Polymer Cubosomes: Infinite Cubic Mazes and Possibilities

Abstract

Conspectus Block copolymers (BCPs) have been indispensable building blocks to create a range of soft nanostructures including discrete particulates (micelles and vesicles) and periodic structures via spontaneous assembly in bulk and in solution. The size, shape, and phase of these structures can be controlled by the rational design of the molecular structure of building blocks based on the structural analogy of BCPs to lipids and small molecule surfactants. Inverse bicontinuous cubic mesophases of polymers, or polymer cubosomes when in colloidal forms, are emerging nanostructures composed of triply periodic minimal surfaces (TPMSs) of block copolymer bilayers. Created by spontaneous assembly of BCPs in solution, polymer cubosomes internalize two nonintersecting nanochannel networks arranged in a cubic crystalline order. As well-defined porous particles with highly ordered internal structures and high surface-area-to-volume ratios, polymer cubosomes can be used for chemical reactors or bioreactors, carriers capable of cargo loading and release, and scaffolds for nanotemplating. However, despite their structural similarity to lipid cubosomes and applicability, polymer cubosomes have been only sporadically observed as an outcome of serendipity until recent studies demonstrated that BCPs could form well-defined polymer cubosomes in solution. In this Account, we describe our recent progress in creating polymer cubic mesophases and their colloidal particles (polymer cubosomes) in dilute solution. BCPs with nonlinear architectures (dendritic–linear, branched–linear, and branched–branched BCPs) preferentially self-assembled to inverse mesophases in solution when the block ratio (f), defined as a molecular weight ratio of the hydrophilic block to that of the hydrophobic block, was small (<10%). The resulting lyotropic structures transformed from flat bilayers to cubic phases of primitive cubic and double diamond lattices and finally to inverted hexagonal phases as f decreased. We proposed that the architecture of a BCP plays an important role in the preferential formation of polymer cubosomes in solution. The presence of the bulky hydrophilic block limited chain stretching of the hydrophobic polymer block, which would increase the packing parameter of the BCP to greater than unity, a prerequisite for inverse mesophase formation. The structural characteristics of polymer cubosomes, such as lattice symmetries, pore sizes, and lattice parameters, could also be controlled by fine-tuning the structural parameters of BCPs. We also suggested nonsynthetic methods to precisely control the phase and internal lattice of inverse mesophases of BCPs by the coassembly of two BCPs with different block ratios (mix-and-match approach) and the modulation of the affinity of the common solvent toward the hydrophobic block of the BCP. To investigate the potential applications of polymer cubosomes, we prepared inorganic photonic crystals using a cubosome-templated synthesis. We also discussed the utilization of cubosomes as chemical reactors by...

Past Decade Work Done on Cubosomes and its Factorial Design: A Fast Track Information for Researchers

“…CF are gaining attraction as they are biocompatible, simple, stable, non-toxic, and high loading 66 . CF can be made by topdown 67 and bottom-up techniques 68 . Once the Cubosomes are formulated they have to assess for outlook, surface morphology, particle size, ZP, EE, drug release, and stability by accelerated stability studies 69,70 .…”

Polymerization‐Induced Self‐Assembly for the Synthesis of Poly(N,N‐dimethylacrylamide)‐b‐Poly(4‐tert‐butoxystyrene) Particles with Inverse Bicontinuous Phases

“…In principle, it is possible to access inverse morphologies if the solvophobic/solvophilic block ratio is sufficiently high to satisfy p > 1. [ 7 ] However, in practice, solvent, temperature, additive, and polymer concentration can all influence the outcome of BCP self‐assembly, and such complex conditions have rendered effective preparation of inverse morphologies rather elusive. Since Eisenberg and coworkers reported the observation of hexagonally packed hollow hoops (HHHs) or hexasomes, [ 8 ] there have been only a few studies reporting the preparation of inverse morphologies.…”

Recent Progress in Polymer Cubosomes and Hexosomes

“…The advance of research in lipid cubosomes and hexosomes has certainly stimulated the interest in their polymer analogs with numerous intrinsic advantages. [ 1g,h,11 ] Due to the presence of hydrophilic polymer block, there is no need for stabilizing agents for polymer cubosomes and hexosomes. [ 1h,11a ] Because of the high molecular weight of polymers, polymer cubosomes and hexosomes exhibit even higher mechanical and chemical stabilities than their lipid analogs.…”