Biomimetic superstructures from amphiphilic ABA-triblock copolymers

The spontaneous formation of nanostructured materials by molecular self-assembly of block copolymers is an active area of research, driven both by its inherent beauty and by a wealth of potential technological applications. The so-called “supramolecular” structures can be used to build functional materials with nanoscopic dimensions, such as sensors for biochips or smart drug delivery vehicles.
Block copolymer vesicles have attracted increasing interest, particularly in view of possible applications in drug delivery and in protein reconstitution. Conventional methods utilizing synthetic lipid membranes for protein functionality assays have yielded much information with respect to the membrane protein behavior. Furthermore, amphiphilic block copolymer membrane, allowing proper protein refolding while preserving protein function, have been developed to improve the efficiency of these proteins in robust devices.
Even if spherical structures are still the most common supramolecular structures generated by self-assembly of block copolymers, a remarkable variety of other morphologies have now been demonstrated, such as rod-like micelles and nanotubes. Soft nanotubes made from biocompatible organic molecules and polymers could find applications in biotechnology and medicine. However, polymer hollow tubes are rare and have so far only been described in organic solvents where their fabrication often requires elaborate procedures.
Recently, a series of ABA triblock copolymer composed of poly(dimethylsiloxane)-block- poly(2-methyloxazoline)-block- poly(dimethylsiloxane) (PMOXA-b-PDMS-b-PMOXA) able to mimic biomembranes has been introduced. The PMOXA blocks have hydroxyl end groups that allow functionalization with methacrylic acid. In aqueous solution, the triblock macromonomers form supramolecular assemblies that can be chemically cross-linked by polymerization of the methacrylic acid groups.
Established and new preparation methods have been used to prepare superstructures in water with various hydrophobic-hydrophilic ratios of the PMOXA-b-PDMS-b-
PMOXA ABA-triblock copolymers. Suitable choice of the block lengths and preparation method allowed controlling the shape of the self-assemblies.
We have particularly introduced a preparation method for nanovesicles using detergents and bio-beads that is a suitable alternative devoid of organic solvents leading to improved reconstitution of functional membrane proteins.
We have also developed a simple method for the preparation of soft, water-filled nanotubes via self-assembly of PMOXA-b-PDMS-b-PMOXA in aqueous media. Polymer nanotubes have been loaded with water-soluble substances and used as highly specific templates for inorganic synthesis.