymersomes in the polyamide network. Based on the results of a series of characterization the better water permeation of the PBM is believed to result from larger globular features containing highly water permeable polymersomes, which created a higher void fraction in the selective layer, whereas the highly cross-linked polyamide selective layer as well as the polymersome bilayer’s impermeability to NaCl may led to the enhanced salt rejection. Surprisingly, at an elevated NaCl concentration up to 32,000 ppm, the PBM exhibited ~ 60% water flux enhancement and even better NaCl rejection as compared with commercial seawater RO membranes. In general, the PBM presented a water flux similar to the RO membranes with loose polyamide matrix (BW30), but a rejection behavior close to the dense RO membranes (SW30). This study provides a paradigm shift in developing new-generation RO membranes for energy and cost-effective desalination process.NRF (Natl Research Foundation, S’pore)EDB (Economic Devt. Board, S’pore)Accepted versio

Reproducible Preparation of Proteopolymersomes via Sequential Polymer Film Hydration and Membrane Protein Reconstitution

Film rehydration method is commonly used for membrane protein (MP) reconstitution into block copolymer (BCP), but the lack of control in the rehydration step formed a heterogeneous population of proteopolymersomes that interferes with the characterization and performance of devices incorporating them. To improve the self-assembly of polymersomes with simultaneous MP reconstitution, the study reported herein aimed to understand the effects of different variants of the rehydration procedure on the MP reconstitution into BCP membranes. The model MP used in this study was AquaporinZ (AqpZ), an α-helical MP that has been shown to have a high permeation rate exclusive to water molecules. Comparing four rehydration methods differing in the hydration time (i.e., brief wetting or full hydration) and medium (i.e., in buffer or AqpZ stock solution), prehydration with buffer prior to adding AqpZ was found to be most desirable and reproducible reconstitution method because it gave rise to the highest proportion of well-formed vesicles with intact AqpZ functionality as evidenced by the transmission electron microscopy images, dynamic light scattering, and stopped-flow analyses. The mechanisms by which effective AqpZ reconstitution takes place were also investigated and discussed. Small-angle X-ray scattering analysis shows that hydrating the initially dry multilamellar BCP films allows the separation of lamellae. This is anticipated to increase the membrane fluidity that facilitates a fast and spontaneous integration of AqpZ as the detergent concentration is considerably lowered below its critical micelle concentration. Dilution of detergent can result in precipitation of proteins in the absence of well-fluidized membranes for protein integration that underscores the importance of membrane fluidity in MP reconstitution