Self‐assembly and responsiveness of polypeptide‐based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

Abstract

Polypeptide-based amphiphilic block copolymers are an attractive class of materials given their ability to form welldefined aqueous nanoassemblies that respond to external stimulus through secondary structure transitions. This report will highlight recent literature in the area of polypeptide-based block copolymer self-assembly, with the major focus being on how the responsive nature and structural complexity of the polypeptide blocks can be incorporated into systems with complex topologies such as ABA/BAB/ABC triblock copolymers, AB 2 and A 2 B star copolymers, and miktoarm l-ABC star terpolymers. In particular, the role of interfacial curvature changes and how they result in morphology transitions will be discussed. The 'smart' assembly properties of peptides in complex block copolymer topologies can lead to enhanced responsiveness, morphological complexity, and unique morphological transitions with varying solution conditions. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 508-523 KEYWORDS: amphiphiles; biomimetic; block copolymers; selfassembly INTRODUCTION Amphiphilic block copolymers are able to self-assemble into well-defined nanostructures in aqueous solution. [1][2][3][4][5] The equilibrium morphology and aggregation number of diblock copolymer assemblies is primarily determined by the balance of three energetic factors: (1) interfacial tension, (2) corona chain crowding, and (3) core chain stretching. The balance of these three factors dictates an equilibrium curvature for the aggregate. 6-8 Typically, solution morphologies formed by amphiphilic block copolymers follow a trend of increasing interfacial curvature. As the hydrophilic fraction is increased in the copolymer, vesicles, cylindrical micelles, and spherical micelles (in the order of increasing interfacial curvature,) are the most common morphologies (Figure 1). 5,9,10 Physically, this is explained as a balance between entropic freedom of the hydrophilic coronal chains and shielding of the hydrophobic blocks from the aqueous solution; as the hydrophilic fraction increases, the chains are more able to effectively stabilize these assemblies without close-packing, and the free energy of the system is lowered when the coronal chains are provided more entropic freedom/mobility through increased curvature.

Designing peptide nanoparticles for efficient brain delivery

“…A similar trend can be seen in amphiphilic diblock copolymers where , the mass of the hydrophilic block divided by the total mass of polymer, plays the largest single role in determining the morphology of the selfassembled structure [68]. The relation is even more qualitative but, roughly, when , vesicles are formed, when cylindrical micelles are formed, and for spherical micelles are most often seen [63,69]. Kinetic factors and the greater conformational complexity of polymers also play a major role in determining system morphology [70,71].…”

Multiple morphologies of a poly(methyl methacrylate)‐block‐poly(N,N‐dimethyl aminoethyl methacrylate) copolymer with pH‐responsiveness and thermoresponsiveness

“…Amphiphilic block polymers can self‐assemble into well‐defined nanostructures with regulatable morphologies and sizes in solution and can act as functional materials in applications such as biotechnology and medical materials . Stimuli‐responsive amphiphilic polymers have captured more and more attention, not only on account of their response to environmental stimuli but also because of their diverse structures .…”

Ring-Opening Polymerization of N-Carboxyanhydrides for Preparation of Polypeptides and Polypeptide-Based Hybrid Materials with Various Molecular Architectures

“…When polypeptides are combined with other polymers, hybrid materials are prepared, which combine the functionality and ability of self-organization of polypeptides with properties of more conventional polymers, this expanding the possible applications even further. Recently, there have been a number of excellent reviews published on the synthetic polypeptides and polypeptoids prepared by ROP of NCA and their potential applications focusing mainly on the mechanisms and synthesis of complex macromolecular architectures [1,2], biomedical applications [3,4], stimuli responsive polypeptides [5] and their self-assembly [6], or polypeptoids [7]. In this work we will present a general overview of a very fast developing field of synthetic polypeptides with regard to the mechanism of polymerization using different conventional as well as some more recently developed initiators for preparation of polypeptides with welldefined chain lengths and chain-end functionality.…”