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

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.

Breaking of Lateral Symmetry in Two-Dimensional Crystallization-Driven Self-Assembly on a Surface

Symmetry breaking is prevalent in nature and provides distinctive access to hierarchical structures for artificial materials. However, it is rarely explored in two-dimensional (2D) entities, especially for lateral asymmetry. Herein, we describe a unique symmetry breaking process in surface-initiated 2D living crystallization-driven self-assembly. The 2D epitaxial growth occurs only at one lateral side of the immobilized cylindrical micelle seeds, accessing unilateral platelets with the yield increasing with the seed length, the growth temperature, and poly(2-vinylpyridine) corona length (maximum = 92%). Generally, the tilted immobilization of seeds blocks one lateral side and triggers the lateral symmetry breaking, where the intensity and spatial arrangement of seed-surface interactions dictate the regulation. Segmented unilateral platelets with segmented corona regions are further fabricated with the addition of different blended unimers. Remarkably, discrete slope-like and dense blade-like platelet arrays grow off the surface when seeds are compactly aligned either with spherical micelles or themselves. This strategy provides nanoscale insights into the symmetry breaking in long-range self-assembly and would be promising for the design of innovative colloids and smart surfaces.

Regulation of Two-Dimensional Platelet Micelles with Tunable Core Composition Distribution via Coassembly Seeded Growth Approach

Seeded growth termed "living" crystallization-driven self-assembly (CDSA) has been identified as a powerful method to create one- or two-dimensional nanoparticles. Epitaxial crystallization is usually regarded as the growth mechanism for the formation of uniform micelles. From this perspective, the unimer depositing rate is largely related to the crystallization temperature, which is a key factor to determine the crystallization rate and regulate the core composition distribution among nanoparticles. In the present work, the coassembly of two distinct crystallizable polymers is explored in detail in a one-pot seeded growth protocol. Results have shown that polylactone containing a larger number of methylene groups (-CH2-) in their repeating units such as poly(η-octalactone) (POL) has a faster crystallization rate compared to poly(ε-caprolactone) (PCL) with a smaller number of -CH2- at ambient temperature (25 °C), thus a block or blocky platelet structure with heterogeneous composition distribution is formed. In contrast, when the crystallization temperature decreases to 4 °C, the difference of crystallization rate between both cores become negligible. Consequently, a completely random component distribution within 2D platelets is observed. Moreover, we also reveal that the core component of seed micelles is also paramount for the coassembly seeded growth, and a unique structure of flower-like platelet micelle is created from the coassembly of PCL/POL using POL core-forming seeds. This study on the formation of platelet micelles by one-pot seeded growth using two crystallizable components offers a considerable scope for the design of 2D polymer nanomaterials with a controlled core component distribution.

Temperature-Sensitive Janus Particles PEG/SiO2/PNIPAM-PEA: Applications in Foam Stabilization and Defoaming

The current study presents a scalable approach for the preparation of temperature-responsive PEG/SiO2/PNIPAM-PEA Janus particles and, for the first time, investigates their potential applications in stabilizing foam and defoaming by adjusting the temperature. The method utilizes a (W1 + O)/W2 emulsion system, which incorporates appropriate surfactants to stabilize the emulsion and prevent rapid dissolution of the hydrophilic triblock polymer PEG-b-PTEPM-b-PNIPAM in water. The PEG/SiO2/PNIPAM-PEA Janus particles with temperature-responsive characteristics were synthesized in a single step that combined the sol-gel reaction and photoinduced free radical polymerization. The contact angle of the hydrophilic PEG/SiO2/PNIPAM surface was measured to be 54.7 ± 0.1°, while the contact angle of the hydrophobic PEA surface was found to be 122.4 ± 0.1°. By incorporating PEG/SiO2/PNIPAM-PEA Janus particles at a temperature of 25 °C, the foam's half-life is significantly prolonged from 42 s to nearly 30 min. However, with an increase in temperature to 50 °C, the foam's half-life rapidly diminished to only 44 s. This innovative application effectively enhances foam stabilization at low temperatures and facilitates the rapid dissipation of foam at high temperatures.

Preparation of Non-Spherical Janus Particles via an Orthogonal Dissolution Approach

Post-synthesis modifications are valuable tools to alter functionalities and induce morphology changes in colloidal particles. Non-spherical polymer particles with Janus characteristics are prepared by combining seeded growth polymerization and selective dissolution. First, spherical polystyrene (PS) particles have been swollen with methyl methacrylate (MMA) with an activated swelling method. This is followed by polymerization that led to particles with two well-separated faces: one made of PS and the second of polymethyl methacrylate (PMMA). Subsequently, non-spherical particles are obtained by exposing the Janus colloids to various solvents. Using the two polymers' orthogonal solubility, solvents are identified to selectively dissolve only one face, leading to hemispherical PS or PMMA particles. It is further investigated how changing the composition of the PMMA face - by either co-polymerization with glycidyl methacrylate or by adding a cross-linker - affects the particles' morphology. The poly-methacrylate face can gain total or partial resistance towards the solvents, resulting in intriguing shapes, such as mushroom-like and Janus dimpled particles. The dissolution mechanisms are investigated via optical microscopy, where total or partial dissolutions can be directly observed. Lastly, prematurely quenching the dissolution of the particle's lobes with water can be used to control the Janus mushroom-like particle aspect ratio.

Uniform segmented platelet micelles with compositionally distinct and selectively degradable cores

The creation of nanoparticles with controlled and uniform dimensions and spatially defined functionality is a key challenge. The recently developed living crystallization-driven self-assembly (CDSA) method has emerged as a promising route to one-dimensional (1D) and 2D core-shell micellar assemblies by seeded growth of polymeric and molecular amphiphiles. However, the general limitation of the epitaxial growth process to a single core-forming chemistry is an important obstacle to the creation of complex nanoparticles with segmented cores of spatially varied composition that can be subsequently exploited in selective transformations or responses to external stimuli. Here we report the successful use of a seeded growth approach that operates for a variety of different crystallizable polylactone homopolymer/block copolymer blend combinations to access 2D platelet micelles with compositionally distinct segmented cores. To illustrate the utility of controlling internal core chemistry, we demonstrate spatially selective hydrolytic degradation of the 2D platelets-a result that may be of interest for the design of complex stimuli-responsive particles for programmed-release and cargo-delivery applications.

Multicompartment polymeric colloids from functional precursor Microgel: Synthesis in continuous process

Raspberry-like poly(oligoethylene methacrylate-b-N-vinylcaprolactam)/polystyrene (POEGMA-b-PVCL/PS) patchy particles (PPs) and complex colloidal particle clusters (CCPCs) were fabricated in two-, and one-step (cascade) flow process. Surfactant-free, photo-initiated reversible addition-fragmentation transfer (RAFT) precipitation polymerization (Photo-RPP) was used to develop internally cross-linked POEGMA-b-PVCL microgels with narrow size distribution. Resulting microgel particles were then used to stabilize styrene seed droplets in water, producing raspberry-like PPs. In the cascade process, different hydrophobicity between microgel and PS induced the self-assembly of the first formed raspberry particles that then polymerized continuously in a Pickering emulsion to form the CCPCs. The internal structure as well as the surface morphology of PPs and CCPCs were studied as a function of polymerization conditions such as flow rate/retention time (Rt), temperature and the amount of used cross-linker. By performing Photo-RPP in tubular flow reactor we were able to gained advantages over heat dissipation and homogeneous light distribution in relation to thermally-, and photo-initiated bulk polymerizations. Tubular reactor also enabled detailed studies over morphological evolution of formed particles as a function of flow rate/Rt.

Interfacial Imide Polymerization of Functionalized Filled Microcapsule Templates by the Pickering Emulsion Method for the Rapid Removal of 3,4,5-Trichlorophenol from Wastewater

In this work, an olive oil-filled composite capsule (C-O/W) adsorbent was prepared for the adsorption of 3,4,5-trichlorophenol (3,4,5-TCP) by the emulsion templating method. Using methylene diisocyanate (HDI) and 1,6-hexanediamine (HMDA) as functional monomers, olive oil was encapsulated in a shell layer composed of graphene oxide and a polymer by interfacial imine polymerization. The contaminant target was efficiently removed by the hydrophobic interaction between olive oil and chlorophenols. The removal of 3,4,5-TCP was remarkable, with an encapsulation rate of 85%. The unique microcapsule structure further enhanced the kinetic performance, which reached 92% of the maximum value within 40 min. The adsorption of different chlorophenols was investigated using 2-chlorophenol (2-CP), 2,6-dichlorophenol (2,6-DCP), and 3,4,5-TCP. The adsorption of 3,4,5-TCP by the C-O/W microcapsules was found to be much higher than that of other chlorophenols. When analyzing a real sample, the content of 3,4,5-TCP was significantly reduced after adsorption by the C-O/W microcapsules, demonstrating that the C-O/W microcapsules were also capable of removing 3,4,5-TCP from a complex environment. This simple and inexpensive preparation strategy provides a new method for the synthesis of functionalized C-O/W microcapsule adsorbents and an effective adsorbent of 3,4,5-TCP.

Amphiphilic Janus Microspheres Prepared by Caged Photoactivatable Alkoxysilane

A simple photolysis route was proposed to prepare Amphiphilic Janus Particles (AJP) based on SiO2 microspheres. The surface of SiO2 microspheres were modified by photoactive alkoxysilane, which was synthesized by dealcoholization condensation of 6-nitroveratroyloxycarbonyl and isocyanatopropyl-triethoxysilane. UV irradiation caused eater-breaking allowed for the precise control of hydrophilic modification of the hemispherical exposed particles surfaces. The component and morphology of the obtained particles were characterized by fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the Janus feature was evaluated by scanning electron microscopy, transmission electron microscopy, and dispersity in the oil–water dual-phases. The following results were obtained. The AJP with 450 nm size processes the hydrophilic amino groups on one side and the hydrophobic 6-nitroveratryloxycarbonyl moieties on the other. Additionally, the AJP were located at the phase boundary between water and n-hexane, and the negative charged gold nanoparticles with 25 nm size were adsorbed only onto the side with the positive charged amino groups. The AJP have interfacial adsorption energies that can be as much as three times larger than that of homogeneous particles and thus exhibit excellent surface activities.

Exploring the "Living" Growth of Block Copolymer Nanofibers from Surface-Confined Seeds by In Situ Solution-Phase Atomic Force Microscopy

Living crystallization-driven self-assembly of polymeric and molecular amphiphiles is of growing interest as a seeded growth route to uniform 1D, 2D, and more complex micellar nanoparticles with controlled dimensions and a range of potential applications. Although most studies have been performed using colloidally stable seeds in bulk solution, growth of block copolymer (BCP) nanofibers from seeds confined to a surface is attracting increased attention. Herein, we have used atomic force microscopy (AFM) to undertake detailed studies of the growth of BCP nanofibers from immobilized seeds located on a Si surface. Through initial ex situ AFM studies and in situ AFM video analysis in solution, we determined that growth occurred in four stages, whereby an initial surface-bound growth regime transitions to surface-limited growth. As the nanofiber length increases, surface influence is diminished as the newly grown micelle segment is no longer bound to the Si substrate. Finally, a surface-independent regime occurs where nanofiber growth continues into bulk solution. In addition to the anticipated nanofiber elongation, our studies revealed occasional examples of AFM tip-induced core fragmentation. In these cases, the termini of the newly formed fragments were also active to further growth. Furthermore, unidirectional growth was detected in cases where the seed was oriented at a significant angle with respect to the surface, thereby restricting unimer access to one terminus.

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.