Aggregation behavior of graft copolymer with rigid backbone

DNA-Based Complexes and Composites: A Review of Fabrication Methods, Properties, and Applications

Deoxyribonucleic acid (DNA), a macromolecule that stores genetic information in organisms, has recently been gradually developed into a building block for new materials due to its stable chemical structure and excellent biocompatibility. The efficient preparation and functional integration of various molecular complexes and composite materials based on nucleic acid skeletons have been successfully achieved. These versatile materials possess excellent physical and chemical properties inherent to certain inorganic or organic molecules but are endowed with specific physiological functions by nucleic acids, demonstrating unique advantages and potential applications in materials science, nanotechnology, and biomedical engineering in recent years. However, issues such as the production cost, biological stability, and potential immunogenicity of DNA have presented some unprecedented challenges to the application of these materials in the field. This review summarizes the cutting-edge manufacturing techniques and unique properties of DNA-based complexes and composites and discusses the trends, challenges, and opportunities for the future development of nucleic acid-based materials.

Helical Superstructures from the Hierarchical Self-Assembly of Coil-Coil Block Copolymer Guided by Side Chain Amyloid-β(17-19) LVF Peptide

The rational design of precisely controlled hierarchical chiral nanostructures from synthetic polymers garnered inspiration from sophisticated biological materials. Since chiral peptide motifs induce helix formation in macromolecules, herein we report the synthesis of a novel type of hybrid polymer consisting of a β-sheet forming a LVF [L = leucine, V = valine, and F = phenylalanine] tripeptide pendant polymethacrylate block and a poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) block. The designed block copolymer self-organized into helical superstructures with a left-handed twisting sense, as visualized by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. This intriguing hierarchical self-assembly is driven by the minimalistic peptide motif that itself has a high propensity to adopt an antiparallel β-sheet conformation. We also report the generation of a diverse array of nanostructures, including spherical micelles, spindle micelles, rod-like micelles, vesicles, helical supramolecular fibers, and helical toroids via self-assembly of the designed block copolymer in tetrahydrofuran/water mixed solvents. To realize the observable helical superstructure, a twisted two-dimensional core-shell tape is proposed as a structure model in which the peptide segments form an antiparallel β-sheet with a polymer shell. The findings contribute to the advancement of a helical polymer or the superhelical self-assembly of polymers, paving the way for diverse applications in materials science and related fields.

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

Synthesis and Characterization of Functional Cellulose-Ether-Based PCL- and PLA-Grafts-Copolymers

The use of biodegradable materials such as cellulose and polyesters can be extended through the combination, as well as modification, of these biopolymers. By controlling the molecular structure and composition of copolymers of these components, it should also be possible to tailor their material properties. We hereby report on the synthesis and characterization of cellulose-based graft copolymers with a precise molecular composition and copolymer architecture. To prepare such materials, we initially modified cellulose through the regioselective protection of the 6-OH group using trityl chloride. The 6-O protected compound was then alkylated, and deprotection at the 6-OH group provided the desired 2,3-di-O-alkyl cellulose compounds that were used as macroinitiators for ring opening polymerization. Regioselective modification was hereby necessary to obtain compounds with an exact molecular composition. Ring opening polymerization, catalyzed by Sn(Oct)₂, at the primary 6-OH group of the cellulose macroinitiator, using L-lactide or ε-caprolactone, resulted in graft copolymers with the desired functionalization pattern. The materials were characterized using Fourier-transform infrared spectroscopy, ¹H- and ¹³C- nuclear magnetic resonance spectroscopy, size exclusion chromatography as well as X-ray diffraction, and differential scanning calorimetry. PCL-based copolymers exhibited distinct melting point as well as a crystalline phase of up to 47%, while copolymers with PLA segments were highly amorphous, showing a broad amorphous reflex in the XRD spectra, and no melting or crystallization points were discernible using differential scanning calorimetry.

Liquid-liquid phase separated microdomains of an amphiphilic graft copolymer in a surfactant-rich medium

The liquid-liquid phase separation (LLPS) of amphiphilic thermoresponsive copolymers can lead to the formation of micron-sized domains, known as simple coacervates. Due to their potential to confine active principles, these copolymer-rich droplets have gained interest as encapsulating agents. Understanding and controlling the conditions inducing this LLPS is therefore essential for applicative purposes and requires thorough fundamental studies on self-coacervation. In this work, we investigate the LLPS of a comb-like graft copolymer (PEG-g-PVAc) consisting of a poly(ethylene glycol) backbone (6 kDa) with ∼2-3 grafted poly(vinyl acetate) chains, and a PEG/PVAc weight ratio of 40/60. Specifically, we report the effect of various water-soluble additives on its phase separation behavior. Kosmotropes and non-ionic surfactants were found to decrease the phase separation temperature of the copolymer, while chaotropes and, above all, ionic surfactants increased it. We then focus on the phase behavior of PEG-g-PVAc in the presence of sodium citrate and a C_14-15 E₇ non-ionic surfactant (N45-7), defining the compositional range for the generation of LLPS microdomains at room temperature and monitoring their formation with fluorescence confocal microscopy. Finally, we determine the composition of the microdomains through confocal Raman microscopy, demonstrating the presence of PEG-g-PVAc, N45-7, and water. These results expand our knowledge on polymeric self-coacervation, clarifying the optimal conditions and composition needed to obtain LLPS microdomains with encapsulation potential at room temperature in surfactant-rich formulations.

Tunable AggregationInduced Emission Fluorophore with the Assistance of the SelfAssembly of Block Copolymers by Controlling the Morphology and Secondary Conformation for Bioimaging

Aggregation-induced emission (AIE) luminogens with highly tunable properties show great potential for many applications. In this study, we synthesized a new family of AIE-type poly(ethylene glycol)-block-poly(9-anthrylmethyl lysine) (PEG-b-PLys-An) diblock copolymers by taking advantage of amphiphilic self-assembly and rigid helical backbones. These copolymers can self-assemble into various assemblies through nanoprecipitation methods. The micelles using N,N-dimethylformamide (DMF) as a cosolvent present brighter fluorescence than the vesicles prepared from tetrahydrofuran (THF). We demonstrate that the decreased solubility of copolymers in DMF results in the formation of more compact micelles with more excimer formation during the self-assembly process, while better solvent THF favors the formation of vesicles with stretched core chains. In addition, the secondary conformation of the polypeptide block shows pronounced effects on the fluorescence property. We further show the internalization of the assemblies using two types of cells by cellular uptake experiments. By the delicate design of the block copolymer, we successfully prepare the morphology- and conformation-dependent AIE materials for potential biomedical applications.

Recent advances in the self-assembly of sparsely grafted amphiphilic copolymers in aqueous solution

This review describes the self-assembly of sparsely grafted amphiphilic copolymers and highlights the effects of structural factors and solvents on their self-assembly behaviour.

Well-Defined Thermo- and pH-Responsive Double Hydrophilic Graft Copolymer Bearing a Pyridine-Containing Backbone

Graft copolymers have extensive applications in material science because of their tunable composition of backbone and side chains and diverse morphologies of aggregates. Recent studies mainly focused on the amphiphilic...

Fluorescent homopolypeptide toroids

Toroids are important ring-like nanostructures in living systems; intrinsically luminogenic toroids are promising in bioimaging but it is challenging to synthesize such nanoparticles. Herein, we report a fluorescent toroid that...

Programmable Assembly of π-Conjugated Polymers

π-Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including crystallinity, orientation, morphology, domain size, and π-π interactions. Programming, or deliberately controlling the composition and ordering of π-conjugated polymers by well-defined inputs, is a key facet in the development of organic electronics. Here, π-conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π-π interactions, and morphological length-scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid-state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order-dependent features and assembly techniques that are unique to π-conjugated polymers. This should serve as a guide for delineating the many ways of directing π-conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.

Spiral- and meridian-patterned spheres self-assembled from block copolymer/homopolymer binary systems

Spiral nanostructures, mainly in the 2D form, have been observed in polymer self-assembly, while well-defined 3D spirals are rarely reported. Here we report that a binary system containing polypeptide-based block copolymers and homopolymers can self-assemble into well-defined spiral spheres (3D spirals), in which the homopolymers form the core and the copolymers form the spirals. Upon increasing the preparation temperature, meridian spheres were obtained. Mixing polypeptide block copolymers with opposite backbone chirality also leads to the formation of meridian spheres. In the meridian patterns, a tighter packing manner of the phenyl groups appended to the polypeptide blocks was observed, which is responsible for the spiral-to-meridian transitions. This work enriches the research of spiral assemblies and provides a facile route to switch chiral/achiral nanostructures by regulating the packing manner of the pendant groups.

Novel Amphiphilic Dendronized Copolymers Formed by Enzyme-Mediated "Green" Polymerization

This study reports the first enzyme-mediated polymerization of dendritic macromonomers. The enzyme substrates are prepared by "click" conjugation between tyrosine and hydrophilic triethylene glycol (TrEG)-based dendrons of three generations (G1, G2, and G3). The resulting enzyme-polymerizable dendrons are defect-free as revealed by mass spectrometry, size-exclusion chromatography, and spectroscopic techniques. The phenol-containing macromonomers are water soluble and their polymerizations into dendronized polymers (denpols) are catalyzed by laccase (an oxidoreductase) under benign conditions (45 °C and aqueous medium at pH = 4.0) with copolymer yields between 30 and 40%. The resulting denpols consist of unnatural poly(tyrosine) backbones and dendritic poly(ether-ester) side chains and have molecular masses up to ∼13 000 Da (generation 1), ∼20 000 Da (generation 2), and ∼36 000 Da (generation 3) determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) analyses. They display amphiphilic properties and self-assemble in aqueous solutions to form aggregates with generation-dependent morphologies.

Amphiphilic Star Polypept(o)ides as Nanomeric Vectors in Mucosal Drug Delivery

Mucosal delivery across the gastrointestinal (GI) tract, airways, and buccal epithelia is an attractive mode of therapeutic administration, but the challenge is to overcome the mucus and epithelial barriers. Here, we present degradable star polypept(o)ides capable of permeating both barriers as a promising biomaterial platform for mucosal delivery. Star polypept(o)ides were obtained by the initiation of benzyl-l-glutamate N-carboxyanhydride (NCA) from an 8-arm poly(propyleneimine) (PPI) dendrimer, with subsequent chain extension with sarcosine NCA. The hydrophobic poly(benzyl-l-glutamate) (PBLG) block length was maintained at 20 monomers, while the length of the hydrophilic poly(sarcosine) (PSar) block ranged from 20-640 monomers to produce star polypept(o)ides with increasing hydrophilic: hydrophobic ratios. Transmission electron microscopy (TEM) images revealed elongated particles of ∼120 nm length, while dynamic light scattering (DLS) provided evidence of a decrease in the size of polymer aggregates in water with increasing poly(sarcosine) block length, with the smallest size obtained for the star PBLG₂₀-b-PSar₆₄₀. Fluorescein isothiocyanate (FITC)-conjugated PBLG₂₀-b-PSar₆₄₀ permeated artificial mucus and isolated rat mucus, as well as rat intestinal jejunal tissue mounted in Franz diffusion chambers. An apparent permeability coefficient (P_app) of 15.4 ± 3.1 ×10^-6 cm/s for FITC-PBLG₂₀-b-PSar₆₄₀ was calculated from the transepithelial flux obtained with the apical-side addition of 7.5 mg polypept(o)ide to jejunal tissue over 2 h. This P_app could not be accounted for by flux of unconjugated FITC. Resistance to trypsin demonstrated the stability of FITC-labeled polypept(o)ide over 2 h, but enzymatic degradation at the mucus-epithelial interface or during flux could not be ruled out as contributing to the P_app. The absence of any histological damage to the jejunal tissue during the 2 h exposure suggests that the flux was not associated with overt toxicity.

Associative properties of poly(ethylene glycol)-poly(vinyl acetate) comb-like graft copolymers in water

The self-assembly of amphiphilic graft copolymers is generally reported for polymer melts or polymers deposited onto surfaces, while a small number of cases deal with binary mixtures with water. We report on the associative properties of poly(ethylene glycol)-graft-poly(vinyl acetate) (PEG-g-PVAc) comb-like copolymers in water, demonstrating the existence of a percolative behaviour when increasing the PEG-g-PVAc content. Rheology, light- and small-angle X-ray scattering experiments, together with dissipative particle dynamics simulations, reveal a progressive transition from spherical polymer single-chain nanoparticles (SCNPs) towards hierarchically complex structures as the weight fraction of the polymer in water increases. The ability of PEG-g-PVAc to attain different nano- and microstructures is of great importance in numerous applications such as in the fields of cosmetics, detergency and drug delivery.

Chitosan-graft-poly(methyl methacrylate) amphiphilic nanoparticles: Self-association and physicochemical characterization

In this work, we synthesized and characterized the self-assembly behavior of a chitosan-poly(methyl methacrylate) graft copolymer and the properties of the formed nanoparticles by static and dynamic light scattering, small-angle neutron scattering, and transmission electron microscopy. Overall, our results indicate that the hydrophobization of the chitosan side-chain with PMMA leads to a complex array of small unimolecular and/or small-aggregation number "building blocks" that further self-assemble into larger amphiphilic nanoparticles.

Anisotropic polymer nanoparticles with solvent and temperature dependent shape and size from triblock copolymers

By the combination of RAFT and N-carboxyanhydride (NCA) polymerisation triblock copolymers were designed able to form responsive spherical and non-spherical particles.

Melamine-mediated supramolecular assembly of nucleobase-modified poly(l-lysine)

Melamine (M) was used to drive the supramolecular assembly of thymine (T)-modified poly(l-lysine) into fibers or spherical micelles through simply adjusting the substitution degree of T and the concentration of M.

Polypeptide self-assemblies: nanostructures and bioapplications

Polypeptide copolymers can self-assemble into diverse aggregates. The morphology and structure of aggregates can be varied by changing molecular architectures, self-assembling conditions, and introducing secondary components such as polymers and nanoparticles. Polypeptide self-assemblies have gained significant attention because of their potential applications as delivery vehicles for therapeutic payloads and as additives in the biomimetic mineralization of inorganics. This review article provides an overview of recent advances in nanostructures and bioapplications related to polypeptide self-assemblies. We highlight recent contributions to developing strategies for the construction of polypeptide assemblies with increasing complexity and novel functionality that are suitable for bioapplications. The relationship between the structure and properties of the polypeptide aggregates is emphasized. Finally, we briefly outline our perspectives and discuss the challenges in the field.

Compact Vesicles Self-Assembled from Binary Graft Copolymers with High Hydrophilic Fraction for Potential Drug/Protein Delivery

Hollow vesicles self-assembled from amphiphilic copolymers are of great interest in biomedicine field as drug and protein carriers. Efficient preparation of polymeric vesicles with high stability in vivo is highly desirable. Herein, a novel cooperative self-assembly of two graft copolymers (GCPs) with reversed hydrophilic-hydrophobic segments is investigated to achieve morphology control for biomedical application. Interestingly, nanosized vesicles are obtained for the binary system with relatively high hydrophilic fraction (f_hydrophilic, ∼60%), contrary to what is found in its single-component counterpart. The cooperative self-assembly endowed the hybrid vesicles with excellent resistance to protein adsorption, prolonged blood circulation time, as well as low leakage of hydrophilic drugs/proteins. Furthermore, the biological activity of the protein is well preserved inside the cooperative vesicles, making it a promising candidate as the protein carrier.

Toroid Formation through a Supramolecular "Cyclization Reaction" of Rodlike Micelles

Constructing polymeric toroids with a uniform, tunable size is challenging. Reported herein is the formation of uniform toroids from poly(γ-benzyl-l-glutamate)-graft-poly(ethylene glycol) (PBLG-g-PEG) graft copolymers by a two-step self-assembly process. In the first step, uniform rodlike micelles are prepared by dialyzing the polymer dissolved in tetrahydrofuran (THF)/N,N'-dimethylformamide (DMF) against water. With the addition of THF in the second step, the rodlike micelles curve and then close end-to-end to form uniform toroids, which resemble a cyclization reaction.

Detailed Structural Analysis of a Self-Assembled Vesicular Amphiphilic NCN-Pincer Palladium Complex by Using Wide-Angle X-Ray Scattering and Molecular Dynamics Calculations

Wide-angle X-ray scattering experiments and all-atomistic molecular dynamics calculations were performed to elucidate the detailed structure of bilayer vesicles constructed by self-assembly of an amphiphilic palladium NCN-pincer complex. We found an excellent agreement between the experimental and calculated X-ray spectra, and between the membrane thickness determined from a TEM image and that calculated from an electron-density profile, which indicated that the calculated structure was highly reliable. The analysis of the simulated bilayer structure showed that in general the membrane was softer than other phospholipid bilayer membranes. In this bilayer assemblage, the degree of alignment of complex molecules in the bilayer membrane was quite low. An analysis of the electron-density profile shows that the bilayer assemblage contains a space through which organic molecules can exit. Furthermore, the catalytically active center is near this space and is easily accessible by organic molecules, which permits the bilayer membrane to act as a nanoreactor. The free energy of permeation of water through the bilayer membrane of the amphiphilic complex was 12 kJ mol^-1 , which is much lower than that for phospholipid bilayer membranes in general. Organic molecules are expected to pass though the bilayer membrane. The self-assembled vesicles were shown to be catalytically active in a Miyaura-Michael reaction in water.

Nanoparticle-Induced Ellipse-to-Vesicle Morphology Transition of Rod-Coil-Rod Triblock Copolymer Aggregates

Cooperative self-assembly behavior of rod-coil-rod poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol)-block-poly(γ-benzyl-l-glutamate) (PBLG-b-PEG-b-PBLG) amphiphilic triblock copolymers and hydrophobic gold nanoparticles (AuNPs) was investigated by both experiments and dissipative particle dynamics (DPD) simulations. It was discovered that pure PBLG-b-PEG-b-PBLG copolymers self-assemble into ellipse-like aggregates, and the morphology transforms into vesicles as AuNPs are introduced. When the hydrophobicity of AuNPs is close to that of the copolymers, AuNPs are homogeneously distributed in the vesicle wall. While for the AuNPs with higher hydrophobicity, they are embedded in the vesicle wall as clusters. In addition to the experimental observations, DPD simulations were performed on the self-assembly behavior of triblock copolymer/nanoparticle mixtures. Simulations well reproduced the morphology transition observed in the experiments and provided additional information such as chain packing mode in aggregates. It is deduced that the main reason for the ellipse-to-vesicle transition of the aggregates is attributed to the breakage of ordered and dense packing of PBLG rods in the aggregate core by encapsulating AuNPs. This study deepens our understanding of the self-assembly behavior of rod-coil copolymer/nanoparticle mixtures and provides strategy for designing hybrid polypeptide nanostructures.

Ultrasmall polymersomes of poly-α,β-(N-2-hydroxyethyl l-aspartamide)-graft-poly(l-lactic acid) copolymers as a potential drug carrier

Ultrasmall polymersomes are suggested as a drug delivery platform based on their suitable size, narrow size distribution, uniform morphology, and high thermodynamic stability.

Ultra-large sheet formation by 1D to 2D hierarchical self-assembly of a “rod–coil” graft copolymer with a polyphenylene backbone

This study presents a unique ultra-large sheet formation through 1D to 2D hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone tethered with flexible poly(ethylene oxide) side chains.

POSS semitelechelic Aβ17–19 peptide initiated helical polypeptides and their structural diversity in aqueous medium

Polyhedral oligomeric silsesquioxane (POSS) semitelechelic Aβ_17–19 peptide which initiated polymerization of γ-benzyl l-glutamate N-carboxyanhydride (BLG-NCA) was studied to prepare peptide–polypeptide conjugates with α-helical conformation.

Hierarchical nanostructures self-assembled from a mixture system containing rod-coil block copolymers and rigid homopolymers

Self-assembly behavior of a mixture system containing rod-coil block copolymers and rigid homopolymers was investigated by using Brownian dynamics simulations. The morphologies of formed hierarchical self-assemblies were found to be dependent on the Lennard-Jones (LJ) interaction ε_RR between rod blocks, lengths of rod and coil blocks in copolymer, and mixture ratio of block copolymers to homopolymers. As the ε_RR value decreases, the self-assembled structures of mixtures are transformed from an abacus-like structure to a helical structure, to a plain fiber, and finally are broken into unimers. The order parameter of rod blocks was calculated to confirm the structure transition. Through varying the length of rod and coil blocks, the regions of thermodynamic stability of abacus, helix, plain fiber, and unimers were mapped. Moreover, it was discovered that two levels of rod block ordering exist in the helices. The block copolymers are helically wrapped on the homopolymer bundles to form helical string, while the rod blocks are twistingly packed inside the string. In addition, the simulation results are in good agreement with experimental observations. The present work reveals the mechanism behind the formation of helical (experimentally super-helical) structures and may provide useful information for design and preparation of the complex structures.

Synthesis and self-assembly of a fluorine-containing amphiphilic graft copolymer bearing a perfluorocyclobutyl aryl ether-based backbone and poly(acrylic acid) side chains

Fluorine-containing amphiphilic graft copolymers made of a semi-fluorinated PMBTFVB backbone and hydrophilic PAA side chains were synthesized by the combination of thermal cycloaddition polymerization and ATRP.

Constructing semi-fluorinated PDEAEMA-b-PBTFVBP-b-PDEAEMA amphiphilic triblock copolymer via successive thermal step-growth cycloaddition polymerization and ATRP

Amphiphilic triblock copolymers containing semi-fluorinated PBTFVBP and hydrophilic PDEAEMA segments were synthesized by the site transformation strategy.

Main-chain PPEGMEMA-b-PBTFVPP-b-PPEGMEMA perfluorocyclobutyl aryl ether-based amphiphilic ABA triblock copolymer: synthesis and self-assembly

A novel perfluorocyclobutyl aryl ether-based amphiphilic ABA triblock copolymers were synthesized via the site transformation strategy using sequential thermal [2π + 2π] step-growth cycloaddition polymerization and ATRP.

Molecular assembly of alkyl chain-grafted poly(l-lysine) tuned by backbone chain length and grafted alkyl chain

Alkyl chain-grafted poly(l-lysine) vesicles with tunable molecular assembly were prepared by varying the polypeptide chain length and grafted alkyl chains.