Hierarchical Superstructures by Combining Crystallization-Driven and Molecular Self-Assembly

Hierarchical Structures of Amino Acid Derived Polyhydroxyurethanes: Promising Candidates as Drug Carriers and Cell Adhesive Scaffolds

In this study, we examined the self-assembly of a series of biodegradable and biocompatible amino acid-based polyhydroxyurethanes (PHUs), investigating the structural influence of these polymers on their self-assembly and the resulting morphological features. The presence of hydrophilic and hydrophobic segments, along with carbonyl urethane, ester, and hydroxyl groups in the PHU backbone, facilitates intermolecular hydrogen bonding, enabling the formation of self-assemblies with hierarchical nanodimensional morphologies. We determined the critical aggregation concentration (CAC) and found that it largely depends on the PHU's structure. In-depth morphological studies demonstrated that the evolution of morphology proceeds in four steps: (1) the initial formation of micelles, which act as seeds at very low concentrations, (2) the elongation of these micelles into nanorod or nanopalette shapes below the CAC range, (3) the epitaxial growth of nanofibers at the CAC, and (4) the complete formation of fibrous mats above the CAC. Additionally, these hierarchical structures were utilized for the encapsulation and release of the drug doxorubicin (DOX). We observed that 75% of the encapsulated DOX was readily released in a mildly acidic environment, similar to the physiological conditions of cancer cells. Cellular uptake studies confirmed the effective uptake of the drug-loaded nanoassemblies into the cytoplasm of cells. Our studies also confirmed that these self-assembled structures can serve as effective cell adhesive scaffolds for tissue engineering applications.

Nucleus-Spike 3D Hierarchical Superstructures via a Lecithin-Mediated Biomineralization Approach

3D hierarchical superstructures (3DHSs) are key products of nature's evolution and have raised wide interest. However, the preparation of 3DHSs composed of building blocks with different structures is rarely reported, and regulating their structural parameters is challenging. Herein, a simple lecithin-mediated biomineralization approach is reported for the first time to prepare gold 3DHSs composed of 0D nucleus and 1D protruding dendritic spikes. It is demonstrated that a hydrophobic complex by coordination of disulfiram (DSF) with a share of chloroauric acid is the key to forming the 3DHSs. Under the lecithin mediation, chloroauric acid is first reduced to form the 0D nucleus, followed by the spike growth through the reduction of the hydrophobic complex. The prepared 3DHSs possess well-defined morphology with a spike length of ≈95 nm. Notably, the hierarchical spike density is systematically manipulated from 38.9% to 74.3% by controlling DSF concentrations. Moreover, the spike diameter is regulated from 9.2 to 12.9 nm by selecting different lecithin concentrations to tune the biomineralization process. Finite-difference time-domain (FDTD) simulations reveal that the spikes form "hot spots". The dense spike structure endows the 3DHSs with sound performance in surface-enhanced Raman scattering (SERS) applications.

Size Segregation of Gold Nanoparticles into Bilayer-like Vesicular Assembly

Size segregation of nanoparticles with different sizes into highly ordered, unique nanostructures is important for their practical applications. Herein, we demonstrate spontaneous self-assembly of the binary mixtures of small and large gold nanoparticles (GNPs; 5/15, 5/20, or 10/20 in diameter) in the presence of a tetra(ethylene glycol)-terminated octafluoro-4,4'-biphenol ligand, namely, TeOFBL, resulting in a size-segregated assembly. The outer single layer of large GNPs forming a gold nanoparticle vesicle (GNV) encapsulated the inner vesicle-like assembly composed of small GNPs, which is referred to as bilayer-like GNV and similar to the molecular bilayer structure of a liposome. The size segregation was driven by the solvophobic feature of the TeOFBLs on the surface of GNPs. A time-course study indicated that size segregation occurred instantaneously during the mixing stage of the self-organization process. The size-segregated precursors quickly fused with each other through the inner-inner and outer-outer layer fashion to form the bilayer-like GNV. This study provides a new approach to creating biomimetic bilayer capsules with different physical properties for potential applications such as surface-enhanced Raman scattering and drug delivery.

Asymmetric Polymerization-Induced Crystallization-Driven Self-Assembly of Helical, Rod-Coil Poly(aryl isocyanide) Block Copolymers

Polymerization-induced crystallization-driven self-assembly (PI-CDSA) is combined, for the first time, with helical, rod-coil block copolymer (BCP) self-assembly to enable scalable and controllable in situ synthesis of chiral nanostructures of variable shape, size, and dimensionality. Herein, we report newly developed asymmetric PI-CDSA (A-PI-CDSA) methodologies in the synthesis and in situ self-assembly of chiral, rod-coil BCPs composed of poly(aryl isocyanide) (PAIC) rigid-rod and poly(ethylene glycol) (PEG) random-coil components. Using PEG-based nickel(II) macroinitiators, the construction of PAIC-BCP nanostructures with variable chiral morphologies is accomplished at solids contents ranging 5.0-10 wt %. At low core-to-corona ratios for PAIC-BCPs, we demonstrate the scalable formation of chiral one-dimensional (1D) nanofibers via "living" A-PI-CDSA whose contour lengths can be tuned through alterations to unimer-to-1D seed particle ratio. At high core-to-corona ratios, A-PI-CDSA was implemented for the rapid fabrication of molecularly thin, uniform hexagonal nanosheets via spontaneous nucleation and growth aided by vortex agitation. Investigations into 2D seeded, living A-PI-CDSA revealed a brand-new paradigm in the context of CDSA where hierarchically chiral, M helical spirangle morphologies (i.e., hexagonal helicoids) are size-tuned in three dimensions (i.e., heights and areas) via alterations to unimer-to-seed ratio. These unique nanostructures are formed in situ at scalable solids contents up to 10 wt % via rapid crystallization about screw dislocation defect sites in an enantioselective fashion. The liquid crystalline nature of PAIC blocks dictates the hierarchical assembly of these BCPs, with chirality translated across length scales and in multiple dimensions affording large amplifications in chiroptical activity with g-factors reaching -0.030 for spirangle nanostructures.

Functional Mesostructured Electrospun Polymer Nonwovens with Supramolecular Nanofibers

Functional, hierarchically mesostructured nonwovens are of fundamental importance because complex fiber morphologies increase the active surface area and functionality allowing for the effective immobilization of metal nanoparticles. Such complex functional fiber morphologies clearly widen the property profile and enable the preparation of more efficient and selective filter media. Here, we demonstrate the realization of hierarchically mesostructured nonwovens with barbed wire-like morphology by combining electrospun polystyrene fibers, decorated with patchy worm-like micelles, with solution-processed supramolecular short fibers composed of 1,3,5-benzenetricarboxamides with peripheral N,N-diisopropylaminoethyl substituents. The worm-like micelles with a patchy microphase-separated corona were prepared by crystallization-driven self-assembly of a polyethylene based triblock terpolymer and deposited on top of the polystyrene fibers by coaxial electrospinning. The micelles were designed in a way that their patches promote the directed self-assembly of the 1,3,5-benzenetricarboxamide and the fixation of the supramolecular nanofibers on the supporting polystyrene fibers. Functionality of the mesostructured nonwoven is provided by the peripheral N,N-diisopropylaminoethyl substituents of the 1,3,5-benzenetricarboxamide and proven by the effective immobilization of individual palladium nanoparticles on the supramolecular nanofibers. The preparation of hierarchically mesostructured nonwovens and their shown functionality demonstrate that such systems are attractive candidates to be used for example in filtration, selective separation and heterogenous catalysis. This article is protected by copyright. All rights reserved.

Visualizing molecular weights differences in supramolecular polymers

Molecular weight determinations play a vital role in the characterization of supramolecular polymers. They are essential to assessing the degree of polymerization, which in turn can have a significant impact on the properties of the polymer. While numerous characterization methods have been developed to estimate the number-average molecular weight (M_n) of supramolecular polymers, a simple visual method could provide advantages in terms of ease of use. We have now developed a system wherein differences in the fluorescent signature, including changes in color, allow variations in the M_n of an anion-responsive supramolecular polymer [M1·Zn(OTf)₂]_n to be readily monitored. The present visual differentiation strategy provides a tool that may be used to characterize supramolecular polymers.

Issues of molecular weight determination have been central to the development of supramolecular polymer chemistry. Whereas relationships between concentration and optical features are established for well-behaved absorptive and emissive species, for most supramolecular polymeric systems no simple correlation exists between optical performance and number-average molecular weight (M_n). As such, the M_n of supramolecular polymers have to be inferred from various measurements. Herein, we report an anion-responsive supramolecular polymer [M1·Zn(OTf)₂]_n that exhibits monotonic changes in the fluorescence color as a function of M_n. Based on theoretical estimates, the calculated average degree of polymerization (DP_cal) increases from 16.9 to 84.5 as the monomer concentration increases from 0.08 mM to 2.00 mM. Meanwhile, the fluorescent colors of M1 + Zn(OTf)₂ solutions were found to pass from green to yellow and to orange, corresponding to a red shift in the maximum emission band (λ_max). Therefore, a relationship between DP_cal and λ_max could be established. Additionally, the anion-responsive nature of the present system meant that the extent of supramolecular polymerization could be regulated by introducing anions, with the resulting change in M_n being readily monitored via changes in the fluorescent emission features.

Self-Assembled Polymeric Materials: Design, Morphology, and Functional-Oriented Applications

This Review focuses on the current research advances of the synthesis of various amphiphilic block copolymers (ABCs), such as conventional ABCs and newly-presented polyprodrug amphiphiles (PPAs), and the development of corresponding self-assemblies in selective solvents driven by the intermolecular interactions, like noncovalent hydrophobic interactions, π-π interactions, and hydrogen bonds, between ABCs or preformed small polymeric nanoparticles. The design of these assemblies is systematically introduced, and the diverse examples concerning the unique assembly structures along with the fast development of their exclusive properties and various applications in different fields were discussed. Possible perspectives on the existential challenges and glorious future were elucidated finally. We hope this review will provide a convenient way for readers to motivate more evolutional innovative concepts and methods to design next generation of novel polymeric nanoassemblies, and fill the gap between material design and practical applications. This article is protected by copyright. All rights reserved.

Janus Micelles by Crystallization-Driven Self-Assembly of an Amphiphilic, Double-Crystalline Triblock Terpolymer

Surface-compartmentalized micellar nanostructures (Janus and patchy micelles) have gained increasing interest due to their unique properties opening highly relevant applications, e.g., as efficient particulate surfactants, compatibilizers in polymer blends, or templates for catalytically active nanoparticles. We present a facile method for the production of worm-like Janus micelles based on crystallization-driven self-assembly of a double-crystalline triblock terpolymer with a crystallizable polyethylene middle block and two highly incompatible corona blocks, polystyrene and poly(ethylene oxide). This approach enables the production of amphiphilic Janus micelles with excellent interfacial activity by a comparably simple heating and cooling protocol directly in solution.